An SLD circular polarization output device, composite liquid crystal polarization grating and preparation method thereof

Abstract

An SLD circular polarization output device, a composite liquid crystal polarization grating, and a method for making the same belong to the technical field of optical devices, specifically to the technical field of gratings and their preparation processes. To address the significant optical power loss caused by the series connection of multi-stage polarization optical elements and the difficulty of wave plate-type devices in achieving consistent polarization control within the wide spectral range covered by SLDs, the present invention proposes a composite liquid crystal polarization grating, which is formed by gluing together two layers of polarization gratings with different grating periods, one of which has a period that is half that of the other. The present invention also provides an SLD circular polarization output device, which utilizes the composite liquid crystal polarization grating to convert the optical signal generated by a ridge-type tilted SLD into circularly polarized light. The present invention also provides a method for making the composite liquid crystal polarization grating, including the steps of cleaning the glass substrate, spin-coating a light-controlled orientation material, forming gratings of different periods by polarization holographic exposure, injecting liquid crystals, and finally gluing. The method is applicable to the technical field of optical coherence tomography.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical devices, and in particular relates to the technical field of gratings and their preparation processes. Background Art

[0002] Optical Coherence Tomography (OCT), as a non-contact, high-resolution optical imaging method, has been widely used in biomedical imaging, industrial non-destructive testing and other fields. With the continuous improvement of imaging depth and resolution requirements, the performance of the wide-spectrum, low-coherence light source used in the OCT system, especially its polarization characteristics, plays a vital role in imaging quality. Superluminescent Diode (SLD) has become the first choice for the core light source in the OCT system due to its excellent spectral width and coherence control capabilities. However, traditional SLD outputs mostly unpolarized or linearly polarized light. When penetrating complex media such as biological tissues or multi-layered structural materials, it is easily affected by multiple scattering and polarization state changes, resulting in reduced imaging contrast and significant attenuation of deep information signals, which seriously limits the application effect of OCT technology.

[0003] To improve imaging performance in highly scattering media, researchers have gradually introduced polarization control technology, especially the application of circularly polarized light in OCT systems has attracted widespread attention. Due to its spiral wavefront structure, circularly polarized light has a natural ability to distinguish between forward ballistic light and randomly scattered light during propagation. Combined with polarization filtering, it can effectively suppress backscattering noise, thereby improving the image signal-to-noise ratio and structural resolution. In the biomedical field, circularly polarized OCT technology is particularly suitable for the detection of arterial plaques in the cardiovascular system. It can not only enhance the imaging sensitivity of the fiber cap area, but also use its birefringence and depolarization characteristics to identify vulnerable plaques; in industrial inspection, circularly polarized light can be used to penetrate multi-layer transparent structures, such as mobile phone display modules, optical film layers, etc., which can reduce the polarization distortion problem caused by material anisotropy, and can reveal microstructural defects such as microcracks and interface delamination in conjunction with interference signal processing.

[0004] Currently, traditional circularly polarized light generation relies primarily on back-end modulation of linearly polarized light through external polarization components such as quarter-wave plates. Although this approach is relatively simple, it suffers from two major issues: First, the series connection of multiple polarization optical components results in significant optical power loss, including transmittance limitations of the components themselves, incomplete polarization state matching, and multi-interface reflections, which in turn reduces the overall output efficiency of the SLD light source. Second, the phase delay of waveplate-type components is extremely sensitive to wavelength, making it difficult to achieve consistent polarization control across the wide spectral range covered by the SLD. This causes the circular polarization state to shift as the wavelength broadens, affecting the polarization purity of the output light and the consistency of the system imaging. Summary of the Invention

[0005] To address the above shortcomings, the present invention proposes a composite liquid crystal polarization grating and a method for preparing the same. An SLD circular polarization output device is constructed based on the composite liquid crystal polarization grating prepared by the method. The specific scheme is as follows:

[0006] A composite liquid crystal polarization grating is formed by gluing together two layers of polarization gratings with different grating periods, wherein the grating period of one layer is half of the other layer.

[0007] A SLD circular polarization output device comprises: a ridge-tilted SLD, a coupled microlens array, an optical fiber, and a composite liquid crystal polarization grating according to the present invention; the optical signal generated by the ridge-tilted SLD is corrected by the coupled microlens array, then emitted to the composite liquid crystal polarization grating through the optical fiber, and converted into circularly polarized light by the composite liquid crystal polarization grating.

[0008] A method for preparing a composite liquid crystal polarization grating, the method comprising:

[0009] S1, cleaning and drying two layers of transparent glass substrates to obtain two layers of pure glass substrates;

[0010] S2, dissolving the photo-controlled alignment material in an organic solvent to prepare a solution, and spin-coating the solution on two layers of pure glass substrates to obtain two layers of photo-controlled alignment films;

[0011] S3, performing polarization holographic exposure on the two layers of the optical alignment films using a laser light source, wherein the exposure process includes splitting the laser light source, adjusting the polarization state, and interfering on the surface of the optical alignment film to obtain two layers of polarization gratings with different grating periods;

[0012] S4, placing two layers of polarization gratings with different grating periods on a heating platform and preheating them for 3 minutes, and then injecting liquid crystal into the polarization gratings in the preheated state to obtain two layers of liquid crystal polarization gratings with different grating periods;

[0013] S5. Bond two layers of liquid crystal polarization gratings with different grating periods to obtain a composite liquid crystal polarization grating.

[0014] Furthermore, the two polarization gratings with different grating periods satisfy the following conditions:

[0015] , , ,

[0016] in is the working wavelength, is the birefringence difference of the liquid crystal, is the period of the first layer of grating, is the period of the second grating layer, is the thickness of the first polarization grating, is the thickness of the second polarization grating.

[0017] Furthermore, the method of dissolving the photo-controlled alignment material in an organic solvent to prepare a solution in S2 is: the photo-controlled alignment material is azo dye SD1, and the organic solvent is dimethylformamide, and the two are prepared into a solution with a concentration of 1% (w / v).

[0018] Furthermore, the method for obtaining the photo-controlled alignment film described in S2 is: first spin coating at 1000RPM for 10 seconds, then spin coating at 3000RPM for 30 seconds, and then annealing at 100°C for 10 minutes to obtain a photo-controlled alignment film with a thickness of 15 to 20nm.

[0019] Furthermore, the wavelength of the laser light source in S3 is 365 nm.

[0020] Furthermore, the polarization holographic exposure method described in S3 is: splitting a laser light source into two laser beams, the two laser beams have equal light intensities and orthogonal linear polarizations, and the two laser beams are converted into orthogonal circularly polarized light through 1 / 4 wave plates with mutually perpendicular fast axis directions, and finally interfere with each other on the surface of the light-controlled orientation film.

[0021] Furthermore, in S3, the grating period of the obtained polarization grating is controlled by adjusting the angle between the two beams of orthogonal circularly polarized light.

[0022] Furthermore, the preheating temperature in S4 is 135°C.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The composite liquid crystal polarization grating described in this invention utilizes polarization holographic exposure on two layers of optical alignment films to form alignment structures with varying ratios and periods. Liquid crystal is injected into the same device and then bonded together. This allows for efficient conversion of linearly polarized light to circularly polarized light in a single transmission, avoiding the multiple interface reflections and transmission losses introduced by conventional polarizers and wave plates in series. Compared to prior art solutions employing multi-stage external polarization elements, the present invention significantly improves optical power utilization, enabling higher and more stable SLD light source output. The preparation method described in this invention utilizes optical alignment materials for holographic exposure under a broad-spectrum ultraviolet laser, combined with the birefringence of liquid crystal molecules, to maintain a stable phase delay across the entire SLD operating bandwidth, thereby outputting consistent and higher-purity circularly polarized light. Compared to prior art methods that rely on fixed-thickness wave plates, which result in polarization mismatch at different wavelengths, the present invention achieves consistent polarization performance across a wide spectral range through full-field phase control, thereby improving the signal-to-noise ratio and imaging quality of deep-layer OCT systems. The SLD circular polarization output device described in this invention directly couples a composite liquid crystal polarization grating with an SLD light source, eliminating the need for additional quarter-wave plates, linear polarizers, or mechanical alignment brackets. Polarization state conversion is achieved through molecular alignment within the liquid crystal layer, eliminating complex optical alignment and mechanical structures, resulting in a compact, integrated module. Compared to prior art methods that require multiple external optical components, which increase system volume and susceptibility to vibration and thermal drift, the present invention achieves a miniaturized and modularized light source design, making the system more stable and reliable in portable applications. The preparation method described in this invention utilizes conventional spin-coating equipment, holographic exposure equipment, and liquid crystal injection technology, from the preparation of the photo-controlled alignment material, spin-coating the alignment film, polarization holographic exposure, to liquid crystal injection and interlayer bonding. The process parameters are easily controlled, the equipment requirements are moderate, and standardized production is possible. Compared to prior art methods that require multi-stage mechanical assembly and an ultra-clean environment, the present invention offers the advantages of stable process, high repeatability, and high mass production efficiency, providing reliable support for industrial applications. The composite liquid crystal polarization grating described in this invention enables precise design of the grating period, device thickness, and polarization response band to meet the performance requirements of OCT systems by adjusting the angle of the exposure interference beam, selecting different birefringent liquid crystal materials, and controlling the liquid crystal injection process. Compared to existing devices with fixed structures and limited customization, this invention offers a high degree of adjustability and adaptability, meeting the diverse requirements of circularly polarized light sources for different applications.The present invention has the characteristics of compact structure, high output efficiency, wide spectral adaptability, high polarization purity, and easy integration and batch manufacturing. It is suitable for the field of optical coherence tomography technology, such as cardiovascular plaque detection, retinal imaging, ophthalmology and cardiac interventional imaging equipment; it is also suitable for the field of industrial non-destructive testing technology, such as the detection of microcracks and interface defects in multi-layer transparent materials and anisotropic composite coatings; it is also suitable for technical fields such as laser processing, precision spectral analysis and polarization optical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 1 is a schematic structural diagram of an SLD circular polarization output device according to embodiment 11, wherein reference numerals are: superluminescent diode 8, coupled microlens array 9, optical fiber 10, composite liquid crystal polarization grating 11;

[0026] Figure 2 1. It is a schematic structural diagram of a ridge-type tilted superluminescent diode according to the eleventh embodiment;

[0027] Figure 3 1 is a schematic cross-sectional view of a tilted ridge superluminescent diode according to an eleventh embodiment, wherein reference numerals are: lower electrode 1, lower substrate 2, lower confinement layer 3, quantum well active layer 4, upper confinement layer 5, upper substrate 6, upper electrode 7;

[0028] Figure 4 1 is a front view of the coupled microlens array according to the eleventh embodiment, with reference numerals: fast-axis collimating microlens 12, slow-axis collimating microlens 13;

[0029] Figure 5 is a top view of the coupled microlens array described in embodiment 11;

[0030] Figure 6 1 is a top view of the composite polarization grating structure according to the eleventh embodiment, with reference numerals: is the period of the first grating layer, is the period of the second grating layer. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described 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 those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] Implementation Method 1

[0033] A composite liquid crystal polarization grating is formed by gluing together two layers of polarization gratings with different grating periods, wherein the grating period of one layer is half of the other layer.

[0034] This embodiment forms a composite structure by bonding two layers of polarization gratings with grating periods of different ratios, where the grating period of one layer is half that of the other. This achieves matching compensation for light of different wavelengths during a single transmission process, giving the composite liquid crystal polarization grating high broadband adaptability and high polarization purity output capabilities, thereby meeting the diverse needs for circularly polarized light sources in various application scenarios.

[0035] Implementation Method 2

[0036] This embodiment further limits the first embodiment. Furthermore, the two polarization gratings with different grating periods satisfy the following conditions:

[0037] , , ,

[0038] in is the working wavelength, is the birefringence difference of the liquid crystal, is the period of the first layer of grating, is the period of the second grating layer, is the thickness of the first polarization grating, is the thickness of the second polarization grating.

[0039] This embodiment achieves synergy between the first and second grating layers in generating the circular polarization state by ensuring that the two grating layers meet the design conditions during the polarization grating preparation process, so that the thickness of the liquid crystal layer and the birefringence difference precisely correspond at a specific operating wavelength. This ensures birefringence compensation and high purity of the outgoing circularly polarized light.

[0040] Implementation Method 3

[0041] A SLD circular polarization output device comprises: a ridge-type tilted SLD, a coupled microlens array, an optical fiber, and the composite liquid crystal polarization grating of the present invention; the optical signal generated by the ridge-type tilted SLD is corrected by the coupled microlens array, then emitted to the composite liquid crystal polarization grating through the optical fiber, and converted into circularly polarized light by the composite liquid crystal polarization grating.

[0042] This embodiment realizes the integrated integration of SLD light source and polarization conversion by directly combining the prepared composite liquid crystal polarization grating with a ridge-type tilted SLD, a coupled microlens array, and an optical fiber to form a circular polarization output device. This does not require an external wave plate or additional mechanical bracket, which simplifies the optical path design and effectively suppresses thermal drift and assembly errors. This makes the light source module compact and highly stable, making it suitable for highly integrated OCT systems and portable imaging devices.

[0043] Implementation Method 4

[0044] A method for preparing a composite liquid crystal polarization grating, the method comprising:

[0045] S1, cleaning and drying two layers of transparent glass substrates to obtain two layers of pure glass substrates;

[0046] S2, dissolving the photo-controlled alignment material in an organic solvent to prepare a solution, and spin-coating the solution on two layers of pure glass substrates to obtain two layers of photo-controlled alignment films;

[0047] S3, performing polarization holographic exposure on the two layers of the optical alignment films using a laser light source, wherein the exposure process includes splitting the laser light source, adjusting the polarization state, and interfering on the surface of the optical alignment film to obtain two layers of polarization gratings with different grating periods;

[0048] S4, placing two layers of polarization gratings with different grating periods on a heating platform and preheating them for 3 minutes, and then injecting liquid crystal into the polarization gratings in the preheated state to obtain two layers of liquid crystal polarization gratings with different grating periods;

[0049] S5. Bond two layers of liquid crystal polarization gratings with different grating periods to obtain a composite liquid crystal polarization grating.

[0050] This embodiment performs polarization holographic exposure on two layers of light-controlled alignment films, injects liquid crystal, and then bonds them together to form a composite liquid crystal polarization grating. This allows only a single device to complete phase modulation and polarization conversion when converting linear polarized light to circular polarized light, avoiding the optical power loss caused by the series connection of multiple polarization elements, thereby improving the output efficiency of the SLD light source and simplifying the optical system structure.

[0051] Implementation Method Five

[0052] This embodiment is a further limitation of embodiment three. Furthermore, the method of dissolving the photo-controlled alignment material in an organic solvent to prepare a solution in S2 is: the photo-controlled alignment material is azo dye SD1, and the organic solvent is dimethylformamide, and the two are prepared into a solution with a concentration of 1% (w / v).

[0053] This embodiment uses azo dye SD1 and dimethylformamide to formulate a 1% (w / v) photo-controlled orientation material solution, ensuring that the orientation film can form a uniform and stable grating orientation layer under ultraviolet irradiation, thereby improving the fabrication accuracy and reproducibility of the polarization grating, making the grating performance more stable and reliable after subsequent liquid crystal injection.

[0054] Implementation Method 6

[0055] This embodiment is a further limitation of embodiment three. Furthermore, the method for obtaining the photo-controlled alignment film described in S2 is: first spin coating at 1000RPM for 10 seconds, then spin coating at 3000RPM for 30 seconds, and then annealing at 100°C for 10 minutes to obtain a photo-controlled alignment film with a thickness of 15 to 20nm.

[0056] This embodiment is repeated until two layers of photo-controlled alignment films are obtained.

[0057] In this embodiment, a photo-controlled alignment film with a thickness of 15 to 20 nm is obtained by spin coating at 1000 RPM for 10 seconds and then at 3000 RPM for 30 seconds, and annealing at 100°C for 10 minutes. This achieves thickness uniformity and surface flatness of the alignment layer, provides a reliable substrate for polarization holographic exposure, ensures the uniformity of the grating period and orientation effect, and thus improves the polarization conversion consistency of the final device.

[0058] Implementation Method Seven

[0059] This embodiment is a further limitation of the third embodiment. Furthermore, the wavelength of the laser light source described in S3 is 365 nm.

[0060] This embodiment uses a 365nm wavelength laser for polarization holographic exposure, so that the photo-controlled alignment film can quickly undergo molecular rearrangement and solidify into the desired orientation structure under ultraviolet excitation, avoiding the problems of low orientation efficiency and insufficient resolution during the exposure process of longer wavelength light sources, thereby improving the production efficiency of the polarization grating and its adaptability to wide-spectrum SLD light sources.

[0061] Implementation Method Eight

[0062] This embodiment is a further limitation of embodiment three. Furthermore, the method of polarization holographic exposure described in S3 is: splitting the laser light source into two laser beams, the two laser beams have equal light intensities and orthogonal linear polarizations, and the two laser beams are respectively converted into orthogonal circularly polarized light through 1 / 4 wave plates with mutually perpendicular fast axis directions, and finally interfere with each other on the surface of the light-controlled orientation film.

[0063] This embodiment converts laser beams with equal intensity and orthogonal linear polarization after splitting into orthogonal circularly polarized light through quarter-wave plates with mutually perpendicular fast axes, and forms interference on the surface of the orientation film, thereby achieving the preparation of a bidirectional spiral-oriented polarization grating structure on a single-layer orientation film, ensuring the orderly arrangement of liquid crystal molecules and the high purity of the circularly polarized output, thereby improving the signal-to-noise ratio and deep contrast of OCT imaging.

[0064] Implementation Method Nine

[0065] This embodiment is a further limitation of the seventh embodiment. Furthermore, in S3, the grating period of the obtained polarization grating is controlled by adjusting the angle between the two beams of orthogonal circularly polarized light.

[0066] This embodiment precisely controls the grating period of the polarization grating by adjusting the angle between two beams of orthogonal circularly polarized light. This allows the grating period formed by the first and second layers of the orientation films to precisely meet the design requirements, achieving adaptive matching for different operating bands and birefringent materials, thereby ensuring the efficient polarization conversion performance of the liquid crystal polarization grating over a wide spectral range.

[0067] Implementation Method 10

[0068] This embodiment further limits the first embodiment. Furthermore, the preheating temperature in S4 is 135°C.

[0069] This embodiment preheats two polarization gratings with different grating periods at 135°C for 3 minutes before injecting liquid crystal into the polarization gratings. This allows the liquid crystal to fully flow and fill the alignment layer structure during the injection process, ensuring close contact and alignment consistency between the liquid crystal molecules and the alignment film, thereby improving the filling integrity and service life of the liquid crystal polarization grating.

[0070] Implementation Method Eleven

[0071] This embodiment integrates the technical solutions described in the aforementioned multiple embodiments, combines actual application scenarios and the use process of the computer program product that implements the method described in the present invention, and further verifies and explains the technical effects of the present invention through specific examples.

[0072] The present invention proposes an integrated solution for a superluminescent diode circular polarization output device based on a composite liquid crystal polarization grating. Figure 1 As shown, the output device of the present invention consists of four parts from left to right: a superluminescent diode 8, a coupled microlens array 9, an optical fiber 10 and a composite liquid crystal polarization grating 11 connected in sequence.

[0073] like Figure 2-3As shown, the superluminescent diode 8 is a ridge-type inclined structure, which is composed of the following from bottom to top: lower electrode 1, lower substrate 2, lower confinement layer 3, quantum well active layer 4, upper confinement layer 5, upper substrate 6, and upper electrode 7. Specifically:

[0074] Lower electrode 1

[0075] Material selection: Ti / Pt / Au (40nm / 40nm200nm);

[0076] Function: Together with the upper electrode, it forms the current injection channel of the device, uniformly injecting the external drive current into the active area, and has both electrical contact and heat dissipation functions.

[0077] Lower substrate 2

[0078] Material: AlGaAs, thickness 2.5μm;

[0079] Function: As the peeling layer and substrate for epitaxial growth, it provides good lattice matching and surface flatness to ensure the quality of subsequent epitaxial layer growth; at the same time, it provides flat mechanical support for device processing.

[0080] Lower restriction layer 3

[0081] Material: AlGaAs, thickness 0.35 to 0.65 μm;

[0082] Function: It forms a lower optical and carrier sandwich, limits the vertical diffusion of the light field, and ensures that the optical waveguide is effectively bound in the active layer; at the same time, it acts as a barrier layer for carrier injection, preventing electrons and holes from crossing the active area and causing efficiency loss.

[0083] Quantum well active layer 4

[0084] Material: InGaAs, thickness 0.1 to 0.2 μm;

[0085] Structure: The ridge-type tilted SLD has a tilt angle of 6° and a ridge width of 5µm.

[0086] Function: As the core area of ​​photogenerated carrier recombination and luminescence, it realizes radiative recombination and produces narrowband light output through InGaAs quantum wells; the ridge-shaped tilted structure can cause lateral displacement between the output end face and the non-output end face in space, effectively suppressing optical feedback, improving the stability of superradiant state output and suppressing laser oscillation.

[0087] Upper Restriction Layer 5

[0088] Material: AlGaAs, thickness 0.35 to 0.65µm;

[0089] Function: It forms an optical and carrier sandwich above the active layer, and together with the lower confinement layer, it builds a complete double-sided waveguide structure to achieve vertical confinement of the light field in the quantum well region; at the same time, it laterally confines the carriers to reduce scattering and leakage, thereby improving device efficiency.

[0090] Upper substrate 6

[0091] Material: AlGaAs, thickness 1.1µm;

[0092] Function: Located between the confinement layer and the upper electrode, it protects the underlying active area and interlayer and provides a smooth electrical contact interface for the upper electrode. It also participates in the formation of the top surface waveguide structure, further optimizing the optical mode distribution.

[0093] Upper electrode 7

[0094] Material: Ni / AuGe / Ni / Au (10nm / 100nm / 15nm / 300nm);

[0095] Function: Connect current together with the upper electrode.

[0096] like Figure 4-5 As shown, the coupled microlens array 9 consists of two parts, namely a fast-axis collimating microlens and a slow-axis collimating microlens. The fast-axis collimating microlens (12) is designed for the SLD to have a divergence angle of 31° in the vertical direction (fast axis). Its cylindrical curvature is large, and it can achieve strong light convergence and collimation in the vertical dimension; the slow-axis collimating microlens (13) is designed for the SLD to have a divergence angle of 12° in the horizontal direction (slow axis). Its cylindrical curvature is relatively small, and it is suitable for fine collimation in the horizontal direction. The two are arranged in combination to form a cylindrical microlens array, which realizes independent correction of fast and slow axis light.

[0097] The SLD light source exhibits significant differences in divergence angles in the vertical (fast axis) and horizontal (slow axis) directions. Traditional single spherical lenses are unable to simultaneously correct for both divergence characteristics. The synergistic effect of two cylindrical microlenses, one on the fast axis and the other on the slow axis, allows for independent adjustment of divergence angles of 31° and 12°, respectively. The fast-axis microlens effectively converges light with large angles of divergence, while the slow-axis microlens finely corrects light with smaller angles of divergence. Together, they efficiently collimate the SLD's output light and couple it into the optical fiber, improving fiber coupling efficiency and reducing optical loss.

[0098] like Figure 6 As shown, the composite liquid crystal polarization grating 11 is formed by gluing two layers of conventional polarization gratings together, and the periods of the two layers of gratings satisfy a two-fold relationship. The thickness of the first layer of polarization grating is Satisfy the half-wave delay condition , the period of the first grating layer Determined by the holographic exposure process, it is used to achieve phase reversal of a specific wavelength; the thickness of the second polarization grating Satisfy the quarter-wave delay condition , the period of the second grating , combined with the first grating layer, it provides additional phase compensation for the incident light. The two layers are bonded together to form a composite structure. Light passing through the first layer first experiences a half-wave phase delay, and then through the second layer experiences a quarter-wave delay, ultimately outputting a stable circular polarization state.

[0099] Function: The composite liquid crystal polarization grating, through the sequential action of two polarization gratings of varying thickness and period, converts linearly polarized light from an optical fiber into left-handed or right-handed circularly polarized light across a wide spectral range. By adjusting the position or angle of incident light on the composite grating surface, the user can select either left-handed or right-handed circular polarization state, providing a high-purity, wide-bandwidth circularly polarized light source for subsequent OCT systems or other polarization-sensitive applications.

[0100] The solution described in this embodiment utilizes two layers of liquid crystal polarization gratings with different grating periods to achieve efficient all-optical phase modulation of linearly polarized light within a single device, without the need for mechanical rotation or cascading of multiple polarizers, thus completely eliminating the optical power loss and wavelength sensitivity problems caused by traditional polarizer cascading.

[0101] The linearly polarized light generated by the SLD first passes through a tilted ridge structure to correct for reflection noise on the output surface. Fast-axis collimation and slow-axis collimation microlens arrays then precisely control the divergence angles of the fast and slow axes, respectively, efficiently coupling the light energy into the optical fiber. By precisely adjusting the incident angle between the fiber end face and the liquid crystal polarization grating, the output mode can be flexibly switched between left-handed and right-handed circular polarization, enabling dynamic control of the circular polarization state over a wide spectral range. This integrated design fills a technological gap in the circular polarization output of broadband SLD light sources, providing a device-level compact, low-loss, and high-polarization-purity solution for highly scatter-resistant applications such as optical coherence tomography.

[0102] Based on the collaborative design of a ridge-type tilted SLD light source, a fast-slow axis microlens array, and a composite liquid crystal polarization grating, the present invention further constructs a highly integrated SLD circularly polarized light source device architecture. The ridge-type tilted structure forms a controllable displacement between the SLD output end face and the non-output end face, effectively suppressing the end face reflection noise; the fast-axis collimation and slow-axis collimation microlens arrays independently adjust the SLD fast-axis and slow-axis divergence angles to achieve efficient focusing and coupling of light energy at the fiber end face; the composite liquid crystal polarization grating utilizes its periodic birefringence phase modulation principle to maintain a stable circular polarization state output under wide spectrum conditions, overcoming the insufficient spectral adaptability and energy loss problems of the traditional polarizer cascade structure. This architecture highly integrates functional modules with optical path optimization, giving the entire light source system outstanding advantages such as small size, high integration, strong anti-scattering performance, and excellent polarization conversion efficiency, providing an innovative technical path for the miniaturization and high-performance application of wide-spectrum circularly polarized SLD light sources.

[0103] The technical solution provided by the present invention is further described in detail through the above specific embodiments in order to highlight the advantages and benefits of the technical solution provided by the present invention. However, the above specific embodiments are not intended to limit the present invention. Any reasonable modification and improvement of the present invention, combination of embodiments and equivalent replacement, etc. based on the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0104] Those skilled in the art will understand that the above description is only a preferred embodiment of the present invention, and the various embodiments disclosed in the present invention and / or the features described in the claims can be combined or coupled in various ways, even if such combinations or couplings are not explicitly described in the disclosure of the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0105] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such changes and modifications as fall within the scope of the claims and their equivalents.

Claims

1. A method for preparing a composite liquid crystal polarization grating, characterized in that: The method comprises: S1, cleaning and drying two layers of transparent glass substrates to obtain two layers of pure glass substrates; S2, dissolving the photo-controlled alignment material in an organic solvent to prepare a solution, and spin-coating the solution on two layers of pure glass substrates to obtain two layers of photo-controlled alignment films; S3, performing polarization holographic exposure on the two layers of the optical alignment films using a laser light source, wherein the exposure process includes splitting the laser light source, adjusting the polarization state, and interfering on the surface of the optical alignment film to obtain two layers of polarization gratings with different grating periods; S4, placing two layers of polarization gratings with different grating periods on a heating platform and preheating them for 3 minutes, and then injecting liquid crystal into the polarization gratings in the preheated state to obtain two layers of liquid crystal polarization gratings with different grating periods; S5, bonding two layers of liquid crystal polarization gratings with different grating periods to obtain a composite liquid crystal polarization grating; The two polarization gratings with different grating periods satisfy the following conditions: ， ， ， in is the working wavelength, is the birefringence difference of the liquid crystal, is the period of the first layer of grating, is the period of the second grating layer, is the thickness of the first polarization grating, is the thickness of the second polarization grating.

2. The preparation method according to claim 1, characterized in that The method of dissolving the photo-controlled alignment material in an organic solvent to prepare a solution in S2 is as follows: the photo-controlled alignment material is azo dye SD1, and the organic solvent is dimethylformamide, and the two are prepared into a solution with a concentration of 1% (w / v).

3. The preparation method according to claim 1, characterized in that The method for obtaining the photo-controlled alignment film described in S2 is: first spin coating at 1000RPM for 10 seconds, then spin coating at 3000RPM for 30 seconds, and then annealing at 100°C for 10 minutes to obtain a photo-controlled alignment film with a thickness of 15 to 20nm.

4. The preparation method according to claim 1, characterized in that The wavelength of the laser light source described in S3 is 365nm.

5. The preparation method according to claim 1, characterized in that The polarization holographic exposure method described in S3 is: splitting a laser light source into two laser beams, the two laser beams have equal light intensities and orthogonal linear polarizations, and the two laser beams are converted into orthogonal circularly polarized light through 1 / 4 wave plates with mutually perpendicular fast axis directions, and finally interfere with each other on the surface of the light-controlled alignment film.

6. The preparation method according to claim 5, characterized in that In S3, the grating period of the obtained polarization grating is controlled by adjusting the angle between the two orthogonal circularly polarized light beams.

7. The preparation method according to claim 1, characterized in that The preheating temperature in S4 is 135°C.

8. The preparation method according to claim 1, characterized in that The composite liquid crystal polarization grating is formed by gluing together two layers of polarization gratings with different grating periods, and the grating period of one layer is half of the other layer.

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