JP2001166118A - Prism, projection optical system and projection display - Google Patents

Abstract

(57) [Problem] To increase the number of prisms used in a projection display device or the like, there are caused practical problems such as an increase in the weight and volume of the device and an increase in cost due to a large amount of use of optical materials. Was. SOLUTION: A variable mirror element 3 in which a light beam 20 incident from the outside is totally reflected and the light beam after reflection is arranged outside.
The first inner surface 114A provided on the side far from the variable mirror element 3 so as to irradiate the variable mirror element 3 and the first inner surface 114A provided on the side close to the variable mirror element 3 and totally reflecting the off ray bundle 22 from the variable mirror element 3 The prism 1 includes a second inner surface 122 through which the ON light beam 21 from the variable mirror element 3 is transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism, a projection optical system using the prism, and a projection display using the projection optical system.

[0002]

2. Description of the Related Art In recent years, a projector device (projection display device) has attracted attention as a large-screen image display device. CRT projector using small, high-definition, high-brightness CRT, liquid crystal projector using liquid crystal panel, D
DMD projectors and the like using MDs (Digital Micromirror Devices) have been commercialized.

[0003] AVs such as movies and TV programs
The category of data projectors that project computer images as well as the source is rapidly expanding the market, and the remarkable performance such as the brightness and contrast of the projection screen, the high resolution, and the uniformity of brightness is improved. Improvements have been made.

[0004] Above all, uniformity of brightness has become one of the most basic required specifications with the expansion of the market for data projectors. For example, uniform illumination technology such as a fly-eye integrator has been introduced in a liquid crystal projector device.
It is compatible with the improvement of brightness.

[0005] Light valves such as the aforementioned LCD and DMD can be roughly divided into a transmission type and a reflection type.
In the former, it is easy to arrange the illumination optical axis for illuminating the light valve and the optical axis of the projection lens coaxially.

Accordingly, the design of the illumination optical system is relatively easy, which is advantageous in securing the basic performance of uniformly and brightly illuminating the light valve.

On the other hand, the latter method is disadvantageous in that it is often difficult to make the illumination optical axis and the optical axis of the projection lens coaxial, and a complicated optical system must be constructed. It is.

For an illumination optical system of such a reflection type light valve, see AG Dewey, "Projection Systems for
Light Valves, "Proc. SID, vol. 18/2, pp.134-146,
1977., etc.

FIGS. 28 to 31 are schematic views of an illumination optical system introduced in the above-mentioned document as an illumination system of a reflection type light valve.

(First Prior Art) FIG. 28 shows a typical example of an off-axis illumination optical system, which is characterized in that a light valve is illuminated from a direction deviated from its normal.

In FIG. 28, reference numeral 300 denotes a light valve;
00 is a light source, 801 is a condenser lens, 802 is the last lens on the light valve side of the projection lens, and 810 is the light source 80
0 shows an image. 600 is the light valve 30
A normal line of 0 and 601 is an optical axis of the projection lens.

In FIG. 28, an illuminating light beam represented by a solid line (a light beam is also referred to as a light beam; the same applies hereinafter) is applied to a light source 8.
After emitting the light beam 00, the light beam is converged by the condenser lens 801 and is incident on the light valve 300. Immediately before the light is incident on the final lens 802 on the light valve side of the projection lens, the light beam diameter becomes the smallest and an image 810 of the light source 800 is formed.

The projection lens has a post-aperture lens in which a diaphragm is arranged in the air outside the final lens 802 on the light valve side in accordance with the projection lens. Optical axis 601 of projection lens
Is parallel to the normal 600 of the light valve,
0, 601 are not coaxial, so that the direction of the projection light is inclined with respect to the normal 600 as shown by the dotted arrow.

Further, since the diameter of the final lens 802 on the light valve side of the projection lens can be reduced by the post-aperture type, it is suitable for avoiding physical collision between the projection lens and the illumination optical system.

(Second Prior Art) FIG. 29 is a schematic diagram of an off-axis illumination optical system different from FIG. The reference numerals in FIG. 29 are the same as the reference numerals in FIG. 28, and the description of the reference numerals in FIG. 29 is omitted.

The present optical system has a high possibility of being configured with a lens type that is easier to design than the one shown in FIG. 28 in that the aperture of the projection lens is arranged inside the projection lens system.

As described above, the off-axis optical system as shown in the first and second prior arts does not easily generate a keystone distortion (trapezoidal distortion) in which the screen is distorted into a trapezoid even when projected in a posture looking up at the screen. It is excellent in that the focus blur in the screen can be minimized. That is, the device axis (usually,
It can be said that the illumination optical system is suitable for a front projection type projector device in which it is highly necessary to provide a constant elevation angle in the projection direction with respect to an axis extending along the vertical direction).

On the other hand, since the light valve is obliquely illuminated, it is essentially difficult to improve the illumination uniformity.

(Third Prior Art) Further, the above-mentioned literature introduces a type in which a prism as shown in FIG. 30 is inserted, and a type in which a reflecting mirror is arranged in a light beam as shown in FIG. I have. 30, reference numeral 803 denotes a prism, 602 denotes an illumination light beam, 603 denotes a light beam in the normal direction of the light valve 300 bent by the insertion of the prism 803, and 604 denotes a projection light beam.

In this method, the angle between the illumination light and the projection light can be controlled to some extent, and the degree of freedom in the configuration of the optical system is increased. On the other hand, astigmatism and chromatic aberration of the projection lens are greatly affected. Is said to be low.

(Fourth Prior Art) On the other hand, FIG. 31 shows a case where a mirror is arranged at a stop position in a projection lens, and a light source image formed on the stop is reflected by a light valve 300, and then the mirror is again placed near the mirror. 5 shows a self-focusing relay optical system for forming an image.

Although this system is superior in the distortion of the projected image and the illumination performance as compared with the three types of illumination optical systems described in the first to third prior arts, the illumination light reflected by the mirror is used. When the light enters the lens 802, reflected light is generated on the surface of the lens 802, and this reflected light becomes ghost light and reaches the screen.

As in this example, the reflection type light valve 30
When the lens 802 is arranged near 0, it is necessary to sufficiently consider the effect of the light beam passing through the lens 802 twice.

As described above, the fourth to fourth prior arts have been described.
Although the types of illumination optical systems have been briefly described, it is difficult for all optical systems to achieve both uniform illumination of the light valve and avoidance of collision between the illumination optical system and the projection lens system.

However, an optical system suitable for illuminating a variable mirror element such as a DMD is disclosed in US Pat. No. 5,604,624 (hereinafter referred to as U.S. Pat.
SP5, 604, 624).

(Fifth Prior Art) FIG.
It is a longitudinal cross-sectional view which shows the conventional reflection type light valve illumination optical system disclosed by P5,604,624.

In FIG. 32, reference numeral 140 denotes a prism;
142 is a side surface of the prism 140, 143 is an entrance surface of the prism 140, 144 and 145 are a first surface and a second surface provided inside the prism 140,
0 is a variable mirror element as a reflection type light valve, 80
4 is a light source, 210 and 211 are light beams incident on the prism 140, and 210A and 211A are light beams emitted from the prism 140 and traveling toward the variable mirror element 30.

The side surfaces 141 and 142 are parallel to each other, and the incident surface 143 is inclined with respect to the plane direction of the side surfaces 141 and 142. The first surface 144 and the second surface 145 provided inside the prism 140 are kept substantially parallel, and a gap (air gap) is interposed between the two.

Also, the first surface 144, the second surface 145,
The side surface 141, the side surface 142, and the incident surface 143 are included in planes perpendicular to the corresponding paper surfaces, respectively. In addition, the prism 140 is an integral structure in which two pieces of prism are combined, but functionally, two parts (parts), namely, the side surface 142, the incident surface 143, and the first It can be considered that the first part surrounded by the surface 144 and the second part including the second surface 145 and the side surface 141 are formed.

Although there is a description that the prism 140 may be made of a material having any optical quality, a prism using PMMA is disclosed.

Now, the first surface 144 is the first surface 1
The light beams 210 and 211 incident on the prism 140 from the light source 804 are arranged as shown in FIG.
After being largely deflected as shown in FIG.
Led to.

When light substantially parallel to the principal ray enters the prism 140 from the light source 804, the parallel light can be varied while maintaining the parallelism of the light beam by the total reflection on the first surface 144. The light enters the mirror element 30.

Therefore, it is possible to illuminate the variable mirror element 30 with an illumination light beam whose luminance distribution of the light source 804 is substantially maintained. In this respect, the optical system shown in FIG. 32 is an optical system which is very advantageous for uniform illumination. It can be said.

Further, the light beam reflected from the variable mirror element 30 does not satisfy the condition of total reflection on the first surface 144, passes through the first surface 144, passes through the air gap, and passes through the second surface 145. The light is guided to the projection lens 500. Therefore, it is easy to avoid physical collision between the illumination optical system and the projection lens system.

As described above, the prior art is excellent in uniform illumination of the light valve (variable mirror element 30) and collision avoidance between the illumination optical system and the projection lens system. However, the first surface 144 causes different effects on the incident light beam from the light source 804 and the reflected light from the variable mirror element 30, that is, here, the first surface 1
Reference numeral 44 totally reflects the incident light beam from the light source 804 and transmits the reflected light from the variable mirror element 30.

Here, a brief description will be given of an example of a DMD as a typical variable mirror element that reflects light in the normal direction of the element with respect to oblique incidence of the illumination light beam.

The DMD is a device in which a large number of micro mirrors each having a size of more than 10 μm square are arranged in a matrix on a silicon substrate by using a semiconductor manufacturing technique. ) Is a reflection type light valve.

The DMD tilts each micromirror by electrical control to reflect the incident light in the normal direction of the DMD, and tilts the incident light by a predetermined angle from the normal. And a second reflection state that reflects in the direction.

As a result, when viewed from the reflected side, for example, the first reflection state corresponding to white display (the reflected light at this time is referred to as ON light) and the second reflection state corresponding to black display ( An image is displayed by a combination (modulation) of the reflected light at this time is called OFF light).

As described above, the light modulated by the DMD is projected on a screen (not shown) via the projection lens 500 to display video information.

FIG. 33 is a perspective view showing an example of two micro mirrors (corresponding to two pixels) constituting the DMD. In FIG. 33, reference numerals 310 and 311 denote micromirrors as micromirrors, and reference numeral 312 denotes a base thereof.
Reference numeral 610 denotes a normal line of the base 312. The two micromirrors 310 and 311 are respectively +1 from the normal line 610.
It shows a position inclined to 0 degrees or −10 degrees.

Reference numeral 611 denotes a normal to the micromirror 310 (in the example shown in FIG. 33, a normal 610 to the base 312).
612 is a normal to the micromirror 311 (in FIG. 33,
(It is inclined by -10 degrees with respect to the normal 610 of the base 312).

The micromirrors 310 and 311 have aluminum deposited on their surfaces, and act as square mirrors having high reflectivity. In the case shown in FIG. 33, the inclination of the micromirrors 310 and 311 is the normal 610.
Are ± 10 degrees, respectively, and as a result, the micromirror 310 reflects light incident from a direction inclined by 20 degrees from the normal 610 in the direction of the normal 610 (corresponding to the first reflection state). , The micro mirror 311 is normal 61
Light incident from a direction inclined by 20 degrees from 0 is reflected in a direction inclined by 40 degrees from the normal 610 (corresponding to the second reflection state).

The operation and other details of the DMD are described in Larry J. Hornbeck, "Digital Light Proc.
essing for High-Brightness, High-Resolution Applic
ations. ", SPIE Vol.3013, pp.27-40, etc., and further description is omitted here.

When using the DMD as described above,
Care must be taken so that unnecessary light generated in the second reflection state is not reflected on the projection screen. Because the normal 610
If the OFF light traveling in the direction inclined by 40 degrees from the scattered light in the optical path in the projection optical system causes a stray light component or the ghost light produced by traveling (entering) inside the projection lens, projection occurs. This is because it causes a reduction in the contrast of the displayed image.

In this case, in order to improve the contrast of the projection screen, it is necessary to guide the OFF light to the outside of the optical path using some means, or to absorb the OFF light by a light shielding member.

For example, the description has been given with reference to FIG.
In the optical system having the characteristic of the post-aperture lens, since the image side aperture of the projection lens can be reduced,
The optical system is essentially advantageous in that it can prevent FF light from entering.

Here, the description has been given with reference to FIG.
With reference to FIG. 34, the behavior of OFF light in a conventional illumination optical system will be described. An example using a DMD as the variable mirror element 30 will be described (hereinafter, referred to as DMD 30).

In FIG. 34, reference numeral 146 denotes a prism 140
, Reference numeral 40 denotes a cover glass disposed above the DMD 30, reference numeral 613 denotes a normal line of the DMD, and other symbols are the same as those in FIG.

The OFF light in the above-mentioned second reflection state is emitted from the DMD 30 as shown by an arrow in FIG. 34, and a part of the OFF light is reflected by the prism 140 as a light ray surrounded by a solid ellipse (A in FIG. 34). The side 146 is reached.

Most of the remaining light rays are emitted from the side surface 141 to the outside of the prism 140, and then travel as surrounded by a dotted ellipse (B in FIG. 34). In this case, the processing of the OFF light reaching the side surface 146 can be performed relatively easily, for example, by applying a light absorbing agent on the side surface 146.

On the other hand, according to the arrangement shown in FIG.
It is considered that a considerable proportion of the rays emitted from 41 enter the projection lens 500. The proportion of the ray bundle component surrounded by the dotted ellipse B in the entire OFF light is the thickness of the prism 140 in the direction of the normal 613, that is, the side 1
Since it depends on the distance between 41 and 142 and the size of DMD 30, it is not easy to make a quantitative consideration.

However, the intensity of OFF light (light intensity)
Is almost the same as the intensity of the ON light, and when the projection lens 500 is a telecentric lens that is advantageous for increasing the peripheral light amount ratio of the screen, the final lens on the DMD side becomes considerably large, so that the In consideration of the fact that the number of components entering the lens tends to increase (the possibility of entering the lens increases), it is more necessary to prevent the entry of OFF light that causes stray light or ghost light.

In the above-mentioned US Pat. No. 5,604,624, O
An optical system for preventing the FF light from entering the projection lens is also disclosed, and this is shown in FIG.

In FIG. 35, reference numeral 1400 denotes a prism composed of three prism pieces, 1401 and 1402 denote a pair of surfaces via an air gap which has the same effect as the pair of surfaces 145 and 144 described with reference to FIG. Reference numeral 1403 denotes a surface from which OFF light is emitted. Other reference numerals are the same as those in FIG. 32, and a description thereof will be omitted.

According to the prism 1400 as shown in FIG. 35, the first pair of surfaces 144 and 145 make the D
Selective transmission and / or reflection of the illumination light to the MD 30 and the reflected light from the DMD 30 can be realized.

Further, a second pair of surfaces 1401 and 1
402 selectively transmits ON light and OFF light and / or
Alternatively, a reflection effect can be realized. Therefore, in the prism 1400, it is possible to almost eliminate the reduction in contrast caused by the OFF light entering the projection lens 500, which is a problem in the optical system shown in FIG.

[0058]

However, in order to realize the above-described behavior of each light beam, the prism 140 constituted by integrally combining prism pieces is used.
It is clear from FIG. 35 that 0 has to take a considerably larger shape than the prism 140 of FIG.

The prism 14 for the projection lens 500
00 can be regarded as a plane-parallel plate defined by the side surfaces 141 and 142. In the design in that case, the distance between the side surfaces 141 and 142 is a parameter directly related to the difficulty of the optical design, and it is necessary to increase the back focal length of the projection lens 500 as the distance increases. Therefore, the difficulty of the design becomes extremely high.

In addition, as the prism 1400 increases, the weight and volume of the projector apparatus increase,
Or, practical problems such as an increase in cost due to a large amount of use of the optical material are caused.

US Pat. No. 5,604,624 does not particularly mention such a practical problem, and a compact prism suitable for a variable mirror element such as a reflection type light valve, particularly a DMD, And providing an illumination optical system.

An object of the present invention is to obtain a compact prism, projection optical system and projection display device.

[0063]

The invention according to claim 1 is
A prism disposed between an external variable mirror element and an external projection lens having a projection optical axis parallel to a normal direction of the variable mirror element, wherein the prism is separated by a first distance from the variable mirror element. A first end portion and a second end portion, which are inclined in a direction away from the variable mirror element from the first end portion toward the second end portion, so that a light beam incident from the outside is totally A first inner surface capable of reflecting and propagating the reflected external incident light beam toward the variable mirror element side;
A first end portion and a second end portion which are respectively separated by a second distance and a third distance from the variable mirror element, and wherein the external incident light beam totally reflected by the first inner surface is incident on the external incident light beam When the first bundle of light rays in the first reflection state is incident on the variable mirror element, the first bundle of light rays in the first reflection state is incident on the first reflection state light ray. A second reflection that is incident when a first bundle of light rays in a second reflection state different from the first reflection state among the light ray bundles reflected by the variable mirror element is incident while transmitting one bundle. A second inner surface capable of totally reflecting a first bundle of state rays, wherein the first distance is greater than the third distance, the third distance is greater than the second distance, and the first inner surface is Transmitted through the second inner surface First bundle of serial first reflection state rays, characterized in that the can by transmitting a first bundle of said first reflection state light is propagated to the projection lens side when the incident.

The invention according to claim 2 is the prism according to claim 1, wherein the prism is on the same plane as the first inner surface, and is separated from the variable mirror element by a fourth distance and a third distance, respectively. And a second bundle of first reflection state light rays that have entered without being incident on the second inner surface, can be transmitted and propagated to the projection lens side, and The second incident without incident on the inner surface
The image processing apparatus may further include a third inner surface capable of transmitting a second bundle of reflected light rays, wherein the second end of the second inner surface corresponds to the second end of the third inner surface.

According to a third aspect of the present invention, there is provided the prism according to the second aspect, wherein the prism is disposed at a position facing the first inner surface and transmits the incident external light beam to enter the first inner surface.
A first outer surface, which is an incident surface capable of propagating through the prism toward the inner surface, and a position facing the variable mirror element, the second inner surface, and the third inner surface; A first end corresponding to one end and a second end corresponding to the first end of the third inner surface, for transmitting the external incident light beam transmitted through and incident on the second inner surface; A second outer surface, which is a light working surface capable of entering the prism with the light beam reflected by the variable mirror element while being emitted toward the variable mirror element side, and a surface substantially parallel to the second outer surface. A second end of the third inner surface, the first end being located above the first end of the third inner surface, and being adjacent to the second end of the first inner surface. A second end portion, wherein the first reflection state is transmitted through the first inner surface and is incident. A third outer surface that is an exit surface capable of transmitting a first bundle of lines and a second bundle of the first reflection state light rays that pass through the third inner surface and enter the second outer surface and the third outer surface. The second inner surface, the third inner surface, and the first inner surface are provided between the outer surface and the second inner surface.

The invention according to a fourth aspect is the prism according to the third aspect, wherein the prism is disposed at a position facing the first outer surface, the first inner surface, and the third inner surface. A fourth outer surface having a first end connected to a first end and a second end located above and adjacent to the second end of the second outer surface; and a fourth end disposed on the fourth outer surface; A light-shielding member that absorbs a second bundle of the second reflection state light rays that are transmitted through the third inner surface and incident.

According to a fifth aspect of the present invention, there is provided the prism according to the fourth aspect, wherein the first end portion is located on the same plane as the second outer surface and is adjacent to the first end portion of the second outer surface. A fifth outer surface including the first outer surface and a second end connected to the first outer surface is further provided.

The invention according to claim 6 is the prism according to claim 5, wherein a first prism piece including the first outer surface, the fifth outer surface, and the first inner surface; A second prism piece having a second inner surface and the third inner surface; a third prism piece having the third outer surface and the fourth outer surface; and the first prism piece, the second prism piece, and the second prism piece. An arbitrary prism piece of the third prism piece is disposed so as to face the other two prism pieces via an air gap, and the third outer face and the fourth prism piece are included in the outer faces of the third prism piece. The surface sandwiched between the outer surfaces faces the first inner surface of the first prism piece and the third inner surface of the second prism piece, and the first inner surface of the first prism piece has the first surface.
A surface sandwiched between the inner surface and the fifth outer surface faces the second inner surface of the second prism piece.

According to a seventh aspect of the present invention, there is provided the prism according to the sixth aspect, wherein the first prism piece, the second prism piece, and the third prism piece face each other. The pieces are fixed by a spacer and an adhesive having a coefficient of thermal expansion substantially equal to the coefficient of thermal expansion of the two prism pieces.

The invention according to claim 8 is the prism according to claim 6, wherein the two prisms opposing each other among the first prism piece, the second prism piece and the third prism piece. The pieces are opposed to each other via a thin film coating provided on one of the opposing faces so as to avoid a light beam passage portion.

According to a ninth aspect of the present invention, there is provided a prism disposed between an external variable mirror element and an external projection lens having a projection optical axis parallel to a normal direction of the variable mirror element, A first prism piece that can selectively deflect a first reflection state light beam and a second reflection state light beam corresponding to different first reflection state and second reflection state generated by the variable mirror element, respectively; And the second prism piece and the third
(A) the first prism piece has a first surface through which a light beam incident from the outside can be transmitted;
While totally reflecting the external incident light beam transmitted through the surface,
A second surface for transmitting the first reflection state light beam that propagates and enters the first prism piece, and the first surface after total reflection.
A third surface that transmits the externally incident light beam that propagates and enters the prism piece and transmits the incident first reflection state light beam into the first prism piece;
(B) the second prism piece faces the third surface, transmits the external incident light beam that is transmitted through the third surface and enters, and propagates through the second prism piece; The first reflection state light beam propagating in the second prism piece and entering is transmitted toward the third surface, and the second reflection state light beam propagating in the second prism piece and incident. A fourth surface that totally reflects the light, the externally incident light beam that is opposed to the variable mirror element and propagates through the second prism piece and is incident is transmitted and propagated toward the variable mirror element, The incident first light beam generated by irradiating the variable mirror element with the external incident light beam
The reflected state light beam and the second reflected state light beam are both transmitted and propagate in the second prism piece, and after being totally reflected by the fourth surface, propagate in the second prism piece and enter. A fifth surface capable of at least reflecting the second reflection state light beam, and the fourth surface after transmitting through the fifth surface.
The first reflection state light beam and the second reflection state light beam that propagate and enter the second prism piece without reaching the surface are both transmitted, and the first reflection state light beam and the second reflection state light beam are transmitted at least after being reflected by the fifth surface. The second reflection beam which propagates through the inside of the second prism and transmits the second reflection state light beam which enters and transmits through the inside of the second prism after being totally reflected by the fourth surface. And (c) the third prism piece faces the second surface and the sixth surface, and emits the first prism piece. A first reflection state light beam that is transmitted through the second prism piece and a seventh surface that transmits both the first reflection state light beam and the second reflection state light beam that are emitted and incident; Facing the projection lens, the seventh
And an eighth surface capable of transmitting the first reflection state light beam that enters the third prism piece after being transmitted after passing through the surface and transmits the light beam to the projection lens side.

The invention according to claim 10 is the prism according to claim 9, wherein the second surface and the seventh surface are parallel, and the third surface and the fourth surface are parallel. The sixth surface and the seventh surface are parallel to each other, and an air gap is provided between the parallel surfaces.

The invention according to claim 11 is the prism according to claim 9, wherein the second surface and the sixth surface are in the same plane.

According to a twelfth aspect of the present invention, in the prism according to the ninth aspect, the angle between the first surface and the second surface is defined as α, and the angle between the fifth surface and the sixth surface is defined as α. Is defined as β, and the angle between the fourth surface and the fifth surface is defined as κ, the angle α is larger than 38.0 ° and smaller than 50.4 ° Within the range, the angle β is within a range of greater than 25.0 ° and less than 37.4 °, and the angle κ is an angle greater than 16.2 °.

According to a thirteenth aspect of the present invention, in the prism according to the ninth aspect, (c) the third prism piece includes a side face sandwiched between the seventh face and the eighth face; And a light shielding member disposed above and capable of shielding the second reflection state light beam that propagates and enters the third prism piece after transmission through the seventh surface.

According to a fourteenth aspect of the present invention, there is provided a light source, a condensing optical system for condensing a light beam from the light source, and an incident surface on which condensed light condensed by the condensing optical system is incident. A light intensity equalizing element having an emission surface for emitting a light beam having a substantially uniform light intensity distribution, a transmission optical system for transmitting a light beam emitted from the emission surface of the light intensity equalization element, and the transmission 10. The prism according to claim 9, wherein the light beam transmitted by the optical system is incident as a light beam incident from the outside, and the reflection surface and the emission surface of the light intensity equalizing element outside the prism. Are disposed at positions that are in a conjugate relationship through the transmission optical system and the prism, and correspond to different reflection states when light beams incident from the prism are reflected by their reflection surfaces. 1 reflection state ray bundle A variable mirror element that generates a reflection state light beam; and a projection lens that enters the prism from the variable mirror element and thereafter emits the first reflection state light beam that exits the prism. I do.

According to a fifteenth aspect of the present invention, in the projection optical system according to the fourteenth aspect, the projection optical system avoids a portion of the prism through which the light beam and the first reflection state light beam from the transmission optical system pass. A prism holding member that holds the prism by contacting a part of the outer shape of the prism is further provided.

According to a sixteenth aspect of the present invention, in the projection optical system according to the fifteenth aspect, the prism holding member has a portion for shielding the second reflection state light beam emitted from the prism. And

According to a seventeenth aspect of the present invention, in the projection optical system according to the fifteenth aspect, the prism holding member has a surface facing the projection lens, and the opposing surface of the prism holding member is the second surface. It is characterized by having a light exit aperture having a dimension through which a light beam in one reflection state can pass.

According to an eighteenth aspect of the present invention, in order to generate an electric signal for driving the projection optical system according to the fourteenth aspect and the variable mirror element and output the electric signal to the variable mirror element, It is characterized by comprising a signal generator provided and a screen for receiving a light beam projected from the projection optical system.

According to a nineteenth aspect of the present invention, there is provided a light source, a condensing optical system for condensing a light beam from the light source, an incident surface on which condensed light condensed by the condensing optical system is incident, A light intensity equalizing element having an emission surface for emitting a light beam having a substantially uniform light intensity distribution, a transmission optical system for transmitting a light beam emitted from the emission surface of the light intensity equalization element, and the transmission 4. The prism according to claim 3, wherein the light beam transmitted by the optical system is incident as a light beam incident from the outside, and the reflection surface and the emission surface of the light intensity equalizing element outside the prism. Are disposed at positions that are in a conjugate relationship through the transmission optical system and the prism, and correspond to different reflection states when light beams incident from the prism are reflected by their reflection surfaces. 1 reflection state ray bundle A variable mirror element that generates a reflection state light beam; and a projection lens that enters the prism from the variable mirror element and thereafter emits the first reflection state light beam that exits the prism. I do.

According to a twentieth aspect of the present invention, in order to generate an electric signal for driving the projection optical system according to the nineteenth aspect and the variable mirror element and output the electric signal to the variable mirror element, It is characterized by comprising a signal generator provided and a screen for receiving a light beam projected from the projection optical system.

[0083]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Projection Display Apparatus) The projection display apparatus includes a variable mirror element (element 3 in FIG. 1) capable of producing the above-described first and second reflection states, and a video signal input from the outside. A signal generating unit (part 2 in FIG. 1) for generating an electric signal for driving the variable mirror element so as to correspond to the electric signal reflecting the information of FIG. Receiving a light beam projected from the projection optical system including the portion 1) of FIG.
And a screen (portion 90 in FIG. 27) for projecting an image on the surface.

In the following description, the F-number refers to the incident surface of the light beam (the incident surface corresponds to the surface of the object on which the light beam is incident. The same applies to the entrance surface hereinafter). Is incident, this ray bundle is equivalently considered as a ray bundle emitted from one lens (equivalent lens), and the focal length of such an equivalent lens is f0.
And a value defined by expressing an equivalent lens aperture diameter as D0, that is, F = f0 / D0. In the following description of the embodiments, expressions such as the F-number of the illumination light flux, the F-number of the telecentric lens, the F-number of the projection lens, and the F-number of the reflected light flux will be used. These definitions are based on the description here.

Embodiment 1 FIG. 1 is a diagram schematically showing a vertical cross-sectional structure of a prism according to the first embodiment of the present invention, together with a block diagram of a signal generation unit 2. In FIG.
1 is a prism, 3 is a variable mirror element, 5 is a projection lens,
Reference numeral 8 denotes an illumination light source, and the illumination optical system includes these four basic optical elements 8, 1, 3, and 5. Reference numeral 4 denotes a cover glass provided above the variable mirror element 3.

Reference numeral 20 denotes an illumination light beam which enters the prism 1 and illuminates the variable mirror element 3, 21 denotes an ON light or a first reflection state light beam reflected from the variable mirror element 3, and 22 and 23 denote light beams from the variable mirror element 3. Reference numeral 6 denotes a light beam indicating the locus of the reflected OFF light (second light beam in the second reflection state). Reference numeral 6 denotes a projection optical axis parallel to the normal direction of the variable mirror element 3.
Indicates an illumination optical axis.

The variable mirror element 3 is provided with a DMD (Digit
al Micromirror Device), which selects the direction of reflection of incident light by changing the inclination of a micromirror (micromirror), and modulates the incident light beam based on image information. (Based on the image information, the reflected light is ON
Light and OFF light).

The ON light 21 is a light ray reflected toward the projection lens 5, and FIG. 1 shows the outermost light ray entering the projection lens 5. Reference numeral 50 schematically shows a lens portion of the projection lens 5.

The light is taken into (entered by) the projection lens 5.
The light beam (here, the ON light 21) provides a white display state of the image (corresponding to a bright spot on the screen).

On the other hand, the OFF lights 22 and 23 are light rays having a certain spread and reflected in a direction inclined at a predetermined angle from the projection optical axis 6, and most of them are the third prism pieces 1.
The light reaches the light blocking member 7 provided on the third side surface 132 and is absorbed by the same member 7.

Accordingly, since the OFF lights 22 and 23 are not taken into the projection lens 5 (because they do not enter), a black display state of the image (corresponding to a dark spot on the screen) is provided.

As shown in FIG. 1, the first prism piece 1
1, second prism piece 12 and third prism piece 13
Constitutes the prism 1 as a whole as a whole, while being disposed at predetermined small intervals to be described later with respect to the other two prism pieces.

The outer surface 114 including the first outer surface 111, the fifth outer surface 112, the fourth inner surface 113, and the first inner surface 114A is a plane characterizing the outer surface of the first prism piece 11,
Second outer surface 121, second inner surface 122, and third inner surface 123
Is a plane that characterizes the outer surface of the second prism piece 12, and includes a fifth inner surface 131, a fourth outer surface 132, and a third outer surface 1
33 is a plane characterizing the outer surface of the third prism piece 13.

The first prism piece 11 having a square cross section and the second prism piece having a triangular cross section shown in FIG.
Each of the prism piece 12 and the third prism piece 13 having a right-angled triangular cross-section has a three-dimensional structure formed by a surface in which each side corresponding to each prism piece shown in FIG. It is.

The features of the structure of the prism 1 shown in FIG.
It is as follows.

First, the prism 1 has a first inner surface 114A, a second inner surface 122, a third inner surface 123, a fourth inner surface 113, and a fifth inner surface 131 therein.

Here, the first inner surface 114A is a part of the surface 114, has a first end 1E1 separated by a first distance from the variable mirror element 3, and has a second end from the first end 1E1. It is inclined with respect to the projection optical axis 6 so as to move away from the variable mirror element 3 toward 1E2. The first inner surface 114 </ b> A can totally reflect the light beam 20 incident from the outside and propagate the reflected external light beam 20 toward the variable mirror element 3 in the prism 1.
When the first reflection state light ray bundle 21 transmitted through the second and fourth inner surfaces 113 is incident, the first reflection state light ray bundle 21 is transmitted and propagates through the prism 1 toward the projection lens 5. It has optical properties to be obtained. In order to satisfy such optical characteristics, a dielectric multilayer film (not shown) is coated on the first inner surface 114A, and the dielectric multilayer film is provided with a light amount of the incident first reflection state light beam 21. Is set to be able to transmit most of the light (for example, the transmittance can be designed to be 99%).

The second inner surface 122 is provided with the variable mirror element 3
And a first end 2E1 and a second end 2E2 which are separated by a second distance larger than the second distance and smaller than the first distance by a third distance, respectively, and have the following optical characteristics. That is, when the external incident light beam 20 totally reflected by the first internal surface 114A enters, the second inner surface 122 transmits the external incident light beam 20, irradiates the variable mirror element 3 and is reflected by the variable mirror element 3. When the first bundle of rays in the first reflection state is incident on the first bundle of rays, the first bundle 21 of the incident first reflection state rays is transmitted, while the first bundle of rays reflected by the variable mirror element 3 is transmitted. Of the light ray in a second reflection state different from the first reflection state within the first
When the bundle enters, the first of the incident second reflection state rays
The bundle 22 may be totally reflected. Also in this case, the second inner surface 122 can transmit most of the light amount of the incident first reflection state light beam 21 (for example, the transmittance is 99%).
On the inner surface 122, a dielectric multilayer film (not shown) is coated.

Here, the first distance, the second distance, the third distance, and the fourth distance described later are distances from the center of the reflecting surface of the variable mirror element 3 intersecting the projection optical axis 6 to the object. Defined. In this definition, (first distance)> (third distance)> (second distance), and (second distance) <(fourth distance). Alternatively, the first distance, the second distance, the third
The distance and the fourth distance are defined as the shortest distances when the target is viewed from a plane including the reflecting surface of the variable mirror element 3. In this definition, it can be considered that (second distance) = (fourth distance).

Further, the third inner surface 123 is
A first end 3E1 and a second end 3E2 are located on the same plane as A and are separated from the variable mirror element 3 by the fourth distance and the third distance, respectively. The second end 2E2 of the second inner surface 122 corresponds to the second end 3E2 of the third inner surface 123. In other words, both sides 122, 1
Reference numeral 23 crosses or connects at the end 2E2 (3E2). In addition, the third inner surface 123 is
The second bundle 21 of the first reflection state light rays incident without incident on the inner surface 122 can be transmitted and propagated to the projection lens 6 side, and the second reflection state light rays incident without incident on the second inner surface 122 can be transmitted. It has optical characteristics that allow the second bundle 23 to pass through. Furthermore, the third inner surface 123 is
The first bundle 22 of the second reflection state light rays which are totally reflected by
Is totally reflected by the second inner surface 122, and is secondarily reflected again by the second outer surface 121 and enters.
The first bundle 22 of reflected light rays may be transmitted. even here,
For the same purpose, a dielectric multilayer film (not shown) is coated on the third inner surface 123.

The fourth inner surface 113 is arranged in parallel with the second inner surface 122, and almost all of the external incident light beam 20 totally reflected and incident on the first inner surface 114A and the first reflected light It has optical characteristics that allow most of the first bundle 21 of state light to pass through. Here, for the same purpose, a dielectric multilayer film (not shown) is coated on the fourth inner surface 113.

The fifth inner surface 131 is provided on the first inner surface 114A.
And the third inner surface 123 are disposed in parallel with each other.
It has an optical characteristic that allows most of the light beam incident after exiting both prism pieces 11 and 12 to pass through. Here, for the same purpose, the fifth inner surface 131 is coated with a dielectric multilayer film (not shown).

On the other hand, the prism 1 has the following outer surface. That is, the prism 1 includes the first outer surface 111 and the second outer surface 111.
An outer surface 121, a third outer surface 133, a fourth outer surface 132,
It has a fifth outer surface 112 and an exposed portion 114B of the surface 114.

Here, the first outer surface 111 is the first inner surface 11
The incident surface is disposed at a position facing 4A, and is capable of transmitting an incident external incident light beam 20 and propagating through the prism 1 toward the first inner surface 114A.

The second outer surface 121 is arranged at a position facing the variable mirror element 3, the second inner surface 122 and the third inner surface 123, and corresponds to the first end 2E1 of the second inner surface 122. It has one end and a second end corresponding to the first end 3E1 of the third inner surface 123. And the second outer surface 1
Reference numeral 21 denotes an externally incident light beam 20 which is transmitted through the second inner surface 122 and is emitted to the variable mirror element 3 side, and is reflected by the variable mirror element 3.
1, 22 and 23 are light working surfaces that can enter the prism 1.

The third outer surface 133 is a surface substantially parallel to the second outer surface 121 and is disposed at a position facing the projection lens 5, and is located above the first end 3E1 of the third inner surface 123. And a second end 3OE2 adjacent to the second end 1E2 of the first inner surface 114A. In addition, the third outer surface 133 is formed by the first bundle 21 of the first reflection state light beam that passes through the first inner surface 114A and enters the third inner surface 123.
This is an exit surface that can transmit the second bundle 21 of the first reflection state light rays that are transmitted through the first reflection state light.

The fourth outer surface 132 is the first outer surface 111,
The first end 30 of the third outer surface 133 is disposed at a position facing the inner surface 114A, the third inner surface 123, and the fifth inner surface 131.
It has a first end connected to E1 and a second end located above and adjacent to the second end 3E1 of the second outer surface 121.

The fifth outer surface 112 is in the same plane as the second outer surface 121, and has a first end adjacent to the first end 2E1 of the second outer surface 121 and a second end connected to the first outer surface 111. Is provided.

Except for the fourth outer surface 132 (however, as described later, when the light shielding member 7 is provided above the fourth outer surface 132, the fourth outer surface 132 is also included), the other outer surfaces 11
1, 121, 133, 112, and 114B are coated with a dielectric multilayer film (not shown) for the same purpose.

As described above, the second outer surface 121 and the third outer surface 1
33 inside the prism 1 along the direction from the variable mirror element 3 toward the projection lens 5.
, A fourth inner surface 113, a first inner surface 114A, and a fifth inner surface 131
Are sequentially arranged, and the third inner surface 123 and the fifth
The inner surface 131 and the inner surface 131 are sequentially arranged.

In FIG. 1, light rays indicated by arrows represent trajectories of light rays included in a plane (meridional plane) parallel to the drawing.

Hereinafter, the optical operation of the illumination optical system will be described with reference to FIG. 1 and the drawings described later.

(Deflection Action) First, the deflection action for the light incident on the prism 1 will be described with reference to FIG.

The illumination light beam 20 illuminating the variable mirror element 3
Is incident on the first prism piece 11 from a surface 111 (first surface; an incident surface on which a light beam incident from the outside can enter) perpendicular to the illumination optical axis 60.

The surface 114 of the first prism piece 11 (second surface, which is provided as a first reflecting surface on the side far from the variable mirror element 3) and the surface 131 of the third prism piece 13 (seventh surface) The illumination light beam 20 travels inside the first prism piece 11 to reach the surface 114, where the illumination light beam 20 reaches the surface 114. Is totally reflected at the interface with.

That is, the surface 114 is the incident illumination light 2
0 is inclined with respect to the illumination optical axis 60 such that total reflection occurs.

A part of the illumination light beam 20 deflected by the total reflection on the surface 114 passes through the adjacent second prism piece 12 and then exits from the prism 1 to be output from the variable mirror element 3.
To reach.

Since the cover glass 4 can be regarded as an optical plane-parallel plate, a detailed description is omitted here as it is an element that merely changes the optical path length.

Now, the surface 113 of the first prism piece 11
(Third surface) and the surface 122 of the second prism piece 12
(A fourth surface, which is provided as a second reflecting surface on the side closer to the variable mirror element 3), is also opposed to each other via a minute air gap as described later, and is arranged in a positional relationship parallel to each other. Therefore, a part of the illumination light beam 20 totally reflected on the surface 114 is transmitted to the surface 113 of the first prism piece 11.
And the air layer between the second prism piece 12 and the surface 122.

Strictly speaking, the presence of this air layer (the air layer in the air gap) refracts the illumination light beam 20, and the traveling direction of the illumination light beam 20 slightly deviates from the straight traveling direction. Has a thickness of about several μm as described later, and is set to be substantially constant along the extending direction of the both surfaces 113 and 122. Therefore, the influence of this refraction should be almost ignored. Can be.

Also, the surface 112 of the first prism piece 11 and the surface 121 of the second prism piece 12 (fifth surface. (A light-emitting surface that emits a light beam that irradiates the mirror element 3 and that can also receive reflected light from the variable mirror element 3). The behavior of the light ray 20 emitted from the prism 1 toward the variable mirror element 3 can be considered to be the same regardless of the emission position.

That is, when the prism 1 is viewed with respect to the deflecting action of the prism 1, the first prism piece 11 and the second prism
One prism piece having a triangular cross-sectional shape in which the prism piece 12 is integrated can be assumed.

Next, the prism 1
Will be described.

The variable mirror element 3 can create two different reflection states, such as the first reflection state and the second reflection state described above.

First, in the first reflection state, the variable mirror element 3 reflects the incident illumination light beam 20 toward the projection lens 5.

The ON light (first reflected state light beam) in FIG.
Numeral 21 passes through the prism 1 almost linearly and reaches the projection lens 5.

As shown in FIG. 1, the ON light 21 is applied to an air layer (between three opposing surfaces of the three prism pieces constituting the prism 1, ie, the first to third prism pieces 11 to 13). Air gap) is likely to be transmitted.

However, these air layers (air gaps) each have a thickness (surface interval) of about several μm, and have a substantially constant thickness, as will be described later. Are set to be parallel to each other, it is possible to minimize the influence of refraction on the ON light 21 caused by passing through the air layer.

Of course, the surface 114 of the first prism piece 11 and the surface 123 (sixth surface) of the second prism piece 12 are arranged so as to be flush with each other. 11 and the surface 121 of the second prism piece 12
Are the same plane, and these two surfaces 112, 12
1 and the surface 133 of the third prism piece 13 (eighth surface, which is also an emission surface substantially parallel to the surface 121 capable of emitting a light beam from the variable mirror element 3 as a light beam going to the projection lens 5). Are arranged parallel to each other.

As described above, the prism 3 constituting the prism 1
Regarding the first prism piece 11 and the second prism piece 12 among the one prism pieces 11, 12, and 13, one prism piece (for example, the first prism piece 11) is connected to the other two prism pieces (for example, Second and third prism pieces 12, 1
3) and two opposing surfaces opposing each other via an air gap, and the first and second reflecting surfaces 114 and 12 described above.
2 corresponds to one of the two opposing surfaces.

Therefore, when viewed macroscopically, the ON light 21 can be regarded as being transmitted through an optically parallel flat plate disposed between the variable mirror element 3 and the projection lens 5.

On the other hand, in the second reflection state, the illumination light beam 20 is emitted (reflected and deflected) on the opposite side to the incident direction of the illumination light beam 20 with the projection optical axis 6 interposed therebetween, and is turned off as shown in FIG.
Light (second reflected state light beam) 22 (first light beam) and 23
(Second bundle).

Since these OFF lights 22 and 23 are light rays deviating from the light receiving angle of the projection lens 5, this second reflection state is when the image light projected on the screen is OFF.
, Ie, black display.

In this state, the OFF light (the first bundle of light rays in the second reflection state) 22 is applied to the surface 12 of the second prism piece 12.
2, the light is totally reflected, and its traveling direction is largely deflected to the right in FIG.

That is, the surface 122 of the second prism piece 12
Is arranged at a predetermined angle with respect to the projection optical axis 6 and totally reflects light rays having an incident angle equal to or greater than a certain value (an angle satisfying the total reflection condition).

The OFF light ray 22 totally reflected by the surface 122 propagates inside the second prism piece 12 rightward in FIG. 1, and a part of the OFF light 22 reaches the surface 121 and is incident at this time. Since the angle is very large, the light is totally reflected again on the surface 121 and travels in the second prism piece 12 rightward in FIG. Also, the OFF light 22 that has reached the surface 123 directly after being totally reflected by the surface 122 is also totally reflected by the surface 123 and then reaches the surface 121 because the incident angle at this time is very large. Since the incident angle is not large, a part of the light is reflected by the surface 121 and reaches the surface 123 again. Thus, most of the OFF light 22 totally reflected by the surface 122 is
The light passes through both surfaces 123 and 131 and reaches the surface 132 of the third prism piece 13. Further, the OFF light (the second bundle of the second reflection state rays) 23 also reaches the surface 132 through the two surfaces 123 and 131. Therefore, these OFF lights 22,
The light shielding member 7 is arranged on the surface 132 in order to absorb the light 23.

With this configuration, the OFF
Most of the light 22 and 23 do not enter (are not taken into) the inside of the projection lens 5, and are caused by scattering on the inner surface of the lens barrel of the projection lens 5 and the lens surface (lens surface, boundary surface). The generation of ghost light can be reduced, and an improvement in contrast can be realized mainly by suppressing light output in a black display state on a screen.

The illumination light beam 2 propagating in the first prism piece 11 before reaching the surface 114 of the first prism piece 11
0 does not collide with the surface 113 of the first prism piece 11. Therefore, the surface 122 of the second prism piece 12
To the OFF light 22 reflected by the variable mirror element 3.
Can be arranged at a position where total reflection can be performed. or,
Surface 113 of first prism piece 11 and second prism piece 1
The air layer (air gap) interposed between the second surface 122 and
The illumination light 20 and the ON light 21 are hardly affected. In the present prism 1, the OFF lights 22 and 23 can be effectively guided to the light shielding member 7.

(Prism Design Example) Now, in order to more specifically explain the effect of improving the contrast of the prism 1, a design example of the prism 1 will be shown and qualitative consideration will be made. here,
A DMD is assumed as a specific example of the variable mirror element 3, and a specific example of the prism 1 according to the characteristics of the DMD described above is shown (hereinafter, an example of the variable mirror element 3 is D
An example using an MD is shown and referred to as DMD3).

The design of the prism 1 is as follows.
The design can be broadly divided into a DMD 3-side prism piece composed of the first and second prism pieces 12, that is, a design of an illumination light-side prism piece and a design of an image light-side prism piece composed of a third prism piece 13.

FIG. 2 is a schematic diagram for explaining the design parameters in the design of the prism 1. In FIG.
Is an illumination optical axis for the DMD 3, 62 is an illumination optical axis inside the first prism piece 11 after total reflection on the surface 114 of the first prism piece 11, and α and β are apex angles characterizing the shape of the prism 1.

The other reference numerals are the same as in FIG. 1 and the description is omitted. The description will be made on the assumption that the angle between the projection optical axis 6 and the illumination optical axis 61 is 20 °.

First, the first prism piece 11 on the DMD 3 side
And the second prism piece 12 are integrated, the apex angle α and the apex angle β in the meridional plane (in the paper plane) are obtained, and the design is started by designing a prism satisfying the illumination condition of the DMD 3.

As a design condition of the apex angles α and β, all illumination light fluxes incident on the prism 1 satisfy the condition of total reflection on the surface 114 of the first prism piece 11 and are deflected to the DMD 3 side. 1 illuminates the DMD 3 with an incident light beam angle of 20 °.

It is necessary to satisfy two conditions that reflected light (ON light) traveling from the DMD 3 to the projection lens (not shown) is transmitted through the total reflection surface. The condition can be easily obtained by assuming a wedge-shaped prism shown in FIG.

FIG. 3 is a schematic diagram for explaining the behavior of light rays assuming a virtual solid. FIG. 3 shows a prism piece 10 in which the first prism piece 11 and the second prism piece 12 in FIG. 2 are integrated, and a three-dimensional contour obtained by mirror-inverting the same piece 10 in plane symmetry with respect to the total reflection surface 115. Is indicated by a dotted line.

When considering the setting of the apex angles α and β, a wedge-shaped virtual prism formed by the prism piece 10 and the dotted line may be considered. In FIG. 3, 200 indicated by a solid arrow.
Indicates the behavior of a light beam that is perpendicularly incident on the incident surface 116 of the prism piece 10.

The actual exit surface of the prism 10 is a surface 118.
Reference numeral 119 denotes a virtual exit surface of a prism (virtual prism) imagined corresponding to the exit surface 118 on the entity.

Since the angle between the projection optical axis 6 and the illumination optical axis 61 is set to 20 °, the ray emitted from the virtual exit surface 119 is only 20 ° with respect to the normal 63 of the virtual exit surface 119. Assume a state of inclination. At this time, assuming that the incident angle on the virtual emission surface 119 is θ, the following relational expression (1) holds between α, β, and θ.

[0151]

(Equation 1)

Here, n is the refractive index of the material forming the prism piece 10.

(Total reflection condition on prism piece)
A condition is determined in which all light rays incident on the prism piece 10 exhibit total reflection.

FIG. 4 is a schematic diagram for explaining the conditions for total reflection of light rays. In FIG. 4, a solid arrow indicated by 201 indicates an outermost angle ray incident on the total reflection surface 115 at the smallest angle among rays incident on the prism piece 10, and this ray can satisfy the total reflection condition. If this is the case, all incident light rays will exhibit total reflection.

In FIG. 4, γ is the ray 201 and the total reflection surface 115.
And the incident angle with respect to the total reflection surface 115. At this time, the F number of the illumination light beam is defined by the angle δ in FIG.

[0156]

(Equation 2)

The following expression (3) is established by the incident angle γ of the light ray 201 on the total reflection surface 115 and the refraction of the light ray on the incident surface 116.

[0158]

(Equation 3)

Since the incident ray 201 satisfies the condition of total reflection on the total reflection surface 115,

[0160]

(Equation 4)

Holds. Further, the following expression (5) is established from the expressions (3) and (4).

[0162]

(Equation 5)

Note that α when both sides of the equation (5) are equal is particularly α1.

The illumination light beam to the DMD 3 is transmitted to the total reflection surface 11.
5 is not only totally reflected, but also the virtual exit surface 1 of FIG.
It is also necessary that all rays pass through 19 (this is the condition for ensuring that the illumination ray bundle is illuminated to the DMD 3).

FIG. 5 shows the behavior of the light beam 202 which is incident on the illumination optical axis 60 at an angle δ on the opposite side to that shown in FIG.

In FIG. 5, ω is the angle between the light ray 202 and the normal 63 of the virtual exit surface 119, and indicates the angle of incidence on the virtual exit surface 119.

Since the light ray 202 enters the virtual exit surface 119 at the largest angle ω, it must be confirmed that total reflection occurs here and the light ray is not confined in the prism piece 10. In this case, first, the following equation (6) holds for the angle ω.

[0168]

(Equation 6)

The condition under which total reflection does not occur on the virtual exit surface 119 can be expressed by the following equation (7).

[0170]

(Equation 7)

Therefore, the following equation (8) is established from the equations (6) and (7).

[0172]

(Equation 8)

FIG. 6 is a graph in which both sides are plotted as a function of the refractive index n based on the equation (8).
However, the F-number of the illuminating light beam bundle defined in Expression (2) was set to 3. In FIG. 6, what is indicated by a broken line is a function of the refractive index n corresponding to the left side of Expression (8), and a solid line similarly indicates the function of the right side.

From the graph shown in FIG. 6, it can be seen that the inequality of equation (8) holds between 1.45 and 1.85, which is the range of the refractive index of general optical materials.

(Condition of Prism Vertex Angle) Next, the condition of the prism vertex angles α and β based on the behavior of the ON light traveling from the DMD 3 to the projection lens is obtained.

FIG. 7 shows two prism pieces 10 and 13
And a prism 100 composed of DMD3
3 shows a ray 203 that enters the total reflection surface 115 at the largest incident angle ν from among the ON lights from the light source 203. Also,
Numeral 64 denotes a normal line of the total reflection surface 115, and other symbols are as described above.

Now, if the light beam 203 is transmitted toward the prism piece 13 without being totally reflected on the total reflection surface 115,
All the image light from the DMD 3 is transmitted to the prism piece 13 side. First, the following equation (9) holds for the incident angle ν.

[0178]

(Equation 9)

The condition under which total reflection does not occur can be expressed by the following equation (10), similarly to equation (7).

[0180]

(Equation 10)

From equations (9) and (10), the following inequality (1)
1) is obtained.

[0182]

[Equation 11]

It is to be noted that α, when both sides of the equation (11) are assumed to be equal, is α2 in particular.

From the above, the conditional expressions relating to the apex angles α and β that define the basic shape of the prism 10 have been derived. In this case, in order to determine the shape of the prism 10, the vertex angle α that satisfies both the conditions of Expressions (5) and (11) may be obtained, and β may be obtained from Expression (1).

FIG. 8 is a plot of the angle α1 according to equation (5) and the angle α2 according to equation (11) as a function of the refractive index n of the prism material. The horizontal axis is the refractive index of the prism material, and the vertical axis is the angle.

From the relationship between the ranges represented by the two inequalities of Expressions (5) and (11), the range between the dotted line indicating the angle α1 and the solid line indicating the angle α2 (the angle selection range described later) changes from the apex angle α.
You can choose the value of

As can be easily understood with reference to FIG. 8, the refractive index of the practical optical material is 1.
In the range of 45 to 1.85, the angle α is about 3
An optimal value can be chosen between 8.0 ° and about 50.4 °.

In this case, the angle β can be easily associated with the equation (1), and an optimum value can be selected between about 25.0 ° and about 38.0 °.

As a practical specific example, the material of the prism 10 is BK7 (nd = 1.5168), the F number of the illumination light beam of the DMD 3 is 3, the illumination optical axis of the DMD 3 and the DM
Assuming that the angle between the normal of D3 and the normal is 20 ° as described above (that is, equivalent to illuminating the DMD3 with the incident angle of the illumination light beam of 20 °), the apex angle α is 47.55 °.
The optimal value may be selected between the range of 47 ° to 47.97 °. At this time, the angle β obtained from the equation (1) is 34.52 °
And a value between 34.94 °.

FIG. 9 shows the material of the prism 10 (in this case, B
Considering the chromatic dispersion in K7), the C-line (656.2)
7 nm. The refractive index at this wavelength is denoted by nC, the d-line (587.56 nm; the refractive index at this wavelength is denoted by nd), and the F 'line (479.99 nm; the refractive index at this wavelength is denoted by nF'). The value of each apex angle α in the case is plotted, and the horizontal axis and the vertical axis are the same as in FIG.

Thus, considering the wavelength dispersion of the material of the prism 10, it can be understood that α ≒ 47.7 ° is preferable, and in this case, β ≒ 34.7 °. Not limited to this value, if the range in which the refractive index due to the wavelength dispersion of the material can be taken is included in the angle selection range shown in FIG. 8, it is a visible light region and the refractive index is about 1.45 to 1.85. In this range, a suitable prism material can be selected.

On the other hand, the prism piece 13 shown in FIG.
Is the same regardless of whether the prism on the DMD 3 side is a single prism piece or a composite of a plurality of prism pieces. As shown in FIG.
3 is parallel to the surface 121 of the second prism piece 12.
Therefore, it can be considered that one relatively thick glass plate is arranged between the DMD 3 and the projection lens 5.
As described above, since the prism 1 is constituted by the parallel flat plate constituted by the plane perpendicular to the projection optical axis 6, the design of the projection lens 5 can be made very simple.

FIG. 10 shows a ray trajectory when the reflected light from the DMD 3 is incident on the prism 10 composed of two prism pieces based on the above design. FIG. 10 illustrates both ON light that travels with a predetermined spread in the direction of the DMD 3 normal line and OFF light that travels in a direction inclined by a predetermined angle from the DMD 3 normal line.

Although the light shielding member 7 is provided on the side surface of the prism 13, there is a high possibility that the OFF light reaching the area surrounded by the dotted ellipse in FIG. 10 enters the projection lens as it is.

The reason is that a telecentric lens is often used as a projection lens of a projector for the purpose of increasing the peripheral light amount of a screen, and such a telecentric lens receives all ON light shown in FIG. This is because, in many cases, a lens having a large lens aperture is used, so that a situation arises in which OFF light easily enters the projection lens.

An example in which the ray tracing is performed by computer simulation using an example of a telecentric lens and the manner in which OFF light enters the projection lens will be described below.

FIG. 11 is an output of a computer simulation by an optical system in which a telecentric lens 51 having an F-number of 3 is disposed immediately after the prism 100, and is an enlarged view of a portion necessary for explanation.

Referring to FIG. 11, a part of the OFF light emitted from DMD 3 enters projection lens 51, and repeatedly reflects on the inner lens surface of projection lens 51, and further proceeds inside projection lens 51. You can see how it goes.

In the case shown in FIG. 11, the number of OFF light rays is shown to be small for easy understanding, and it seems that the influence is small, but actually more OFF light is projected. Unnecessarily entering the lens.

In principle, light rays entering at an angle larger than the F-number of the projection lens 51 are absorbed by the stop surface in the lens, the inner surface of the lens barrel of the projection lens 51, etc., and reach the projection screen (screen). Should not be done.

However, the light absorption of the stop surface and the inner surface of the lens barrel is not actually perfect (not a perfect absorber), and the imperfections of the anti-reflection coating applied to the surface of each lens (reflection In reality, stray light is generated at various positions, and the stray light reaches the screen, thereby reducing the contrast of the projected image.

Therefore, if the OFF light can be prevented from entering the projection lens 51, the contrast of the projected image can be directly and greatly improved.

(Regarding the Design of Prism Pieces) Therefore, in the following, OFF is likely to enter the projection lens mainly.
A method for designing the prism piece 12 (FIG. 1) that effectively acts on light rays will be described.

In order to design such a prism piece 12, the behavior of the OFF light reflected from the DMD 3 and the behavior of the light beam incident on the prism piece 12 and reaching the total reflection surface of the prism piece 12 are examined. There is a need.

FIG. 12 is a schematic diagram showing the behavior of the OFF light reflected from the DMD 3.

A ray 204 is a ray reflected from the leftmost portion of the DMD 3 in FIG.
(Here, an example in which the projection optical axis 6 and the normal line of the DMD 3 match will be described. For convenience, the normal line of the DMD 3 is
OF emitted in a direction inclined by 40 ° from
A ray tilted further outward (in a direction closer to the normal 6) by an angle δ from the optical axis 65 of the F light is shown.

Reference numeral 66 denotes a direction axis of the light beam 204, 205
Is a ray passing through a point P on the reflection surface 122 and defining the position of the reflection surface 122.

The OFF ray bundle reflected by the left end of the DMD 3 in FIG. 12 and entering the prism piece 12 has a distribution spread from the optical axis 65 to the left and right in FIG. Therefore, if the OFF light 204 can be totally reflected by the reflecting surface 122 of the prism piece 12, all the reflected light having other angles is totally reflected by the reflecting surface 122 and travels rightward in FIG. Become. Therefore, based on the condition of the total reflection, the required vertex angle κ of the prism piece 12 is obtained.
Can be obtained.

FIG. 13 is an enlarged view showing the prism piece 12 in an enlarged manner. The derivation of the apex angle κ will be described with reference to FIG. In FIG. 13, reference numeral 67 denotes a normal line of the reflection surface 122.

The angle ε between the light beam 204 and the normal 6 of the DMD 3 when the light beam 204 enters the inside of the prism piece 12 can be expressed by the following equation (12).

[0211]

(Equation 12)

Further, there is a relationship between the angles ε, κ and μ as shown in the following equation (13).

[0213]

(Equation 13)

Here, the angle μ needs to satisfy the following expression (14) from the condition of total reflection of the light ray 204.

[0215]

[Equation 14]

From the equations (12), (13) and (14), the following inequality holds.

[0219]

(Equation 15)

FIG. 14 shows the refractive index n of the material of the prism 12.
Is a parameter obtained by calculating the value of the vertex angle κ with respect to the F-number of the illumination light beam based on Equation (15), and plotting the calculation result.

According to FIG. 14, the material of the prism 12 has a refractive index of 1.45 to 1.45 which is a range of a practical refractive index.
85, the minimum value of the apex angle κ is about 16.2.
It can be seen that it takes a value between ° and 24.5 °.

As a practical example, when the material of the prism 12 is BK7 (n _d = 1.5168) and the F-number of the light beam reflected from the DMD 3 is 3, the angle κ obtained based on the equation (15) Is about 21.753 °.

The DMD 3 is provided on the reflection surface 122 shown in FIG.
It is not necessary that all of the OFF light from the light source enter the side surface 132 of the prism piece 13 like the light ray 204 shown in FIG.
It is only necessary to reflect only light rays that are likely to enter the projection lens without reaching.

However, regarding the prism piece 11 of FIG. 1, if the light beam 20 shown in FIG. 1 reaches the surface 113 before reaching the total reflection surface 114, a part of the illumination light beam is cut off and lost. Therefore, attention must be paid to the position of the air gap (air gap) provided between the prism pieces 11 and 12.

On the other hand, the light ray 20 passing through the point P shown in FIG.
5 preferably reaches the side surface 132 of the prism piece 13 (preferably, the light shielding member is provided on the upper side of the side surface 132). This is because the light beam 204 emitted from the leftmost portion of the DMD 3 in FIG. , Under the condition that the light is reflected by the reflection surface 122.

(Method for Obtaining Point P) Here, a method for obtaining the position of the point P will be described with reference to an example shown in FIG.

In FIG. 15, R is the radius of the light beam incident on the incident surface 111 of the prism 1, and point Q is the point where the outermost ray 206 of the incident light beam reaches the reflecting surface 114. I have.

Since the refraction angle δ ′ in the prism 1 is known, if the distance from the vertex S forming the apex angle α to the illumination optical axis 60 is determined, the position of the point Q is determined by using the parameters in FIG. It can be obtained from simple geometric calculations.

The point P may be located on the vertex T side from the point Q.
At this time, it is sufficient to confirm that the outermost ray 207 emitted from the DMD 3 reaches the reflection surface 122.

FIG. 16 is an output example of a computer simulation (ray tracing simulation) performed using a prism composed of two prism pieces designed according to the above-described design procedure. By obtaining the angle κ, the position of the point P or the position of the reflection surface 122 can be easily determined from such a ray trajectory.

FIG. 17 shows an output diagram obtained by ray tracing the state in which the OFF light has entered the prism 1 composed of three prism pieces designed as described above. As can be seen from FIG. 17, the total reflection surface 122 allows most of the unnecessary light rays that enter the projection lens to enter the side surface 132 of the prism.
You can go to.

In the light beam shown in FIG.
Although light rays that directly reach the final emission surface 133 are drawn, it is possible to eliminate such light rays by adjusting the position of the point P.

In this way, while maintaining the outer shape of the prism constituted by the two prism pieces, the thickness of the prism 1 when viewed from the projection lens is changed as a plane-parallel plate. In addition, the processing of the OFF light, which is a main factor of the contrast reduction, can be reliably performed.

Since the effect of improving the contrast ratio differs depending on the specifications of the entire projection optical system, it is difficult to show specific numerical values. However, the role of the OFF light processing is performed on the surface 132 and the light shielding provided on the surface 132. Since the OFF light can be concentrated on the member 7 and the OFF light is not taken in (incident) by the projection lens, the optics using the prism composed of the two prism pieces as shown in the fifth related art described above is introduced. An improvement in contrast that is several times higher than that of the system can be expected.

FIG. 18 shows a projection lens similar to that shown in FIG. 11 and a prism 1 composed of three prism pieces.
FIG. 9 is a part of an output of a computer simulation performed on an optical system in which the above is combined.

According to the output result of this simulation, it is understood that the light beam reflected by the DMD 3 and once having reached the total reflection surface 122 reaches the side surface 132 without going out of the prism 1. Therefore, the side 132
Of the OFF light that is not caught by the light blocking member provided on the upper part of the lens, almost no light ray directly enters the projection lens.

(Preparation of Prism 1) In preparing the prism 1, the accuracy of the shape and flatness of each prism piece, the stability of material characteristics, and the air gap (air gap) provided between each prism piece are considered. The formation accuracy (that is, the arrangement accuracy of each prism piece) is
Is a factor that affects the performance of

The accuracy of the shape and flatness of each prism piece is
These are the basic specifications of this prism.
The accuracy of the parallel flat plate disposed between the MD3 and the MD3 is an important factor relating to the resolution of the projected image.

Each prism piece constituting the prism 1, DM
D surface, each optical surface such as a lens surface constituting a projection lens, it is preferable to improve the transmittance by the anti-reflection coating, the surface other than the optical surface has a large effect on handling improvement and processing of stray light, for example, It is also preferable to perform a sand rubbing treatment.

Also, the value of the tolerance or dispersion of the refractive index of the prism material is important for satisfying the condition of total reflection. As will be described later, the coefficient of thermal expansion is also an important parameter for producing a prism.

The air gap (air gap) is provided to cause a total reflection effect. However, it is necessary to consider the following point, that is, a light beam transmitted without causing a total reflection effect. However, it is necessary to consider that the size and accuracy of the air gap greatly affects the performance of the optical system, particularly the resolution of the projected image.

(Formation of Air Gap) In forming an air gap (air gap), generally, a method of sandwiching a spacer, which is a member separate from the prism piece, is most often employed.
In this case, since the change in the length of the air gap due to the thermal expansion of the prism material needs to be constant regardless of the location, it is necessary to use a spacer material having the same thermal expansion coefficient as that of the prism material. Desirable (for example, when BK7 is used for the material of the prism, BK7 is used for the material of the spacer).

The degradation of the resolution due to the air gap depends first on the size of the air gap itself.

FIG. 19 is based on the assumption that a light beam having an F-number of 3 is incident on the prism 100 composed of the two prism pieces 10 and 13 shown in FIG. 7, and the DMD shown in FIG.
The relationship between the air gap inclined at a predetermined angle with respect to the optical axis 6 and the MTF used for evaluating the resolution is calculated.

The allowable deterioration of the MTF depends on the required performance of the system. If the deterioration is, for example, several%, the spatial frequency range (72 lp / m2) shown in FIG.
Spatial frequency range up to m. Here, lp / mm = li
The design condition that the air gap at (ne pair / mm) must be several microns or less can be obtained.

It is ideal that the planes forming the air gap are parallel to each other, but if the plane is biased (the air gap is relatively inclined beyond the limit that can be regarded as optically parallel). In this case, astigmatism of the projection lens is generated, causing a significant deterioration in image quality.

FIG. 20 is an example of calculation of the effect on the MTF when the air gap is biased and two surfaces that are supposed to be parallel are inclined and the air gap becomes wedge-shaped.

This calculation also assumes the optical system used for the calculation in FIG. 19, but depending on the setting of the inclination of the air gap with respect to the optical axis 6 of the DMD 3, the optical axis 6 of the DMD 3 is set.
Since the above MTF is not always the best, it is not easy to derive an allowable value of the inclination angle of the air gap.

However, the above calculation is useful for the purpose of roughly grasping the magnitude of the allowable tilt angle from the relationship between the desired resolution and the spatial frequency.

Considering the above calculation results, there is a high possibility that a prism having excellent resolution characteristics can be manufactured by setting the air gap to about 2 μm or 3 μm.

In order to realize such a minute air gap, for example, a method of coating a dielectric multilayer film or a metal film only in a predetermined minute range is preferable.

FIG. 21 is a perspective view showing such an example. In FIG. 21, reference numeral 9 denotes each of the prism pieces 11, 12 and 13 on a surface where each of the prism pieces faces another prism piece. FIG. 21 shows the provided spacer.
As shown in (1), avoid an effective area through which light rays pass (do not block), for example, a spacer 9 is provided at a corner portion of each surface.
Is arranged.

In order to form these spacers 9, coating of a multilayer film or a metal film by vapor deposition or sputtering can be adopted. In the case of the above-described spacer (spacer not depending on the coating of the multilayer film), As compared with the above, an air gap in which the space between the opposing surfaces and the occupied area of the spacer itself are much smaller can be stably formed.

Further, since minute projections having a coating laminated structure can be formed directly on the surface of each prism piece, compared with the case of using the above-described spacer (a spacer which does not depend on the multilayer coating). This simplifies the operation (step) of determining the relative positions of the adjacent prism pieces.

Further, in the case where the spacer is formed by using the coating of the multilayer film as described above, the use of an adhesive necessary for fixing the spacer can be avoided, and the function of fixing the adjacent prism pieces can be avoided. In that it can be prevented from being carried by the spacer.

The air gap between the prism pieces is secured by the above-described coating of the spacer and the multilayer film. To fix the relative positions of the prism pieces in that state, for example, an ultraviolet curable resin is used. An adhesive containing at least one of a thermosetting resin (including a silicone rubber-based resin) and a cyan-based resin can be used.

Also, the part to which the adhesive is applied is a part which satisfies the condition for avoiding the effective area through which the light beam passes, for example, the part where the spacer and the prism piece come into contact with each other. It can be applied to any of the above, or can be applied to a portion near a ridge line forming the opposing surface of the prism piece.

Alternatively, the spacer may be provided substantially with the effect of an adhesive without providing a special spacer.

Thus, the prism pieces are fixed to each other by the spacer (including an adhesive having a substantially spacer effect) and the adhesive having a coefficient of thermal expansion substantially equal to the coefficient of thermal expansion of each prism piece. .

(Regarding Fixing of Prism Pieces) With respect to the fixing of the prism pieces, a surface other than the optically active surface of the prism as a surface through which light involved in projection passes until the illumination light beam enters the projection lens. Is practically effective.

FIG. 22 is a schematic diagram showing a method of fixing the prism 1 composed of three prism pieces with a plate made of the same material as the prism material.

In FIG. 22, reference numeral 14 denotes a plate-shaped fixing member, which is used for fixing the prism pieces 11, 12, and 13 to each other.

In this case, each of the fixing members 14 has a size and a shape (areas indicated by oblique lines in the drawing) having a size and a shape capable of contacting all three prism pieces 11, 12 and 13. An adhesive may be applied to a portion corresponding to a part of the prism piece and fixed.

For the fixing in this case, an adhesive having suitable characteristics can be selected from various types of adhesives, but an adhesive whose deterioration due to light absorption or temperature change or material deformation is remarkable. Must be avoided.

When the bonding surface is not the entire contact surface between the fixing member 14 and the side surface of the prism, but is divided into a plurality of minute regions, deformation of the adhesive due to light absorption, temperature change, change over time, etc. In addition, it is necessary to select a position where the adhesive is applied so that a large stress that changes the air gap (that causes deformation of the air gap) does not act on each prism piece.

FIG. 23 is an example showing the position of the adhesive for fixing the fixing member 14 and the respective prism pieces 11, 12, and 13.

In FIG. 23, the hatched portions 15 indicate the positions where the adhesive is applied, and as shown in FIG.
The adhesive is applied to each of the positions 2 and 13 at a plurality of positions.

As described above, by dividing the location to which the adhesive is applied into a plurality of locations for one prism piece, an effect of dispersing the stress caused by the deformation of the adhesive can be obtained.

Of course, it is desirable that the thermal expansion coefficient of the adhesive has a value close to that of the material of the prism and the material of the fixing member 14.

(Regarding Light Shielding Member) Next, as an important factor related to the improvement of the contrast, the light shielding member 7 provided above the side surface 132 of the prism piece 13 will be described (illustrated in FIGS. 1 and 17). ).

The light-shielding member 7 may be a light-absorbing material made of black paint simply applied on the side surface 132, but may have an adverse effect on the prism 1 due to heat generation due to absorption of light (for example, temperature If a shape distortion due to elevation, etc.) is conceivable, a light-shielding member using a member different from the black paint may be used.

When a black paint is directly applied on the side surface 132 so as to be in close contact with the side surface 132, the side surface 1
32 is a rough surface (for example, sand rubbing is included in this)
In this case, the light reflecting effect on the side surface 132 may be suppressed to promote the light absorbing effect.

When the light is absorbed by another member, the light beam arriving at the side surface 132 is emitted to the outside of the prism 1 as it is without reflection.
In some cases, it is preferable to process the surface into a polyhedral shape instead of a plane. In this case, the outside that is separated from the prism 1 (for the one described here,
The light absorbing layer can be disposed on the outside (separated from the outside 32), and by doing so, conduction of heat generated by light absorption to the prism 1 can be suppressed as much as possible. Become.

FIG. 24 is a simulation result showing an example of the shape of the side surface 132 for efficiently emitting the light beam reaching the side surface 132 to the outside of the prism 1.

The OFF light incident on the prism piece 130 is
“OFF light2” in FIG. 24 and the total reflection surface 12
2, “OFF lig” which passes through the surface 123 without being incident on
ht 1 ”.

As shown in FIG. 24, as shown in FIG.
The side 132 of “OFF light 1” and “OFF
light 2 ”, and it can be seen that the OFF light has been successfully led to the outside of the prism 1 without fail.

If the light-shielding member (light-absorbing material) 7A is arranged, for example, at the position shown by the dotted line in FIG.
The OFF light can be processed (absorbed) without causing a rise in the temperature of the prism piece 130 itself (the prism 1 itself).

(Regarding Holding of Prism) Prism 1
When a light shielding member (light absorbing material) is disposed separately from the prism piece 13 described above, a holding member 70 for holding the prism 1 as shown in FIG. The inner surface (particularly, in this case, the prism piece 1
If a light-absorbing material is added to the inner surface facing the side surface of the prism 30, two functions such as holding the prism 1 and absorbing the OFF light can be achieved at the same time. Can be reduced.

In FIG. 25, reference numeral 70 denotes a holding member which is attached to the base portion 71 of the prism 1 and holds the prism 1. The light absorbing material is applied to the surface of the holding member 70 where the OFF light transmitted from the prism 1 is incident. (A black paint or the like).

It is to be noted that the holding member 70 is provided so that the ON light is not blocked by the holding member 70 as shown in FIG.
As shown in FIG. 5, it is preferable that the prism 1 is held at the corners (corner portions) of the prism 1 and the position thereof is fixed.

By holding in this manner, it is possible to suppress the movement of the prism 1 in the direction of contact with the base portion 71 and the movement in the direction along the projection optical axis 6.

As still another example of the shape, FIG. 26 shows a prism holding member 72 provided with an opening 74 through which light can be emitted (light emitting opening 74).

The holding member 72 not only covers the upper surface of the prism 1 (the surface including the region through which the light emitted to the projection lens passes) except for the light emission opening 74, and also includes (part of the outer shape of the prism 1). The shape 73 that covers the inclined portion 114P of the prism piece 11 (however, the holding member 72 is provided so that an air gap is interposed between the prism piece 11 and the holding member 72). That is, the holding member 7
2 (which is arranged so that the surface of the prism piece 11 does not come into contact with the opposite surface (corresponding to the back surface of the inclined portion 73)).

By doing so, the surface of the prism piece 11 can be shielded from light and dust can be prevented, and the OFF light or stray light caused by the entry of the OFF light can be prevented from being transmitted to the projection lens as much as possible. In addition, there is an advantage that the efficiency of the total reflection effect on the surface 114 of the prism piece 11 due to dirt on the surface 114 (the portion 114P exposed as the prism 1) is prevented.

Further, in order to form a prism that is less likely to change optical performance in response to external environmental changes, that is, a prism that is strong against environmental changes, the space created by the air gap may be sealed with a sealing agent or the like. desirable. In this way, for example, fogging of the optical surface due to dew condensation and deterioration due to chemical change of the glass polished surface can be suppressed as much as possible.

Note that the first, second and third prism pieces 11,
Each of 12 and 13 may be configured as a prism piece composed of a combination of a plurality of prism pieces. Further, the surface 114B of the first prism piece 11 may be an outer surface parallel to the surface 112.

As described above, the prism composed of the three prism pieces has been described from the basic configuration as shown in FIG. 1 to various modifications, but not only the embodiment described here but also the object of the present invention. It goes without saying that various modifications can be made without departing from the application and without changing the gist of the application.

[0286] Embodiment 2 (Optical System of Projector Apparatus) FIG. 27 is a diagram showing an optical system of the projector apparatus according to the second embodiment of the present invention. In FIG. 27, reference numeral 1 denotes a prism described in the first embodiment, reference numeral 5 denotes a projection lens, and reference numeral 80 denotes an illumination optical system for providing an illumination light beam to the entrance surface of the prism 1.

As an example of a variable mirror element as a light valve, the DMD 3 described in Embodiment 1 is assumed, and a single-panel type projector apparatus which performs enlarged display using only one of them will be described below. .

The optical system of the projector is mainly
Elements: prism 1, projection lens 5, DMD
The light emitted from the projection lens 5 is enlarged and projected on a screen 90 to provide a large-screen image to a viewer.

In FIG. 27, reference numeral 81 denotes a light source lamp;
Is a condensing lens for condensing the light beam emitted from the light source lamp 81, 83 is a rod element for making the intensity distribution of the convergent light beam of the condensing lens 82 uniform, and 84 is a light beam emitted from the rod element 83. An imaging lens system that forms an image on the DMD 3 at a predetermined magnification, and is generally configured to include a plurality of lenses.
8 is the optical axis of the light source lamp 81, and 85 is the optical axis
It is a reflection mirror that provides the illumination optical axis 60 of the MD3, and can be arranged at any position as needed.

Reference numeral 86 denotes a virtual opening (referred to as a light exit opening) assuming the final output surface of the illumination optical system 80.
Reference numeral 87 denotes a rotary color filter having an optical color filter region including at least three primary colors of red (R), green (G), and blue (B). For example, it is an optical element for performing colorization in a field sequential manner by rotating in synchronization with a synchronization signal of a video signal.

As described above, the illumination optical system 80 is composed of several optical elements, and serves as an optical system for illuminating the DMD 3 efficiently. When the illumination optical system 80 is viewed from the prism 1, the light exit aperture 86 immediately before the illumination optical system 80 corresponds to the illumination light source 8 shown in FIG.

As described above in the first embodiment, telecentric illumination is suitable for illuminating the DMD 3 via the prism 1.

An imaging lens system 84 used in this device
Is a lens system configured so that the light emitting surface formed on the emission end face P of the rod element 83 and having a substantially uniform light intensity distribution has a conjugate relationship with the DMD 3, and this is referred to as a telecentric lens system. With the configuration (design), the light transmission efficiency before and after the light enters and exits the DMD 3 can be improved.

In designing such a lens system, the prism 1 may be an optical element having the wedge shape described with reference to FIG. 3, but it is more simply designed as a parallel plane plate. Is also possible.

When the prism 1 is designed to have a wedge shape, after the prism 1 is emitted, the opening angle of the wedge shape becomes
It is necessary to pay attention to the change in the F-number of the illuminating light beam because it appears as a deviation of the angle of the light beam toward the DMD 3.

Actually, since the incident angle of the marginal ray incident on the DMD 3 becomes large, the F-number (the F-number 3 in the example described so far) obtained by the specification of the DMD 3 is determined according to the design of the prism 1. In some cases, an imaging lens system having a large F-number may be suitable.

A light-emitting surface having a uniform intensity distribution formed on the emission end face P of the rod element 83 is provided by a combination of the light source lamp 81, the condenser lens 82 and the rod element 83.

As an example of this combination, the light source lamp 81 is constituted by a lamp system comprising a combination of a parabolic mirror and a discharge lamp, and a substantially parallel light beam emitted from the light source lamp 81 is condensed by a condenser lens. There is a system that converges using the light guide 82 and efficiently guides the light to the incident surface S of the rod element 83.

For such an optical system (projector optical system) of a projector device that uses the rod element 83 to improve the uniformity of the illuminating light beam, for example, USP
No. 5,634,704 describes the details.

Of course, the configuration of the illumination optical system 80 in this case is not limited to that illustrated in FIG.
It is possible to provide an illuminating light flux that has high consistency with the prism 1 and that can efficiently illuminate the DMD 3 and obtain predetermined brightness and contrast when the illumination optical system 80 is enlarged and projected by the projection lens 5. For example, such an illumination optical system can be applied to the projector device.

For example, in general, a fly-eye integrator system may be employed in order to improve the uniformity of the illuminating light beam distribution, but it is possible to apply this to the present embodiment without any problem. .

[0302] Also, regarding the colorization of the projector device, there is no need to use the rotating color filter 87, and any colorization unit that has high matching with the illumination optical system 80 and can provide a highly efficient projector device. For example, it is possible to arrange this colorization part in a part of the illumination optical system in place of the rotary color filter 87 without any problem.

The above two embodiments have been described with reference to the present invention. The present invention is not limited to these two embodiments, and it is needless to say that various modifications can be made without departing from the purpose of the present invention and without changing the gist thereof.

[0304]

Since the present invention is configured as described above, it has the following effects.

According to the prisms of the first and second aspects of the present invention, a smaller prism can be obtained as compared with a conventional one (for example, the one shown in FIG. 35).

Further, according to the prism of the third aspect of the present invention, it is possible to obtain a prism capable of shortening the back focal length of a projection lens disposed outside.

Further, the prism according to claims 4 and 5 of the present invention can reliably shield the reflected light in the second reflection state of the variable mirror element.

In the prism according to the sixth aspect of the present invention, it is possible to suppress the deterioration of the resolution based on the relationship between the opposing surfaces of the adjacent prism pieces and realize a reflecting surface using the total reflection effect.

Further, the prism according to the seventh aspect of the present invention can suppress the fluctuation of the relative position of the adjacent prism piece due to the change of the temperature environment, and can suppress the performance deterioration due to the fluctuation.

In the prism according to the eighth aspect of the present invention, the air gap between the prism pieces can be stably formed, and the air gap with high accuracy can be realized.

According to the prism of the ninth aspect of the present invention, a smaller prism can be obtained as compared with the prior art.

Further, in the prism according to the tenth aspect of the present invention, it is possible to suppress the deterioration of the resolution based on the relationship between the opposing surfaces of the adjacent prism pieces, and realize the reflecting surface using the total reflection effect.

Further, according to the prism of the eleventh aspect of the present invention, it is possible to obtain a prism which can easily combine prism pieces.

Further, the prism according to the twelfth aspect of the present invention can reliably realize total reflection on a predetermined surface within the range of the refractive index of a practical prism material.

Further, the prism according to the thirteenth aspect of the present invention can reliably shield the reflected light in the second reflection state of the variable mirror element.

The projection optical system according to claims 14 and 19 of the present invention can realize a bright and high-contrast projection optical system.

Further, in the projection optical system according to the fifteenth aspect of the present invention, the prism can be reliably held without blocking each light beam.

The projection optical system according to the sixteenth aspect of the present invention can hold a prism and have a light blocking function, and can realize a projection optical system with high contrast.

Further, in the projection optical system according to the seventeenth aspect of the present invention, it is possible to suppress deterioration in performance due to dirt on the prism.

The projection display device according to claims 18 and 20 of the present invention can realize a projection display device that is bright and has high contrast.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a prism according to a first embodiment.

FIG. 2 is a schematic diagram illustrating design parameters in prism design.

FIG. 3 is a schematic diagram illustrating the behavior of light rays assuming a virtual solid.

FIG. 4 is a schematic diagram illustrating conditions for total reflection of light rays incident on a prism.

FIG. 5 is a schematic diagram illustrating the behavior of a light beam transmitted through a prism.

FIG. 6 is a graph plotting the relationship of the inequalities shown in equation (8).

FIG. 7 is a schematic diagram illustrating the behavior of a light beam transmitted through a prism composed of two prism pieces.

FIG. 8 is a graph plotting the relationship between the inequalities of Expression (5) and Expression (11).

FIG. 9 is a graph showing the wavelength dispersion dependence of the apex angle.

FIG. 10 is a diagram of ray tracing using a prism composed of two prism pieces.

FIG. 11 is an output diagram of a computer simulation for examining the intrusion of unnecessary light into the projection lens in the case of a prism composed of two prism pieces.

FIG. 12 is a schematic diagram illustrating the operation of a second prism piece.

FIG. 13 is a schematic diagram illustrating the operation of the second prism piece.

FIG. 14 is a graph showing a relationship between a vertex angle of a second prism piece and an F number of an illumination light beam.

FIG. 15 is a schematic diagram illustrating a method of determining coordinates of a point defining a second prism piece.

FIG. 16 is an output diagram of a computer simulation in which an illumination light beam deflected by a prism composed of two prism pieces is analyzed.

FIG. 17 is a ray tracing diagram illustrating the operation of a prism composed of three prism pieces.

FIG. 18 is an output diagram of a computer simulation for investigating intrusion of unnecessary light into a projection lens in the case of a prism including three prism pieces.

FIG. 19 is a graph showing the relationship between the size of the air gap of the prism piece and the MTF.

FIG. 20 is a graph showing a relationship between the inclination of a plane forming an air gap and MTF.

FIG. 21 is a schematic diagram illustrating an arrangement of spacers for defining a size of an air gap between each prism piece.

FIG. 22 is a schematic diagram illustrating an arrangement of fixing members for fixing the respective prisms to each other.

FIG. 23 is a schematic diagram illustrating an arrangement of an adhesive provided on a fixing member.

FIG. 24 is a schematic diagram illustrating a side surface shape for guiding unnecessary light reaching the prism side surface to the outside of the prism.

FIG. 25 is a schematic view showing the shape and arrangement of light absorbing means.

FIG. 26 is a schematic view showing the shape and arrangement of a light absorbing unit having an opening.

FIG. 27 is a schematic diagram of a projector optical system according to the second embodiment.

FIG. 28 is a schematic view illustrating an illumination method of a conventional reflective light valve.

FIG. 29 is a schematic view illustrating an illumination method of a conventional reflection type light valve.

FIG. 30 is a schematic view illustrating an illumination method of a conventional reflective light valve.

FIG. 31 is a schematic view illustrating an illumination method of a conventional reflective light valve.

FIG. 32 is a schematic view of an illumination optical system composed of two prism pieces according to a conventional invention.

FIG. 33 is a schematic diagram illustrating the operation of a DMD (two mirrors).

FIG. 34 is a schematic diagram illustrating a problem to be solved in an illumination optical system including two prism pieces according to a conventional invention.

FIG. 35 is a schematic view of an illumination optical system composed of three prism pieces according to a conventional invention.

[Explanation of symbols]

1, 10, 100 prisms, 3 variable mirror elements (D
MD), 5 projection lenses, 20 rays (illumination rays), 2
DESCRIPTION OF SYMBOLS 1 ON light, 22 OFF light, 6 Projection optical axis, 60 Illumination optical axis, 7 Shielding member, 8 Illumination light source, 50 lens means, 11 First prism piece, 12 Second prism piece, 13 Third prism piece , 111, 112, 11
3,114 (characterizing the first prism piece 11) plane, 121,122,123 (second prism piece 12
Planes 131, 132, 133 (third
The prism piece 13).

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03B 21/00 G03B 21/00 F 21/10 21/10 Z 21/14 21/14 Z G09F 9/00 360 G09F 9/00 360K H04N 5/74 H04N 5/74 A

Claims (20)

[Claims] A prism disposed between an external variable mirror element and an external projection lens having a projection optical axis parallel to a normal direction of the variable mirror element, wherein A first end and a second end separated by one distance, and inclined in a direction away from the variable mirror element from the first end toward the second end; A first inner surface capable of totally reflecting the reflected light beam and propagating the reflected externally incident light beam toward the variable mirror element; and a first inner surface separated by a second distance and a third distance from the variable mirror element, respectively. An end portion and a second end portion, when the external incident light beam totally reflected on the first inner surface is incident, transmits the external incident light beam, irradiates the variable mirror element, and irradiates the variable mirror element with the variable mirror element. Of the reflected ray bundle When the first bundle of light rays in the first reflection state enters, the first bundle of incident first reflection state light rays is transmitted, and the first bundle of light rays reflected by the variable mirror element is transmitted. A second inner surface capable of totally reflecting a first bundle of incident second reflection state light rays when a first bundle of light rays in a second reflection state different from the reflection state is incident; and wherein the first distance is equal to the first distance. The third distance is greater than the second distance, and the first inner surface is the first reflection when the first bundle of the first reflection state light beams transmitted through the second inner surface is incident. A prism capable of transmitting a first bundle of state light rays and propagating the same toward the projection lens. 2. The prism according to claim 1, wherein the first end portion is located on the same plane as the first inner surface, and is separated from the variable mirror element by a fourth distance and a third distance, respectively. A second bundle of first reflection state light rays that have entered without being incident on the second inner surface, can be transmitted and propagated to the projection lens side;
A second inner surface of the third inner surface, the second inner surface of the third inner surface being capable of transmitting a second bundle of the second reflection state light beams incident without being incident on the inner surface;
A prism, which corresponds to an end. 3. The prism according to claim 2, wherein the prism is disposed at a position opposed to the first inner surface, transmits the incident external light beam flux, and enters the prism toward the first inner surface. A first outer surface that is an incident surface capable of transmitting light, and a first mirror that is disposed at a position facing the variable mirror element, the second inner surface, and the third inner surface, and corresponds to the first end of the second inner surface. An end portion and a second end portion corresponding to the first end portion of the third inner surface, wherein the external incident light beam transmitted through the second inner surface is transmitted and emitted to the variable mirror element side. A second outer surface, which is a light working surface capable of entering the light beam reflected by the variable mirror element into the prism; and a surface substantially parallel to the second outer surface, facing the projection lens. The first inner surface of the third inner surface. A first end located above the end, and a second end adjacent to the second end of the first inner surface, wherein the first reflected state light beam transmitted through the first inner surface is incident. And a third outer surface that is an exit surface capable of transmitting a first bundle and a second bundle of the first reflection state light rays that are transmitted through the third inner surface and are incident thereon, wherein the second outer surface and the third outer surface are provided. The prism, wherein the second inner surface, the third inner surface, and the first inner surface are arranged between the prisms. 4. The prism according to claim 3, wherein the prism is disposed at a position facing the first outer surface, the first inner surface, and the third inner surface, and is connected to the first end of the third outer surface. A fourth outer surface having a first end portion and a second end portion located above and adjacent to the second end portion of the second outer surface; and a fourth outer surface disposed on the fourth outer surface and transmitting through the third inner surface. A light-blocking member that absorbs a second bundle of the second reflection state light beams that are incident upon the prism. 5. The prism according to claim 4, wherein the first outer surface is in the same plane as the second outer surface, and is connected to the first outer surface adjacent to the first end of the second outer surface. A fifth outer surface having a second end portion. 6. The prism according to claim 5, wherein a first prism piece having the first outer surface, the fifth outer surface, and the first inner surface; a second outer surface, the second inner surface; A second prism piece having three inner surfaces; a third prism piece having the third outer surface and the fourth outer surface; and a first prism piece, a second prism piece, and a third prism piece. An arbitrary prism piece is disposed opposite to the other two prism pieces via an air gap, and is sandwiched between the third outer face and the fourth outer face within the outer face of the third prism piece. The surface is the first prism piece.
An inner surface faces the third inner surface of the second prism piece, and a surface sandwiched between the first inner surface and the fifth outer surface of the outer surface of the first prism piece is the second prism piece. The second of
A prism characterized by being opposed to an inner surface. 7. The prism according to claim 6, wherein, of the first prism piece, the second prism piece, and the third prism piece, two prism pieces facing each other are the two prism pieces. A prism having a coefficient of thermal expansion substantially equal to the coefficient of thermal expansion of two prism pieces, the prism being fixed by a spacer and an adhesive. 8. The prism according to claim 6, wherein, of the first prism piece, the second prism piece, and the third prism piece, two prism pieces facing each other are mutually opposed. A prism, wherein the prism is disposed opposite to one of the opposing surfaces via a thin film coating provided so as to avoid a light beam passage portion. 9. A prism disposed between an external variable mirror element and an external projection lens having a projection optical axis parallel to a normal direction of the variable mirror element, wherein the prism is formed by the variable mirror element. A first prism piece and a second prism piece capable of selectively deflecting a first reflection state light beam and a second reflection state light beam respectively corresponding to different first reflection state and second reflection state. (A) the first prism piece is capable of transmitting a light beam incident from the outside, a first surface, and totally reflecting the external light beam transmitted through the first surface, A second surface for transmitting the first reflection state light beam that propagates and enters the first prism piece; and transmits the external incident light beam that propagates and enters the first prism piece after total reflection. And the first A third surface for transmitting the reflected light beam into the first prism piece; and (b) the second prism piece faces the third surface and is transmitted through the third surface to be incident. The externally incident light beam is transmitted and propagated in the second prism piece, and the first reflection state light beam that propagates and enters the second prism piece is transmitted toward the third surface side. And a fourth surface that totally reflects the second reflection state light beam that propagates and enters the second prism piece, and is opposed to the variable mirror element, and propagates through the second prism piece. The incident externally incident light beam is transmitted and propagated toward the variable mirror element, and the externally incident light beam is incident upon the first reflection state light beam generated by irradiating the variable mirror element, and Second
The second light beam, which is transmitted through the second prism piece after being totally reflected by the fourth surface while being transmitted through the second prism piece while transmitting the reflected light beam bundle together,
A fifth surface capable of at least reflecting the reflection state light beam, and the first reflection state light beam that propagates through the second prism piece and enters without entering the fourth surface after passing through the fifth surface; Transmitting the second reflected state light beam together;
The second reflection state light flux that propagates and enters the second prism piece after being reflected at least by the fifth surface is transmitted, and the second prism after being totally reflected by the fourth surface A sixth surface capable of totally reflecting the second reflection state light beam that propagates through the inside of the piece again; and (c) the third prism piece faces the second face and the sixth face. The first reflection state light beam that exits and enters the first prism piece, and the first reflection state light beam and the second reflection state light beam that exits and enters the second prism piece And a seventh surface that transmits both of the first and second reflection state light beams that are opposed to the projection lens and that propagate through the third prism piece and enter after being transmitted through the seventh surface. And an eighth surface capable of propagating to the projection lens side. Characteristic, prism. 10. The prism according to claim 9, wherein the second surface is parallel to the seventh surface, the third surface is parallel to the fourth surface, and the sixth surface is parallel to the sixth surface. A prism parallel to the seventh surface, wherein an air gap is provided between the parallel surfaces. 11. The prism according to claim 9, wherein the second surface and the sixth surface are in the same plane. 12. The prism according to claim 9, wherein an angle formed between the first surface and the second surface is defined as α, and an angle formed between the fifth surface and the sixth surface is defined as β. When the angle between the fourth surface and the fifth surface is defined as κ, the angle α is larger than 38.0 ° and 50.4 °
Angle β is greater than 25.0 ° and 37.4 °
Wherein the angle κ is an angle greater than 16.2 °. 13. The prism according to claim 9, wherein (c) the third prism piece is disposed on the side surface sandwiched between the seventh surface and the eighth surface, and disposed on the side surface. And a light shielding member that can shield the second reflection state light beam that propagates through and enters the third prism piece after transmitting through the seventh surface. 14. A light source, a condensing optical system for condensing a light beam from the light source, an incident surface on which condensed light condensed by the condensing optical system is incident, and a substantially uniform light intensity distribution A light-intensity equalizing element having an emission surface for emitting a light beam; a transmission optical system for transmitting a light beam emitted from the emission surface of the light-intensity equalization element; and a transmission optical system. The prism according to claim 9, wherein the light beam is incident as a light beam incident from the outside, and the reflection surface and the emission surface of the light intensity equalizing element outside the prism are the transmission optical system. And a first reflection state light beam that is disposed at a position that is in a conjugate relationship via the prism, and corresponds to different reflection states when the light beam incident from the prism is reflected by its reflection surface. The second reflected state ray bundle A variable mirror element to be generated, incident from the variable mirror element to the prism, then, characterized in that it comprises a projection lens, wherein the first reflection state light beam emitted said prism is incident, the projection optical system. 15. The projection optical system according to claim 14, wherein one of the outer shapes of the prism avoids a portion of the prism through which the light beam from the transmission optical system and the first reflection state light beam pass. A projection optical system, further comprising a prism holding member that holds the prism by being in contact with the unit. 16. The projection optical system according to claim 15, wherein the prism holding member includes a portion that shields the second reflection state light beam emitted from the prism. . 17. The projection optical system according to claim 15, wherein the prism holding member has a surface facing the projection lens, and the facing surface of the prism holding member has a first reflection state light beam. A projection optical system comprising a light exit aperture having a size that allows passage. 18. The projection optical system according to claim 14, further comprising: a signal generator arranged to generate an electric signal for driving the variable mirror element and output the electric signal to the variable mirror element. And a screen for receiving a light beam projected from the projection optical system. 19. A light source, a condensing optical system for condensing a light beam from the light source, an incident surface on which condensed light condensed by the condensing optical system is incident, and a substantially uniform light intensity distribution A light-intensity equalizing element having an emission surface for emitting a light beam; a transmission optical system for transmitting a light beam emitted from the emission surface of the light-intensity equalization element; and a transmission optical system. 4. The prism according to claim 3, wherein the light beam is incident as a light beam incident from the outside, and the reflection surface and the light exit surface of the light intensity equalizing element outside the prism are the transmission optical system. And a first reflection state light beam that is disposed at a position that is in a conjugate relationship via the prism, and corresponds to different reflection states when the light beam incident from the prism is reflected by its reflection surface. The second reflected state ray bundle A variable mirror element to be generated, incident from the variable mirror element to the prism, then, characterized in that it comprises a projection lens, wherein the first reflection state light beam emitted said prism is incident, the projection optical system. 20. The projection optical system according to claim 19, and a signal generator arranged to generate an electric signal for driving the variable mirror element and output the electric signal to the variable mirror element. And a screen for receiving a light beam projected from the projection optical system.