A filter and a method of manufacturing the same

Abstract

The application provides a filter and a preparation method thereof. The filter comprises a substrate, and low-refractive material film layers and high-refractive material film layers arranged alternately on the substrate; from the side close to the substrate, the variation trend of the thickness of the low-refractive material film layers comprises at least two stages in sequence, a first descending section and a first ascending section; the variation trend of the thickness of the high-refractive material film layers comprises at least two stages in sequence, a second ascending section and a second descending section; the filter is designed to have a film stack structure with regularly varied thickness for specific filtering requirements, has almost no invalid film layers, greatly improves film coating quality and film coating efficiency, and through further optimization of the film coating method, the film coating time is obviously reduced, the operation process is simple, and the method is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of optical thin film technology, specifically relating to a filter and its preparation method. Background Technology

[0002] Optical filters are used to select the desired radiation wavelength. To meet certain filtering requirements, the film stacking structure can generally be found using relevant film system design software. However, in some cases, the stacking structure found by software is often unsatisfactory, easily resulting in problems such as disordered film stacking structure, excessive number of film layers, excessive total film thickness, and too many ineffective film layers. It can also lead to low coating efficiency, long development cycle, and poor coating stability, which is detrimental to industrial production.

[0003] CN206804910U discloses a dual-pass filter for day and night use. The filter comprises an optical glass substrate and a filter film deposited on the optical glass substrate. The filter film consists of 38 layers, which are formed by alternating stacks of a high-refractive-index TiO2 film and a low-refractive-index SiO2 film. This filter allows visible light in the 430–630 nm range and specified infrared light around 940 nm to pass through, with an average transmittance greater than 95%. It blocks ultraviolet light in the 350–410 nm range and infrared light in the 670–900 nm and 1000–1150 nm ranges, with an average transmittance of less than 2%.

[0004] CN111596394A discloses a blue-violet edge-suppressing anti-red-exposure filter film, its manufacturing method, and the filter itself. The filter is composed of 39 layers stacked sequentially, primarily consisting of alternating stacks of Ta2O5 and SiO2 layers. This filter effectively blocks blue-violet light dispersion below 400nm, exhibits high transmittance in visible light (420–650nm) during the day and near-infrared light (830–950nm) for nighttime illumination, and provides good cutoff for near-infrared light (700–780nm) that tends to produce a "red-exposure" spectrum during the day.

[0005] However, both of the above-mentioned preparation methods suffer from long processing times and low production efficiency. Furthermore, neither meets the filtering requirements of this invention (a passband in the visible light band of 420nm–700nm, a stopband in the near-infrared band of 780nm–820nm, and a passband in the near-infrared band of 840nm–880nm). Therefore, optimizing the film system design and preparation process while meeting specific filtering requirements to further improve production efficiency has become an urgent problem to be solved. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention aims to provide a filter and its preparation method. The filter is designed for specific filtering requirements, and a film layer stacking method has been independently developed, resulting in almost no ineffective film layers. The preparation method is based on a special film layer stacking structure, which effectively improves production efficiency and is beneficial for industrial production and application.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a filter comprising a substrate and alternating layers of low-refractive-index material and high-refractive-index material on the substrate, wherein the first layer is preferably a low-refractive-index material film. In the present invention, either a low-refractive-index material film or a high-refractive-index material film may be deposited on the substrate first, as long as alternating deposition is ensured. The terms "high" and "low" refer to the two materials in comparison. In the art, "L" is generally used to represent a low-refractive-index material film and "H" is used to represent a high-refractive-index material film.

[0009] Measured from the side closest to the substrate, the variation trend of the thickness of the low-refractive-index material film includes at least two sequentially occurring stages: a first decreasing stage and a first increasing stage; the variation trend of the thickness of the high-refractive-index material film includes at least two sequentially occurring stages: a second increasing stage and a second decreasing stage.

[0010] The filter described in this invention optimizes the film stacking structure for specific filtering requirements, making it exhibit a more regular variation. The low-refractive-index material film structure and the high-refractive-index material film structure both exhibit a basically symmetrical structure, and the overall film structure has no ineffective film layers, which greatly improves the coating efficiency.

[0011] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0012] As a preferred technical solution of the present invention, the change trend of the low refractive index material film layer further includes a first stable segment between the first descending segment and the first ascending segment;

[0013] Regarding the variation trend of the high refractive index material film, a second stable segment is also included between the second rising segment and the second falling segment.

[0014] For the two types of films in this invention, whether the trend is upward, stable, or downward, the description is a general trend. There may be individual jump points, but they do not affect the overall trend change or the final overall effect.

[0015] As a preferred technical solution of the present invention, when the first layer is a low refractive index material film layer, the total number of film layers of the filter is not less than 47 layers, and is an odd number of layers, such as 47 layers, 51 layers, 55 layers, 59 layers, 61 layers, 63 layers, 65 layers, 75 layers, 79 layers, 81 layers, 83 layers, 85 layers, 87 layers, 89 layers, 93 layers, or 99 layers, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 47 to 99 layers, and more preferably 79 to 89 layers.

[0016] When the first layer is the high refractive index material film layer, the number of layers is not less than 46 layers and is an even number of layers, such as 46 layers, 50 layers, 54 layers, 58 layers, 62 layers, 66 layers, 68 layers, 70 layers, 74 layers, 78 layers, 84 layers, 86 layers, 88 layers, 90 layers, 94 layers or 98 layers, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. Preferably, it is 46 to 98 layers, and more preferably 78 to 88 layers.

[0017] In this invention, when the film stack structure only meets the minimum layer requirement, the thickness variation trend of the low-refractive-index material film layer only includes a sequentially occurring decreasing segment and a increasing segment, and the thickness variation trend of the high-refractive-index material film layer only includes a sequentially occurring increasing segment and a decreasing segment. As the number of layers increases, a stable segment begins to appear in both types. Even with the appearance of a stable segment, the thickness variation trends of the two types of film layers still exhibit a basically symmetrical pattern.

[0018] The number of stacked layers in the above membrane stack structure does not need to be too many. While increasing the number of membrane layers will improve the noise filtration effect, it will lead to excessive costs and may even cause a decline in membrane quality.

[0019] As a preferred technical solution of the present invention, the refractive index of the low refractive index material is 1.38 to 1.65, such as 1.38, 1.40, 1.42, 1.46, 1.50, 1.52, 1.60 or 1.65, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the refractive index of the high refractive index material is 1.8 to 2.2, such as 1.8, 1.9, 2.0, 2.1 or 2.2, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] Preferably, the low refractive index material includes SiO2.

[0022] Preferably, the high refractive index material includes at least one of Si3N4, ZrO2, or La2Ti2O7. That is, for any one layer of high refractive index material film, at least one of the above materials can be selected, such as a mixture of Si3N4, ZrO2, La2Ti2O7, a mixture of Si3N4 and ZrO2, a mixture of Si3N4 and La2Ti2O7, a mixture of ZrO2 and La2Ti2O7, or a mixture of Si3N4, ZrO2, and La2Ti2O7, etc.

[0023] For example, 1) Assuming a total of 89 film layers, including 44 high refractive index material film layers, then the first 20 layers can be Si3N4 film layers and the last 24 layers can be ZrO2 film layers; 2) Assuming a total of 89 film layers, including 44 high refractive index material film layers, then 20 of them can be Si3N4 film layers, 10 of them can be mixed material film layers of ZrO2 and La2Ti2O7 materials, and 14 of them can be ZrO2 film layers.

[0024] In this invention, the low refractive index material includes MgF2 or SiO2, preferably SiO2; the high refractive index material also includes HfO2, wherein La2Ti2O7 is a high refractive index low absorption coating material developed by Merck, but preferably Si3N4.

[0025] In this invention, for the selection of high-refractive-index or low-refractive-index materials, as long as the optical thickness of the replacement material is basically the same as that of its corresponding material, the same filtering effect can be obtained.

[0026] As a preferred technical solution of the present invention, the standard deviation of the thickness of each film layer is ±10%, such as ±1%, ±2%, ±3%, ±4%, ±5%, ±6%, ±7%, ±8%, ±9%, or ±10%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] In this invention, during practical application, the thickness of each layer, whether it is a low-refractive-index material film or a high-refractive-index material film, can fluctuate within ±10% of the reference thickness without affecting the coating effect and coating efficiency.

[0028] In addition, when depositing a low-refractive-index material (SiO2) film first, since the substrate is quartz, the optical constants of SiO2 and quartz substrate are almost the same. Therefore, the first layer of SiO2 does not affect the overall filtering effect, and its thickness can be chosen arbitrarily. However, considering the symmetrical structure of the overall film stack and better film adhesion, the thickness of the first layer is basically consistent with the thickness of the last layer.

[0029] As a preferred technical solution of the present invention, for the low refractive index material film, the thickness of each film layer in the first descending segment decreases sequentially from 300nm to 195nm, the thickness of each film layer in the first stable segment is independently 190-195nm, and the thickness of each film layer in the first ascending segment increases sequentially from 195nm to 300nm.

[0030] Preferably, for the high refractive index film, the thickness of each film layer in the second rising segment increases sequentially from 4 nm to 45 nm, the thickness of each film layer in the second stable segment is independently 45–50 nm, and the thickness of each film layer in the second falling segment decreases sequentially from 50 nm to 10 nm.

[0031] In this invention, "in order" means based on the total number of film layers in ascending order.

[0032] Preferably, the total thickness of the low-refractive-index material film is more than three times the total thickness of the high-refractive-index material film, such as 3 times, 3.1 times, 3.2 times, 3.3 times, 3.4 times, 3.5 times, 3.6 times, 3.7 times, 3.8 times, 3.9 times, or 4 times, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In fact, the total thickness of the high refractive index material film can be more than three times that of the low refractive index material film. However, considering the coating efficiency, this application prefers that the total thickness of the low refractive index material film is more than three times that of the high refractive index material film.

[0034] In a second aspect, the present invention provides a method for preparing the filter described in the first aspect, the method comprising the following steps:

[0035] A filter is obtained by alternately depositing low-refractive-index material layers and high-refractive-index material layers on a substrate according to a set thickness using evaporation or sputtering deposition.

[0036] As a preferred technical solution of the present invention, a magnetron sputtering coating equipment is used for coating.

[0037] Preferably, when the low refractive index material film is a SiO2 film and the high refractive index material is a Si3N4 film, the magnetron sputtering coating equipment includes at least one plasma generating mechanism and at least one sputtering target containing Si.

[0038] Preferably, the operating power of the Si-containing sputtering target is 5 to 10 kW, such as 5 kW, 6 kW, 7 kW, 8 kW, 9 kW or 10 kW; the operating frequency is 20 to 100 kHz, such as 20 kHz, 30 kHz, 40 kHz, 50 kHz, 60 kHz, 70 kHz, 80 kHz or 100 kHz. The selection of the above values ​​is not limited to the listed values, and other unlisted values ​​within their respective ranges are also applicable.

[0039] Preferably, the operating power of the plasma generating mechanism is 2 to 3.5 kW, such as 2 kW, 2.5 kW, 3 kW or 3.5 kW; the operating frequency is 13 to 14 MHz, such as 13 MHz, 13.2 MHz, 13.4 MHz, 13.6 MHz, 13.8 MHz or 14 MHz. The selection of the above values ​​is not limited to the listed values, and other unlisted values ​​within their respective ranges are also applicable.

[0040] As a preferred technical solution of the present invention, when the low refractive index material film is a SiO2 film, the working gas is a mixture of oxygen and argon. The oxygen flow rate is 80-160 sccm, for example, 80 sccm, 100 sccm, 120 sccm, 140 sccm or 160 sccm; the argon flow rate is 30-150 sccm, for example, 30 sccm, 60 sccm, 90 sccm, 120 sccm or 150 sccm. The selection of the above values ​​is not limited to the listed values, and other unlisted values ​​within their respective ranges are also applicable.

[0041] Preferably, when the high refractive index material film is a Si3N4 film, the working gas is a mixture of nitrogen and argon. The flow rate of nitrogen is 100–180 sccm, such as 100 sccm, 120 sccm, 140 sccm, 160 sccm, or 180 sccm; the flow rate of argon is 30–150 sccm, such as 30 sccm, 60 sccm, 90 sccm, 120 sccm, or 150 sccm. The selection of the above values ​​is not limited to the listed values, and other unlisted values ​​within their respective ranges are also applicable.

[0042] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0043] (1) The substrate is placed on the workpiece disk or workpiece holder of the magnetron sputtering coating equipment, and the workpiece disk or workpiece holder drives the substrate to rotate; the magnetron sputtering coating equipment includes at least one plasma generating mechanism and at least one set of Si-containing twin targets.

[0044] (2) During the magnetron sputtering process, each group of Si-containing sputtering targets is filled with 40 to 120 sccm of argon gas until the coating is completed.

[0045] The ICP mechanism is filled with argon gas at 30-150 sccm and discharged at a power of 2-3.5 KW until the coating is completed;

[0046] (3) Deposit the first layer—SiO2 film layer. The working power of each group of Si-containing twin targets is 5 to 10KW. Keep the conditions in step (2) unchanged and add 80 to 160 sccm of oxygen to the plasma generation mechanism.

[0047] (4) Deposit the second layer—Si3N4 film, stop the oxygen supply in the plasma generator, and simultaneously fill with 100-180 sccm of nitrogen gas, while keeping the other conditions in step (3) unchanged.

[0048] (5) Deposit the third layer—SiO2 film layer, with the same deposition conditions as in step (3);

[0049] (6) Deposit the fourth layer—Si3N4 film, with the same deposition conditions as in step (4);

[0050] (7) Continue in this manner until the set number of plating layers is completed.

[0051] In this invention, under the basic principles of the film stack structure described in the first aspect, when SiO2 is selected as the low-refractive-index material and Si3N4 is selected as the high-refractive-index material, the above method can further improve the coating efficiency. Compared with the conventional coating time of more than ten hours, the coating method of this invention can be completed in less than 3.5 hours, with almost no ineffective film layer, high coating quality, fast coating efficiency, and good application prospects.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] (1) The filter described in this invention is designed with a film stack structure with a regular thickness variation to meet the filtering requirements of the visible light band of 420nm to 700nm, the near-infrared band of 780nm to 820nm, and the near-infrared band of 840nm to 880nm. This improves the coating quality and coating efficiency and provides strong support for actual production.

[0054] (2) Based on the designed film stack structure, the preparation method of the present invention further improves the coating efficiency by selecting suitable coating materials and combining effective coating technology, so that the coating time is controlled within 3.5 hours. The operation process is simple and suitable for large-scale production. Attached Figure Description

[0055] Figure 1This is a diagram showing the thickness variation of each film layer in a filter provided in Embodiment 1 of the present invention.

[0056] Figure 2 This is an envelope diagram formed by the thickness variations of two types of film layers in a filter provided in Embodiment 1 of the present invention.

[0057] Figure 3 This is a diagram illustrating the filtering effect of a filter provided in Embodiment 1 of the present invention.

[0058] Figure 4 This is a diagram showing the thickness variation of each film layer in a filter provided in Embodiment 2 of the present invention.

[0059] Figure 5 This is a diagram showing the thickness variation of each film layer in a filter provided in Embodiment 3 of the present invention.

[0060] Figure 6 This is a diagram showing the thickness variation of each film layer in a filter provided in Embodiment 4 of the present invention.

[0061] Figure 7 This is a diagram showing the thickness variation of each film layer in a filter provided in Embodiment 5 of the present invention.

[0062] Figure 8 These are comparison diagrams of the filtering effects of the filters obtained in Examples 1-5 of this invention.

[0063] Figure 9 This is a comparison chart of the signal-to-noise ratio of the filters obtained in Examples 1-5 of the present invention.

[0064] Figure 10 These are comparison diagrams of the filtering effects of the filters obtained in Embodiments 1, 6, and 7 of this invention.

[0065] Figure 11 These are comparison diagrams of the filtering effects of the filters obtained in Embodiments 1, 8, and 9 of this invention.

[0066] Figure 12 These are comparison diagrams of the filtering effects of the filters obtained in Embodiments 1 and 10 of the present invention.

[0067] Figure 13 This is a diagram showing the thickness variation of each film layer in a filter provided in Comparative Example 1 of the present invention.

[0068] Figure 14 This is a diagram illustrating the filtering effect of a filter provided in Comparative Example 1 of the present invention.

[0069] Figure 15 This is a diagram showing the thickness variation of each film layer in a filter provided in Comparative Example 2 of the present invention.

[0070] Figure 16 This is a diagram illustrating the filtering effect of a filter provided in Comparative Example 2 of the present invention. Detailed Implementation

[0071] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention will be further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the contents of the claims.

[0072] In the specific embodiments described below, the thickness of each film layer can vary within ±10% without changing the filtering effect.

[0073] The following are typical but non-limiting embodiments of the present invention:

[0074] Example 1:

[0075] This embodiment provides a filter with fused silica as the substrate material, which has a diameter of 30 mm and a thickness of 1 mm. The specific film stack structure of the filter is shown in Table 1.

[0076] Table 1

[0077]

[0078]

[0079] The variation of the thickness of each membrane layer in the above membrane stack structure is shown in the figure below. Figure 1 As shown, the envelope diagrams formed by the changes in the thickness of the two types of films are as follows: Figure 2 As shown, its filtering effect is as follows: Figure 3 As shown.

[0080] from Figure 1 It can be seen that the membrane stack structure designed in this invention exhibits a basically regular change and is basically symmetrical from front to back. For the SiO2 membrane layer, roughly, the 21st layer is the inflection point between its falling segment and the stable segment, and the 71st layer is the inflection point between its stable segment and the rising segment; for the Si3N4 membrane layer, the 22nd layer is the inflection point between its rising segment and the stable segment, and the 70th layer is the inflection point between its stable segment and the falling segment.

[0081] from Figure 2 It can be seen that the envelope formed by the thickness variation of the high refractive index material film and the envelope formed by the thickness variation of the low refractive index material film exhibit a basically symmetrical structure about x≈121nm.

[0082] Based on the above, the present invention has further discovered that while the overall envelope does not change much when shifted up and down along the y-axis, it does cause a left and right shift in the spectral curve. Therefore, other applicable filtering requirements can be achieved through the above methods.

[0083] This embodiment also provides a method for preparing the above-mentioned filter, the method comprising:

[0084] (1) Using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material, the substrate is placed on the workpiece disk of the magnetron sputtering coating equipment, and the workpiece disk drives the substrate to rotate; the magnetron sputtering coating equipment includes 2 sets of inductively coupled plasma (ICP) generating mechanisms and 3 sets of Si-containing sputtering targets; the number of sets here refers to the smallest unit that can work independently.

[0085] (2) During the magnetron sputtering process, each group of Si-containing sputtering targets is filled with argon gas at 80 sccm until the coating is completed.

[0086] The ICP mechanism is filled with 100 sccm of argon gas and discharged at a power of 3KW until the coating is completed.

[0087] (3) Deposit the first layer—SiO2 film layer. The working power of each group of Si-containing twin targets is 8KW. Keep the conditions in step (2) unchanged and add 120sccm of oxygen to the ICP mechanism.

[0088] (4) Deposit the second layer—Si3N4 film, stop the oxygen supply in the ICP mechanism, and simultaneously introduce 140 sccm of nitrogen gas, while keeping the other conditions in step (3) unchanged.

[0089] (5) Deposit the third layer—SiO2 film layer, with the same deposition conditions as in step (3);

[0090] (6) Deposit the fourth layer—Si3N4 film, with the same deposition conditions as in step (4);

[0091] (7) Continue in this manner until the set number of plating layers is completed.

[0092] The preparation process can complete the deposition of 89 film layers in just 3.4 hours.

[0093] Example 2:

[0094] This embodiment provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. The substrate has 99 alternating layers of low-refractive-index material (SiO2) and high-refractive-index material (Si3N4), as shown in the specific film stack structure. Figure 4 As shown.

[0095] Example 3:

[0096] This embodiment provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. The substrate has 79 alternating layers of low-refractive-index material (SiO2) and high-refractive-index material (Si3N4), as shown in the specific film stack structure. Figure 5As shown.

[0097] Example 4:

[0098] This embodiment provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. The substrate has 69 alternating layers of low-refractive-index material (SiO2) and high-refractive-index material (Si3N4), as shown in the specific film stack structure. Figure 6 As shown.

[0099] Example 5:

[0100] This embodiment provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. The substrate has 59 alternating layers of low-refractive-index material (SiO2) and high-refractive-index material (Si3N4), as shown in the specific film stack structure. Figure 7 As shown.

[0101] Comparing the filtering effects of the filters obtained in Examples 1-5, the results are as follows: Figure 8 As shown. From Figure 8 It can be seen that the membrane stack structure designed by the present invention can meet the specific light filtering requirements well in the range of 59 to 99 layers.

[0102] The signal-to-noise ratio (T550nm / T770nm) of the filters obtained in Examples 1-5 was calculated to evaluate the noise filtering effect of the membrane stack structure designed in this invention. The results are as follows: Figure 9 As shown. From Figure 9 It is known that when the number of membrane layers is 59 or more, a certain noise filtering effect is achieved (signal-to-noise ratio greater than 6000); when the number of membrane layers reaches 89, a sufficiently high noise filtering effect is achieved (signal-to-noise ratio greater than 7 million); if the number of membrane layers is more, the noise filtering effect will be better (e.g., with 99 layers, the signal-to-noise ratio exceeds 90 million), but more layers are unnecessary, as they will not only increase production costs but may even cause a decline in membrane quality.

[0103] Example 6:

[0104] This embodiment provides a filter, which is the same as the filter in Embodiment 1, except that the high refractive index material film layer is replaced with a ZrO2 film layer.

[0105] Example 7:

[0106] This embodiment provides a filter, which is the same as the filter in Embodiment 1, except that the high refractive index material film is replaced with a La2Ti2O7 film.

[0107] Example 8:

[0108] This embodiment provides a filter, which is the same as the filter in Embodiment 1, except that the high refractive index material film layer is replaced with an HfO2 film layer.

[0109] Example 9:

[0110] This embodiment provides a filter, which is the same as the filter in Embodiment 1, except that the high refractive index material film is replaced with a Ta2O5 film.

[0111] The filtering effects of the filters obtained in Comparative Examples 1, 6, and 7 are as follows: Figure 10 As shown. From Figure 10 It can be seen that replacing Si3N4 with ZrO2 and La2Ti2O7 does not significantly change the filtering properties.

[0112] Comparing the filtering effects of the filters obtained in Examples 1, 8, and 9, the results are as follows: Figure 11 As shown. From Figure 11 It can be seen that replacing Si3N4 with HfO2 and Ta2O5 still results in relatively good control of the passband ripple, but the cutoff band changes.

[0113] Example 10:

[0114] This embodiment provides a filter, which is the same as the filter in Embodiment 1, except that the low refractive index material film layer is replaced with a MgF2 film layer.

[0115] Comparing the filtering effects of the filters obtained in Examples 1 and 10, the results are as follows: Figure 12 As shown. From Figure 12 It can be seen that although replacing SiO2 with MgF2 results in better control of the passband ripple, the cutoff band becomes wider.

[0116] Understandably, in Examples 6-10, for the selection of high-refractive-index or low-refractive-index materials, as long as the optical thickness of the replacement material is basically the same as that of its corresponding material, the same filtering effect can be obtained.

[0117] Comparative Example 1:

[0118] This comparative example provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. Alternating layers of low-refractive-index material—SiO2—and high-refractive-index material—Si3N4—are disposed on the substrate, with the SiO2 layer thickness consistently at 193.96 nm and the Si3N4 layer thickness consistently at 48.17 nm. The film stack structure of this filter (i.e., the variation in the thickness of each layer) is as follows: Figure 13 As shown, its filtering effect is as follows: Figure 14 As shown. From Figure 14It can be seen that the passband ripple of the filter is severe and the signal strength is low, which cannot meet the required filtering requirements.

[0119] Comparative Example 2:

[0120] This comparative example provides a filter using fused silica with a diameter of 30 mm and a thickness of 1 mm as the substrate material. Alternating layers of low-refractive-index material—SiO2—and high-refractive-index material—Nb2O5—are disposed on the substrate. The film stack structure (i.e., the variation in thickness of each layer) is as follows: Figure 15 As shown, the filtering effect is as follows Figure 16 As shown.

[0121] from Figure 15-16 It can be seen that although the existing filters can meet certain filtering requirements, they have a large number of layers and a chaotic and disordered structure, which seriously affects the coating quality and coating efficiency. It takes more than 13 hours to complete the coating of this film stack structure, which is not conducive to production applications.

[0122] As can be seen from the above embodiments and comparative examples, the filter of the present invention, designed with a regular and varied film stack structure, improves the coating quality and coating efficiency, providing strong support for actual production, for the filtering requirements of a passband in the visible light 420nm-700nm band, a stopband in the near-infrared 780nm-820nm band, and a passband in the near-infrared 840nm-880nm band. The filter further improves the coating efficiency by selecting suitable coating materials and combining effective coating technology, keeping the coating time within 3.5 hours, and the operation process is simple and suitable for large-scale production.

[0123] This invention has been illustrated with the above embodiments to demonstrate the product and detailed method of the invention. However, the invention is not limited to the above-described product and detailed method, meaning that the invention does not necessarily depend on the above-described product and detailed method for implementation. Those skilled in the art should understand that any improvements to the invention, equivalent substitutions for the operation of the invention, additions of auxiliary operations, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A filter, characterized in that, The filter includes a substrate, and alternating layers of low-refractive-index material and high-refractive-index material disposed on the substrate; Measured from the side closest to the substrate, the variation trend of the thickness of the low-refractive-index material film includes at least a first decreasing segment, a first stable segment, and a first increasing segment appearing sequentially; the variation trend of the thickness of the high-refractive-index material film includes at least a second increasing segment, a second stable segment, and a second decreasing segment appearing sequentially. When the first layer is a low-refractive-index material film, the total number of film layers of the filter is 79 to 89, and is an odd number; when the first layer is a high-refractive-index material film, the number of layers is 78 to 88, and is an even number. For the low-refractive-index material film, the thickness of each film layer in the first descending segment decreases sequentially from 300 nm to 195 nm, the thickness of each film layer in the first stable segment is independently 190~195 nm, and the thickness of each film layer in the first ascending segment increases sequentially from 195 nm to 300 nm; for the high-refractive-index film, the thickness of each film layer in the second ascending segment increases sequentially from 4 nm to 45 nm, the thickness of each film layer in the second stable segment is independently 45~50 nm, and the thickness of each film layer in the second descending segment decreases sequentially from 50 nm to 10 nm.

2. The filter according to claim 1, characterized in that, The refractive index of the low-refractive-index material is 1.38~1.

65.

3. The filter according to claim 1, characterized in that, The refractive index of the high refractive index material is 1.8~2.

2.

4. The filter according to claim 1, characterized in that, The low-refractive-index material includes SiO2.

5. The filter according to claim 1, characterized in that, The high refractive index material includes at least one of Si3N4, ZrO2, or La2Ti2O7.

6. The filter according to claim 1, characterized in that, The standard deviation of the thickness of each film layer is ±10%.

7. The filter according to claim 1, characterized in that, The total thickness of the low-refractive-index material film is more than three times the total thickness of the high-refractive-index material film.

8. A method for preparing a filter as described in any one of claims 1-7, characterized in that, The preparation method includes the following steps: A filter is obtained by alternately depositing low-refractive-index material layers and high-refractive-index material layers on a substrate according to a set thickness using evaporation or sputtering deposition.

9. The method for preparing the filter according to claim 8, characterized in that, The coating was performed using magnetron sputtering equipment.

10. The method for preparing the filter according to claim 9, characterized in that, When the low refractive index material film is a SiO2 film and the high refractive index material is a Si3N4 film, the magnetron sputtering coating equipment includes at least one plasma generating mechanism and at least one sputtering target containing Si.

11. The method for preparing the filter according to claim 10, characterized in that, The working power of the Si-containing sputtering target is 5~10KW, and the working frequency is 20~100kHz.

12. The method for preparing the filter according to claim 10, characterized in that, The plasma generating mechanism has a power output of 2~3.5KW and a working frequency of 13~14MHz.

13. The method for preparing the filter according to claim 8, characterized in that, When the low refractive index material film is a SiO2 film, the working gas is a mixture of oxygen and argon, with an oxygen flow rate of 80~160 sccm and an argon flow rate of 30~150 sccm.

14. The method for preparing the filter according to claim 8, characterized in that, When the high refractive index material film is a Si3N4 film, the working gas is a mixture of nitrogen and argon, with a nitrogen flow rate of 100~180 sccm and an argon flow rate of 30~150 sccm.

15. The method for preparing the filter according to claim 8, characterized in that, The preparation method includes the following steps: (1) The substrate is placed on the workpiece disk or workpiece holder of the magnetron sputtering coating equipment, and the workpiece disk or workpiece holder drives the substrate to rotate; the magnetron sputtering coating equipment includes at least one plasma generating mechanism and at least one set of Si-containing twin targets. (2) During the magnetron sputtering process, each group of Si-containing sputtering targets is filled with 40~120 sccm of argon gas until the coating is completed; The ICP mechanism is filled with argon gas at 30~150 sccm and discharged at a power of 2~3.5KW until the coating is completed; (3) Deposit the first layer—SiO2 film layer. The working power of each group of Si-containing twin targets is 5~10KW. Keep the conditions in step (2) unchanged and add 80~160sccm of oxygen to the plasma generation mechanism. (4) Deposit the second layer—Si3N4 film, stop the oxygen supply in the plasma generator, and simultaneously fill with 100~180 sccm of nitrogen gas, while keeping the other conditions in step (3) unchanged; (5) Deposit the third layer—SiO2 film, with the same deposition conditions as in step (3); (6) Deposit the fourth layer—Si3N4 film, with the same deposition conditions as in step (4); (7) Continue in this manner until the set number of plating layers is completed.

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