A method for manufacturing a 0.9-1.7 mu m narrow-band linearly variable filter

Abstract

The application discloses a preparation method of a 0.9-1.7 mu m narrow-band linearly graded filter. The 0.9-1.7 mu m narrow-band linearly graded filter comprises a substrate and a first distributed Bragg reflector, the first distributed Bragg reflector comprises a plurality of dielectric films arranged in a stack, and the preparation method comprises the following steps: preparing the substrate; determining target thickness information and target transmittance information of the dielectric films according to target spectral performance of the linearly graded filter; determining a film plating time of the dielectric films according to the thickness information and the transmittance information; preparing the dielectric films on one side of the substrate by using an ion beam reactive sputtering film plating process; acquiring real-time thickness information and real-time light transmittance information of the dielectric films; and adjusting the film plating time according to the real-time thickness information, the real-time light transmittance information, the target thickness information and the target transmittance information to complete preparation of the dielectric films and further complete preparation of the first distributed Bragg reflector. The application can improve the spectral precision, stability, transmittance and batch consistency of the 0.9-1.7 mu m narrow-band linearly graded filter.

Description

Technical Field

[0001] This invention relates to the field of optical thin film device manufacturing technology, and in particular to a method for preparing a 0.9-1.7μm narrowband linear gradient filter. Background Technology

[0002] Near-infrared spectroscopy has broad application prospects in agriculture, food, pharmaceuticals, and chemicals. As the core spectroscopic element of a portable near-infrared spectrometer, the performance of the linear variable filter (LVF) directly determines the spectral resolution and measurement accuracy of the entire instrument.

[0003] Currently, the traditional methods for fabricating linear graded filters mainly suffer from the following technical problems: 1. Limited spectral accuracy: Existing narrowband filtering technologies based on laser coating suffer from wedge-angle interference, leading to severe crosstalk between channels, and the spectral accuracy is typically only around 20nm. 2. Poor stability: Films prepared by traditional evaporation coating methods have low density and weak adhesion, and are prone to drift when the ambient temperature changes (wavelength drift can reach more than 10nm), seriously affecting the long-term stability of the instrument. 3. Insufficient passband transmittance: Linear graded filters prepared by existing processes typically have an average transmittance of less than 80% and a peak transmittance of less than 85% in the 950-1700nm band, resulting in low light energy utilization and affecting the detection signal-to-noise ratio. 4. Difficulty in ensuring batch consistency: Due to the lack of precise online monitoring methods, the center wavelength deviation between different batches of products is large (more than ±5nm), which is not conducive to the standardized production of instruments and model portability. Summary of the Invention

[0004] This invention provides a method for preparing a 0.9-1.7μm narrowband linear graded filter, in order to solve the problems of low spectral accuracy, poor stability, low transmittance, and difficulty in ensuring batch consistency in existing linear graded filter preparation methods.

[0005] This invention provides a method for fabricating a 0.9-1.7μm narrowband linear graded filter. The 0.9-1.7μm narrowband linear graded filter includes a substrate and a first distributed Bragg mirror. The first distributed Bragg mirror includes multiple dielectric films stacked together. The fabrication method includes: Preparation of substrate; The target thickness and target transmittance information of the dielectric film are determined based on the target spectral performance of the linear graded filter. The coating time of the dielectric film is determined based on the thickness information and the transmittance information; The dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process; Obtain the real-time thickness and real-time transmittance information of the dielectric film; The coating time is adjusted according to the real-time thickness information, the real-time transmittance information, the target thickness information, and the target transmittance information to complete the preparation of the dielectric film, thereby completing the preparation of the first distributed Bragg mirror. The dielectric film includes multiple first dielectric films and multiple second dielectric films, which are periodically stacked alternately. The refractive index of the first dielectric film is greater than that of the second dielectric film.

[0006] Optionally, after preparing the substrate, the preparation method further includes: The substrate is mounted on a planetary fixture and fed into a vacuum chamber, wherein the planetary fixture adopts a combined rotation and revolution motion mode. The dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process, comprising: The reaction gas and argon gas are introduced into the vacuum chamber; The ion source is controlled to emit an argon ion beam toward the target material to generate target atoms; The target atoms react chemically with the reactive gas to generate the dielectric film.

[0007] Optionally, the reactant gas includes oxygen; The oxygen flow rate Q1 satisfies: 10 sccm ≤ Q1 ≤ 50 sccm; the argon flow rate Q2 satisfies: 30 sccm ≤ Q2 ≤ 80 sccm; The power of the ion source satisfies: 800W≤P1≤1500W; The air pressure P2 in the vacuum chamber satisfies: 1×10 -3 Pa≤P2≤5×10 -3 Pa.

[0008] Optionally, before controlling the ion source to emit an argon ion beam towards the target to generate target atoms, the preparation method further includes: The target material is pre-melted.

[0009] Optionally, after mounting the substrate onto the planetary fixture and feeding it into the vacuum chamber, the preparation method further includes: The surface of the substrate is cleaned by ion bombardment using the ion source, wherein the power P3 of the ion source satisfies: 100W≤P3≤300W, the ion bombardment cleaning time t1 satisfies: 5min≤t1≤15min, and the voltage U1 applied to the substrate satisfies: -100V≤U1≤-300V.

[0010] Optionally, after preparing the substrate, the preparation method further includes: The substrate is polished; The polished substrate is cleaned to achieve a surface accuracy of λ / 4@632.8nm and a parallelism of less than 3arcmin.

[0011] Optionally, the 0.9-1.7μm narrowband linear gradient filter further includes a resonant cavity layer and a second distributed Bragg mirror; The preparation method further includes: A resonant cavity layer is fabricated on the side of the first distributed Bragg reflector away from the substrate, wherein the thickness of the resonant cavity layer varies linearly along a first direction, which intersects the thickness direction of the substrate; The second distributed Bragg reflector is fabricated on the side of the resonant cavity layer away from the substrate. The 0.9-1.7μm narrowband linear gradient filter has a peak transmittance greater than or equal to 90%@1325nm±50nm, an average transmittance greater than or equal to 85%, and a half-bandwidth range of 6-8nm.

[0012] Optionally, after fabricating the second distributed Bragg reflector on the side of the resonant cavity layer away from the substrate, the fabrication method further includes: The 0.9-1.7μm narrowband linear gradient filter is subjected to cooling treatment.

[0013] Optionally, after mounting the substrate onto the planetary fixture and feeding it into the vacuum chamber, the preparation method further includes: The vacuum chamber is evacuated to reduce the gas pressure inside to less than 1 × 10⁻⁶. -5 Pa.

[0014] Optionally, evacuating the vacuum chamber includes: Start the mechanical pump to reduce the air pressure in the vacuum chamber to less than 10 Pa; Start the molecular pump to reduce the gas pressure in the vacuum chamber to less than 1 × 10⁻⁶. -5 Pa, and maintain for the preset time.

[0015] The technical solution of this invention, by setting up an ion beam reactive sputtering coating process to prepare a dielectric film, and adjusting the coating time of the dielectric film according to the real-time thickness information, real-time transmittance information, target thickness information, and target transmittance information of the dielectric film, can improve the density of the generated dielectric film and achieve precise control over the thickness and transmittance of the dielectric film. This is beneficial to improving the spectral accuracy, stability, transmittance, and batch consistency of linear gradient filters.

[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a method for fabricating a 0.9-1.7μm narrowband linear graded filter, as provided in an embodiment of the present invention; Figure 2 A schematic diagram of the substrate and the first distributed Bragg mirror in a 0.9-1.7μm narrowband linear gradient filter provided for an embodiment of the present invention; Figure 3 A flowchart illustrating another method for preparing a 0.9-1.7μm narrowband linear graded filter according to an embodiment of the present invention; Figure 4 This is a cross-sectional schematic diagram of the resonant cavity layer in a 0.9-1.7μm narrowband linear gradient filter provided for an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices. The terms "upper," "lower," "left," "right," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings and are only used to describe the relative positional relationships between components or constituent parts, and do not specifically limit the specific installation orientation of each component or constituent part.

[0021] Figure 1 The flowchart illustrates a method for fabricating a 0.9-1.7 μm narrowband linear graded filter, as provided in this embodiment of the invention. (Refer to...) Figure 1 The method for preparing the linear graded filter in this embodiment of the invention includes: S110, Prepare the substrate.

[0022] Figure 2 This is a schematic diagram of the substrate and the first distributed Bragg mirror in a 0.9-1.7μm narrowband linear graded filter, provided as an embodiment of the present invention. (Refer to...) Figure 2 The substrate 10 can be prepared using fused silica or single-crystal germanium materials. The maximum outer circular diameter of the substrate 10 does not exceed 30 mm and the thickness does not exceed 3 mm.

[0023] Optionally, after preparing the substrate 10, the preparation method in this embodiment of the invention further includes: polishing the substrate 10; cleaning the polished substrate 10 so that the surface accuracy of the substrate 10 reaches λ / 4@632.8nm and the parallelism is less than 3arcmin.

[0024] For example, the substrate 10 can be precision polished until the surface accuracy of the substrate 10 reaches λ / 4@632.8nm, the surface finish reaches the 60-40 standard, and the parallelism is better than 3 arcmin. It should be noted that the 60-40 standard refers to a scratch grade of 60 and a pitting grade of 40.

[0025] For example, the cleaning steps for the polished substrate 10 can be as follows: First, use a special optical cleaning agent to perform ultrasonic cleaning for 10-15 minutes to remove organic contaminants; then, immerse the substrate 10 in deionized water for multiple rinses for 5 minutes to remove residual cleaning agent; then, immerse the substrate 10 in high-purity anhydrous ethanol or acetone for ultrasonic cleaning for 5 minutes to remove water stains and oil; next, use high-purity nitrogen (purity ≥99.999%) to dry the surface of the substrate 10, ensuring that there are no water stains or particles on the surface; finally, store the cleaned substrate 10 in a Class 100 cleanroom for later use.

[0026] Optionally, after preparing the substrate 10, the preparation method in this embodiment of the invention further includes: mounting the substrate 10 on a planetary fixture and sending it into a vacuum chamber, wherein the planetary fixture adopts a combined rotation and revolution motion mode.

[0027] For example, a clean substrate 10 is precisely mounted onto the planetary fixture of the coating machine to ensure good contact between the substrate 10 and the fixture without stress concentration. After mounting the substrate 10 onto the planetary fixture, the planetary fixture loaded with the substrate 10 can be sent into the vacuum chamber through the chamber door, and then the chamber door is closed for sealing. To convert the wedge angle interference of the linear graded filter into a controllable linear gradient, thereby significantly improving the spectral uniformity and imaging quality of the linear graded filter, the planetary fixture in this embodiment of the invention adopts a combined revolution and rotation motion mode, and the substrate 10 can perform a combined revolution and rotation motion with the fixture. Specifically, the revolution speed of the planetary fixture ranges from 1 rpm to 5 rpm, and the rotation speed ranges from 10 rpm to 30 rpm.

[0028] Optionally, after mounting the substrate 10 onto the planetary fixture and feeding it into the vacuum chamber, the preparation method in this embodiment of the invention further includes: evacuating the vacuum chamber to make the gas pressure in the vacuum chamber less than 1×10⁻⁶. -5 Pa.

[0029] Vacuuming before preparing the dielectric film is to eliminate the influence of oxygen, water vapor, and various impurities in the vacuum chamber on the formation of the dielectric film, which can improve the optical performance, appearance quality, and adhesion of the dielectric film.

[0030] As a feasible implementation method, evacuating the vacuum chamber includes: starting a mechanical pump to reduce the gas pressure in the vacuum chamber by 10 Pa; and starting a molecular pump to reduce the gas pressure in the vacuum chamber by less than 1 × 10⁻⁶ Pa. -5 Pa, and maintain for the preset time.

[0031] During the vacuuming process, mechanical pumps can quickly remove atmosphere, water vapor, and most impurity gases, which helps to shorten the vacuuming time; molecular pumps can operate at high efficiency under low pressure to achieve high vacuum. To ensure that the vacuum chamber is fully degassed, the above-mentioned preset time should be greater than 30 minutes.

[0032] Optionally, after mounting the substrate 10 on the planetary fixture and sending it into the vacuum chamber, the preparation method in this embodiment of the invention further includes: using an ion source to perform ion bombardment cleaning on the surface of the substrate 10, wherein the power P3 of the ion source satisfies: 100W≤P3≤300W, the ion bombardment cleaning time t1 satisfies: 5min≤t1≤15min, and the voltage U1 applied to the substrate 10 satisfies: -100V≤U1≤-300V.

[0033] For example, the ion source is turned on, ionizing argon gas to form a high-energy argon ion beam, which is then directed to bombard the surface of the substrate 10 to perform plasma ion cleaning. This removes adsorbed gases and trace contaminants from the last few atomic layers of the substrate 10 surface, improving the adhesion between the film layer and the substrate. It should be noted that when using the ion source to perform ion bombardment cleaning on the surface of the substrate 10, the argon gas flow rate is in the range of 10 sccm-30 sccm.

[0034] S120. Determine the target thickness and target transmittance information of the dielectric film based on the target spectral performance of the linear gradient filter.

[0035] For example, the film structure of a linearly graded filter can be designed based on the target spectral performance of the filter. The target spectral performance can include the passband range (e.g., 950nm-1700nm) and half-bandwidth range (e.g., 6nm-8nm) of the linearly graded filter. The film structure can include the target thickness and target transmittance information of the dielectric film. In this embodiment, the linearly graded filter uses a multilayer film structure with alternating deposition of Ta2O5 and SiO2 dielectric films, and the number of dielectric films can be 80-150 layers. It should be noted that the refractive indices of the Ta2O5 and SiO2 dielectric films are different; the refractive index of the Ta2O5 dielectric film is greater than that of the SiO2 dielectric film.

[0036] It is understood that the thickness of the dielectric film is mainly determined by the coating time and deposition rate. In order to achieve precise control over the thickness of the generated dielectric film, this embodiment of the invention also uses a crystal oscillator control system to calibrate the deposition rate.

[0037] S130. Determine the coating time of the dielectric film based on the thickness and transmittance information.

[0038] It is understood that the thickness of the dielectric film is mainly determined by the coating time and deposition rate. In this embodiment of the invention, the thickness of the generated dielectric film can be precisely controlled by stabilizing the calibration rate and changing the coating time.

[0039] S140. A dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process.

[0040] As a feasible implementation method, a dielectric film is prepared on one side of a substrate using an ion beam reactive sputtering deposition process, which includes: introducing a reactive gas and argon gas into a vacuum chamber; controlling an ion source to emit an argon ion beam toward a target to generate target atoms; and the target atoms reacting chemically with the reactive gas to generate a dielectric film.

[0041] For example, the reaction gas includes oxygen; the oxygen flow rate Q1 satisfies: 10 sccm ≤ Q1 ≤ 50 sccm; the argon flow rate Q2 satisfies: 30 sccm ≤ Q2 ≤ 80 sccm; the ion source power satisfies: 800W ≤ P1 ≤ 1500W; and the gas pressure P2 in the vacuum chamber satisfies: 1 × 10⁻⁶. -3 Pa≤P2≤5×10 -3 Pa.

[0042] For example, the specific deposition process for each dielectric film can be as follows: 1. Introduce reactive gas: High-purity oxygen (purity ≥99.999%) is precisely introduced into the vacuum chamber using a mass flow meter. The flow rate of this reactive gas is controlled within the range of 10 sccm-50 sccm. Simultaneously, argon gas is also introduced into the vacuum chamber, with a flow rate controlled within the range of 30 sccm-80 sccm. The oxygen to argon flow ratio is controlled between 1:3 and 1:5. 2. Activate the ion source: The ion source is activated to generate an argon ion beam. The power range of the main ion source is 800W-1500W, and the beam current density range is 0.5 mA / cm². 2 -2.0mA / cm 2 3. Sputtering targets: Under an electric field acceleration, an argon ion beam bombards metal or oxide targets at high speed. Sputtering a Ta target can generate tantalum pentoxide (Ta₂O₅), with a refractive index n≈2.1@1000nm. Sputtering a Si target can generate silicon dioxide (SiO₂), with a refractive index n≈1.45@1000nm. The sputtering voltage range is 400V-600V. The deposition rate of Ta₂O₅ ranges from 0.3-0.8nm / s, and the deposition rate of SiO₂ ranges from 0.5-1.2nm / s. 4. Reactive sputtering film formation: The bombarded target atoms (Ta and Si atoms) fly towards the rotating substrate. During flight, they react chemically with oxygen atoms to form the desired oxide molecules (Ta₂O₅, SiO₂). The oxide molecules reach the substrate surface with high kinetic energy and adhere firmly, accumulating layer by layer to form a dense and uniform dielectric film.

[0043] Optionally, before controlling the ion source to emit an argon ion beam towards the target to generate target atoms, the preparation method in this embodiment of the invention further includes: pre-melting the target.

[0044] For example, Ta and Si targets are pre-melted for 5-10 minutes respectively. The ion source power during pre-melting can be 80% of that during normal sputtering. By pre-melting the target materials, the target surface can be purified and the evaporation rate can be stabilized, eliminating oxide and impurity layers on the target surface.

[0045] S150. Obtain real-time thickness and real-time transmittance information of the dielectric film.

[0046] For example, a dual monitoring system can be used to monitor the growth of the dielectric film in real time. Specifically, crystal oscillator monitoring can monitor the thickness change of the dielectric film in real time, and optical monitoring can monitor the transmittance / reflectance change of the dielectric film at characteristic wavelengths in real time.

[0047] S160. Adjust the coating time according to the real-time thickness information, real-time transmittance information, target thickness information and target transmittance information to complete the preparation of the dielectric film, and then complete the preparation of the first distributed Bragg mirror. The dielectric film includes multiple first dielectric films and multiple second dielectric films. The first dielectric films and second dielectric films are periodically stacked alternately. The refractive index of the first dielectric film is greater than the refractive index of the second dielectric film.

[0048] For example, the coating time can be adjusted by comparing real-time thickness information with target thickness information, and by comparing real-time transmittance information with target transmittance information. When the dielectric film thickness reaches the target thickness and the transmittance reaches the target transmittance, the sputtering power supply of the corresponding target source is automatically turned off, and then the deposition process of the next layer of film material is started. The finally fabricated first distributed Bragg mirror is shown below. Figure 2 As shown, Figure 2 The first distributed Bragg reflector 20 includes multiple dielectric films 21 stacked together. The multiple dielectric films 21 include multiple first dielectric films 211 (Ta2O5 dielectric films) and multiple second dielectric films 212 (SiO2 dielectric films). The first dielectric films 211 and the second dielectric films 212 are periodically stacked alternately. The refractive index of the first dielectric film 211 is greater than the refractive index of the second dielectric film 212.

[0049] Existing technologies lack precise online monitoring methods, resulting in significant deviations in center wavelength between different batches of products (above ±5nm), which is detrimental to standardized instrument production and model portability. This invention improves batch consistency by adjusting the coating time based on real-time thickness information, real-time transmittance information, target thickness information, and target transmittance information.

[0050] The technical solution of this invention, by setting up an ion beam reactive sputtering coating process to prepare the dielectric film 21, and adjusting the coating time of the dielectric film 21 according to the real-time thickness information, real-time transmittance information, target thickness information, and target transmittance information of the dielectric film 21, can improve the density of the generated dielectric film 21 and achieve precise control over the thickness and transmittance of the dielectric film 21, which is beneficial to improving the spectral accuracy, stability, transmittance, and batch consistency of the linear gradient filter.

[0051] Figure 3 A flowchart illustrating another method for fabricating a 0.9-1.7 μm narrowband linear graded filter according to an embodiment of the present invention. Figure 3 The illustrated embodiments enrich the process flow for fabricating 0.9-1.7 μm narrowband linear graded filters. (Refer to...) Figure 4 The method for preparing the linear graded filter in this embodiment of the invention includes: S210, Prepare the substrate.

[0052] S220. Determine the target thickness and target transmittance information of the dielectric film based on the target spectral performance of the linear gradient filter.

[0053] S230. Determine the coating time of the dielectric film based on the thickness and transmittance information.

[0054] S240. A dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process.

[0055] S250: Obtain real-time thickness and real-time transmittance information of the dielectric film.

[0056] S260. Adjust the coating time according to the real-time thickness information, real-time transmittance information, target thickness information and target transmittance information to complete the preparation of the dielectric film, and then complete the preparation of the first distributed Bragg mirror. The dielectric film includes multiple first dielectric films and multiple second dielectric films. The first dielectric films and second dielectric films are periodically stacked alternately. The refractive index of the first dielectric film is greater than the refractive index of the second dielectric film.

[0057] S270. A resonant cavity layer is prepared on the side of the first distributed Bragg mirror away from the substrate, wherein the thickness of the resonant cavity layer varies linearly along a first direction, which intersects with the thickness direction of the substrate.

[0058] Figure 4 This is a cross-sectional schematic diagram of the resonant cavity layer in a 0.9-1.7μm narrowband linear graded filter provided in an embodiment of the present invention, with reference to... Figure 4In the fabrication of the resonant cavity layer 30, embodiments of the present invention can use a mask blocking method combined with planetary fixture movement to make the thickness of the resonant cavity layer distributed in a gradient manner. The thickness can be linearly varied by controlling the mask position or adjusting the deposition time through computer control.

[0059] S280. A second distributed Bragg mirror is fabricated on the side of the resonant cavity layer away from the substrate. The peak transmittance of the 0.9-1.7μm narrowband linear gradient filter is greater than or equal to 90%@1325nm±50nm, the average transmittance is greater than or equal to 85%, and the half-bandwidth range is 6-8nm.

[0060] The second distributed Bragg reflector in this embodiment of the invention is a multilayer reflective structure consisting of periodically alternating low-refractive-index dielectric films and high-refractive-index dielectric films. The high-refractive-index dielectric film can be made of tantalum pentoxide, and the low-refractive-index dielectric film can be made of silicon dioxide. It can be fabricated using ion beam reactive sputtering, and the specific fabrication method is the same as that of the first distributed Bragg reflector described above, and will not be repeated here. The difference between the second and first distributed Bragg reflectors is that the first distributed Bragg reflector fabricates the high-refractive-index dielectric film first and then the low-refractive-index dielectric film, while the second distributed Bragg reflector fabricates the low-refractive-index dielectric film first and then the high-refractive-index dielectric film.

[0061] Optionally, after fabricating the second distributed Bragg mirror on the side of the resonant cavity layer 30 away from the substrate 10, the fabrication method in this embodiment of the invention further includes: cooling the 0.9-1.7μm narrowband linear gradient filter.

[0062] For example, after the coating is completed, the linear gradient filter can be left in the vacuum chamber to cool naturally under vacuum for 2-4 hours; alternatively, cold air can be blown into the vacuum chamber first to cool the linear gradient filter, and then after the temperature of the vacuum chamber drops below 50°C, high-purity nitrogen gas can be slowly introduced into the vacuum chamber to restore the pressure of the vacuum chamber to atmospheric pressure. Finally, the chamber door can be opened, the linear gradient filter can be carefully removed from the fixture, its appearance can be checked, and batch information can be recorded.

[0063] Before the linear graded filter is put into storage, its spectral performance, geometric parameters, and environmental reliability can be tested, including adhesion, abrasion resistance, salt spray, humidity, and high and low temperature cycling tests.

[0064] For example, a UV-Vis-NIR spectrophotometer (such as the PerkinElmer Lambda series) can be used to measure the full-band spectral curve of a linear graded filter for spectral performance testing. Specifically, the passband range, peak transmittance, average transmittance, full-width that half maximum (FWHM), and out-of-band rejection of the linear graded filter can be determined based on the obtained full-band spectral curve. The verification standards for the above parameters are as follows: passband range: 950-1700nm, peak transmittance: ≥90%@1325nm±50nm, average transmittance: ≥85% (within the range of 950-1700nm), full-width that half maximum (FWHM): 6-8nm, out-of-band rejection: OD3 or higher.

[0065] For example, when performing geometric parameter testing, an interferometer can be used to test surface accuracy and parallelism, and a thickness gauge can be used to test the total film thickness and uniformity.

[0066] For example, when conducting environmental reliability testing, samples can be taken from each batch for the following tests: 1. Adhesion test: tape peel test (ASTM D3359), requiring a rating of 4B or higher; 2. Abrasion resistance test: rubber friction test (MIL-C-675C), requiring no visible damage; 3. Salt spray test: no corrosion after 24 hours of spraying with 5% NaCl solution at 35°C (ASTM B117); 4. Humidity test: no performance degradation after 48 hours in an environment of 50°C / 95%RH; 5. High and low temperature cycling: 5 cycles between -40°C and +70°C, with no cracking or peeling of the film layer and a wavelength drift of less than 2nm.

[0067] Finally, the linear graduated filters that have passed all inspections are purged with high-purity nitrogen, sealed in anti-static lens bags in a Class 1000 cleanroom, placed in a special lens case with desiccant, and accompanied by the test report, thus completing the warehousing process.

[0068] In one specific embodiment, the substrate is a fused silica disc with a diameter of 25 mm and a thickness of 2 mm, with a parallelism of less than 2 arcmin and a surface accuracy of λ / 6@632.8 nm. Target parameters: passband range 950-1700 nm, half-width at half-maximum 7 nm, peak transmittance ≥91%.

[0069] The process flow is as follows: 1. The substrate is pre-treated with polishing and cleaning as described above. The surface particle size of the substrate after polishing and cleaning is better than grade 10 (according to MIL-STD-1246C standard). 2. A mechanical pump and a molecular pump are used in combination to achieve an ultimate vacuum of 8×10⁻⁶ in the vacuum chamber. -63. Perform ion cleaning on the substrate. The auxiliary ion source power is 200W, the argon flow rate is 20sccm, the bombardment time is 10 minutes, and the substrate bias voltage is -200V. 4. Pre-melt the Ta and Si targets for 8 minutes each, with a power of 85% of the actual sputtering power. 5. Perform film deposition. The specific parameters and control methods are as follows: the high refractive index dielectric film material is Ta2O5, the high refractive index dielectric film material is SiO2, and the dielectric film consists of 90 layers; the ion source power is 1200W; the argon flow rate is 50sccm; the oxygen flow rate is 15sccm; and the background vacuum of the vacuum chamber is 5×10⁻⁶. -5 Pa; Working pressure of the vacuum chamber: 2×10 -3 Pa; Deposition temperature control: The substrate temperature is controlled at 150±10℃ (natural temperature rise); Gradient control: A wedge-shaped mask is set along the X-axis of the substrate, and the mask opening width changes linearly from 0.5mm to 3.0mm. The planetary fixture moves at a revolution speed of 2rpm and a rotation speed of 20rpm; The deposition time of the high refractive index dielectric film is about 120 seconds, the deposition time of the high refractive index dielectric film is about 90 seconds, and the total deposition time is about 180 minutes; Cooling and sampling method: After natural cooling in vacuum for 3 hours, the sample is removed after being filled with nitrogen.

[0070] The test results of the linear graded filter produced using the above process are as follows: peak transmittance: 91.3%@1330nm; average transmittance (950-1700nm): 86.2%; half-width: 7.2nm; wavelength linearity: R 2 =0.9987; Cutoff depth: OD3.5; Wavelength drift after high and low temperature cycling: 1.5nm.

[0071] In another specific embodiment, the substrate is a 20mm×20mm×2.5mm single-crystal germanium square sheet; target parameters: passband range 1000-1650nm, half-bandwidth 6nm, peak transmittance ≥88%.

[0072] Compared to the specific embodiment described above, the process parameters were adjusted as follows: Due to the high refractive index of the germanium substrate (n≈4.0), the film system needed to be redesigned, an antireflection coating layer (specifically for Ge substrates) was added, and the deposition temperature was reduced to 120°C. The remaining process flow is the same as in the specific embodiment described above.

[0073] The test results of the generated linear gradient filter are as follows: peak transmittance is 88.7%@1400nm; average transmittance is 84.5%; half bandwidth is 6.3nm, and all five environmental reliability tests have been passed.

[0074] The test results of a linear gradient filter of the same specifications prepared using a traditional thermal evaporation coating process are as follows: peak transmittance is 82%, average transmittance is 76%, half-width is 18nm, wavelength drift is 12nm after high and low temperature cycling, and film peeling occurs after salt spray testing. Comparing the two specific embodiments above, it is evident that the process of the present invention is significantly superior to the traditional process.

[0075] Compared with existing technologies, this invention has the following significant advantages: Spectroscopic accuracy is significantly improved, from 20nm to 6-8nm; film quality is excellent, with high density, low internal stress, and strong adhesion of the film formed by ion beam sputtering. Its hard film characteristics allow it to withstand harsh environmental tests, meeting the long-term use requirements of industrial sites; transmittance is high, with optimized film system design and precise process control achieving a peak transmittance of over 90% and an average transmittance of 85%, significantly improving light energy utilization and system signal-to-noise ratio; temperature stability is good, with the thermal expansion coefficient matching design of the dense film layer controlling wavelength drift within 2nm within the operating temperature range, meeting the needs of field and industrial applications; batch consistency is good, with the fully automated deposition process and real-time monitoring system ensuring that the center wavelength deviation of different batches is within ±1nm, facilitating the establishment of instrument-independent general chemometric models; production efficiency is high, with multiple filters prepared on the same substrate in a single coating cycle, suitable for mass production and reducing per-filter cost.

[0076] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for fabricating a 0.9-1.7μm narrowband linear graded filter, wherein the 0.9-1.7μm narrowband linear graded filter comprises a substrate and a first distributed Bragg mirror, the first distributed Bragg mirror comprising a plurality of dielectric films stacked together, characterized in that, The preparation method includes: Preparation of substrate; The target thickness and target transmittance information of the dielectric film are determined based on the target spectral performance of the linear graded filter. The coating time of the dielectric film is determined based on the thickness information and the transmittance information; The dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process; Obtain the real-time thickness and real-time transmittance information of the dielectric film; The coating time is adjusted according to the real-time thickness information, the real-time transmittance information, the target thickness information, and the target transmittance information to complete the preparation of the dielectric film, thereby completing the preparation of the first distributed Bragg mirror. The dielectric film includes multiple first dielectric films and multiple second dielectric films, which are periodically stacked alternately. The refractive index of the first dielectric film is greater than that of the second dielectric film.

2. The preparation method according to claim 1, characterized in that, After preparing the substrate, the preparation method further includes: The substrate is mounted on a planetary fixture and fed into a vacuum chamber, wherein the planetary fixture adopts a combined rotation and revolution motion mode. The dielectric film is prepared on one side of the substrate using an ion beam reactive sputtering deposition process, comprising: The reaction gas and argon gas are introduced into the vacuum chamber; The ion source is controlled to emit an argon ion beam toward the target material to generate target atoms; The target atoms react chemically with the reactive gas to generate the dielectric film.

3. The preparation method according to claim 2, characterized in that, The reacting gas includes oxygen; The oxygen flow rate Q1 satisfies: 10 sccm ≤ Q1 ≤ 50 sccm; the argon flow rate Q2 satisfies: 30 sccm ≤ Q2 ≤ 80 sccm; The power of the ion source satisfies: 800W≤P1≤1500W; The air pressure P2 in the vacuum chamber satisfies: 1×10 -3 Pa≤P2≤5×10 -3 Pa.

4. The preparation method according to claim 2, characterized in that, Before controlling the ion source to emit an argon ion beam toward the target to generate target atoms, the preparation method further includes: The target material is pre-melted.

5. The preparation method according to claim 2, characterized in that, After mounting the substrate onto a planetary fixture and placing it into a vacuum chamber, the preparation method further includes: The surface of the substrate is cleaned by ion bombardment using the ion source, wherein the power P3 of the ion source satisfies: 100W≤P3≤300W, the ion bombardment cleaning time t1 satisfies: 5min≤t1≤15min, and the voltage U1 applied to the substrate satisfies: -100V≤U1≤-300V.

6. The preparation method according to claim 1, characterized in that, After preparing the substrate, the preparation method further includes: The substrate is polished; The polished substrate is cleaned to achieve a surface accuracy of λ / 4@632.8nm and a parallelism of less than 3arcmin.

7. The preparation method according to claim 1, characterized in that, The 0.9-1.7μm narrowband linear gradient filter also includes a resonant cavity layer and a second distributed Bragg reflector; The preparation method further includes: A resonant cavity layer is fabricated on the side of the first distributed Bragg reflector away from the substrate, wherein the thickness of the resonant cavity layer varies linearly along a first direction, which intersects the thickness direction of the substrate; The second distributed Bragg reflector is fabricated on the side of the resonant cavity layer away from the substrate. The 0.9-1.7μm narrowband linear gradient filter has a peak transmittance greater than or equal to 90%@1325nm±50nm, an average transmittance greater than or equal to 85%, and a half-bandwidth range of 6nm-8nm.

8. The preparation method according to claim 7, characterized in that, After fabricating the second distributed Bragg reflector on the side of the resonant cavity layer away from the substrate, the fabrication method further includes: The 0.9-1.7μm narrowband linear gradient filter is subjected to cooling treatment.

9. The preparation method according to claim 2, characterized in that, After mounting the substrate onto a planetary fixture and placing it into a vacuum chamber, the preparation method further includes: The vacuum chamber is evacuated to reduce the gas pressure inside to less than 1 × 10⁻⁶. -5 Pa.

10. The preparation method according to claim 9, characterized in that, Evacuating the vacuum chamber includes: Start the mechanical pump to reduce the air pressure in the vacuum chamber to less than 10 Pa; Start the molecular pump to reduce the gas pressure in the vacuum chamber to less than 1 × 10⁻⁶. -5 Pa, and maintain the preset time.

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