JP2006017931A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device which attains low power consumption and high durability, and additionally, in particular attains downsizing and cost reduction. <P>SOLUTION: The image display device has a plurality of light sources 1-1, 1-2, 1-3 which generate visible light rays with respectively different wavelengths, variable diffraction gratings 3-1, 3-2 on which the light rays emitted from the plurality of light sources are made incident, and which controls advancing directions of the respective light rays by controlling the diffraction efficiency to make them into light rays advancing on the identical optical path and emit them, an image forming element 7 which has a number of pixels and forms an image by controlling the respective pixels with electric signals and controlling the light rays emitted from the diffraction gratings and a screen 9 on which the image formed with the image forming element 7 is projected via a projection lens 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus for forming an image by controlling light from a light source through an image element such as a liquid crystal panel, and in particular, in addition to power saving and high durability, an image forming apparatus that can be miniaturized. And a projector using the image forming apparatus.

  As an image forming apparatus that forms an image by controlling light from a light source through an image element such as a liquid crystal panel, for example, those described in Patent Document 1 and Patent Document 2 are known. The device described in Patent Document 1 is a device that guides light from a light source to a liquid crystal panel and uses it as a backlight, and observes an image displayed on the liquid crystal panel through an eyepiece. 10 and 11 are explanatory views for explaining the principle of the image forming apparatus described in Patent Document 1. FIG. The apparatus shown in FIG. 10 arranges a red (R) LED, a green (G) LED, and a blue (B) LED in three orthogonal incident directions of the cross dichroic mirror 40, although not shown. The light emitted from these is guided to the same optical path by the cross dichroic mirror 10 and irradiated to the liquid crystal panel to form an image. In this case, in the dichroic mirror 10, red light is reflected by the red reflecting dichroic mirror 10R, blue light is reflected by the blue reflecting dichroic mirror 10B, and green light passes as it is.

  The apparatus shown in FIG. 11 has a blue (B) reflecting dichroic mirror 20B, a red (R) reflecting dichroic mirror 20R, and a green (G) LED arranged on the same optical path, and a direction orthogonal to the optical path. By disposing the blue (B) LED and the red (R) LED at positions facing the blue (G) reflective dichroic mirror 20B and the red (R) reflective dichroic mirror 20R, respectively. , R, G, and B light are guided on the same optical path, and the liquid crystal panel is irradiated to form an image.

  In this case, when a color liquid crystal panel is used as the liquid crystal panel, the light emitted from each LED of red (R), green (G), and blue (B) is synthesized on the same optical path by a half mirror, and substantially white light Then irradiate the liquid crystal panel. When a monochrome liquid crystal panel is used, red (R), green (G), and blue (B) image signals are sequentially sent to the monochrome liquid crystal panel, and each of R, G, B is synchronized with each color image signal. The LED light sources are sequentially switched to emit light of each color. Thereby, a color image display is performed.

The apparatus described in Patent Document 2 is a projector that guides light from a light source to a DMD (digital micromirror device) panel and projects an image formed by the DMD panel onto a screen or the like by a projection lens. This device uses red (R), green (G), and blue (B) LED arrays as light sources, and the light emitted from these LEDs is sent to the same light by a cross dichroic prism (XDP) via a fly-eye lens array. The light is guided onto the road to illuminate the DMD panel, and the on / off signals of the red (R), green (G), and blue (B) LED arrays are synchronized with the on / off signals of the corresponding pixels of the DMD. By doing so, a color image is formed. The point which guide | induces the light of R, G, B to the same optical path using a cross dichroic prism (mirror) is the same as that of the apparatus of patent document 1. FIG.
Japanese Patent No. 3298324 JP 2003-186110 A

  By the way, according to the inventor's research, the above-described conventional image display device uses a half mirror such as a cross dichroic mirror to guide R, G, B light to the same optical path. It has been found that the utilization efficiency is not always sufficient, and there is a limit to downsizing the device and reducing the manufacturing cost. 12 and 13 are explanatory diagrams of the light utilization efficiency of the above-described conventional apparatus. Hereinafter, the light utilization efficiency of the conventional apparatus will be described with reference to these drawings.

Now, as shown in FIG. 12, it is assumed that the LED 11 used as the light source has a collimator lens 11b disposed in front of the LED chip 11a. In this case, the LED chip 11a as a light source has a finite size. Therefore, when collimating the light with the collimator lens 11b disposed in front of the light source, the light from the center of the light source is parallel to the optical axis O, but from a light source position that is separated by y from the center of the light source. Light exits from the collimator lens at an angle of θ shown by the following relational expression.
tan (Θ) = y / f
Here, the symbols represent the following.
Θ: angle from optical axis y: image height of light source f: focal length of collimator lens

  In the case of the apparatus shown in FIG. 10, the green light (G) emitted from the LED 11 enters the cross dichroic mirror (prism) 10 as shown in FIG. 13, and the red (R) reflecting dichroic mirror 10R and the blue light. (B) The liquid crystal panel is irradiated through the reflective dichroic mirror 10B. Here, attention is focused on the dichroic mirror 10R reflecting red (R). The green light (G) is incident on the red (R) reflecting dichroic mirror 10R at an angle determined by the above equation, corresponding to the image height of the light source. For example, light emitted from the center of the light source enters at 45 °. However, light emitted from other than the center of the light source is incident at an angle other than 45 °.

  Now, for example, as shown in FIG. 13, it is assumed that light is incident on the dichroic mirror 10R reflecting red (R) at 45 °, 38.4 °, and 51.6 °. FIG. 14 is a diagram illustrating an example of the light reflection characteristics of the dichroic mirror and the light emission characteristics of the R, G, and B LEDs. The dichroic mirror is a so-called film-shaping sharp cut filter, and the cutoff wavelength depends on the incident angle to the filter. In the example shown in FIG. 14, when the incident angle is 51.6 °, a part of the emission wavelength of the green LED is reflected. For this reason, the light use efficiency is reduced accordingly. In addition, in the blue (B) reflection dichroic mirror for the blue LED, when the light incident angle is 51.6 °, a part of the blue light is transmitted, so that the spectral utilization efficiency is lowered.

  Further, in the above-described conventional apparatus, when a cross dichroic mirror (prism) is used, a 90-degree right angle prism as shown in the figure is generally used in order to configure the cross dichroic mirror (prism) at low cost. . If it does in this way, LED will be arrange | positioned in three directions around a prism, and a comparatively big space is needed. In addition, in the case of combining with a mirror as shown in FIG. 11, a relatively large space is required in the horizontal direction in the figure.

Furthermore, the dichroic mirror that is a sharp cut filter requires that the transmittance rises (falls) sharply and that the wavelength of the rise (fall) is stable within a predetermined range between products. Several layers of coating are required for a sharp start-up, but it is not easy to produce such a multilayer coating with a high yield. Therefore, in the end, dichroic mirrors are inevitably expensive. In addition, since expensive equipment is required for film formation, capital investment is also difficult.
The present invention has been made under the above-described background, and an object of the present invention is to provide an image display apparatus that can be particularly reduced in size and cost in addition to power saving and high durability.

As means for solving the above-mentioned problem, the first means is:
A plurality of light sources each generating visible light of a different wavelength;
A variable diffraction grating device that emits light emitted from the plurality of light sources and emits light that travels on the same optical path by controlling the traveling direction of each light by controlling diffraction efficiency; and
An image forming element having a large number of pixels and forming an image by controlling the light emitted from the diffraction grating device by controlling each pixel with an electrical signal;
An image forming apparatus comprising:

The second means is
In the variable diffraction grating device, whether the incident light is allowed to pass through or is diffracted to change the traveling direction by controlling the diffraction grating function by turning on and off the voltage applied to the liquid crystal. The image forming apparatus according to the first means is characterized in that the above control is performed.

The third means is
The image forming apparatus according to the first or second means, wherein the light source includes three types of light sources corresponding to red, green, and blue colors.

The fourth means is
One of the light emitted from the plurality of light sources travels straight and passes through the variable diffraction grating device to reach the image forming element, and light emitted from another light source emits the variable diffraction grating device. The plurality of light sources and the variable diffraction grating device are arranged so as to travel to the image forming apparatus through the same optical path as that of the single light that travels straight by changing the course of the light. The image forming apparatus according to any one of the first to third means.

The fifth means is
The plurality of variable diffraction grating devices include diffraction gratings having different grating intervals, and each diffraction grating function can be independently controlled by an electric signal. An image forming apparatus according to any one of 1 to 5.

The sixth means is
An image forming apparatus according to a fifth means, wherein the number of the plurality of variable diffraction grating devices is a number obtained by subtracting 1 from the number of light sources.

The seventh means is
The image forming apparatus according to any one of the first to sixth means, wherein the image forming element is a transmissive liquid crystal panel.

The eighth means is
Each of the light sources can be instantaneously turned on and off by a control circuit,
The control circuit of each of the light source, the variable diffraction grating device, and the image forming element is controlled to turn on / off each light source, the control timing of each variable diffraction grating device, and the image formation. By synchronizing the image forming timing of the element, red light (R), green light (G), and blue light (B) sequentially reach the image forming element, respectively. It is possible to display a color image by forming an image of each color of R, G, B when light of each color of G, B reaches the image forming element. An image system apparatus according to any one of the first to seventh means.

The ninth means is
A projector comprising a projection optical system that projects an image formed by an image forming element in an image forming apparatus according to first to eighth means onto a screen.

  According to the above-described means, by controlling the diffraction function using the variable diffraction grating device, the traveling direction of the light from the plurality of light sources is controlled to be the light traveling on the same optical path and led to the image forming element. To form an image. Thereby, in addition to power saving and high durability, particularly miniaturization and low cost are enabled. This is because by using a diffraction grating, an image forming apparatus that consumes less power, has high durability, and is small and low cost can be configured relatively easily.

  That is, as a diffraction grating, for example, there is a diffraction grating using a liquid crystal that can turn on / off the diffraction grating function by voltage ON / OFF (refer to the document “Optics & Photonics News April 2003 P54 Electrically Switchable BRAGG GRATING”). . This diffraction grating can be produced by the same means as HOE (volume hologram) produced by ordinary two-beam interference, and can be provided with excellent mass productivity and at low cost. When a voltage is applied to the prepared liquid crystal, the refractive index distribution disappears to be similar to a transparent plate. When no voltage is applied, the refractive index distribution appears and functions as a diffraction grating. This switchable diffraction grating can be used as a means for synthesizing light emitted from a light source such as an LED.

  In addition, since the change of the light traveling direction by the diffraction grating is not a change of a large angle like a mirror or the like, it is possible to arrange the position of the light source with high space utilization efficiency, and a compact illumination optical system. Easy to configure. In addition, in this case, a single liquid crystal panel or DMD panel is used as the image forming element, and the R, G, B LEDs, the diffraction grating, and the panel as the light source are controlled in synchronization, thereby enabling a very compact color image. A forming device can be obtained.

  FIG. 1 is a diagram showing a configuration of a projector according to a first embodiment of the invention. Hereinafter, a projector according to a first embodiment will be described with reference to FIG. 1, and an image forming apparatus according to an embodiment of the present invention that constitutes a main part of the projector will be described. In FIG. 1, reference numeral 1-1 is a green (G) LED (light emitting diode) chip, reference numeral 1-2 is a red (R) LED chip, and reference numeral 1-3 is a blue (B) LED chip. The G, R, and B light emitted from each of the G, R, and B LED chips are respectively in close contact with each other through two collimator lenses 2-1, 2-2, and 2-3. The light is incident on the variable diffraction grating devices 3-1 and 3-2. The variable diffraction grating devices 3-1 and 3-2 are provided with voltage application devices 4-1 and 4-2 for applying a voltage to the internal liquid crystal, respectively, and are controlled by an external control circuit (not shown). It has come to be.

  In this case, in the green (G) LED chip 1-1 and the blue (B) LED chip 1-3, the light emitted from the green (G) LED chip 1-1 and the diffraction gratings 3-1 and 3- 2 so as to be incident on 2. Further, the red (R) LED chip 1-2 is disposed so that light emitted from the red (R) LED chip 1-2 travels on the optical axis O. Then, on the front side (right direction in the figure) of the diffraction gratings 3-1 and 3-2, the optical axis O and the optical axis are shared, the field lens 5, the light pipe 6, the transmissive liquid crystal panel 7, and the projection. The lens 8 and the screen 9 are sequentially arranged toward the front side. Thereby, the light of G, R, and B emitted from the LED chips 1-1, 1-2, and 1-3 of G, R, and B is the same by the two diffraction gratings 3-1, 3-2. The light is guided onto the optical path, is incident on the light pipe 6 through the field lens 5 and is adjusted to uniform light, and is then applied to the transmissive liquid crystal panel 7. The image thus formed is projected onto the screen 9 via the projection lens 8. Note that the image forming apparatus according to the present embodiment is a portion obtained by removing the projection lens 8 and the screen 9 from the configuration of the projector. The same applies to the following embodiments.

FIG. 2 is an operation explanatory diagram of the variable diffraction grating devices 3-1 and 3-2. As shown in FIG. 2, in the variable diffraction grating devices 3-1, 3-2, counter electrodes 3c, 3d are formed on the inner side surfaces of two transparent substrates 3a, 3b, and a photosensitive prepolymer 3e is formed between them. The nematic liquid crystal 3f is arranged with a certain regularity inside. This is manufactured as follows. That is, the photosensitive prepolymer 3e and the nematic liquid crystal 3f are enclosed between the counter electrodes 3c and 3d, and this is exposed to exposure light having diffraction fringes in the same manner as a normal HOE (holographic element). Polymerization occurs when exposed in correspondence with the diffraction fringes. As a result, a liquid crystal rich portion and a polymer rich portion can be formed. The refractive index n _{LC of the} liquid crystal is larger than the refractive index n _{p of the} polymer. Therefore, a refractive index distribution is created according to the interference fringes, and this becomes a diffraction grating (see FIG. 2A). In addition, when a voltage is applied from both sides of the diffraction grating device, the liquid crystal molecules have positive dielectric anisotropy, so that the molecules are aligned in the direction in which the electric field is applied (see FIG. 2B). The refractive index n _{LC in} this state is equal to n _p of the polymer. As a result, the refractive index becomes uniform when voltage is applied, and the function of the diffraction grating is lost.

The response speed of the variable diffraction grating devices 3-1 and 3-2 is 100 microseconds or less. The parameters of the diffraction grating for blue light and green light are as follows.
Blue light; wavelength 460nm
Incident angle; 40 degrees
Output angle: 0 degree
Refractive index; 1.52
Refractive index amplitude; 0.07
Thickness: 3.5 microns
Lattice spacing; 0.699 microns
Green light; wavelength 535nm
Incident angle; 40 degrees
Output angle: 0 degree
Refractive index; 1.52
Refractive index amplitude; 0.08
Thickness: 3.5 microns
Lattice spacing: 0.813 microns Driving voltage
Larger than the driving voltage of the liquid crystal (usually 5V or less), 20V-80V
It may be necessary. It depends on the material and the material thickness of the diffraction grating.

  By controlling the variable diffraction grating devices 3-1 and 3-2, the light from the three light sources R, G, and B is guided to the same optical path as follows. First, the R light has two diffraction gratings as they are without the action of the diffraction grating, that is, with the voltage applied to both the variable diffraction grating devices 3-1 and 3-2. To be transparent. As a result, the R light is incident on the light pipe 6 through the field lens 5 and is adjusted to a uniform light, and is then applied to the transmissive liquid crystal panel 7. In this case, the power supply of the red LED 1-2 itself is also turned on in synchronization with the voltage application to the diffraction grating. Next, with respect to the G light, the green LED 1-1 is turned on in a state where both the red LED 1-2 and the blue LED 1-3 are turned off and the voltage applied to the variable diffraction grating device 3-2 is turned on. And the applied voltage of the variable diffraction grating device 3-1 is turned off to make the diffraction grating function. Further, for the B light, the blue LED 1-3 is turned on with both the red LED 1-2 and the green LED 1-1 turned off and the voltage applied to the variable diffraction grating device 3-1 is turned on. The diffraction grating functions by turning on and turning off the voltage applied to the variable diffraction grating device 3-2. FIG. 3 summarizes the above relationships in a table.

  The light emission wavelength distributions of the three colors of the green (G) LED chip 1-1, the red (R) LED chip 1-2, and the blue (B) LED chip 1-3 are as shown in FIG. The collimator lenses 2-1, 2-2, 2-3 make light from each LED chip substantially parallel. That is, the emitted light emitted from the light source having a size is made to be substantially parallel light. By doing so, it is possible to efficiently guide the diverging light on the optical path, thereby increasing the irradiation efficiency to the transmissive liquid crystal panel 7 which is an image forming element. The field lens 5 projects light from the green (G) LED chip 1-1, the red (R) LED chip 1-2, and the blue (B) LED chip 1-3 onto the entrance of the light pipe 6. To do. Since the radiance from these LEDs is generally non-uniform, a non-uniform light intensity distribution image can be formed at the entrance of the light pipe 6. As is well known, the light intensity is made uniform in the process in which light having an uneven light intensity distribution at the entrance of the light pipe 6 is reflected in the light pipe 6. Although the uniformity depends on the number of reflections, it is preferable that the light pipe 6 has a small entrance because the compactness of the length of the light pipe 6 leads to miniaturization of the apparatus. However, the size of the entrance that can take in the light from the LED 1 is necessary, and the size of the entrance is determined from these factors. The size of the light pipe exit is the size of the projection panel. By doing so, the light made uniform at the exit of the light panel 6 enters the transmissive liquid crystal panel 7.

  The transmissive liquid crystal panel 7 has the G. As a result of the control of the R and B LED chips and the variable diffraction grating device, when light of any one color of G, R and B guided on the optical path is irradiated, in synchronization with this, Although not shown, the color image is formed by being controlled by a drive circuit. That is, the transmissive liquid crystal panel 7 has G.P. R and B images are sequentially formed at approximately 3 times speed. This enables display as a color image. In this case, G. The lighting times of the R, B3 color LEDs are not necessarily the same. What is necessary is just to set the lighting pulse time of each color so that the radiation intensity of LED and the combined light of three colors become white. FIG. 4 is a block diagram of a control circuit for the light source, the variable diffraction grating device, and the transmissive liquid crystal panel. As shown in FIG. 4, the drive circuit for the light source, the drive circuit for the variable diffraction grating device, and the drive circuit for the transmissive liquid crystal panel are controlled by a synchronization control circuit.

  FIG. 5 is a diagram showing a configuration of a projector according to the second embodiment of the present invention. In the first embodiment described above, an example in which two variable diffraction grating devices are used has been described. However, in this embodiment, three variable diffraction grating devices 3-1, 3-2, 3 and 3 are used. -3 is used. These variable folding lattices act in the order of R, B, G from the LED side. This order can be exchanged. Further, drive circuit units 4-1, 4-2 and 4-3 for applying a voltage to each variable diffraction grating device are also provided corresponding to the three variable diffraction grating devices.

  G. As for the LEDs of the R and B light sources, only one color is sequentially turned on, and the colors to be sequentially turned on are the same as in the case of the first embodiment. The operations of the collimators 2-1, 2-2, 2-3 are the same. The light from the G (green) LED 1-1 enters the variable diffraction grating device 3-1. In order to diffract this light in the direction of the field lens 5, a voltage is applied to the variable diffraction grating device 3-3 for diffracting the R light so that the G light is not affected. Similarly, a voltage is applied to the variable diffraction grating 3-2 that diffracts the B light so that the G light is not affected. The G light variable diffraction grating device 3-1 is not applied with a voltage, but acts as a diffraction grating on green light. As a result, the G light is diffracted in the direction of the field lens 5 and irradiated to the transmissive liquid crystal panel 7 via the field lens 5 and the light pipe 6.

  The light from the R (red) LED 1-2 is incident on the variable diffraction grating device 3-3. In order to diffract this light in the direction of the field lens 5, first, the voltage application to the variable diffraction grating device 3-3 for diffracting the R light is canceled to function as a diffraction grating. Diffraction in the direction of the axis O. On the other hand, a voltage is applied to the variable diffraction grating 3-2 that diffracts the B light so that the R light is not affected. Similarly, a voltage is applied to the variable diffraction grating device 3-1 for G light so as not to affect the R light. As a result, the R light is diffracted in the direction of the field lens 5 and irradiated to the transmissive liquid crystal panel 7 via the field lens 5 and the light pipe 6.

  Further, the light from the B (blue) light LED 1-3 is incident on the variable diffraction grating device 3-2. In order to diffract this light in the direction of the field lens 5, a voltage is applied to the variable diffraction grating device 3-3 for diffracting the R light so as not to affect the B light. Similarly, a voltage is applied to the variable diffraction grating 3-1 that diffracts the G light so that the B light is not affected. The variable light diffraction grating device 3-2 for the B light is not applied with a voltage but acts as a diffraction grating on the green light. As a result, the B light is diffracted in the direction of the field lens 5 and irradiated to the transmissive liquid crystal panel 7 through the field lens 5 and the light pipe 6. FIG. 6 summarizes the above relationship in a table.

  FIG. 7 is a diagram illustrating a configuration of a projector according to the third embodiment. The projector according to this embodiment is an example in which the variable diffraction grating device according to the second embodiment is a reflection type. In order for the light of the G (green) LED 1-1 to enter the variable diffraction grating device 3-1 and be reflected in the direction of the field lens 5, first, the variable diffraction grating device 3 for diffracting the R light is used. A voltage is applied to -3 so that the light is transmitted as it is without affecting the G light. Similarly, a voltage is applied to the variable diffraction grating 3-2 that diffracts the B light so that the G light is not affected. In this case, R light and B light may be either on or off, but off is preferable. The G light variable diffraction grating device 3-1 is not applied with a voltage, but acts as a diffraction grating on green light. As a result, the G light is reflected in the direction of the field lens 5 without being affected by the variable diffraction grating devices 3-2 and 3-3, and is transmitted to the transmissive liquid crystal panel 7 via the field lens 5 and the light pipe 6. Irradiated.

  In order for the light from the R (red) LED 1-2 to enter the variable diffraction grating device 3-3 and be reflected in the direction of the field lens 5, first, the variable diffraction grating device 3 for diffracting the R light is used. The voltage application to -3 is canceled to function as a diffraction grating, and the R light is reflected in the direction of the optical axis O. On the other hand, a voltage is applied to the variable diffraction grating 3-2 that diffracts the B light so that the R light is not affected. Since the variable diffraction grating device 3-1 for G light is not relevant, voltage application may or may not be applied. In this case, the B light and the G light may be either on or off, but are preferably off. As a result, the R light is reflected in the direction of the field lens 5 and is applied to the transmissive liquid crystal panel 7 via the field lens 5 and the light pipe 6.

  Further, in order for the light from the B (blue) LED 1-3 to be incident on the variable diffraction grating device 3-2 and reflected in the direction of the field lens 5, a voltage is applied to the variable diffraction grating device 3-2 for B light. It is made to act as a diffraction grating on green light without being applied. At this time, a voltage is applied to the variable diffraction grating device 3-3 for diffracting the R light and the variable diffraction grating 3-1 for diffracting the G light so as not to affect the B light, or , G light and R light are turned off. Preferably, since the variable diffraction grating device 3-3 for diffracting the R light and the variable diffraction grating 3-1 for diffracting the G light are not related to the B light, the voltage may or may not be applied. May be. In this case, R light and G light are turned off. As a result, the B light is diffracted in the direction of the field lens 5 and irradiated to the transmissive liquid crystal panel 7 through the field lens 5 and the light pipe 6. FIG. 8 summarizes the above relationship in a table.

  FIG. 9 is a diagram showing a comparison between a schematic dimension example of a projector according to an embodiment of the present invention and a schematic dimension example of a conventional projector. In FIG. 9, it is assumed that the same light source, field lens, and the like other than the mirror and the diffraction grating device, which are devices for mixing the three primary color lights of R, G, and B, are used. As shown in FIG. 9, in any case, the dimension from the field lens to the screen is the same. However, the dimensions from the light source to the field lens are quite different. That is, among the conventional projectors, the conventional projector using the cross dichroic mirror 10 has a dimension from the light source to the field lens of about 30 mm. Similarly, the one using one mirror 20G and two half mirrors 20R and 20B is about 40 mm. On the other hand, in the case of the projector according to the above-described embodiment, the dimension can be about 20 mm. Thus, according to the apparatus concerning this Embodiment, it turns out that an apparatus can be reduced in size significantly compared with the past.

  The present invention relates to an image forming apparatus for forming an image by controlling light from a light source through an image element such as a liquid crystal panel, and in particular, in addition to power saving and high durability, an image forming apparatus that can be miniaturized. And it can be used as a projector using this image forming apparatus.

It is a figure which shows the structure of the projector concerning the 1st Embodiment of this invention. It is operation | movement explanatory drawing of the variable type diffraction grating apparatus 3-1, 3-2. It is operation | movement explanatory drawing of red LED1-2, blue LED1-3, green LED1-1, and the variable diffraction grating apparatus 3-1, 3-2. It is a block diagram of a control circuit of a light source, a variable diffraction grating device, and a transmissive liquid crystal panel. It is a figure which shows the structure of the projector concerning the 2nd Embodiment of this invention. It is operation | movement explanatory drawing of red LED1-2, blue LED1-3, green LED1-1, and variable type diffraction grating device 3-1, 3-2, 3-3. It is a figure which shows the structure of the projector concerning the 3rd Embodiment of this invention. It is operation | movement explanatory drawing of red LED1-2, blue LED1-3, green LED1-1, and variable type diffraction grating device 3-1, 3-2, 3-3. It is the figure which compared and showed the schematic dimension example of the projector concerning embodiment of this invention, and the schematic dimension example of the conventional projector. FIG. 10 is an explanatory diagram for explaining in principle the image forming apparatus described in Patent Document 1; FIG. 10 is an explanatory diagram for explaining in principle the image forming apparatus described in Patent Document 1; It is explanatory drawing of the light utilization efficiency of the conventional apparatus. It is explanatory drawing of the light utilization efficiency of the conventional apparatus. It is a figure which shows the example of the light reflection characteristic of a dichroic mirror, and the light emission characteristic of each LED of R, G, B.

Explanation of symbols

1-1 Green (G) LED (light emitting diode) chip 1-2 Red (R) LED chip 1-3 Blue (B) LED chips 2-1, 2-2, 2-3 Collimator lenses 3-1, 3- 2 Variable diffraction grating device 4-1, 4-2 Voltage application device 5 Field lens 6 Light pipe 7 Transmission type liquid crystal panel 8 Projection lens 9 Screen

Claims (9)

A plurality of light sources each generating visible light of a different wavelength;
A variable diffraction grating device that emits light emitted from the plurality of light sources and emits light traveling on the same optical path by controlling the traveling direction of each light by controlling the diffraction grating function;
An image forming element having a large number of pixels and forming an image by controlling the light emitted from the diffraction grating device by controlling each pixel with an electrical signal;
An image forming apparatus comprising:   In the variable diffraction grating device, whether the incident light is allowed to pass through or is diffracted to change the traveling direction by controlling the diffraction grating function by turning on and off the voltage applied to the liquid crystal. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein the light source includes three types of light sources corresponding to red, green, and blue colors.   One of the light emitted from the plurality of light sources travels straight and passes through the variable diffraction grating device to reach the image forming element, and light emitted from another light source emits the variable diffraction grating device. The plurality of light sources and the variable diffraction grating device are arranged so as to travel on the same optical path as that of the one light that travels straight to reach the image forming element by changing the path by The image forming apparatus according to claim 1.   The plurality of variable diffraction grating devices are provided with diffraction gratings having different grating intervals, and each diffraction grating function can be independently controlled by an electric signal. The image forming apparatus according to claim 1.   6. The image forming apparatus according to claim 5, wherein the number of the plurality of variable diffraction grating devices is a number obtained by subtracting 1 from the number of light sources.   The image forming apparatus according to claim 1, wherein the image forming element is a transmissive liquid crystal panel. Each of the light sources can be instantaneously turned on and off by a control circuit,
The control circuit of each of the light source, the variable diffraction grating device, and the image forming element is controlled to turn on / off each light source, the control timing of each variable diffraction grating, and the image forming element. The red light (R), the green light (G), and the blue light (B) sequentially reach the image forming element by synchronizing with the image forming timing of the image forming element. , B color light can be displayed by forming an image of each color of R, G, B when light of each color reaches the image forming element. Item 8. The image forming apparatus according to any one of Items 1 to 7. 9. A projector comprising a projection optical system that projects an image formed by an image forming element in the image forming apparatus according to claim 1 onto a screen.

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