Optical device, method for manufacturing an optical device, and polarization measuring device

Abstract

The application 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 arranged in a laminated mode. The first liquid crystal box comprises a first substrate, a second substrate and a first liquid crystal layer. The arrangement direction of liquid crystal molecules in the first liquid crystal layer is controlled by a first alignment layer and a second alignment layer. The second liquid crystal box comprises a third substrate, a fourth substrate and a second liquid crystal layer. The arrangement direction of liquid crystal molecules in the second liquid crystal layer is controlled by a third alignment layer and a fourth alignment layer. The first alignment layer and the second alignment layer encode a vortex phase of q=-0.5, and the third alignment layer and the fourth alignment layer encode a geometric phase of a grating. The optical device provided by the application can overcome the limitations of a conventional polarization testing device, such as a narrow testing waveband and a lack of compactness, and realizes polarization detection covering visible light to near infrared. Furthermore, an image form of polarization analysis is constructed.

Description

Technical Field

[0001] This 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 measurement device. Background Technology

[0002] Polarization is a vector property of electromagnetic waves, describing the direction of the electric component oscillation of an electric field, and plays a crucial role in optics. The polarization state (SoP) determines the interaction of light with anisotropic, chiral, and magnetized matter, thus forming the basis of many optical technologies such as polarization spectroscopy, ellipsometric measurement, sensing, and imaging.

[0003] The most direct method for 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 employ spatial beam splitting techniques (spatial segmentation) or rotating waveplates (time segmentation) to perform a series of intensity measurements. Therefore, complex optical setups are usually required, necessitating precise adjustments and resulting in bulky and time-consuming solutions. Furthermore, the narrow-bandwidth limitations of individual elements such as waveplates significantly hinder the broadband feasibility of traditional polarimeters. Simultaneously, existing commercial polarization cameras struggle to achieve 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] This invention provides an optical device, a method for fabricating the optical device, and a polarization measurement device. This optical device can overcome the limitations of traditional polarization testing devices, such as narrow test bands and insufficient compactness, and realize polarization detection covering visible light to near-infrared light, and construct an image-based polarization analysis method.

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

[0006] The first liquid crystal cell includes 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 the side of the first substrate closer to the second substrate, and a second alignment layer is disposed on the side of the second substrate closer to the first substrate. The first alignment layer and the second alignment layer control the alignment direction of liquid crystal molecules in the first liquid crystal layer.

[0007] The second liquid crystal cell includes 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 disposed on the side of the third substrate near the fourth substrate, and a fourth alignment layer is disposed on the side of the fourth substrate near the third substrate. The third alignment layer and the fourth alignment layer control the alignment direction of liquid crystal molecules in the second liquid crystal layer.

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

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

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

[0011] Optionally, 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;

[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 orientation layer, the second orientation layer, the third orientation layer, and the fourth orientation layer include at least one of photocrosslinking materials, photodegradable materials, and photoinduced cis-trans isomers.

[0014] Optionally, the liquid crystal materials of the first liquid crystal layer and the second liquid crystal layer are positive liquid crystals. Under the action of an external electric field, the liquid crystal molecules deflect as the electric field increases and eventually align along the direction of the electric field. At the same time, the liquid crystal molecules will follow the orientation of the molecules in the light-controlled alignment 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 resolution of the light alignment region of the first liquid crystal cell and the second liquid crystal cell is 1μm to 2μm.

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

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

[0018] A first substrate, a second substrate, a third substrate, and a fourth substrate are provided;

[0019] A photo-aligning agent is spin-coated onto 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 then dried.

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

[0021] The first liquid crystal cell and the second liquid crystal cell are irradiated with preset polarized light, so that the photo-aligning agent in the first liquid crystal cell encodes a vortex phase of q = -0.5, and the photo-aligning agent in the second liquid crystal cell encodes the geometric phase of the grating.

[0022] Liquid crystals are filled into the first liquid crystal cell and the second liquid crystal cell and stacked to form the optical device.

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

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

[0025] The polarized beam incident on the optical device produces three diffraction patterns. The middle zero-order diffraction pattern reveals the amplitude ratio of orthogonally circularly polarized light, while the positive and negative first-order diffraction patterns characterize the phase difference of 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] The optical device provided in this embodiment of the invention includes a first liquid crystal cell and a second liquid crystal cell stacked together. The first liquid crystal cell includes 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 the side of the first substrate near the second substrate, and a second alignment layer is disposed on the side of the second substrate near the first substrate. The first alignment layer and the second alignment layer control the alignment direction of liquid crystal molecules in the first liquid crystal layer. The second liquid crystal cell includes 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 disposed on the side of the third substrate near the fourth substrate, and a fourth alignment layer is disposed on the side of the fourth substrate near the third substrate. The third alignment layer and the fourth alignment layer control the alignment direction of liquid crystal molecules in the second liquid crystal layer. The first alignment layer and the second alignment layer encode a vortex phase of q = -0.5, and the third alignment layer and the fourth alignment layer encode the geometric phase of the grating. The optical device provided in this invention can be used for polarization measurement. When a polarized beam is incident on the optical device, a first liquid crystal cell can characterize the phase difference of the circularly polarized light, and a second liquid crystal cell can characterize the amplitude ratio of the circularly polarized light. The amplitude ratio and phase difference of orthogonally polarized light are revealed based on the diffraction pattern to determine the polarization state of the incident polarized beam. This optical device can be used in a full liquid crystal polarization measuring instrument with a total thickness of less than 1.2 mm. The polarization measuring instrument is electrically tunable, thus suitable for broadband Stokes measurements from visible light to near-infrared. By changing the thickness of the liquid crystal layer, the tunable range of the operating frequency band can be further extended. Accurate characterization of SoP using a compact polarimeter is crucial for various polarization measurements.

[0028] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

[0032] Figure 3 These are schematic diagrams and example results of optical characterization according to embodiments of the present invention;

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

[0034] Figure 5 This is a schematic flowchart illustrating a method for fabricating an optical device according to an embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram of the structure of a polarization measurement device provided in an embodiment of the present invention;

[0036] Figure 7 The polarization characterization results are shown in the figure provided in the embodiment of the present invention. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort 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, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0039] Figure 1 This is a schematic diagram of an optical device structure provided in an embodiment of the present invention, with reference to... Figure 1The optical device includes a first liquid crystal cell 10 and a second liquid crystal cell 20 stacked together. The first liquid crystal cell 10 includes a first substrate 11, a second substrate 12, and a first liquid crystal layer 13 located between the first substrate 11 and the second substrate 12. A first alignment layer 14 is disposed on the side of the first substrate 11 near the second substrate 12, and a second alignment layer 15 is disposed on the side of the second substrate 12 near the first substrate 11. The first alignment layer 14 and the second alignment layer 15 control the alignment direction of the liquid crystal molecules in the first liquid crystal layer 13. The second liquid crystal cell 20 includes a third substrate 21. The third substrate 21 and the fourth substrate 22 are located between the third substrate 21 and the fourth substrate 22. A third alignment layer 24 is disposed on the side of the third substrate 21 near the fourth substrate 22, and a fourth alignment layer 25 is disposed on the side of the fourth substrate 22 near the third substrate 21. The third alignment layer 24 and the fourth alignment layer 25 control the alignment direction of the liquid crystal molecules in the second liquid crystal layer 23. The first alignment layer 14 and the second alignment layer 15 encode the vortex phase with q = -0.5, and the third alignment layer 24 and the fourth alignment layer 25 encode the geometric phase of the grating.

[0040] The first substrate 11, second substrate 12, third substrate 21, and fourth substrate 22 all include flexible 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. The first alignment layer 14 and the second alignment layer 15 are parallel light alignment layers, and the third alignment layer 24 and the fourth alignment layer 25 are also parallel light alignment layers. The light alignment layers are inscribed with alignment patterns that control the specific arrangement of liquid crystal molecules, which can be achieved through photo-controlled alignment. The light alignment layers have an in-plane parallel anchoring effect on the liquid crystal molecules in the corresponding liquid crystal layers, thereby ensuring that the arrangement of the adjacent liquid crystal molecules is consistent with the alignment pattern of the light alignment layers. Under the action of an applied electric field, the liquid crystal molecules deflect as the electric field increases and eventually align along the direction of the electric field. Simultaneously, the liquid crystal molecules align with the orientation of the molecules in the photo-controlled alignment layers, thus carrying a fixed phase. The applied electric field only changes the efficiency of the optical device and has no effect on the phase.

[0041] In a specific implementation, when applying an external electric field to the optical device, the optical device can be directly placed in the external electric field. In another embodiment, optionally, 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. When a preset voltage is applied 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 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. When a preset voltage is applied 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 alignment layer 14, the second alignment layer 15, the third alignment layer 24, and the fourth alignment layer 25 include at least one of photocrosslinking materials, photodegradable materials, and photoinduced cis-trans isomers. For example, SD1 is a rod-shaped molecule whose asymmetric molecular structure results in dichroic absorption, meaning its absorptivity along the long axis is higher than that along the short axis. Under isopolarized ultraviolet light irradiation, the long axis of the SD1 molecules tends to align perpendicular to the linear polarization direction of the irradiated light, thereby achieving a stable alignment configuration. The orientational order of the SD1 molecules can be transferred to the liquid crystal molecules through intermolecular interactions, thereby controlling the orientation of the liquid crystal molecules and achieving various patterned liquid crystal orientations. Besides SD1, photosensitive alignment materials such as Brilliant Yellow can also be used as photoalignment 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 optical alignment region resolution of the first liquid crystal cell 10 and the second liquid crystal cell 20 is 1μm to 2μm, and the thickness of the first liquid crystal cell 10 and the second liquid crystal cell 20 is 4μm to 6μm. In specific implementations, the design can be tailored to the actual situation.

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

[0045] Figure 2 This is a schematic diagram illustrating the polarization detection principle of an optical device provided in an embodiment of the present invention. (Refer to...) Figure 2 A polarization measuring instrument 1 is formed using the optical devices provided in this embodiment of the invention. The polarization measuring instrument 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 with the polarization direction along the y-direction. When a polarized beam is incident on the polarization measuring instrument 1, it will be diffracted into three orders of light spots. The -1st, 0th, and +1st orders correspond to the 5th, 6th, and 7th orders, respectively. A notch will be generated for the 0th order diffracted light. The orientation of the notch is used to characterize the phase difference of the circular polarization base of the incident polarized light.

[0046] The technical solution of this invention involves designing a specific liquid crystal molecule arrangement and using a polarizing mask exposure system to transfer the liquid crystal molecule alignment 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 proposed all-liquid crystal polarimeter 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 is electrically tunable, making it suitable for broadband Stokes measurements from the visible to near-infrared range. The adjustable range of the operating frequency band can be further extended by adjusting the LC thickness. Accurate characterization of SoP using a compact polarimeter is crucial for various polarization measurements. The proposed polarimeter achieves accuracy comparable to commercial polarimeters. The feasibility of using a patterned phase retarder for polarization imaging was verified by introducing an LC q-plate array. Rayleigh-Sommerfeld vector diffraction theory was also used to simulate LC polarization for polarization imaging, demonstrating extremely high consistency between the input polarization and the measured values. The accuracy of polarization imaging can be further improved through pre-calibration or by combining it 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 These are schematic diagrams and example results of optical characterization according to embodiments of the present invention. a and b are phase diagrams of the LC q-plate and orthogonal polarized light microscopy results; c and d are phase diagrams of the LCPG and orthogonal polarized light microscopy results. The scale bar of the images is 200 μm. e shows the relationship between the operating voltage and diffraction efficiency of the liquid crystal element. Under voltages of 0–10 V, the points of highest diffraction efficiency for different wavelengths are not consistent. The solid line represents the highest diffraction efficiency value, which is also the operating voltage of the LC q-plate, while the dashed line represents half of the highest diffraction efficiency value, which is also the operating voltage of the LCPG. f shows the diffraction results at different wavelengths under linearly polarized incident light, verifying that the optical device provided in this embodiment of the present invention can be applied in the range of 470 nm to 1100 nm.

[0048] Figure 4This diagram illustrates the polarization detection accuracy provided in an embodiment of the invention. The center of the diagram is a Poincaré sphere, where each point can be used to describe any polarization state. To verify the accuracy of the proposed LC cascade polarimeter, rotating waveplates convert the incident linear polarization into a specific SoP (Solar Point). A half-wave plate rotates from 0° to 90° in 15° increments to obtain six individual points on the equator, while a quarter-wave plate rotates from -45° to 45° in 15° intervals to generate two opposite circular polarization states and four ellipsoidal polarization states. All generated SoPs are detected by the LC cascade polarimeter and a commercial polarimeter for reference. The measurement results are marked on the Poincaré sphere. The close matching between the stars (the polarization measuring instrument proposed in this embodiment) and the points (commercial polarimeters) is observed. The calculated root mean square errors (RMSE) of S1, S2, and S3 are 0.052, 0.066, and 0.045, respectively. The theoretical diffraction pattern is calculated using Rayleigh-Sommerfeld vector diffraction theory based on the spherical coordinates (u, v) of the preset SoP. The experimental results agree well with the simulation results, demonstrating the accuracy of the LC polarization detection proposed in this embodiment of the invention.

[0049] Figure 5 This is a schematic flowchart of a method for fabricating an optical device according to an embodiment of the present invention, used to fabricate the optical device provided in the above embodiment. (Refer to...) Figure 5 The preparation method includes:

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

[0051] The first substrate, second substrate, third substrate, and 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 with an ITO coating on its surface.

[0052] S120: Spin-coat a photo-aligning 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 then dry them.

[0053] Optionally, before forming the photoalignment film, to increase the wettability and adhesion between the photoalignment film and the corresponding substrate, the film is ultrasonically cleaned for 30 minutes with ITO (indium tin oxide) cleaning solution, and then cleaned twice with ultrapure water for 10 minutes each time. After drying in an oven at 120°C for 40 minutes, it is then cleaned with UVO (ultraviolet ozone) for 30 minutes.

[0054] The spin-coating parameters for spin-coating the photo-aligning agent on one side of the substrate can be as follows: spin-coat the photo-aligning material onto a clean glass substrate at a rotation speed of 800 rpm (5 s) + 3000 rpm (35 s). Optionally, after spin-coating, the substrate can be annealed at 100°C 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 each other to form a first liquid crystal cell. The third substrate and the fourth substrate are arranged opposite each other to form a second liquid crystal cell. The side of the first substrate with the photo-aligning agent spin-coated is opposite to the side of the second substrate with the photo-aligning agent spin-coated, and the side of the third substrate with the photo-aligning agent spin-coated is opposite to the side of the fourth substrate with the photo-aligning agent spin-coated.

[0056] The process for preparing a liquid crystal cell can be as follows: using UV adhesive with spacers, a liquid crystal cell of a set thickness is prepared, and then cured under UV light to form a solid liquid crystal cell.

[0057] S140. Irradiate the first liquid crystal cell and the second liquid crystal cell with preset polarized light, so that the photo-aligning agent in the first liquid crystal cell encodes the vortex phase of q = -0.5, and the photo-aligning agent in the second liquid crystal cell encodes the geometric phase of the grating.

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

[0059] S150. Liquid crystals are filled into the first liquid crystal cell and the second liquid crystal cell and stacked to form an optical device.

[0060] The liquid crystal material filling process can be as follows: utilizing the capillary action of the liquid crystal material, it is filled into the empty liquid crystal cell at the liquid crystal clearing point, and then slowly cooled to room temperature. For example, the liquid crystal filling can be completed on a hot stage at 70°C, and then slowly cooled to room temperature.

[0061] Figure 6 This is a schematic diagram of a polarization measurement device provided in an embodiment of the present invention, with reference 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 arranged sequentially along the 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 orthogonally circularly polarized light, and the positive and negative first-order diffraction patterns characterize the phase difference of 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 can be a light-emitting diode (LED), and the imaging unit 300 can be a CCD camera. (Continue to refer to...) Figure 6The polarization measurement device may also include a beam expander (BE) 400, a filter 500, an x-axis polarizer (x-LP) 600, a lens 700, and a y-axis polarizer (y-LP) 700. The beam emitted by the LED 100 is expanded and collimated using the beam expander (BE) 400. The expanded beam passes through the filter (490nm filter) 400 to narrow the wavelength range of the light. A q-plate array is used to acquire phase information at different locations. For demonstration purposes, the diffraction pattern is collected by the lens 700 and recorded by the CCD 300. Notably, inserting a lens 700 between the q-plate array and the LCPG constitutes the experimental setup for polarization imaging. Here, to obtain a clear image for polarization analysis, the q-plate array is placed in front of the lens and imaged onto the CCD. The LCPG is used to separate the image into three images. Therefore, the thickness of the polarization imaging is no longer as thin as 1.2mm.

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

[0064] Figure 7 The diagram shows the polarization characterization results provided for embodiments of the present invention. If the q-plate is replaced with 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 as a, implying a polarization imaging resolution of 100 μm. An embodiment of the present invention fabricates a patterned phase retarder b to generate a specific patterned polarization distribution. The polarization ellipse is characterized by a commercial polarimeter. Dark and light ellipses represent left-handed and right-handed polarization, respectively. Based on diffraction pattern c, r and Δφ can be calculated point-by-point in a manner similar to that used for uniform polarization detection. d shows the polarization distribution reconstructed from measurements by an LC cascade polarimeter, consistent with the results shown in b. 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 colors of the ruler with a pair of crossed polarizers, caused by stress-induced birefringence. A small area is selected, and f shows the corresponding birefringence color change under a p-polarizing microscope. Based on diffraction pattern g, the polarization distribution is calculated as shown in h, consistent with the color change of the interfering object.

[0065] The polarization measurement device of this invention provides an application based on the optical device provided in the above embodiments, namely a full-liquid crystal polarization measuring instrument for polarization detection and imaging. It is composed of a cascaded LC q-plate and LCPG. Matching and mismatch of half-wave conditions are maintained separately by applying appropriate voltages to individual elements. The amplitude contrast and phase difference between two orthogonal spins are read directly from the diffraction pattern. The intensity contrast between ±1st-order diffraction spots and the rotation angle of the dark split of the 0th-order spot reveal the amplitude contrast and phase difference, respectively. Broadband tunability from visible to near-infrared light is demonstrated. The accuracy is comparable to commercial polarimeters when characterizing feature points on a Poincaré sphere. Furthermore, polarization imaging has been validated on patterned phase retarders and birefringent rulers. It provides a practical solution for broadband polarization detection, overcoming the shortcomings of conventional techniques, and may promote advancements in polarization spectroscopy, elliptometrics, and many other advanced photonic applications.

[0066] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An optical device, characterized in that, It includes a first liquid crystal cell and a second liquid crystal cell stacked together. The first liquid crystal cell includes 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 the side of the first substrate closer to the second substrate, and a second alignment layer is disposed on the side of the second substrate closer to the first substrate. The first alignment layer and the second alignment layer control the alignment direction of liquid crystal molecules in the first liquid crystal layer. The second liquid crystal cell includes 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 disposed on the side of the third substrate near the fourth substrate, and a fourth alignment layer is disposed on the side of the fourth substrate near the third substrate. The third alignment layer and the fourth alignment layer control the alignment direction of liquid crystal molecules in the second liquid crystal layer. The first and second orientation layers encode the vortex phase with q = -0.5, and the third and fourth orientation layers encode the geometric phase of the grating. A polarized beam is incident on the optical device. The first liquid crystal cell is used to characterize the phase difference of the circularly polarized light, and the second liquid crystal cell is used to characterize the amplitude ratio of the circularly polarized light. The amplitude ratio and phase difference of the orthogonally circularly polarized light are revealed according to the diffraction pattern to determine the polarization state of the incident polarized beam.

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

3. 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.

4. The optical device according to claim 1, characterized in that, The materials of the first orientation layer, the second orientation layer, the third orientation layer and the fourth orientation layer include at least one of photocrosslinking materials, photodegradable materials and photoinduced cis-trans isomers.

5. The optical device according to claim 1, characterized in that, The liquid crystal materials of the first liquid crystal layer and the second liquid crystal layer are positive liquid crystals. Under the action of an external electric field, the liquid crystal molecules deflect as the electric field increases and eventually align along the direction of the electric field. At the same time, the liquid crystal molecules will follow the orientation of the molecules in the light-controlled alignment 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.

6. The optical device according to claim 1, characterized in that, The light orientation region resolution of the first liquid crystal cell and the second liquid crystal cell is 1μm~2μm.

7. 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 4μm~6μm.

8. A method for fabricating an optical device, characterized in that, The method for preparing the optical device according to any one of claims 1 to 7 comprises: A first substrate, a second substrate, a third substrate, and a fourth substrate are provided; A photo-aligning agent is spin-coated onto 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 then dried. The first substrate and the second substrate are arranged opposite each other to form a first liquid crystal cell, and the third substrate and the fourth substrate are arranged opposite each other to form a second liquid crystal cell, wherein the side of the first substrate with photo-alignment agent spin-coated is opposite to the side of the second substrate with photo-alignment agent spin-coated, and the side of the third substrate with photo-alignment agent spin-coated is opposite to the side of the fourth substrate with photo-alignment agent spin-coated. The first liquid crystal cell and the second liquid crystal cell are irradiated with preset polarized light, so that the photo-aligning agent in the first liquid crystal cell encodes a vortex phase of q=-0.5, and the photo-aligning agent in the second liquid crystal cell encodes the geometric phase of the grating. Liquid crystals are filled into the first liquid crystal cell and the second liquid crystal cell and stacked to form the optical device.

9. A polarization measurement device, characterized in that, It includes a light source arranged sequentially along the optical axis, an optical device as described in any one of claims 1 to 7, and an imaging unit; The light source is used to emit a polarized beam of light to be detected; The polarized beam incident on the optical device produces three diffraction patterns. The middle zero-order diffraction pattern reveals the amplitude ratio of orthogonally circularly polarized light, while the positive and negative first-order diffraction patterns characterize the phase difference of 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