Optical filter and application thereof

Abstract

The invention discloses an optical filter which comprises a first substrate and a second substrate which are oppositely arranged, and the first substrate and / or the second substrate are / is a graphene / glass transparent substrate composed of glass and a graphene film arranged on the surface of the glass; the cholesteric liquid crystal is arranged between the first substrate and the second substrate and is in contact with the graphene film; and the first electrode and the second electrode are arranged on the graphene film of the graphene / glass transparent substrate. By changing the voltage applied to the two ends of the optical filter, the Bragg reflection band of the temperature response type or electric field response type cholesteric liquid crystal moves, and the hue attribute of the color of emergent light is dynamically and continuously adjusted; further, by changing adopted polaroids (a linear polaroid, a left-hand circular polaroid and a right-hand circular polaroid) and utilizing the dichroism of cholesteric liquid crystal to circularly polarized light, the adjustment of the saturation attribute of the color of emergent light is realized; by adjusting the radiation power (represented as the brightness of the light source) of the white light source, the brightness attribute of the color of the emergent light is managed.

Description

Technical Field

[0001] The present invention belongs to the field of optical elements, and particularly relates to a variable-color color filter and a variable-color light source including the same. Background Art

[0002] Variable-color light sources are extremely common in people's scientific research, production, and daily life, and have a wide range of applications in fields such as optical experimental platforms, display technologies, indoor lighting, stage lighting, and photographic lighting. In order to meet the requirements of more application scenarios, it is necessary to develop a light source that can provide continuously adjustable colors within a wide color gamut.

[0003] Generally speaking, people mainly adopt two strategies to obtain light with continuously adjustable colors. First, select light sources with different emission wavelengths (colors) (such as red, green, and blue), mix the light emitted by them, and adjust the color of the mixed light by adjusting the brightness of each light source. This strategy has the advantage of a wide adjustable color gamut. However, since it is necessary to independently control each monochromatic light source, the corresponding light source device structure and color mixing mechanism are relatively complex, and the cost is relatively high. Therefore, its application in daily life is relatively limited. Second, select a white light source and install a disk-shaped or wheel-shaped gradient filter in front of it. By adjusting the position of the filter irradiated by the white light source, continuous adjustment of the color of the transmitted light can be achieved. The light source device structure corresponding to this strategy is relatively simple, and it is convenient to adjust a single color attribute (one of brightness, hue, and saturation) of the transmitted light. However, the introduction of a large-sized disk-shaped or wheel-shaped gradient color filter is not conducive to the miniaturization and compactness of the device, which poses a challenge to the construction of a portable variable-color light source. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a color filter and a variable-color light source including the color filter.

[0005] The present invention provides a color filter, including: a first substrate and a second substrate disposed opposite to each other, wherein the first substrate and / or the second substrate is a graphene / glass transparent substrate composed of glass and a graphene thin film disposed on the surface of the glass; a cholesteric liquid crystal disposed between the first substrate and the second substrate and in contact with the graphene thin film; a first electrode and a second electrode disposed on the graphene thin film of the graphene / glass transparent substrate.

[0006] According to an embodiment of the present invention, both the first substrate and the second substrate are graphene / glass transparent substrates, and the first electrode and the second electrode are respectively disposed on the first substrate and the second substrate.

[0007] According to another embodiment of the present invention, the first substrate is glass, the second substrate is a graphene / glass transparent substrate, and the first electrode and the second electrode are disposed on the second substrate.

[0008] According to another embodiment of the present invention, the graphene film is directly grown on the glass surface by chemical vapor deposition to obtain the graphene / glass transparent substrate.

[0009] According to another embodiment of the present invention, the light transmittance of the graphene / glass transparent substrate is greater than 80%, and the sheet resistance is 10 2 Ω·sq -1 -10 4 Ω·sq -1 , and the thickness of the graphene film is 1 nm - 5 nm.

[0010] According to another embodiment of the present invention, the first electrode and the second electrode are respectively a silver electrode, an ITO electrode, an FTO electrode or a copper electrode.

[0011] According to another embodiment of the present invention, the cholesteric liquid crystal is selected from one or more of small molecule liquid crystals, polymer dispersed liquid crystals, polymer stabilized liquid crystals, and liquid crystal polymers; preferably a small molecule liquid crystal.

[0012] According to another embodiment of the present invention, the cholesteric liquid crystal includes one or more of the compounds shown in Formula I, Formula II, and Formula III;

[0013]

[0014] wherein, n1, n2, n3, and n4 are respectively selected from any integers from 3 to 11.

[0015] According to another embodiment of the present invention, the cholesteric liquid crystal includes a non-hydrogen bond type liquid crystal monomer and a hydrogen bond type liquid crystal monomer, and the mass ratio of the non-hydrogen bond type liquid crystal monomer to the hydrogen bond type liquid crystal monomer is 2:8 - 3:7.

[0016] According to another embodiment of the present invention, the cholesteric liquid crystal further includes a chiral dopant accounting for 2% - 3% of the total mass of the cholesteric liquid crystal.

[0017] According to another embodiment of the present invention, the temperature range of the cholesteric liquid crystal is 35°C - 100°C, preferably 45°C - 93°C.

[0018] According to another embodiment of the present invention, the distance between the first substrate and the second substrate is 20 μm - 40 μm, preferably 20 μm.

[0019] According to another embodiment of the present invention, the first substrate and the second substrate are sealed with a sealant, and the sealant is an ultraviolet curable adhesive.

[0020] The present invention also provides a variable light source, which includes a white light source, a polarizer group, and a filter that are coaxially arranged in sequence; wherein, the brightness of the white light source is adjustable; the polarizer group includes a linearly polarized sheet, a left-handed circular polarizer, and a right-handed circular polarizer that can be switched arbitrarily; the filter is the above-mentioned filter, and the filter is arranged parallel to the polarizer.

[0021] The present invention further provides an application of the above variable light source in display devices, household lighting sources, stage lighting sources, and photographic lighting sources.

[0022] The filter of the present invention uses cholesteric liquid crystal. Since cholesteric liquid crystal is a liquid crystal material with a unique helical twist superstructure, it has novel optical properties such as wavelength-selective reflection (Bragg reflection), dichroism for circularly polarized light, and optical rotation. Among them, the Bragg reflection band (or transmission spectrum) can change continuously with external stimuli such as temperature or electrostatic field, so it can be used as an ideal color-changing filter medium to obtain transmitted light with continuously adjustable color. Graphene has properties such as transparency and conductivity. The novel graphene / glass composite material obtained by directly compounding graphene onto the glass surface can be used as a transparent conductive electrode, which can convert the externally input voltage signal into an electrostatic field or Joule heat, thereby effectively driving the color-changing behavior of cholesteric liquid crystal. Therefore, the variable-color color filter obtained by combining the graphene / glass composite material with cholesteric liquid crystal provides a new idea for the construction of portable color-changing light sources.

[0023] The color-changing light source of the present invention changes the voltage applied across the filter, causing the Bragg reflection band of the temperature-responsive or electric-field-responsive cholesteric liquid crystal to shift, thereby realizing the dynamic continuous adjustment of the hue attribute of the color of the emitted light; by changing the polarizer used (linearly polarized sheet, left-handed circular polarizer, and right-handed circular polarizer), and utilizing the dichroism of cholesteric liquid crystal for circularly polarized light, the saturation attribute of the color of the emitted light is adjusted; by adjusting the radiation power of the white light source itself (manifested as the brightness of the light source), the lightness attribute of the color of the emitted light is managed. In addition, the color-changing filter of the present invention can effectively simplify the device structure of the color-changing light source and help reduce the size of the device. Therefore, it is expected to obtain a variable-color color light source with a simple device structure and color-tuning mechanism, easy to miniaturize and compactify, and capable of continuously adjusting the color of the emitted light within a wide color gamut. Description of the Drawings

[0024] Figure 1 It is a schematic flow chart for preparing an electric-field-responsive cholesteric liquid crystal filter.

[0025] Figure 2 It is a schematic flow chart for preparing a temperature-responsive cholesteric liquid crystal filter.

[0026] Figure 3 It is a schematic diagram of the variable light source of the present invention.

[0027] Figure 4 It is the Raman spectrum of the graphene / glass transparent substrate prepared in Example 1.

[0028] Figure 5 It is the structural formula of four cholesteric liquid crystal monomer molecules used in Example 1.

[0029] Figure 6 It is the transmission spectrum of the filter at different heating voltages when the incident light is unpolarized light or linearly polarized light.

[0030] Figure 7 It is the transmission spectrum of the filter at different heating voltages when the incident light is right-handed circularly polarized light.

[0031] Figure 8 It is the transmission spectrum of the filter at different heating voltages when the incident light is left-handed circularly polarized light.

[0032] Figure 9 It is according to Figures 6 - 8 the CIE 1931 x-y chromaticity coordinates (standard observer: CIE 1931 2° field of view; light source: D65 white light source) calculated from the transmission spectrum in

[0033] Among them, the description of the reference numerals is as follows:

[0034] 11, 21 - the first substrate; 12, 22 - the second substrate; 13, 23 - the first electrode; 14, 24 - the second electrode; 15, 25 - the spacer; 16, 26 - the curing glue; 17, 27 - the cholesteric liquid crystal; 31 - the white light source; 32 - the polarizer; 33 - the filter Detailed implementation manners

[0035] The present invention will be described in detail below in conjunction with the detailed implementation manners.

[0036] In this patent, "the first" and "the second" are only used to distinguish different components, and do not intend to limit the importance of the components.

[0037] The filter of the present invention includes: a first substrate and a second substrate disposed opposite to each other, a cholesteric liquid crystal, and a first electrode and a second electrode. The first substrate and / or the second substrate is a graphene / glass transparent substrate composed of glass and a graphene thin film disposed on the surface of the glass. The cholesteric liquid crystal is disposed between the first substrate and the second substrate and is in contact with the graphene thin film. The first electrode and the second electrode are disposed on the graphene thin film of the graphene / glass transparent substrate. The first electrode and the second electrode have opposite polarities. The cholesteric liquid crystal is a liquid crystal material with a unique helical twist superstructure and has novel optical properties such as wavelength-selective reflection (Bragg reflection), dichroism for circularly polarized light, and optical rotation. Among them, the Bragg reflection band (or transmission spectrum) can change continuously with external stimuli such as temperature or electrostatic field, and thus can be used as an ideal color-changing filter medium to obtain transmitted light with continuously adjustable colors. Graphene has properties such as transparency and conductivity. The novel graphene / glass composite material obtained by directly compounding graphene onto the glass surface can be used as a transparent conductive electrode, which can convert an externally input voltage signal into an electrostatic field or Joule heat, thereby effectively driving the color-changing behavior of the cholesteric liquid crystal.

[0038] The filter of the present invention can be divided into an electric field-responsive type and a temperature-responsive type. The structures of these two types of filters are slightly different, and the following will introduce these two types of filters separately. Figure 1 and Figure 2 respectively show the preparation flowcharts of the electric field-responsive type and the temperature-responsive type filters.

[0039] As Figure 1 shown, both the first substrate 11 and the second substrate 12 of the electric field-responsive type filter are graphene / glass transparent substrates. The first substrate 11 and the second substrate 12 can be placed in an interleaved manner, and the first electrode 13 and the second electrode 14 are respectively disposed on the first substrate 11 and the second substrate 12. Of course, the first substrate 1 and the second substrate 12 can also be arranged with their four sides flush. To control the distance between the first substrate 11 and the second substrate 12, it can be controlled by setting a spacer 15 between the first substrate 11 and the second substrate 12. The height of the spacer 15 is the distance between the first substrate 11 and the second substrate 12. The spacer is disposed on both sides of the first substrate 11 and the second substrate 12, such as the long side in the figure. The spacer 15 can be made of any suitable material that does not affect the performance of the cholesteric liquid crystal, such as but not limited to plastic. A fixing glue 16 can be coated on the outer side of the spacer 15 to encapsulate the long sides of the first substrate 11 and the second substrate 12 to form a liquid crystal cell. The short sides of the liquid crystal cell are the openings. The fixing glue 16 can be an ultraviolet light-curing glue. Then, molten liquid crystal is dipped and dropped at the opening of the slit space of the liquid crystal cell, so that the cholesteric liquid crystal 17 diffuses inward under the action of capillary force until the entire slit space is filled. Then, the two short sides are sealed with the fixing glue 16 to seal the liquid crystal in the liquid crystal cell.

[0040] In the above embodiments, the use of "long side" and "short side" is for convenience of description and is not intended to limit the present invention. Those skilled in the art can understand that the "long side" and "short side" described in the above embodiments can be replaced with each other and still achieve the purpose of the present invention. In the following embodiments, the meanings of "long side" and "short side" are the same as those in the above embodiments.

[0041] As Figure 2 shown, the first substrate 21 of the temperature-responsive filter is glass, the second substrate 22 is a graphene / glass transparent substrate, the area of the first substrate 21 can be smaller than that of the second substrate 22, and the first substrate 21 and the second substrate 22 are arranged opposite to each other. Of course, the area of the first substrate 21 can be equal to that of the second substrate 22, and the four sides of the two substrates are flush. The first electrode 23 and the second electrode 24 are arranged on the second substrate 22, that is, on the graphene film of the graphene / glass transparent substrate. The setting methods of the spacer 25, the fixing glue 26 and the cholesteric liquid crystal 27 are the same as those in Figure 1 the shown embodiment and will not be repeated here. The cholesteric liquid crystal 27 is temperature-responsive.

[0042] In an alternative embodiment, the graphene / glass transparent substrate can be obtained by directly growing a graphene film on transparent glass by chemical vapor deposition. The light transmittance of the graphene / glass transparent substrate is greater than 80%, and the sheet resistance is 10 2 Ω·sq -1 -10 4 Ω·sq -1 , and the thickness of the graphene film is 1 nm - 2 nm.

[0043] In an alternative embodiment, the first electrode and the second electrode can be a silver electrode, an ITO electrode, an FTO electrode or a copper electrode respectively.

[0044] In an alternative embodiment, the cholesteric liquid crystal is selected from one or more of small molecule liquid crystals, polymer dispersed liquid crystals, polymer stabilized liquid crystals and liquid crystal polymers. Preferably, it is a small molecule liquid crystal. The "small molecule" liquid crystal in this patent is relative to the "polymer" dispersed liquid crystal and "polymer" stabilized liquid crystal in the following categories. That is, in the small molecule liquid crystal, there is no formation of polymer, only liquid crystal molecule monomers.

[0045] In an alternative embodiment, the cholesteric liquid crystal includes one or more of the compounds shown in Formula I, Formula II, and Formula III;

[0046]

[0047] wherein, n1, n2, n3 and n4 are respectively selected from any integer in 3 - 11.

[0048] In an alternative embodiment, the cholesteric liquid crystal comprises a non-hydrogen-bonded liquid crystal monomer and a hydrogen-bonded liquid crystal monomer, and the mass ratio of the non-hydrogen-bonded liquid crystal monomer to the hydrogen-bonded liquid crystal monomer is 2:8 - 3:7.

[0049] In an alternative embodiment, the cholesteric liquid crystal further comprises a chiral dopant accounting for 2% - 3% of the total mass of the cholesteric liquid crystal.

[0050] In an alternative embodiment, the temperature range of the cholesteric liquid crystal is 35°C - 100°C, preferably 45°C - 93°C.

[0051] In an alternative embodiment, the distance between the first substrate and the second substrate is 20μm - 40μm, preferably 20μm.

[0052] The present invention also discloses a variable light source using the above filter. As Figure 3 shown, the variable light source includes a white light source 31, a polarizer group, and a filter 33 arranged coaxially in sequence. The brightness of the white light source 31 is adjustable, and the white light source 31 can be any feasible artificial light source such as an incandescent lamp, a fluorescent lamp, an LED light source, etc. The polarizer group includes a linearly polarizing plate, a left-handed circular polarizing plate, and a right-handed circular polarizing plate that can be switched arbitrarily. Figure 3 The polarizer 32 in [[ ]] is one of the linearly polarizing plate, the left-handed circular polarizing plate, and the right-handed circular polarizing plate. The filter 33 is arranged parallel to the polarizer 32.

[0053] The above variable light source can be applied to display devices, home lighting sources, stage lighting sources, and photographic lighting sources.

[0054] The present invention is further described below through specific examples. However, these examples are merely exemplary and do not constitute any limitation to the protection scope of the present invention. In the following examples and comparative examples, the reagents, materials, and instruments used can be obtained commercially without special instructions.

[0055] Example 1: Temperature-responsive

[0056] (1) Preparation of the first substrate and the second substrate

[0057] Quartz glass with dimensions of 6 cm × 3 cm was selected as the growth substrate for graphene. It was ultrasonically cleaned in deionized water, acetone, and isopropyl alcohol for 10 minutes each in sequence. After being dried with a nitrogen gun, it was placed on a quartz carrier plate and positioned at the center of the first temperature zone of a three-inch three-temperature-zone resistive tube furnace, and the reaction chamber was sealed. A separate Ar gas path for bubbling was set up and introduced into a bubbling tank filled with deionized water, and then connected to the growth system to provide water vapor etchant. Among them, the temperature of the deionized water in the bubbling tank was maintained at about 25 °C by means of heating tape heating. 1000 sccm of Ar was introduced into the reaction chamber to exhaust the air, which lasted for 20 min. Then, 400 sccm of Ar was introduced into the growth system as the carrier gas and 400 sccm of H 2 As the reducing gas, after 20 minutes, the heating switch of the tube furnace was turned on, and the reaction chamber was heated from room temperature to ~1120 °C within 70 minutes and stabilized at this temperature for 20 minutes. Subsequently, the flow rate of Ar was adjusted to 375 sccm, and 25 sccm of bubbling Ar and 18 sccm of methane carbon source were introduced into the growth system for the growth of graphene, and the growth process lasted for 6 hours. After the growth was completed, the methane and bubbling Ar gas paths were closed and the gas supply was stopped, and the heating switch of the tube furnace was turned off. The sample in the growth chamber was cooled to room temperature with the furnace and then taken out to obtain the graphene / glass transparent substrate. During the growth process, a small amount of water vapor introduced (volume fraction of ~0.1%) can be cracked at high temperature to generate oxygen-containing etching species (such as O atoms, OH free radicals, etc.), which helps to reduce the nucleation density of graphene, increase the size of the single-crystalline domain region of graphene, and improve the thickness uniformity of the graphene film.

[0058] The prepared graphene / glass transparent substrate was characterized by Raman spectroscopy. As Figure 4 shown, three significant characteristic peaks appeared in the Raman spectrum at ~1340 cm -1 , ~1580 cm -1 and ~2690 cm -1 respectively, corresponding to the D peak, G peak, and 2D peak of graphene. Among them, the intensity ratio of the 2D peak to the G peak was mainly distributed between 0.75 - 1. This result indicates that a graphene film with a thickness mainly of 2 - 3 layers was formed on the surface of the quartz glass. The transmittance and sheet resistance of this graphene / glass sample were measured, and the transmittance of the sample was ~88%, and the sheet resistance was ~900 Ω / sq -1 .

[0059] (2) Preparation of the filter

[0060] See Figure 2, place two plastic strips (with a thickness of ~20 μm) as spacers 25 at the long edge on the surface of the second substrate 22 prepared in step (1). Then stack a square quartz glass sheet in the middle above the second substrate 22 as the first substrate 21. Clamp the edge of the stack with a clip, and dip and apply ultraviolet curable glue at the joint between the second substrate 22 and the first substrate 21. After the ultraviolet curable glue diffuses to the plastic spacers under the action of capillary force, place the stacked structure in an ultraviolet curing box and cure it at a power of ~400 W for 20 minutes. After the ultraviolet curable glue is completely cured, remove the clip to obtain a liquid crystal cell. Brush conductive silver paste on the two short edges of the second substrate 22 respectively, and the width of the silver paste pattern is ~1 cm. Place the liquid crystal cell with the silver paste pattern on a hot stage and bake it at ~130 °C for 15 minutes to remove the solvent molecules in the silver paste pattern and make it cure to form silver electrodes as the first electrode 23 and the second electrode 24 respectively.

[0061] According to the mass ratio of 5:7:4:4 Figure 5 The shown compound (M 1 , M 2 , M 3 and M 4 ) are mixed at ~100 °C, and the four monomer molecules combine through hydrogen bonds to form rod-like liquid crystal molecules. Then mix ~2.6% by mass of a chiral dopant S5011 (left-handed or right-handed) into it to obtain the required liquid crystal sample, and its cholesteric phase temperature range is about 45 °C - 93 °C.

[0062] Place the test tube containing the above cholesteric liquid crystal against a test tube oscillator, and heat the sample with a hair dryer to obtain a molten liquid crystal with a uniform composition distribution. Place the liquid crystal cell on a hot stage and keep it at 80 °C for a period of time. Dip and apply the molten liquid crystal at the opening of the slit space of the liquid crystal cell, and make the liquid crystal diffuse inward under the action of capillary force until it fills the entire slit space. During this process, the frictional shear force between the liquid crystal and the upper and lower walls of the internal space of the liquid crystal cell makes the liquid crystal molecules orient parallel to the substrate to form a planar texture. At the same time, the addition of a chiral dopant (left-handed or right-handed) can induce the liquid crystal molecules to twist layer by layer along the thickness direction to form a helical twist superstructure with a specific chirality (left-handed or right-handed), that is, to form a cholesteric liquid crystal. The unique chiral helical twist superstructure enables the cholesteric liquid crystal to selectively reflect circularly polarized light with the same chirality within a specific wavelength band (Bragg reflection band), resulting in the cholesteric liquid crystal showing different reflection / transmission characteristics for light with different polarization states, which will help to provide transmitted light with different color saturations. As the temperature increases, the pitch (the period of the helical twist superstructure in the thickness direction) of the cholesteric liquid crystal gradually decreases, thus causing the reflection band to shift to the blue, which will help to achieve dynamic continuous adjustment of the hue attribute of the color of the transmitted light.

[0063] After the liquid crystal molecules fill the liquid crystal cell, the liquid crystal cell is encapsulated to form a filter.

[0064] (3) Explanation of the color-changing mechanism of the variable light source

[0065] Through the transmission spectrum characterization and corresponding colorimetric analysis of the above-prepared thermochromic color filter, combined with Figures 6 - 9 Elaborate on the adjustment mechanism and process of the hue and saturation attributes of the color of the light emitted by the variable color light source.

[0066] As is well known, the color of light is determined by the spectral power distribution of light. For the variable color light source involved in the present disclosure, the spectral power distribution of the emitted light is the product of the spectral power distribution of the white light source and the transmission spectrum of the variable color filter. Among them, by adjusting the radiation power of the white light source (manifested as the brightness of the light source), the numerical value of the spectral power distribution of the emitted light can be changed in an almost equal proportion, that is, the adjustment of the brightness attribute of the color of the emitted light can be achieved. When the radiation power of the white light source is constant, the color of the emitted light is completely determined by the transmission spectrum of the thermochromic color filter in the visible light band. From the relevant discussion of the above thermochromic color filter, it can be seen that the transmission spectrum of the thermochromic color filter depends on the heating voltage (temperature) applied across its two ends and the polarization state of the incident light. Therefore, in this test example, the transmission spectra of the thermochromic color filter (using right-handed cholesteric liquid crystal) under different heating voltages and different polarization states of the incident light were characterized, and colorimetric analysis was performed on the obtained spectral data based on the CIE 1931 XYZ standard colorimetric system.

[0067] As Figure 6 shown, when a polarizer is not used (the incident light is unpolarized light) or a linear polarizer is selected (the incident light is linearly polarized light), a trough appears in the transmission spectrum of the thermochromic color filter, which is the Bragg reflection band of the cholesteric liquid crystal. It should be noted that the transmittance value within the reflection band is significantly lower than that outside the reflection band. This is because unpolarized light and linearly polarized light can be regarded as being formed by the superposition of two beams of left-handed circularly polarized light and right-handed circularly polarized light with equal intensity. The right-handed cholesteric liquid crystal can selectively reflect the right-handed circularly polarized light component within the band and allow the left-handed circularly polarized light component to pass through. When the heating voltage is increased from 24V to 60V, the center wavelength of the reflection band of the filter shifts from ∼635nm to ∼470nm, corresponding to the structural color (reflection color) of the cholesteric liquid crystal changing from red to blue in hue. This is caused by the pitch of the temperature-responsive cholesteric liquid crystal gradually decreasing with increasing temperature. As Figure 9 shown, the corresponding colorimetric analysis results show that, as the complementary color of the structural color, the hue of the transmitted light color changes continuously from bright blue - blue - purple - yellow.

[0068] As Figure 7As shown, when a right-handed circular polarizer is selected (i.e., the incident light is right-handed circularly polarized light), a Bragg reflection band also appears in the transmission spectrum of the thermochromic color filter. However, the transmittance within the band is close to 0 because the right-handed circularly polarized light within the band is completely reflected by the right-handed cholesteric liquid crystal. As the heating voltage increases, a similar blue shift also occurs in the reflection band. As Figure 9 shown, the corresponding chromaticity analysis results show that the hue of the transmitted light color also changes from bright blue - blue - purple - yellow. Interestingly, compared with the case without using a polarizer or using a linear polarizer, when using a right-handed circular polarizer, the color of the transmitted light obtained exhibits higher saturation.

[0069] As Figure 8 shown, when a left-handed circular polarizer is selected (i.e., the incident light is left-handed circularly polarized light), no significant Bragg reflection band appears in the transmission spectrum of the thermochromic color filter at each heating voltage, and the transmittance changes little with wavelength within the visible light band. As Figure 9 shown, the corresponding chromaticity analysis results show that at each heating voltage, the color of the transmitted light is very close to neutral colors (i.e., black, white, and neutral gray), showing extremely low saturation.

[0070] The above test results and corresponding analysis show that by adjusting the radiation power (brightness) of the white light source, changing to different polarizers, and adjusting the heating voltage applied across the thermochromic color filter, the brightness, saturation, and hue attributes of the color of the output light can be effectively adjusted respectively.

[0071] The mechanism of variable light source color change using an electric field-responsive filter is the same as that of the temperature-responsive type. By changing the voltage applied across the filter, the Bragg reflection band of the temperature-responsive or electric field-responsive cholesteric liquid crystal is shifted, realizing the dynamic and continuous adjustment of the hue attribute of the color of the output light. By changing the polarizer used (linear polarizer, left-handed circular polarizer, and right-handed circular polarizer), using the dichroism of cholesteric liquid crystal to circularly polarized light, the saturation attribute of the color of the output light is adjusted; by adjusting the radiation power of the white light source itself (manifested as the brightness of the light source), the brightness attribute of the color of the output light is managed, that is, the mechanism of using the filter for a variable light source is the same.

[0072] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A filter, characterized in that, comprising: A first substrate and a second substrate arranged oppositely, wherein the first substrate and / or the second substrate is a graphene / glass transparent substrate composed of glass and a graphene thin film provided on the surface of the glass; A cholesteric liquid crystal, provided between the first substrate and the second substrate and in contact with the graphene thin film; A first electrode and a second electrode, provided on the graphene thin film of the graphene / glass transparent substrate.

2. The filter according to claim 1, characterized in that, both the first substrate and the second substrate are graphene / glass transparent substrates, and the first electrode and the second electrode are respectively provided on the first substrate and the second substrate.

3. The filter according to claim 1, characterized in that, the first substrate is glass, the second substrate is a graphene / glass transparent substrate, and the first electrode and the second electrode are provided on the second substrate.

4. The filter according to claim 1, characterized in that, the graphene thin film is directly grown on the surface of the glass by chemical vapor deposition to obtain the graphene / glass transparent substrate.

5. The filter according to claim 1, characterized in that, The light transmittance of the graphene / glass transparent substrate is greater than 80%, and the sheet resistance is 10 2 Ω·sq -1 -10 4 Ω·sq -1 , and the thickness of the graphene film is 1 nm - 5 nm.

6. The filter according to claim 1, characterized in that, the first electrode and the second electrode are respectively a silver electrode, an ITO electrode, an FTO electrode or a copper electrode.

7. The filter according to claim 1, characterized in that, the cholesteric liquid crystal is selected from one or more of small molecule liquid crystal, polymer dispersed liquid crystal, polymer stabilized liquid crystal and liquid crystal polymer; preferably small molecule liquid crystal.

8. The filter according to claim 7, characterized in that, the cholesteric liquid crystal comprises one or more of the compounds shown in Formula I, Formula II and Formula III; wherein, n1, n2, n3 and n4 are respectively selected from any integer in 3-11.

9. The filter according to claim 1, characterized in that, the cholesteric liquid crystal comprises a non-hydrogen bond type liquid crystal monomer and a hydrogen bond type liquid crystal monomer, and the mass ratio of the non-hydrogen bond type liquid crystal monomer to the hydrogen bond type liquid crystal monomer is 2:8 - 3:

7.

10. The filter according to claim 1, characterized in that, the cholesteric liquid crystal further comprises a chiral dopant accounting for 2% - 3% of the total mass of the cholesteric liquid crystal.

11. The filter according to claim 3, characterized in that, the temperature range of the cholesteric liquid crystal is 35°C - 100°C, preferably 45°C - 93°C.

12. The filter according to claim 1, characterized in that, the distance between the first substrate and the second substrate is 20μm - 40μm, preferably 20μm.

13. The filter according to claim 1, characterized in that, the first substrate and the second substrate are sealed with a sealant, and the sealant is an ultraviolet curable adhesive.

14. A variable light source, characterized in that, comprising a white light source, a polarizer group and a filter arranged coaxially in sequence; wherein, the brightness of the white light source is adjustable; the polarizer group comprises a linearly polarizing plate, a left-handed circular polarizing plate and a right-handed circular polarizing plate that can be switched arbitrarily; The filter is the filter described in any one of claims 1-13, and the filter is arranged in parallel with the polarizer.

15. Application of the variable light source according to claim 14 in a display device, a household lighting source, a stage lighting source, and a photographic lighting source.

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