JP2000009992A - Field lens and projection optics - Google Patents

Abstract

[PROBLEMS] To reduce the size of a projection optical device and obtain a high-definition and bright projection image. A light source emitted from a light source (1), collected by a condenser mirror (2), and emitted from a first opening (4) travels along an illumination optical axis (AX).
The light is substantially collimated by the field lens 7, is incident on the display element 8, is provided with display information, is reflected by the reflection layer 9, passes through the field lens 7 along the imaging optical axis BX, and is near the second opening 11. An image is formed and projected from the projection lens 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a projection type optical device having a field lens, an optical element, and a reflection type optical system.

[0002]

2. Description of the Related Art A projection type optical device aims to project an image on a screen which is separated by a predetermined distance and to obtain a larger image than a direct-view type optical device. As an optical element having a light scattering property that can be used in a projection optical device, a suspension display element, a laser writing mode liquid crystal element, a liquid crystal element of dynamic scattering, and the like have been conventionally known.

[0003] SID Proceedings Vol. 18
/ 2, 1977, pp. 134-146, "Projection System for Light Valve" (Conventional Example 1) shows a projection optical device in which various light modulating means and a schlieren optical system are combined. As the light modulating means, a PLZT or a liquid crystal element is exemplified, and a configuration of a reflection type projection optical device other than a transmission type configuration is also shown.

Further, they are called a liquid crystal / polymer composite element, a liquid crystal / resin composite element, or a dispersion type liquid crystal element, and have a high scattering performance and a high transmittance when driven by an electric field. Japanese Patent Application Laid-Open No. 5-196923 (prior art 2) discloses an invention relating to a transmission-scattering type liquid crystal optical element capable of performing brighter and higher-contrast display and a reflection type projection optical apparatus using a parallelizing lens. And
It was disclosed in Japanese Patent Application Laid-Open No. 7-5419 (Conventional Example 3).

Further, after using a transmission-scattering type liquid crystal optical element as a reflection type element and separating a white light source into three colors of BGR, three reflection type display elements for modulating each color light and a parallelizing lens are provided. There has been known a color projection type liquid crystal display device using the same. For example, it is described in FIG. 5 of JP-A-4-142528 (conventional example 4) and FIG. 1 of JP-A-4-232917 (conventional example 5).

In each of these conventional examples, an elliptical mirror is used as a condenser mirror of a light source optical system, and divergent light emitted from the light source optical system is collimated by one convex lens, and then transmitted and scattered by three light scattering mirrors. Into a liquid crystal optical element of the reflection type.
As a color separation / synthesis system, a dichroic prism intersecting at 45 ° with each other was disposed between the convex lens for parallelizing light and the reflective element.

Further, auxiliary optical elements such as an integrator lens for increasing the utilization efficiency of the light source light flux of the light source optical system as much as possible and making the illuminance distribution in the projection screen as uniform as possible have been incorporated in the light source optical system. (Conventional example 6).

[0008]

In the prior art represented by the prior arts 1 to 5, a biconvex spherical lens or a plano-convex lens is mainly used as a lens means (hereinafter also referred to as a field lens) having a function of collimating a light beam. Spherical lenses were used. The light beam emitted from the opening of the illumination optical system is made substantially parallel and made incident on the surface of the reflective liquid crystal display element. Then, after being reflected by the reflection surface of the liquid crystal display element, the light flux emitted as display light out of the liquid crystal display element surface is placed near the aperture stop (first aperture) position of the projection optical system. An image is formed at approximately the same size as the portion (first opening).

However, no specific configuration of the light source optical system and the projection optical system to be combined when the shape of the field lens is changed has been disclosed. Further, even when the integrator lens of the conventional example 6 is used for the light source optical system, if the plano-convex spherical lens is used, much of the light flux from the first opening of the light source optical system, which has been efficiently uniformed, is largely increased by the second opening. As a result, the illuminance distribution difference in the projection screen is increased.

As one of the means for solving this problem,
It is conceivable to improve the aberration of the field lens.
For this purpose, the field lens may be composed of a plurality of synthetic lens systems. However, the production of the field lens is not easy and productivity is deteriorated. In addition, the field lens becomes thick and large in the optical axis direction.

As described above, the transmission and reflection of the reflection type optical element
A compact, lightweight, and simple structure projection-type optical device capable of projecting a high-density display light onto a screen as a bright and high-contrast ratio projection image while maintaining good scattering characteristics and using light source light efficiently. Was desired.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. That is, the first aspect of the present invention is a field lens incorporated in a projection optical device, and satisfies the following expression (2). To provide a field lens.

[0013]

H = (x ² + y ² ) ^1/2 (1) −80 ≦ k ≦ 20 (2) −5 * 10 ⁻ⁱ ≦ A _i ≦ 5 * 10 ⁻ⁱ (i Is an integer of 4 or more) (3) 1/270 ≦ (1 / R ₁ −1 / R ₂ ) ≦ 1 / 13.5 (4) Z ₁ = (h ² / R ₁ ) / (1+ (1− (k + 1) * (h / R ₁ ) ² ) ^1/2 ) + Σ (A _i * h ⁱ ) (5) Z ₂ = (h ² / R ₂ ) / (1+ (1 − (K + 1) * (h / R ₂ ) ² ) ^1/2 ) + {(A _i * h ⁱ ) (6) R ₁ } and / or R ₂ } (7)

(A) x and y are coordinate values of the lens surface in rectangular coordinates (X axis, Y axis) defined in a plane perpendicular to the optical axis of the field lens, and Z ₁ and Z ₂ are (x, y) (B) k is the conic constant of the lens surface, (c) A _i is the i-th aspherical coefficient of the first lens surface or the second lens surface, and (d) R ₁ is The paraxial radius of curvature at the center of the optical axis of the first lens surface (e) R ₂ is the paraxial radius of curvature at the center of the optical axis of the second lens surface. (F) Σ is the total term of (A _i * h ⁱ ). sum

In the embodiment 2, R ₂ = ∞ and 1
The field lens according to the aspect 1, which satisfies 3.5 mm ≦ R ₁ ≦ 270 mm is provided.

In the embodiment 3, R ₁ = ∞ and -2.
The field lens according to aspect 1, which satisfies 70 mm ≦ R ₂ ≦ −13.5 mm, is provided.

In a fourth aspect, the first lens surface or the second lens surface is provided.
The field lens according to aspect 1, 2 or 3, wherein the lens surface is an eccentric lens surface. That is, the center of the optical axis of the field lens does not coincide with the normal passing through the diagonal center point of the optical element and is decentered in the vertical or horizontal direction. A field lens according to 2, 3, or 4.

According to a sixth aspect, a light source system, an optical element having a reflective layer, a field lens, and a projection optical system are provided.
An illumination optical axis between the light source system and the optical element, a central optical axis perpendicular to the optical element surface, an imaging optical axis between the optical element and the projection optical system are set, and the central optical axis and the illumination optical axis And an intersection angle δ between the central optical axis and the imaging optical axis (intersection angle γ ≠ intersection angle δ). Or 1 field lens described in 5
The light source light emitted from the light source system proceeds along the illumination optical axis, enters the first lens surface of the field lens, exits from the second lens surface, enters the optical element, and is displayed by the optical element. Information is provided, reflected by the reflective layer, emitted from the optical element as display light, and after the display light is incident on the second lens surface of the field lens,
A projection optical device is provided, which is emitted from a lens surface, travels along an imaging optical axis, and is formed on the imaging optical axis by the field lens. In the sixth aspect, various display elements having substantially transmission / scattering operation modes can be used as display elements in addition to the above-mentioned dispersion type liquid crystal element.

[0019] In each embodiment described above, it preferably has a refractive index n _d of the field lens material is 1.45 to 1.60 (measured at a wavelength = 587.6 nm of e-line).

[0020]

First, FIG. 18 shows an example of the basic configuration of the present invention (configuration example 2). The light source light emitted from the first opening 4 of the light source optical system including the light source 1, the condenser mirror 2 (an elliptical mirror, etc.) and the first opening 4 travels along the illumination optical axis AX, and is not shown in the drawing. The light is color-separated by a mirror to become colored light, and is converted into substantially parallel light by a plano-convex aspheric field lens 7, is incident on a display element 8, is given display information, is reflected by a reflection layer 9, and is reflected again by the field lens 8.
Through the projection optical system (projection lens 10, second aperture 11)
Is formed on the imaging optical axis BX, and then projected.

The normal to the diagonal center of the surface of the display element is defined as the central optical axis, and the intersection angle γ between the central optical axis and the illumination optical axis is represented by:
An intersection angle δ is provided between the central optical axis and the imaging optical axis. In the present invention, the shape of the field lens, that is,
In the configuration example 2, the second lens element is a flat surface, and the shape of the first lens surface is formed to be aspherical, thereby giving excellent characteristics to the entire optical system.

Next, Comparative Example 1 will be described. One plano-convex spherical lens is arranged for one panel of the liquid crystal optical element, and its shape and optical specifications are shown in Table 1. FIGS. 3 (optical axis sectional view) and FIG.
(Perspective view) and FIG. 5 (geometric optical aberration diagram). One size is about 2.54 cm.

[0023]

[Table 1]

3 and 4, FLS is a plano-convex spherical lens, 8 is a reflective liquid crystal display element, and 9 is a reflective surface provided on the back side thereof. φA is the diameter of the first aperture (light source optical system), 2H is the diagonal effective diameter of the liquid crystal display element, φL is the outer diameter of the plano-convex spherical lens, and φB is the first due to the plano-convex spherical lens and the reflection surface of the liquid crystal display element. It is a real image of an aperture. That is, the second
It corresponds approximately to the diameter of the opening. W is the horizontal distance from the vertex of the field lens to the center of the first opening.
In the case of a plano-convex spherical lens, W has a value substantially equal to the focal length f.

Here, in the arrangement of the comparative example 1, the first lens is arranged such that the aberration state due to the spherical surface of the plano-convex spherical lens can be clearly understood.
An ideal coaxial optical system in which the center of the aperture, the optical axis of the plano-convex spherical lens, and the center of the diagonal of the liquid crystal display element were all matched.
Actually, the first aperture and the real image by the plano-convex spherical lens,
That is, the second openings are not overlapped with each other. Furthermore, in order to prevent mechanical interference between the components of the light source optical system and the optical components such as the lens barrel of the projection optical system, the vertical line passing through the diagonal center of the liquid crystal display element is shifted vertically or in other directions as the axis of symmetry. That is, it is necessary to dispose it eccentrically.

In this case, astigmatism due to eccentric incidence / emission is further added, and the light collection performance is further deteriorated.
In order to eliminate the influence of aberration due to the eccentricity, an ideal perfect coaxial optical system as described above was used as a model.

In FIG. 5, Y is a representative object point (light beam emission point) on the radius of the first aperture for calculating the geometrical optical aberration, and in Comparative Example 1, on the optical axis center (Y = 0.0
mm), the maximum point of the radius of the first opening, that is, the end point (Y = 1
0.5 mm) and one point in the middle (Y = 6.3 mm).

H is the effective diagonal radius of the liquid crystal display element.
On the other hand, this is the radius of the entrance (exit) pupil of the field lens and also shows the point corresponding to the height (h) in the radial direction. SA represents the spherical aberration in the optical axis direction of the light beam corresponding to h, and DX and DY represent the luminous flux of the light beam emitted from the above-described representative three object points in the X and Y directions in the first aperture plane. The graph shows aberration, that is, lateral aberration in the X and Y directions in the second aperture plane.

AS is an image plane (second aperture plane) of principal rays in both the X and Y directions emitted from each object point within a radius in the first aperture plane.
, Ie, astigmatism. All of the above units are mm. Dist. Is distortion, and this unit is shown in%.

As can be seen from FIGS. 3 and 4, in the case of the light source optical system of Comparative Example 1, the light beam emitted from the first aperture is ideally focused by a plano-convex spherical lens, that is, the projection optical system. An “image” having a size substantially equal to the diameter of the first opening should be formed at a position conjugate with the light source in the system (the position of the second opening 11 in FIG. 1). However, in practice, the light source image has a spread several times larger than that due to the aberration (spherical aberration or the like) of the plano-convex spherical lens. FIG.
As can be seen from the above, among the geometrical optical aberrations, particularly, both the spherical aberration in the optical axis direction and the lateral aberration in both the x and y directions become extremely large.

In an actual projection optical device, as described above, the first opening and the second opening, which are in a co-ordinate relationship with each other, are provided so as to be eccentric in the vertical or in another direction so as not to overlap. However, the distance from the plano-convex spherical lens is almost the same distance. Further, the second opening of the projection optical system of the projection optical device is placed near the position of the second opening. At this time, it is necessary to make the aperture stop several times larger than the first aperture as shown in FIGS. 3 and 4 so that the light beam emitted from the first aperture can be almost taken in, and the diameter of the projection lens is very large. It will be.

Normally, the aperture stop of the projection lens is located within the projection lens. Therefore, the pupil magnification of the rear group lens from the field lens to the aperture stop may be equal to or smaller than the first aperture. Many. That is, although the use of a plano-convex spherical lens in the optical system constituting the reflection type optical system has the advantage of reducing the manufacturing cost, the efficiency of utilization of the illuminating light flux is reduced, and as a result, the brightness of the projection screen is reduced. Is one of the causes of the lack.

On the other hand, the light source of the light source optical system has an intensity distribution, and the intensity is often lower at the peripheral portion than at the central portion. Furthermore, of the light flux emitted from the effective surface size of the display image of the liquid crystal display element and incident on the projection optical system, all the light fluxes going outside the aperture diameter of the projection lens are cut off. The closer the light beam is to the periphery, the greater the probability of being truncated. For this reason,
Even if the peripheral luminous flux is intentionally truncated, a brightness with no practical problem can be obtained. However, the difference in the illuminance distribution in the projection screen is further increased.

Next, FIGS. 1 and 2 are a schematic view of a side view and a plan view of a configuration example 1 of the projection optical apparatus of the present invention. Sign 1
Is a light source, 2 is a condensing and reflecting mirror (such as an elliptical mirror), 3 is an illumination light beam equalizing element (such as the above-described integrator), and 4 is a first aperture to constitute a light source optical system. Reference numerals 5 and 6 are dichroic mirrors for color separation / synthesis, 7, 17, and 27 are aspherical field lenses, 8, 18, and 28 are reflection-type liquid crystal display elements,
19 and 29 are the reflection surfaces.

Reference numeral 10 denotes a projection lens barrel, 11 denotes a second aperture, and 10 and 11 constitute a projection optical system. Reference numeral 12 denotes a normal line at the center of the diagonal line of the reflective liquid crystal display element surface, which is used as the central optical axis of the projection optical device.

Normally, the optical axis of the field lens is often coincident with this central optical axis as shown in FIG. 1, but in the present invention, the optical axis center of the field lens is shifted or tilted from this central optical axis. An eccentric field lens is used. In addition, it is also called a shift field lens or a tilt field lens. Reference numeral 13 denotes an image forming optical axis of the projection optical system, and reference numeral 14 denotes a housing of the entire optical system.

Γ is the inclination angle (incident angle) of the illumination optical axis AX of the light source optical system with respect to the central optical axis 12, δ is the inclination angle (output angle) of the imaging optical axis BX of the projection optical system with respect to the central optical axis 12, and α is The angle of the first opening from the diagonal center point of the liquid crystal display element, β
Is the angle of the second opening from the diagonal center point of the liquid crystal display element, φA is the diameter of the first opening, φB is the diameter of the second opening, ΔA is the distance between the center of the first opening and the central optical axis, and ΔB is the second. The distance between the center of the aperture or the optical axis of the projection lens and the central optical axis.

Further, in FIG. 1, θψ⊥ and 角 are angles in the diagonal effective diameter of the liquid crystal display element in the vertical direction from the center of the first opening and the center of the second opening, respectively, and θ // and ψ // are the figures. 2 is an angle that allows the horizontal diagonal effective diameter of the liquid crystal display element from the center of the first opening and the center of the second opening, respectively. W is the horizontal distance between the vertex of the field lens and the center point of the first aperture, but even in the case of a plano-convex aspheric lens,
The focal length has a value substantially equal to f.

First, the light-collecting performance of the configuration example 1 of the present invention employing the aspherical shape is compared with the “spherical shape” of the field lens of the comparative example 1 described above. Table 2 shows the specifications in the case of the plano-convex shape. In this configuration example 1, the center of the first aperture, the optical axis of the plano-convex aspheric lens, and the center of the diagonal line of the reflective liquid crystal display element are all matched to form an ideal coaxial optical system. FIGS. 6 and 7 show comparative examples. 1 shows an optical axis sectional view and a perspective view, respectively. FIG. 8 shows the geometrical optical aberration diagram. Reference numeral FLA in FIGS. 6 and 7 denotes an aspheric field lens.

[0040]

[Table 2]

As is apparent from FIGS. 6 and 7, the size of the second opening is almost as small as the size of the first opening. 8, the astigmatism (AS) and the distortion (Dist.) Do not change much, but both the spherical aberration SA and the lateral aberration in the optical axis (Z) direction are reduced by one digit or more. You can see that.

That is, in the field lens adopting the aspherical shape according to the method of the present invention, the light beam emitted from the first aperture and incident on the field lens is collimated to be incident on the reflection type liquid crystal display element and further reflected. Almost all the light beams reflected by the reflection surface of the liquid crystal display element form an "image" having a size substantially equal to the diameter of the first opening, that is, an effective second opening at a conjugate position of the first opening position. We can see that we can do it.

As described above, by using the aspherical field lens of the present invention instead of the spherical lens,
The light flux of the light source optical system can be taken into the projection optical system with almost no reduction. Hereinafter, in the present invention,
The specification range and the condition range of the aspheric field lens for increasing the brightness of the projection screen will be further described.

First, the shape specification of the field lens is preferably determined according to the size of the liquid crystal display element mounted on the projection optical device. Although the present invention is not limited to the size of the field lens, it is aimed at a relatively small and lightweight projection optical device, and the size of the liquid crystal display element is as small as about 1 to 3 in diagonal size. It is preferable to mount a display element. That is, the outer diameter of the field lens may be slightly larger than the size of the liquid crystal display element. The shape does not need to be circular, and may be rectangular which is similar to the shape of the liquid crystal display element.

In the case of a transmission scattering type liquid crystal display device,
As long as the decrease in the amount of light is not a problem, the smaller the inclination angle of the incident light from the first opening to the liquid crystal display element, the better the performance. That is, in FIGS. 1 and 2, γ and δ are
It is preferable that the light source optical systems denoted by reference numerals 1 to 4 and the projection optical systems denoted by reference numerals 10 and 11 be as small as possible without causing spatial interference, and that α, β, φA, and φB are also small. Specifically, the range of Expression 3 is shown.

[0046]

[Equation 3] 2 ° ≦ γ δ ≦ 15 ° 4 ° ≦ α β ≦ 30 °

The angle θ (θ⊥, θ //) at which the maximum diagonal diameter 2H of the liquid crystal display element is estimated is preferably in the range of Equation 4 for the same reason as α and β.

[0048]

[Equation 4] 4 ° ≦ θ (θ⊥, θ //) ≦ 30 °

On the other hand, in the present invention, the field lens is constituted by a single lens per display element. The lens shape may be a curved surface having a radius of curvature that is not flat on both surfaces instead of a plano-convex lens. Since the light beam incident on the liquid crystal display element from the field lens is made substantially parallel and incident, it can be used within a range in which Equation 5 is satisfied. At this time, it is necessary to make the center thickness of the field lens not too large. Unnecessarily increasing the lens thickness increases the weight and reduces the productivity.

[0050]

[Expression 5] f５W

Further, a relationship expressed by Equation 6 is established between the diagonal size 2H of the liquid crystal display element and f and θ.

[0052]

H = 2 * f * tan (θ / 2)

From the above, when the size of the liquid crystal display element is set to one size, f of the field lens is preferably in the range of Expression 7, and when it is set to three sizes, the range of Expression 8 is preferable.

[0054]

## EQU7 ## 47.4 mm ≦ f ≦ 363.7 mm

[0055]

(8) 142.2 mm ≦ f ≦ 1091.0 mm

In practice, as f increases, the size of the projection optical device itself also increases. Therefore, practically, in a projection optical device equipped with liquid crystal optical elements of about 1 to 3 sizes, the focal length of the field lens is preferably in the following range of Expression 9.

[0057]

## EQU9 ## 45.0 mm ≦ f ≦ 300.0 mm

In other words, in the embodiments described later, the focal length of the field lens adopts the range of Expression 8, but the aspherical surface of the present invention can be used even when the reflection type liquid crystal display element to be mounted is not about 1 to 3 sizes. There is a possibility that the focal length of the field lens deviates from the range of Expressions 5, 6, and 7.
However, the function and effect of the aspherical field lens of the present invention are similarly exhibited.

Next, regarding the surface shape of the field lens, even in the case of a single lens, there are roughly three types of shapes, that is, biconvex, convex meniscus, and plano-convex lens. The spherical aberration is generally good in the order of convex meniscus, plano-convex, and biconvex. In terms of the radius of curvature R, it can be said that the larger R is, the smaller the degree of aberration is when comparing the normalized focal length. However, this is also a relative comparison, and when both surfaces are configured by the spherical surface or the flat surface as described above, a considerably large spherical aberration in the optical axis direction or the image surface (in the second aperture plane) direction is generated as in the comparative example. Remain unchanged.

Instead, the radius of curvature of the field lens is first determined as one parameter that determines the basic shape and focal length of the lens. And the optical performance as a collimated field lens in the projection optical device is:
At least one of the lens surfaces has an aspherical shape based on a spherical shape near the optical axis. With this configuration, the above-described geometric optical aberration can be reduced as much as possible. One of the examples which can be achieved at the lowest cost is the above-mentioned plano-convex aspheric lens. When the reference spherical shape is a convex meniscus or a biconvex shape, the degree of freedom in design increases, but good performance can be sufficiently obtained even with a plano-convex aspheric lens.

Further, by making one surface of the field lens flat, it is possible to greatly reduce the manufacturing cost associated with polishing and a mold. Further, by bonding the flat surface of the liquid crystal display element with the refractive index adjusting liquid, the AR coating on the two surfaces can be eliminated simultaneously. Further, as a secondary effect of integrating with the liquid crystal display element, the position adjusting mechanism can be simplified.

However, the present invention is not particularly limited to a plano-convex aspheric lens. Dare, by using a biconvex, convex meniscus shape, bubbles at the time of bonding the plane of the field lens and the liquid crystal display surface, foreign matter, peeling at the time of temperature change,
There is an advantage that measures such as cracks are not required. Further, when the degree of freedom for independent arrangement is provided, there is an advantage that interference between planes can be prevented if the planes remain as they are. For this reason, even for an aspherical single lens having a convex or concave surface on one side, an aspherical shape that reduces residual aberration due to the spherical shape on both surfaces is adopted for at least one surface. With this combined configuration, geometrical optical aberrations can be sufficiently reduced. Here, the focal length f of the spherical single lens is generally given by Expression 10.

[0063]

1 / f = (n−1) * (1 / R ₁ −1 / R
_{2) + (n-1)} 2 * t / (n * R 1 * R 2)

Where n is the refractive index of the single lens material, R
₁ and R ₂ are the radii of curvature of both surfaces. When R ₁ is positive, and when R ₂ is negative, they represent convex surfaces outward. Also, t represents the center thickness of the lens.

Here, comparing the first term and the second term in the equation (10), the value of the first term is dominant, and it is particularly advantageous in terms of manufacturing to make the single lens as thin as possible. Therefore, it can be considered that the influence of the center thickness is the smallest. In other words, generality is not lost even if Expression 10 is simplified as Expression 11 with t = 0.

Since f is preferably in the range of Expression 9, Expression 12 holds. Furthermore, since n is the refractive index of a single lens material, it is considered that the range of the refractive index of a general lens material is in the range of Expression 13.

[0067]

F = ((n-1) * (1 / R ₁ -1 / R
₂ )) ^-1

[0068]

(12) 1/300 ≦ (n−1) * (1 / R ₁ −1 /
R ₂ ) ≦ 1/45

[0069]

[Expression 13] 1.3 ≦ n ≦ 1.9

From the equations (12) and (13), when the aspherical field lens is constituted by a single lens, the reference curvature radius R on both surfaces is obtained.
It is necessary that ₁ and R ₂ satisfy the relationship of Expression 14.

[0071]

[Expression 14] 1/270 ≦ (1 / R ₁ −1 / R ₂ ) ≦ 1 /
13.5

In the aspherical field lens used in the present invention, the luminous flux diverging from the first aperture plane of the light source optical system is made substantially parallel and made incident on the reflection type liquid crystal display element surface. It has a function of converging the reflected light beam in the second opening surface. For this reason, it is necessary to have any of the biconvex, planoconvex, and convex meniscus shapes. That is, when constituting the field lens in a single lens, since at least one surface must be convex, when the R ₁ and positive, R ₂ is in a range satisfying the equation 14, it takes a negative range from the positive sell.

On the other hand, the focal length of the field lens is an important factor that determines the size of the projection optical device. One of the factors, the lens refractive index, is specified by the material, and the possible range is also limited. Therefore, the degree of freedom for aberration correction cannot be so high. Also, if the degree of freedom R ₁ is determined from the same limitation on the focal length f, the degree of freedom R ₂ is also almost limited, so that it can be seen that the degree of freedom for aberration correction cannot be so high.

That is, even if the above-described example of a plano-convex spherical lens is changed to a combination of a double-sided spherical lens, the degree of freedom for aberration correction is not so high. In the case where the combination of R ₁ and R ₂ is only a spherical shape, when the diagonal effective diameter of the liquid crystal display element has a size of about 1 or more, the spherical aberration and the like due to the luminous flux entering and exiting the peripheral portion are particularly eliminated. Not expected.

[0075] Thus, if one surface, for example, assuming a plano-convex single lens with an R ₂ a plane, as to freely change the lens surface of the R _1, consider the aberration correction conditions due to the surface shape. Even in this case, it is sufficiently effective, and in fact, there is little need to make both surfaces spherical or aspherical even from the above-mentioned example of the plano-convex aspherical shape. However, as described above, the present invention includes the case where both sides are non-planar. Assuming that R ₂ is a plane, R ₂ = 0, and thus Equation 14 and Equation 15 are obtained.

[0076]

## EQU15 ## 13.5 mm ≦ R ₁ ≦ 270 mm

That is, in the case of a plano-convex single lens, the range that R ₁ can take is preferably the range of Expression 15. Here, even if R ₂ is not a plane but a spherical surface, as described above, R _{2
Since 2} needs to satisfy Equation 12, the degree of freedom for aberration correction cannot be sufficient. Even if it is set as the degree of freedom in design, the effect is insufficient. Therefore, by introducing an aspherical surface as in the present invention the surface shape of the R _1, without affecting the focal length limit, it is possible to satisfactorily correct spherical aberration.

The aspherical shape equation defining the aspherical shape is expressed by a general aspherical shape equation using a conical constant term as a quadratic aspherical term as shown in Expression 16. I will. Here, the second-order aspherical coefficient can be expressed not by the conical constant term but by adding the A ₂ * h ² term. In any of the equations, the shape of one surface of the field lens is the light of the surface. What is necessary is just to be able to determine the range of the continuous surface shape of the distance Z to the x, y plane at the axis vertex. In the present invention, Equation 16
Is expressed using the aspherical shape formula of

[0079]

H = (x ² + y ² ) ^1/2 (1) Z ₁ = (h ² / R ₁ ) / (1+ (1- (k + 1) * (h / R ₁ ) ² ) ^{1 / 2} ) + {(A _i * h ⁱ ) (5) Z ₂ = (h ² / R ₂ ) / (1+ (1- (k + 1) * (h / R ₂ ) ² ) ^1/2 ) + Σ (A _i * h ⁱ ) (6)

Where (a) x and y are the coordinate values of the lens surface in rectangular coordinates (X axis, Y axis) defined in a plane perpendicular to the optical axis of the field lens, and Z ₁ and Z ₂ are (x, (b) k is the conic constant of the lens surface N. (c) A _i is the i-th aspherical coefficient of the lens surface n. (d) R ₁ is the first lens. The radius of paraxial curvature at the center of the optical axis of the surface (e) R ₂ is the radius of paraxial curvature at the center of the second lens surface at the optical axis. (F) Σ is the sum of all terms of (A _i * h ⁱ ).

Here, in the case of the above-mentioned plano-convex aspheric lens,
When the conical constant k was -2.40, a favorable aberration state was obtained.
However, in this case, the spherical aberration is insufficiently corrected at the position of −2.0, and the correction is excessively corrected at the position of −2.8.
The amount of luminous flux protruding outside the opening increases. In this case, since the liquid crystal display element having the specifications shown in Table 2 and the conical constant obtained when the lens shape specification was optimized, such a range of k was the best.

However, when looking closely at the aberration diagram in FIG. 8, the spherical aberration SA in the optical axis direction goes too far in the negative direction from the positive range of the spherical surface, and the lateral aberration is Y = Y at the center of the first light source. 0.0
And the inclination of the light beam emitted from the outermost peripheral portion Y = 10.0 is reversed, which is not necessarily an ideal aberration state.

Nevertheless, it should be noted that the amount of aberration is about 1/10 to 1/20 smaller than that of the spherical lens, and the size of the second opening is also reduced to almost the same size as the first opening. At first glance, it can be said that the level is sufficiently practicable. However, to obtain a better aberration state, it is difficult to correct only the conical constant k, and a combination with a higher order aspheric coefficient is required.

On the other hand, although there are various ways of obtaining the aspherical coefficient, from equation (16), the peripheral part of the lens is more susceptible to the value of the aspherical coefficient, and the higher the power coefficient, the greater the effect. , Is expected to directly affect the lateral aberration.

If the coefficient of a high power is too large, not only the aberration but also the shape change of the peripheral portion becomes large, resulting in a field lens which is difficult to manufacture. Therefore, the power of the aspheric coefficient is not particularly limited,
An exponent of the following order is preferable, and in practice, the order of the lower order often sufficiently satisfies the purpose of error correction.

Further, the power of the aspheric coefficient term is preferably smaller as the power is as high as possible, and is preferably such a coefficient value that the negative power is increased so that the influence of each aspheric term becomes the same. . That is, in the present invention, the range of the conical constant and the aspherical surface coefficient is preferably a range as shown in Expression 17, as will be shown in Examples described later.

[0087]

-80 ≦ k ≦ 20 (2) −5 * 10 ⁻ⁱ ≦ A _i ≦ 5 * 10 ⁻ⁱ (i is an integer of 4 or more) (3)

Here, the reason why the range of k is slightly large is that k tends to be large because the degree of freedom is small when trying to suppress aberrations without using higher order aspheric coefficient terms. Because as we increase the higher order aspheric coefficient term,
It is getting smaller. Nevertheless, if the value of k exceeds the negative limit, aberration correction will be excessive, and if it exceeds the positive limit, correction will be insufficient. Similarly, if each aspheric coefficient exceeds the negative or positive limit value, the amount of aberration correction by the lower order aspheric coefficient is insufficiently corrected or excessively corrected.

Thus, the conic constant k and the aspherical coefficient A _i
In the combination of the above, correction of aberrations that are undercorrected or overcorrected with low-order aspherical coefficients in a range of coefficients satisfying Equation 17 and well-balanced with higher-order aspherical coefficients are optimally corrected. Thereby, the aspherical shape of the field lens in the target aberration state can be determined more accurately. The same applies to not only a plano-convex lens but also an aspherical shape of a lens having a biconvex or convex meniscus shape.

The above-described aspherical field lens is supposed to be arranged such that its optical axis coincides with the normal passing through the diagonal center of the liquid crystal display element. However, the present invention is also effective when the optical axis of the aspherical field lens does not coincide with the normal passing through the diagonal center of the liquid crystal display element, that is, in the case of an eccentric field lens.

This is because the liquid crystal display element is disposed so as to include the diagonal effective surface within the aperture diameter centered on the optical axis of the field lens.
This is because, if the aspherical lens shape as described above is applied, the aberration correction effect by the aspherical surface can be exactly the same. However, in this case, since the outer diameter and the center thickness of the aspherical lens become large, it becomes somewhat difficult to correct aberration.

However, by decentering the optical axis of the aspherical field lens in this manner, high-intensity illumination light is reflected by the field lens surface without relying on the antireflection coating performance of the field lens surface to project the projection optical system. There is an advantage that it is possible to prevent the formation of an unpleasant luminescent spot due to incidence on the light. In addition, it is preferable to delete a lens portion of a portion through which a light beam does not pass.

The optical material of the aspherical field lens is the same as the conventional spherical field lens, and conventionally known transparent optical glass and plastic optical material can be used. The range of the refractive index of the lens material is generally in the range of Expression 18.

[0094]

[Expression 18] 1.3 ≦ n ≦ 1.9

However, among them, in the case of a plano-convex aspheric lens shape in which the lens is in close contact with the surface of the liquid crystal display element and integrated with the surface of the liquid crystal display element, in order to prevent a reduction in the amount of light due to interfacial reflection on both surfaces and unnecessary images such as ghosts, It is preferable that the refractive index of the material and the glass surface of the liquid crystal display element be as close as possible. Usually, the refractive index of the glass surface of the liquid crystal display element is about 1.52, so that the range of the refractive index of the lens material that can tolerate the influence of the interfacial reflection is preferably the range of Expression 19. As a result, the interface reflectance can be set to approximately 0.1% or less.

Further, by selecting a material having a refractive index between the lens material and the glass surface of the liquid crystal display element as the refractive index adjusting liquid, the interface reflectance can be further reduced. Alternatively, since the refractive index range of Expression 19 can be expanded, an effect of increasing the possibility of usable lens materials can be expected. Hereinafter, an embodiment of the present invention will be described using an optical system specification table, an optical path diagram, and an optical performance diagram.

[0097]

[Number 19] 1.45 ≦ n _d ≦ 1.60

[0098] (where, n _d is the wavelength of the H _e 58
(Refractive index for 7.6 nm)

[0099]

(Example 1) In Example 1, the aspherical field lens described in Configuration Example 1 was decentered, and the light source optical system and the projection optical system were arranged so as not to cause spatial interference. The curvature radius and the aspheric coefficient value are slightly different from those of the configuration example 1. 9, 10, and 11 show an optical axis sectional view, a perspective view, and a geometric optical aberration diagram of the ray tracing optical path diagram. 9 and 10, FL1 is the aspherical field lens of the present example.

[0100]

[Table 3]

In the present example, the size φB of the second opening for substantially taking in the light flux from the first opening of the light source optical system remains at a slightly large state of about 26.7 mmφ. This is because the above configuration example is non-eccentric and completely coaxial, whereas this example is an eccentric optical system in which the optical axis is inclined by 10 ° with respect to the field lens. This is because the correction was not perfect and some aberrations remained. However, the ratio is φB / φA = 1.27.
And it became a compact size that could not be realized with a lens with only a spherical surface.

The conic constant and the lens center thickness in Table 3 are:
The difference from the case of the completely coaxial example is that the aberration correction amount changes because of the decentered optical system. This is because the center thickness and the peripheral thickness of the field lens are not increased unnecessarily, the manufacturing cost is reduced, and unnecessary aberrations are reduced as much as possible.

Example 2 Example 2 shows an example in which a slightly larger liquid crystal display element having a diagonal effective diameter of 3 is mounted. With such a size, there is no major problem even with a plano-convex lens shape. However, the outer diameter of the corresponding field lens naturally increases, and accordingly the lens center thickness and weight also increase. For this reason, in this example, instead of a plano-convex aspherical lens, a single lens having one surface aspherical and the other surface spherical is used. And the structure which does not bond a field lens and a liquid crystal display element was adopted.

Thus, the bonding yield is prevented from lowering due to bubbles and foreign matter when the large-area flat surfaces are bonded to each other, and the center thickness of the field lens is reduced by providing curvature on both sides of the field lens. This has the advantage that the lens weight is reduced and the material cost is reduced. However, it is preferable to arrange the liquid crystal optical element and the field lens very close to each other.

In order to arrange the light source optical system and the projection optical system so as not to cause spatial interference, “light source optical system—field lens—liquid crystal display element—projection optical system”
In the optical system composed of, the central optical axis is decentered with respect to the optical axis of the field lens. Although the setting of the aspherical shape of the field lens can be variously taken, in this case, among the biconvex lenses, | R ₁ | = | R ₂
|, And, R ₂ is as only spherical, tried to optimize only R ₁ aspherical. With this configuration, the center thickness can be minimized, and a decrease in productivity due to the aspherical surface can be suppressed.

(Examples 2-a to 2-e) On the other hand, as described above, even if there is a range of aspheric coefficient values and how to take them, various combinations of the numerical values are conceivable. Table 5 shows five examples. In each of the examples, although the order of selection and coefficient values of the aspherical coefficients in the present embodiment are different, the effects of the present invention are sufficiently exhibited, and the optical performance shows good results.

FIG. 12, FIG. 13 and FIG.
In Example 2-a, a cross-sectional view of an optical axis of a ray tracing optical path diagram, a perspective view, and a geometric optical aberration diagram are shown. Other illustrations of the design examples are omitted, but in all cases, the aspherical shape on the light source side and the optical aberration are slightly different, almost the same shape,
Aberration. 12 and 13, FL2 is the aspherical field lens of the present example.

[0108]

[Table 4]

[0109]

[Table 5]

(Example 3) This example shows a projection optical apparatus equipped with a liquid crystal display element having a small diagonal effective diameter of one size. With such a size, the outer diameter, the lens center thickness and the weight are not so important especially for a plano-convex lens without being a biconvex lens or a convex meniscus shape. In addition, since the bonding area is relatively small, in this example, a plano-convex aspheric single lens is used to bond the liquid crystal display element. In this case, since the liquid crystal display element is small, there is an advantage that the projection optical device can be very small.

However, also in this example, in order to arrange the light source optical system and the projection optical system so as not to cause spatial interference, the central light in the “light source optical system—field lens—liquid crystal display device—projection optical system” is used. The axis was decentered with respect to the optical axis of the field lens. Also, regarding the optical performance of aspherical field lenses, light collection performance close to the limit is also required, and strict design technology and manufacturing are required to arrange and hold optical elements with high precision in a narrow space. Technology is required.

Table 6 shows an example of specifications of the aspherical lens mounted on the projection optical apparatus of this embodiment. 15, 16, and 17 show an optical axis cross-sectional view, a perspective view, and a geometric optical aberration diagram of the ray tracing optical path diagram. 15 and 16, FL2 is an aspheric field lens.

[0113]

[Table 6]

In this example, the aspherical coefficient was used up to the 14th order. However, in addition to the decentered optical system, the shape was a plano-convex lens, its R ₁ was small, and the light source aperture diameter and the diagonal effective diameter were large. is there. For this reason, the aspherical coefficient is considerably large for aberration correction, and the aspherical surface correction is considerably strong. For this reason, the size φB of the second aperture for taking in the light flux from the first aperture is about 11.5 mmφ, and the ratio is:
It can be seen that φB / φA = 1.1, which is a very small shape that cannot be realized with a plano-convex spherical lens.

[0115]

According to the present invention, a high-performance aspherical field lens whose optical aberration is greatly improved is adopted as a field lens of a reflection type projection optical device. With this configuration, it is possible to make the light emitted from the light source system substantially parallel and make it incident on the display element, and to realize a small-sized, high-performance reflective optical device capable of obtaining a simple and bright projection screen. .

[Brief description of the drawings]

FIG. 1 is a side view of Configuration Example 1 of the present invention.

FIG. 2 is a plan view of Configuration Example 1 of the present invention.

FIG. 3 is an optical axis cross-sectional view of Comparative Example 1.

FIG. 4 is a perspective view of Comparative Example 1.

FIG. 5 is a diagram showing a geometric optical aberration of Comparative Example 1.

FIG. 6 is an optical axis cross-sectional view of Configuration Example 1.

FIG. 7 is a perspective view of Configuration Example 1.

FIG. 8 is a diagram showing a geometric optical aberration of Configuration Example 1.

FIG. 9 is an optical axis sectional view of Example 1 of the present invention.

FIG. 10 is a perspective view of Example 1 of the present invention.

FIG. 11 is a diagram showing a geometric optical aberration of Example 1 of the present invention.

FIG. 12 is an optical axis cross-sectional view of Example 2 of the present invention.

FIG. 13 is a perspective view of Example 2 of the present invention.

FIG. 14 is a diagram showing a geometric optical aberration of Example 2 of the present invention.

FIG. 15 is an optical axis sectional view of Example 3 of the present invention.

FIG. 16 is a perspective view of Example 3 of the present invention.

FIG. 17 is a diagram showing a geometric optical aberration of Example 3 of the present invention.

FIG. 18 is a perspective view of Configuration Example 2 of the present invention.

[Explanation of symbols]

1: Light source 2: Reflector 3: Uniform element 4: Aperture stop (first aperture) 5, 6: Dichroic mirror for color separation / synthesis 7, 17, 27: Field lens 8, 18, 28: Display element 9, 19 , 29: reflective layer 10: projection lens barrel 11: aperture stop (second aperture) of projection optical system 12: normal to center of diagonal of display element surface (center optical axis) AX: illumination optical axis BX: imaging light Axis 14: Housing α: Angle at which the aperture of the light source optical system is viewed from the center of incidence of the display element β: Angle at which the aperture of the projection optical system is viewed from the center of emission of the display element γ: The angle between the central optical axis and the illumination optical axis Inclination angle δ: Inclination angle between the central optical axis and the imaging optical axis φA: First aperture diameter φB: Second aperture diameter ΔA: Distance between first aperture center and central optical axis ΔB: Second aperture center and central optical axis Θ⊥: angle from the center of the first opening to the diagonal effective diameter of the display element in the vertical direction ψ⊥: Angle at which the diagonal effective diameter in the vertical direction of the display element is viewed from the center of the second opening θ //: Angle at which the horizontal diagonal effective diameter of the display element is viewed from the center of the first opening ψ //: Display element from the center of the second opening W: Angle in the horizontal direction between the vertex of the field lens and the center point of the first aperture.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02F 1/157 G02F 1/157

Claims (6)

[Claims] 1. A field lens incorporated in a projection optical device, wherein the field lens satisfies Expression 1. H = (x ² + y ² ) ^1/2 (1) −80 ≦ k ≦ 20 (2) −5 * 10 ⁻ⁱ ≦ A _i ≦ 5 * 10 ⁻ⁱ (i Is an integer of 4 or more) (3) 1/270 ≦ (1 / R ₁ −1 / R ₂ ) ≦ 1 / 13.5 (4) Z ₁ = (h ² / R ₁ ) / (1+ (1− (k + 1) * (h / R ₁ ) ² ) ^1/2 ) + Σ (A _i * h ⁱ ) (5) Z ₂ = (h ² / R ₂ ) / (1+ (1 − (K + 1) * (h / R ₂ ) ² ) ^1/2 ) + {(A _i * h ⁱ ) (6) R ₁ } and / or R ₂ } (7) (a) ) X and y are coordinate values of the lens surface in orthogonal coordinates (X axis, Y axis) defined in a plane perpendicular to the optical axis of the field lens, and Z ₁ and Z ₂ are lenses determined with respect to (x, y). (B) k is the conic constant of the lens surface, (c) _Ai is the first lens surface or the (D) R ₁ is the paraxial radius of curvature at the center of the optical axis of the first lens surface. (E) R ₂ is the paraxial radius of curvature at the center of the optical axis of the second lens surface. (F) Σ is the sum of all terms in (A _i * h ⁱ ) 2. R ₂ = ∞ and 13.5 mm ≦ R ₁ ≦
The field lens according to claim 1, which satisfies 270 mm. 3. R ₁ = ∞ and -270 mm ≦ R ₂ ≦
The field lens according to claim 1, which satisfies -13.5 mm. 4. The field lens according to claim 1, wherein the first lens surface or the second lens surface is an eccentric lens surface. 5. The field lens according to claim 1, wherein the field lens has a plano-convex shape. 6. A light source system, an optical element having a reflective layer, a field lens, and a projection optical system are provided, an illumination optical axis between the light source system and the optical element, a central optical axis perpendicular to the optical element surface,
An imaging optical axis is set between the optical element and the projection optical system, and an intersection angle γ is provided between the central optical axis and the illumination optical axis, and an intersection angle δ is provided between the central optical axis and the imaging optical axis. (Intersecting angle γ ≠ intersecting angle δ), and for one optical element, claim 1, 2, 3, 4
Or one of the field lenses described in 5, wherein the light source light emitted from the light source system travels along the illumination optical axis, enters the first lens surface of the field lens, and then exits from the second lens surface to form an optical element. , Display information is given by the optical element, reflected by the reflective layer, emitted from the optical element as display light, and emitted from the first lens surface after being incident on the second lens surface of the field lens. And a projection optical device which travels along the image forming optical axis and is formed on the image forming optical axis by the field lens.