JP2002277771A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an electrostatic actuator system optical modulator to be driven by a low voltage. SOLUTION: An intermediate electrode 10 to be displaced is arranged between a reflection board 1 and an opposite electrode 2 so as to constitute an electrostatic actuator between the reflection board 1 and the opposite electrode 2. A displacing amount being equal to that of the reflection board 1 is secured by a driving voltage which is lower than that in the case of the modulator without the intermediate electrode 10. Besides the amount of displacement of the reflection board 1 is increased by the same driving voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator and, more particularly, to an optical modulator that performs optical switching by displacing a reflector by electrostatic force.

[0002]

2. Description of the Related Art As a light modulator of this type, a cantilever constituting a reflector is bent by electrostatic force.
KE Peterse is a device that performs optical switching (modulation) by changing the direction of light reflection and a modulation system using it.
n in 1977 (Applied Physics Le
tters, Vol. 31, No. 8, pp. 521-523). An optical modulator using a similar cantilever reflector is disclosed in, for example, Japanese Patent Publication No. 7-56531.
This is also disclosed in the official gazette. Japanese Patent Application Laid-Open No. 7-49460 discloses an optical modulator in which a reflector is formed by a circular thin-film diaphragm, the diaphragm is deformed by electrostatic force, and the focus is changed.

[0003]

Light modulators for changing the direction of light reflection by displacing a reflector are used in displays and projectors. In such applications,
The reflector is associated with each pixel of the display image and is formed in a minute size such as several tens to several hundreds μm.

There are various methods of driving the reflector, but no force other than a force for deforming the reflector is required, a relatively large displacement can be obtained, and power consumption is low. For this reason, electrostatic force is often used. The reflector is made of a conductive material to serve as an electrode.An additional electrode is provided at a position facing the reflector, and a voltage is applied (ON) between the electrodes to apply an electrostatic force to move the reflector to the opposite electrode. To bend. When the applied voltage is released (OFF), the reflector returns to its own spring property. Therefore, voltage ON / O
Optical switching can be performed by driving the reflection plate by the FF. That is, the reflection plate and the counter electrode constitute an electrostatic actuator. Various light modulators using such an electrostatic actuator have been proposed in addition to the one disclosed in Japanese Patent Publication No. 7-56531.

In order to increase the displacement of the reflector, the distance between the reflector and the counter electrode must be increased. However, since the strength of the electrostatic force acting between the electrodes is inversely proportional to the square of the distance between the electrodes, there is a problem that increasing the distance between the reflector and the counter electrode causes a significant increase in the driving voltage.

Further, a space (hereinafter, referred to as a gap) for displacing and vibrating the reflector is secured between the reflector and the counter electrode, but the air in the gap is compressed by the displacement of the reflector. (Referred to as an air damper effect). Due to this air damper effect, the actual displacement of the reflector is smaller than the displacement of the reflector calculated statically under the condition that there is no air in the gap. There is a problem that the driving voltage for obtaining the voltage increases. This air damper effect is also a factor that impairs the response characteristics of the reflector.

The amount of displacement of the reflector is three times the thickness of the reflector.
Since it is inversely proportional to the power, the thickness of the reflector needs to be reduced in order to lower the driving voltage while securing the displacement of the reflector. However, when the thickness of the reflector is reduced, it is difficult to form the reflector in a uniform thickness, and it is difficult to make the characteristics uniform. Therefore, the thickness of the reflector is also limited.

Therefore, an object of the present invention is to increase the displacement of the reflector without increasing the driving voltage, or to drive the reflector at a low voltage without decreasing the displacement of the reflector. An object of the present invention is to provide a light modulation device. Another object of the present invention is to provide an optical modulation device which can reduce the air damper effect, can be driven at a low voltage, and has good responsiveness. Another object of the present invention is
An object of the present invention is to provide an optical modulation device capable of simplifying a driving circuit or a driving method. Other objects of the present invention will become apparent from the following description.

[0009]

The basic features of the optical modulator according to the present invention are as follows: a displaceable reflector serving also as a first electrode; and a displaceable reflector facing the reflector. A non-displaceable second electrode, and at least one displaceable intermediate electrode disposed between the reflector and the second electrode; The intermediate electrode and the reflection plate are displaced by the generated electrostatic force.

Another feature of the light modulation device according to the present invention is that, as described in claim 2, at least the intermediate electrode closest to the reflector has a structure in which the surface facing the reflector is formed of a conductive material. is there. Another feature is that the intermediate electrode is made of a dielectric material. Another one
One feature is that the intermediate electrode has lower rigidity than the reflector. Another feature is that the intermediate electrode has through holes on both sides thereof.

Further, according to the present invention, there is provided a method for driving an optical modulation device, comprising the steps of:
Or in the optical modulation device according to 5, by controlling the application timing of the drive voltage to each of the electrodes such that the displacement start of the reflector is not delayed at least from the displacement start of the intermediate electrode closest to the reflector. is there. Another feature is that, in the optical modulator according to the third aspect, a driving voltage is applied only to the first electrode and the second electrode.

The above-described objects and features of the present invention and other objects and features of the present invention will be specifically described below with reference to embodiments.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to facilitate understanding of the present invention,
First, an example of a basic configuration of a light modulation device to which the present invention can be applied will be described with reference to FIG.

FIG. 1 is a schematic sectional view of a light modulation device. In FIG. 1, the reflection plate 1 is fixed to the electrode substrate 3 by a fixed support portion 9 and is held so as to cover a concave portion of the electrode substrate 3. The reflection plate 1 also serves as an electrode. For example, a reflection plate and a metal layer acting as an electrode are formed on the upper surface of a thin beam, or the reflection plate 1 is integrally formed of a conductive material. At the bottom of the concave portion of the electrode substrate 3, a counter electrode 2 facing the reflector 1 is provided, and a gap 8 is formed between the counter electrode 2 and the reflector 1. The counter electrode 2 and the reflector 1 constitute an electrostatic actuator.

The reflector 1 is formed separately from the electrode substrate 3 and is laminated on the electrode substrate 3 by a film forming process, a sacrifice layer process, or the like, when the electrode 1 is bonded to the electrode substrate 3 later. There are cases.

When no voltage is applied between the reflection plate 1 and the counter electrode 2 (when the voltage is OFF), the reflection plate 1 is substantially parallel to the counter electrode 2 as shown in FIG. The incident light 4 is reflected by the reflector 1 like the reflected light 5.

On the other hand, when a voltage is applied between the reflection plate 1 and the counter electrode 2 from a drive circuit (not shown) (when the voltage is ON), an attractive force of static electricity acts between the reflection plate 1 and the counter electrode 2. I do. Since the reflecting plate 1 is made thin, the reflecting plate 1 is displaced toward the counter electrode 2 by the electrostatic force.
The state shown in FIG. In this state, the incident light 6 is reflected by the reflector 1 like the reflected light 7. Although not shown, when the reflector 1 comes into contact with the counter electrode 2, the reflector 1 and the counter electrode 2
An insulating film is formed on one or both contacting surfaces.

As described above, the light can be modulated by switching the light reflection direction by turning on and off the voltage between the reflection plate 1 and the counter electrode 2. A display device can be configured by providing a color filter, a lens, and the like (not shown) in the light reflection direction. Further, application to an optical writing system of an electrophotographic apparatus is also possible.

In the light modulator having the basic configuration as shown in FIG. 1, if the distance between the reflector 1 and the counter electrode 2 is increased in order to increase the displacement of the reflector 1, as described above. A very large driving voltage must be applied between the reflector 1 and the counter electrode 2. According to the present invention, the amount of displacement of the reflector 1 can be increased without increasing the drive voltage, or a predetermined amount of displacement of the reflector 1 can be secured to lower the drive voltage.

Hereinafter, an embodiment in which the present invention is applied to an optical modulation device having a basic configuration as shown in FIG. 1 will be described with reference to FIGS.

FIG. 2 is a schematic sectional view showing an embodiment of the light modulation device according to the present invention. 2, the same reference numerals as those in FIG. 1 indicate the same elements. FIG. 2A shows a non-driving state (when the voltage is OFF), and FIG. 2B shows a driving state (when the voltage is ON).

In the present embodiment, the gap 8 between the reflector 1 and the counter electrode 2
A thin intermediate electrode 10 is provided so as to partition into two gaps. The intermediate electrode 10 may be entirely formed of a conductive material such as a metal, or may be formed of a conductive material such as a metal on a thin plate or a film made of an insulating material or a semiconductor material. It is good also as a structure which formed the electrode by. In addition, the intermediate electrode 10 may be formed as a component independent of the electrode substrate 3 and joined to a step provided in the middle of the concave portion of the electrode substrate 3. The intermediate electrode 10 may be formed using a sacrifice layer process or the like.

In the above configuration, when no drive voltage is applied between any of the reflector 1, the intermediate electrode 10, and the counter electrode 2 (when the voltage is OFF), as shown in FIG. Each electrode is in a parallel state, and the incident light 4 is reflected by the reflector 1 like the reflected light 5.

On the other hand, between the counter electrode 2 and the intermediate electrode 10,
When a voltage is applied from a drive circuit (not shown), the intermediate electrode 10 is displaced toward the counter electrode 2 by an electrostatic force.
Similarly, when a voltage is applied between the reflection plate 1 and the intermediate electrode 10 from a drive circuit (not shown), the reflection plate 1 is displaced toward the intermediate electrode 10 by an electrostatic force. The electrostatic force acts equally between the intermediate electrode 10 and the counter electrode 2 and between the intermediate electrode 10 and the reflection plate 1.
Since the intermediate electrode 10 is also made thin, the intermediate electrode 10 is drawn to the counter electrode 2 side that is not displaced, resulting in a state as shown in FIG. 2B. Therefore, the reflector 1 reflects the incident light 6 like the reflected light 7.

Assuming that the absolute displacement of the reflector 1 in the light modulator of the present embodiment is equal to that of FIG. 1, the displacement of the intermediate electrode 10 is also smaller than that of the reflector. Since the amount of relative displacement with respect to the electrode 10 is also small, the drive voltage applied between the electrodes can be lower than in the case of FIG. Conversely, if driven by the same drive voltage as in FIG. 1, the reflector 1 can be displaced more greatly.

In this embodiment, only one intermediate electrode 10 is provided between the reflector 1 and the counter electrode 2. Although not shown,
According to another embodiment of the present invention, the reflection plate 1 and the counter electrode 10
A plurality of intermediate electrodes similar to the intermediate electrode 10 are provided so as to partition the gap 8 between them into three or more. According to the configuration in which a plurality of intermediate electrodes are provided as described above, it is apparent that the distance between the electrodes can be reduced and the driving voltage can be further reduced.

Note that, in order to prevent an electrical short circuit due to contact between the intermediate electrode 10 and the reflection plate 1 or the counter electrode 2 (when a plurality of intermediate electrodes are provided, to prevent an electrical short circuit due to contact with another intermediate electrode). Although not shown, an insulating means such as forming at least an insulating protective film is provided on a portion where contact is assumed.

When two or more intermediate electrodes 10 are provided, the characteristics of the electrostatic actuator composed of the reflector 1 and the closest intermediate electrode 10 have the greatest effect on the displacement characteristics of the reflector 1. When the intermediate electrode 10 has a thin plate made of an insulating material or a semiconductor material or a structure in which a film of a conductive material as an electrode is formed on the surface of the film, the intermediate electrode 10 at least closest to the reflector 1 is used. It is preferable to form a film of a conductive material as an electrode on the surface facing the reflection plate 1. In this case, the reflection plate 1 and the nearest intermediate electrode 1 are compared with the case where a film of a conductive material as an electrode is formed on the opposite surface.
Since the distance to zero can be shortened, the driving voltage of the electrostatic actuator constituted by them can be reduced and the driving characteristics can be improved.

Now, in FIG. 2B, the intermediate electrode 1
0 and the reflector 1 were both in non-contact with the other electrode generating electrostatic force (non-contact drive). However, when the drive voltage applied was further increased, the electrode and the reflection plate 1 were brought into contact with the other electrode (this contact). Contact drive). In the case of contact drive, due to variations in design parameters, fluctuations in drive voltage, and other external factors,
The intermediate electrode 10 may come into contact with the counter electrode 2 earlier than the reflector 1 comes into contact with the intermediate electrode 10. This is shown in FIG.

In FIG. 3A, the reflector 1 is connected to the intermediate electrode 10.
Is in contact with. In this case, the intermediate electrode 10 is subsequently displaced toward the counter electrode 2, but since the distance between the intermediate electrode 10 and the counter electrode 2 is the same as in the initial state (when the voltage is OFF), there is no inconvenience in driving. .

On the other hand, in FIG.
0 indicates a state in which it is in contact with the counter electrode 2. In this case, the reflecting plate 1 is subsequently displaced toward the intermediate electrode 10, but the distance between the reflecting plate 1 and the intermediate electrode 10 is larger than in the initial state. As described above, since the electrostatic force is inversely proportional to the square of the distance between the electrodes, the driving of the reflector 1 is larger in the state of FIG. 3B than in the state of FIG. There is a disadvantage that a voltage is required.

In order to avoid such an inconvenient state, according to the light modulator driving method of the present invention, the start of displacement of the reflection plate 1 is applied to each electrode so that the start of displacement of the intermediate electrode 10 is not delayed. The timing of applying the driving voltage is controlled. With such a driving method, an inconvenient state as shown in FIG. 3B is reliably avoided, and stable driving with a low voltage is possible.

The method of driving the light modulation device according to the present invention uses the reflection plate 1
The same can be applied to a case where a plurality of intermediate electrodes 10 are provided between and the counter electrode 2. That is, by controlling the application timing of the drive voltage to each electrode so that the start of the deformation of the reflector 1 is not delayed at least from the start of the deformation of the intermediate electrode 10 closest to the reflector 1, as shown in FIG. Avoid such inconveniences.

Such a driving method can be applied not only to the case where the reflection plate and the intermediate electrode are driven in contact but also to the case where non-contact driving is performed. Note that it is desirable to appropriately adjust the timing of applying the drive voltage to each electrode according to the rigidity of the reflector 1 and the intermediate electrode 10.

As described above, the driving voltage can be reduced by the intermediate electrode 10. However, if the rigidity of the intermediate electrode 10 is high and the energy required for its deformation is large, the driving voltage increases. May be caused. Therefore,
According to one embodiment of the present invention, the intermediate electrode 10 is so formed that the rigidity of the intermediate electrode 10 is at least lower than the rigidity of the reflector 1.
0 is formed. This is advantageous for lowering the drive voltage of the intermediate electrode 10, and also improves the responsiveness of the electrostatic actuator constituted by the intermediate electrode 10.

Although not shown, according to another embodiment of the present invention, the intermediate electrode 10 is formed of a dielectric. In such a configuration, when a voltage is applied between the counter electrode 2 and the reflector 1, an electric charge is induced on the counter electrode 2 side of the intermediate electrode 10 in such a manner as to be attracted by the counter electrode 2. ,
A charge of the opposite polarity is also induced on the opposite side of the intermediate electrode 10 from the counter electrode 2, and a voltage is also generated between the reflector 1 and the intermediate electrode 10. , The same driving of the reflector 1 is possible. As described above, the intermediate electrode 10 functions as an electrode for generating an electrostatic force. However, since there is no need to provide an electrode for applying a voltage from the outside, the structure of the intermediate electrode 10 becomes very simple. This is advantageous for improving the productivity and reliability of the light modulation device. Also, since it is only necessary to apply a driving voltage to only the reflection plate 1 and the counter electrode 2, the driving circuit can be simplified. The method of driving the light modulation device by applying a drive voltage only to the reflection plate 1 and the counter electrode 2 as described above is also included in the present invention.

When the reflecting plate 1 is driven for displacement, the air inside the gap 8 is compressed with the displacement of the reflecting plate 1 and the pressure rises, and the reflecting plate 1 is pushed back by the pressure inside the gap 8. The actual amount of displacement of the reflector 1 is smaller than the amount of displacement of the reflecting plate 1 statically calculated under the condition that there is no air inside the reflector 8. The pressure rise ΔP is expressed by the following equation.

ΔP = Po · ΔV / (V−ΔV) (1) where Po is the initial pressure in the gap 8, V is the initial volume of the gap, and ΔV is the volume change due to the displacement of the reflector 1.

In order to reduce the pressure increase in the gap 8 due to the displacement of the reflector 1, that is, the air damper effect, to achieve a lower driving voltage and an improved response.
It is effective to increase the initial volume V of the gap 8.

In FIG. 2, the gap 8 is divided by the intermediate electrode 10 into two upper and lower gaps. Assuming that the total volume of each of the divided gaps is the same as the gap volume in the case of FIG. 1, the volume of each of the divided gaps is smaller than that of FIG. The indicated initial volume V of the gap becomes small.

Therefore, according to one embodiment of the present invention, FIG.
As shown in FIG. 1, a through hole 12 is provided in the intermediate electrode 10. When the intermediate electrode 10 is deformed toward the counter electrode 2, the air in the gap between the intermediate electrode 10 and the counter electrode 2 that has been compressed due to the deformation moves through the through hole 12 to the gap on the reflector 1 side. Therefore, a pressure increase in the gap on the counter electrode 2 side can be suppressed. Due to this reaction, the pressure in the gap on the side of the reflection plate 1 increases. However, since the gaps communicate with each other through the through holes 12, the pressure in the gap 8 is averaged, and the increase in the air damper effect is suppressed as a whole. Therefore, low voltage driving is possible.

It is preferable to fill the gap 8 with a substance having a high dielectric constant, for example, glycerin or ferroelectric liquid crystal, in order to reduce the voltage of the electrostatic actuator. However, such a substance has an extremely low volume compression ratio. Since it is small, the damper effect becomes remarkable. Therefore, it is generally preferable to fill the gap 8 with a substance having a small volume compressibility, for example, a gas such as air or an inert gas.

Although not shown, according to another embodiment of the present invention, at least one side of the reflector 1 is opened, and the gap 8 is not completely sealed by the reflector 1. For example, the reflection plate 1 is configured to be cantilevered by the electrode substrate 3 at only one end thereof. Even in such a configuration,
Since the air damper effect exists, the provision of the through hole in the intermediate electrode 10 is effective in reducing the air damper effect.

Although not shown, according to another embodiment of the present invention, at least one side of the intermediate electrode 10 is also opened. For example, the intermediate electrode 10 is configured to be cantilevered in a recess of the electrode substrate 3 at only one end thereof. Since the open portion of the intermediate electrode 10 operates in the same manner as the through hole 12, the air damper effect can be reduced without providing a special through hole.

Although not shown, according to another embodiment of the present invention, the intermediate electrode 10 has a mesh structure having a large number of through holes.

It should be understood that the present invention also encompasses a device in which the light modulation device of each of the above embodiments is regarded as one element and a plurality of elements are arranged one-dimensionally or two-dimensionally.

[0047]

As apparent from the above description, (1)
According to the first to fifth aspects of the present invention, the drive voltage can be reduced without reducing the displacement of the reflector, or the displacement of the reflector can be increased without increasing the drive voltage. (2) The invention according to claim 2 is to reduce the driving voltage of the electrostatic actuator composed of the reflector and the intermediate electrode closest to the reflector, which has the greatest influence on the displacement characteristics of the reflector, and to reduce the Improvement can be achieved.
(3) According to the third aspect of the present invention, it is not necessary to provide an electrode for applying a driving voltage from the outside to the intermediate electrode itself, and the structure of the intermediate electrode becomes very simple.
This is advantageous in improving the productivity and reliability of the light modulation device, and eliminates the need to externally apply a drive voltage to the intermediate electrode, so that the drive circuit of the light modulation device can be simplified. (4) According to the fourth aspect of the present invention, the energy required for deformation of the intermediate electrode is reduced, which is advantageous for lowering the driving voltage, and the responsiveness of the electrostatic actuator constituted by the intermediate electrode. Can also be improved. Also,
(5) According to the fifth aspect of the invention, an increase in the air damper effect due to the provision of the intermediate electrode can be suppressed. (6) According to the invention described in claim 6, the phenomenon that the distance between the reflection plate and the intermediate electrode facing the reflection plate is prevented from being widened, and stable driving at low voltage becomes possible. (7) According to the seventh aspect of the invention, it is only necessary to apply a drive voltage between the first electrode and the second electrode, so that the drive circuit of the optical modulation device can be simplified. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a basic configuration of a light modulation device to which the present invention can be applied.

FIG. 2 is a schematic sectional view showing an example of a light modulation device according to the present invention.

FIG. 3 is a schematic sectional view for explaining a driving method of the light modulation device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflector (1st electrode) 2 Counter electrode (2nd electrode) 3 Electrode board 8 Gap 10 Intermediate electrode 12 Through hole

Claims (7)

[Claims] 1. A displaceable reflector serving also as a first electrode, a non-displaceable second electrode disposed opposite to the reflector, and between the reflector and the second electrode. And at least one displaceable intermediate electrode disposed in the optical modulator, wherein the intermediate electrode and the reflector are displaced by an electrostatic force acting between the electrodes. 2. The light modulation device according to claim 1, wherein at least the intermediate electrode closest to the reflector has a surface facing the reflector made of a conductive material. 3. The light modulation device according to claim 1, wherein the intermediate electrode is made of a dielectric. 4. The light modulation device according to claim 1, wherein the intermediate electrode has lower rigidity than the reflection plate. 5. The light modulation device according to claim 1, wherein the intermediate electrode has holes penetrating on both surfaces thereof. 6. The method of driving a light modulation device according to claim 1, wherein the start of displacement of the reflector is at least delayed from the start of displacement of the intermediate electrode closest to the reflector. Controlling the application timing of the drive voltage to each of the electrodes as described above. 7. The method of driving an optical modulation device according to claim 3, wherein a driving voltage is applied only to the first electrode and the second electrode. .