JP4029489B2 - Spatial light modulator and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spatial light modulation device suitable for an optical switching element (light valve) used in optical communication, optical computation, an optical storage device, an optical printer, an image display device, and the like, and a control method thereof.
[0002]
[Prior art]
As a spatial light modulator capable of controlling light on / off, a device using liquid crystal is known. FIG. 9 shows a schematic configuration thereof. This spatial light modulation device is realized as an optical switching element 900, and is composed of polarizing plates 901 and 908, glass plates 902 and 903, transparent electrodes 904 and 905, and liquid crystals 906 and 907, and a voltage is applied between the transparent electrodes. By doing so, the direction of the liquid crystal molecules is changed to rotate the polarization plane to perform optical switching. For example, such an optical switching element (liquid crystal cell) can be arranged two-dimensionally to constitute an image display device as a liquid crystal panel.
[0003]
[Problems to be solved by the invention]
The optical switching element (spatial light modulation device) using this liquid crystal has poor high-speed response characteristics and operates only at a response speed of about several milliseconds at most. For this reason, a spatial light modulation device using liquid crystal is difficult for optical communication, optical computation, optical storage devices such as hologram memory, optical printers and the like that require high-speed response. In addition, in the spatial light modulator using liquid crystal, there is a problem that the light use efficiency is lowered by the polarizing plate.
[0004]
There is a need for a spatial light modulator capable of high-speed operation that can handle these applications. For this reason, a spatial light modulator that can be modulated at high speed by mechanically moving a switching element that can control light has been developed. . One of them is a micromirror device, which supports the mirror so as to be pivotable by a yoke, and changes the angle of the mirror so as to modulate and emit incident light corresponding to an electrical or optical input. It has become.
[0005]
In addition, it is possible to modulate the incident light by moving the switching part with reflection function or transmission function in parallel while supporting it with an elastic body, and it is also possible to configure a spatial light modulation device based on such principle It is. The evanescent light is extracted by bringing the extraction surface of the switching unit into contact with the total reflection surface of the light guide unit, which the applicant of the present application has applied for and can transmit light by total reflection, and about one wavelength or less of the switching unit One of them is an optical switching element capable of modulating and controlling light at a high speed by a minute movement of the light. In this optical switching element using evanescent light, the switching unit is supported by an elastic support member such as a thin film, and the switching unit is driven by an electrostatic force by supplying power to the electrode, so that the total reflection surface is opposed. The position of the extraction surface of the switching unit can be moved. Then, when the extraction surface of the switching unit is substantially in contact with the total reflection surface, the light is extracted and emitted. Further, when the extraction surface is separated from the total reflection surface, no light is extracted, so that the light is not emitted and is turned off. As described above, the optical switching element using the evanescent wave can modulate the incident light by moving the position of the extraction surface by a minute distance with respect to the total reflection surface. As one of them, the intensive development is progressing toward realization.
[0006]
In a spatial light modulator that drives the switching unit by combining such elastic force and electrostatic force, it is an important issue to perform a stable operation at the lowest possible drive voltage, and the evanescent light under development is used. The same applies to the optical switching element.
[0007]
If the distance that the switching unit moves to turn on and off the light is d and the driving voltage is Vd, the elastic force Fg and the electrostatic force Fs acting in the process can be expressed as follows.
[0008]
Fg = K × x (1)
Fs = C × Vd ² / (D−x) ² (2)
Here, x is the moving distance of the switching unit, K is an elastic coefficient of the support member, and C is a constant that takes into account the area and dielectric constant of the electrode. Since the moving position of the switching unit is a stable position where the elastic force Fg and the electrostatic force Fs are balanced, it is desirable to lower the elastic force Fg and shorten the moving distance d in order to lower the drive voltage Vd. However, when the elastic coefficient K is lowered, the moving speed of the switching unit is lowered and the response speed is lowered. Further, when the moving distance x is shortened, it becomes difficult to obtain on / off contrast. Therefore, it is difficult to lower the drive voltage Vd. Furthermore, if the on / off operation is performed at a stable position where the elastic force Fg and the electrostatic force Fs are balanced, the posture of the switching unit may not be stabilized, and the light modulation capability may be deteriorated. For example, in a switching element using an evanescent wave, a minute gap is generated between the total reflection surface and the extraction surface, and the amount of light that can be extracted can be reduced.
[0009]
Therefore, in the present invention, the spatial light modulation device capable of reducing the drive voltage Vd even under the condition that the moving distance d or the elastic constant K is kept constant, and further capable of stably controlling the attitude of the switching unit, and its control method The purpose is to provide. It is another object of the present invention to provide a spatial light modulator that can be driven at high speed, with high light contrast, and at a low voltage.
[0010]
[Means for Solving the Problems]
For this reason, in the present invention, the driving voltage for driving the switching unit is reduced by applying a constant bias voltage having the same polarity as the driving voltage between the electrodes for driving the switching unit. In addition, a holding force larger than the force by the bias voltage is secured at the ON position so that the posture can be stably held at the position where the switching unit is turned ON / OFF, especially at the ON position even when the bias voltage is applied. I can do it. That is, the spatial light modulation device according to the present invention includes a first position where light can be modulated and at least one switching unit movable to a second position away from the first position, and the switching unit is elastic. A supporting member for supporting the switching unit, and electrostatic driving means capable of driving the switching unit with an electrostatic force acting between at least one pair of electrodes. Further, the switching unit is driven by the electrostatic driving unit. Drive control capable of applying a constant bias voltage capable of ensuring a holding voltage for holding the switching unit stably at least at the first position by electrostatic force or elastic force and having the same polarity as this driving voltage It has the means. Further, according to the control method of the spatial light modulation device of the present invention, the support member includes the first position where the light can be modulated and the at least one switching unit which can move to the second position away from the first position. A method for controlling a spatial light modulator capable of elastically supporting and driving a switching unit by electrostatic driving means having at least one pair of electrodes, wherein the switching unit is driven with respect to the electrostatic driving means. A control step of applying a voltage and a constant bias voltage having the same polarity as the driving voltage and capable of securing a holding force for stably holding the switching unit at least in the first position by electrostatic force or elastic force It is characterized by that.
[0011]
By applying a constant bias voltage, the drive voltage applied when driving the switching unit can be lowered, so that the power supply voltage of the drive control means can be lowered. Therefore, the withstand voltage of the control circuit or the like constituting the drive control means can be reduced to simplify the configuration, and the power consumption can also be reduced. In addition, by ensuring a sufficient holding force capable of holding the switching unit at the first position, the posture of the switching unit can be stabilized in a state where a bias voltage is applied. For this reason, even when the switching unit is in the first position, it is possible to continuously apply the bias voltage, and control of the bias voltage is unnecessary or simplified.
[0012]
Furthermore, a stopper that secures a minimum gap between the electrodes is provided at a position where the holding force is obtained by the driving voltage among the first or second positions, and the switching unit is located at the first or second position. It is desirable that the electrostatic force due to the bias voltage does not increase infinitely but stays within a certain range, and the bias voltage is such that the elastic force of the support member is not reached at the position of the stopper. In this way, since the switching unit can be moved only by turning on / off the drive voltage, it is possible to always apply a constant bias voltage, and it becomes unnecessary to control the bias voltage.
[0013]
On the other hand, the bias voltage may be periodically changed so as to be smaller than the elastic force at the first or second position of the support member. For example, by changing the bias voltage in synchronization with the operation clock, the switching unit can be moved from the first or second position by the elastic force of the support member at the timing of the operation clock. Therefore, even if the bias voltage is not controlled in conjunction with the drive voltage, the switching unit can be operated in response to the change of the drive voltage only by changing the bias voltage at a constant timing. For this reason, it is easy to control the bias voltage. Furthermore, since the bias voltage can be made higher than the elastic force of the support member, the drive voltage can be further reduced.
[0014]
Also, by providing a stopper that secures the minimum gap between the electrodes, the electrostatic force due to the bias voltage can be kept within a certain range, so that the bias voltage does not reach the elastic force of the support member periodically at the position of the stopper. By setting the value, the switching unit can respond to the drive voltage. Therefore, the fluctuation range of the bias voltage can be suppressed, the circuit for controlling the bias voltage can be simplified, and the power consumption can be reduced.
[0015]
The holding force for holding the switching unit in the first position is such that the switching unit is moved from the second position to the first position by the support member, and is held in the first position by the elastic force of the support member. Can be obtained. That is, the first position is not a stable point where the electrostatic force due to the bias voltage and the elastic force of the support member are balanced, but a stable holding force is obtained by making the elastic force of the support member larger than the electrostatic force. be able to. Further, the electrostatic force increases in inverse proportion to the square of the distance as shown in the equation (2). For this reason, by setting the position where the elastic force that the support member is appropriately displaced acts as the first position, even if the driving force has a stable point at one or more positions with the elastic force of the support member, If the driving voltage has no stable point from the first position to the second position, the switching unit can be stably driven by a voltage lower than the driving voltage having no stable point with the elastic force of the support member. . Therefore, the drive voltage can be reduced even when the bias voltage is not set. Of course, the driving voltage can be further reduced by the combination with the bias voltage.
[0016]
In addition, the switching member can be supported substantially in the middle between the first and second positions when electrostatic force does not act on the support member, and the switching unit is held at the first position as electrostatic driving means. By providing an electrode pair and a second electrode pair to be held at the second position and alternately applying a driving voltage, a holding force can be obtained by electrostatic force at each position. Furthermore, since the distance moved by each electrode pair can be halved without changing the distance between the first and second positions, the working distance of the electrostatic force Fs is substantially reduced as shown in the equation (2). The driving voltage can be greatly reduced by reducing the driving voltage by half. Therefore, the drive voltage can be reduced even when the bias voltage is not set. Of course, the driving voltage can be further reduced by combining with the bias voltage.
[0017]
Thus, in the spatial light modulation device and the control method thereof according to the present invention, the drive voltage is reduced without changing the interval between the first and second positions of the switching unit and without changing the elastic coefficient of the support member. It is possible. Therefore, a spatial light modulator that can operate at high speed and has a high contrast can be driven at a low voltage, and can be manufactured at low cost, and a spatial light modulator that consumes less power can be provided.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
FIG. 1 is a cross-sectional view showing a schematic configuration of an image display device 2 in which a spatial light modulation device according to the present invention is realized as an optical switching element 1 and a plurality of the optical switching elements 1 are two-dimensionally arranged in an array. It is. FIG. 2 shows an enlarged schematic configuration of the optical switching element 1. In the optical switching element 1 of the present invention, the switching unit 30 provided with the translucent extraction surface 32 is brought into contact with the total reflection surface 22 of the light guide unit 20 capable of transmitting the introduced light 10 by total reflection, thereby evanescent. It is a switching element that can extract a wave. The extracted light is reflected by the switching unit 30 in the direction of the light guide unit 20 to become output light 12, and is output to the outside through the output surface 21 of the light guide unit 20. The optical switching element 1 can modulate (on / off control) the incident light 10 at a high speed by a minute movement of about one wavelength or less of the switching unit 30. For this reason, the electrostatic force and the spring force are used. A drive unit 40 that drives the switching unit 30 and a control unit 70 that supplies and controls power to the drive unit 40 are provided.
[0019]
The configuration of the optical switching element 1 will be described in more detail. The optical switching element 1 includes a light guide (light guide unit, cover glass) 20 that is made of glass and has a high transmittance of incident light 10. The incident light 10 is incident at an appropriate angle with respect to the total reflection surface 22 so that the incident light 10 is totally reflected. Then, as shown in the switching element 1a of FIG. 2, when the extraction surface 32 of the switching unit 30 approaches or comes into close contact with the total reflection surface 22 and reaches a position (first position or on) P1 where evanescent light can be extracted, Incident light 10 is extracted from the light unit 20 to the switching unit 30. The switching unit 30 of the present example includes a microprism 34 that can reflect the extracted incident light 10 toward the light guide unit 20, and the extracted light passes through the light guide unit 20 and is substantially vertically emitted light 12. And output. On the other hand, as shown in the switching element 1b of FIG. 2, when the switching unit 30 is separated from the first position and the extraction surface 32 is at a position (second position or off) P2 away from the total reflection surface 22, The light 10 is totally reflected by the total reflection surface 22 and is not extracted as evanescent light from the light guide unit 20. Therefore, the emitted light 12 cannot be obtained.
[0020]
Thus, the optical switching element 1 of the present example is a spatial light modulation device that can modulate the incident light 10 as the outgoing light 12 by moving the switching unit 30 to the first and second positions. Therefore, since the output light 12 can be controlled on and off using the optical switching element 1, the optical switching element 1 is arranged in an array as shown in FIG. It can be used similarly to a spatial light modulation device such as a micromirror device. Furthermore, since the evanescent light can be controlled by moving the switching unit 30 by moving a distance of about a wavelength or less, the switching unit 30 can be operated at a very high speed, and as an optical switching element having a high operating speed. Can be realized.
[0021]
Below the switching unit 30, a layer of a driving unit 40 that moves the optical switching unit 30 and a layer of a silicon substrate (IC chip) 70 on which a control IC that controls the driving unit 40 is configured are stacked. The drive unit 40 includes a base electrode 62 provided on the silicon substrate 70 side (lower side) of the switching unit 30 and an address electrode 60 provided on the upper surface of the silicon substrate 70 so as to face the base electrode 62. The combination of these electrodes 60 and 62 generates an electrostatic force so that the switching unit 30 can be driven. Furthermore, the drive unit 40 includes a thin-film elastic yoke (support member) 50 extending from the post 44 disposed around the switching unit 30 to the switching unit 30. Therefore, in the switching element 1 of the present example, the switching unit 30 is shown in the switching element 1a by the electrostatic force Fs of the electrostatic drive means composed of the pair of electrodes 60 and 62 and the elastic force Fg of the yoke 50. It can be moved to a position P1 and a second position P2 shown in the switching element 1b.
[0022]
A conductive thin film material having appropriate elasticity, such as an Al film, a Pt film, and an Ag film, can be used as the yoke 50 that supports the switching unit 30. In this example, the conductive film is made of a boron-doped silicon thin film. And an elastic thin film is adopted. By employing such a yoke 50, a bias voltage described later can be uniformly supplied from the control unit 70 or the like to the base electrode 62 of the switching element 1 constituting the image display device 2.
[0023]
Further, the switching element of the present example is set so that the deflection (initial displacement) 49 remains in the yoke 50 at the first position P1, and the elastic force Fg due to the initial displacement 49 becomes the holding force and becomes the first force. The switching unit 30 is pressed against the light guide unit 20 at the position P1. Accordingly, the extraction surface 32 of the switching unit 30 comes into close contact with the total reflection surface 22 at the first position P1 (on position), and an evanescent wave can be extracted efficiently. Further, a T-shaped spacer 42 is inserted between the switching unit 30 and the yoke 50 so that the portion of the yoke 50 that has been initially displaced 49 does not interfere with the switching unit 30.
[0024]
In the switching element of this example, a stopper 65 is installed between the electrodes 60 and 62. Therefore, when the driving voltage Vd is supplied from the control unit 70 to the address electrode 60 and the electrostatic force Fs is generated between the electrodes 60 and 62, and the switching unit 30 moves to the second position P2 by the force, the stopper The electrode stops at the position 65, and the electrodes 60 and 62 can secure an appropriate gap (gap) G without being in close contact.
[0025]
In FIG. 3, the relationship between the electrostatic force Fs and the elastic force (spring force) Fg in the drive part 40 of the switching element 1 of this example is shown. The electrostatic force Fs indicates the force when the drive voltage Vd is 10, 20, 30, 40, and 50 V, respectively. In the switching element 1 shown in FIG. 3, the distance between the electrodes 60 and 62 is 0.5 μm, and when the electrostatic force Fs is applied, the gap between the electrodes 60 and 62 is 0.1 μm by the stopper 65. G opens. Further, the yoke 50 is set so as to be displaced by 0.5 μm (initial displacement x0) at the first position P1. Therefore, when considering the displacement x of the yoke 50, the switching unit 30 sets an interval d0 of 0.4 μm from 0.5 μm to 0.9 μm of the initial displacement x0 from the first position P1 to the second position P2 (stopper position). Along with this, the elastic force Fg shown in the equation (1) is generated. Further, in this interval d0, when the drive voltage Vd is applied, as shown in the equation (2), the electrostatic force Fs when the inter-electrode d moves with a displacement x between 0.5 μm. Will occur.
[0026]
First, the drive voltage Vd that moves the switching unit 30 from the first position P1 to the second position P2 will be considered. In order to move the switching unit 30 from the first position P1 toward the second position P2 against the spring force Fg, the drive voltage Vd that always provides an electrostatic force Fs greater than the spring force Fg is applied to the electrodes 60 and 62. Need to be applied. That is, it is necessary to apply the drive voltage Vd that can exhibit the spring force Fg and the electrostatic force Fs that does not have a stable point. In the example shown in FIG. 3, the voltage for generating the electrostatic force Fs having no stable point is 50V, and the switching unit 30 can be reliably moved to the second position P2 by applying 50V as the drive voltage Vd. However, as described above, in the switching element 1 of this example, the yoke 50 has the initial displacement x0 at the first position P1, and the driving voltage Vd has a stable point at the displacement x equal to or less than the initial displacement x0. However, the switching unit 30 can be moved without any problem. That is, since the electrostatic force Fs is inversely proportional to the square of the distance (d−x), there is an initial displacement x0, and the interelectrode distance (d−x) is substantially smaller than the displacement x of the yoke. A low voltage can be used as the drive voltage Vd. In FIG. 3, it corresponds to the case where the drive voltage Vd is 40V. When the drive voltage Vd is 40 V, there are stable points s1 and s2 where the spring force Fg and the electrostatic force Fs are equal and the movement of the switching unit 30 stops in a region where the displacement x is smaller than the initial displacement x0, which is suitable for the drive voltage. Absent. However, in the region where the displacement x is greater than or equal to the initial displacement x0, the electrostatic force Fs is always greater than the spring force Fg and there is no stable point, so that it can be adopted as the drive voltage Vd.
[0027]
As described above, by introducing the initial displacement x0, the switching unit 40 can be stably held at the first position P1, and the drive voltage Vd can be reduced from 50V to 40V.
[0028]
Further, since the spring force Fg works at the first position P1 due to the initial displacement x0, a voltage that gives an electrostatic force Fs below this spring force Fg can be applied between the electrodes 60 and 62 as the bias voltage Vb. . For example, if 10V is set as the bias voltage Vb in FIG. 3, the electrostatic force Fs due to the bias voltage Vb at the first position P1 becomes the value B1 in the figure. Therefore, even when the bias voltage Vb is applied, the difference Fk1 from the spring force Fg at the first position P1 acts as a holding force, so that the switching unit 30 can be stably held. On the other hand, when the bias voltage Vb is applied, the electrostatic force Fs when the drive voltage Vd is 40 V can be obtained by applying 30 V as the drive voltage Vd, so that the switching unit 30 can be driven. Therefore, the drive voltage Vd can be further lowered by 10V.
[0029]
The bias voltage Vb can be applied in common to the switching elements 1 constituting the image display device 2 shown in FIG. For example, when the drive voltage Vd is driven by applying a high potential drive voltage Vd to the address electrode 60 that drives the switching element 1 when the reference voltage of the drive voltage Vd is 0 V, the base electrode 62 common to these switching elements 1 is used. In addition, the bias voltage Vb having the same polarity as the drive voltage Vd can be set by uniformly applying −10V to the drive voltage Vd. Of course, it is possible to build a circuit for setting the bias voltage Vb so that the reference voltage of the drive voltage Vd is increased by 10V.
[0030]
Furthermore, in the switching element 1 of the present example, since the gap G due to the stopper 65 exists between the electrodes 60 and 62 at the second position P2, the electrostatic force Fs does not increase infinitely. For this reason, when the bias voltage Vb is 10 V, the electrostatic force Fs generated thereby is the value of C1 in the drawing at the second position P2, and does not reach the spring force Fg. Therefore, when the drive voltage Vd is eliminated, the spring force Fg becomes larger than the electrostatic force Fs at the second position P2 even when the bias voltage Vb is applied, and the switching unit 30 is moved from the second position P2 by the spring force Fg. Move to the first position P1. Therefore, even when the bias voltage Vb is applied, the switching unit 30 can be on / off controlled only by controlling the drive voltage Vd.
[0031]
As described above, in the case where the bias voltage Vb that does not reach the spring force Fg is applied at the second position P2, it is possible to continuously apply a constant bias voltage Vb to all the switching elements. The control of the bias voltage Vb is very simple. Therefore, the bias voltage Vb can be applied without complicating the configuration of the control unit 70, and the drive voltage Vd can be reduced by the bias voltage Vb. Therefore, the withstand voltage of the control unit 70 can be reduced or the configuration can be simplified, so that the size of the control unit 70 can be reduced and the manufacturing can be performed at lower cost. Furthermore, since the power supply voltage of the drive voltage can be lowered, power consumption can be suppressed. On the other hand, the holding force Fk1 that stably holds the switching unit 30 can be secured at the first position P1. In addition, since the moving distance d0 of the switching unit 30 does not need to be changed, a sufficient contrast can be obtained. Furthermore, since it is not necessary to change the elastic coefficient K of the yoke 50, the driving speed of the switching unit 30 hardly changes. As can be seen from FIG. 3 even when the bias voltage Vb is applied, the electrostatic force Fs due to the bias voltage Vb rapidly decreases in inverse proportion to the square of the distance, and thus moves from the second position P2 to the first position P1. The speed at the moment is not so influential.
[0032]
Next, consider the case where the bias voltage Vb is 20V. The electrostatic force Fs due to the bias voltage Vb (20 V) at the first position P1 has a value of B2 in the drawing. Accordingly, since the holding force Fk2 is obtained as a difference from the spring force Fg, the switching unit 30 can be stably held. On the other hand, in order to obtain the electrostatic force Fs of 40 V required for driving the switching unit 30, the driving voltage Vd of 20 V may be applied, and the driving voltage Vd can be further reduced by 10 V compared to the above case. However, at the second position P2, if the bias voltage Vb is 20 V, the electrostatic force Fs exceeds the spring force Fg, so that the switching unit 30 from the second position P2 to the first position even if the drive voltage Vd is turned off. It does not move to position P1. For this reason, in order to move the switching unit 30 from the second position P2, the bias voltage Vb needs to be set to 0 or to a voltage that is smaller than the spring force Fg, for example, 10V. is there. Such control of the bias voltage Vb may be performed at the timing when the switching unit 30 is moved from the second position P2 to the first position P1. However, for example, it can be performed periodically in synchronization with a clock signal for driving the switching unit 30. Even if the bias voltage Vb fluctuates at the first position P1, the holding force Fk2 only increases. When the switching unit 30 is held at the second position P2, the drive voltage Vd is applied. Therefore, even if the bias voltage Vb is turned off, the switching unit 30 does not move. If the bias voltage Vb is periodically changed in synchronization with a clock signal or the like, the potentials of the base electrodes 62 of the plurality of switching elements 1 arranged in an array are simply controlled as shown in FIG. Good. Therefore, the drive voltage Vd can be further reduced without complicating the control circuit for the bias voltage Vb.
[0033]
FIG. 4 is a timing chart showing how the switching unit 30 is controlled using the drive voltage Vd and the bias voltage Vb. When the bias voltage Vb decreases from 20V to 10V at time t1 and the drive voltage Vd becomes 0V, the switching unit 30 at the second position P2 moves to the first position P1 by the spring force Fg. Even if the bias voltage Vb increases from 10V to 20V at time t2, the spring force Fg is larger at the first position P1, so that the position of the switching unit 30 can be held stably. A drive voltage Vd of 20 V is applied at time t3 one clock after time t1, and the bias voltage Vb is reduced to 10 V at the same timing. Therefore, at time t3, only the electrostatic force Fs due to a potential difference of 30 V works between the electrodes, so that the switching unit 30 does not move. However, when the bias voltage Vb increases at time t4, an electrostatic force Fs due to a potential difference of 40 V works between the electrodes, and the switching unit 30 moves from the first position P1 to the second position P2. When the driving voltage Vd becomes 0 V at time t5, which is one clock after time t3, the switching unit 30 moves from the second position P2 to the first position P1 as at time t1. In this way, by increasing or decreasing the bias voltage Vb so as not to reach the spring force Fg at the second position P2 in the clock cycle, it is possible to apply the bias voltage Vb exceeding the spring force Fg, and further drive The switching unit 30 can be moved according to the voltage Vd. Therefore, the drive voltage Vd can be lowered by the bias voltage Vb. For this reason, the structure of the control part 70 which controls the drive voltage Vd can be further simplified, and the withstand voltage can be lowered, so that it can be made compact. In addition, since the power supply voltage of the drive voltage can be lowered, power consumption can be reduced.
[0034]
Further, after the drive voltage Vd becomes high level at time t6 and the switching unit 30 moves to the second position, if the drive voltage Vd is maintained at time t7 which is the next clock cycle, the bias voltage Vb decreases. However, since a potential of 30 V is applied between the electrodes, the electrostatic force Fs exceeds the spring force Fg, and the switching unit 30 does not move. Similarly, when the drive voltage Vd becomes 0 V at time t8 and the switching unit 30 moves to the first position P1, and the drive voltage Vd is not applied at time t9 in the next clock cycle, the bias voltage Vb increases or decreases. However, at the first position P1, the electrostatic force Fs does not exceed the spring force Fg, so the switching unit 30 does not move. Thus, even if the bias voltage Vb is increased or decreased periodically, all the movements of the switching unit 30 can be controlled by the drive voltage Vd. In this example, when the drive voltage Vd changes to a high level, a delay occurs in the operation of the switching unit 30 only while the bias voltage Vb increases or decreases. However, the time during which the bias voltage Vb increases or decreases is switched by the spring force Fg. Since it is only necessary to start the unit 30, it can be performed in a very short time, and the possibility of causing an influence in image display or the like is very small.
[0035]
In this example, the bias voltage Vb is increased or decreased in the range of 10-20V, but the bias voltage Vb may be changed in the range of 0-20V. However, since the stopper 65 is provided at the second position P2, the electrostatic force Fs does not increase infinitely, and the spring force Fg is increased and the switching unit 30 is moved only by reducing the bias voltage Vb to 10V. What can be done is as described above. Therefore, the variation range of the bias voltage Vb is also set to a range of 10 to 20 V, so that the circuit for controlling the bias voltage Vb can be simplified, and the power consumption accompanying the increase or decrease of the base voltage can be reduced.
[0036]
Of course, the drive voltage and the bias voltage shown above are the values exemplified for examining each case, and if the voltage satisfies the above-described conditions, the corresponding effects can be obtained even if the values are not shown above. Of course. In addition, the values of the driving voltage and the bias voltage shown in this example are values under the conditions assumed in FIG. 3, and the driving voltage and the bias voltage according to the present invention are not limited to the values exemplified in this specification. is there.
[0037]
[Second Embodiment]
FIG. 5 shows an example in which the spatial light modulation device according to the present invention is realized as an optical switching element 1 different from the above. The optical switching element 1 of this example is also an optical switching element that can extract the evanescent wave and irradiate the emitted light 12, and the light guide unit 20, the reflection type optical switching unit 30, the drive unit 40, and the control unit 70 are stacked. Has been configured. For this reason, about the part which is common in said embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted. The optical switching element 1 of this example has a pair of electrodes 60 and 62 (hereinafter referred to as a second electrode pair) E2 for moving the switching unit 30 from the first position P1 to the second position P2 in the driving unit 40. In addition, a pair of electrodes 64 and 66 (hereinafter referred to as a first electrode pair) E1 for moving from the second position P2 to the first position P1 is provided. Therefore, a substantially U-shaped notch 38 is provided at a symmetrical position on the side surface of the buffer member 35 for supporting the prism 34 from the spacer 42. An auxiliary column 47 extending from the column 44 is inserted into the space 38, an electrode 66 serving as an address electrode is fixed to the column side, and an electrode 64 serving as a base electrode (common electrode) is fixed to the buffer member 45 side. Has been.
[0038]
In the optical switching element 1 of this example, the yoke 50 is further set so that the intermediate position P3 between the first position P1 and the second position P2 is balanced, that is, the displacement x is zero. For this reason, the switching unit 30 moves from the first position P1 to the intermediate position by the elastic force Fg of the yoke 50, and thereafter to the second position P2 by the electrostatic force Fs of the second pair E2 of the electrodes 60 and 62. Moving. In the reverse direction, it moves with the elastic force Fg from the second position P2 to the intermediate position P3, and thereafter moves with the electrostatic force Fs of the first pair E1 of the electrodes 64 and 66 to the first position P1. Then, at the first position P1, the electrostatic force Fs of the first pair E1 works as a holding force. The distance between the electrodes 64 and 66 is set such that the gap G is opened with the total reflection surface 22 serving as a stopper at the first position P1, and at the first position P1 as with the second position P2. Also, the electrostatic force Fs can be stopped within a certain range.
[0039]
The balanced position of the core 50 is an intermediate position P3 between the first and second positions, and the first and second electrode pairs E1 and E2 provide the second position from the intermediate position to the second position from the intermediate position. In the drive unit 40 that drives between the positions P2, the interval at which the electrode pairs E1 and E2 function as electrostatic drive means may be half of the interval d0 between the first and second positions. Therefore, since the interval at which the electrostatic force Fs works can be halved without changing the moving interval d0 of the switching unit 30, the interval d can be halved as can be seen from the above equation (2). The drive voltage Vd for obtaining the electrostatic force Fs is also halved. Furthermore, since the electrostatic force Fs can be used as the holding force at the first position P1, the initial displacement x0 for securing the holding force with the spring force Fg is not necessary. Accordingly, the electrostatic force Fs required to counter this initial displacement x0 is not necessary, and the drive voltage Vd can be further lowered.
[0040]
Further description will be given based on FIG. In FIG. 6, when the position where the displacement x of the core is 0 is the first position P1, and the position where the displacement x is 0.5 μm is the second position P2, the drive system has the holding force at the first position P1. Is not obtained, but the switching unit 30 can be moved from the second position P2 to the first position P1 by the spring force Fg. If the driving voltage Vd can obtain an electrostatic force Fs having no stable point from the first position P1 to the second position P2 with respect to such a spring force Fg, the switching unit 30 is moved from the first position P1. It can move to the second position P2. In the example shown in FIG. 6, when the drive voltage Vd is 20V, the switching unit 30 can be moved against the spring force Fg. Therefore, this case corresponds to a case where the switching element has the same configuration as that shown in FIG. 3 and the holding force cannot be obtained at the first position P1 by the spring force Fg. That is, a driving voltage Vd of 20 V is required to drive the switching unit 30 against the spring force Fg that does not provide a holding force.
[0041]
On the other hand, in the switching element 1 of the present example including the two electrode pairs E1 and E2 shown in FIG. 5, the position where the core displacement x is 0 as shown by the brackets in FIG. The position where the core displacement x is 0.25 can be the first position P1 or the second position P2. Then, the second electrode pair E2 composed of the electrodes 60 and 62 moves the switching unit 30 from the intermediate position P3 against the spring force Fg to the second position P2, and similarly the first electrode composed of the electrodes 64 and 66. The pair E1 moves the switching unit 30 from the intermediate position P3 against the spring force Fg to the first position P1. Since the state in which the switching unit 30 is driven by the electrode pairs E1 and E2 is the same, in order to move the switching unit 30 against the spring force Fg from the intermediate position P3, the second position from the intermediate position P3 is described based on the electrode pair E2. A drive voltage Vd that provides an electrostatic force Fs having no stable point between the positions P2 may be applied. In this example, when the drive voltage Vd of 7 V is applied, the switching unit 30 can be moved from the intermediate position P3 to the second position P2. Therefore, in the switching element 1 of this example, the switching unit 30 can be driven by alternately applying the drive voltage Vd of 7 V to the two electrode pairs E1 and E2. For this reason, compared with the above, it becomes possible to reduce the drive voltage Vd from 20V to 7V to about 1/3. Furthermore, since it can be moved from the intermediate position P3 to the first position P1 using the electrostatic force Fs and can be held by the electrostatic force Fs, it is possible to obtain a holding force for holding the switching unit 30 at the first position P1. .
[0042]
Further, similarly to the above embodiment, in this example, the drive voltage Vd can be further lowered by applying the bias voltage Vb. FIG. 7 is an enlarged view of the spring force Fg and the electrostatic force Fs shown in FIG. 6, and further shows the electrostatic force Fs with the voltage Vd of 5V, 4V and 2V added. When 2V is applied between the electrodes 60 and 62, 64 and 66 as the bias voltage Vb, the electrostatic force Fs when the drive voltage Vd is 7V is obtained by applying the drive voltage Vd of 5V at the intermediate position P3. Therefore, the switching unit 30 can be driven with the drive voltage Vd of 5V. In addition, in the first position P1 or the second position P2, the spring force Fg is larger than the electrostatic force Fs having a bias voltage Vb of 2V. Therefore, the switching unit 30 is simply turned on / off the 5V drive voltage Vd. Can be driven. Further, since the same bias voltage Vb is applied to the two electrode pairs E1 and E2, the electrostatic force Fs due to the bias voltage Vb is balanced at the intermediate position P3, and the intermediate position P3 is unlikely to fluctuate. On the other hand, when the switching unit 30 starts moving toward one of the positions, the interval between the other electrode pair becomes wide, and the electrostatic force Fs decreases in inverse proportion to the square of the distance. Therefore, once the switching unit 30 starts moving in the direction of one of the electrode pairs, the influence of the bias voltage Vb between the other electrode pair hardly occurs.
[0043]
Such a bias voltage Vb can be supplied by applying a common potential to the base electrode 62 of the second electrode pair E2 that moves together with the switching unit 30 and the base electrode 64 of the first electrode pair E1. Furthermore, in order to apply a bias voltage having the same polarity as the drive voltage Vd, a voltage lower than the reference voltage of the drive voltage, for example, when the reference voltage is 0 V, −2 V is used as the bias voltage Vb and is common to the base electrodes 62 and 64. This can be realized by applying the voltage to.
[0044]
It is also possible to further increase the bias voltage Vb and apply a 4V bias voltage Vb. In this case, an electrostatic force Fs of 7 V can be obtained by applying a driving voltage Vd of 3 V, and the switching unit 30 can be driven with a driving voltage Vd of 3 V. At the intermediate position P3, since the bias voltage Vb is balanced between the two electrode pairs, only the electrostatic force Fs of 3V is effective, but since the spring force Fg is 0, the switching unit 30 starts moving, When the movement is started, the influence of the bias voltage Vb of the other electrode pair is almost eliminated as described above, so that the switching unit 30 can be moved smoothly without causing the spring force Fg and the stable point.
[0045]
On the other hand, in the first position P1 or the second position P2, the electrostatic force Fs by the bias voltage Vb of 4V is stronger than the spring force Fg, so that the switching unit 30 moves even if the drive voltage Vd is turned off. Do not start. Therefore, in this case, it is necessary to reduce the bias voltage Vb to 0 V or 2 V where the spring force Fg is superior in synchronization with the clock signal. Then, the switching unit 30 can be driven by increasing or decreasing the 4V bias voltage Vb in synchronization with the clock signal to alternately apply the 3V drive voltage Vd to the first and second electrode pairs. Therefore, in the switching element 1 of the present example, the drive voltage as high as 50V, which is most commonly adopted as described in the above embodiment, can be reduced to a voltage level that is easy to use in a semiconductor circuit of 3V. Therefore, the circuit scale of the control unit 70 can be greatly reduced, and power consumption can be greatly reduced.
[0046]
FIG. 8 is a timing chart showing how the switching unit 30 of the switching element 1 of this example is controlled using the drive voltage Vd and the bias voltage Vb. When the bias voltage Vb decreases from 4V to 2V at time t11 and the drive potential Vd2 of the second electrode pair E2 that drives the switching unit 30 toward the second position P2 is turned off (from 3V to 0V), the second The total voltage of electrode pair E2 decreases from 7V to 2V. Therefore, since the spring force Fg becomes larger than the electrostatic force Fs, the switching unit 30 moves from the second position P2 toward the intermediate position P3. At time t12, when the drive potential Vd1 of the first electrode pair E1 that drives the switching unit 30 toward the first position P1 is turned on (from 0 V to 3 V) and the bias voltage Vb is 4 V, the first electrode The total voltage of the pair E1 is 7V, and the switching unit 30 moves to the first position P1 and is held at that position. At this time, the total voltage of the second electrode pair E2 becomes 4V by the bias voltage Vb. However, since the interval between the second electrode pair E2 is wide, the electrostatic force Fs is almost negligible.
[0047]
When the bias voltage Vb decreases from 4 V to 2 V at time t13, one clock after time t11, and the drive voltage Vd1 of the first electrode pair E1 is turned off, the switching unit 30 moves from the first position P1 to the intermediate position P3. To start moving. At time t14, when the drive voltage Vd2 of the second electrode pair E2 is turned on and the bias voltage Vb becomes 4V, the total voltage of the second electrode pair E2 becomes 7V. It moves to the position P2 and is held.
[0048]
Further, when the bias voltage Vb decreases at time t15, which is one clock after time t13, the drive voltage Vd2 is turned off, and then the drive voltage Vd1 is turned on, the switching unit 30 moves from the second position P2 to the first position. Move to P1. In this state, even if the bias voltage Vb decreases at time t16, which is one clock after time t15, if the drive voltage Vd1 is on, the total voltage of the first electrode pair E1 is maintained at 5V. The unit 30 is held at the first position P1. Conversely, after the drive voltage Vd1 is turned off at time t17 and the drive voltage Vd2 is turned on and the switching unit 30 is moved to the second position, the bias voltage Vb is changed from 4 V at time t18 and time t19 in the clock cycle. Since the drive voltage Vd2 is on even when the voltage is reduced to 2V, the switching unit 30 is held at the second position P2. When the drive voltage Vd2 is turned off at time t20 and the drive voltage Vd1 is turned on, the switching unit 30 moves from the second position P2 to the first position P1.
[0049]
Thus, in the switching element 1 of this example, the switching unit 30 can be driven by changing the drive voltage Vd from 0 to 3V. Also, the bias voltage Vb may be changed within the range of 2-4V with a clock cycle. Therefore, the switching element 1 of the present example can greatly reduce the voltage for driving the switching unit 30, and can be driven at a normal battery power level. In addition, the image display apparatus in which the plurality of switching elements shown in FIG. 1 are arranged in an array can be driven by the voltage of the battery voltage level. By reducing the drive voltage in this way, the voltage level that can be controlled by the control circuit can be lowered, and the withstand voltage characteristic may be low. Therefore, the switching element and the image display device using the switching element are integrated with the conventional semiconductor integrated circuit. It can also be directly driven by a circuit. Further, since the power supply voltage may be low, power consumption can be greatly reduced. On the other hand, the performance as a switching element, for example, the elastic coefficient of the yoke 50, the moving distance of the switching element, and the ability to hold the switching unit 30 in the ON position can be maintained as they are. Therefore, a switching element having high contrast and capable of stable operation at high speed can be supplied at low cost. Further, by arranging the switching elements in an array, a high-resolution and bright image can be displayed at high speed, and an image display device with low power consumption can be provided at low cost.
[0050]
In the above example, the present invention has been described by taking an optical switching element using an evanescent wave as an example. However, the present invention is not limited to a spatial light modulator that moves a planar element that changes to an extraction surface of a switching unit in parallel. Various types of spatial light modulators, such as a spatial light modulator that changes the angle to change the incident light by changing the position of the switching unit, and the polarization direction or the phase of the reflected light Of course, the present invention can be applied. Moreover, although the example which used the yoke which consists of thin film materials as an elastic material was demonstrated in the above example, of course, it is also possible to employ | adopt elastic materials of other shapes, such as a coil spring.
[0051]
【The invention's effect】
As described above, the spatial light modulation device of the present invention can drive the switching unit using elastic force and electrostatic force to modulate the light, and can appropriately hold the switching unit in the on position. By applying a bias voltage in the range, the drive voltage can be reduced without sacrificing the characteristics of the switching unit. Furthermore, by receiving two pairs of electrodes that provide an electrostatic force, the driving voltage can be reduced from a conventional fraction to a voltage that is one digit less or less. Therefore, it is possible to provide a spatial light modulation device that can move the switching unit at high speed, has a short response time, and has a high response speed, and can be driven at a low voltage, and a control method thereof.
[0052]
The spatial light modulation device according to the present invention can be provided as a switching element or as an image display device in which switching elements are arranged in an array, and the drive voltage can be greatly reduced. Thus, the switching element or the image display device can be directly driven. For this reason, it becomes possible to significantly reduce the cost of these switching elements or image display devices. Further, since the drive voltage can be lowered, the power consumption of the switching element or the image display device can be greatly reduced. Therefore, according to the present invention, the switching element or the image display device can be driven with limited power such as a battery using an evanescent wave having excellent high-speed response characteristics. Therefore, the present invention is very useful for applying a spatial light modulation device using an evanescent wave or the like that modulates light by moving the position of the switching unit in various fields in the future.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of an image display device in which optical switching elements using evanescent light according to a first embodiment of the present invention are arranged in an array.
2 is an enlarged cross-sectional view showing a configuration of a switching unit of the optical switching element shown in FIG. 1. FIG.
3 is a diagram showing a relationship between an elastic force (spring force) and an electrostatic force in the optical switching element shown in FIG. 1 with respect to a moving amount (displacement) of a switching unit.
4 is a timing chart showing how the optical switching element shown in FIG. 1 is driven by a bias voltage. FIG.
FIG. 5 is a diagram illustrating a configuration example of an optical switching element according to a second embodiment of the present invention.
6 is a graph for comparing the driving power of the switching element shown in FIG. 5 with the driving power of the switching element shown in FIG. 1;
7 is a diagram showing the relationship between the elastic force (spring force) and the electrostatic force in the optical switching element shown in FIG. 5 with respect to the movement amount (displacement) of the switching unit.
FIG. 8 is a timing chart showing how the optical switching element shown in FIG. 5 is driven with a bias voltage as a drive voltage.
FIG. 9 is a diagram showing an optical switching element using a conventional liquid crystal.
[Explanation of symbols]
1. Spatial light modulator
2. Image display device
10. Incident light
12. ・ Outgoing light
20. ・ Light guide
22. Total reflection surface
30 .. Switching part
32 .. Extraction surface
33 ・ ・ Micro Prism
38 ... Gap
40 ・ ・ Driver
44 .. Post (post)
49. Deflection (initial displacement)
50 ・ ・ Yoke (elastic body)
60 .. Address electrode (second electrode pair)
62 .. Base electrode (second electrode pair)
64 .. Base electrode (first electrode pair)
65. ・ Stopper
66 .. Address electrode (first electrode pair)
70 .. Control part
908 .. Polarizing plate
903..Glass plate
904, 905 ... Transparent electrode
906, 907 ... Liquid crystal

Claims (13)

A first position capable of modulating light, and at least one switching part movable to a second position remote from the first position;
A support member that elastically supports the switching unit;
Electrostatic driving means capable of driving the switching unit by electrostatic force acting between at least one pair of electrodes;
The electrostatic driving means has a driving voltage for driving the switching unit, and a holding force that stably holds the switching unit at least in the first position by electrostatic force or elastic force, with the same polarity as the driving voltage. Drive control means capable of applying a certain bias voltage that can be secured,
The spatial light modulator according to claim 1, wherein the drive control unit applies the bias voltage that is periodically smaller than an elastic force of the support member at the first or second position. In claim 1, a stopper that secures a minimum gap between the electrodes is provided at a position of the first or second position where a holding force is obtained by the driving voltage.
The spatial light modulation device, wherein the drive control means applies the bias voltage that does not reach the elastic force of the support member at the position of the stopper. In claim 1, a stopper that secures a minimum gap between the electrodes is provided at a position at which a holding force is obtained by the electrostatic force of the electrostatic driving means, in the first or second position.
The spatial light modulator according to claim 1, wherein the drive control means applies the bias voltage that does not reach the elastic force of the support member at the position of the stopper periodically.   2. The space according to claim 1, wherein the switching unit is moved from the second position to the first position by the support member and is held at the first position by an elastic force of the support member. Light modulation device.   5. The drive voltage according to claim 4, wherein the drive control means applies a drive voltage that does not establish a stable state only between the first and second positions when the switching unit is moved from the first position to the second position. A spatial light modulation device applied to the electrostatic drive means. In Claim 1, when the electrostatic force does not work, the support member can support the switching unit at approximately the middle between the first and second positions.
The electrostatic driving means includes a first electrode pair that holds the switching unit at the first position and a second electrode pair that holds the switching unit at the second position,
The spatial light modulation device, wherein the drive control means applies a drive voltage alternately to the first and second electrode pairs. A first position capable of modulating light, and at least one switching part movable to a second position remote from the first position;
A support member that elastically supports the switching unit, is movable from the second position to the first position by an elastic force, and can hold the switching unit at the first position;
Electrostatic driving means capable of driving the switching unit by electrostatic force acting between at least one pair of electrodes;
Drive control for applying a drive voltage that does not establish a stable state only between the first and second positions when the switching unit is moved from the first position to the second position. And a spatial light modulation device. A first position capable of modulating light, and at least one switching part movable to a second position remote from the first position;
A support member that elastically supports the switching unit and is capable of supporting the switching unit substantially in the middle of the first and second positions when an electrostatic force does not work;
Electrostatic driving means comprising a first electrode pair for holding the switching unit in the first position, and a second electrode pair for holding the switching part in the second position;
A spatial light modulator comprising: drive control means for supplying a drive voltage alternately to the first and second electrode pairs of the electrostatic drive means.   9. The light guide unit according to claim 1, further comprising a light guide unit including a total reflection surface capable of transmitting the introduced light by total reflection, wherein the switching unit is configured to perform the total reflection at the first position. A spatial light modulator characterized by extracting evanescent light leaking from the total reflection surface in contact with the surface. At least one switching unit movable to a first position where light can be modulated and a second position separated from the first position is elastically supported by a support member, and at least one set of the switching units is provided. A method of controlling a spatial light modulation device that can be driven by electrostatic drive means comprising the electrodes of:
A driving voltage for driving the switching unit and a holding force for stably holding the switching unit at least at the first position by electrostatic force or elastic force with the same polarity as the driving voltage with respect to the electrostatic driving unit. A control step of applying a constant bias voltage capable of ensuring
In the control step, the bias voltage that is smaller than the elastic force of the support member at the first or second position is periodically applied. In claim 10, a stopper that secures a minimum gap between the electrodes is provided at a position where a holding force is obtained by the driving voltage, of the first or second positions,
In the control step, the bias voltage that does not reach the elastic force of the support member is applied at the position of the stopper, and the control method of the spatial light modulation device, At least one switching unit movable to a first position where light can be modulated and a second position separated from the first position is elastically supported by a support member, and at least one set of the switching units is provided. A method of controlling a spatial light modulation device that can be driven by an electrostatic drive means having a plurality of electrodes, wherein the switching unit is moved from the second position to the first position by the support member, and the support member Is held in the first position by the elastic force of
When the switching unit is moved from the first position to the second position, a driving voltage that does not establish a stable state only between the first and second positions is applied to the electrostatic driving means. A control method of the spatial light modulator. At least one switching unit movable to a first position where light can be modulated and a second position separated from the first position is elastically supported by a support member, and at least one set of the switching units is provided. A method of controlling a spatial light modulation device that can be driven by electrostatic drive means having a plurality of electrodes, wherein the support member is positioned between the first and second positions when no electrostatic force is applied. The electrostatic driving means includes a first electrode pair that holds the switching unit at the first position and a second electrode pair that holds the switching part at the second position.
A control method for a spatial light modulator, wherein a drive voltage is alternately applied to the first and second electrode pairs.

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