MEMS Fabry-Perot filter with double anti-reflection structures

Abstract

The invention relates to the technical field of optical MEMS micro-nano devices, and particularly discloses an MEMS Fabry-Perot filter with a double-anti-reflection structure, which 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 is provided with 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 is the same as that of the first low-refractive-index thin film layer; and the microstructure and the compensation structure form a double-anti-reflection structure. The compensation structure improves the reflectivity of the lower Bragg reflector and compensates the stress of the lower Bragg reflector at the same time, so that the flatness is increased, and the utilization rate of light energy in the Fabry-Perot cavity is increased; the transmissivity of the transmission spectrum of the whole MEMS Fabry-Perot filter is improved through the combined action of the two, and the filtering quality is greatly improved.

Description

Technical Field

[0001] The 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] The MEMS Fabry-Perot filter is based on the principle of multi-beam interference. The light waves reflect back and forth in the Fabry-Perot cavity. The light waves that meet the phase modulation requirements are transmitted out of the Fabry-Perot cavity, and the light waves that do not meet the requirements are reflected back and forth in the Fabry-Perot cavity until they disappear. The cavity length of the Fabry-Perot cavity is tuned by electrostatic drive to achieve the effect of phase modulation, and the selective transmission enhancement of infrared light waves is realized. Since the mechanism of multi-beam interference is the superposition of phases, the change of phase has a great relationship with the optical path difference, so 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 produce tensile stress and compressive stress respectively, so the germanium, silicon dioxide, and germanium films will produce additional stress, resulting in a decrease in the flatness of the lower Bragg reflector, which will reduce the interference intensity in the Fabry-Perot cavity and reduce 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 anti-reflection structure, which can improve the transmittance of the MEMS Fabry-Perot filter and enhance the filtering quality of the MEMS Fabry-Perot filter.

[0004] To solve the above problems, the present invention adopts the following technical solutions:

[0005] A MEMS Fabry-Perot filter with a double anti-reflection 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 centrally symmetrical structure.

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

[0008] The thickness of the compensation structure and the first low-refractive-index 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 anti-reflection structure.

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

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

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

[0013] In the MEMS Fabry-Perot filter with a dual anti-reflection 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 anti-reflection 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 anti-reflection structure provided by 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 anti-reflection 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 double anti-reflection 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 thickness; when the light wave enters the compensation structure, a specific phase change continues to occur, so that the light wave continues to be reflected to the surface of the lower Bragg reflector, thereby 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 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 two work together to improve the transmittance of the entire MEMS Fabry-Perot filter transmission spectrum, and the filtering quality is greatly improved. 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 double anti-reflection 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 anti-reflection structure provided in Example 1 of the present invention;

[0027] Figure 3 A transmission spectrum diagram of a MEMS Fabry-Perot filter with a double 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 for 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 diagram of a MEMS Fabry-Perot filter with a microstructure provided in Comparative Example 1 of the present invention;

[0031] Figure 7 A cross-sectional view of a MEMS Fabry-Perot filter 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] Fig. 9 A cross-sectional view of a MEMS Fabry-Perot filter having a microstructure of gold material provided for Comparative Example 3 of the present invention;

[0034] Fig.10 A transmission spectrum diagram of a MEMS Fabry-Perot filter having a gold material microstructure provided in Comparative Example 3 of the present invention;

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

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

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

[0038] Fig.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] Fig.15 A three-dimensional structure diagram of a conventional MEMS Fabry-Perot filter provided as Comparative Example 5 of the present invention;

[0040] Fig.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 figure:

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

[0043] The technical solutions in the embodiments will be described clearly and completely below in conjunction with the drawings in the embodiments. 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 the 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 overlapped 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 cavity 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 reaction 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 orientation or position relationship indicated by the terms "upper" and "lower" is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship in which the product of the invention is usually placed when used. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the equipment or components referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0059] Since the mechanism of multi-beam interference is the superposition of phases, and the change of phases 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 produce tensile stress and compressive stress respectively, so the germanium, silicon dioxide, and germanium films will produce additional stress, which will cause the flatness of the lower Bragg reflector to decrease, causing the interference intensity in the Fabry-Perot cavity to decrease, resulting in 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 anti-reflection 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 anti-reflection structure according to Embodiment 1 of the present invention is given. The MEMS Fabry-Perot filter with a dual anti-reflection 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 disposed 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 nanorod has a side length of 500 nm and a thickness of 550 nm, and the material of the nanorods is germanium.

[0066] The driving structure is composed of a support structure, a cantilever structure 3, an upper electrode structure and a lower electrode structure. The support structure is composed of a silicon flat plate 2 and a silicon dioxide support body 4 arranged in sequence from top to bottom. The length and width of the silicon flat plate 2 are both 500 μm and the thickness is 5 μm. The length and width of the silicon dioxide support body 4 are both 50 μm and the thickness is 1.5 μm.

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

[0068] Specifically, the materials of the silicon flat 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 in the same layer. The length and width of the upper electrode structure 8 are both 500μm, the thickness is 1μm, and there is a first circular notch with a radius of 150μm in the middle (not shown). The upper Bragg reflector is a circular structure with a radius of 150μm, which is stacked by a high refractive index film layer I7, a first low refractive index film layer 9 and a high refractive index film layer II10. The materials of the three film layers are germanium, silicon dioxide and germanium, respectively, with thicknesses of 250nm, 700nm and 250nm, respectively, which are all quarter the central wavelength thickness of the transmission spectrum. The refractive index of germanium is 4, and the refractive index of silicon dioxide is 1.46, which is embedded in the first circular center notch of the upper electrode structure 8.

[0070] The lower electrode structure 11 is disposed 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 a 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 stacked by a high refractive index film layer III12, a second low refractive index film layer 13 and a high refractive index film layer IV14. The materials of the three film layers are germanium, silicon dioxide and germanium, respectively, with thicknesses of 250 nm, 700 nm and 250 nm, respectively, all of which are the thickness of 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 thickness of one quarter of the central wavelength of the transmission spectrum. That is, 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 a width of 500 μm and a thickness of 300 μm. The material of the substrate 6 is silicon.

[0075] The MEMS Fabry-Perot filter is based on the principle of multi-beam interference. Light waves are reflected back and forth in the Fabry-Perot cavity. Light waves that meet the phase modulation requirements are transmitted out of the Fabry-Perot cavity, and light waves that do not meet the requirements are reflected back and forth in the cavity until they disappear. The Fabry-Perot cavity length is tuned by electrostatic drive to achieve the effect of phase modulation, realizing the selective transmission enhancement of infrared light waves.

[0076] The transmitted light field at the interface of silicon flat plate 2 is two orthogonal circularly polarized components, which are divided into 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 at the same time. 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 component and the cross-polarized component in the transmitted light field of silicon flat plate 2 is adjusted. The designed microstructure 1 has the function of phase body regulation. By combining it with silicon flat plate 2, the geometric phase of the transmitted light is regulated, so as to achieve the effect of enhancing the transmitted light at the interface of silicon flat plate 2.

[0077] Since the mechanism of multi-beam interference is the superposition of phases, and the change of phases 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 designed germanium and silicon dioxide films of the lower Bragg reflector will produce 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 produce additional tensile stress, which will cause the flatness of the lower Bragg reflector to decrease, causing the interference intensity in the Fabry-Perot cavity to decrease, resulting in 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, and the film thickness of the lower Bragg reflector is a quarter or three quarters of the optical thickness of the designed central 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 a phase change 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, constructive interference occurs on the surface of the lower Bragg reflector, the reflection response is enhanced, and the design of a high reflector is achieved.

[0080] However, when part of the light wave reaches the interface between the lower Bragg reflector and the substrate 6, the difference in refractive index between the two is small, which reduces the reflection of light at the interface and causes the loss of reflected light. The designed compensation structure 5 is arranged between the lower Bragg reflector and the substrate 6 to compensate for the reflected light. The compensation structure 5 is designed to be a low refractive index material and the thickness is designed to be one quarter or three quarters of the wavelength thickness. When the light wave enters the compensation structure 5, a specific phase change continues to occur, so that the light wave continues to be reflected to the surface of the lower Bragg reflector, achieving constructive interference and enhancing the reflectivity of the lower Bragg reflector.

[0081] The material selection of the designed compensation structure 5 needs to consider reasonable optical parameters and facilitate process preparation. The material system with the same low refractive index as the designed Bragg reflector structure is used as the compensation structure 5, and its thickness is a quarter wavelength optical thickness. During the preparation process, a low-temperature, low-stress plasma chemical vapor deposition method is selected to grow the film.

[0082] The effect of the MEMS Fabry-Perot filter with a dual anti-reflection structure in the embodiment will be further explained below in conjunction with a comparative example.

[0083] Comparative Example 1

[0084] See also Figure 4 , a MEMS Fabry-Perot filter with a microstructure is provided. The MEMS Fabry-Perot filter does not have a 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 nanocolumn is 0.5 μm. The MEMS Fabry-Perot filter does not have a 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 Fig. 9, a 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 a 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 Fig.11 , a MEMS Fabry-Perot filter having a compensation structure 5 is provided. 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 Example 1.

[0091] Comparative Example 5

[0092] See also Fig.15 and 16 , a MEMS Fabry-Perot filter prepared by a conventional method is provided. 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, the transmission spectrum is obtained by Lumerical v202 FDTD simulation analysis software. When the MEMS Fabry-Perot filter does not have the microstructure 1, part of the incident light is reflected at the interface of the silicon plate 2, reducing the transmission at the interface between the silicon plate 2 and the upper Bragg reflector, resulting in the loss of the transmitted light. The transmittance of the silicon plate 2 in the 3-5μm band is less than 70%. The transmittance of the transmission peak of the MEMS Fabry-Perot filter is 62%.

[0094] The MEMS Fabry-Perot filter of comparative example 1 has a microstructure 1. Due to the presence of the microstructure 1, the light wave undergoes a specific phase change, so that the reflected light on the surface of the silicon plate 1 has an opposite phase, achieving destructive interference, and the transmittance of the silicon plate 2 in the 3-5 μm band is above 90%. The transmittance of the transmission peak of the MEMS Fabry-Perot filter is increased to 73%.

[0095] like Figure 8 As shown, the MEMS Fabry-Perot filter described in Comparative Example 2 has a microstructure 1, the period of the microstructure 1 is 1.5 μm, and the side length of the nanocolumn is 0.5 μm. Due to the presence of the microstructure 1, the phase of the reflected light undergoes other changes, which enhances the reflected light on the surface of the silicon plate 2 and reduces the transmittance. The transmittance of the transmission peak of the MEMS Fabry-Perot filter is reduced to 28%.

[0096] like Fig.10As shown, the MEMS Fabry-Perot filter described in Comparative Example 3 has a microstructure 1, and the material of the microstructure 1 is gold. Due to the presence of the gold microstructure 1, the light wave resonates with other wavelengths in the Fabry-Perot cavity. The two transmission peaks of the MEMS Fabry-Perot filter seriously affect the filtering quality.

[0097] like Fig.12 As shown, the MEMS Fabry-Perot filter described in comparative example 4 has a compensation structure 5, and part of the light waves enter the compensation structure 5 and continue to undergo a specific phase change, so that the light waves continue to be reflected to the surface of the lower Bragg reflector to achieve constructive interference. The reflectivity of the Bragg reflector in the 3-5μm band is above 90%.

[0098] like Fig.13 As shown, the stress distribution diagram of the lower Bragg reflector obtained by testing with the FST 5000 stress tester is shown. The germanium and silicon dioxide films in the lower Bragg reflector without the compensation structure 5 will generate tensile stress and compressive stress respectively, so the germanium, silicon dioxide, and germanium films will generate additional stress, with an average of 54.48 MPa. After adding the compensation structure 5, the stress of the lower Bragg reflector is reduced to an average of 5.08 MPa through the stress compensation of the compensation structure 5.

[0099] like Fig.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 the stress and the reflectivity of the lower Bragg reflector.

[0100] like Figure 3 As shown, the MEMS Fabry-Perot filter with a double anti-reflection structure increases the light input into the Fabry-Perot cavity through the design of the microstructure 1, and then increases the reflectivity of the lower Bragg reflector by the compensation structure 5, 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, the designed microstructure is configured on the upper surface of the silicon plate, and the light field energy incident to the MEMS Fabry-Perot cavity is enhanced by combining the microstructure with the silicon plate. By designing appropriate structural parameters of the microstructure, adjusting the ratio of the co-polarization component and the cross-polarization component in the silicon plate transmitted light field, and regulating the geometric phase of the incident light, the reflected light undergoes destructive interference, thereby achieving the effect of 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 the thickness is also designed to be a quarter-wavelength thickness. 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.

[0104] The material selection of the designed compensation structure needs to consider reasonable optical parameters, and its refractive index parameter should be lower than the refractive index of the substrate. In order to facilitate the process preparation, the same material system as the low refractive index film layer in the designed lower Bragg reflector is used as the compensation structure, and its thickness is a quarter wavelength optical thickness.

[0105] The designed microstructure increases the light input into the MEMS Fabry-Perot cavity. The designed compensation structure increases the reflectivity of the lower Bragg reflector and 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 two work together to improve the transmittance of the entire MEMS Fabry-Perot filter transmission spectrum, and the filtering quality is greatly improved.

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 centrally symmetrical structure; The lower Bragg reflector has a first low-refractive-index thin film layer, and the compensation structure is made of the same material as the first low-refractive-index thin film layer; 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; Wherein, the microstructure and the compensation structure constitute a double anti-reflection structure.

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, characterized in that: The square nanocolumn has a period of 780 nm, a side length of 500 nm, and a thickness of 550 nm. The nanocolumn is made of germanium.

4. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 1, characterized in that: The first low-refractive-index film layer and the compensation structure are both made of silicon dioxide.

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

6. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 1, characterized in that: The driving structure includes a supporting structure, a cantilever structure, an upper electrode structure and a lower electrode structure.

7. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 6, characterized in that: 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.

8. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 6, characterized in that: The cantilever structure includes four L-shaped cantilevers; The four L-shaped cantilevers are respectively located around the silicon flat plate.

9. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 7, characterized in that: The upper electrode structure is arranged on the lower surface of the silicon flat plate, and a first circular notch is arranged 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 disposed 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.

10. The MEMS Fabry-Perot filter with a dual antireflection structure according to claim 9, characterized in that: The lower Bragg reflector and the upper Bragg reflector form a Fabry-Perot cavity.

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