High refractive index GRIN infrared lens and method of making same

Abstract

The application discloses a high-refractive GRIN infrared lens and a preparation method thereof, the high-refractive GRIN infrared lens is composed of Ge-As-Se-Te, the refractive index of the high-refractive GRIN infrared lens is gradually distributed along an axial direction, and the high-refractive GRIN infrared lens has the advantages of high refractive index (>3.1), good thermal stability, easy processing and die pressing. The preparation method of the high-refractive GRIN infrared lens disclosed by the application, the GRIN infrared lens preparation technology and the prepared infrared lens have the advantages that the refractive index distribution of the infrared lens is linearly increased, the maximum refractive index difference in the axial direction is large, and the infrared lens can be further combined with a precise die pressing forming technology to prepare a precise infrared lens. The GRIN lens can reduce the volume and weight of an optical system, provide additional optical design freedom, including providing additional thermal or chromatic aberration correction and lightweight design, and has a wide application prospect in the fields of infrared imaging and infrared optics.

Description

Technical Field

[0001] This invention relates to a high refractive index GRIN infrared lens and its preparation method, belonging to the field of infrared optical materials technology. Background Technology

[0002] With the development of infrared detection technology and the increasing demand for infrared optical materials in national defense, existing infrared optical lenses, due to their large size, heavy weight, and high cost, can no longer meet the lightweight design requirements (size, weight, and performance) of shipborne or portable imaging systems. To reduce weight and provide additional optical freedom for design, a high-refractive-index GRIN lens for infrared optics is proposed. This lens refracts axially transmitted light and gradually reduces the radial distribution of refractive index. Theoretical design results in infrared optics show that, while maintaining the same thermal imaging effect, using an axially gradient refractive index infrared lens can reduce the number of lenses and significantly decrease lens size, thereby reducing the weight and size of the optical system. However, infrared gradient refractive index optical lenses are currently relatively rare in the market, mostly remaining in the laboratory research stage.

[0003] Researchers at Ningbo University, led by Lin, obtained a gradient refractive index infrared chalcogenide glass-ceramic by controlling crystallization. Through the precipitation of Ga₂Se₃ or In₂Se₃ nanocrystals, the refractive index difference Δn of the resulting gradient refractive index material can reach 0.20, but the material's intrinsic refractive index is only 2.6-2.7. Professor Xiang-hua Zhang of the University of Rennes 1 in France and Professor Richardson of the University of Central Florida in the United States also prepared IR-GRINs using controlled crystallization. The resulting refractive index distribution is determined by the precipitated grains, often exhibiting a high refractive index at the edges and a low refractive index at the center, making it difficult to achieve self-converging lenses. Furthermore, this method requires extremely precise temperature control, and the resulting glass-ceramic contains a large number of grains, leading to additional Rayleigh scattering and a decrease in lens transmittance.

[0004] In optical design, using high-refractive-index lenses allows for a shorter focal length, optical path, and lens size while maintaining a fixed lens shape. Lenses made of high-refractive-index materials are also thinner and lighter for the same focal length. Therefore, developing GRIN lenses with even higher refractive indices is essential. Summary of the Invention

[0005] In response to the scarcity of existing high-refractive-index infrared optical materials and the need for lightweight optical systems, this invention provides a high-refractive-index GRIN lens with a refractive index higher than 3.1 at 10 μm and an operating range of 2-18 μm. This lens can reduce the weight and volume of infrared optical systems, providing more flexible optical freedom for optical design. It is simple to prepare, easy to control, low in cost, and easy to mass-produce.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A high-refractive-index GRIN infrared lens, its composition is Ge a As b Se c Te d Among them, the value of a ranges from 9 to 18, the value of b ranges from 17 to 66.5, the value of c ranges from 5 to 16, and the value of d ranges from 19 to 66.5; the refractive index of the high refractive index GRIN infrared lens is greater than 3.1, and the refractive index of the high refractive index GRIN infrared lens is gradually distributed along the axial direction.

[0008] Preferably, the value of a ranges from 9.5 to 18, the value of b ranges from 19 to 57, the value of c ranges from 5 to 14, and the value of d ranges from 25.8 to 66.5; or, the value of a is 9.5, the value of b is 19 to 66.5, the value of c is 5, and the value of d ranges from 19 to 66.5; or, the value of a is 17.2, the value of b is 17.2, the value of c is 10.5 to 16, and the value of d ranges from 49.6 to 55.1.

[0009] The aforementioned high-refractive-index GRIN infrared lens is formed by stacking six types of high-refractive-index infrared glass in order of increasing refractive index, followed by hot pressing and diffusion; the refractive index of all six types of high-refractive-index infrared glass is greater than 3.1 at 10 μm.

[0010] To improve the optical performance of the GRIN infrared lens, as one preferred embodiment, the composition of the six high-refractive-index infrared glasses is as follows: Ge 9.5 As 19 Se5Te 66.5 、Ge 9.5 As 38 Se5Te 47.5 、Ge 9.5 As 41.5 Se5Te 38 、Ge 9.5 As 57 Se5Te 28.5 、Ge 18 As 45 Se 10 Te 27 and Ge 17.2 As 43 Se 14 Te 25.8The refractive indices at 10 μm of the six high-refractive-index infrared glasses were 3.4589, 3.3766, 3.3079, 3.2487, 3.1952, and 3.1355, respectively. The refractive index difference Δn of the product prepared by this method reached 0.3234.

[0011] As another implementation scheme, the compositions of the six high-refractive-index infrared glasses are Se5(Ge) 0.10 As 0.20 Te 0.70 ) 95 Se5 (Ge 0.10 As 0.30 Te 0.60 9. Se5 (Ge 0.10 As 0.40 Te 0.50 ) 95 Se5 (Ge 0.10 As 0.50 Te 0.40 ) 95 Se5 (Ge 0.10 As 0.60 Te 0.30 ) 95 and Se5 (Ge 0.10 As 0.70 Te 0.20 ) 95 The refractive indices at 10 μm of the six high-refractive-index infrared glasses were 3.4589, 3.4421, 3.3766, 3.3079, 3.2487, and 3.1952, respectively. The refractive index difference Δn of the product prepared by this method reached 0.2637.

[0012] As another implementation scheme, the composition of the six high-refractive-index infrared glasses is Ge 17.2 As 17.2 Se x Te (65-x) Where x = 10.5, 12, 13, 14, 14.5 and 16. The refractive indices at 10 μm of the six infrared glasses with high refractive indices are 3.2580, 3.2280, 3.1953, 3.1663, 3.1532 and 3.1371, respectively, all greater than 3.1.

[0013] The present invention is based on Ge 17.2 As 17.2 Se x Te (65-x)The high-refractive-index GRIN lens of this series of glass offers a wider transmission range, a higher refractive index, and a linearly increasing refractive index distribution along the axial direction. Compared to GRIN lenses based on As2Se3 matrix glass, the high-refractive-index GRIN lens of this invention covers the mid-infrared region, providing a wider operating range and adaptability to more working environments. This offers additional freedom in optical design, including additional thermal or chromatic aberration correction and lightweight design.

[0014] To further ensure the optical performance of the product, the above-mentioned method for fabricating a high-refractive-index GRIN infrared lens includes the following specific steps:

[0015] The first step: six types of high-refractive-index infrared glass are processed into matrix glass discs with the same thickness and diameter, and the surfaces are precision polished to a surface roughness Ra<0.05;

[0016] The second step: After cleaning the matrix glass discs obtained in the first step, stack them together in order of increasing refractive index. Place the stacked discs into a hot press mold, then place the hot press mold into a hot press furnace. Evacuate the gas pressure in the hot press furnace to below 10 Pa, set the hot press furnace pressure to 10-100 kPa, and raise the temperature to 250-320 ℃ at a heating rate of 4-10 ℃ / min, and hold for 12-36 h.

[0017] Third step: Open the vent valve of the hot press furnace. After the gas pressure inside the furnace reaches the standard atmospheric pressure, take out the glass sample from the hot press mold and polish the surface with sandpaper to a mirror finish to obtain a GRIN lens.

[0018] Step 4: Place the polished GRIN lens horizontally into the spherical lens mold, place the GRIN lens and the spherical lens mold into the hot press furnace, evacuate the hot press furnace cavity to below 10 Pa, and raise the temperature to 250-320 ℃ at a heating rate of 4-10 ℃ / min without applying pressure, apply a pressure of 10-100 kPa, and hold for 30-60 min;

[0019] Step 5: Open the vent valve of the hot press furnace. After the gas pressure inside the furnace reaches the standard atmospheric pressure, take out the GRIN lens and polish the surface to a mirror finish to obtain a spherical GRIN lens.

[0020] In the above preparation process, controlling the process parameters is crucial. For example, in the first step, roughness control is very important. If the roughness is too high, the interfaces between the glass layers will be obvious and loose, making the lens prone to voids and hindering diffusion. In the second step, if the heating rate is too fast, it will lead to uneven pressure, an uneven glass surface, and a tendency to break. If the heating rate is too slow, it will cause crystallization on the glass surface, resulting in decreased transmittance. Too high a temperature will lead to preparation failure, while too low a temperature will cause delamination, preventing the formation of a complete whole.

[0021] The method described above is applicable to the fabrication of GRIN infrared lenses of any size.

[0022] To meet general production needs, in the first step, the thickness of the matrix glass disc is 1-2 mm and the diameter is 8-30 mm; in the third step, the thickness of the GRIN lens is 2-5 mm and the diameter is 15-50 mm; in the fifth step, the center thickness of the spherical GRIN lens is 2-5 mm and the diameter is 15-50 mm.

[0023] In the second step described above, the hot pressing mold includes matching upper and lower planar mold cores, and a matching first sleeve is provided around the upper and lower planar mold cores; in the second step, the side walls of the upper and lower planar mold cores and the inner wall of the first sleeve are all provided with graphite paper layers to prevent contamination or damage to the mold.

[0024] In the fourth step above, the spherical lens mold includes upper and lower spherical mold cores that match each other. The upper and lower spherical mold cores are surrounded by matching second sleeves. The upper and lower spherical mold cores are made of high-temperature resistant materials such as aluminum alloy, tungsten alloy or stainless steel.

[0025] The method for preparing high-refractive-index infrared glass in this application includes the following steps:

[0026] (1) Quartz tube pretreatment: In order to prevent insoluble impurities on the surface of the quartz tube from being introduced into the glass during the melting process, the inner wall of the quartz tube is first etched with hydrofluoric acid. Hydrofluoric acid is added into the quartz tube with a pipette until the liquid level is about 1 cm from the tube opening. Let it stand for 5-10 minutes to remove the insoluble impurities present in the quartz tube. Then, the hydrofluoric acid in the quartz tube is thoroughly cleaned with deionized water (more than 6 times). The cleaned glass tube is sealed with tin foil at the end, two small holes are made with a needle, and it is placed in an oven and baked at 120 ℃ for more than 12 hours. Before weighing the raw materials, it is taken out and cooled to room temperature.

[0027] (2) Raw material weighing: The weighing process must be completed in the glove box. According to the stoichiometric ratio of each high refractive index infrared glass, use an electronic balance to weigh Ge, As, Se and Te respectively. When weighing, the raw material mass is retained to 4 decimal places. The raw material is loaded into the quartz tube through a small funnel. The quartz tube opening is sealed with rubber bands and self-sealing bags. After all the raw materials are weighed, they are placed in a small transition chamber and vacuumed for later use.

[0028] (3) Vacuum sealing: Open the small transition chamber of the glove box and take out a quartz tube. Evacuate the small transition chamber to prevent the raw materials in other quartz tubes from being oxidized. Quickly remove the self-sealing bag from the quartz tube opening and connect the hose to the vacuum pump. Turn on the mechanical pump switch, slowly unscrew the sealing valve between the quartz tube and the hose, and then close this valve. Unscrew the valve between the hose and the molecular pump to remove the gas in the hose, and close this valve. Repeat the above steps 3 times. After the mechanical pump reaches a reading of 10 Pa, turn on the molecular pump to reach 10⁻⁴ Pa. Use an oxyhydrogen flame torch to seal the quartz tube. The sealing should be done in a spiral shape to ensure the quartz tube is sealed.

[0029] (4) High-temperature melting: Based on the length of the quartz tube, place quartz wool at the bottom of the oscillating furnace chamber to ensure that the raw material is positioned at the thermocouple position within the furnace chamber. Then, wrap a ring of quartz wool around the quartz tube and slowly place it into the furnace chamber. Quartz wool should also be placed at the furnace opening to prevent the glass from shaking during melting. To prevent the glass from colliding with the quartz tube before melting, select a temperature of 250 ℃ (higher than the melting point of Se) before turning on the oscillating mechanism. Hold the glass at 250 ℃ for 60 minutes, then raise the temperature to 460 ℃ and hold for 60 minutes, then raise the temperature to 620 ℃ and hold for 60 minutes, then raise the temperature to 850 ℃ and hold for at least 24 hours. Stop the oscillating mechanism 2 hours before the cooling process begins and allow the temperature to drop to the furnace outlet temperature of 600 ℃ and hold for at least 2 hours. This is to release air bubbles in the molten glass. Finally, turn off the program and prepare for unloading.

[0030] (5) Quenching and annealing: Fill an iron bucket with cold water for later use. Open the furnace lid, use tongs to slowly remove the quartz wool from the top of the furnace, and then slowly remove the quartz tube. Let it stand in the air for 10-15 seconds, then quickly put it into the cold water for quenching. Observe the glass detachment from the wall inside the quartz tube. After the glass has completely detached from the wall, put the quartz tube into the muffle furnace for annealing. Set the annealing temperature to 190±10 ℃ and adjust the holding time to 2h.

[0031] Any techniques not mentioned in this invention are based on existing technologies.

[0032] The high refractive index GRIN infrared lens disclosed in this invention is composed of Ge a As b Se c Te d The working range is 2-18 μm, and the refractive index n 10 > 3.1, Abbe number ν 10 >200 has advantages such as high refractive index, transparency in the long-wave infrared band (8-12 μm), good thermal stability (the selected glass material has no crystallization peak), easy processing, and moldability. The axial distribution of refractive index increases linearly, and the refractive index difference Δn can reach 0.3234, which provides more flexible freedom for optical design, including providing additional thermal or chromatic aberration correction and lightweight design. It has broad application prospects in the fields of infrared imaging and infrared optics. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the fabrication process of the high-refractive-index GRIN infrared lens of the present invention.

[0034] Figure 2 The refractive indices of the six high-refractive-index infrared glasses of this invention are shown below.

[0035] Figure 3 This is the hot pressing mold used in the fabrication of the GRIN lens of this invention;

[0036] Figure 4 This is a spherical lens mold used in the fabrication of the spherical GRIN lens of the present invention;

[0037] Figure 5 This is a schematic diagram of the imaging device of the present invention;

[0038] Figure 6 The infrared transmission spectrum of the high refractive index GRIN infrared lens of this invention;

[0039] Figure 7 Infrared transmission spectra of six types of high refractive index infrared glasses of the present invention;

[0040] Figure 8 The elemental distribution diagrams are for the high refractive index GRIN infrared lenses obtained by long-term diffusion (12 h) and short-term diffusion (20 min) of the present invention.

[0041] Figure 9 This is an interface photograph of the high refractive index GRIN infrared lens obtained by long-term diffusion (12 h) and short-term diffusion (20 min) of the present invention;

[0042] Figure 10 A schematic diagram illustrating the use of the high-refractive-index GRIN infrared lens (b) of the present invention to replace the existing lens (a) for imaging;

[0043] Figure 11 The DSC curve of the high-refractive-index GRIN lens of this invention;

[0044] In the figure, 1 is a glass preform, 2 is a matrix glass disc, 3 is a GRIN lens, 4 is a spherical lens mold, 5 is a spherical GRIN lens, 6 is the upper and lower planar mold cores, 7 is the first sleeve, 8 is the upper and lower spherical mold cores, 9 is the second sleeve, 10 is a grid, 11 is a hot plate, and 12 is a thermal imaging camera. Detailed Implementation

[0045] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0046] The preparation methods of the high refractive index infrared glass in each example include the following steps:

[0047] (1) Quartz tube pretreatment: Use a pipette to add 40% hydrofluoric acid to the quartz tube until the liquid level is about 1 cm away from the tube opening. Let it stand for 8 min, then wash the quartz tube with deionized water. Seal the end of the cleaned quartz tube with tin foil, poke two small holes with a needle, and put it in an oven to bake at 120 ℃ for 20 h. Before weighing the raw materials, take it out and cool it to room temperature.

[0048] (2) Raw material weighing: The entire weighing process must be completed in the glove box. According to the stoichiometric ratio of the high refractive index infrared glass, use an electronic balance to weigh Ge, As, Se and Te respectively (the raw material mass is retained to 4 decimal places when weighing). Put the raw materials into the quartz tube through a small funnel, seal the quartz tube opening with rubber bands and self-sealing bags, and put it into the small transition chamber for vacuuming after all weighing is completed.

[0049] (3) Vacuum sealing: Open the small transition chamber of the glove box and take out a quartz tube. Evacuate the small transition chamber to prevent the raw materials in other quartz tubes from being oxidized. Quickly remove the self-sealing bag from the quartz tube opening and connect the hose to the vacuum pump. Turn on the mechanical pump switch, slowly unscrew the sealing valve between the quartz tube and the hose, and then close this valve. Unscrew the valve between the hose and the molecular pump to remove the gas in the hose, and close this valve. Repeat the above steps 3 times. After the mechanical pump reaches a reading of 10 Pa, turn on the molecular pump to reach 10⁻⁴ Pa. Use an oxyhydrogen flame torch to seal the quartz tube. The sealing should be done in a spiral shape to ensure the quartz tube is sealed.

[0050] (4) High-temperature melting: Based on the length of the quartz tube, place quartz wool at the bottom of the oscillating furnace cavity to ensure that the raw material is positioned at the thermocouple position in the furnace cavity. Then wrap a ring of quartz wool around the outside of the quartz tube and slowly place it into the furnace cavity. Place quartz wool at the furnace opening to prevent the glass from shaking during melting. To prevent the glass from colliding with the quartz tube before melting, select a temperature that has been raised to 250 ℃ (higher than the melting point of Se) before turning on the oscillating. Hold the glass at 250 ℃ for 60 min, raise the temperature to 460 ℃ for 60 min, raise the temperature to 620 ℃ for 60 min, raise the temperature to 850 ℃ for 30 h, stop the oscillating and let it stand for 2 h before the cooling program begins. Lower the temperature to the furnace outlet temperature of 600 ℃ and hold for 3 h, then turn off the program and prepare to unload the glass.

[0051] (5) Quenching and annealing: Fill an iron bucket with cold water for later use. Open the furnace lid, use tongs to slowly remove the quartz wool from the top of the furnace, and then slowly remove the quartz tube. Let it stand in the air for 12 seconds, then quickly put it into the cold water for quenching. Observe the glass detachment from the wall inside the quartz tube. After the glass has completely detached from the wall, quickly put the quartz tube into the muffle furnace for annealing. Set the annealing temperature to 190±10 ℃ and adjust the holding time to 2h. After annealing, let it cool naturally to room temperature to obtain high refractive index infrared glass.

[0052] Example 1

[0053] In this embodiment, the process and performance parameters for fabricating the high-refractive-index GRIN lens are shown in Table 1.

[0054] Specifically, the fabrication of the high-refractive-index GRIN lens in Example 1, such as... Figure 1 As shown, it includes the following steps:

[0055] The first step: Process six types of high-refractive-index infrared glass into matrix glass discs of uniform thickness and diameter. The composition of the six types of high-refractive-index infrared glass is Ge. 9.5 As 19 Se5Te 66.5 、Ge 9.5 As 38 Se5Te 47.5 、Ge 9.5 As 41.5 Se5Te 38 、Ge 9.5 As 57 Se5Te 28.5 、Ge 18 As 45 Se 10 Te 27 and Ge 17.2 As 43 Se 14 Te 25.8 The linear refractive index of six types of high-refractive-index infrared glass was measured, such as... Figure 2 The refractive index exhibits a gradient distribution. The refractive indices at 10 μm for the six types of infrared glass with high refractive indices are 3.4589, 3.3766, 3.3079, 3.2487, 3.1952, and 3.1355, respectively. The surfaces of the matrix glass discs are precision polished, with a thickness controlled at 1.5 mm and a diameter of 10 mm, and the roughness requirement is Ra<0.05.

[0056] The second step: After cleaning the six types of matrix glass discs obtained, stack them together according to their refractive index from low to high (a total of six discs). Then, place the stacked lenses into... Figure 3 The hot press mold shown (between the upper and lower planar mold cores) includes matching upper and lower planar mold cores. The upper and lower planar mold cores are surrounded by matching first sleeves. The side walls of the upper and lower planar mold cores and the inner wall of the first sleeve are all covered with graphite paper layers. The mold is placed in a hot press furnace, the gas pressure in the hot press furnace is evacuated to below 10 Pa, the pressure of the hot press furnace is set to 10 kPa, and the temperature is raised to 270 ℃ at a heating rate of 6 ℃ / min and held for 12 h.

[0057] The third step: Open the vent valve of the hot press furnace. After the gas pressure inside the furnace reaches the standard atmospheric pressure, take out the glass sample from the hot press mold and polish the surface with sandpaper to a mirror finish to obtain a GRIN lens with a thickness of 2 mm and a diameter of 21 mm.

[0058] Step 4: Place the polished GRIN lens horizontally as shown in the image. Figure 4 The spherical lens mold shown has tungsten alloy used for the upper and lower spherical mold cores. The GRIN lens and the mold are placed in a hot press furnace. The furnace cavity of the hot press is evacuated to below 10 Pa. Without applying pressure, the temperature is raised to 270 ℃ at a heating rate of 6 ℃ / min. A pressure of 10 kPa is applied and the temperature is held for 30 min.

[0059] Step 5: Open the vent valve of the autoclave. After the internal pressure reaches standard atmospheric pressure, remove the glass sample and polish the surface to a mirror finish to obtain a spherical GRIN lens with a center thickness of 2 mm, a diameter of 21 mm, a working range of 2-20 μm, and a refractive index of n. 10 > 3.1, Abbe number ν 10 > 200.

[0060] To observe the imaging of the obtained high-refractive-index spherical GRIN lens, a system was constructed as shown in the attached diagram. Figure 5 The illustrated simple imaging device includes a grid 9, a hot plate 10, and a thermal imaging camera 11. The grid is imaged through the sample by the thermal imaging camera. When the grid passes through a high-refractive-index GRIN lens, the grid will be significantly distorted. Figure 5 (b) The image of the spherical GRIN lens is removed. (c) The image of the spherical GRIN lens is retained. The distortion effect is very clearly removed. It can be seen that the grid has excellent imaging effect through the high refractive index GRIN lens.

[0061] The infrared transmission spectrum of the obtained high-refractive-index spherical GRIN lens is as follows: Figure 6 As shown, the infrared transmission spectra of six matrix glasses are compared (e.g., Figure 7 As shown in the figure, the long-wave infrared transmittance is still very good.

[0062] Elemental distributions of a high-refractive-index GRIN infrared lens after long-term diffusion (12 h) and short-term diffusion (20 min) are as follows: Figure 8 As shown, the horizontal axis represents the axial height of the lens, from... Figure 8 It can be seen that after long-term diffusion, the elemental distribution (i.e., refractive index distribution) tends to change linearly with distance. For example... Figure 9As shown, after 20 minutes of diffusion, the interfaces between the layers of the GRIN lens are obvious (right), and after 12 hours of diffusion, the layers of the GRIN lens have diffused uniformly (left), the interfaces between the layers have disappeared, forming a whole, with no holes or cracks inside, and Δn reaches 0.3234.

[0063] The resulting high-refractive-index spherical GRIN lens can be combined with lenses made of other materials to form an optical system. It benefits from both its high refractive index (>3.1) and gradient refractive index, such as... Figure 10 As shown in the diagram, this further reduces the size and weight of the optical system, providing optical designers with additional freedom.

[0064] like Figure 11 As shown, the prepared GRIN lens still did not have a crystallization peak at 350℃.

[0065] Examples 2-8:

[0066] In Examples 2-8, except for the differences in the parameters in Table 1 (the hot-pressing parameters in the second step), the preparation methods of the high-refractive-index GRIN lenses are the same as in Example 1, and the performance and cross-sectional refractive index change curves of the obtained high-refractive-index GRIN lenses are similar to those in Example 1. The process and performance parameters for preparing high-refractive-index GRIN lenses in each example are listed in Table 1.

[0067] Table 1. Process and performance parameters of each embodiment

[0068] Example Temperature (°C) Time (h) Pressure (kPa) Transmittance @10μm Single piece thickness (mm) Single piece diameter (mm) Center thickness (mm) Lens diameter (mm) Example 1 270 12 10 45.98% 1.5 10 2 21 Example 2 250 12 10 44.77% 1.2 8 2 15 Example 3 260 12 50 43.54% 1.5 15 3 26 Example 4 280 24 50 43.09% 1 15 3 21 Example 5 290 24 80 41.58% 1 20 4 25 Example 6 300 36 80 40.56% 2 25 4 43 Example 7 310 36 100 40.07% 2 25 5 39 Example 8 320 36 100 40.55% 2 30 4 50 Example 9 270 12 10 40.37% 8 80 4.8 200

[0069] In Table 1, temperature, time, and pressure refer to the highest temperature, holding time, and pressure of hot pressing in the second step, respectively.

[0070] Example 10

[0071] Unlike Example 1, in the first step, the six materials were replaced with Se5 (Ge) 0.10 As 0.20 Te 0.70 ) 95 Se5 (Ge 0.10 As 0.30 Te 0.60 9. Se5 (Ge 0.10 As 0.40 Te 0.50 ) 95 Se5 (Ge 0.10 As 0.50 Te 0.40 ) 95 Se5 (Ge 0.10 As 0.60 Te 0.30 ) 95and Se5 (Ge 0.10 As 0.70 Te 0.20 ) 95 The refractive indices at 10 μm of the six high-refractive-index infrared glasses were 3.4589, 3.4421, 3.3766, 3.3079, 3.2487, and 3.1952, respectively. In the second and fourth steps, the temperature was raised to 260°C, and the rest were the same as in Example 1. The interfaces between the layers of the resulting GRIN lens disappeared, forming a whole, and the refractive index changed smoothly along the axial direction, with Δn reaching 0.2637.

[0072] Comparative Example 1

[0073] Unlike Example 1, in the first step, no surface precision polishing was performed, and the surface roughness Ra of each matrix glass disc was 0.2. The rest were the same as in Example 1. The interfaces between the glass layers were obvious and not tight, resulting in void defects in the lens, making diffusion difficult and uneven. The transmittance of the GRIN lens prepared in Example 1 decreased by 20%.

[0074] Comparative Example 2

[0075] The difference from Example 1 is that in the second step, the heating rate is 15°C / min, while the rest is the same as in Example 1. Due to the excessively rapid heating rate, the glass softens quickly, leading to uneven pressure, an uneven glass surface, and breakage during the preparation process.

[0076] Comparative Example 3

[0077] The difference from Example 1 is that in the second step, the heating rate is 2°C / min, while the rest is the same as in Example 1. Due to the slow heating rate, the glass did not soften and the pressure was applied for too long, resulting in crystallization on the glass surface. As a result, the transmittance of the lens obtained in Example 1 decreased by 18%.

[0078] Comparative Example 4

[0079] Unlike Example 1, in the second step, the temperature was raised to 350°C, while the rest was the same as in Example 1. Due to the excessively high temperature, the viscosity of the glass melt was too low, causing it to flow out of the mold during diffusion, resulting in preparation failure.

[0080] Comparative Example 5

[0081] Unlike Example 1, in the second step, the temperature was raised to 220°C, while the rest of the steps were the same as in Example 1. Because the temperature was too low, the glass did not soften completely, and diffusion did not occur between the layers, resulting in lens delamination.

[0082] Comparative Example 6

[0083] The difference from Example 1 is that in the second step, the heat preservation time is 40 hours, while the rest is the same as in Example 1. Due to the excessively long heat preservation time, the molten glass adheres tightly to the inner wall of the mold, causing the glass edges to shatter upon demolding.

[0084] Comparative Example 7

[0085] The difference from Example 1 is that in the second step, the heat preservation time is 10 hours, while the rest is the same as in Example 1. Due to the short heat preservation time, the diffusion distance between the glass layers is short, and the refractive index still exhibits a step-like distribution.

Claims

1. A method for fabricating a high-refractive-index GRIN infrared lens, characterized in that: The high-refractive-index GRIN infrared lens is formed by stacking six types of high-refractive-index infrared glass in order of increasing refractive index, followed by hot pressing and diffusion; the refractive index of all six types of high-refractive-index infrared glass is greater than 3.1 at 10 μm. The refractive index of the high-refractive-index GRIN infrared lens increases linearly along the axial direction, with a refractive index difference Δn reaching 0.3234; The compositions of the six high-refractive-index infrared glasses are Ge 9.5 As 19 Se5Te 66.5 、Ge 9.5 As 38 Se5Te 47.5 、Ge 9.5 As 41.5 Se5Te 38 、Ge 9.5 As 57 Se5Te 28.5 、Ge 18 As 45 Se 10 Te 27 and Ge 17.2 As 43 Se 14 Te 25.8 The refractive indices at 10 μm of the six high-refractive-index infrared glasses were 3.4589, 3.3766, 3.3079, 3.2487, 3.1952 and 3.1355, respectively. The fabrication method of a high-refractive-index GRIN infrared lens includes the following specific steps: The first step: six types of high-refractive-index infrared glass are processed into matrix glass discs with the same thickness and diameter, and the surfaces are precision polished to a surface roughness Ra<0.05; The second step: After cleaning the matrix glass discs obtained in the first step, stack them together in order of increasing refractive index. Place the stacked discs into a hot press mold, and then place the hot press mold into a hot press furnace. Evacuate the gas pressure in the hot press furnace to below 10 Pa, set the hot press furnace pressure to 10-100 kPa, and raise the temperature to 250-320℃ at a heating rate of 4-10 ℃ / min, and hold for 12-36 h. Third step: Open the vent valve of the hot press furnace. After the gas pressure inside the furnace reaches the standard atmospheric pressure, take out the glass sample from the hot press mold and polish the surface with sandpaper to a mirror finish to obtain a GRIN lens. Step 4: Place the polished GRIN lens horizontally into the spherical lens mold, place the GRIN lens and the spherical lens mold into the hot press furnace, evacuate the hot press furnace cavity to below 10 Pa, and raise the temperature to 250-320 ℃ at a heating rate of 4-10 ℃ / min without applying pressure, apply a pressure of 10-100 kPa, and hold for 30-60 min; Step 5: Open the vent valve of the hot press furnace. After the gas pressure inside the furnace reaches the standard atmospheric pressure, take out the GRIN lens and polish the surface to a mirror finish to obtain a spherical GRIN lens.

2. The preparation method according to claim 1, characterized in that: The compositions of the six high-refractive-index infrared glasses are Se5(Ge) 0.10 As 0.20 Te 0.70 ) 95 Se5 (Ge 0.10 As 0.30 Te 0.60 9. Se5 (Ge 0.10 As 0.40 Te 0.50 ) 95 Se5 (Ge 0.10 As 0.50 Te 0.40 ) 95 Se5 (Ge 0.10 As 0.60 Te 0.30 ) 95 and Se5 (Ge 0.10 As 0.70 Te 0.20 ) 95 The refractive indices at 10 μm of the six high-refractive-index infrared glasses were 3.4589, 3.4421, 3.3766, 3.3079, 3.2487 and 3.1952, respectively.

3. The preparation method according to claim 1 or 2, characterized in that: In the first step, the matrix glass disc has a thickness of 1-2 mm and a diameter of 8-30 mm; in the third step, the GRIN lens has a thickness of 2-5 mm and a diameter of 15-50 mm; in the fifth step, the spherical GRIN lens has a center thickness of 2-5 mm and a diameter of 15-50 mm.

4. The preparation method according to claim 1 or 2, characterized in that: In the second step, the hot pressing mold includes matching upper and lower planar mold cores, and a matching first sleeve is provided around the upper and lower planar mold cores; in the second step, the side walls of the upper and lower planar mold cores and the inner wall of the first sleeve are all provided with graphite paper layers.

5. The preparation method according to claim 1 or 2, characterized in that: In the fourth step, the spherical lens mold includes upper and lower spherical mold cores that match each other. The upper and lower spherical mold cores are surrounded by matching second sleeves. The upper and lower spherical mold cores are made of aluminum alloy, tungsten alloy or stainless steel.

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