Optical device, preparation method of optical device and polarization measurement device

Abstract

The invention discloses an optical device, a preparation method of the optical device and a polarization measurement device. The optical device comprises a first liquid crystal box and a second liquid crystal box which are stacked. The first liquid crystal box comprises a first substrate, a second substrate and a first liquid crystal layer, and the first orientation layer and the second orientation layer control the arrangement direction of liquid crystal molecules in the first liquid crystal layer; the second liquid crystal box comprises a third substrate, a fourth substrate and a second liquid crystal layer, and the third orientation layer and the fourth orientation layer control the arrangement direction of liquid crystal molecules in the second liquid crystal layer; the first orientation layer and the second orientation layer encode vortex phases of q =-0.5, and the third orientation layer and the fourth orientation layer encode geometric phases of the grating. The optical device provided by the invention can overcome the limitation that a traditional polarization testing device is narrow in testing wave band, not compact enough and the like, polarization detection covering visible light to near-infrared light is realized, and a polarization analysis mode in an image form is constructed.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to an optical device, a method for preparing the optical device and a polarization measuring device. Background Art

[0002] Polarization is a vector property of electromagnetic waves that describes the direction in which the electric component of the electric field oscillates, and plays a crucial role in optics. The state of polarization (SoP) determines how light interacts with anisotropic, chiral and magnetized matter, thus forming the basis for a variety of optical techniques such as polarization spectroscopy, ellipsometry, sensing and imaging.

[0003] The most direct approach to polarization measurement is to simultaneously detect the amplitude contrast and phase between two orthogonal polarization states. However, the difficulty in capturing phase information makes direct polarization measurement extremely challenging. Traditional methods typically use spatial beam splitting techniques (spatial division) or rotating wave plates (temporal division) to perform a series of intensity measurements. Therefore, complex optical setups are usually required that require precise adjustment, making the solution bulky and time-consuming. In addition, the broadband feasibility of conventional polarimeters is greatly hindered by the narrowband limitations of individual components such as wave plates. At the same time, existing commercial polarization cameras have difficulty in achieving chirality measurements. In modern optics and informatics, there is an urgent need to explore compact, high-speed, and broadband-available polarization measurement methods for polarization detection. Summary of the invention

[0004] The embodiments of the present invention provide an optical device, a method for preparing the optical device, and a polarization measurement device. The optical device can overcome the limitations of traditional polarization test devices such as narrow test band and lack of compactness, realize polarization detection covering visible light to near infrared, and construct a polarization analysis method in image form.

[0005] According to one aspect of the present invention, there is provided an optical device, comprising a first liquid crystal cell and a second liquid crystal cell which are stacked;

[0006] The first liquid crystal box comprises a first substrate, a second substrate and a first liquid crystal layer located between the first substrate and the second substrate, a first alignment layer is disposed on a side of the first substrate close to the second substrate, and a second alignment layer is disposed on a side of the second substrate close to the first substrate, and the first alignment layer and the second alignment layer control the arrangement direction of liquid crystal molecules in the first liquid crystal layer;

[0007] The second liquid crystal box comprises a third substrate, a fourth substrate and a second liquid crystal layer located between the third substrate and the fourth substrate, a third alignment layer is arranged on a side of the third substrate close to the fourth substrate, and a fourth alignment layer is arranged on a side of the fourth substrate close to the third substrate, and the third alignment layer and the fourth alignment layer control the arrangement direction of liquid crystal molecules in the second liquid crystal layer;

[0008] The first orientation layer and the second orientation layer encode the vortex phase of q=-0.5, and the third orientation layer and the fourth orientation layer encode the geometric phase of the grating.

[0009] Optionally, a polarized light beam is incident on the optical device, the first liquid crystal box is used to characterize the phase difference of the circularly polarized light, the second liquid crystal box is used to characterize the amplitude ratio of the circularly polarized light, and the amplitude ratio and phase difference of the orthogonal circularly polarized light are revealed according to the diffraction pattern to determine the polarization state of the incident polarized light beam.

[0010] Optionally, the first substrate, the second substrate, the third substrate and the fourth substrate all include flexible substrates or rigid substrates with a light transmittance greater than or equal to 85%.

[0011] Optionally, the first liquid crystal box further includes a first electrode layer disposed on one side of the first substrate and a second electrode layer disposed on one side of the second substrate;

[0012] The second liquid crystal cell further includes a third electrode layer disposed on one side of the third substrate and a fourth electrode layer disposed on one side of the fourth substrate.

[0013] Optionally, the materials of the first alignment layer, the second alignment layer, the third alignment layer and the fourth alignment layer include at least one of a photo-crosslinking material, a photo-degradable material and a photo-induced cis-trans isomerization material.

[0014] Optionally, the liquid crystal material of the first liquid crystal layer and the second liquid crystal layer is positive liquid crystal. Under the action of an external electric field, the liquid crystal molecules are deflected as the electric field increases, and are finally arranged along the direction of the electric field. At the same time, the liquid crystal molecules will follow the molecular orientation of the light-controlled orientation layer, thereby carrying a fixed phase. The external electric field only changes the efficiency of the optical device and has no effect on the phase.

[0015] Optionally, the light alignment area resolution of the first liquid crystal cell and the second liquid crystal cell is 1 μm to 2 μm.

[0016] Optionally, the thickness of the first liquid crystal box and the second liquid crystal box is 4 μm to 6 μm.

[0017] According to another aspect of the present invention, a method for preparing an optical device is provided, for preparing the above optical device, the method comprising:

[0018] providing a first substrate, a second substrate, a third substrate and a fourth substrate;

[0019] Spin-coating a photo-controlled alignment agent on one side of the first substrate, one side of the second substrate, one side of the third substrate, and one side of the fourth substrate, and drying the same;

[0020] The first substrate and the second substrate are arranged opposite to each other to form a first liquid crystal empty cell, and the third substrate and the fourth substrate are arranged opposite to each other to form a second liquid crystal empty cell, wherein the side of the first substrate coated with the photo-controlled alignment agent is opposite to the side of the second substrate coated with the photo-controlled alignment agent, and the side of the third substrate coated with the photo-controlled alignment agent is opposite to the side of the fourth substrate coated with the photo-controlled alignment agent;

[0021] Irradiating the first liquid crystal cell and the second liquid crystal cell with preset polarized light, so that the light-controlled alignment agent in the first liquid crystal cell encodes a vortex phase of q=-0.5, and the light-controlled alignment agent in the second liquid crystal cell encodes a geometric phase of a grating;

[0022] Liquid crystal is poured into the first liquid crystal empty cell and the second liquid crystal empty cell and stacked to form the optical device.

[0023] According to another aspect of the present invention, there is provided a polarization measurement device, comprising a light source, the above optical device and an imaging unit sequentially arranged along an optical axis;

[0024] The light source is used to emit a polarized light beam to be detected;

[0025] The polarized light beam incident on the optical device generates three diffraction patterns, wherein the middle zero-order diffraction pattern reveals the amplitude ratio of the orthogonal circularly polarized light, and the positive and negative first-order diffraction patterns represent the phase difference of the circularly polarized light;

[0026] The imaging unit is used to receive the three diffraction patterns and calculate the polarization state of the polarized light based on the diffraction patterns.

[0027] An optical device provided by an embodiment of the present invention comprises a first liquid crystal box and a second liquid crystal box which are stacked; the first liquid crystal box comprises a first substrate, a second substrate and a first liquid crystal layer located between the first substrate and the second substrate, a first orientation layer is arranged on a side of the first substrate close to the second substrate, a second orientation layer is arranged on a side of the second substrate close to the first substrate, and the first orientation layer and the second orientation layer control the arrangement direction of liquid crystal molecules in the first liquid crystal layer; the second liquid crystal box comprises a third substrate, a fourth substrate and a second liquid crystal layer located between the third substrate and the fourth substrate, a third orientation layer is arranged on a side of the third substrate close to the fourth substrate, a fourth orientation layer is arranged on a side of the fourth substrate close to the third substrate, and the third orientation layer and the fourth orientation layer control the arrangement direction of liquid crystal molecules in the second liquid crystal layer; wherein the first orientation layer and the second orientation layer encode a vortex phase of q=-0.5, and the third orientation layer and the fourth orientation layer encode a geometric phase of a grating. The optical device provided by the embodiment of the present invention can be used for polarization measurement. When a polarized light beam is incident on the optical device, the first liquid crystal cell can characterize the phase difference of the circularly polarized light, and the second liquid crystal cell can characterize the amplitude ratio of the circularly polarized light. The amplitude ratio and phase difference of the orthogonal circularly polarized light are revealed according to the diffraction pattern to determine the polarization state of the incident polarized light beam. The optical device can be used in a full liquid crystal polarimeter with a total thickness of less than 1.2 mm. The polarimeter can be electrically tuned and is therefore suitable for broadband Stokes measurements from visible light to near infrared. By changing the thickness of the liquid crystal layer, the adjustable range of the operating frequency band can be further extended. Accurate characterization of SoP using a compact polarimeter is essential for various polarization measurements.

[0028] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A schematic diagram of the structure of an optical device provided by an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the polarization detection principle of an optical device provided in an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of optical characterization of an embodiment of the present invention and an example result diagram;

[0033] Figure 4 A schematic diagram of polarization detection accuracy provided by an embodiment of the present invention;

[0034] Figure 5 A schematic flow chart of a method for preparing an optical device provided in an embodiment of the present invention;

[0035] Figure 6 A schematic structural diagram of a polarization measurement device provided by an embodiment of the present invention;

[0036] Figure 7 A diagram of polarization characterization results provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0038] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0039] Figure 1 A schematic diagram of an optical device structure provided by an embodiment of the present invention, referring to Figure 1The optical device comprises a first liquid crystal cell 10 and a second liquid crystal cell 20 which are stacked; the first liquid crystal cell 10 comprises a first substrate 11, a second substrate 12 and a first liquid crystal layer 13 between the first substrate 11 and the second substrate 12; a first orientation layer 14 is arranged on the side of the first substrate 11 close to the second substrate 12; a second orientation layer 15 is arranged on the side of the second substrate 12 close to the first substrate 11; the first orientation layer 14 and the second orientation layer 15 control the arrangement direction of the liquid crystal molecules in the first liquid crystal layer 13; the second liquid crystal cell 20 comprises a third substrate 21 , a fourth substrate 22 and a second liquid crystal layer 23 located between the third substrate 21 and the fourth substrate 22, a third orientation layer 24 is arranged on the side of the third substrate 21 close to the fourth substrate 22, and a fourth orientation layer 25 is arranged on the side of the fourth substrate 22 close to the third substrate 21, the third orientation layer 24 and the fourth orientation layer 25 control the arrangement direction of liquid crystal molecules in the second liquid crystal layer 23; wherein the first orientation layer 14 and the second orientation layer 15 encode a vortex phase of q=-0.5, and the third orientation layer 24 and the fourth orientation layer 25 encode the geometric phase of the grating.

[0040] Among them, the first substrate 11, the second substrate 12, the third substrate 21 and the fourth substrate 22 all include flexible substrates or rigid substrates with a light transmittance greater than or equal to 85%. Exemplarily, the substrate material may include quartz glass or ordinary glass with ITO coated on the surface. The first orientation layer 14 and the second orientation layer 15 are parallel optical orientation layers, and the third orientation layer 24 and the fourth orientation layer 25 are parallel optical orientation layers. The optical orientation layer is written with an orientation pattern that controls the liquid crystal molecules to be arranged in a specific manner, which can be achieved by optical orientation. The optical orientation layer has an in-plane parallel anchoring effect on the liquid crystal molecules in the corresponding liquid crystal layer, so that the arrangement of the liquid crystal molecules adjacent to it is consistent with the orientation pattern of the optical orientation layer. Under the action of an external electric field, the liquid crystal molecules deflect as the electric field increases, and are finally arranged along the direction of the electric field. At the same time, the liquid crystal molecules will follow the molecular orientation of the optical orientation layer, thereby carrying a fixed phase. The external electric field only changes the efficiency of the optical device and has no effect on the phase.

[0041] In a specific implementation, when an external electric field is applied to the optical device, the optical device can be directly set in the external electric field. In another embodiment, optionally, the first liquid crystal box also includes a first electrode layer arranged on one side of the first substrate and a second electrode layer arranged on one side of the second substrate. When a preset voltage is loaded between the first electrode layer and the second electrode layer, an electric field is formed to control the deflection of liquid crystal molecules in the first liquid crystal layer; the second liquid crystal box also includes a third electrode layer arranged on one side of the third substrate and a fourth electrode layer arranged on one side of the fourth substrate. When a preset voltage is loaded between the third electrode layer and the fourth electrode layer, an electric field is formed to control the deflection of liquid crystal molecules in the second liquid crystal layer.

[0042] Optionally, the materials of the first orientation layer 14, the second orientation layer 15, the third orientation layer 24 and the fourth orientation layer 25 include at least one of a photo-crosslinking material, a photodegradable material and a photoinduced cis-trans isomerization material. Exemplarily, SD1 is a rod-shaped molecule whose asymmetric molecular structure causes it to have the characteristic of dichroic absorption, that is, the absorptivity in the long axis direction is higher than that in the short axis direction. Under the irradiation of polarized light such as ultraviolet light, the long axis of the SD1 molecule tends to be arranged perpendicular to the linear polarization direction of the irradiated light, thereby obtaining a stable orientation configuration. The orientation order of the SD1 molecule can be transferred to the liquid crystal molecules through intermolecular interactions, thereby controlling the orientation of the liquid crystal molecules and realizing various patterned liquid crystal orientations. In addition to SD1, photosensitive orientation materials such as Brilliant Yellow can also be used as photo-orientation layer materials.

[0043] Optionally, the first liquid crystal layer 13 and the second liquid crystal layer 23 can be made of E7 or other commonly used positive nematic liquid crystal materials. The light alignment area resolution of the first liquid crystal cell 10 and the second liquid crystal cell 20 is 1 μm to 2 μm, and the thickness of the first liquid crystal cell 10 and the second liquid crystal cell 20 is 4 μm to 6 μm, which can be designed according to actual conditions during implementation.

[0044] Optionally, a polarized light beam is incident on an optical device, the first liquid crystal box is used to characterize the phase difference of the circularly polarized light, the second liquid crystal box is used to characterize the amplitude ratio of the circularly polarized light, and the amplitude ratio and phase difference of the orthogonal circularly polarized light are revealed according to the diffraction pattern to determine the polarization state of the incident polarized light beam.

[0045] Figure 2 Schematic diagram of polarization detection principle of an optical device provided in an embodiment of the present invention, refer to Figure 2 , a polarimeter 1 is formed by using the optical device provided by the embodiment of the present invention, wherein the polarimeter 1 includes a first liquid crystal cell 10 (q-plate), a second liquid crystal cell 20 (liquid crystal polarization grating LCPG) and a polarizer 30 whose polarization direction is along the y direction. When a polarized light beam enters the polarimeter 1, it will be diffracted into three levels of light spots, -1 level, 0 level, and +1 level corresponding to 5, 6, and 7 respectively. A notch will be generated for the 0th order diffracted light, and the direction of the notch is used to characterize the phase difference of the circular polarization basis of the incident polarized light.

[0046] The technical solution of the embodiment of the present invention designs a specific arrangement of liquid crystal molecules and uses a polarization mask exposure system to transfer the liquid crystal molecular orientation to the bottom photo-alignment layer. Due to the existence of intermolecular forces, the arrangement of liquid crystal molecules in the liquid crystal layer will follow the arrangement of molecules in the bottom alignment layer. Figure 2The all-liquid crystal polarimeter shown has a total thickness of less than 1.2 mm. It consists of an LC (liquid crystal) q-plate, an LCPG and a y-polarizer. The polarimeter can be electrically tuned and is therefore suitable for broadband Stokes measurements from the visible to the near-infrared. The adjustable range of the operating frequency band can be further extended by adjusting the LC thickness. Accurate characterization of the SoP using a compact polarimeter is essential for various polarization measurements. The accuracy of the proposed polarimeter is comparable to that of commercial polarimeters. The feasibility of polarization imaging using a patterned phase retarder is verified by introducing an LC q-plate array. The Rayleigh-Sommerfeld vector diffraction theory can also be used to simulate the LC polarization for polarization imaging, and an extremely high consistency between the input polarization and the measured value is demonstrated. The accuracy of polarization imaging can be further improved by pre-calibration or in combination with a deep convolutional neural network. The resolution of polarization imaging can be improved by reducing the size of a single q-plate.

[0047] Figure 3 Schematic diagrams and example result diagrams of the optical characterization of the embodiments of the present invention. a and b are phase schematic diagrams of the LC q-plate and the orthogonal polarization microscopy results, c and d are phase schematic diagrams of the LCPG and the orthogonal polarization microscopy results, and the scale of the picture is 200μm. e is the relationship between the operating voltage and diffraction efficiency of the characterized liquid crystal element. Under the voltage of 0 to 10V, the highest points of diffraction efficiency corresponding to different wavelengths are also inconsistent. The solid line represents the highest value of the diffraction efficiency and is also the operating voltage of the LC q-plate, while the dotted line represents half of the highest value of the diffraction efficiency and is also the operating voltage of the LCPG. f is the diffraction result at different wavelengths when linearly polarized incident, verifying that the optical device provided by the embodiment of the present invention can be applied at 470nm to 1100nm.

[0048] Figure 4Schematic diagram of polarization detection accuracy provided by an embodiment of the present invention. The center of the figure is the Poincare sphere, and each point on the sphere can be used to describe any polarization state. In order to verify the accuracy of the proposed LC cascade polarimeter, the rotating wave plate converts the incident linear polarization into a certain SoP. The half-wave plate is rotated from 0° to 90° in increments of 15° to obtain six individual points on the equator, while the quarter-wave plate is rotated from -45° to 45° at intervals of 15° to produce two opposite circular polarization states and four elliptical polarization states. All generated SoPs are detected by the LC cascade polarimeter and the commercial polarimeter for reference. The measurement results are marked on the Poincare sphere. Observe the close match between the star (polarimeter proposed in the embodiment of the present invention) and the point (commercial polarimeter). The calculated root mean square errors (RMSE) of S1, S2 and S3 are 0.052, 0.066 and 0.045 respectively. According to the spherical coordinates (u, v) of the preset SoP, the theoretical diffraction pattern is calculated using the Rayleigh-Sommerfeld vector diffraction theory. The experimental results are in good agreement with the simulation results, demonstrating the accuracy of the LC polarization detection proposed in the embodiment of the present invention.

[0049] Figure 5 A schematic diagram of a method for preparing an optical device provided in an embodiment of the present invention is provided, which is used to prepare the optical device provided in the above embodiment, with reference to Figure 5 , the preparation method comprises:

[0050] S110 , providing a first substrate, a second substrate, a third substrate and a fourth substrate.

[0051] The first substrate, the second substrate, the third substrate and the fourth substrate all include flexible substrates or rigid substrates with a light transmittance greater than or equal to 85%. For example, the substrate material may include quartz glass or ordinary glass coated with ITO on the surface.

[0052] S120 , spin-coating a photo-controlled alignment agent on one side of the first substrate, one side of the second substrate, one side of the third substrate, and one side of the fourth substrate, and drying the spin-coating.

[0053] Optionally, before forming the photo-alignment film, in order to increase the wettability and adhesion between the photo-alignment film and the corresponding substrate, ultrasonic cleaning is performed with ITO (indium tin oxide conductive film) washing liquid for 30 minutes, and then washed twice with ultrapure water, each for 10 minutes. After drying in a 120°C oven for 40 minutes, UVO (ultraviolet ozone) cleaning is performed for 30 minutes.

[0054] The spin coating parameters for spin coating the photo-controlled alignment agent on one side of the substrate can be: spin coating the photo-controlled alignment material on the cleaned glass substrate at a speed of 800 rpm (5s) + 3000 rpm (35s). Optionally, after spin coating, annealing is performed on a 100°C temperature table for 10 minutes to evaporate the solvent and form a uniform alignment film.

[0055] S130, the first substrate and the second substrate are arranged opposite to each other to form a first liquid crystal empty box, and the third substrate and the fourth substrate are arranged opposite to each other to form a second liquid crystal empty box, wherein the side of the first substrate coated with the photo-control orientation agent is opposite to the side of the second substrate coated with the photo-control orientation agent, and the side of the third substrate coated with the photo-control orientation agent is opposite to the side of the fourth substrate coated with the photo-control orientation agent.

[0056] The process of preparing the empty liquid crystal box may be: using UV glue configured with spacers to prepare a liquid crystal box of a set thickness, and curing under UV to form a firm liquid crystal box.

[0057] S140, irradiating the first liquid crystal empty cell and the second liquid crystal empty cell with preset polarized light, so that the light-controlled alignment agent in the first liquid crystal empty cell encodes a vortex phase of q=-0.5, and the light-controlled alignment agent in the second liquid crystal cell encodes a geometric phase of the grating.

[0058] The writing of liquid crystal orientation patterns is achieved through a digital micromirror device (DMD) optical orientation system. DMD optical orientation is a non-contact liquid crystal orientation technology that can write any predefined pattern distribution information generated by a computer.

[0059] S150, pouring liquid crystal into the first liquid crystal empty cell and the second liquid crystal empty cell and stacking them to form an optical device.

[0060] The process of pouring the liquid crystal material may be: pouring the liquid crystal material into the empty liquid crystal box at the clearing point by using the capillary action of the liquid crystal material, and slowly cooling it down to room temperature. For example, the liquid crystal can be poured on a hot plate at 70° C., and then slowly cooled down to room temperature.

[0061] Figure 6 A schematic diagram of a polarization measurement device provided by an embodiment of the present invention, referring to Figure 6 The polarization measurement device includes a light source 100, an optical device 200 provided in the above embodiment, and an imaging unit 300, which are sequentially arranged along an optical axis; the light source 100 is used to emit a polarized light beam to be detected; the polarized light beam is incident on the optical device 200 to generate three diffraction patterns, the middle zero-order diffraction pattern reveals the amplitude ratio of the orthogonal circularly polarized light, and the positive and negative first-order diffraction patterns represent the phase difference of the circularly polarized light; the imaging unit 300 is used to receive the three diffraction patterns and calculate the polarization state of the polarized light based on the diffraction patterns.

[0062] The light source 100 may be a light emitting diode (LED), and the imaging unit 300 may be a CCD camera. Figure 6, the polarization measurement device may also include a beam expander (BE) 400, a filter 500, an x-direction polarizer (x-LP) 600, a lens (Lens) 700, and a y-direction polarizer (y-LP) 700. The light beam emitted by the LED 100 is expanded and collimated using a beam expander (BE) 400. The expanded light passes through the filter (490nm filter) 400 to narrow the wavelength range of the light. The q-plate array is used to obtain phase information at different positions. For ease of demonstration, the diffraction pattern is collected by the lens 700 and recorded by the CCD 300. It is worth noting that inserting a lens 700 between the q-plate array and the LCPG is an experimental device for polarization imaging. Here, in order to obtain a clear image for polarization analysis, the q-plate array is placed before the lens and imaged onto the CCD. The LCPG is used to separate the image into three images. Therefore, the thickness of polarization imaging is no longer as thin as 1.2 mm.

[0063] Alternatively, the introduction of thickness limitations mainly relies on bulky lenses, which can be replaced by polarization-independent flat lenses.

[0064] Figure 7 Polarization characterization result diagram provided for an embodiment of the present invention. If the q-plate is changed to a q-plate array, the polarimeter can be used to identify spatially varying polarization fields, in other words, it is suitable for polarization imaging. A portion of the q-plate array is shown in a, which means that the resolution of polarization imaging is 100μm. A patterned phase retarder b is manufactured in an embodiment of the present invention to produce a specific patterned polarization distribution. The polarization ellipse is characterized by a commercial polarimeter. The dark and light ellipses represent left-handed and right-handed polarizations, respectively. According to the diffraction pattern c, r and Δφ can be calculated point by point in a similar manner to uniform polarization detection. d shows the polarization distribution reconstructed from the results measured by the LC cascade polarimeter, which is consistent with the results shown in b. In order to further verify the versatility of the LC cascade polarimeter, it is used to measure the polarization distribution of light passing through a ruler. e shows the interference color of a ruler with a pair of crossed polarizers, which is caused by stress-induced birefringence. We selected a small area, and f shows the corresponding birefringence color change under a polarizing microscope. According to the diffraction pattern g, the polarization distribution is calculated, as shown in h, which is consistent with the change in the color of the interferent.

[0065] The polarization measurement device of the embodiment of the present invention provides an application of the optical device provided by the above embodiment, namely, an all-liquid crystal polarimeter for polarization detection and imaging. It is composed of a cascade of an LC q-plate and an LCPG. By applying appropriate voltages to individual elements, the matching and mismatching of the half-wave conditions are maintained respectively. The amplitude contrast and phase difference between two orthogonal spins are read directly from the diffraction pattern. The intensity contrast between the ±1-order diffraction spots and the rotation angle of the dark splitting of the 0-order spot reveal the amplitude contrast and phase difference respectively. Broadband tunability from visible light to near-infrared is demonstrated. When characterizing feature points on the Poincare sphere, the accuracy is comparable to that of a commercial polarimeter. In addition, polarization imaging has been verified on both patterned phase retarders and birefringence rulers. It provides a practical solution for broadband polarization detection, overcomes the shortcomings of traditional technologies, and may promote the advancement of polarization spectroscopy, elliptical polarization, and many other advanced photonic applications.

[0066] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An optical device, characterized in that: It includes a first liquid crystal cell and a second liquid crystal cell which are stacked; The first liquid crystal box comprises a first substrate, a second substrate and a first liquid crystal layer located between the first substrate and the second substrate, a first alignment layer is disposed on a side of the first substrate close to the second substrate, and a second alignment layer is disposed on a side of the second substrate close to the first substrate, and the first alignment layer and the second alignment layer control the arrangement direction of liquid crystal molecules in the first liquid crystal layer; The second liquid crystal box comprises a third substrate, a fourth substrate and a second liquid crystal layer located between the third substrate and the fourth substrate, a third alignment layer is arranged on a side of the third substrate close to the fourth substrate, and a fourth alignment layer is arranged on a side of the fourth substrate close to the third substrate, and the third alignment layer and the fourth alignment layer control the arrangement direction of liquid crystal molecules in the second liquid crystal layer; The first orientation layer and the second orientation layer encode the vortex phase of q=-0.5, and the third orientation layer and the fourth orientation layer encode the geometric phase of the grating.

2. The optical device according to claim 1, characterized in that A polarized light beam is incident on the optical device, the first liquid crystal box is used to characterize the phase difference of the circularly polarized light, and the second liquid crystal box is used to characterize the amplitude ratio of the circularly polarized light. The amplitude ratio and phase difference of the orthogonal circularly polarized light are revealed according to the diffraction pattern to determine the polarization state of the incident polarized light beam.

3. The optical device according to claim 1, characterized in that: The first substrate, the second substrate, the third substrate and the fourth substrate each include a flexible substrate or a rigid substrate having a light transmittance greater than or equal to 85%.

4. The optical device according to claim 1, characterized in that The first liquid crystal cell further includes a first electrode layer disposed on one side of the first substrate and a second electrode layer disposed on one side of the second substrate; The second liquid crystal cell further includes a third electrode layer disposed on one side of the third substrate and a fourth electrode layer disposed on one side of the fourth substrate.

5. The optical device according to claim 1, characterized in that: The materials of the first alignment layer, the second alignment layer, the third alignment layer and the fourth alignment layer include at least one of a photo-crosslinking material, a photo-degradable material and a photo-induced cis-trans isomerization material.

6. The optical device according to claim 1, characterized in that: The liquid crystal material of the first liquid crystal layer and the second liquid crystal layer is positive liquid crystal. Under the action of an external electric field, the liquid crystal molecules are deflected as the electric field increases, and are finally arranged along the direction of the electric field. At the same time, the liquid crystal molecules will follow the molecular orientation of the light-controlled orientation layer to carry a fixed phase. The external electric field only changes the efficiency of the optical device and has no effect on the phase.

7. The optical device according to claim 1, characterized in that: The light alignment area resolution of the first liquid crystal cell and the second liquid crystal cell is 1 μm to 2 μm.

8. The optical device according to claim 1, characterized in that: The thickness of the first liquid crystal cell and the second liquid crystal cell is 4 μm to 6 μm.

9. A method for preparing an optical device, characterized in that: Used to prepare the optical device according to any one of claims 1 to 8, the preparation method comprising: providing a first substrate, a second substrate, a third substrate and a fourth substrate; Spin-coating a photo-controlled alignment agent on one side of the first substrate, one side of the second substrate, one side of the third substrate, and one side of the fourth substrate, and drying the same; The first substrate and the second substrate are arranged opposite to each other to form a first liquid crystal empty cell, and the third substrate and the fourth substrate are arranged opposite to each other to form a second liquid crystal empty cell, wherein the side of the first substrate coated with the photo-controlled alignment agent is opposite to the side of the second substrate coated with the photo-controlled alignment agent, and the side of the third substrate coated with the photo-controlled alignment agent is opposite to the side of the fourth substrate coated with the photo-controlled alignment agent; Irradiating the first liquid crystal cell and the second liquid crystal cell with preset polarized light, so that the light-controlled alignment agent in the first liquid crystal cell encodes a vortex phase of q=-0.5, and the light-controlled alignment agent in the second liquid crystal cell encodes a geometric phase of a grating; Liquid crystal is poured into the first liquid crystal empty cell and the second liquid crystal empty cell and stacked to form the optical device.

10. A polarization measurement device, characterized in that: It comprises a light source arranged in sequence along an optical axis, an optical device according to any one of claims 1 to 8, and an imaging unit; The light source is used to emit a polarized light beam to be detected; The polarized light beam incident on the optical device generates three diffraction patterns, wherein the middle zero-order diffraction pattern reveals the amplitude ratio of the orthogonal circularly polarized light, and the positive and negative first-order diffraction patterns represent the phase difference of the circularly polarized light; The imaging unit is used to receive the three diffraction patterns and calculate the polarization state of the polarized light based on the diffraction patterns.

Images