CN105425496A - Blue phase liquid crystal phase modulator and polarization non-independent method thereof - Google Patents

Abstract

The invention discloses a method for reducing the driving voltage of a blue-phase liquid crystal polarization-independent phase modulation device through an electric control polymerization process. The blue-phase liquid crystal phase modulation device includes an upper substrate, a lower substrate, a blue-phase liquid crystal layer, and an electrode layer, wherein the electrode layer They are respectively located between the upper substrate and the blue-phase liquid crystal layer, and the lower substrate and the blue-phase liquid crystal layer, and are used to apply voltage to control the polymerization process. By applying a polymerization voltage during the polymerization process, the potential energy of the liquid crystal molecules is increased to reduce the anchoring energy of the polymer network, which can effectively reduce the driving voltage of the polymer-stabilized blue-phase liquid crystal; at the same time, due to the macroscopic optical isotropy of the blue-phase liquid crystal, the The phase modulation device can modulate unpolarized light when the upper and lower electric fields act, so that the device has polarization-independent characteristics, solves the problem that conventional liquid crystal phase modulation devices need to perform polarization conversion, and reduces loss. The invention effectively reduces the driving voltage of the blue-phase liquid crystal phase modulation device, and at the same time can realize the polarization-independent characteristic of the phase modulation device.

Description

A blue-phase liquid crystal phase modulation device and its polarization-independent method

technical field

The invention relates to the field of blue-phase liquid crystals, in particular to a method for realizing polarization-independent phase modulation devices, and a method for realizing low-voltage driving of blue-phase liquid crystal phase modulation devices by controlling the polymerization process of polymer-stabilized blue-phase liquid crystals through a polymerization electric field.

Background technique

In recent years, blue-phase liquid crystal has the characteristics of sub-millisecond response time, no alignment treatment, optical isotropy without external electric field, and periodic three-dimensional helical structure in the visible light band. Potential applications in the direction of , phase modulators, and three-dimensional tunable photonic crystals have attracted many people's attention. Although the narrow temperature bandwidth of blue-phase liquid crystals has been broadened to more than 60K by curing the disclination lines in the polymer network, other problems, such as high driving voltage, hysteresis, and residual birefringence, limit the blue-phase liquid crystals. wide application. Currently, there are generally two methods for reducing the driving voltage of a blue-phase liquid crystal device. One is to improve the driving performance by improving the material properties, and the other is to increase the effective electric field by optimizing the device structure; but these two methods have other problems such as complex device design, and other parameters of blue phase liquid crystals. It cannot be applied to large-scale commercial production. On the other hand, the phase modulator composed of nematic liquid crystals requires surface alignment to produce phase modulation, and has polarization-dependent characteristics. A polarizer needs to be added to the optical system, which leads to certain energy loss and occupies certain device resources. with space.

Therefore, those skilled in the art are committed to developing a method for reducing the driving voltage of blue-phase liquid crystal polarization-independent phase modulation devices and devices thereof, which can effectively reduce the driving voltage of blue-phase liquid crystal phase modulation devices and realize phase modulation devices. Polarization-independent, reducing energy loss, saving device resources and space.

Contents of the invention

In view of the above-mentioned defects in the prior art, the technical problem to be solved by the present invention is how to effectively reduce the driving voltage of the blue-phase liquid crystal polarization-independent phase modulation device while realizing the polarization-independent characteristics of the phase modulation device.

To achieve the above object, the invention provides a polarization-independent method for a blue-phase liquid crystal phase modulation device, comprising the following steps:

Step 1, pouring the blue-phase liquid crystal into the phase modulation device of the blue-phase liquid crystal, and cooling down to the polymerization temperature;

Step 2, the polymerization electric field is applied to both ends of the common electrode and the pixel electrode layer; the electric field strength of the polymerization electric field is different according to the blue phase liquid crystal material;

Step 3, polymerization or thermal polymerization under ultraviolet light;

Step 4, obtaining polymer-stabilized blue-phase liquid crystals in the process of electrically controlled polymerization.

Further, the cooling rate is 0.5°C/min.

Further, the electric field strength of the polymerization electric field is 2V/μm.

Further, the frequency of the aggregation electric field is 1 kHz to 1000 kHz.

Further, the aggregation electric field is a set of square wave or sine wave or triangular wave alternating electric field.

The present invention also provides a blue-phase liquid crystal phase modulation device, which is characterized in that it includes an upper substrate, a common electrode layer, a blue-phase liquid crystal layer, a pixel electrode layer and a lower substrate, and the common electrode layer is formed between the upper substrate and the blue-phase liquid crystal. Between the layers, the pixel electrode layer is between the lower substrate and the blue phase liquid crystal layer; when polymerizing the blue phase liquid crystal polymer mixture, the common electrode layer and the pixel electrode layer are configured to apply a polymerization electric field.

Further, the upper substrate is glass or plastic; the lower substrate is a silicon substrate.

Further, the common electrode layer is a plate-shaped electrode formed of a transparent conductive metal oxide or a transparent conductive organic polymer material or a strip-shaped electrode parallel to each other.

Further, the pixel electrode layer is a group of parallel strip electrodes or block electrodes formed of opaque conductive metal with high reflectivity.

Further, the transparent conductive metal oxide is ITO, the transparent conductive organic polymer material is PEDOT, and the high-reflectivity opaque conductive metal layer is AL.

The present invention aims to provide a simple method for reducing the driving voltage of the blue-phase liquid crystal polarization-independent phase modulation device, while keeping other parameters of the blue-phase liquid crystal phase modulation device unchanged. In order to achieve the above object, the present invention proposes a method for stabilizing the blue-phase liquid crystal polymerization process with an electrically controlled polymer. When the blue-phase liquid crystal polymer mixture is polymerized, a polymerization voltage is applied to the common electrode layer and the pixel electrode layer of the liquid crystal device. superior.

The present invention is realized through the following technical solutions:

Pour the blue phase liquid crystal into the liquid crystal device, and lower the temperature to the polymerization temperature, apply the polymerization voltage to both ends of the common electrode layer and the pixel electrode layer, and polymerize under ultraviolet light or other wavelengths of light for 10 minutes, or thermally polymerize for a period of time to obtain electric current. Polymers with controlled polymerization process stabilize blue-phase liquid crystals. The range of the polymerization electric field is 2V/μm, or other electric field strengths, and the frequency range is 1kHz-1000kHz. The polymerization electric field applied reduces the anchoring energy of the polymer network, thereby reducing the driving voltage of the blue phase liquid crystal.

The electric field control polymerization process proposed by the present invention reduces the driving voltage of the polymer stable blue phase liquid crystal phase modulation device. The method is simple. By applying a polymerization electric field to the blue phase liquid crystal during polymerization, the potential energy of the liquid crystal molecules is increased, and the anchoring energy of the polymer network is reduced, thereby It can effectively reduce the driving voltage of the blue-phase liquid crystal, and at the same time, the phase modulation device can modulate non-polarized light when the upper and lower electric fields act, so that the device has polarization-independent characteristics, which solves the problem that the conventional liquid crystal phase modulation device needs to perform polarization conversion. Reduced losses.

The idea, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, features and effects of the present invention.

Description of drawings

Fig. 1 is a blue-phase liquid crystal phase modulation device structure and its polarization-independent characteristic explanatory diagram of a preferred embodiment of the present invention;

Fig. 2 is a blue phase liquid crystal phase retardation and electric field intensity relation curve of a preferred embodiment of the present invention;

Fig. 3 is a schematic diagram of an electronically controlled polymerization process method in a preferred embodiment of the present invention.

detailed description

Fig. 1 is a diagram illustrating the structure of a blue-phase liquid crystal phase modulation device and its polarization-independent characteristics. a is the cross-sectional view of the phase modulation device when no power is applied in the blue phase liquid crystal phase state, and b is the cross-sectional view of the phase modulation device after power is applied in the blue phase liquid crystal phase state. The structure of the blue-phase liquid crystal phase modulation device mainly includes a lower substrate 1 , a pixel electrode layer 2 , a blue-phase liquid crystal layer 3 , a common electrode layer 4 and an upper substrate 5 .

Pour the mixture of blue-phase liquid crystal polymers into the liquid crystal device shown in a in Figure 1 in an isotropic state, control the sample to cool down at a certain rate on the temperature control platform, and adjust the temperature to within a wide range of blue-phase liquid crystal temperature Inside, the blue phase liquid crystal is uniformly dispersed in the blue phase liquid crystal layer 3 . It can be seen from a that since the blue phase liquid crystal has macroscopically isotropic properties, the refractive index distribution of the liquid crystal molecules is spherical, so the device has the same characteristics under the incident light of different polarization directions. In b, the voltage is applied to the pixel Between the electrode layer 2 and the common electrode layer 4, the refractive index distribution of the blue phase liquid crystal molecules changes from spherical to ellipsoidal, and the direction of the optical axis is perpendicular to the upper and lower substrates. When the light is vertically incident from the upper substrate, in the direction perpendicular to the light propagation direction, The blue-phase liquid crystal molecules still have the same refractive index under incident light with different polarization directions, thus realizing the polarization-independent characteristics of the phase modulation device.

Fig. 2 shows the relationship curve between the phase retardation of the blue phase liquid crystal material and the electric field intensity.

Taking the existing blue-phase liquid crystal material parameters and laser light source as an example, polymerize the blue-phase liquid crystal material without any electric field, use He-Ne laser (λ=633nm) to measure its characteristics, and fit the results to get The saturated birefringence of the blue phase liquid crystal material is Δn _sat = 0.153, and the saturated electric field strength E _s = 6.75V/μm, from which the Cole constant K of the material can be calculated = 5.3nm·V ^-2 , and its phase retardation and electric field strength The relationship curve is shown in Figure 2. In Figure 2, the horizontal axis is the electric field strength, the value interval is 1V/μm, and the vertical axis is the phase delay. It can be seen from the figure that when the electric field strength is in the range of 0-2V/μm, the phase delay curve changes slowly. When the electric field When the intensity is 2-6V/μm, the phase delay curve begins to have a large change rate, which means that the phase delay is sensitive to the change of the electric field intensity in this range of electric field intensity. Based on this characteristic, during the polymerization process, an electric field of a certain intensity (such as 2V/μm) is applied between the pixel electrode layer and the common electrode layer. After a period of polymerization (such as 10 minutes), the liquid crystal molecules are anchored by the polymer network. The orientation of the optical axis of the liquid crystal molecules depends largely on the strength of the electric field applied during the polymerization process. At this time, the blue phase liquid crystal molecules have a certain molecular potential energy, and their refractive index is lower than that without an electric field. time changes, resulting in a certain amount of phase delay. On the basis of this phase delay, apply an electric field between the pixel electrode and the common electrode for phase modulation, and only need to apply a lower electric field to generate an additional phase shift to produce the expected phase delay, thereby realizing low-voltage drive blue-phase liquid crystal phase modulation purpose of the device.

Figure 3 is a schematic diagram of the electronically controlled polymerization process method of the present invention. There are mainly lower substrate 1, pixel electrode layer 2, blue phase liquid crystal layer 3, common electrode layer 4, upper substrate 5, ultraviolet (or other wavelength light source) exposure 6 (polymerization process 6 can also be thermal polymerization).

First, the mixture of the blue phase liquid crystal polymer is poured into the liquid crystal device shown in Figure 3 in an isotropic state, and the blue phase liquid crystal is uniformly dispersed in the blue phase liquid crystal layer 3; the sample is controlled at a certain rate on the temperature control platform (For example, 0.5°C per minute) lower the temperature, observe the blue phase range under the microscope and lower the temperature to the polymerization temperature.

When the mixture of blue phase liquid crystal and polymer is polymerized, the polymerization voltage is applied between the pixel electrode layer and the common electrode layer, and then the sample is exposed directly under the ultraviolet (or other wavelength) light source (the polymerization process can also be thermal Polymerization), through the electric field between the pixel electrode and the common electrode, the potential energy of the liquid crystal molecules is increased, and the anchoring energy of the polymer network is reduced, thereby increasing the Cole constant and reducing the driving voltage of the blue phase liquid crystal. Different blue phase liquid crystal materials require different polymerization electric fields during polymerization.

The invention utilizes the electric field to control the polymerization process of the blue phase liquid crystal in the phase modulation device, increases the potential energy of the liquid crystal molecules through the polymerization electric field, reduces the anchoring energy of the polymer network, increases the Cole constant of the blue phase liquid crystal, reduces the driving voltage of the blue phase liquid crystal, and realizes low The voltage drives the blue-phase liquid crystal phase modulation device; at the same time, due to the macroscopic isotropy of the blue-phase liquid crystal, the polarization independence of the phase modulation device is realized, which greatly reduces energy loss and saves device resources and space.

The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art shall be within the scope of protection defined by the claims.

Claims (10)

1. A polarization-independent method of a blue-phase liquid crystal phase modulation device, characterized in that, comprising the following steps: Step 1, pouring the blue-phase liquid crystal into the phase modulation device of the blue-phase liquid crystal, and cooling down to the polymerization temperature; Step 2, the polymerization electric field is applied to both ends of the common electrode and the pixel electrode layer; the electric field strength of the polymerization electric field is different according to the blue phase liquid crystal material; Step 3, polymerization or thermal polymerization under ultraviolet light; Step 4, obtaining polymer-stabilized blue-phase liquid crystals in the process of electrically controlled polymerization. 2 . The polarization-independent method for a blue-phase liquid crystal phase modulation device according to claim 1 , wherein the cooling rate is 0.5° C./min. 3 . 3. The polarization-independent method for a blue-phase liquid crystal phase modulation device according to claim 1, wherein the electric field strength of the polymerization electric field is 2V/μm. 4 . The polarization-independent method for a blue-phase liquid crystal phase modulation device according to claim 1 , wherein the frequency of the polymerization electric field is 1 kHz˜1000 kHz. 5. The polarization-independent method for a blue-phase liquid crystal phase modulation device according to claim 1, wherein the polymerization electric field is a set of square wave or sine wave or triangular wave alternating electric field. 6. A blue-phase liquid crystal phase modulation device, characterized in that it comprises an upper substrate, a common electrode layer, a blue-phase liquid crystal layer, a pixel electrode layer and a lower substrate, and the common electrode layer is between the upper substrate and the blue-phase liquid crystal layer , the pixel electrode layer is between the lower substrate and the blue phase liquid crystal layer; when polymerizing the blue phase liquid crystal polymer mixture, the common electrode layer and the pixel electrode layer are configured to apply a polymerization electric field. 7. The blue-phase liquid crystal phase modulation device according to claim 6, wherein the upper substrate is glass or plastic; the lower substrate is a silicon substrate. 8. The blue-phase liquid crystal phase modulation device according to claim 6, wherein the common electrode layer is a plate electrode formed by a transparent conductive metal oxide or a transparent conductive organic polymer material or strip electrodes parallel to each other . 9 . The blue-phase liquid crystal phase modulation device according to claim 6 , wherein the pixel electrode layer is a group of parallel strip electrodes or block electrodes formed of opaque conductive metal with high reflectivity. 10. The blue-phase liquid crystal phase modulation device according to claim 8, wherein the transparent conductive metal oxide is ITO, and the transparent conductive organic polymer material is PEDOT.