JPH11249037A - Spatial optical modulator and display optical device using same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the spatial optical modulator which has small secular changes even when restrictions on the quantity of incident light are large and heat is generated by a structure owing to light irradiation and can represent the intermediate quantity of light easily, and the display optical device using the spatial optical modulator. SOLUTION: The light from a lamp 1 is passed through a lens 2 and a deflecting plate 3 and reflected by a polarization beam splitter 4 to pass through a 1/4-wavelength plate 5. This illumination light lightens up a spatial optical modulator array 6 almost vertically. The illumination light made incident on the spatial optical modulator 6a is reflected vertically to become luminous flux 10, which is made incident on a critical- angle prism 7. This reflected luminous flux 10 is reflected by the critical-angle prism and not made incident on the display optical system. The reflected luminous flux 11 from the spatial optical modulating element 6 is reflected at a certain angle from the normal of the substrate. Consequently, the reflected luminous flux 11 does not meet the total reflection conditions and is partially transmitted through the critical- angle prism 7 and projected on an image formation point 13 on a screen 9 by the image forming lens 8 of the display optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a spatial light modulator for controlling one-dimensionally or two-dimensionally the on / off of light passing therethrough and the amount of light, and to a display optical device using the same.

[0002]

2. Description of the Related Art In recent years, various micromachines have been actively researched and developed utilizing semiconductor manufacturing technology. The results of research have also been applied to optical elements that have microscopic mirrors integrated in a plane. In the conventional micro-optical element, a large number of metal mirrors each having a size of several tens of μm are integrated on a substrate surface, and these mirrors are driven by an electrostatic force between the electrodes provided on the substrate and the mirrors, and the angle of the mirror is adjusted. And the reflection angle of each mirror is controlled. (For example, Technical Diegest of the 14th S
ensor Symposium, 1996, pp297.) FIG. 7 is a diagram showing a schematic cross-sectional structure of a conventional micro optical element. An electrode layer 72 is provided on a substrate 71, and a movable mirror portion supported by a torsion hinge 76 is formed on the electrode layer 72. The movable mirror section includes the drive electrode film 73 and the post section 75.
And a reflection mirror unit 74 connected by a.
When a voltage is applied to one of the electrode layers 72, the drive electrode film 73 is attracted to the substrate 71 side, and a rotational force is generated about the torsion hinge 76, whereby the reflection mirror portion 74 is inclined. Thereby, the reflection direction of the light incident on the reflection mirror is controlled. By projecting only light reflected in a specific reflection direction, it can be used as an optical element for a projector.

[0003]

However, in the above-described conventional micromirror, the reflecting mirror surface must be driven over a large angle of as much as 20 ° to turn on and off light. Therefore, a very complicated element structure using a torsion spring as a mechanism for holding the reflection mirror is inevitable, and the production process is very difficult. Also,
Since the reflection mirror must be supported by a soft structure such as a torsion spring, the intensity of incident light is limited. The reason is that when strong light is incident on the mirror, the temperature of the mirror itself rises, which distorts a complicated and soft structure such as a torsion spring due to thermal expansion. Furthermore, the above-mentioned micromirror can only perform digital control of turning light on and off, and in order to express intermediate brightness, it is necessary to repeat on and off intermittently and change the ratio of on time to off time . Therefore, a driving circuit for driving the above-mentioned mirror is also complicated.

The present invention has been made in view of such circumstances, and the amount of incident light is greatly restricted. Even if heat generation of the structure caused by light irradiation occurs, there is little change with time, and the intermediate light amount can be easily obtained. It is an object of the present invention to provide a small spatial light modulator capable of expressing the above and a display optical device using the same.

[0005]

According to a first aspect of the present invention, there is provided a reflector for changing a reflection direction of reflected light, the reflected light from the reflector being incident on a critical angle prism, A spatial light modulator (Claim 1) characterized in that passing or non-passing of light is controlled by changing a reflection direction of reflected light by the reflector.

In this means, the angle of the reflector is changed to change the reflection direction of the reflected light. In the critical angle prism, the relative relationship with the reflection direction of the reflected light is adjusted so that the incident angle of light incident on the prism surface does not exceed or does not exceed the critical angle according to the direction of the incident reflected light. ing. Therefore, when the incident angle of light incident on the prism surface exceeds the critical angle, the light is totally reflected on the prism surface and does not pass through the prism surface. When the incident angle of the light incident on the prism surface is equal to or smaller than the critical angle, the light transmits through the prism surface. By using this, it is possible to control on / off of light.

As the light whose on / off is controlled, any of light passing through the critical angle prism and light reflected by the critical angle prism may be used, but light transmitted through the critical angle prism is used. In this case, it is preferable that the light amount in the off state can be made completely zero.

In this means, since the change in the reflectance of light near the critical angle is used, ON / OFF of the light can be controlled by a slight change in the incident angle.

[0009] A second means for solving the above-mentioned problems is as follows.
The first means, wherein the amount of light passing / reflecting through the critical angle prism is also controlled by adjusting the angle of the reflector (claim 2).
It is.

In the vicinity of the critical angle of the critical angle prism, the amount of light passing through the prism changes steeply but continuously. Therefore, if the angle of incidence of the critical angle prism on the prism surface is adjusted near the critical angle by adjusting the angle of the reflector, the amount of light passing through the critical angle prism or reflected by the critical angle prism The amount of light (brightness) itself can be adjusted together with turning on / off the light.

A third means for solving the above-mentioned problem is as follows.
The first means or the second means, wherein the reflector is provided substantially parallel to the substrate, with one side supported on an electrode provided on the substrate and a column provided on the substrate. And a flexible mirror provided thereon, and the mirror or a support of the mirror is a conductive member (claim 3).

In this means, an electrode provided on the substrate and a conductive mirror or a conductive mirror support are provided.
By applying a potential of the same polarity or a different polarity, the conductive mirror or the conductive mirror support bends due to Coulomb force, and can change the light reflection direction. As will be described later, since the reflector according to this means can be manufactured using a micromachining process, a reflector having a fine and highly integrated two-dimensional array can be easily manufactured.

A fourth means for solving the above-mentioned problem is as follows.
A light source, a polarizing plate, a polarizing beam splitter, a quarter-wave plate, a reflector, a critical angle prism, and a projection lens. The light from the light source is a polarizing plate → a polarizing beam. The beam passes through the devices in the order of a splitter, a quarter-wave plate, a reflector, a quarter-wave plate, a polarizing beam splitter, a critical angle prism, and a projection lens. A spatial light modulator that forms an image on an object, adjusts the angle of the reflector, changes the reflection direction of light therefrom, and controls the amount of light passing / reflecting through the critical angle prism. A display optical device, wherein the display optical device is used.

The light from the light source is converted into linearly polarized light by a polarizing plate, enters a polarizing beam splitter, is changed in direction by 90 °, is further converted into circularly polarized light by a quarter-wave plate, and is reflected by a reflector. This reflected light passes through the quarter-wave plate again to become linearly polarized light, travels straight through the polarizing beam splitter, and then enters the critical angle prism. Then, since the angle of incidence on the critical angle prism changes according to the angle of the reflector, the amount of light transmitted and reflected by the critical angle prism changes, and the light transmitted and reflected changes on and off accordingly. . Light transmitted or reflected by the critical angle prism is projected by a projection lens.
The image is projected onto a projection target such as a screen, and an image of the reflector is formed on the projection target.

Since the image of the reflector is formed on the projection object by the projection lens, even if the direction of reflection of light from the reflector slightly changes, the position of the image formed on the projection object is changed. Does not change. Further, if a plurality of reflectors are provided and arranged in a two-dimensional array, for example, two-dimensional light quantity control and on / off control can be performed on the projection target.

If necessary, another optical device such as another lens, another beam splitter, a slit, etc. may be provided in the middle of the above-mentioned components of the optical device. It goes without saying that it falls within the range of 4.

In any of the first to fourth means, the light incident on the critical angle prism is preferably P-polarized with respect to the critical angle prism surface. here,
The critical angle prism surface refers to a prism surface that causes total reflection among the surfaces of the critical angle prism.

As will be described later, the change in reflectance near the critical angle on the critical angle prism surface is steeper for P-polarized light than for S-polarized light. Therefore, by using P-polarized light, it is possible to control the on / off of the light and the change in brightness with a slight change in the angle of the reflector.

In any one of the first means, the second means and the fourth means, a flexible mirror and a material having a different coefficient of thermal expansion from the flexible mirror are bonded as a reflector. Further, those having a resistance wire bonded to them can be used.

In this way, when an electric current is passed through the resistance wire, the temperature of the flexible mirror and a material obtained by bonding the flexible mirror and a material having a different coefficient of thermal expansion rises, and the difference in the coefficient of thermal expansion increases. The flexible mirror can bend to change the direction of the reflected light. Since the reflector according to this means can also be manufactured by using a micromachining process, it is possible to easily manufacture a reflector having a fine, highly integrated two-dimensional array.

Further, the first means, the second means,
Alternatively, in any of the fourth means, a reflector formed by laminating a flexible mirror and a flexible piezoelectric element can be used.

In this case, when a voltage is applied to the piezoelectric element, the piezoelectric element expands and contracts, whereby the flexible mirror bends and the direction of the reflected light can be changed. Since the reflector according to this means can also be manufactured by using a micromachining process, it is possible to easily manufacture a reflector having a fine, highly integrated two-dimensional array.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention. In FIG. 1, 1 is a lamp, 2
Is a lens, 3 is a polarizing plate, 4 is a polarizing beam splitter, 5
Is a quarter-wave plate, 6 is a spatial light modulator array, 6a, 6b
Is an element of the spatial light modulator array 6, a spatial light modulator having a mirror whose surface is variable in angle, 7 is a critical angle prism, 8 is an imaging lens (projection lens), 9 is a screen, 10 and 11, , 12 is a light beam, 13 is a spatial light modulator 6
b is an image forming point of the reflected light from the mirror b.

The light from the lamp 1 is converted into a substantially parallel light beam by the lens 2 and is converted into linearly polarized light by the deflecting plate 3. The deflected light is reflected by the polarization beam splitter 4, and
The light passes through the four-wavelength plate 5. Here, the linearly polarized illumination light changes to circularly polarized light. This illumination light illuminates the spatial light modulator array 6 almost vertically.

Here, the illumination light reflected by each element of the spatial light modulation will be considered. The surface of the mirror of the spatial light modulator 6a in FIG. 1 is in a state substantially orthogonal to the incident illumination light. Therefore, the illumination light incident on the mirror of the spatial light modulator 6a is reflected in the vertical direction (incident direction) from the surface of the mirror of the spatial light modulator 6a as a light flux 10 in FIG. This reflected light passes through the quarter-wave plate 5 again to become linearly polarized light, and the polarization direction is orthogonal to the polarization plane of the incident light. Therefore, the reflected light is polarized beam splitter 4
And enters the critical angle prism 7. Here, the critical angle prism 7 is a prism whose angle is adjusted so that the vertical reflected light from the spatial light modulator array 6 is totally reflected near the total reflection angle. Therefore, the reflected light beam 10 is reflected by the critical angle prism and does not enter the display optical system.

On the other hand, consider the reflected light from the mirror of another spatial light modulator 6b in FIG. In the spatial light modulator 6b, the angle of the mirror slightly changes upward as shown in the figure. Therefore, the light beam 11 reflected from the mirror surface of the spatial light modulator 6b is reflected at a certain angle from the incident direction. The reflected light beam passes through the quarter-wave plate 5 to become linearly polarized light, passes through the polarization beam splitter 4, and enters the critical angle prism 7, similarly to the above-described reflected light beam. Here, the reflected light beam 11 is incident on the interface of the prism 7 at an angle closer to vertical than the reflected light beam 10 described above. That is, the incident angle in this case is smaller than the critical angle. Therefore, the reflected light beam 11 does not satisfy the condition of total reflection, and starts to partially pass through the critical angle prism 7. The reflected light beam 11 transmitted through the critical angle prism 7 is projected onto an image forming point 13 on the screen 9 by the image forming lens 8 of the display optical system.

The reflected light flux when the inclination angle of the mirror of the spatial light modulator 6b is further increased is indicated by a dotted line 12 in FIG. The reflected light flux 12 is similar to the above-described reflected light flux 11,
The light passes through the 波長 wavelength plate 5 and becomes linearly polarized light, passes through the polarization beam splitter 4, and enters the critical angle prism 7. Here, the reflected light beam 12 is incident on the interface of the prism 7 set at a critical angle at an angle closer to vertical than the reflected light beam 11 described above. Therefore, the reflected light flux 12 no longer satisfies the condition of total reflection, and most of the reflected light passes through the critical angle prism 7.

The reflected light flux 12 which has largely passed through the critical angle prism 7 is projected on a screen 9 by an imaging lens 8 of a display optical system. Moreover, the intensity of the reflected light 12 incident on the screen 9 is higher than the intensity of the reflected light 11 when the mirror has a small inclination angle, and the brightness of the image forming point 13 becomes brighter. The image forming point 13 is the same as the image forming point formed by the reflected light 11 when the angle of the mirror is not so upward. That is, the image of the mirror of the spatial light modulator 6 b is changed by the imaging lens 8 to the image forming point 1 on the screen 9.
3, the position of the imaging point 13 does not change even if the direction of the reflected light from the mirror of the spatial light modulator 6b changes.

Next, the change in the amount of light reflected and transmitted by the critical angle prism depending on the incident angle will be described with reference to FIG. FIG. 2 is a diagram in which the reflectance of the prism surface is plotted against the angle of incidence on the prism interface. In this figure, the prism has a refractive index of 1.54. The critical angle in this case is 33.4
1 °. Here, two curves are drawn in the figure, because the reflectance is different depending on whether the incident light is P-polarized light (curve p) or S-polarized light (curve s) with respect to the prism boundary surface. is there. From FIG. 2, it can be seen that a sharp change in reflectance occurs near the critical angle with respect to the P-polarized incident light. Therefore, by using the P-polarized light, the brightness of the dots on the display screen can be largely changed by a slight change in the mirror surface of the spatial light modulator.

Next, the spatial light modulator used in the above embodiment will be described with reference to FIG. FIG. 3A is a conceptual perspective view of the spatial light modulator according to the embodiment of the present invention. In FIG. 3, 21 is a substrate, 22 is a mirror, 23 is a backing layer, 2
4 is a post and 24 is an electrode.

On a substrate 21 made of an insulator, a mirror 22 that modulates by reflecting light is supported by a post 24. The back surface of the mirror 22 is lined with a backing layer 23 for reinforcement. An electrode 25 is provided on the substrate 21 to change the angle of the mirror 22. FIG. 3B shows a method of modulating light by slightly changing the angle of the mirror 22. In FIG. 3B, the post 24 supporting the mirror 22 has conductivity.
There is electrical conduction with the mirror 22 supported on the post 24.

Here, charges of the same polarity (positive charges in the figure) are injected into the mirror 22 and the electrode 25 provided on the substrate 21 so as to face the mirror 22 by applying a voltage (post 24). And the electrode 25 are insulated). Then, a Coulomb force acts between the mirror 22 and the electrode 25 and repel each other. The angle of the mirror 22 can be minutely changed by this Coulomb force. Of course, by applying charges of different polarities to the mirror 22 and the electrode 25, an attractive force may be exerted between the two to deform the mirror 22.

Further, the mirror 22 is not made conductive,
The same operation and effect can be obtained even if the backing layer 23 is made of a conductive material and a charge is applied thereto. Further, a wiring may be separately connected to the mirror 22 without making the post 24 conductive, and a potential may be applied to the mirror 22 by the wiring.

In the above-described embodiment, the Coulomb force is used for driving the mirror. However, a bimorph actuator or a PZT thin film may be used. When a bimorph actuator is used, a substance having a different coefficient of thermal expansion from that of the mirror is attached to the mirror, and a resistance wire is attached. When the mirror portion is heated by energizing the resistance wire, the mirror portion is curved due to a difference in coefficient of thermal expansion, and the light reflection direction is different. When using a PZT thin film, a mirror and PZT
When a thin film is bonded and a voltage is applied to the PZT thin film, PZT
The expansion and contraction of the T thin film causes the mirror portion to bend and the light reflection direction to be different.

Next, referring to FIG.
An electric circuit when operating as an array of x2 cells will be described. In FIG. 4, reference numerals 31a to 31d denote corner elements of the spatial light modulator equivalently as capacitors.
2 is a voltage supply circuit, 33 and 34 are shift registers, 35
a, 35b, 36a to 36d are transistors, 37, 3
8 is a line.

In order to apply a voltage from the voltage supply circuit 32 to each element 31a to 31d of an arbitrary spatial light modulator, shift registers 33 and 34 are connected to wirings connected to vertical and horizontal transistors, respectively. . According to the output from the shift register 33, the transistors 35a,
When either of the switches 35b is turned on, the voltage of the voltage supply circuit 32 is supplied to one of the lines 37 and 38.

At this time, the transistors 36a and 36c or the transistors 36b and
6d is turned on, one of the elements 31a to 31d of the spatial light modulator is selected, and the voltage supply circuit 3
2 are supplied. The electric charge of each of the elements 31a to 31d of the spatial light modulator that is not selected cannot flow out because the transistor provided in the corresponding line is off, and the electric potential is kept as it is.

Therefore, the spatial light modulators 31a to 31d are controlled by selecting the respective elements 31a to 31d of the spatial light modulator by the shift registers 33 and 34 and changing the voltage of the voltage supply circuit 32 at that time. be able to.

In the case where the spatial modulator is operated as an array of n × n cells, similarly, if a transistor for operating each cell and a shift register having a bit number are used, each element of each spatial modulator is similarly used. Can be controlled.

Next, an example of a method of manufacturing the spatial light modulator according to the embodiment of the present invention described above will be described with reference to FIGS.

First, as a semiconductor substrate, a thickness of 250 μm,
On the upper surface of the silicon single crystal substrate 40 having the (100) plane orientation,
A transistor circuit which can sequentially drive the spatial light modulator which is the above-described electric circuit is formed. This process is not shown in the figure. Next, the counter electrode 25 for driving the spatial light modulator is formed by the lift-off method (a).

Next, a polysilicon layer 41 having a thickness of 2.5 μm is grown on the upper surface of the silicon substrate by a low pressure CVD method. Here, the polysilicon layer 41 is doped n-type or p-type and has electric conductivity. A resist 42 is applied thereon (b).

Next, the polysilicon layer 41 grown on the upper surface by photolithography is patterned and etched so as to leave a portion other than the portion serving as the support 24 of the spatial light modulator (c).

Thereafter, when a resist 43 is applied on the patterned polysilicon support 24, it is planarized as shown in FIG.

Next, the resist layer 43 and the polysilicon 24 are etched back by dry etching under the condition that the resist 43 and the polysilicon 24 are etched at the same rate, thereby exposing the upper surface 44 of the support (e).

Then, an n-type or p-type doped polysilicon layer 45 as a reinforcing material for the mirror of the spatial light modulator is grown on the upper surface 44 of the support 24 by low-pressure CVD to a thickness of 500 nm. A gold layer 46 of about 300 nm is grown thereon by a vapor deposition method as a mirror of the spatial light modulator. Thereafter, a resist 47 is applied to the upper surface of the substrate (f), and a region other than the mirror portion of the spatial light modulator is removed by photolithography by etching (g).

Finally, the resists 43 and 47 are removed by ashing to complete an array of spatial light modulators (h).

[0048]

As described above, the present invention utilizes the fact that the transmittance of the prism changes abruptly near the critical angle. Therefore, the display of dots on the display screen can be controlled only by a small angle change of the mirror of the spatial light modulator, and there is no need to drive a large angle mirror as large as 20 ° unlike the conventional DMD.

When the incident light is P-polarized light, the angle of the mirror is set to 1
Only by changing the angle, the transmittance of the prism changes by about 90%. Therefore, even if the rigidity of the spatial light modulator itself is increased, this angle change can be easily realized by the Coulomb force, the bimorph actuator, the PZT thin film actuator, and the like.

As another advantage that the rigidity of the spatial light modulator can be increased, even if the spatial light modulator is affected by thermal expansion or the like by increasing the light intensity of the incident light, the effect is small. Therefore, the display can be brightened. Therefore, when this display element is used as a projector, for example, there is no inconvenience such that the display cannot be seen unless the indoor lighting is darkened.

Further, in the present invention, since the critical angle prism is used, display of intermediate brightness can be easily realized by slightly changing the angle of the mirror.
Therefore, there is no need to drive a complicated display element such as a conventional DMD that periodically turns on and off a mirror and expresses an intermediate light amount by a ratio of the on time to the off time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the angle of incidence on the prism interface and the reflectance.

FIG. 3 is a diagram showing an outline of a spatial light modulator according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of an electric circuit when operating a spatial light modulator.

FIG. 5 is a diagram showing an example of a method for manufacturing a spatial light modulator according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a method for manufacturing a spatial light modulator according to an embodiment of the present invention.

FIG. 7 is a diagram showing a schematic cross-sectional structure of a conventional micro optical element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Lamp, 2 ... Lens, 3 ... Polarizing plate, 4 ... Polarizing beam splitter, 5 ... 1/4 wavelength plate, 6 ... Spatial light modulator array, 6a, 6b ... Spatial light modulating element, 7 ... Critical angle prism, 8: imaging lens (projection lens), 9: screen,
Reference numerals 10, 11, 12: light flux, 13: imaging point of light reflected from the mirror of the spatial light modulator 6b, 21: substrate, 22: mirror, 23: backing layer, 24: post, 24: electrode, 31
a to 31d: spatial light modulator, 32: voltage supply circuit, 3
3, 34 shift registers, 35a, 35b, 36a to
36d: transistor, 37, 38 ... line

Claims (4)

[Claims] 1. A reflector for changing the direction of reflection of reflected light is provided, light reflected from the reflector is made incident on a critical angle prism, and the direction of reflection of light reflected by the reflector is changed. A spatial light modulator characterized by controlling passage and non-passage. 2. The spatial light modulator according to claim 1, wherein the amount of light passing / reflecting through the critical angle prism is controlled by adjusting the angle of the reflector. 3. The reflector comprises: an electrode provided on a substrate; and a flexible mirror supported on one side on a support provided on the substrate and provided substantially parallel to the substrate. The spatial light modulator according to claim 1, wherein the mirror or a support of the mirror is a conductive member. 4. A light source, a polarizing plate, a polarizing beam splitter, a quarter-wave plate, a reflector, a critical angle prism,
And a projection lens sequentially, the light from the light source,
Polarizing plate → polarizing beam splitter → 1/4 wavelength plate → reflector → 1/4 wavelength plate → polarizing beam splitter → critical angle prism → projection lens A body image is formed on a projection target, and the angle of the reflector is adjusted to change the direction of light reflected therefrom and control the amount of light passing / reflecting through the critical angle prism. A display optical device using a spatial light modulator.