An infrared radial GRIN lens based on chalcogenide glass and a preparation method thereof
By introducing In2S3 nanocrystals into a chalcogenide glass matrix and combining laser and heat treatment techniques, a continuous radial gradient refractive index structure was constructed, solving the problem of insufficient refractive index modulation in existing lenses and realizing a key component of a high-performance, compact infrared optical system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGBO UNIV
- Filing Date
- 2026-02-03
- Publication Date
- 2026-06-12
Smart Images
Figure CN122194358A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of infrared optical device technology, specifically to an infrared radial GRIN lens based on chalcogenide microcrystalline glass and its fabrication method. Background Technology
[0002] Over the past few decades, advancements in key fields such as medicine, biology, aerospace, and environmental monitoring have driven the rapid development of infrared (IR) imaging technology. Next-generation infrared imaging systems focus on improving size, weight, power, and cost (SWaP-C) and developing lighter, smaller optical systems. However, traditional infrared imaging systems, composed of expensive non-planar lenses and complex lens assemblies, struggle to achieve high integration and lightweight designs, thus failing to meet the SWaP-C goals. Gradient-index (GRIN) lenses, optical elements with a gradually changing refractive index (n), offer optical designers greater design flexibility and more freedom.
[0003] To reduce optical aberrations, traditional optical imaging systems, especially multispectral fusion systems, often require expensive non-planar lenses and complex lens assemblies, making miniaturization and weight reduction difficult. In contrast, gradient refractive index elements (GRIN elements) are suitable for a longer wavelength range. Their optical function is based on the continuous axial or radial variation of the refractive index distribution within the material. This characteristic provides additional degrees of freedom in optical design, helping to make optical systems more compact, reduce the number of components, and correct optical defects such as chromatic aberration. Furthermore, GRIN optical elements have characteristics such as large numerical aperture and short focal length, which can significantly reduce the size and weight of optical systems.
[0004] Chalcogenide glasses (ChG) have become a promising material for thermal imaging and infrared optical lenses due to their wide infrared transmission range (2–18 μm), excellent thermal and chemical stability, relatively mature fabrication processes, and the ability to flexibly customize optical properties by adjusting their composition. Studies have shown that heat treatment of chalcogenide glasses can effectively control their optical properties. Furthermore, some glasses can achieve controlled crystallization through heat treatment. With the formation of microcrystals, their refractive index and other optical properties will change accordingly, thus providing further possibilities for the optical design of the material.
[0005] In recent years, laser-induced crystallization technology has provided a new approach to constructing refractive index gradients in glass. For example, laser-induced vitrification (LIV) and femtosecond laser direct writing can achieve local refractive index modulation in chalcogenide glasses and have been used to fabricate micro-optical components such as infrared gratings and GRIN microlenses. However, research on radial GRIN infrared chalcogenide glass lenses that better meet the needs of optical design is still relatively scarce. The maximum reported refractive index difference Δn is generally below 0.1, which cannot yet meet the requirements of high-performance devices for commercial applications. Summary of the Invention
[0006] This invention aims to overcome the technical deficiency of insufficient refractive index modulation in existing radially gradient refractive index infrared chalcogenide glass lenses, and provides an infrared radial GRIN lens based on chalcogenide microcrystalline glass and its fabrication method. This lens achieves a refractive index change Δn greater than 0.1 in the 5.78 μm band and maintains good transmittance across a wide infrared band from 0.5 μm to 12 μm. It can reduce the number and complexity of lens elements in infrared optical systems, providing a key component for system miniaturization, weight reduction, and performance improvement. The fabrication method of this invention exhibits high process stability and repeatability, can construct a smooth radial refractive index gradient within the glass, and is not dependent on a strict subwavelength structure. It is suitable for the fabrication of functional optical devices in the mid-infrared band, providing a feasible technical approach for realizing high-performance, compact infrared optical systems.
[0007] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: an infrared radial GRIN lens based on chalcogenide microcrystalline glass, wherein the lens uses chalcogenide glass with a molar composition of 65GeS2-25In2S3-10CsCl as the matrix material, and the matrix material contains In2S3 nanocrystals; the In2S3 nanocrystals are selectively distributed in the optical functional area of the lens, and their crystallinity decreases continuously from the center to the edge along the radial direction of the optical functional area, thereby forming a corresponding radially continuously changing gradient refractive index structure inside the lens.
[0008] The lens of this invention uses a specific composition of 65GeS2-25In2S3-10CsCl chalcogenide glass as the matrix material. Through a continuous radial gradient distribution of In2S3 nanocrystals decreasing in crystallinity from the center to the edge within the optical functional region, a continuous and smooth radial gradient refractive index structure is constructed within the glass. This structure allows the lens to achieve a refractive index change Δn greater than 0.1 in the 5.78 μm band and maintain good transmittance across a wide infrared band from 0.5 μm to 12 μm. The gradient refractive index distribution helps to converge light rays and correct aberrations, thereby reducing the number and complexity of lens elements in infrared optical systems. This provides a key component for miniaturization, weight reduction, and performance improvement of the system.
[0009] A method for fabricating the above-mentioned infrared radial GRIN lens based on chalcogenide glass includes the following steps: (1) Weigh the raw materials according to the molar composition of 65GeS2-25In2S3-10CsCl, put them into a clean quartz tube, and then evacuate the quartz tube to 1×10⁻⁶. -4 Below Pa and fused to seal the quartz tube; (2) The packaged quartz tube is placed in a swing furnace for high-temperature melting. The melting temperature is 900~990℃ and the melting time is 12~24 h. After melting, the quartz tube is placed in cold water for quenching. After the glass body is detached from the wall, the quartz tube is taken out. (3) The quartz tube is placed in an annealing furnace for annealing at a temperature of 300-320℃ for 10-12 h. After annealing, it is slowly cooled to room temperature at a rate of 9-10℃ / h. The quartz tube is then opened to obtain 65GeS2-25In2S3-10CsCl chalcogenide glass matrix material, which is then cut into glass sheets. The glass sheets are then ground and polished to obtain the lens preform. (4) A femtosecond laser is used to perform laser irradiation scanning along a preset concentric ring path in the same plane of the lens preform, keeping the single-ring scanning linewidth constant to form a high refractive index modification zone. The unscanned area between adjacent rings is used as a low refractive index zone. By adjusting the radial spacing between adjacent rings, the spatial duty cycle of the high refractive index modification zone changes in a gradient along the radial direction. (5) The scanned lens preform is heat-treated at 330~335℃ under inert atmosphere protection to induce In2S3 nanocrystals to precipitate radially in the laser irradiation area, thereby forming the optical functional area of the lens and forming a radially continuously changing gradient refractive index structure inside the lens.
[0010] This invention utilizes a controlled laser-induced crystallization process to write concentric circular scanning paths into a chalcogenide glass matrix of a specific composition. Employing a two-dimensional path design with a fixed scanning linewidth and adjustable ring spacing, and without altering single-line processing parameters, combined with heat treatment, radial gradient precipitation of In₂S₃ nanocrystals is achieved, thus enabling continuous and controllable manipulation of the equivalent refractive index within the glass. This method exhibits high process stability and repeatability, avoiding complex real-time parameter adjustments. It can construct a smooth radial refractive index gradient within the glass and is not dependent on a strictly subwavelength structure, making it suitable for fabricating functional optical devices in the mid-infrared band. This provides a feasible technical approach for realizing high-performance, compact infrared optical systems.
[0011] Preferably, in step (1), the raw materials include the corresponding compounds or elemental raw materials used to form GeS2, In2S3 and CsCl.
[0012] As a further preferred option, in step (1), the raw materials are germanium, indium, sulfur, and cesium chloride, wherein the purity of the germanium, indium, and sulfur raw materials is 5N, and the purity of the cesium chloride raw material is 4N. Using raw materials with the above-mentioned purity can effectively reduce the introduction of impurity elements, ensuring that the chalcogenide glass matrix material has high purity and uniform component distribution, laying the foundation for obtaining a high-quality gradient refractive index structure with consistent optical performance.
[0013] Preferably, in step (4), the repetition frequency of the femtosecond laser is 100 kHz, and the average laser power is 45~70 mW; the number of concentric rings is 300~400 rings, and the radial spacing of the rings gradually increases from the center to the edge, thus exhibiting a distribution pattern of dense in the middle and sparse at the edge. The above-mentioned optimized process parameters can effectively induce material modification without causing cracks, ablation, or other damage to the chalcogenide glass matrix material, and provide a precursor structure for the spatially selective gradient precipitation of In2S3 nanocrystals through subsequent heat treatment, ensuring the acquisition of a radially continuously varying gradient refractive index structure.
[0014] Preferably, under heat treatment temperatures of 330–335 °C and average laser power of 45–70 mW, the crystallinity of In₂S₃ nanocrystals increases with increasing heat treatment temperature and average laser power, and the change in refractive index of the lens is positively correlated with the crystallinity of the In₂S₃ nanocrystals. These optimized process parameters provide a direct technological basis for precisely controlling the refractive index at different radial positions within the lens. By controlling the heat treatment temperature and average laser power, controllable fabrication of a gradient refractive index structure with continuous radial variation can be achieved.
[0015] Compared with the prior art, the present invention has the following advantages: 1) The lens of this invention achieves a refractive index change Δn greater than 0.1 in the 5.78 μm band and maintains good transmittance across a wide infrared band from 0.5 μm to 12 μm by constructing a continuous and smooth radial gradient refractive index structure within the glass. This gradient refractive index distribution helps to converge light rays and correct aberrations, thereby reducing the number and complexity of lens elements in infrared optical systems and providing a key component for miniaturization, weight reduction, and performance improvement of the system.
[0016] 2) The preparation method of this invention achieves radial gradient precipitation of In2S3 nanocrystals through a controlled laser-induced crystallization process combined with heat treatment, thereby realizing continuous and controllable regulation of the equivalent refractive index inside the glass. This method exhibits high process stability and repeatability, avoiding complex real-time parameter adjustments. It can construct a smooth radial refractive index gradient inside the glass and does not depend on a strictly subwavelength structure, making it suitable for the fabrication of functional optical devices in the mid-infrared band. This provides a feasible technical approach for realizing high-performance, compact infrared optical systems. Attached Figure Description
[0017] Figure 1 A schematic diagram of the fabrication process for constructing a radial gradient refractive index structure inside a lens preform using a femtosecond laser. Figure 2A schematic diagram illustrating the structural principle of radial equivalent refractive index control by adjusting the width of the gap between adjacent low refractive indices to fix the linewidth of the high refractive index annular zone. Figure 3 Microscopic observation of a concentric ring structure processed using a femtosecond laser; Figure 4 The radial equivalent refractive index distribution curve is obtained by calculating and fitting the radial refractive index distribution corresponding to the obtained concentric ring structure. Figure 5 This is a radial distribution curve of the crystallinity of In2S3 nanocrystals obtained by confocal Raman spectroscopy line scanning of the prepared lens sample from the center to the edge of the In2S3 crystallization region. Figure 6 for Figure 5 Distribution of peak points of different curves. Detailed Implementation
[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0019] Example 1: An infrared radial GRIN lens based on chalcogenide microcrystalline glass. The lens uses chalcogenide glass with a molar composition of 65GeS2-25In2S3-10CsCl as the substrate material, which contains In2S3 nanocrystals. The In2S3 nanocrystals are selectively distributed within the optical functional region of the lens, and their crystallinity decreases continuously from the center to the edge radially along this region, thus forming a radially continuously varying gradient refractive index structure inside the lens. The preparation method of this lens includes the following steps: (1) Accurately weigh germanium, indium, and sulfur raw materials with a purity of 5N and cesium chloride raw material with a purity of 4N according to the molar composition of 65GeS2-25In2S3-10CsCl. Place them into a clean quartz tube with an inner diameter of 10 mm that has been soaked in aqua regia, washed with distilled water, and dried. Then, evacuate the quartz tube to a vacuum of 1×10. -4 The material is sealed by using an oxyhydrogen flame to seal the quartz tube below Pa.
[0020] (2) The packaged quartz tube is placed in a swing furnace for high-temperature melting. The melting temperature is 990℃ and the melting time is 14 h. After the melting is completed, the quartz tube is placed in cold water for quenching. After the glass body is detached from the wall, the quartz tube is taken out immediately.
[0021] (3) The quartz tube was quickly placed in an annealing furnace for annealing at a temperature of 315°C for 10 h. After annealing, it was slowly cooled to room temperature at a rate of 10°C / h. The quartz tube was opened to obtain 65GeS2-25In2S3-10CsCl chalcogenide glass matrix material, which was then cut into glass sheets with a thickness of 3 mm. The glass sheets were then ground and polished to obtain the lens preform.
[0022] (4) Constructing a three-dimensional optical processing platform based on a femtosecond laser. A femtosecond laser with a center wavelength of 1030 nm and a pulse width of 300 fs was used as the light source. First, the pulse energy of the femtosecond laser was set to 50~750 nJ and the repetition frequency to 25~300 kHz. A single-point laser irradiation experiment was conducted to screen out laser parameters that would not cause damage to the inside of the glass. Then, the non-damaging laser parameters were selected to conduct a wire-laying experiment in a 1 mm × 1 mm matrix area inside the glass. The wire spacing was controlled to be 6.6~10 μm and the scanning speed to be 0.5~3 mm / s. The sample was then heat-treated to record the material modification and blackening data. Subsequently, based on the blackening data, a concentric ring structure was prepared. See [link to relevant documentation]. Figure 1 After passing through a beam expander and collimator, the laser beam is focused inside the lens preform by a high numerical aperture objective lens. Within the same plane, the laser focus is controlled to scan along a pre-defined concentric ring path. The number of concentric rings is 300-400, and the radial spacing between the rings gradually increases from the center to the edge. During scanning, multiple ring paths form concentric rings, maintaining a constant single-turn scan linewidth to create a high refractive index modification region. The unscanned areas between adjacent rings serve as low refractive index regions. By adjusting the radial spacing between adjacent rings, the spatial duty cycle of the high refractive index modification region changes radially in a gradient manner. Figure 2 The diagram illustrates the structural principle of this method, which involves fixing the linewidth of the high-refractive-index ring and adjusting the width of the gap between adjacent low-refractive-index rings to achieve radial equivalent refractive index control. Figure 2 middle, w Represents line width, n H The value representing a high refractive index. n L The value representing a low refractive index, Gap i Gap represents the i-th gap. i+kLet represent the (i+k)th gap, n(r) represent the refractive index of different regions, and r represent the radius of the rings. The design concept is to transform the process of controlling the refractive index within the material into a spatial structure arrangement design problem, while maintaining the single-circle scanning linewidth of the femtosecond laser and the corresponding processing parameters constant. Specifically, by adjusting only the radial spacing between adjacent concentric rings, the ratio of high-refractive-index modified regions to low-refractive-index unmodified regions within the material at different radial positions can be adjusted. Since the combined response of high and low refractive-index regions within this radial position during light propagation can be equivalently characterized as an equivalent refractive index, the radial variation of the duty cycle of the high-refractive-index modified region can be transformed into a continuous radial gradient distribution of refractive index. This allows for a stable and repeatably controllable radial gradient refractive index structure without changing the single-line processing conditions.
[0023] (5) The scanned lens preform is placed in a programmable temperature controlled annealing furnace and heat-treated at 330~335℃ for 2~3 h under inert atmosphere protection. Then it is slowly cooled to room temperature at a rate of 10℃ / h to induce In2S3 nanocrystals to precipitate radially in the laser irradiation area, thereby forming the optical functional area of the lens and forming a radially continuously changing gradient refractive index structure inside the lens.
[0024] Specifically, in Example 1, the scanning speed was set to 1 mm / s, the repetition frequency to 100 kHz, and the average laser power to 65 mW. Two repeated scans were performed at a sample depth of approximately 150 μm to write a concentric ring structure (such as...) inside the glass. Figure 3 (As shown in the figure). Then, the sample with the pattern written on it was heat-treated at 335℃ for 3 h and slowly cooled to room temperature at a rate of 10℃ / h. The radial refractive index distribution corresponding to the obtained concentric ring structure was calculated and fitted, and the results are shown in the figure. Figure 4 As shown, Figure 4 The three curves in the middle show linear distribution, x-square distribution, and x-power distribution, respectively. Figure 4 It is evident that the equivalent refractive index decreases continuously and smoothly from the center to the edge along the radial direction, and its overall distribution is consistent with the preset radial gradient design function, without any abrupt changes or discontinuities. This result demonstrates that by maintaining a constant linewidth for the concentric rings and gradually increasing the radial spacing between adjacent rings, the volume fraction of the high-refractive-index modified region within the material can be effectively controlled, thereby achieving a continuous radial change in the equivalent refractive index within the glass. This provides a reliable theoretical basis for subsequently obtaining a practical gradient refractive index structure through laser-induced crystallization.
[0025] The lens sample prepared in Example 1 was characterized by confocal Raman spectroscopy. Starting from the center of the In2S3 crystallization region (i.e., the optical functional region) and moving radially towards the edge, with the center point of the optical functional region as point 1, line scans were performed sequentially at 200 μm intervals along a radial path of 3 mm radius (scanning points are denoted as points 2 to 16). The Raman scattering intensity of the characteristic peaks of the In2S3 structural units at each scanning point was extracted. The results are as follows: Figure 5 and Figure 6 As shown. Figure 5 The 16 curves from top to bottom correspond to points 1 to 16 respectively. Figure 6 The 16 data points from top to bottom correspond to points 1 to 16. Figure 5 and Figure 6 It is evident that laser irradiation alters the local bonding state, resulting in a significant enhancement of the characteristic peak intensity. The introduction of CsCl causes Cl to... - Partially replaces S 2- , forming [InS 4-x Cl x [InS4] is a mixed tetrahedron; due to the similar atomic weights of sulfur and chlorine, [InS4] and [InS] are different. 4-x Cl x The vibrational energies of [ ] are close, and their Raman bands are in the range of 280~315cm. -1 The overlapping within the range can be attributed to the symmetrical bond stretching vibrations of both. Test results show that within this measurement range, the Raman characteristic peak intensity of the In2S3 nanocrystals exhibits a continuous decreasing trend radially from the center to the edge, proving that the crystallinity of the material gradually decreases radially from the center to the edge. In this material system, the change in refractive index of the lens is positively correlated with the crystallinity of the In2S3 nanocrystals. Therefore, the aforementioned gradient distribution of crystallinity confirms that a radial gradient refractive index structure has been formed inside the lens, i.e., the refractive index gradually decreases from the center to the edge. Specifically, experiments have determined that under heat treatment temperatures of 330–335 °C and average laser power of 45–70 mW, the crystallinity of the In2S3 nanocrystals increases with increasing heat treatment temperature and average laser power, and the change in refractive index of the lens is positively correlated with the crystallinity of the In2S3 nanocrystals.
Claims
1. An infrared radial GRIN lens based on chalcogenide glass, characterized in that, The lens uses a chalcogenide glass with a molar composition of 65GeS2-25In2S3-10CsCl as the matrix material, which contains In2S3 nanocrystals. The In2S3 nanocrystals are selectively distributed in the optical functional area of the lens, and their crystallinity decreases continuously from the center to the edge along the radial direction of the optical functional area, thereby forming a corresponding radially continuously varying gradient refractive index structure inside the lens.
2. A method for fabricating an infrared radial GRIN lens based on chalcogenide microcrystalline glass as described in claim 1, characterized in that, Includes the following steps: (1) Weigh the raw materials according to the molar composition of 65GeS2-25In2S3-10CsCl, put them into a clean quartz tube, and then evacuate the quartz tube to 1×10⁻⁶. -4 Below Pa and fused to seal the quartz tube; (2) The packaged quartz tube is placed in a swing furnace for high-temperature melting. The melting temperature is 900~990℃ and the melting time is 12~24 h. After melting, the quartz tube is placed in cold water for quenching. After the glass body is detached from the wall, the quartz tube is taken out. (3) The quartz tube is placed in an annealing furnace for annealing at a temperature of 300-320℃ for 10-12 h. After annealing, it is slowly cooled to room temperature at a rate of 9-10℃ / h. The quartz tube is then opened to obtain 65GeS2-25In2S3-10CsCl chalcogenide glass matrix material, which is then cut into glass sheets. The glass sheets are then ground and polished to obtain the lens preform. (4) A femtosecond laser is used to perform laser irradiation scanning along a preset concentric ring path in the same plane of the lens preform, keeping the single-ring scanning linewidth constant to form a high refractive index modification zone. The unscanned area between adjacent rings is used as a low refractive index zone. By adjusting the radial spacing between adjacent rings, the spatial duty cycle of the high refractive index modification zone changes in a gradient along the radial direction. (5) The scanned lens preform is heat-treated at 330~335℃ under inert atmosphere protection to induce In2S3 nanocrystals to precipitate radially in the laser irradiation area, thereby forming the optical functional area of the lens and forming a radially continuously changing gradient refractive index structure inside the lens.
3. The method for fabricating an infrared radial GRIN lens based on chalcogenide microcrystalline glass as described in claim 1, as claimed in claim 2, is characterized in that, In step (1), the raw materials include the corresponding compounds or elemental raw materials used to form GeS2, In2S3 and CsCl.
4. The method for fabricating an infrared radial GRIN lens based on chalcogenide microcrystalline glass as described in claim 1, as claimed in claim 3, is characterized in that, In step (1), the raw materials are germanium, indium, sulfur and cesium chloride, wherein the purity of germanium, indium and sulfur raw materials is 5N and the purity of cesium chloride raw material is 4N.
5. A method for fabricating an infrared radial GRIN lens based on chalcogenide microcrystalline glass as described in claim 1, as claimed in claim 2, characterized in that, In step (4), the repetition frequency of the femtosecond laser is 100 kHz, and the average laser power is 45~70 mW; the number of concentric rings is 300~400 rings, and the radial spacing of the rings gradually increases from the center to the edge.
6. A method for fabricating an infrared radial GRIN lens based on chalcogenide microcrystalline glass as described in claim 1, as claimed in claim 2, characterized in that, Under heat treatment temperatures of 330–335 °C and average laser power of 45–70 mW, the crystallinity of In2S3 nanocrystals increases with increasing heat treatment temperature and average laser power, and the change in refractive index of the lens is positively correlated with the crystallinity of In2S3 nanocrystals.