A MEMS Fabry-Perot filter with a double antireflection structure

Abstract

The present invention relates to the technical field of optical MEMS micro-nano devices, and specifically discloses a MEMS Fabry-Perot filter with a dual anti-reflection structure. The filter comprises a microstructure, a driving structure, an upper Bragg reflector, a lower Bragg reflector, a compensation structure, and a substrate, which are arranged in sequence. The lower Bragg reflector has a first low-refractive-index thin film layer, and the compensation structure and the first low-refractive-index thin film layer are made of the same material. The compensation structure and the first low-refractive-index thin film layer have the same thickness. The microstructure and the compensation structure constitute a dual anti-reflection structure. The compensation structure improves the reflectivity of the lower Bragg reflector and simultaneously compensates for the stress of the lower Bragg reflector, thereby increasing the flatness and the utilization rate of the light energy in the Fabry-Perot cavity. The combined effect of the two improves the transmittance of the entire MEMS Fabry-Perot filter transmission spectrum, significantly improving the filtering quality.

Description

Technical Field

[0001] The present invention relates to the technical field of optical MEMS micro-nano devices, and in particular to a MEMS Fabry-Perot filter with a double anti-reflection structure. Background Art

[0002] MEMS Fabry-Perot filters are based on the principle of multi-beam interference. Light waves reflect back and forth within a Fabry-Perot cavity. Waves that meet the phase modulation requirements are transmitted through the cavity, while those that do not meet the requirements reflect back and forth until they disappear. Phase modulation is achieved by tuning the cavity length of the Fabry-Perot cavity through electrostatic actuation, thereby enhancing the selective transmission of infrared light. Because the mechanism of multi-beam interference is phase superposition, and the phase change is closely related to the optical path difference, the flatness of the Bragg reflector structure is crucial. Poor flatness reduces the interference intensity of the light waves, which in turn affects the filtering quality. The germanium and silicon dioxide films in the designed lower Bragg reflector generate tensile and compressive stresses, respectively. This additional stress in the germanium, silicon dioxide, and germanium films degrades the flatness of the lower Bragg reflector, reducing the interference intensity within the Fabry-Perot cavity and, consequently, the transmittance of the MEMS Fabry-Perot filter. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a MEMS Fabry-Perot filter with a double antireflection structure, which can improve the transmittance of the MEMS Fabry-Perot filter and enhance the filtering quality of the MEMS Fabry-Perot filter.

[0004] In order to solve the above problems, the present invention adopts the following technical solutions:

[0005] A MEMS Fabry-Perot filter with a double antireflection structure comprises a microstructure, a driving structure, an upper Bragg reflector, a lower Bragg reflector, a compensation structure and a substrate which are arranged in sequence.

[0006] The microstructure has a plurality of nanocolumns, the plurality of nanocolumns form a periodic array, and the shape of the nanocolumns is a centrosymmetric structure.

[0007] The lower Bragg reflector has a first low-refractive-index thin film layer, and the compensation structure and the first low-refractive-index thin film layer are made of the same material.

[0008] The thickness of the compensation structure and the first low-refractive-index thin-film layer are both one-quarter or three-quarters of the wavelength optical thickness.

[0009] Wherein, the microstructure and the compensation structure constitute a double antireflection structure.

[0010] In the MEMS Fabry-Perot filter with a dual antireflection structure provided by at least one embodiment of the present disclosure, the nanopillar is one of a square nanopillar, a circular nanopillar, and a cross-shaped nanopillar.

[0011] In the MEMS Fabry-Perot filter with a dual antireflection structure provided in at least one embodiment of the present disclosure, the square nanorods have a period of 780 nm, a side length of 500 nm, and a thickness of 550 nm, and are made of germanium.

[0012] In the MEMS Fabry-Perot filter with a dual antireflection structure provided in at least one embodiment of the present disclosure, the first low-refractive-index thin film layer and the compensation structure are both made of silicon dioxide.

[0013] In the MEMS Fabry-Perot filter with a dual antireflection structure provided by at least one embodiment of the present disclosure, the length and width of the compensation structure are the same as the length and width of the lower Bragg reflector.

[0014] In the MEMS Fabry-Perot filter with a dual antireflection structure provided in at least one embodiment of the present disclosure, the driving structure includes a supporting structure, a cantilever structure, an upper electrode structure, and a lower electrode structure.

[0015] In the MEMS Fabry-Perot filter with a dual antireflection structure provided in at least one embodiment of the present disclosure, the support structure includes a silicon plate and a silicon dioxide support body, and the silicon plate and the silicon dioxide support body are arranged in sequence from top to bottom.

[0016] In the MEMS Fabry-Perot filter with a dual antireflection structure provided by at least one embodiment of the present disclosure, the cantilever structure includes four L-shaped cantilevers.

[0017] The four L-shaped cantilevers are respectively located around the silicon flat plate.

[0018] In the MEMS Fabry-Perot filter with a dual antireflection structure provided in at least one embodiment of the present disclosure, the upper electrode structure is configured on the lower surface of the silicon plate, and a first circular notch is provided in the middle of the upper electrode structure, and the upper Bragg reflector is embedded in the first circular notch.

[0019] The lower electrode structure is configured at the lower end of the silicon dioxide support body, and the lower electrode structure is provided with a second circular notch corresponding to the first circular notch.

[0020] The upper Bragg reflector is configured to be located at the same layer as the upper electrode structure, and the lower Bragg reflector is configured on the lower surface of the lower electrode structure.

[0021] In the MEMS Fabry-Perot filter with a dual antireflection structure provided by at least one embodiment of the present disclosure, the lower Bragg reflector and the upper Bragg reflector form a Fabry-Perot cavity.

[0022] The beneficial effects of the present invention are as follows: the compensation structure is arranged between the lower Bragg reflector and the substrate to compensate for the reflected light. The compensation structure is designed to be a low-refractive-index material and the thickness is also designed to be one-quarter or three-quarters of the wavelength. When the light wave enters the compensation structure, a specific phase change continues to occur, causing the light wave to continue to be reflected to the surface of the lower Bragg reflector, achieving constructive interference and enhancing the reflectivity of the lower Bragg reflector.

[0023] The compensation structure improves the reflectivity of the lower Bragg reflector and compensates for its stress, increasing flatness and boosting the utilization of light energy within the Fabry-Perot cavity. The combined effect of these two factors improves the transmittance of the entire MEMS Fabry-Perot filter's transmission spectrum, significantly enhancing filtering quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A structural diagram of a MEMS Fabry-Perot filter with a dual antireflection structure provided in Example 1 of the present invention;

[0026] Figure 2 A cross-sectional view of a MEMS Fabry-Perot filter with a dual antireflection structure provided in Example 1 of the present invention;

[0027] Figure 3 A transmission spectrum diagram of the MEMS Fabry-Perot filter with a dual antireflection structure provided in Example 1 of the present invention;

[0028] Figure 4 A cross-sectional view of a MEMS Fabry-Perot filter with a microstructure provided in Comparative Example 1 of the present invention;

[0029] Figure 5 The transmittance of the silicon flat plate with microstructure provided in Comparative Example 1 of the present invention;

[0030] Figure 6 A transmission spectrum of a MEMS Fabry-Perot filter with a microstructure provided in Comparative Example 1 of the present invention;

[0031] Figure 7 Cross-sectional views of MEMS Fabry-Perot filters having microstructures of different sizes provided for Comparative Example 2 of the present invention;

[0032] Figure 8 Transmission spectra of MEMS Fabry-Perot filters with different microstructure sizes provided for Comparative Example 2 of the present invention

[0033] Figure 9 A cross-sectional view of a MEMS Fabry-Perot filter having a gold microstructure provided in Comparative Example 3 of the present invention;

[0034] Figure 10 This is a transmission spectrum of a MEMS Fabry-Perot filter having a gold material microstructure provided in Comparative Example 3 of the present invention;

[0035] Figure 11 A cross-sectional view of a MEMS Fabry-Perot filter with a compensation structure provided in Comparative Example 4 of the present invention;

[0036] Figure 12 A reflection spectrum diagram of a lower Bragg reflector with a compensation structure provided in Comparative Example 4 of the present invention;

[0037] Figure 13 A stress distribution diagram of a lower Bragg reflector with a compensation structure provided in Comparative Example 4 of the present invention;

[0038] Figure 14 A transmission spectrum diagram of a MEMS Fabry-Perot filter with a compensation structure provided in Comparative Example 4 of the present invention;

[0039] Figure 15 A three-dimensional structure diagram of a conventional MEMS Fabry-Perot filter provided as Comparative Example 5 of the present invention;

[0040] Figure 16 A cross-sectional view of a conventional MEMS Fabry-Perot filter is provided for Comparative Example 5 of the present invention.

[0041] In the picture:

[0042] 1. Microstructure; 2. Silicon plate; 3. Cantilever structure; 4. Silicon dioxide support; 5. Compensation structure; 6. Substrate; 7. High refractive index thin film layer I; 8. Upper electrode structure; 9. First low refractive index thin film layer; 10. High refractive index thin film layer II; 11. Lower electrode structure; 12. High refractive index thin film layer III; 13. Second low refractive index thin film layer; 14. High refractive index thin film layer IV. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments, rather than all the embodiments.

[0044] It should be noted that the terms used in this application are generally terms commonly used by those skilled in the art. If there is any inconsistency with commonly used terms, the terms in this application shall prevail.

[0045] In the present invention, the term "circular polarization component" refers to a polarization state in which the electric field vector of a light wave rotates in a spiral trajectory along the propagation direction.

[0046] In the present invention, the term "cross-polarization component" refers to a light wave component that is orthogonal (perpendicular) to a desired polarization direction.

[0047] In the present invention, the term "circularly polarized component" refers to the electric field component of the light wave that has circular polarization characteristics.

[0048] In the present invention, the term "chirality" refers to a geometric property that describes the characteristic that an object or system cannot be completely superimposed with its mirror image in space through rotation or translation.

[0049] In the present invention, the term "multi-beam interference" refers to the phenomenon that when multiple light beams meet in the same space, they overlap and interfere with each other to produce an interference pattern.

[0050] In the present invention, the term "quarter or three-quarter wavelength optics" refers to a quarter of the wavelength corresponding to the transmission peak of the MEMS Fabry-Perot filter.

[0051] In the present invention, the term "infrared filtering" refers to screening a specific infrared band.

[0052] In the present invention, the term "central wavelength of the transmission spectrum" refers to the wavelength corresponding to the maximum transmittance of the transmission spectrum.

[0053] In the present invention, the term "constructive interference" refers to the phenomenon that when two or more light waves meet, their phases are consistent or differ by an integer multiple of the wavelength, resulting in the addition of the amplitudes of the waves, thereby producing a composite wave with a larger amplitude.

[0054] In the present invention, the term "tuning" refers to increasing or decreasing the length of the Fabry-Perot cavity.

[0055] In the present invention, the term "optical path difference" refers to the difference between the geometric path lengths of two light beams multiplied by the refractive index of the medium.

[0056] In the present invention, the term "flatness" refers to the surface smoothness of the Bragg reflector structure film.

[0057] In the present invention, the term "plasma chemical vapor deposition" refers to a technology that uses plasma to activate reactive gases to promote chemical reactions on the surface of a substrate or in the space near the surface to form a solid film.

[0058] In the present invention, the terms "upper" and "lower" indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or the directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the equipment or components referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the present invention.

[0059] Because the mechanism of multi-beam interference is phase superposition, and phase changes are closely related to optical path difference, the flatness of the Bragg reflector structure is very important. The worse the flatness, the lower the light wave interference intensity, which in turn affects the filtering quality. The germanium and silicon dioxide films of the designed lower Bragg reflector will produce tensile stress and compressive stress, respectively. Therefore, the germanium, silicon dioxide, and germanium films will generate additional stress, causing the flatness of the lower Bragg reflector to decrease, resulting in a decrease in the interference intensity within the Fabry-Perot cavity and a decrease in the transmittance of the MEMS Fabry-Perot filter.

[0060] The purpose of the present invention is to solve the above technical problems and to provide a MEMS Fabry-Perot filter with a double antireflection structure, which can improve the transmittance of the MEMS Fabry-Perot filter and enhance the filtering quality of the MEMS Fabry-Perot filter.

[0061] Example 1

[0062] See also Figure 1 and Figure 2 , a MEMS Fabry-Perot filter with a dual antireflection structure according to embodiment 1 of the present invention is provided. The MEMS Fabry-Perot filter with a dual antireflection structure comprises a microstructure 1, a driving structure, an upper Bragg reflector, a lower Bragg reflector, a compensation structure 5, and a substrate 6, which are arranged in sequence from top to bottom.

[0063] The microstructure 1 and the compensation structure 5 form a double antireflection structure.

[0064] The microstructure 1 is arranged on the upper surface of the driving structure. The microstructure 1 is a periodic array composed of nanocolumns. The shape of the nanocolumns is a centrally symmetrical structure. The nanocolumns are any one of square nanocolumns, circular nanocolumns, and cross-shaped nanocolumns.

[0065] The arrangement period of the nanorods is 780 nm or other possible values. In one example, the nano-square nanorods have a side length of 500 nm and a thickness of 550 nm, and the material of the nanorods is germanium.

[0066] The drive structure consists of a support structure, a cantilever structure 3, an upper electrode structure, and a lower electrode structure. The support structure consists of a silicon flat plate 2 and a silicon dioxide support 4, arranged in order from top to bottom. The silicon flat plate 2 is 500 μm long and wide, and 5 μm thick. The silicon dioxide support 4 is 50 μm long and wide, and 1.5 μm thick.

[0067] The cantilever structure 3 includes four L-shaped cantilevers. The total length of the L-shaped cantilevers is 600 μm, the width is 50 μm, and the thickness is 5 μm. The four L-shaped cantilevers are respectively arranged on four sides of the silicon plate 2 .

[0068] Specifically, the materials of the silicon plate 2 and the cantilever structure 3 are both silicon. The material of the silicon dioxide support 4 is silicon dioxide.

[0069] like Figure 2 As shown, below the silicon flat plate 2 is the upper electrode structure 8 and the upper Bragg reflector, which are distributed on the same layer. The upper electrode structure 8 is 500μm in length and width, 1μm thick, and has a first circular notch (not shown) with a radius of 150μm in the center. The upper Bragg reflector is a circular structure with a radius of 150μm, composed of a high-refractive-index thin film layer I7, a first low-refractive-index thin film layer 9, and a high-refractive-index thin film layer II10. The three thin film layers are made of germanium, silicon dioxide, and germanium, with thicknesses of 250nm, 700nm, and 250nm, respectively, all of which are thicknesses corresponding to a quarter of the central wavelength of the transmission spectrum. The refractive index of germanium is 4, and the refractive index of silicon dioxide is 1.46. They are embedded in the first circular notch of the upper electrode structure 8.

[0070] The lower electrode structure 11 is provided at the lower end of the silicon dioxide support 4, and has a length and width of 500 μm. The lower electrode structure 11 is provided with a second circular notch (not shown) corresponding to the first circular notch. The upper electrode structure 8 and the lower electrode structure 11 are made of gold and have a thickness of 1 μm.

[0071] Below the lower electrode structure 11 is the lower Bragg reflector, with a length and width of 500 μm and the same material and thickness as the upper Bragg reflector. The lower Bragg reflector is composed of a stack of high-refractive-index thin-film layer III 12, a second low-refractive-index thin-film layer 13, and a high-refractive-index thin-film layer IV 14. These three thin-film layers are made of germanium, silicon dioxide, and germanium, respectively, with thicknesses of 250 nm, 700 nm, and 250 nm, respectively, corresponding to a quarter of the central wavelength of the transmission spectrum.

[0072] The compensation structure 5 is located below the lower Bragg reflector, and has a length and width of 500 μm and a thickness of 700 nm, which is a quarter of the central wavelength of the transmission spectrum. In other words, the length and width of the compensation structure 5 are the same as those of the lower Bragg reflector.

[0073] During the preparation process, a low-temperature, low-stress plasma chemical vapor deposition method is selected to grow and prepare the compensation structure 5 .

[0074] Below the compensation structure 5 is a substrate 6, which has a length and width of 500 μm and a thickness of 300 μm. The substrate 6 is made of silicon.

[0075] MEMS Fabry-Perot filters are based on the principle of multi-beam interference. Light waves reflect back and forth within a Fabry-Perot cavity. Waves that meet the phase modulation requirements are transmitted through the cavity, while those that do not meet the requirements are reflected back and forth within the cavity until they disappear. Phase modulation is achieved by tuning the cavity length through electrostatic drive, thereby enhancing the selective transmission of infrared light waves.

[0076] The light field transmitted through the interface of silicon slab 2 consists of two orthogonal circularly polarized components: a cross-polarized component and a co-polarized component. The chirality of the cross-polarized component is reversed relative to the incident light field, and a phase shift occurs simultaneously. The chirality of the co-polarized component is the same as the incident light. By designing appropriate structural parameters of microstructure 1, the ratio of the co-polarized and cross-polarized components in the light field transmitted through silicon slab 2 can be adjusted. The designed microstructure 1 acts as a phase regulator. By combining with silicon slab 2, it modulates the geometric phase of the transmitted light, thereby enhancing the light transmitted through the interface of silicon slab 2.

[0077] Since the mechanism of multi-beam interference is phase superposition, and the change in phase is closely related to the optical path difference, the flatness of the Bragg reflector structure is very important. The worse the flatness, the worse the light wave interference intensity, which in turn affects the filtering quality. The germanium and silicon dioxide films of the designed lower Bragg reflector will generate tensile stress and compressive stress respectively. Since the tensile stress generated by germanium is much greater than the compressive stress generated by silicon dioxide, the germanium, silicon dioxide and germanium films will generate additional tensile stress, causing the flatness of the lower Bragg reflector to decrease, resulting in a decrease in the interference intensity within the Fabry-Perot cavity, and a decrease in the transmittance of the MEMS Fabry-Perot filter. The designed compensation structure 5 is a silicon dioxide material layer of the same thickness as the second low-refractive-index film layer 13 in the lower Bragg reflector, which can provide stress compensation for the lower Bragg reflector, reduce tensile stress, and increase the flatness of the lower Bragg reflector.

[0078] The designed lower Bragg reflector is composed of a high refractive index film layer III12, a second low refractive index film layer 13 and a high refractive index film layer IV14 stacked alternately. The film thickness of the lower Bragg reflector is an optical thickness of one quarter or three quarters of the design center wavelength.

[0079] When light waves pass through different interfaces, due to the refractive index difference between the designed high and low refractive index film materials and the existence of a quarter-wavelength optical thickness of the film, the light waves undergo phase changes when propagating in the film, causing the reflected light to be in the same phase during interference. The phase of the reflected light is consistent, and constructive interference occurs on the surface of the lower Bragg reflector, enhancing the reflection response and realizing the design of a high reflector.

[0080] However, when some light waves reach the interface between the lower Bragg reflector and substrate 6, the difference in refractive index between the two is small, reducing the reflection of light at this interface and causing loss of reflected light. A compensation structure 5 is designed to compensate for the reflected light. Compensation structure 5 is designed to be made of a low-refractive-index material and has a thickness of one-quarter or three-quarters of a wavelength. When light waves enter compensation structure 5, they continue to undergo a specific phase change, causing them to continue reflecting onto the surface of the lower Bragg reflector, achieving constructive interference and enhancing the reflectivity of the lower Bragg reflector.

[0081] The material selection for the designed compensation structure 5 required consideration of reasonable optical parameters and ease of fabrication. The material used for the compensation structure 5, which has the same low refractive index as the Bragg reflector structure, was chosen, with a thickness of one-quarter wavelength. During fabrication, the film was grown using low-temperature, low-stress plasma chemical vapor deposition.

[0082] The effect of the MEMS Fabry-Perot filter with a dual antireflection structure in the embodiment will be further explained below with reference to comparative examples.

[0083] Comparative Example 1

[0084] See also Figure 4 , provides a MEMS Fabry-Perot filter with a microstructure. The MEMS Fabry-Perot filter does not have the compensation structure 5, and the remaining parameters are the same as those of the MEMS Fabry-Perot filter described in Example 1.

[0085] Comparative Example 2

[0086] See also Figure 7 A MEMS Fabry-Perot filter having a microstructure 1 is provided. The period of the microstructure 1 is 1.5 μm, and the side length of the nanopillars is 0.5 μm. The MEMS Fabry-Perot filter does not have the compensation structure 5, and the remaining parameters are the same as those of the MEMS Fabry-Perot filter of Example 1.

[0087] Comparative Example 3

[0088] See also Figure 9A MEMS Fabry-Perot filter having a gold microstructure 1 is provided. The material of the microstructure 1 is gold. The MEMS Fabry-Perot filter does not have the compensation structure 5, and the remaining parameters are the same as those of the MEMS Fabry-Perot filter of Example 1.

[0089] Comparative Example 4

[0090] See also Figure 11 , provides a MEMS Fabry-Perot filter having a compensation structure 5. The MEMS Fabry-Perot filter does not have the microstructure 1, and the remaining parameters are the same as those of the MEMS Fabry-Perot filter of embodiment 1.

[0091] Comparative Example 5

[0092] See also Figure 15 and 16 , provides a MEMS Fabry-Perot filter manufactured by a conventional method. The MEMS Fabry-Perot filter does not have the microstructure 1 and the compensation structure 5, and the remaining parameters are the same as those of the MEMS Fabry-Perot filter of Example 1.

[0093] like Figure 5 and Figure 6 As shown in the figure, the transmission spectrum was obtained using Lumerical v202 FDTD simulation analysis software. When the MEMS Fabry-Perot filter lacks microstructure 1, some incident light is reflected at the interface of silicon plate 2, reducing transmission at the interface between silicon plate 2 and the upper Bragg reflector, resulting in light loss. The transmittance of silicon plate 2 in the 3-5μm band is consistently below 70%. The peak transmittance of the MEMS Fabry-Perot filter is 62%.

[0094] The MEMS Fabry-Perot filter of Comparative Example 1 has microstructure 1. Due to the presence of microstructure 1, the light wave undergoes a specific phase shift, causing the reflected light from the surface of silicon plate 1 to have an opposite phase, resulting in destructive interference. The transmittance of silicon plate 2 is consistently above 90% in the 3-5 μm band. The transmittance of the MEMS Fabry-Perot filter at its peak transmission reaches 73%.

[0095] like Figure 8 As shown, the MEMS Fabry-Perot filter described in Comparative Example 2 has microstructure 1 with a period of 1.5 μm and nanopillars with a side length of 0.5 μm. Due to the presence of microstructure 1, the reflected light phase undergoes additional changes, increasing the reflected light from the surface of silicon plate 2 and reducing the transmittance. The transmittance of the MEMS Fabry-Perot filter at its peak transmission point is reduced to 28%.

[0096] like Figure 10As shown, the MEMS Fabry-Perot filter described in Comparative Example 3 includes a microstructure 1 made of gold. Due to the presence of gold microstructure 1, light waves resonate at other wavelengths within the Fabry-Perot cavity. This results in two transmission peaks in the MEMS Fabry-Perot filter, severely impacting filtering quality.

[0097] like Figure 12 As shown, the MEMS Fabry-Perot filter described in Comparative Example 4 has a compensation structure 5. Some light waves enter the compensation structure 5 and continue to undergo a specific phase change, causing the light waves to continue to reflect to the surface of the lower Bragg reflector, achieving constructive interference. The reflectivity of the Bragg reflector is above 90% in the 3-5μm band.

[0098] like Figure 13 Figure 2 shows the stress distribution of the lower Bragg reflector, obtained using an FST 5000 stress tester. Without compensation structure 5, the germanium and silicon dioxide films in the lower Bragg reflector generate tensile and compressive stresses, respectively. Consequently, the germanium, silicon dioxide, and germanium films generate additional stress, averaging 54.48 MPa. With the addition of compensation structure 5, the stress compensation provided by the compensation structure reduces the stress in the lower Bragg reflector to an average of 5.08 MPa.

[0099] like Figure 14 As shown, the transmittance of the MEMS Fabry-Perot filter without the compensation structure 5 is 62% at a central wavelength of 4 μm. The transmittance of the MEMS Fabry-Perot filter with the compensation structure 5 is increased to 75% at a central wavelength of 4 μm by compensating for stress and the reflectivity of the lower Bragg reflector.

[0100] like Figure 3 As shown, the MEMS Fabry-Perot filter with a dual anti-reflection structure increases the light input to the Fabry-Perot cavity through the design of the microstructure 1, and then the compensation structure 5 increases the reflectivity of the lower Bragg reflector, thereby improving the utilization rate of the light energy in the cavity. The two work together to increase the transmittance of the MEMS Fabry-Perot filter to 90%, thereby improving the filtering quality.

[0101] In summary, the MEMS Fabry-Perot filter with a dual antireflection structure of Example 1 has the following advantages:

[0102] In the structure of the present invention, a microstructure is designed and placed on the top surface of a silicon slab. The combination of the microstructure and the silicon slab enhances the energy of the light field incident on the MEMS Fabry-Perot cavity. By designing appropriate structural parameters for the microstructure and adjusting the ratio of co-polarization and cross-polarization components in the light field transmitted by the silicon slab, the geometric phase of the incident light is controlled, resulting in destructive interference of the reflected light, thereby enhancing the transmitted light.

[0103] The designed compensation structure is configured between the lower Bragg reflector and the substrate to compensate for the reflected light. The compensation structure is designed to be a low-refractive-index material and its thickness is also designed to be a quarter-wavelength thick. When the light wave enters the compensation structure, it continues to undergo a specific phase change, causing the light wave to continue to reflect to the surface of the lower Bragg reflector, achieving constructive interference and enhancing the reflectivity of the lower Bragg reflector.

[0104] The material selection for the designed compensation structure requires consideration of reasonable optical parameters, and its refractive index should be lower than that of the substrate. To facilitate fabrication, the compensation structure is made of the same material system as the low-refractive-index thin film layer in the designed lower Bragg reflector, with a thickness of one-quarter wavelength.

[0105] The designed microstructure increases the amount of light entering the MEMS Fabry-Perot cavity. The designed compensation structure improves the reflectivity of the lower Bragg reflector while compensating for stress, increasing flatness and boosting the utilization of light energy within the Fabry-Perot cavity. These two combined effects enhance the transmittance of the entire MEMS Fabry-Perot filter's transmission spectrum, significantly improving filtering quality.

Claims

1. A MEMS Fabry-Perot filter with a double antireflection structure, characterized in that: include: A microstructure, a driving structure, an upper Bragg reflector, a lower Bragg reflector, a compensation structure and a substrate are sequentially arranged; The microstructure has a plurality of nanocolumns, the plurality of nanocolumns form a periodic array, and the shape of the nanocolumns is a centrosymmetric structure; The lower Bragg reflector has a first low-refractive-index thin film layer, and the compensation structure and the first low-refractive-index thin film layer are made of the same material; The thickness of the compensation structure and the first low-refractive-index thin film layer are both one-quarter or three-quarters of the wavelength optical thickness; The microstructure and the compensation structure constitute a double antireflection structure; The driving structure includes a supporting structure, a cantilever structure, an upper electrode structure and a lower electrode structure; The support structure comprises a silicon flat plate and a silicon dioxide support body, and the silicon flat plate and the silicon dioxide support body are arranged in sequence from top to bottom; The upper electrode structure is configured on the lower surface of the silicon plate, and a first circular notch is provided in the middle of the upper electrode structure, and the upper Bragg reflector is embedded in the first circular notch; The lower electrode structure is configured at the lower end of the silicon dioxide support body, and the lower electrode structure is provided with a second circular notch corresponding to the first circular notch; The upper Bragg reflector is configured to be located at the same layer as the upper electrode structure, and the lower Bragg reflector is configured on the lower surface of the lower electrode structure; The upper Bragg reflector is formed by stacking a high refractive index thin film layer I, a first low refractive index thin film layer and a high refractive index thin film layer II, wherein the materials of the high refractive index thin film layer I, the first low refractive index thin film layer and the high refractive index thin film layer II are germanium, silicon dioxide and germanium respectively; The lower Bragg reflector is formed by stacking a high refractive index thin film layer III, a second low refractive index thin film layer and a high refractive index thin film layer IV, wherein the materials of the high refractive index thin film layer III, the second low refractive index thin film layer and the high refractive index thin film layer IV are germanium, silicon dioxide and germanium respectively; In the lower Bragg reflector, the germanium and silicon dioxide films generate tensile stress and compressive stress, respectively. Since the tensile stress generated by germanium is much greater than the compressive stress generated by silicon dioxide, the germanium, silicon dioxide, and germanium films generate additional tensile stress, which causes the flatness of the lower Bragg reflector to decrease, resulting in a decrease in the interference intensity within the Fabry-Perot cavity and a decrease in the transmittance of the MEMS Fabry-Perot filter. The compensation structure is made of silicon dioxide and has the same thickness as the second low-refractive-index thin film layer in the lower Bragg reflector. It is used to provide stress compensation for the lower Bragg reflector to reduce tensile stress and increase the flatness of the lower Bragg reflector.

2. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 1, characterized in that: The nanocolumn is one of a square nanocolumn, a circular nanocolumn and a cross nanocolumn.

3. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 2, wherein: The square nanocolumns have a period of 780 nm, a side length of 500 nm, and a thickness of 550 nm. The nanocolumns are made of germanium.

4. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 1, wherein: The length and width of the compensation structure are the same as the length and width of the lower Bragg reflector.

5. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 1, wherein: The cantilever structure includes four L-shaped cantilevers; The four L-shaped cantilevers are respectively located around the silicon flat plate.

6. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 5, characterized in that: The lower Bragg reflector and the upper Bragg reflector form a Fabry-Perot cavity.

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