CN103217818B - A method for improving the response speed of a phase-controlled silicon-based liquid crystal device - Google Patents

Abstract

The invention discloses a method for increasing response speed of a phase-control silicon-based liquid crystal device. The method for increasing the response speed of the phase-control silicon-based liquid crystal device comprises the following steps of: S101, determining an adjustment step size m; S102, determining different response intervals according to the thickness and the working temperature of the phase-control silicon-based liquid crystal device by combining the adjustment step size m; and S104, selecting one response interval with the fastest response speed change in all the response intervals to serve as a working interval of phase-control conversion. According to the method for increasing the response speed of the phase-control silicon-based liquid crystal device disclosed by the invention, by adopting an electrically controlled birefringence (ECB) mode, on the basis that original advantages of continuous phase debugging, extremely low quantization errors, high light transmission efficiency, all-phase debugging and the like are met, the goal that the speed of the device is increased is achieved.

Description

A method for improving the response speed of a phase-controlled silicon-based liquid crystal device

technical field

The invention relates to the technical field of liquid crystal display, in particular to a method for improving the response speed of a phase-controlled silicon-based liquid crystal device.

Background technique

LCOS (Phase Only Nematic Liquid Crystal On Silicon) technology has been developed in image and video display for nearly 20 years. It is different from traditional LCD (Liquid Crystal Display) flat panel display technology. It not only makes use of the unique photoelectric characteristics of liquid crystal materials, but also combines the advantages of high-performance and multifunctional CMOS (Complementary Metal Oxide Semiconductor, Complementary Metal Oxide Semiconductor) integrated circuits, using electrical signals to control the deflection of liquid crystal materials. All-phase and continuous debugging of incident light is, in principle, the best for light utilization efficiency. Therefore, the application function of the device is much richer than traditional LCD display and LCOS image display. At present, it has certain advantages in optical communication and holographic projection.

LCOS devices are roughly divided into two categories: the first category is to adjust the amplitude of light, that is, the above-mentioned traditional LCOS display device; the second type is to only adjust the phase of light. The amplitude-adjusted LCOS adjusts the linear polarization direction of the incident light through a linear polarizer, and finally outputs polarized light information, which is similar to the current LCD display principle; while the phase-adjusted LCOS device is loaded on the CMOS circuit. The electrical signal changes the birefringence of the liquid crystal molecules, thereby achieving the effect of delaying the phase of the incident light.

Because the birefringence of the liquid crystal material varies widely, the liquid crystal material is usually used as the light transmission medium in the phase control LCOS device. In phase-tuned LCOS devices, polarizers and other optical devices have no light absorption, so that the light transmission efficiency is the largest. Therefore, phase-controlled LCOS devices are one of the development directions of future light engines.

The structure of the phase-controlled LCOS device is shown in Figure 1. Unlike the "sandwich" structure of the traditional LCD device, one of the glass substrates is replaced by the silicon substrate of the CMOS integrated circuit, which is a reflective device. In order to maximize the fill factor of the pixel array of the silicon backplane (silicon substrate) circuitry of the LCOS, the electronic circuitry is placed under the aluminum pixel array. When the incident light enters the liquid crystal material layer with zero absorption, the analog driving voltage is applied to each pixel of the silicon backplane, and the liquid crystal material is deflected by the electric field, which can cause the phase delay of the incident light during the deflection of the liquid crystal molecules .

Liquid crystal material is a state of matter between solid and liquid. The state of liquid crystal material is divided into nematic liquid crystal state, smectic liquid crystal state (Smectic Phase) and so on. Generally speaking, liquid crystal states are distinguished by the orientation of molecules in space, that is, the distribution of molecular centers of gravity in space. For example, the molecules of nematic liquid crystals are long and thin rods, so the distribution of their molecules should point to a certain direction. Since the liquid crystal molecules have a liquid state at high temperature, that is, any direction state (Isotropic Phase), so to maintain a certain direction property of the liquid crystal, the ambient temperature needs to be kept within a certain range.

As shown in Fig. 2, taking the nematic liquid crystal material as an example, it is one of the common liquid crystal states, its molecules are rod-shaped, and its arrangement has a certain direction. The main optoelectronic materials in current liquid crystal devices are nematic liquid crystal molecules, blue phase liquid crystal molecules or cholesteric liquid crystal molecules. n _e is the special refractive index, which is parallel to the electric field polarization direction of the liquid crystal molecule direction; n _o is the ordinary refractive index, which is perpendicular to the electric field polarization direction of the liquid crystal molecule direction. Birefringence is the difference between two values. Due to the advantages of continuous phase adjustment, nematic liquid crystal materials have been adopted by more and more liquid crystal on silicon devices (LCOS) in recent years.

The selection of liquid crystal materials is the most important part of the performance of phase-controlled LCOS devices. The liquid crystal materials used in this device must meet the following requirements:

1. High birefringence (thick device, slow device response):

${\mathrm{\&tau;}}_{\mathrm{the\; ri}\sin g}=\frac{4\mathrm{\&pi;}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA00003219341400051.png"\; state="\{\{state\}\}">d</figure-callout>}}^2\mathrm{\&gamma;}}{\mathrm{\&Delta;\&epsiv;}(V_{\mathrm{upper}}^2-V_{\mathrm{lower}}^2)-{4\mathrm{\&pi;}}^3{K}_i}$ Formula 1

${\mathrm{\&tau;}}_{\mathrm{decay}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="HDA00003219341400051.png"\; state="\{\{state\}\}">d</figure-callout>}}^2\mathrm{\&gamma;}}{{\mathrm{\&pi;}}^2{K}_i}$ Formula 2

d is the thickness of the device, γ is the dynamic viscosity of the liquid crystal material, Δε is the dielectric constant, K _ii is the elastic coefficient of the liquid crystal material, τ _rising and τ _decay are the rising response time and falling response time. The formula deduces that thickness and velocity are directly proportional.

2. High dielectric constant (low threshold voltage):

From publicity 1 and 2, the dielectric constant is inversely proportional to the speed.

3. The material needs to be stable in both the visible light range and the infrared region:

The molecular performance of many liquid crystal materials in the infrared band is very unstable. This will have a great impact on the application in optical communication systems, so it is very important to choose liquid crystals that are stable in the communication C-band (1530-1565nm).

The working principle of the LCOS device with electrically controlled birefringence (ECB, Electrically Controlled Birefringence) configuration is shown in Figure 3. When no voltage is applied to the device ("off" state), the liquid crystal molecules are aligned in the direction of the alignment layer. At this time n _o is parallel to the Z axis, ne _is parallel to the Y axis. When the analog voltage is applied to the device ("on" state), as the analog voltage gradually increases, the direction of n _o remains parallel to the Z axis, while _ne gradually changes from parallel to the Y axis to parallel to the Z axis, as shown in Fig. The liquid crystal molecules in 3 gradually "stand up", at this time, the value of n _e approaches the value of _no (the birefringence index approaches 0 at the maximum), until the maximum analog voltage is loaded to the device, the two values are equal, the deflection of the liquid crystal molecules with the voltage is completed, that is, the phase adjustment process of the incident light ends. Since no polarized light in other directions is produced in this process, the tuning range of the maximum phase (incident light phase from 0 to 2π) is obtained. The response speed of the device is the time elapsed from n _e to n _o , that is, the time it takes for the phase of the incident light to go from 0 to 2π after being debugged by the LCOS device.

The response time of the device is achieved in the ECB mode of operation, and in the visible and infrared ranges, using binary grating loading, driving each voltage level simultaneously. By measuring the relationship between light intensity and response time, the relationship between phase change and time response is deduced. This basic information will bring great convenience to holographic design engineers, understand the situation of each pixel driving different voltages, and accurately locate the phase change speed.

The response speed of LCOS devices is an important performance index in the application directions of display, projection, 3D holography, and communication. At present, the method to improve the response speed of LCOS devices is mainly to change the device structure and the configuration of liquid crystal materials. The two representative methods are Surface Stablised Ferroelectric Liquid Crystal (SSFLC) in surface stabilization mode and Optically Compensated Birefringence (OCB) in optically compensated birefringence mode.

The application of SSFLC LCOS devices has a certain position in phase-controlled LCOS devices because of its fast response speed and the advantages of not needing to add polarization devices to the system. But the fatal flaws of its devices are: 1. It can only provide binary phase adjustment, but cannot perform continuous phase adjustment in the full range (between 0 and 2π). Although the subframe sequence (Subframe Sequential) technology can provide multi-voltage and multi-level phase adjustment, and is applied in holographic projection, it not only loses half of the light intensity in the symmetrical diffraction order; at the same time, the ferroelectric liquid crystal material needs to be deflected by 90° to Obtain the maximum efficiency of light (<50%); to achieve the above applications, it is necessary to configure a very special ferroelectric material in a device with a certain thickness, and the response speed at this time has been compared with that of LCOS configured with nematic liquid crystal materials The devices are similar. 2. Due to the sub-frame sequence technology, the voltage on the backplane of the device circuit can be adjusted by combining "0 and 1 two-bit voltage adjustment" to achieve continuous phase adjustment, so the device will generate huge quantization noise, so SSFLC is completely unsuitable for use in Optical communication and high-quality image projection.

In LCOS devices configured in ECB, the orientation layers of the glass and silicon substrates are opposite. Therefore, when the device is driven, the deflection of the liquid crystal molecules will be hindered by a torsion force, resulting in a slow response of the device; and in the LCOS device structure of the OCB configuration: the direction of the alignment layer of the glass substrate and the direction of the alignment layer of the silicon-based substrate It is consistent, such a device structure will not produce such torsion force when the liquid crystal molecules are deflected, so the speed of the device is improved. Generally, in OCB devices, the inclination angle of the alignment layer is generally above 8°, and the liquid crystal molecules can only work under bend deformation (Bend Deformation). Although the response speed of the OCB device is very fast, it has the following three fatal defects: 1. The range of its phase adjustment is less than 2π. The inclination angle of the alignment layer of the LCOS device with the general ECB structure is within 2°, which can ensure the phase adjustment of 2π with the greatest efficiency, while the alignment layer of the OCB device should generally be set above 8°, so that the reduction of the value of _ne leads to 2. In the working state of the device, the liquid crystal molecules will produce a twisted state (Twist State), which will lead to light of various polarization directions during the incident light adjustment process, Thereby reducing the optical debugging efficiency of the device; 3. The high inclination angle structure of the alignment layer brings great difficulty to the rubbing process of the alignment layer, and its high-temperature curing process will lead to instability of the pixel aluminum layer and damage the Reflectivity.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for improving the response speed of the phase-controlled silicon-based liquid crystal device, so as to solve the problem of slow response speed of the phase-controlled silicon-based liquid crystal device in the prior art.

In order to solve the above technical problems, on the one hand, the present invention provides a method for improving the response speed of a phase-controlled silicon-based liquid crystal device, including:

Step S101, increasing the driving voltage to the maximum load voltage Vmax, and completing the maximum voltage driving process;

Step S102, the driving voltage is reduced to the target voltage value Vi determined according to the operating temperature of the device to achieve the expected target phase value; at this time, the time required by the device is t _{d_i} ; t _{d_i} is from the maximum voltage to when the gray level is i response time, where i=0, 1, 2,..., 255;

Step S103, obtaining the final phase delay.

Furthermore, the maximum voltage of the phase-controlled LCOS device driven by the analog circuit is 7V, and the gray scale ranges from 0 to 255.

Further, the maximum load voltage Vmax is a load voltage value corresponding to a gray scale value of 255.

Further, the maximum load voltage Vmax is a load voltage value corresponding to a gray scale value of 189.

Further, before step S101, it also includes:

Perform DC balance treatment to make the alternating electric field loaded on the liquid crystal material in the silicon-based liquid crystal device symmetrical.

Further, when the load voltage decreases from the maximum load voltage to the target voltage value, one or more intermediate voltage values are increased, and the load voltage is first reduced from the maximum load voltage to the intermediate voltage value, and then to the target voltage value; at the same time, the driving voltage The front edge and the trailing edge of the square wave voltage waveform are increased by a predetermined intermediate value to reduce the phase swing in a steady state.

Further, before step S101 or after step S103, it also includes:

Determine the adjustment step size m;

According to the thickness of the phase-controlled silicon-based liquid crystal device, combined with adjusting the step size m, different response intervals are determined;

In each response interval, the response interval with the fastest change in response speed is selected as the working interval of the phase control transformation.

Further, in the CMOS backplane of the liquid crystal on silicon device, the size of the pixel is between 1 micron and 20 microns, and the shape of the unit pixel is a rectangle or a square.

Further, the liquid crystal material of the silicon-based liquid crystal device is a nematic liquid crystal material, a blue phase liquid crystal material or a cholesteric liquid crystal material.

Further, the alignment layer of the silicon-based liquid crystal device is composed of a high molecular polymer, and the rubbing mode of the alignment layer is perpendicular to the direction vector of the liquid crystal molecules; The initial rubbing angle is 2°; when the liquid crystal material is applied to a device with an optical compensation structure, the initial rubbing angle of the alignment layer is not less than 8°.

Further, the driving voltage of the liquid crystal on silicon device is a sine wave pulse, a triangular wave pulse or a square wave pulse.

The beneficial effects of the present invention are as follows:

The invention adopts the ECB mode, and on the basis of satisfying the original advantages of continuous phase adjustment, extremely low quantization error, high optical transmission efficiency, and all-phase adjustment, it achieves the purpose of increasing device speed.

Description of drawings

Fig. 1 is the basic structural diagram of LCOS in the prior art;

2 is a uniaxial light indication diagram of the refractive index of a single liquid crystal molecule in the prior art;

Fig. 3 is a working schematic diagram of an LCOS device configured with electrically controlled birefringence in the prior art;

Fig. 4 is a schematic diagram of response time using the prior art;

Fig. 5 is the schematic diagram of response time adopting the solution of the embodiment of the present invention;

Fig. 6 is a comparison diagram of response time and phase control range obtained by respectively adopting the prior art and the scheme of the embodiment of the present invention;

Fig. 7 is the comparative figure of high-frequency component in analog and digital circuit in the embodiment of the present invention;

Fig. 8 is a comparison diagram of response time and phase control depth under different load voltages in the embodiment of the present invention;

FIG. 9 is a relationship diagram of driving voltage and phase adjustment changes in an embodiment of the present invention;

Fig. 10 is a diagram of the relationship between different response intervals and response time in the embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In the LCOS device with ECB configuration, the magnitude of the load voltage and the range of optical phase adjustment have a monotonically increasing relationship, that is, the voltage increases and the depth of phase adjustment increases. After a lot of experiments, the inventor found that the response time of the liquid crystal material decreases according to the increase of the load voltage, that is, increasing the voltage load can accelerate the response of the device, and reducing the voltage load can slow down the response of the device. That is: when the load voltage is greater than the threshold voltage, if the load voltage is increased, the response of the liquid crystal material will be accelerated; this relationship is monotonically increasing. Therefore, in the prior art, when the device debugs a small phase change, the response speed becomes very slow because the voltage required by the device is very low. According to the relationship between the load voltage and the response time, the invention solves the problem that the response speed of the current mainstream phase-controlled silicon-based liquid crystal device is too slow due to its driving mode, and achieves the effect of speeding up the response of the device. The speed-up method currently used is mainly to try to change the device structure and liquid crystal selection. The two mainstream methods (SSFLC and OCB) have huge defects; while the present invention insists on using the ECB mode and matching liquid crystal molecules that meet the conditions. On the basis of meeting the original advantages of continuous phase debugging, extremely low quantization error, high optical transmission efficiency, and full phase debugging, the purpose of device speed-up is achieved by changing the CMOS circuit drive through the following methods.

In amplitude-tuned LCOS devices, response speed is defined as the time it takes for the transmitted light intensity to change from zero to maximum. In the LCOS device with phase adjustment, it is defined as the time for the light intensity of the first-order diffraction to go from 0 to the maximum. Since the loaded grating information is completed by the voltage of the driving device, the relationship between the change of diffracted light intensity and the load voltage can be deduced as the relationship between phase delay and time through mathematical changes. In the industrial field, the basic range of response speed is between 10% and 90% of the transmission intensity, because the gradual band in the saturation area will cause inaccurate degrees.

In the LCOS device with phase adjustment, the embodiments of the present invention aim at the time variation of the diffracted light intensity range from 5% to 95%, so that more phase adjustment information can be recorded and more accurate judgment can be made on the improvement of the response speed. The rise time response is the time required by the device when the voltage rises from 0 voltage to the target voltage value; the fall time refers to the time required by the device when the voltage drops from the target voltage to 0 voltage. When the load voltage is greater than the threshold voltage, if the load voltage is increased, the corresponding speed of the liquid crystal material will be accelerated, and this relationship is monotonically increasing.

Embodiment one:

The embodiment of the present invention relates to a method for improving the response speed of a phase-controlled silicon-based liquid crystal device: including:

Step S101, increasing the driving voltage to the maximum load voltage Vmax, and completing the maximum voltage driving process;

In this step, the maximum voltage of the phase-controlled LCOS device driven by the analog circuit is generally around 7V, and the gray scale ranges from 0 to 255; that is, the voltage gradient is divided into 256 levels, and the variation of each level of voltage is (7/ 255) V. According to the above description, it is assumed that the common response time of the device should be t _i , that is, the response time when the load voltage gray level (N) is i. In the current driving method, the device responds the fastest when adjusting the full phase (2π) value, that is, the moment when the maximum voltage load is applied to the device. According to this feature, before debugging the target phase, first load the maximum load voltage required for the value of "debugging all phases", and then select the voltage corresponding to the target phase, that is, to realize the device speed-up process.

The fastest response speed required by the device is t _N =t ₂₅₅ ; the result of the fastest response speed measured through experiments is t _N =t ₂₅₅ =7ms.

In the liquid crystal on silicon device, the liquid crystal layer is sandwiched between the electrode ITO layer and the aluminum layer; due to the different work functions of the two materials, when a symmetrical alternating voltage is loaded on the liquid crystal layer through such an asymmetrical electrode, its actual loading The voltage is equivalent to the original loading voltage plus a DC bias, and the liquid crystal material cannot enter a stable state. Therefore, in order to obtain a better technical effect, this step also needs to carry out DC balance (DC balance) to symmetrize the alternating electric field loaded on the liquid crystal material in the silicon-based liquid crystal device. If DC balance is not performed, the phenomenon of phase swing will be very obvious, resulting in the performance degradation of the device.

Step S102, the driving voltage is reduced to the target voltage value Vi determined according to the operating temperature of the device to achieve the expected target phase value; at this time, the time required by the device is t _{d_i} ; t _{d_i} is from the maximum voltage to when the gray level is i response time, where i=0, 1, 2,..., 255;

Due to the continuous phase change characteristics of the liquid crystal material and the rotational inertia of the liquid crystal molecules, and the interaction between them, the liquid crystal material will produce different degrees of "flyback" (flyback) after the applied voltage changes, resulting in a corresponding phase swing ( phase flicker). Therefore, in this embodiment, when the load voltage decreases from the maximum load voltage to the target voltage value, one or more intermediate voltage values are increased to reduce the transient phase swing. At the same time, a predetermined intermediate value can also be added on the front and back edges of the square wave voltage waveform of the driving voltage to slow down the "flyback" and reduce the phase swing in the steady state.

Step S103, obtaining the final phase delay.

The process required for the device load voltage from 0 voltage to V _i is 0, Vmax, V _i ; the total response time t _i is:

t _i =t ₂₅₅ +t _{d_i} formula 3

Among them, t ₂₅₅ is the response time when the gray level is 255 (maximum voltage).

In this embodiment, when the temperature of the liquid crystal on silicon device is within the range of [15°, 55°], as the temperature increases, the response speed of the liquid crystal on silicon device will become faster and faster.

In Figure 4, the response time t _i of the device driven by the voltage V _i (using the existing technology, that is, by loading the target voltage and waiting for the liquid crystal to respond, the phase delay is obtained); in Figure 5, according to the speed-up method, the voltage is first set at The maximum V _max (the response time is t255), wait for the response time t ₂₅₅ , and then adjust to the target voltage V _i (the response time is t _{d_i} ), get the final phase delay; apply this method to the response time under the V _i voltage t _i is equal to the sum of t ₂₅₅ and t _{d_i} . According to the actual calculation, it is concluded that the speed-up scheme is feasible and effective.

It should be pointed out that when i=189 or above, the response time of t _i does not need to be accelerated to complete. At this time, the phase adjustment range is 1.96π, which is approximately equal to 98% of the full phase adjustment range, which fully guarantees the integrity of the device operation when errors are considered. This proves that it is completely feasible to speed up the response time without affecting the working performance of the device. In practical applications, it is necessary to load a maximum driving voltage to the pixel matrix before scanning specific image information, and then load the voltage required by the pixel matrix. Applying this kind of driving method may generate a response interval, so it is not suitable for display or projection applications. Different devices correspond to the voltage value required for different phase delays (the voltage value corresponding to i=189), that is to say, the voltage value required for the phase delay is related to the specific device, and it needs to be calibrated before each use. to determine this value.

In Fig. 6, the open circles represent the phase control range of the voltage rising from the original 0 voltage to the target target voltage according to the existing driving mode; the solid circles represent the solution of the embodiment of the present invention, the voltage is first loaded from 0 voltage to the maximum voltage, and then Then reduce to the phase control range of the target voltage; as can be seen from Figure 6, the speed-up scheme of the embodiment of the present invention significantly speeds up the device, and at 189 gray levels, the device has basically completed the entire phase-control range. For example, when there is a small phase change, the speed can be increased by 100ms (phase adjustment <1π), and the rest can basically be increased by tens of ms (1π, 4π).

In this embodiment, in the CMOS backplane of the liquid crystal on silicon device, the size of the pixel is between 1 micron and 20 microns, and the shape of the unit pixel can be rectangular or square. The thickness of the silicon-based liquid crystal device is generally between 1 micron and 5, 6 microns; based on the wavelength, the longer the wavelength, the greater the thickness of the device, and the thickness satisfies the 2pi phase control range. If it is applied in the microwave field (that is, the wavelength more than 3 microns), then the thickness of the device can reach tens of microns.

The choice of liquid crystal on silicon device can be a nematic liquid crystal material (such as BLO37, a nematic liquid crystal material), or a blue phase liquid crystal material (blue phase) or a cholesteric liquid crystal material (chiral nematic) liquid crystal material.

The alignment layer (alignment) of a silicon-based liquid crystal device is generally composed of a high molecular polymer. The rubbing method of the alignment layer is perpendicular to the direction vector of the liquid crystal molecules. The initial rubbing angle of the alignment layer is generally small. The liquid crystal material is used in electronic control. In the structure of the birefringence index, it is generally around 2°; if the liquid crystal material is used in the device of the optical compensation structure, the initial angle of the alignment layer is generally not less than 8°, and the rubbing angle is too large, which will lose the spatial phase of the device debug scope.

The layout of the CMOS integrated circuit part of the liquid crystal on silicon device can be rectangular or square, and the shape of the pixel layer can be rectangular or square. Under special requirements, the pixel layer can be a 1*N matrix.

The pulse of the driving voltage of the liquid crystal on silicon device may be a sine wave (sin) pulse, or a triangular wave pulse or a square wave pulse. ITO (Indium Tin Oxide, Indium Tin Oxide) electrodes can be in a lattice (corresponding to each pixel), or they can cover the glass substrate.

In addition, in the above embodiment, the load voltage can also be stopped at the target voltage value during the process of increasing the load voltage to the maximum load voltage Vmax, so as to obtain the final phase delay. That is: in a certain time interval, a series of pulses of the maximum voltage are applied, and these pulses should be applied before the required pulse voltage.

Since the response time of the device is the shortest when driven by the maximum voltage, and the phase change can reach 2π. Therefore, from a theoretical analysis, in the process of applying an excessive driving voltage, the voltage value corresponding to any phase depth from 0 to 2π can be selected, so as to achieve a fast response of the device. However, when this method is applied in actual circuit driving, it often exceeds the requirements of the target phase. Nevertheless, we can still use this principle to load some high-voltage pulses in the actual circuit to achieve speed-up.

If in the LCOS device, the waveform change rate is greater than the response rate of the liquid crystal material, that is, when the liquid crystal material cannot respond to the high frequency component in the waveform, the liquid crystal material responds according to the root mean square value (RMS) of the waveform loaded arbitrarily, in this case , The method of speeding up the response time is not suitable for use. However, if the low-frequency components in the waveform are similar to the response speed of liquid crystal material molecules, then the liquid crystal material responds according to the instantaneous value of the waveform. In this case, "excessive" voltage driving can be realized.

In high-frequency analog circuits, liquid crystals cannot respond to high-frequency components. If the shaded areas in figure a and figure b in Figure 7 are equal, then their driving of liquid crystal molecules is equivalent; in high-frequency digital circuits The situation is the same as that in the high-frequency analog circuit, as long as the shaded areas in c and d are the same, their drives are equivalent. But in low-frequency analog or digital circuits, the response of liquid crystal molecules is related to individual voltage components.

In Figure 8, the X axis (Time) represents time; the Y axis (Phase Modulation) represents phase control depth. The line close to the X-axis in Figure 8 indicates that when the load is 4.4v, the phase adjustment range is between (0, 1.93π), and full-phase adjustment cannot be achieved, and it takes 21.2ms to complete. The middle line in Figure 8 indicates that when the load is 5.7v, the phase adjustment range basically meets the full phase adjustment, and the required time is 9.7ms. The line close to the Y axis in Figure 8 indicates that when the load is a maximum of 7v, the phase adjustment range meets the full phase adjustment, and the required time is only within 4.6ms. It can be seen from the experimental results that the response speed is the fastest when driven by the maximum load. If in the process of loading the maximum voltage, stop at the target phase, the speed can be increased. For example, if 1π phase adjustment is required, then when the load is 7v, the required speed is about 2.3ms.

Embodiment two:

Considering the error of the production process and the error of the optical environment, under normal circumstances, the thickness of the liquid crystal on silicon device will be larger than the required requirement, the working range of the device reaches 2π, and the manufacturing thickness of the device is often slightly higher than the required value; generally 2.5π, or even 3π. This not only ensures the working performance of the device, but also makes the full-phase debugging range more flexible. According to this feature, in the embodiment of the present invention, the interval of the working range is modified, and the original (0, 2π) is shifted to (m, 2π+m), where m is the adjustment step. The purpose of doing this is to improve the slow response of low voltage while keeping the working range unchanged.

The embodiment of the present invention relates to a method for improving the response speed of a phase-controlled silicon-based liquid crystal device: including:

Step S201, determining the adjustment step size m; the adjustment step size m may be a fixed value or a different value, and the specific determination method shall be determined by a technician according to the characteristics of the device.

Step S202, according to the thickness of the phase-controlled silicon-based liquid crystal device, combined with adjusting the step size m, determine different response intervals, for example, (0, 2π), (m, 2π+m), (2m, 2π+2m), ... ..., (nm, 2π+nm), where the device thickness d=2π+nm.

Step S203, selecting a response interval with the fastest change in response speed among each response interval as the working interval of the phase control transformation.

In Figure 9, the original (0,2π) phase control range is adjusted to the (m,2π+m) interval, making full use of the fastest response interval of liquid crystal molecules, that is, the approximate linear response part in the figure. There are two things to note about this method:

1. Ensure that the working range of the device is above the required range;

2. The device should not be too thick, otherwise the response speed of the device will increase, which requires theoretically estimating the value of m each time before the device is manufactured.

As shown in Figure 10, the x-axis selects different working ranges, such as 0 to 2pi, 0.1 to 2.1pi, 0.4 to 2.4pi, etc.; the y-axis is the response time; the four squares indicate: within the corresponding working range, the phase control depth of 0.2pi The time consumed; the multiplication sign indicates: the time consumed by the 0.8pi phase control depth in the corresponding working range; the triangle indicates: the time consumed by the 1.2pi phase control depth in the corresponding working range; the circle indicates: in the corresponding working range In the interval, the time consumed by the 1.6pi phased depth; the asterisk indicates: the time consumed by the 2pi phased depth in the corresponding working interval. It can be seen that the working range from 0-2pi must be the slowest range; at the same time, as long as the corrected working range is placed in a non-zero position, the response speed will be greatly increased; in the working range of 0.4-2.4pi, the response of each stage The speed is the fastest.

The methods of Embodiment 1 and Embodiment 2 of the present invention can be used in the wavelength range of all current liquid crystal on silicon devices, from visible light to infrared. For different ranges of wavelengths, one of the methods involved in the above embodiments can be selected to increase the speed alone, or can be combined together to increase the speed; for example, for the visible light and infrared bands, the first or second embodiment can be adopted alone, or the two schemes can be adopted together Accelerate the device.

The present invention continues to use the phase-controlled LCOS device based on ECB configuration, because it can meet all phases and continuous debugging; use analog circuits, extremely low quantization noise, and the tilt angle of the orientation layer is very low (maximize the phase control range), and when the device is working There is no generation of other polarized light (the system does not require a polarizer), and the maximum light efficiency is utilized (almost 100%). Therefore, the device can be applied to all areas of current display, projection, holography, communication, etc.

Although preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, and therefore, the scope of the present invention should not be limited to the above-described embodiments.

Claims (9)

1. A method for improving the response speed of a phase-controlled silicon-based liquid crystal device, characterized in that it comprises: Step S101, determining the adjustment step size m; Step S102, according to the thickness and operating temperature of the phase-controlled silicon-based liquid crystal device, combined with adjusting the step size m, determine different response intervals; each response interval is: (0,2π), (m,2π+m), (2m ,2π+2m),...,(nm,2π+nm), where, device thickness d=2π+nm, n=0,1,2,...,; Step S103, selecting a response interval with the fastest changing response speed in each response interval as the working interval of the phase control transformation. 2. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 1, characterized in that, after step S103, further comprising: Increase the driving voltage to the maximum load voltage Vmax to complete the maximum load voltage driving process; Reduce the maximum load voltage to the target voltage value Vi; the time required by the device at this time is t _{d_i} ; t _{d_i} is the response time from the maximum load voltage to the target voltage value Vi corresponding to the gray value i, where i=0, 1, 2, ..., 255; Get the final phase delay. 3. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 2, wherein, before the drive voltage is increased to the maximum load voltage Vmax, it also includes: Perform DC balance treatment to make the alternating electric field loaded on the liquid crystal material in the phase-controlled silicon-based liquid crystal device symmetrical. 4. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 3, characterized in that, in the CMOS backplane of the phase-controlled silicon-based liquid crystal device, the size of the pixel size is between 1 micron and 20 microns, The shape of a unit pixel is a rectangle or a square. 5. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 3, wherein the liquid crystal material of the phase-controlled silicon-based liquid crystal device is a nematic liquid crystal material, a blue phase liquid crystal material or a cholesteric liquid crystal material . 6. the method for improving the response speed of phase-controlled silicon-based liquid crystal device as claimed in claim 5, is characterized in that, the alignment layer of phase-controlled silicon-based liquid crystal device is made up of high molecular polymer, and the rubbing mode of alignment layer is with liquid crystal The direction vector of the molecule is vertical; when the liquid crystal material is applied to the structure of the electrically controlled birefringence, the initial friction angle of the alignment layer is 2°; when the liquid crystal material is applied to the device of the optical compensation structure, the initial friction angle of the alignment layer The angle is not less than 8°. 7. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 3, wherein the driving voltage of the phase-controlled silicon-based liquid crystal device is a sine wave pulse, a triangular wave pulse or a square wave pulse. 8. The method for improving the response speed of a phase-controlled silicon-based liquid crystal device as claimed in claim 6, wherein the phase-controlled silicon-based liquid crystal device driven by an analog circuit has a maximum load voltage of 7V and a gray value from 0 to 255. 9 . The method for increasing the response speed of a phase-controlled silicon-based liquid crystal device according to claim 6 , wherein the maximum load voltage Vmax is a driving voltage value corresponding to a gray value of 255. 10 .

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