Method for manufacturing linearly graded filter and linearly graded filter

Abstract

This invention relates to the field of filter technology, and particularly to a method for fabricating a linear graded filter and the linear graded filter itself. The method for fabricating the linear graded filter includes the following steps: using a glass wafer as a substrate, depositing a reflective layer on the surface of the glass wafer; wherein the lower reflective layer is composed of alternating layers of low-refractive-index materials and multiple layers of high-refractive-index materials; depositing a resonant cavity layer on the side of the lower reflective layer away from the glass wafer using a stepped deposition process; depositing a reflective layer on the side of the resonant cavity layer away from the glass wafer; and depositing a long-wavelength pass layer on the side of the upper reflective layer away from the glass wafer and in a region larger than the center wavelength, thus obtaining the linear graded filter. Compared with existing technologies, the linear graded filter proposed in this invention has superior spectral resolution in the long-wavelength band, smaller energy differences between channels, and excellent wavelength selectivity, and can be used in spectroscopic applications such as miniaturized infrared spectrometers.

Description

Technical Field

[0001] This invention relates to the field of filter technology, and particularly to a method for manufacturing a linear gradient filter and the linear gradient filter itself. Background Technology

[0002] A linear variable filter (LVF) is a multilayer coated filter composed of multiple layers of different materials and thicknesses. The center wavelength of its transmittance curve gradually shifts along a certain direction, showing a positive correlation between the center wavelength and its position.

[0003] A linear graded-variety filter (LVF) is a novel type of spectroscopic device whose spectral characteristics change linearly at different positions. According to the grating equation d = mλ, when the film thickness d changes, the corresponding peak transmission wavelength λ also changes synchronously. Therefore, along the wedge-shaped direction, the center wavelength of a linear graded-variety filter changes continuously and linearly. (See reference...) Figure 1 , Figure 1 This is a schematic diagram illustrating the working principle of a linear graded filter in related technologies. Therefore, as a beam splitter, a linear graded filter can achieve high-precision spectral resolution by obtaining a graded linear filter material with an extremely narrow band; it has high peak transmittance and a wide long-wavelength cutoff region, making it suitable for various applications.

[0004] Currently, there are two main approaches to fabricating linear graded filters: one is to add a special mechanical structure to the coating equipment to complete the fabrication; the other is to use a correction baffle, which is placed in the vacuum chamber of the coating machine. This correction baffle corrects the film thickness based on the evaporation characteristics of each material, achieving precise and controllable material thickness distribution. It is a crucial structure in the fabrication of high-precision linear graded filters, as the deposition error in the film thickness often determines the quality of the coating.

[0005] However, in the above-mentioned approaches to LVF fabrication, the first approach involves adding a special mechanical structure to the coating equipment. This approach has high mechanical structure design costs and significantly impacts the fabrication accuracy of the linear graded filter. The second approach requires repeated single-layer material process experiments to obtain a correction baffle that meets the requirements of a specific linear graded filter specification, thus resulting in high cost and low efficiency. Furthermore, the full width at half maximum (FWHM) of the central peak in the linear graded filter fabricated by the above methods is approximately proportional to the wavelength of the central peak. That is, the larger the wavelength of the channel, the larger its FWHM will be. This leads to lower spectral resolution on the long-wavelength side of the LVF and much higher transmitted energy compared to the short-wavelength side. With the limited dynamic range of the sensor, this results in reduced measurement accuracy on the short-wavelength side.

[0006] Therefore, there is an urgent need for a new method for manufacturing linear gradient filters and a new linear gradient filter to solve the above-mentioned technical problems. Summary of the Invention

[0007] This invention provides a method for manufacturing a linear graded filter and a linear graded filter, aiming to produce a linear graded filter with higher precision and lower cost, so that the linear graded filter has better spectral resolution in the long wavelength band, smaller energy difference between channels, and excellent wavelength selectivity.

[0008] In a first aspect, the present invention provides a method for manufacturing a linear gradient filter, the method comprising the following steps:

[0009] S1. Using a glass wafer as a substrate, a reflective layer is deposited on the surface of the glass wafer; wherein the lower reflective layer is composed of multiple layers of low refractive index material and multiple layers of high refractive index material stacked alternately;

[0010] S2. A resonant cavity layer is deposited on the side of the lower reflective layer away from the glass wafer using a stepped coating process; wherein the resonant cavity layer is composed of multiple layers of the low refractive index material stacked together, and the lower reflective layer includes a variety of film systems with different film thickness coefficients;

[0011] S3. A reflective layer is deposited on the side of the resonant cavity layer away from the glass wafer; wherein the upper reflective layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the upper reflective layer includes a variety of film systems with different film thickness coefficients;

[0012] S4. A long-wavelength pass layer is deposited on the side of the upper reflective layer away from the glass wafer to obtain the linear gradient filter; wherein the long-wavelength pass layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the area where the long-wavelength pass layer is deposited is a region larger than the center wavelength of the linear gradient filter.

[0013] Preferably, the resonant cavity layer includes a first low-refractive-index layer and a mask layer, and step S2 includes the following sub-steps:

[0014] S21. Deposit the low-refractive-index material on the side of the lower reflective layer away from the glass wafer to form the first low-refractive-index layer;

[0015] S22. Using multiple mask plates with different mask regions, the low refractive index material of different thicknesses is deposited sequentially on the side of the first low refractive layer away from the glass wafer to form the mask layer.

[0016] Preferably, the thickness of the low-refractive-index material in each layer of the resonant cavity layer satisfies the following condition:

[0017]

[0018] in, Indicates the maximum film thickness coefficient; Represents the minimum film thickness coefficient; q This represents the thickness of the low-refractive-index material when the quarter-wavelength optical thickness of the low-refractive-index material is 1. n This indicates the number of layers in the current resonant cavity layer.

[0019] Preferably, the resonant cavity layer is composed of eight layers of the low-refractive-index material stacked together.

[0020] Preferably, the lower reflective layer includes a first lower reflective film system with a film thickness coefficient of 1.55, a second lower reflective film system with a film thickness coefficient of 1.0, a third lower reflective film system with a film thickness coefficient of 0.88, and a fourth lower reflective film system with a film thickness coefficient of 0.8.

[0021] The conditions satisfied by the coating of the lower reflective layer are: 1.55 (LH)^1~1.0 (LH)^1~0.88 (LH)^1~0.8 (LH)^1; where L represents the low refractive index material, H represents the high refractive index material, (LH) represents a film system composed of one layer of the low refractive index material and one layer of the high refractive index material, and ~ represents the connecting film system.

[0022] Preferably, the upper reflective layer includes a first upper reflective film system with a film thickness coefficient of 0.8, a second upper reflective film system with a film thickness coefficient of 0.88, a third upper reflective film system with a film thickness coefficient of 1.0, and a fourth upper reflective film system with a film thickness coefficient of 1.55.

[0023] The conditions that the coating of the upper reflective layer must meet are: 0.8(HL)^1~0.88 (HL)^1~1.0 (HL)^1~1.55 (HL)^1.

[0024] Preferably, the low-refractive-index material is silicon dioxide, and the high-refractive-index material is silicon.

[0025] Preferably, the operating frequency band of the linear gradient filter is 1000-1700nm, and the center wavelength of the linear gradient filter is 1375nm.

[0026] Preferably, the refractive index of the glass wafer is 1.52.

[0027] Secondly, the present invention also provides a linear gradient filter, which is manufactured by the method for manufacturing a linear gradient filter as described in any of the above embodiments.

[0028] Compared with existing technologies, this invention achieves modulation of the center peak's full width at half maximum (FWHM) of a linear graded filter over a wider range by using a lower reflective layer and an upper reflective layer composed of multiple film systems with different thickness coefficients. A long-wavelength pass layer is deposited on the side of the upper reflective layer away from the glass wafer and in a region larger than the center wavelength, blocking the secondary peak of the linear graded filter at the short-wavelength end in the long-wavelength channel. Gradual changes in the thickness of different layers within the resonant cavity are achieved using mask plates with different mask regions. Thus, the linear graded filter proposed in this invention exhibits superior spectral resolution in the long-wavelength band, smaller energy differences between channels, and characteristics such as a wide spectral range, high transmittance, and narrow FWHM, making it suitable for applications such as miniaturized infrared spectrometers. Attached Figure Description

[0029] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0030] Figure 1 This is a schematic diagram illustrating the working principle of a linear gradient filter in related technologies;

[0031] Figure 2 This is a flowchart of the method for manufacturing a linear gradient filter provided in an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of the structure of the linear gradient filter provided in an embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of the mask structure for the fabrication method of the linear gradient filter provided in this embodiment of the invention;

[0034] Figure 5 This is a schematic diagram of the coating process of the lower reflective layer, resonant cavity layer and upper reflective layer in the method for fabricating a linear gradient filter provided in an embodiment of the present invention.

[0035] Figure 6 This is a schematic diagram of the transmittance curve of the long-wavelength pass layer of the linear gradient filter provided in an embodiment of the present invention;

[0036] Figure 7 This is a schematic diagram of the transmittance curve of the linear gradient filter under the FP cavity provided in the embodiment of the present invention;

[0037] Figure 8 This is a schematic diagram of the transmittance curves of the resonant cavity layer channel under different film thickness coefficients of the linear gradient filter provided in the embodiments of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Example 1

[0040] Please refer to Figures 2-3 This invention provides a method for manufacturing a linear gradient filter, the method comprising the following steps:

[0041] S1. Using a glass wafer as a substrate, a reflective layer is deposited on the surface of the glass wafer; wherein the lower reflective layer is composed of multiple layers of low refractive index material and multiple layers of high refractive index material stacked alternately, and the lower reflective layer includes a variety of film systems with different film thickness coefficients.

[0042] In this embodiment of the invention, the low-refractive-index material is silicon dioxide, and the high-refractive-index material is silicon. The refractive index of the glass wafer is 1.52. A film system refers to an overall coating composed of multiple layers of thin films of different materials and thicknesses arranged in a specific order and structure. The low-refractive-index material refers to a material with a refractive index below 1.5 in the near-infrared band, and the high-refractive-index material refers to a material with a refractive index above 3 in the near-infrared band.

[0043] The lower reflective layer comprises four different quarter-wavelength optical thicknesses, including a first lower reflective film system with a film thickness coefficient of 1.55, a second lower reflective film system with a film thickness coefficient of 1.0, a third lower reflective film system with a film thickness coefficient of 0.88, and a fourth lower reflective film system with a film thickness coefficient of 0.8.

[0044] The coating formula for the lower reflective layer is (i.e., the conditions satisfied by the coating of the lower reflective layer): 1.55 (LH)^1~1.0 (LH)^1~0.88 (LH)^1~0.8 (LH)^1; where L represents the low refractive index material, H represents the high refractive index material, (LH) represents a film system composed of one layer of the low refractive index material and one layer of the high refractive index material, and ~ represents the connecting film system.

[0045] Specifically, the coating formula is a symbol system used to represent the coating film system, and its rules are as follows:

[0046] (1) Different materials are represented by letters. For example, in this invention, H represents a high refractive index material and L represents a low refractive index material.

[0047] (2) Letters in series represent coating systems with different material combinations, such as HL representing a coating system composed of one layer of H material and one layer of L material.

[0048] (3) (…)^N represents the coating system within the parentheses repeated N times, such as (HL)^2, which is equivalent to HLHL.

[0049] (4) The letter or the number before the parentheses represents the QWOT of all layers in the film system. For example, 2(HL)^2 means that the QWOT of all the internal coatings is 2.

[0050] (5) Use ~ to connect membrane systems, such as (HL)^2~H is equivalent to HLHLH.

[0051] S2. A resonant cavity layer is deposited on the side of the lower reflective layer away from the glass wafer using a stepped coating process; wherein the resonant cavity layer is composed of multiple layers of the low refractive index material stacked together.

[0052] In this embodiment of the invention, the stepped coating process includes mask patterning coating, moving baffle dynamic deposition coating, photolithography-assisted selective etching coating, etc. In the following content, the stepped coating process uses mask patterning coating as an example.

[0053] The resonant cavity layer includes a first low-refractive layer and a mask layer. Step S2 includes the following sub-steps:

[0054] S21. Deposit the low-refractive-index material on the side of the lower reflective layer away from the glass wafer to form the first low-refractive-index layer;

[0055] S22. Using multiple mask plates with different mask regions, the low refractive index material of different thicknesses is deposited sequentially on the side of the first low refractive layer away from the glass wafer to form the mask layer.

[0056] In this embodiment of the invention, the resonant cavity layer is formed by stacking eight layers of the aforementioned low-refractive-index material (i.e., the resonant cavity layer includes a first low-refractive-index layer and seven mask layers stacked thereon). The thickness of each layer of the low-refractive-index material in the resonant cavity layer satisfies the following condition:

[0057]

[0058] in, Indicates the maximum film thickness coefficient; Represents the minimum film thickness coefficient; q This represents the thickness of the low-refractive-index material when the quarter-wavelength optical thickness of the low-refractive-index material is 1. n This indicates the number of layers in the resonant cavity layer. Specifically, when n=1, this layer is the first low-refractive-index layer, and its thickness satisfies... When n > 1, it is a mask layer, and its thickness satisfies In this invention, , , It should be noted that, , as well as The values ​​can be set according to the actual situation and are not limited to the above values.

[0059] Specifically, quarter-wavelength optical thickness (QWOT) is an indicator used to characterize the thickness of optical films, where the refractive index function of the film material is... Film thickness is In the case where the center wavelength of the incident light is QWOT at that time can be calculated by the following formula:

[0060] .

[0061] Please refer to Figure 4 , Figure 4 This is a schematic diagram of the mask structure for the fabrication method of the linear gradient filter provided in this embodiment of the invention. The invention uses different masks to deposit coatings in designated areas. To create a stepped distribution of the resonant cavity to obtain channels with different center wavelengths, the invention uses seven masks for patterned coating. When the length of the glass wafer is A, the first mask covers a region of A / 2 length at the short-wavelength end; the second mask covers regions of A / 4 length every A / 4 length starting from the short-wavelength end, and so on until the seventh mask.

[0062] S3. A reflective layer is deposited on the side of the resonant cavity layer away from the glass wafer; wherein the upper reflective layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the upper reflective layer includes a variety of film systems with different film thickness coefficients.

[0063] In this embodiment of the invention, the upper reflective layer includes a first upper reflective film system with a film thickness coefficient of 0.8, a second upper reflective film system with a film thickness coefficient of 0.88, a third upper reflective film system with a film thickness coefficient of 1.0, and a fourth upper reflective film system with a film thickness coefficient of 1.55.

[0064] The coating formula for the upper reflective layer is (i.e., the conditions that the coating of the upper reflective layer satisfies): 0.8(HL)^1~0.88 (HL)^1~1.0 (HL)^1~1.55 (HL)^1.

[0065] Please refer to Figure 5 , Figure 5This is a schematic diagram illustrating the coating process of the lower reflective layer, resonant cavity layer, and upper reflective layer in the fabrication method of the linear gradient filter provided in this embodiment of the invention. As shown in the figure, since the resonant cavity layer is coated in a stepped shape using a stepped coating process, a similar stepped shape is formed when the upper reflective layer is coated, thereby obtaining channels with different center wavelengths. By using multiple film systems with different film thickness coefficients for the upper and lower reflective layers, modulation of the full width at half maximum (FWHM) of the center peak over a wider range can be achieved.

[0066] S4. A long-wavelength pass layer is deposited on the side of the upper reflective layer away from the glass wafer to obtain the linear gradient filter; wherein the long-wavelength pass layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the area where the long-wavelength pass layer is deposited is a region larger than the center wavelength of the linear gradient filter.

[0067] In this embodiment of the invention, the long-wave pass is composed of ten layers of alternating high-refractive-index and low-refractive-index materials, used by the linear graded filter to cut off the secondary peak at the short-wave end of the long-wave channel. The long-wave pass layer also requires partitioned coating to ensure coverage only of the long-wave band. When the center wavelength of the channel is greater than 1400 nm, the corresponding thickness coefficient of the resonant cavity layer is exactly greater than... Therefore, the mask can be reused for patterned coating.

[0068] The linear gradient filter operates in the frequency band of 1000-1700nm, and its center wavelength is 1375nm.

[0069] like Figure 6 As shown, Figure 6 This is a schematic diagram of the transmittance curve of the long-wavelength pass-through layer of the linear gradient filter provided in this embodiment of the invention; as shown in the figure, the long-wavelength pass-through layer proposed in this invention can effectively block light with a wavelength less than 1200nm and transmit light with a wavelength greater than 1400nm.

[0070] In this embodiment of the invention, a Fabry-Perot (FP) cavity structure is formed by a lower reflective layer, a resonant cavity layer, and an upper reflective layer, creating an LVF film system. Both the lower and upper reflective layers are composite films of high and low refractive index materials, and the resonant cavity layer is a single-layer coating composed of multiple layers of low refractive index materials, as shown in Figure 7. Figure 7 This is a schematic diagram of the transmittance curve of the linear gradient filter under the FP cavity provided in the embodiment of the present invention; it includes a central peak and two secondary peaks, with a cutoff band between the central peak and the secondary peaks.

[0071] For an FP cavity composed of a lower reflective layer, a resonant cavity layer, and an upper reflective layer, its coating formula can be summarized as: a(LH)^n ~ 2aL ~ a(HL)^n, where a(LH)^n and a(HL)^n are the lower and upper reflective layers, respectively, and 2aL is the resonant cavity layer. The film thickness coefficient 'a' controls the transmitted wavelength of the center peak; the larger 'a' is, the larger the transmitted wavelength of the peak. The coefficient 'n' represents the number of layers and controls the full width at half maximum (FWHM) of the center peak; the larger 'n' is, the narrower the FWHM. Therefore, different peak transmitted wavelengths can be obtained by uniformly varying the film thickness coefficient 'a'.

[0072] In the FP cavity coating formula: a(LH)^n ~ 2aL ~ a(HL)^n, when 'a' varies within a certain range, the position of the center peak will also shift accordingly. However, the farther 'a' is from the midpoint 1, the larger the full width at half maximum (FWHM) of the center peak will be. To ensure that the center peak of the linear graded filter has a narrow FWHM across a wide wavelength range of 1000-1700nm, this invention proposes using multiple sets of lower and upper reflective layers with different film thickness coefficients 'a' to achieve modulation of the center peak's FWHM over a wider range.

[0073] In this embodiment of the invention, the thickness of each layer of the LVF film system is calculated according to its coating formula, and Table 1 is a table of film thickness values ​​for each layer of the LVF film system:

[0074] Table 1

[0075]

[0076] Meanwhile, when the central peak moves to the long-wavelength region, a corresponding secondary peak will enter the working range of 1000-1700nm in the short-wavelength region. This invention cuts off the secondary peak by coating a long-wavelength pass-through layer in the region greater than the central wavelength.

[0077] Please refer to Table 2, which shows the film thickness values ​​for each layer of the long-wavelength pass layer:

[0078] Table 2

[0079]

[0080] It should be noted that the film thickness values ​​for each layer in Tables 1 and 2 are calculated based on the coating formula, and are not limited to the values ​​in the tables. They can be modified accordingly based on the actual situation.

[0081] Please refer to Figure 8 , Figure 8This is a schematic diagram showing the transmittance curves of the resonant cavity layer channel under different film thickness coefficients of the linear graded filter provided in this embodiment of the invention. As can be seen from the figure, the stepped linear graded filter designed in this invention has high transmittance (>90%) and a narrow full width at half maximum (<6nm) in the working wavelength range of 1000-1700nm, exhibiting excellent optical performance.

[0082] Compared with existing technologies, this invention achieves modulation of the center peak's full width at half maximum (FWHM) of a linear graded filter over a wider range by using a lower reflective layer and an upper reflective layer composed of multiple film systems with different thickness coefficients. A long-wavelength pass layer is deposited on the side of the upper reflective layer away from the glass wafer and in a region larger than the center wavelength, blocking the secondary peak of the linear graded filter at the short-wavelength end in the long-wavelength channel. Gradual changes in the thickness of different layers within the resonant cavity are achieved using mask plates with different mask regions. Thus, the linear graded filter proposed in this invention exhibits superior spectral resolution in the long-wavelength band, smaller energy differences between channels, and characteristics such as a wide spectral range, high transmittance, and narrow FWHM, making it suitable for applications such as miniaturized infrared spectrometers.

[0083] Example 2

[0084] This invention also provides a linear gradient filter, which includes a glass wafer as a substrate, and a lower reflective layer, a resonant cavity layer, an upper reflective layer, and a long-wavelength pass layer that are sequentially stacked and fixed on one side of the glass wafer. The linear gradient filter is manufactured based on the steps in the manufacturing method of the linear gradient filter in the above embodiments, and can achieve the same technical effect. Refer to the description in the above embodiments, which will not be repeated here.

[0085] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0086] The embodiments of the present invention have been described above with reference to the accompanying drawings. The disclosed embodiments are merely preferred embodiments of the present invention. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many equivalent changes in form without departing from the spirit and scope of the claims of the present invention, and all such changes are within the protection scope of the present invention.

Claims

1. A method for manufacturing a linear gradient filter, characterized in that, The method for manufacturing the linear gradient filter includes the following steps: S1. Using a glass wafer as a substrate, a reflective layer is deposited on the surface of the glass wafer; wherein the lower reflective layer is composed of multiple layers of low refractive index material and multiple layers of high refractive index material stacked alternately, and the lower reflective layer includes a variety of film systems with different film thickness coefficients. S2. A resonant cavity layer is deposited on the side of the lower reflective layer away from the glass wafer using a stepped coating process; wherein the resonant cavity layer is composed of multiple layers of the low refractive index material stacked together. S3. A reflective layer is deposited on the side of the resonant cavity layer away from the glass wafer; wherein the upper reflective layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the upper reflective layer includes a variety of film systems with different film thickness coefficients; S4. A long-wavelength pass layer is deposited on the side of the upper reflective layer away from the glass wafer to obtain the linear gradient filter; wherein, the long-wavelength pass layer is composed of multiple layers of high refractive index material and multiple layers of low refractive index material stacked alternately, and the area where the long-wavelength pass layer is deposited is a region larger than the center wavelength of the linear gradient filter. The resonant cavity layer includes a first low-refractive layer and a mask layer. Step S2 includes the following sub-steps: S21. Deposit the low-refractive-index material on the side of the lower reflective layer away from the glass wafer to form the first low-refractive-index layer; S22. The low-refractive-index material of different thicknesses is deposited sequentially on the side of the first low-refractive layer away from the glass wafer using multiple mask plates with different mask regions to form the mask layer; The lower reflective layer includes a first lower reflective film system with a film thickness coefficient of 1.55, a second lower reflective film system with a film thickness coefficient of 1.0, a third lower reflective film system with a film thickness coefficient of 0.88, and a fourth lower reflective film system with a film thickness coefficient of 0.

8. The conditions satisfied by the coating of the lower reflective layer are: 1.55 (LH)^1~1.0 (LH)^1~0.88 (LH)^1~0.8(LH)^1; where L represents the low refractive index material, H represents the high refractive index material, (LH) represents a film system composed of one layer of the low refractive index material and one layer of the high refractive index material, and ~ represents the connecting film system.

2. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The thickness of the low-refractive-index material in each layer of the resonant cavity layer satisfies the following condition: in, Indicates the maximum film thickness coefficient; Represents the minimum film thickness coefficient; q This represents the thickness of the low-refractive-index material when the quarter-wavelength optical thickness of the low-refractive-index material is 1. n This indicates the number of layers in the current resonant cavity layer.

3. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The resonant cavity layer is composed of eight layers of the aforementioned low-refractive-index material stacked together.

4. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The upper reflective layer includes a first upper reflective film system with a film thickness coefficient of 0.8, a second upper reflective film system with a film thickness coefficient of 0.88, a third upper reflective film system with a film thickness coefficient of 1.0, and a fourth upper reflective film system with a film thickness coefficient of 1.

55. The conditions that the coating of the upper reflective layer must meet are: 0.8(HL)^1~0.88 (HL)^1~1.0 (HL)^1~1.55(HL)^1.

5. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The low-refractive-index material is silicon dioxide, and the high-refractive-index material is silicon.

6. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The linear gradient filter operates in the frequency range of 1000-1700nm, and its center wavelength is 1375nm.

7. The method for manufacturing a linear gradient filter as described in claim 1, characterized in that, The glass wafer has a refractive index of 1.

52.

8. A linear gradient filter, characterized in that, The linear gradient filter is manufactured by the method for manufacturing a linear gradient filter as described in any one of claims 1-7.

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