JP2020079831A - Phase modulation device and phase modulation method - Google Patents

Abstract

To provide a phase modulation device and a phase modulation method for suppressing occurrence of a failure related to a liquid crystal element cased by unnecessary DC components.SOLUTION: A phase modulation device 1 includes: a liquid crystal element 5; a signal analysis unit 4; and a control unit 3. The liquid crystal element 5 has: a pixel region 21; and a light reception unit 6. A plurality of pixel electrodes 24 are disposed in the pixel region 21, and different drive voltages DVs are applied to the plurality of pixel electrodes 24 such that emitted light SL is phase-modulated, and that a wavefront WF of the light SL is changed. The light reception unit 6 receives leaked light of the light SL phase-modulated by the pixel region 21, and generates a received light signal LRS. The signal analysis unit 4 analyzes the received light signal LRS in a predetermined frequency. The control unit 3 controls the liquid crystal element 5 on the basis of an analysis result by the signal analysis unit 4.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a phase modulation device and a phase modulation method using a liquid crystal element.

  In recent years, in order to cope with a rapidly increasing amount of information in the optical communication field, a ring-shaped optical network system and an optical wavelength division multiplexing communication system have been proposed. ROADM (Reconfigurable Optical And Drop Multiplexer) devices that can perform branching or addition of optical signals in these optical communication systems without relaying conversion to electrical signals are used.

  A WSS (Wavelength Selective Switch) device is used as an optical switching device in the ROADM device. As an optical switching element in the WSS device, a MEMS (Micro Electro Mechanical Systems) mirror and a reflective liquid crystal element such as an LCOS (Liquid Crystal on Silicon) element are used.

  The LCOS element is a reflective liquid crystal element having a pixel region in which a plurality of reflective pixel electrodes are arranged in a horizontal direction and a vertical direction. The refractive index of the liquid crystal on each pixel electrode changes by controlling the voltage applied to the liquid crystal for each pixel electrode. The phase velocity of the signal light is controlled for each pixel by changing the refractive index of the liquid crystal on each pixel.

  The LCOS element can change (tilt) the wavefront of the signal light by gradually changing the phase velocity for each pixel. The LCOS element can control the tilt angle of the wavefront of the signal light according to the rate of change of the phase velocity. That is, the LCOS element functions as a phase modulation element that changes the phase velocity for each pixel and reflects the signal light in a predetermined direction.

  The MEMS mirror requires mirrors corresponding to the number of wavelength bands of signal light. Therefore, when changing the wavelength band of signal light or the number thereof, it is necessary to newly manufacture the MEMS mirror in accordance with the changed contents.

  On the other hand, the LCOS element can arbitrarily divide the pixel region into a plurality of pixel blocks and control each pixel block. Therefore, when the wavelength band of signal light or the number thereof is changed, the pixel block can be reconfigured in accordance with the changed contents, and it is not necessary to newly manufacture a liquid crystal element. That is, the LCOS element is superior to the MEMS mirror in the variable grid property. Patent Document 1 describes an example of a phase modulation device using an LCOS element.

JP, 2016-143037, A

  In a phase modulation device using a liquid crystal element such as an LCOS element, a DC component is added to a drive voltage applied between a pixel electrode and a counter electrode when the liquid crystal element becomes in a high temperature state or time elapses. As a result, defects such as flicker or image sticking may occur in the liquid crystal element.

  In the liquid crystal element, a DC component may be added to the drive voltage applied between the pixel electrode and the counter electrode due to storage or use in a high temperature or high humidity environment, temperature change of the liquid crystal element itself, or the like. This causes a display defect such as flicker or burn-in. Even in a phase modulation device using a liquid crystal element such as an LCOS element, flicker or burn-in causes a problem such as an increase in signal noise or crosstalk between fiber ports.

  It is an object of the present invention to provide a phase modulation device and a phase modulation method that can suppress the occurrence of defects in liquid crystal elements due to unnecessary DC components.

  The present invention provides a pixel region in which a plurality of pixel electrodes are arranged, and different drive voltages are applied to the plurality of pixel electrodes to phase-modulate the emitted light to change the wavefront of the light, and A liquid crystal element having a light receiving unit that receives the leaked light of the light phase-modulated by the pixel region and generates a light receiving signal, a signal analyzing unit that analyzes the light receiving signal at a predetermined frequency, and an analysis by the signal analyzing unit Based on the result, a phase modulator including a control unit that controls the liquid crystal element is provided.

  Further, according to the present invention, a liquid crystal element having a pixel region in which a plurality of pixel electrodes are arranged is provided with different drive voltages applied to the plurality of pixel electrodes, so that the emitted light is phase-modulated to perform the light modulation. Of the light, the light receiving section receives the leaked light of the light phase-modulated by the liquid crystal element to generate a light receiving signal, and the signal analyzing section analyzes the light receiving signal at a predetermined frequency and controls the light receiving signal. The section provides a phase modulation method for controlling the liquid crystal element based on the analysis result by the signal analysis section.

  According to the phase modulation device and the phase modulation method of the present invention, it is possible to suppress the occurrence of troubles related to the liquid crystal element due to the unnecessary DC component.

It is a block diagram showing a phase modulation device of one embodiment. It is a top view which shows an example of a liquid crystal element. FIG. 3 is a cross-sectional view of the liquid crystal element taken along the line AA of FIG. 2. It is a figure which shows the phase modulation of the signal light by a reflective liquid crystal element. It is a figure which shows the drive voltage applied to a pixel electrode. It is a figure which shows the refractive index of the liquid crystal on a pixel electrode. It is a figure which shows the normal inversion drive in which the direction of the voltage applied to a liquid crystal repeats normal rotation and inversion by turns. 6 is a flowchart illustrating an example of a phase modulation method according to an embodiment. It is a figure showing the state where the DC component was added to the pixel electrode side voltage. It is a figure which shows the optical response waveform of a light reception signal when a DC component is added to the pixel electrode side voltage. It is a figure which shows the received light signal converted into the frequency component. It is a figure which shows the state in which the counter electrode side voltage was adjusted. It is a figure which shows the optical response waveform of the light reception signal in the state where the counter electrode side voltage was adjusted. It is a figure which shows the frequency component of the light reception signal in the state where the counter electrode side voltage was adjusted.

  A phase modulator according to an embodiment will be described with reference to FIG. The phase modulator 1 includes a controller 3, a signal analyzer 4, and a reflective liquid crystal element 5. The control unit 3 and the signal analysis unit 4 may be configured as an integrated circuit. A light receiving portion 6 is formed on the liquid crystal element 5. The liquid crystal element 5 is, for example, an LCOS element. Hereinafter, the liquid crystal element 5 will be referred to as an LCOS element 5.

  Information data JD is input to the image data generation unit 2. The information data JD includes a parameter indicating the relationship between the position of the input port and the output port of the signal light and the angle of the reflected light with respect to the incident light in the signal light, and the wavelength band of the signal light, that is, the phase that realizes a desired reflected light angle. And a parameter relating to the distribution of the change amount of.

  The amount of phase change is the lead or lag of the phase of the reflected light with respect to the phase of the incident light, and corresponds to the distribution of the phase velocity. The signal light emitted from a predetermined input port is phase-modulated by the phase modulator 1 and is incident on a target output port.

  The image data generator 2 sets the distribution of the amount of change in the phase based on the information data JD. The image data generation unit 2 generates the image data DD based on the distribution of the amount of phase change or the distribution of the phase velocity, and outputs the image data DD to the control unit 3. The phase modulation device 1 may be configured to include the image data generation unit 2.

  The control unit 3 generates the drive control signal DCS based on the image data DD. The drive control signal DCS includes the timing for controlling the driving of the LCOS element 5 and the grayscale data corresponding to each pixel in the LCOS element 5 of the image data DD. The control unit 3 outputs the drive control signal DCS to the LCOS element 5 at the timing of being written in each pixel. The control unit 3 controls driving of the LCOS element 5 by the drive control signal DCS. The LCOS element 5 phase-modulates the signal light for each pixel block based on the drive control signal DCS.

  The light receiving unit 6 photoelectrically converts the leaked light of the signal light that is phase-modulated by the LCOS element 5 to generate a light reception signal LRS. The light receiver 6 outputs the light reception signal LRS to the signal analyzer 4. The signal analysis unit 4 monitors the received light signal LRS continuously, intermittently, or periodically. The signal analysis unit 4 detects the amplitude (signal level) of the received light signal LRS. For example, the signal analysis unit 4 detects the amplitude of the received light signal LRS at a predetermined frequency and analyzes the received light signal LRS based on a predetermined threshold Xt.

  The signal analysis unit 4 detects an unnecessary DC component included in the received light signal LRS based on the analysis result. When the unnecessary DC component is detected, the signal analysis unit 4 generates a detection signal DS indicating that the unnecessary DC component is detected, and outputs the detection signal DS to the control unit 3. The control unit 3 controls the driving of the LCOS element 5 based on the detection signal DS. A specific control method of the LCOS element 5 will be described later.

  A configuration example of the LCOS element 5 will be described with reference to FIGS. 2 and 3. The LCOS element 5 includes a drive substrate 20 (first substrate), a transparent substrate 30 (second substrate), a liquid crystal 11, a sealing material 12, and a light receiving unit 6.

  The drive substrate 20 has a pixel region 21, an alignment film 22, and a plurality of connection terminals 23. In the pixel region 21, a plurality of pixel electrodes 24 having light reflectivity are arranged in the horizontal direction and the vertical direction. One pixel electrode 24 constitutes one pixel. The alignment film 22 is formed at least on the pixel region 21.

  A semiconductor substrate may be used as the drive substrate 20. The drive substrate 20 is, for example, a silicon substrate. A drive circuit for driving each pixel is formed on the drive substrate 20. Aluminum or aluminum alloy may be used as the material of the pixel electrode 24 and the connection terminal 23.

  The light receiving portion 6 is formed around the pixel region 21 on the drive substrate 20 of the LCOS element 5. Specifically, the light receiving section 6 is formed in an area outside the pixel area 21 and in the vicinity of the pixel area 21. The region in the vicinity of the pixel region 21 is a region where the light receiving unit 6 can receive the leaked light of the signal light phase-modulated by the LCOS element 5. The light receiving unit 6 receives the leaked light of the signal light phase-modulated by the LCOS element 5 and photoelectrically converts the leaked light to generate a received light signal LRS. The light receiving unit 6 receives the leaked light of the signal light with which the pixel region 21 is irradiated. Therefore, the received light signal LRS is generated by the leak light of the signal light phase-modulated by the LCOS element 5 and the leak light of the signal light with which the pixel region 21 is irradiated.

  The light receiving unit 6 is, for example, a photodiode. FIG. 2 shows a configuration in which one light receiving unit 6 is formed near the pixel region 21. The shape and the number of the light receiving portions 6 are not limited to the configuration shown in FIG. 2, and can be set to any shape and number. Further, the position of the light receiving unit 6 is not limited to the position shown in FIG. 2, and is a region outside the pixel region 21 and can receive the leaked light of the signal light phase-modulated by the LCOS element 5. If it is a region, it can be formed at any position.

  The wavelength band of light used in an optical switching device such as a WSS device is generally an infrared band in the range of 1200 nm to 1700 nm. For example, wavelength bands called C band and L band are infrared bands in the range of 1530 nm to 1625 nm. A compound semiconductor such as InGaAs (indium gallium arsenide) may be used as the material of the photodiode used as the light receiving unit 6 having the light receiving sensitivity in the infrared band.

  By a semiconductor process, a buffer layer such as a silicon oxide film or a germanium layer is formed on the drive substrate 20, which is a silicon substrate, for example. Next, a compound semiconductor such as InGaAs having a photosensitivity in the infrared band is formed on the buffer layer with a pn junction or an np junction. Further, the formed compound semiconductor film is patterned by the photolithography method. The light receiving portion 6 can be formed on the drive substrate 20 by the above semiconductor process.

  The transparent substrate 30 has a counter electrode 31 and an alignment film 32. The alignment film 32 is formed on the counter electrode 31. The drive substrate 20 and the transparent substrate 30 are fixed with a predetermined gap by the sealing material 12 so that the plurality of pixel electrodes 24 and the counter electrode 31 face each other.

  The transparent substrate 30, the counter electrode 31, and the alignment film 32 are light transmissive. A non-alkali glass substrate or a quartz glass substrate may be used as the transparent substrate 30. ITO (Indium Tin Oxide) may be used as the material of the counter electrode 31. A light-transmitting dielectric film may be formed on the upper and lower sides of the ITO film.

  The sealing material 12 is formed in an annular shape along the outer periphery of the pixel region 21 so as to surround the pixel region 21 and the light receiving unit 6. As the sealing material 12, an ultraviolet curable resin, a thermosetting resin, or a resin which is cured by the combined use of ultraviolet rays and heat may be used.

  The liquid crystal 11 is filled in a predetermined gap between the drive substrate 20 and the transparent substrate 30 and is sealed by the sealing material 12. The antireflection film 33 may be formed on the surface of the transparent substrate 30 opposite to the surface on which the counter electrode 31 is formed. A dielectric multilayer film may be used as the antireflection film 33.

  The plurality of connection terminals 23 are formed on the outer peripheral portion of the drive substrate 20. The drive control signal DCS is input from the control unit 3 to a predetermined connection terminal 23 among the plurality of connection terminals 23. The light reception signal LRS generated by the light receiving unit 6 is output to the signal analysis unit 4 from a predetermined connection terminal 23 of the plurality of connection terminals 23. Further, a predetermined connection terminal 23 among the plurality of connection terminals 23 is connected to an external power source or the like.

  Phase modulation of signal light by the LCOS element 5 will be described with reference to FIGS. 4, 5A, and 5B. Reference numeral 25 shown in FIG. 4 indicates a pixel block including a plurality of pixel electrodes 24. Usually, the pixel block has a configuration in which three or more pixel electrodes 24 are arranged in the horizontal direction and the vertical direction, respectively.

  In order to make the description easy to understand, a case where the pixel block 25 is configured by three pixel electrodes 24 will be described. In order to distinguish each pixel electrode 24, a pixel electrode 24a, a pixel electrode 24b, and a pixel electrode 24c are arranged from the left.

  As shown in FIG. 5A, the pixel electrodes 24a, 24b, and 24c are based on the image data DD corresponding to the distribution of the amount of change in the phase (distribution of the phase velocity) generated by the image data generating unit 2 shown in FIG. Different drive voltages DVa, DVb, and DVc are applied to.

  In practice, the drive voltages DVa, DVb, and DVc applied to the liquid crystal 11 are voltages applied between the pixel electrodes 24a, 24b, and 24c and the counter electrode 31. Since the liquid crystal 11 has anisotropy in the refractive index and dielectric constant of the constituent molecules, the refractive index changes as the tilt of the molecules changes according to the applied drive voltage.

  As a result, as shown in FIG. 5B, the liquid crystal 11 on the pixel electrode 24a has the first refractive index na, the liquid crystal 11 on the pixel electrode 24b has the second refractive index nb, and the liquid crystal 11 on the pixel electrode 24c. The liquid crystal 11 has a third refractive index nc (na>nb>nc). The refractive indexes na to nc are average refractive indexes of the liquid crystal 11 on the pixel electrodes 24a to 24c.

  As shown in FIG. 4, the signal light SL output from the input port enters the pixel block 25 in the pixel region 21 in the state of p-polarized light or s-polarized linearly polarized light. The alignment films 22 and 32 shown in FIG. 3 are formed such that the deflection direction of the signal light SL and the alignment direction of the liquid crystal 11 are the same. The alignment direction is, for example, a direction in which the liquid crystal 11 near the alignment film 22 tilts. The direction in which the liquid crystal 11 near the alignment film 32 is inclined may be the alignment direction.

  By setting the polarization direction of the signal light SL and the alignment direction of the liquid crystal 11 to be the same, the linearly polarized light is modulated to the elliptically polarized light, and the p-polarized light has the s-polarized light component or the s-polarized light has the p-polarized light component. The signal light SL can be efficiently reflected by suppressing the attenuation of the signal light SL caused thereby.

  Pa, pb, and pc shown in FIG. 4 schematically show the difference in phase velocities caused by the difference in the refractive index of the liquid crystal 11 on the pixel electrodes 24a, 24b, and 24c. The WF shown in FIG. 4 schematically shows the wavefront of the signal light SL. The wavefront WF is a surface on which the phases of the signal light SL are aligned. The amount of change in phase or the phase velocity of the signal light SL gradually increases from the pixel electrode 24a toward the pixel electrode 24c. This makes it possible to change (tilt) the wavefront WF of the signal light SL.

  The drive voltages DVa, DVb, and DVc are used to increase the difference in the refractive index of the liquid crystal 11 on the pixel electrodes 24a, 24b, and 24c and increase the difference in the phase change to increase the tilt angle θ of the wavefront WF. You can Further, the inclination angle θ of the wavefront WF can be reduced by reducing the difference in the refractive index of the liquid crystal 11 on the pixel electrodes 24a, 24b, and 24c and the difference in the phase change. The tilt angle θ corresponds to the angle formed by the wavefront WF of the signal light SL and the perpendiculars of the pixel electrodes 24a, 24b, and 24c. The inclination angle θ of the wavefront WF can be changed by changing the number of the pixel electrodes 24.

  Therefore, the information data JD shown in FIG. 1 includes the parameter indicating the relationship between the position of the input port and the output port of the signal light SL and the angle formed by the incidence and reflection of the signal light SL on the pixel electrode 24, and the information light JD of the signal light SL. It includes a wavelength band, that is, a parameter relating to the distribution of the amount of change in phase that realizes a desired reflected light angle.

  The signal light SL is reflected by the pixel electrodes 24a, 24b, and 24c with the wavefront WF having a predetermined inclination angle θ based on the image data DD generated by the image data generation unit 2. Therefore, the LCOS element 5 can reflect the signal light SL in a predetermined direction by gradually changing the phase velocity of the signal light SL for each pixel based on the image data DD.

  The LCOS element 5 can control the inclination angle θ of the wavefront WF of the signal light SL according to the rate of change of the phase velocity. That is, the LCOS element 5 functions as a phase modulation element that changes the phase velocity for each pixel and reflects the signal light SL in a predetermined direction. The LCOS element 5 controls the inclination angle θ of the wavefront WF of the signal light SL, so that the signal light SL is incident on the target output port.

  A phase modulation method of one embodiment, specifically, a control method of the LCOS element 5 (liquid crystal element) will be described with reference to the flowcharts shown in FIGS. 6 and 7 and FIGS. FIG. 6 shows a case of forward inversion drive in which the direction of the voltage applied to the liquid crystal 11 repeats normal rotation and inversion alternately. 6A shows the state at the time of forward rotation, and FIG. 6B shows the state at the time of reversal.

  Reference numeral VpH in FIG. 6A indicates a voltage on the pixel electrode 24 side during normal rotation (hereinafter, referred to as a normal rotation pixel electrode side voltage VpH), and reference numeral VcL indicates a voltage on the counter electrode 31 side during normal rotation ( Hereinafter, the counter electrode side voltage VcL during forward rotation is shown). Reference sign +VLc indicates a differential voltage (hereinafter, referred to as a normal rotation differential voltage +VLc) obtained by subtracting the normal rotation counter electrode side voltage VcL from the normal rotation pixel electrode side voltage VpH, and a voltage applied to the liquid crystal 11 during the normal rotation. Equivalent to. Reference symbol Vpc indicates the optimum value of the center voltage on the pixel electrode 24 side, and reference symbol Vcc indicates the optimum value of the center voltage on the counter electrode 31 side.

  Reference numeral VpL in FIG. 6B indicates a voltage on the pixel electrode 24 side at the time of inversion (hereinafter referred to as pixel electrode side voltage VpL at the time of inversion), and reference numeral VcH indicates a voltage on the counter electrode 31 side at the time of inversion (hereinafter, inversion). The counter electrode side voltage VcH is shown). Reference symbol -VLc represents a difference voltage (hereinafter, referred to as an inversion-time difference voltage -VLc) obtained by subtracting the inversion-time counter electrode-side voltage VcH from the inversion-time pixel electrode side voltage VpL, and corresponds to a voltage applied to the liquid crystal 11 at the time of inversion. To do.

  In the flowchart shown in FIG. 7, the light receiving unit 6 photoelectrically converts the leaked light of the signal light SL that is phase-modulated by the LCOS element 5 to generate a light reception signal LRS in step S<b>1, and outputs the light reception signal LRS to the signal analysis unit 4. ..

  When the LCOS element 5 is in a high temperature state or when time has passed, the LCOS element 5 is stored or used in an environment of high temperature or high humidity, or the temperature of the liquid crystal element itself changes, or the like, and the pixel electrode 24 and the counter electrode In some cases, the DC component may be added to the drive voltage applied to the drive circuit 31. Generally, in the LCOS element, the pixel electrode 24 is formed of a metal having a high reflectance including aluminum as a main component, and the counter electrode 31 is formed of a transparent conductive material such as ITO. The DC component may be added by applying the voltage. Further, the DC component may be added due to the influence of the circuit formed inside the LCOS element or the influence of the ionic substance remaining when handling the organic material such as the liquid crystal 11.

  For example, when the low voltage side of the pixel electrode 24 is 0V and the high voltage side is 3V, the center voltage of the pixel electrode 24 side is 1.5V. For example, when the low voltage side of the counter electrode 31 is 0V and the high voltage side is 3V, the center voltage of the counter electrode 31 side is 1.5V. However, by adding unnecessary DC components, the center voltage on the pixel electrode 24 side and the counter electrode 31 side deviates from the optimum value.

  When the center voltage on the pixel electrode 24 side and the counter electrode 31 side deviates from the optimum value, the differential voltage on the pixel electrode 24 side and the differential voltage on the counter electrode 31 side differ between normal rotation and inversion. As a result, defects such as flicker or burn-in may occur in the LCOS element 5.

  FIG. 8 corresponds to FIG. 6 and shows a state where unnecessary DC components are added to the pixel electrode side voltages VpH and VpL. Since the unnecessary DC component Vdc is added to the normal rotation pixel electrode side voltage VpH, the normal rotation difference voltage becomes +VLc+Vdc. By adding the unnecessary DC component Vdc to the pixel electrode side voltage VpL at the time of inversion, the differential voltage at the time of inversion becomes −VLc+Vdc.

  Therefore, in the state where the unnecessary DC component is added to the pixel electrode side voltages VpH and VpL, the forward rotation difference voltage +VLc+Vdc and the inversion difference voltage −VLc+Vdc are different. Specifically, at the time of forward rotation, a voltage higher than that at the time of inversion is applied between the pixel electrode 24 and the counter electrode 31. FIG. 9 shows an optical response waveform of the received light signal LRS when an unnecessary DC component is added to the pixel electrode side voltages VpH and VpL.

  In step S2, the signal analysis unit 4 converts the received light signal LRS into frequency components by performing processing such as Fourier transform. FIG. 10 shows the received light signal LRS converted into the frequency component. The signal analysis unit 4 analyzes the received light signal LRS converted into frequency components for each predetermined frequency.

  In step S3, the signal analysis unit 4 determines whether or not the amplitude of the received light signal LRS is equal to or larger than the threshold value Sha (second threshold value) at the predetermined frequency fa (second frequency). The frequency fa is set to a very low value so that the DC component of the received light signal LRS can be detected. When it is determined that the amplitude of the received light signal LRS is not equal to or larger than the threshold value Sha (NO), the signal analysis unit 4 determines that the LCOS element 5 is not irradiated with the signal light SL, that is, the signal is not in the signal state, and the processing is performed. To step S2.

  When it is determined that there is no signal, the phase modulation device 1 may control the control unit 3 to reduce the power consumption and put the LCOS element 5 in the standby state.

  When it is determined that the amplitude of the light reception signal LRS is equal to or larger than the threshold value Sha (YES), the signal analysis unit 4 is not in the no signal state, that is, the signal light SL is incident on the pixel block 25 in the pixel region 21. Judge that it is in a state. In step S4, the signal analysis unit 4 acquires the difference Xb between the amplitude of the received light signal LRS at the predetermined frequency fb (first frequency) and the amplitude of the received light signal LRS at frequencies around the frequency fb. The frequency fb is set to a value that can detect the influence of unnecessary DC components.

  Specifically, the frequency fb is set to at least one of the frame frequency of the image data DD and the forward/reverse frequency of the pixel electrode side voltage Vp and the counter electrode side voltage Vc. The frequency fb may be set to a frequency corresponding to the frame frequency and harmonics of the frame frequency. For example, when the frame frequency is 60 Hz, the frequency corresponding to the harmonic is 120 Hz or 240 Hz. In this case, the frequency fb may be set to 60 Hz and at least one of 120 Hz and 240 Hz. FIG. 10 shows a case where two frequencies fb1 and fb2 are set as the frequency fb.

  The difference Xb may be acquired based on the amplitude of the received light signal LRS at the frequency fb and the amplitude of the received light signal LRS at a frequency that is not affected by the frequency fb. The difference Xb may be acquired based on the amplitude of the received light signal LRS at the frequency fb and the average value of the amplitude of the received light signal LRS at frequencies around the frequency fb. That is, it suffices that the amplitude of the received light signal LRS at the frequency fb can be compared with its surrounding level.

  In step S5, the signal analysis unit 4 determines whether or not the difference Xb is greater than or equal to the threshold value Xt (first threshold value). When it is determined that the difference Xb is not equal to or larger than the threshold value Xt (NO), the signal analysis unit 4 determines that there is no influence of the unnecessary DC component, and returns the process to step S2. When it is determined that the difference Xb is equal to or larger than the threshold value Xt (YES), the signal analysis unit 4 determines that there is an influence of an unnecessary DC component. The signal analysis unit 4 generates the detection signal DS and outputs it to the control unit 3 in step S6. The detection signal DS may include information regarding the difference Xb.

  As shown in FIG. 10, the threshold value Xt may be a common value for the plurality of frequencies fb1 and fb2, or may be different values corresponding to the plurality of frequencies fb1 and fb2. For example, the threshold Xt1 corresponding to the frequency fb1 and the threshold Xt2 corresponding to the frequency fb2 may be set.

  In this case, the signal analysis unit 4 acquires the difference Xb1 between the amplitude of the received light signal LRS at the frequency fb1 and the amplitude of the received light signal LRS at frequencies around the frequency fb1. The signal analysis unit 4 acquires a difference Xb2 between the amplitude of the received light signal LRS at the frequency fb2 and the amplitude of the received light signal LRS at frequencies around the frequency fb2. The signal analysis unit 4 determines whether the difference Xb1 is greater than or equal to the threshold value Xt1, and determines whether the difference Xb2 is greater than or equal to the threshold value Xt2. If the difference Xb1 is greater than or equal to the threshold value Xt1 and the difference Xb2 is determined to be greater than or equal to the threshold value Xt2, or if it is determined that the difference Xb1 is greater than or equal to the threshold value Xt1, or the difference Xb2 is greater than or equal to the threshold value Xt2. When it is determined that there is the signal, the signal analysis unit 4 generates the detection signal DS and outputs it to the control unit 3.

  In step S7, the control unit 3 adjusts the voltage corresponding to the unnecessary DC component based on the detection signal DS. The control unit 3 performs voltage adjustment corresponding to an unnecessary DC component with respect to at least one of the pixel electrode side voltage Vp, the counter electrode side voltage Vc, the pixel electrode 24 side center voltage, and the counter electrode 31 side center voltage. .. FIG. 11 corresponds to FIG. 8 and shows a case where the voltage Vc on the counter electrode side is adjusted to correspond to the unnecessary DC component Vdc. The control unit 3 adjusts the counter electrode side voltages VcL and VcH so as to add the voltage corresponding to the unnecessary DC component Vdc to the counter electrode side voltages VcL and VcH, for example.

  Specifically, the control unit 3 adds an arbitrary voltage to the counter electrode side voltage Vc, or subtracts an arbitrary voltage from the counter electrode side voltage Vc. The control unit 3 repeats the above voltage adjustment based on the voltage adjustment result so that the difference Xb becomes smaller. For example, when an arbitrary voltage is added to the counter electrode side voltage Vc, the control unit 3 further adds an arbitrary voltage to the counter electrode side voltage Vc if the difference Xb becomes small, and if the difference Xb becomes large, the counter electrode side voltage. Subtract an arbitrary voltage from Vc. By repeating the above voltage adjustment, the voltage corresponding to the unnecessary DC component Vdc is added to the counter electrode voltages VcL and VcH.

  By adding the voltage corresponding to the unnecessary DC component Vdc to the counter electrode side voltages VcL and VcH, the forward rotation difference voltage becomes +VLc and the inversion difference voltage becomes −VLc. That is, since the differential voltage +VLc at the time of forward rotation and the differential voltage −VLc at the time of inversion have the same absolute value, the same voltage is applied between the pixel electrode 24 and the counter electrode 31 at the time of forward rotation and at the time of inversion. .. FIG. 12 corresponds to FIG. 9 and shows an optical response waveform of the received light signal LRS in a state where the counter electrode side voltage Vc is adjusted. FIG. 13 corresponds to FIG. 10 and shows the frequency components of the received light signal LRS in the state where the counter electrode side voltage Vc is adjusted.

  The phase modulator 1 adjusts the voltage of the LCOS element 5 by continuously, intermittently, or periodically executing steps S1 to S7.

  In the phase modulation device and the phase modulation method of the present embodiment, the light receiving unit 6 photoelectrically converts the leaked light of the signal light SL phase-modulated by the LCOS element 5 to generate the light reception signal LRS, and the signal analysis unit 4 receives the light reception signal. Convert LRS to frequency components. The signal analysis unit 4 acquires the difference Xb at the predetermined frequency fb, and detects an unnecessary DC component based on the difference Xb. The control unit 3 adjusts the voltage corresponding to the unnecessary DC component. As a result, it is possible to suppress the occurrence of defects in the liquid crystal element due to the unnecessary DC component.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present invention.

  In the phase modulation device and the phase modulation method of this embodiment, the LCOS element is used as the liquid crystal element 5, but the liquid crystal element 5 is not limited to this. As the liquid crystal element 5, for example, a reflective liquid crystal panel manufactured by using a TFT (Thin Film Transistor) technique on a substrate such as a glass substrate may be used.

1 Phase Modulator 3 Control Part 4 Signal Analysis Part 5 LCOS Element (Liquid Crystal Element)
6 light receiving part 21 pixel area 24 pixel electrode DV drive voltage LRS light receiving signal SL signal light (light)
WF wavefront

Claims (5)

A pixel region in which a plurality of pixel electrodes are arranged and different drive voltages are applied to the plurality of pixel electrodes to phase-modulate the emitted light to change the wavefront of the light, and a phase of the pixel region A liquid crystal element having a light receiving section that receives the leaked light of the modulated light and generates a light receiving signal;
A signal analysis unit that analyzes the received light signal at a predetermined frequency,
Based on the analysis result by the signal analysis unit, a control unit for controlling the liquid crystal element,
A phase modulation device comprising. The signal analysis unit converts the received light signal into a frequency component, obtains a difference between an amplitude of the received light signal at a first frequency and an amplitude of the received light signal at a frequency around the first frequency, and Determine whether the difference is greater than or equal to a first threshold,
The phase modulation device according to claim 1, wherein, when it is determined that the difference is equal to or larger than the first threshold value, the control unit controls the liquid crystal element so that the difference becomes smaller. The signal analysis unit determines whether or not the amplitude of the received light signal at a second frequency is equal to or higher than a second threshold value, and when it is determined that the amplitude of the received light signal is equal to or higher than the second threshold value. The phase modulator according to claim 2, wherein the difference is acquired. The liquid crystal element,
A drive substrate having the pixel region;
A transparent substrate having a counter electrode facing the plurality of pixel electrodes;
A liquid crystal filled in a gap between the drive substrate and the transparent substrate,
Have
Image data for changing the wavefront of the light is input to the control unit,
The first frequency is set to at least one of a frame frequency of the image data and a forward/reverse frequency in forward/reverse driving in which the direction of the voltage applied to the liquid crystal alternately repeats forward and reverse. The phase modulation device according to claim 2 or 3. A liquid crystal element having a pixel region in which a plurality of pixel electrodes are arranged, by applying different drive voltages to the plurality of pixel electrodes, phase modulates the emitted light to change the wavefront of the light,
The light receiving section receives the leaked light of the light phase-modulated by the liquid crystal element to generate a light receiving signal,
The signal analysis unit analyzes the received light signal at a predetermined frequency,
A phase modulation method in which a control unit controls the liquid crystal element based on an analysis result by the signal analysis unit.

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