Deformable mirror driven by ultrasonic resonance

Abstract

This invention relates to a deformable mirror driven by ultrasonic resonance, comprising a vacuum cavity and a mirror assembly fixedly disposed within the vacuum cavity. The mirror assembly includes a deformable mirror body capable of vibrating and deforming under external force. The vacuum cavity is provided with a light-transmitting window that allows incident and reflected light rays from the deformable mirror body to pass through. This invention can effectively reduce the influence of air resistance on the deformation of the deformable mirror body, thereby ensuring the focal length control accuracy of the deformable mirror, improving the response speed of the deformable mirror, and effectively reducing the low-voltage drive of the deformable mirror body's galvanometer.

Description

Technical Field

[0001] This invention relates to the field of micro-optical device technology, and in particular to a deformable reflector based on ultrasonic resonance driving. Background Technology

[0002] Deformable mirrors possess superior characteristics in optical systems, not only because they are lighter than optical lenses, but also because they can reduce the size of optical systems by folding the optical path. Deformable mirrors achieve zooming by changing the curvature of the mirror surface instead of the traditional method of adjusting the spacing between optical path components, significantly reducing the complexity of the optical path structure and thus improving the stability and reliability of the optical system. In recent years, with the development of MEMS (Micro-Electro-Mechanical Systems) technology, researchers have miniaturized and integrated deformable mirrors, developing various deformable mirror arrays for adaptive optics systems, which can further improve the imaging quality of optical systems in complex environments.

[0003] The core component of existing deformable mirrors includes a deformable mirror surface. This surface can change its curvature under external force, thereby altering the focal length and correcting or compensating for the light beam, thus improving the imaging quality of the optical system. Deformable mirrors can be classified into continuously driven (piezoelectric) or statically driven (electrostatic or hydraulic) types based on their driving mechanism. Continuously driven deformable mirrors typically use piezoelectric devices as the power source for mirror deformation. Applying an alternating voltage with the same frequency as the mirror surface to the piezoelectric device causes it to vibrate at the same frequency, driving resonant deformation of the mirror surface. The amplitude of the piezoelectric device's vibration is controlled by changing the amplitude of the driving voltage applied to it, thereby adjusting the amplitude of the mirror's resonant deformation and ultimately adjusting the focal length of the deformable mirror.

[0004] However, deformable mirrors are affected by air resistance when vibrating, resulting in a slow response speed and an actual vibration amplitude that is smaller than the design value. This affects the focal length control accuracy of the deformable mirror, especially at higher driving voltage frequencies, where air resistance significantly degrades the response speed and control accuracy. To address these issues, existing technologies typically reduce the impact of air resistance on mirror deformation by adjusting the structure of the deformable mirror or by applying a larger driving voltage. However, this increases the driving energy consumption and manufacturing difficulty of the deformable mirror. For example, patent application CN200710171222.X discloses a piezoelectrically driven deformable mirror, comprising a silicon mirror with four support pillars, four PZT piezoelectric actuators, and a base. The base, bonded to a glass substrate and a silicon substrate, is located at the bottom of the mirror. Above the base are the four PZT piezoelectric actuators, and the silicon mirror with four support pillars is bonded to the four PZT piezoelectric actuators. The frame of the silicon mirror is connected to the base. When an adjustable voltage is applied, the normal piezoelectric force generated by the PZT piezoelectric actuator causes the central part of the silicon mirror to deform to its maximum extent, forming a concave-convex surface. As the driving voltage increases from 0V to 200V, the deformation of the deformable mirror can linearly change from 0 nm to 160 nm, thus achieving rapid and precise adjustment. This deformable mirror requires a driving voltage of 0V to 200V to achieve a deformation of 0nm to 160nm, resulting in high driving energy consumption. Furthermore, the numerous components, including a silicon mirror, four support pillars, four PZT piezoelectric actuators, and a base bonded to a glass substrate and a silicon substrate, increase the complexity of assembling the deformable mirror. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a deformable mirror based on ultrasonic resonance drive, which solves the technical problems of slow response speed, low focal length control accuracy and high driving energy consumption of existing deformable mirrors.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] This invention provides a deformable mirror based on ultrasonic resonance, including a vacuum cavity and a mirror assembly fixedly disposed within the vacuum cavity. The mirror assembly includes a deformable mirror body that can vibrate and deform under external force. The vacuum cavity is provided with a light-transmitting window that allows incident and reflected light from the deformable mirror body to pass through.

[0010] The deformable mirror proposed in this invention operates its mirror assembly within a vacuum cavity, effectively reducing the impact of air resistance on the deformation of the deformable mirror. This allows the deformable mirror to deform more quickly and accurately under external excitation, thereby improving its response speed and ensuring precise focal length control. Furthermore, the rapid deformation speed of the deformable mirror enables it to maintain good focal length control accuracy even under high-frequency external excitation. In addition, the low air resistance within the vacuum cavity effectively reduces energy dissipation during the vibration and deformation of the deformable mirror, thus lowering the power requirements for the drive and enabling low-power driving of the deformable mirror.

[0011] Optionally, the gas pressure inside the vacuum chamber is not greater than 2 mbar.

[0012] Optionally, the light-transmitting window includes any one of a sapphire window, a diamond window, or an optically coated window.

[0013] Optionally, the reflector assembly further includes a driving component and a supporting component. The supporting component has a hollow structure formed by a hollowed-out portion in the middle, and the hollowed-out portion penetrates the upper and lower end faces of the supporting component. The upper end face of the supporting component is fixedly connected to the side of the deformable mirror body away from its reflecting surface, and the lower end face of the supporting component is fixedly connected to the driving component. The hollowed-out portion of the supporting component communicates with the internal space of the vacuum cavity outside the supporting component. The cross-sectional shape of the hollowed-out portion near the upper end face is symmetrical about the central axis.

[0014] Optionally, the cross-section of the hollowed-out portion near the upper end face is square, and the side length of the square is 0.5mm to 1.5mm.

[0015] Optionally, the driving component is an annular piezoelectric sheet, with its first end face fixedly connected to the lower end face of the support component, and its second end face fixedly connected to the inner wall of the vacuum cavity; the inner cavity of the annular piezoelectric sheet is connected to the hollow portion of the support component, and a ventilation channel is provided between the second end face of the annular piezoelectric sheet and the inner wall of the vacuum cavity, connecting the inner cavity of the annular piezoelectric sheet to the internal space of the vacuum cavity outside the annular piezoelectric sheet.

[0016] Optionally, the deformable mirror body includes an elastic deformation layer and a reflective layer, the elastic deformation layer is fixedly connected to the reflective layer, and the side of the elastic deformation layer away from the reflective layer is fixedly connected to the upper end surface of the support member.

[0017] Optionally, the elastic deformation layer includes one or more of silicon nitride film, silicon carbide film, boron nitride film, and boron carbon nitride film.

[0018] Optionally, the reflective layer is a metal reflective layer, and the material of the metal reflective layer is any one of gold, silver, copper, and aluminum; the thickness of the reflective layer is 25-60 nm.

[0019] Optionally, the elastic deformation layer is a silicon nitride thin film layer, which is deposited on the upper surface of the support using PECVD (Plasma Enhanced Chemical Vapor Deposition) technology.

[0020] The support component is made of silicon, and the hollow part of the support component is formed by wet etching technology.

[0021] The reflective layer is a gold film layer, which is deposited on the side of the silicon nitride thin film away from the support using EBPVD (Electron Beam Physical Vapor Deposition) technology.

[0022] (III) Beneficial Effects

[0023] The deformable mirror proposed in this invention operates its mirror assembly within a vacuum cavity, effectively reducing the impact of air resistance on the deformation of the deformable mirror. This allows the deformable mirror to deform more quickly and accurately under external excitation, thereby improving its response speed and ensuring precise focal length control. Furthermore, the rapid deformation speed of the deformable mirror enables it to maintain good focal length control accuracy even under high-frequency external excitation. In addition, the low air resistance within the vacuum cavity effectively reduces energy dissipation during the vibration and deformation of the deformable mirror, thus lowering the power requirements for the drive and enabling low-power driving of the deformable mirror. This allows for high-speed, wide-area zooming through the resonance of the deformable mirror.

[0024] Furthermore, the mirror assembly in the deformable mirror proposed in this embodiment of the invention allows the central deformation of the deformable mirror body to change linearly with the driving voltage based on the arrangement of the mirror assembly, further ensuring the focal length control accuracy of the deformable mirror.

[0025] Furthermore, the deformable mirror proposed in this embodiment of the invention has a simple overall structure and small size. The integrated structure formed by the support and the deformable mirror body through PECVD technology, wet etching technology and EBPVD technology reduces the complexity of the overall assembly of the deformable mirror and is suitable for mass production. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a deformable reflector provided in the embodiment;

[0027] Figure 2 This is a schematic diagram of the structure of a reflector assembly provided in the embodiment;

[0028] Figure 3 A schematic diagram of a deformable reflector provided for an embodiment;

[0029] Figure 4 A schematic diagram of the fabrication process of a reflective mirror assembly provided for an embodiment;

[0030] Figure 5 This is a schematic diagram of the transient deformation model of the deformable mirror body under the drive of an alternating voltage excitation power supply in the embodiment.

[0031] Figure 6 (a) shows the correspondence between the central deformation of the working mirror and the amplitude of the driving voltage as measured by an interferometer in the embodiment;

[0032] Figure 6 (b) shows the correspondence between the focal length of the working mirror and the amplitude of the driving voltage in the embodiment;

[0033] Figure 7 This is a schematic diagram of the device and optical path used to measure the focal length of the working mirror in the embodiment.

[0034] Figure 8 The images show the morphology of the working mirror surface under different driving voltage values ​​in the embodiment.

[0035] [Explanation of Labels in the Attached Image]

[0036] 10. Vacuum chamber; 101. Light-transmitting window; 1011. Sapphire window; 102. Housing;

[0037] 20. Mirror assembly;

[0038] 201. Deformable mirror body; 2011. Elastic deformation layer; 2012. Reflective layer;

[0039] 202. Support component; 2021. Hollowed-out section; 2022. Silicon wafer;

[0040] 203. Driving component; 2031. Annular piezoelectric element;

[0041] 204. Adhesive layer;

[0042] 205. Ventilation tube;

[0043] 206. Alternating voltage excitation power supply;

[0044] 207. Wire interface. Detailed Implementation

[0045] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0046] It should be noted that "ultrasonic resonance drive" refers to the change frequency of the external force that drives the deformable mirror to vibrate and deform, which exceeds 20kHz, so that the deformable mirror resonates and deforms in the ultrasonic frequency band, thereby achieving the purpose of controlling the zoom of the deformable mirror.

[0047] Furthermore, since the size differences between the various components of the deformable mirror are significant, in order to clearly reflect the specific structure of the deformable mirror, the dimensions and proportions of some smaller components in the accompanying drawings of this embodiment of the invention have been exaggerated and modified to better illustrate the positional relationships between the components. This exaggeration will not affect those skilled in the art from implementing the technical solutions in the embodiments of the invention in conjunction with the description in the specification.

[0048] Example 1

[0049] like Figure 1 As shown, this embodiment provides a deformable mirror based on ultrasonic resonance drive, including a vacuum cavity 10 and a mirror assembly 20 fixedly disposed in the vacuum cavity 10. The mirror assembly 20 includes a deformable mirror body 201 that can vibrate and deform under external force drive. The vacuum cavity 20 is provided with a light-transmitting window 101 that allows incident light and reflected light from the deformable mirror body 201 to pass through.

[0050] Specifically, the vacuum chamber 10 can be a shell with an internal vacuum setting. The shell shape can be prism, cylinder, frustum, truncated cone, or other shapes adapted to specific application scenarios. To resist the pressure difference between the inside and outside of the shell, the shell can be equipped with support brackets, frames, or other shell strength enhancement devices, or a high-strength material can be directly selected to manufacture the shell. Preferably, to meet the miniaturization requirements of deformable reflectors, the shell can be any one of compression-molded aluminum alloy shell, titanium alloy shell, or alloy steel shell, to save space occupied by the shell.

[0051] Generally, the lower the gas pressure inside the vacuum chamber, the lower the resistance to the deformable mirror 201, and the lower the amplitude requirement for the external excitation driving the deformable mirror 201 to vibrate. As a preferred embodiment of this invention, the gas pressure inside the vacuum chamber 10 is no greater than 2 mbar, so as to effectively reduce the air resistance to the deformable mirror, thereby reducing driving energy consumption and improving focal length control accuracy. It should be noted that the gas pressure inside the vacuum chamber 10 is sometimes also referred to as the vacuum level inside the vacuum chamber 10.

[0052] Specifically, the light-transmitting window 101 can be selected according to actual needs. For example, it can be a sapphire window that allows light of a wider spectrum to pass through, a diamond window with good abrasion resistance and thermal stability, or an optically coated window that has good transmission performance only for light of a specific frequency band. Furthermore, in order to facilitate the replacement of the light-transmitting window 101 as needed, the light-transmitting window 101 can be detachably installed on the vacuum chamber 10, and the sealing of the vacuum chamber 10 is ensured by sealing rings or other sealing components between the light-transmitting window 101 and the vacuum chamber 10.

[0053] Furthermore, the reflector assembly 20 can be fixedly installed within the vacuum chamber according to actual needs. For example, the vacuum chamber 10 is a rectangular flat shell with an internal vacuum. Any pair of opposite sidewalls among the six sidewalls of the shell are referred to as the first sidewall and the second sidewall, respectively. The reflector assembly can be fixedly installed on the inner surface of the second sidewall, with the reflective surface of the deformable mirror 101 facing the first sidewall. Specifically, the reflector assembly can be directly bonded to the inner surface of the second sidewall, or bonded to the inner surface of the second sidewall through a shock-absorbing pad to reduce interference from external vibration sources. It should be noted that the reflective surface refers to the side of the deformable mirror used to reflect light incident from the light-transmitting window 101. Correspondingly, the light-transmitting window 101 is provided on the first sidewall and penetrates through the first sidewall, thereby allowing incident and reflected light from the deformable mirror to pass through the light-transmitting window. Generally, the size of the light-transmitting window 101 is larger than the aperture size of the deformable mirror body 201, so as to ensure that when the incident angle is large, the incident light and the reflected light can also enter or leave the vacuum cavity 10 through the light-transmitting window 101.

[0054] The deformable mirror proposed in this invention operates its mirror assembly within a vacuum cavity, effectively reducing the impact of air resistance on the deformation of the deformable mirror. This allows the deformable mirror to deform more quickly and accurately under external excitation, thereby improving its response speed and ensuring precise focal length control. Furthermore, the rapid deformation speed of the deformable mirror enables it to maintain good focal length control accuracy even under high-frequency external excitation. In addition, the low air resistance within the vacuum cavity effectively reduces energy dissipation during the vibration and deformation of the deformable mirror, thus lowering the amplitude requirements of the external excitation and enabling low-power driving of the deformable mirror.

[0055] Example 2

[0056] To further improve the focal length control accuracy of deformable mirrors and reduce the complexity of manufacturing deformable mirrors, this embodiment of the invention also improves the mirror assembly 20, so that there is a better linear relationship between the central deformation of the deformable mirror body 201 and the external excitation that drives the deformation of the deformable mirror body, and the overall structure is simpler, thereby improving the comprehensive performance of the deformable mirror. This embodiment will be described in detail with reference to the specific structure of the mirror assembly 20.

[0057] This invention provides a deformable reflector driven by ultrasonic resonance, comprising a vacuum cavity and a reflector assembly fixedly disposed within the vacuum cavity.

[0058] The vacuum chamber 10 is a rectangular flat shell with an internal vacuum setting. A light-transmitting window 101 is provided on the first side wall of the shell. A reflector assembly 20 is fixedly installed on the inner wall of the second side wall opposite to the first side wall. The reflector assembly 20 includes a deformable mirror body 201, and the reflective surface of the deformable mirror body 201 faces the light-transmitting window.

[0059] like Figure 2 As shown, the reflector assembly 20 includes a deformable mirror body 201, a support member 202, and a drive member 203. The support member 202 has a hollow structure formed by a hollow portion 2021 in its middle, and the hollow portion 2021 penetrates both the upper and lower end faces of the support member 202. The upper end face of the support member 202 is fixedly connected to the side of the deformable mirror body 201 away from its reflective surface, and the lower end face of the support member 202 is fixedly connected to the drive member 203. The hollow portion 2021 of the support member 202 communicates with the internal space of the vacuum cavity 10 outside the support member 202. It should be noted that the upper and lower end faces of the support member 202 are used to distinguish the first and second ends of the support member 202 that are respectively connected to the deformable mirror body 201 and the drive member 203, and do not limit the specific orientation of the support member 202.

[0060] The deformable mirror body 201 includes an elastic deformation layer 2012 and a reflective layer 2011. The elastic deformation layer 2012 is fixedly connected to the reflective layer 2011, and the side of the elastic deformation layer 2012 away from the reflective layer 2011 is fixedly connected to the upper end face of the support member 202. The elastic deformation layer 2012 can resonate and undergo elastic deformation under the vibration excitation transmitted by the support member 202, forming a convex or concave surface similar to a parabola. The reflective layer 2011 is attached to the surface of the elastic deformation layer 2012 and is used to reflect incident light rays entering the reflective layer 2011 from the light-transmitting window 101. Further, the elastic deformation layer 2012 can be one or more of the following: a polyester film layer, a nitrocellulose film layer, a silicon nitride film layer, a silicon carbide film layer, a boron nitride film layer, and a boron carbon nitride film layer. The thickness of the elastic deformation layer 2012 is 50-200 nm; preferably, the thickness of the elastic deformation layer 2012 is 100-150 nm. The reflective layer 2011 may be a metal reflective layer, and the material of the metal reflective layer may be any one of gold, silver, copper, or aluminum. The thickness of the reflective layer 2011 is 25–60 nm; preferably, the thickness of the reflective layer 2011 is 40–60 nm.

[0061] The support member 202 is disposed between the deformable mirror body 201 and the driving member 203, and is used to transmit the vibration generated by the driving member 203 to the deformable mirror body 201 and to provide support for the deformable mirror body 201. The hollow part 2021 of the support member 202 is used to provide space when the deformable mirror body 201 moves towards the support member 202. At the same time, the hollow part 2021 of the support member 202 is connected to the internal space of the vacuum cavity 10 outside the support member 202, so that the gas pressure on both sides of the deformable mirror body 201 is kept the same, and the deformation of the deformable mirror body 201 is affected by the pressure difference on both sides, thereby reducing the focal length control accuracy of the deformable mirror. Specifically, the connection between the hollow portion 2021 of the support member 202 and the internal space of the vacuum cavity 10 outside the support member 202 can be achieved by providing a through hole in the side wall of the support member 202 that penetrates the inner side wall of the hollow portion 2021 and the outer side wall of the support member 202, or by other means. In particular, the cross-sectional shape of the hollow portion 2021 near its upper end face is symmetrical about its central axis, thereby ensuring a uniform distribution of the thin film system formed by the deformable mirror body 201 in the suspended portion of the hollow portion 2021, resulting in a more regular convex or concave shape formed during the resonant deformation of the thin film system. Specifically, the cross-sectional shape of the hollow portion 2021 near its upper end face can be circular, square, regular hexagonal, regular octagonal, regular dodecagonal, etc. Preferably, the cross-sectional shape of the hollow part 2021 near the upper end is a square, and the side length of the square is 0.5mm to 1.5mm; more preferably, the side length of the square is 0.8mm to 1.2mm.

[0062] The driving element 203 is used to generate vibrations with the same frequency as the natural frequency of the thin film system to drive the resonant deformation of the thin film system. The driving element 203 is fixedly connected to the lower end face of the support element 202, specifically by bonding, snap-fitting, or other fasteners. The driving element 203 can be an actuator made of piezoelectric ceramic material, an actuator made of electrostrictive material, or an actuator made of magnetostrictive material. Specifically, the actuator made of piezoelectric ceramic material can be a piezoelectric ceramic sheet, a piezoelectric ceramic wafer, a ring-shaped piezoelectric sheet, etc. The shape of the lower end face of the support element 202 can be matched with the shape and size of the driving element 203 so that the lower end face of the support element 202 is in full contact with the driving element 203, thereby allowing the vibration generated by the driving element 203 to be transmitted more evenly to the support element 202. Specifically, the periodic excitation applied to the driving element 203 by the excitation source needs to be set according to the specific requirements of the driving element 203. For example, it can be an alternating voltage excitation power supply suitable for piezoelectric ceramic materials, or an alternating current excitation power supply suitable for electrostrictive or magnetostrictive materials.

[0063] Based on the above-described reflector assembly 20, when the driving member receives a periodic excitation from the excitation source, the driving member 203 will expand and contract with the periodic excitation to generate vibrations at the same frequency. This vibration is transmitted to the suspended thin-film system of the deformable mirror body 201 through the support member 202. When the frequency of the periodic excitation matches the natural frequency of the thin-film system, the thin-film system will resonate and undergo periodic stable deformation into a parabolic shape. The central deformation of the deformable mirror body 201 has a linear relationship with the amplitude of the periodic excitation; by adjusting the amplitude of the periodic excitation, the central deformation of the deformable mirror body can be precisely controlled. It should be noted that the central deformation of the deformable mirror body 201 refers to the depth of the parabolic deformation generated when the suspended thin-film system resonates, that is, the maximum normal deformation of the suspended thin-film system.

[0064] Specifically, as the amplitude of the periodic excitation continues to increase, the suspended thin-film system, constrained by the cross-sectional shape and size of the hollow portion 2021 near the upper surface of the support member 202, will exhibit nonlinear resonance, i.e., higher-order resonance. This causes the deformation of the suspended thin-film system to no longer be a regular parabolic surface, but rather maintains the maximum central deformation at the center of the film, while concentric ring deformation resembling a Fresnel lens appears in the edge region of the film near the support member 202. Since the small amplitude deformation of the concentric rings resembling the Fresnel lens also has a focusing effect, it will not affect the focal length control effect of the deformable mirror 201 under periodic excitation.

[0065] Example 3

[0066] To better understand Embodiments 1 and 2, this embodiment will be described in detail with reference to the specific structure and dimensions of the deformable mirror and the mirror assembly 20.

[0067] like Figure 3 As shown, an embodiment of the present invention provides a deformable reflector based on ultrasonic resonance drive, including a vacuum cavity 10 and a reflector assembly 20 fixedly disposed within the vacuum cavity 10.

[0068] The vacuum chamber 10 is a rectangular flat shell 102 with an internal vacuum. A sapphire window 1011 is provided on the first side wall of the shell 102. The sapphire window 1011 is a circular window with a diameter of 25 mm and a thickness of 5 mm. A reflector assembly is fixedly installed on the inner wall of the second side wall opposite the first side wall. The reflector assembly 20 includes a deformable mirror body 201, and the reflective surface of the deformable mirror body 201 faces the sapphire window 1011.

[0069] Specifically, the reflector assembly 20 includes a deformable mirror body 201, a support member 202, and an annular piezoelectric sheet 2031. The support member 202 has a hollow structure formed by a hollow portion 2021 in the middle, and the hollow portion 2021 penetrates the upper and lower end faces of the support member 202. The upper end face of the support member 202 is fixedly connected to the side of the deformable mirror body 201 away from its reflective surface, and the lower end face of the support member 202 is fixedly connected to the first end face of the annular piezoelectric sheet 2031. The second end face of the annular piezoelectric sheet 2031 is fixedly connected to the inner surface of the second side wall of the housing 102. The inner cavity of the annular piezoelectric sheet 2031 is coaxial and connected with the hollow portion 2021 of the support member 202. A channel is provided between the second end face of the annular piezoelectric sheet 2031 and the inner surface of the second side wall of the housing 102, connecting the inner cavity of the annular piezoelectric sheet 2031 with the internal space of the vacuum cavity 10 outside the annular piezoelectric sheet 2031.

[0070] The annular piezoelectric sheet 2031 is used as a driving component of the reflector assembly 20. The annular piezoelectric sheet 2031 is a commercially available finished product. Specifically, in this embodiment, an annular piezoelectric sheet 2031 with an inner diameter of 5 mm, an outer diameter of 10 mm, and a thickness of 1 mm is selected.

[0071] The support 202 is a silicon wafer 2022, and the hollow portion 2021 in the middle of the silicon wafer 2022 is formed by wet etching technology. Specifically, the thickness of the silicon wafer 2022 can be between 180μm and 400μm, preferably 200μm. The shape of the silicon wafer 2022 can be circular or square, preferably, in this embodiment, a square shape with a side length of 7mm is selected.

[0072] The cutout portion 2021 on the silicon wafer 2022 penetrates the upper and lower surfaces of the silicon wafer 2022 along the thickness direction. The upper surface of the silicon wafer 2022 is fixedly connected to the deformable mirror body 201, and the lower surface of the silicon wafer 2022 is fixedly connected to the annular piezoelectric sheet 203. The cross-section of the cutout portion 2021 near the upper surface of the silicon wafer 2022 is square, and the cross-sectional shape of the cutout portion 2021 near the lower surface of the silicon wafer 2022 can be set according to actual needs. Preferably, in order to facilitate the use of wet etching technology to etch the cutout portion 2021 in this embodiment, the cutout portion 2022 is a regular square frustum, and the top surface of the regular square frustum cutout portion 2021 with a smaller area is on the same side as the upper surface of the silicon wafer 2022, and the bottom surface of the regular square frustum cutout portion 2021 with a larger area is on the same side as the lower surface of the silicon wafer 2022. The top side of the frustum-shaped hollow portion 2021 has a side length of 1 mm, and the bottom side of the frustum-shaped hollow portion 2021 has a side length of 5 mm. This ensures that the silicon wafer 2022 does not affect the deformation of the deformable mirror body, and allows the hollow portion 2021 of the silicon wafer to communicate with the internal space of the vacuum cavity 10 outside the annular piezoelectric sheet 2031 through the inner cavity of the annular piezoelectric sheet 2031, eliminating the pressure difference on both sides of the suspended thin film system. It should be noted that the upper surface of the silicon wafer 2022 corresponds to the upper end surface of the support member 202, and the lower surface of the silicon wafer 2022 corresponds to the lower end surface of the support member 202.

[0073] The second end face of the annular piezoelectric element 2031 is fixedly connected to the inner surface of the second side wall of the rectangular flat shell 102. A ventilation channel is provided between the second end face of the annular piezoelectric element 2031 and the inner surface of the second side wall of the shell 102, connecting the inner cavity of the annular piezoelectric element 2031 with the internal space of the vacuum cavity 10 outside the annular piezoelectric element 2031. The ventilation channel can be implemented using various technical means. For example, the ventilation channel is one or more ventilation slots provided on the inner surface of the second side wall of the housing 102; the ventilation channel can also be realized by a fixed bracket suspended between the annular piezoelectric piece 2031 and the second side wall of the housing 102. The fixed bracket can be an annular fixed bracket with the same size as the annular piezoelectric piece 2031. One end face of the annular fixed bracket is bonded to the second end face of the annular piezoelectric piece 2031, and the other end face of the annular fixed bracket is bonded to the inner surface of the second side wall of the housing 102. The supporting part between the two end faces of the annular fixed bracket is a plurality of pillars parallel to the axis of the annular fixed bracket, and the gap between two adjacent pillars is provided to form a ventilation channel.

[0074] like Figure 3As shown, in a preferred embodiment of this invention, the second end face of the annular piezoelectric element 2031 in the aforementioned reflector assembly 20 is bonded to the inner surface of the second sidewall by an adhesive layer 204. A vent pipe 205 is embedded in the adhesive layer 204 along the radial direction of the annular piezoelectric element 2031, with one end of the vent pipe 205 extending into the inner cavity of the annular piezoelectric element 2031 and the other end extending into the internal space of the vacuum chamber 10 outside the annular piezoelectric element 2031. Two electrodes of the annular piezoelectric element 2031 are respectively disposed on the first and second end faces of the annular piezoelectric element 2031. The two electrodes of the annular piezoelectric element 2031 are respectively connected to an alternating voltage excitation power supply 206 outside the housing 102 via wires. The housing 102 is provided with a wire interface 207 that allows the wires to pass through, and the gap between the wires and the wire interface 207 is sealed by a sealant to ensure a vacuum environment inside the housing 102.

[0075] The deformable mirror body 201 includes an elastic deformation layer 2012 and a reflective layer 2011. The elastic deformation layer 2012 is fixedly connected to the reflective layer 2011, and the side of the elastic deformation layer 2012 away from the reflective layer 2011 is fixedly connected to the upper surface of the silicon wafer 2022. Preferably, the elastic deformation layer 2012 is deposited on the upper surface of the silicon wafer 2022 using PECVD technology. To increase the bonding strength between the elastic deformation layer 2012 deposited on the silicon wafer 2022 and the silicon wafer 2022, the elastic deformation layer 2012 can be one or more of silicon nitride thin films, silicon carbide thin films, boron nitride thin films, and boron carbon nitride thin films, which also contain semiconductor elements. The thickness of the elastic deformation layer is 50-200 nm. More preferably, in this embodiment, silicon nitride material is used to deposit the elastic deformation layer 2012 on the upper surface of the silicon wafer 2022 using PECVD technology, and the thickness of the elastic deformation layer 2012 is 100 nm.

[0076] The reflective layer 2011 is a metal reflective layer, which is deposited on the side of the silicon nitride film away from the silicon wafer 2022 using EBPVD technology. The material of the metal reflective layer can be any one of gold, silver, copper, or aluminum. Preferably, in this embodiment, elemental gold is selected to form the reflective layer 2011 by evaporating on the side of the silicon nitride film away from the silicon wafer 2022 using EBPVD technology. The thickness of the reflective layer 2011 is 50 nm.

[0077] In fact, the thin film system (including a silicon nitride thin film layer and a gold film layer) suspended on the hollow portion 2021 of the silicon wafer 2022 is the actual working mirror surface of the deformable mirror body 201, with a size of 1mm × 1mm and an area of ​​1mm². 2 .

[0078] Specifically, such as Figure 4As shown in (a) to (d), the reflector assembly 20 provided in this embodiment can be manufactured by the following steps:

[0079] 101. A 100 nm thick silicon nitride thin film layer 2012 is deposited on the upper surface of a square silicon wafer 2022 with a side length of 7 mm and a thickness of 200 μm using PECVD technology. The intermediate structure prepared in this step is as follows: Figure 4 As shown in (a).

[0080] 102. A frustum-shaped hollow portion 2021 in the shape of a regular square pyramid is etched on a silicon wafer 2022 using wet etching technology. The top side of the frustum-shaped pyramid has a side length of 1 mm, and the bottom side has a side length of 5 mm.

[0081] Specifically, in this step, the silicon wafer 2022 is masked, and then 25 wt.% tetramethylammonium hydroxide (TMAH) is heated to 90°C in a water bath. The silicon wafer 2022 is then anisotropically etched using TMAH to form the aforementioned frustum-shaped hollow portion 2021.

[0082] The intermediate structure prepared in this step is as follows: Figure 4 As shown in (b).

[0083] 103. A gold film layer 2011 is deposited on the side of the silicon nitride thin film 2012 away from the silicon wafer 2022 using PECVD technology. The intermediate structure prepared in this step is as follows: Figure 4 As shown in (c).

[0084] 104. The lower surface of the silicon wafer 2022 is coaxially bonded to the first end face of the annular piezoelectric sheet 2031 to form the reflector assembly 20. The reflector assembly 20 prepared in this step is as follows: Figure 4 As shown in (d).

[0085] As can be seen from the above-mentioned preparation process of the reflector assembly 20, the silicon wafer 2022 and the deformable mirror body 201 are an integral structure. During production and assembly, the reflector assembly 20 can be formed simply by bonding the lower surface of the silicon wafer 2022 to the first end face of the annular piezoelectric sheet 2031. Compared with the complex deformable reflector structure in the prior art, this effectively reduces the assembly difficulty and improves production efficiency.

[0086] The theoretical working model of the mirror assembly 20 obtained based on the above steps is as follows:

[0087] The working mirror surface of the reflector assembly 20 is a parabolic-like surface formed by the thin-film system during resonance. The focal length of the parabolic surface can be changed by adjusting its depth. The transient deformation model of the deformable mirror body 201 under alternating voltage excitation is as follows: Figure 5As shown. The driving voltage provided by the alternating voltage excitation power supply includes positive and negative voltage signals. Therefore, under the excitation of the driving voltage with alternating polarity, the working mirror surface forms a periodic stable deformation with the same frequency as the driving voltage: under the drive of the positive voltage signal, it recesses into the cavity of the hollow part of the silicon wafer, forming a shape like... Figure 5 The concave mirror shown in (a) bulges outwards from the silicon wafer under the drive of a negative voltage signal, forming a shape similar to... Figure 5 (b) shows the convex reflector. Figure 5 The value of 'a' indicates the magnitude of the center shape of the working mirror, which is also the depth of the aforementioned convex or concave mirror. The focal length of the working mirror can be calculated using formula (1). Formula (1) is:

[0088]

[0089] In the formula, f mir denoted by ; x represents half the side length of the top surface of the square pyramidal hollow portion of the silicon wafer, which is 0.5 mm in this embodiment; a represents the depth of the parabolic surface formed by the working mirror, and the value of a is linearly related to the amplitude of the driving voltage.

[0090] The natural frequency of the working mirror is mainly governed by the residual biaxial stress of the thin film system. The natural frequency of the working mirror can be calculated by formula (2), which is:

[0091]

[0092] In the formula, f nm Let represent the natural frequency of the working mirror, ρ represent the average density of the thin film system, σ represent the residual biaxial stress of the thin film system, n represent the resonant mode of the thin film system in the x-axis direction, m represent the resonant mode of the thin film system in the y-axis direction, and l represent the resonant mode of the thin film system in the y-axis direction. x l y These represent the side lengths of the top surface of the square pyramidal cutout portion of the silicon wafer. It should be noted that the x-axis and y-axis mentioned above refer to the x-axis and y-axis in a Cartesian coordinate system established based on the reflective plane of the thin film system under static conditions without external excitation, and the x-axis is parallel to any side of the top surface of the square pyramidal cutout portion of the silicon wafer.

[0093] After the mirror assembly 20 is prepared according to steps 101-104, the natural frequency of the working mirror can be calculated by measuring the residual biaxial stress of the thin film system and the resonant modes of the thin film system in the x-axis and y-axis directions, thereby determining the operating frequency of the alternating voltage excitation power supply. In actual mass production, the residual biaxial stress, resonant modes, and other parameters of the thin film system can be constrained by controlling the production process, so that the mass-produced mirror assemblies have the same natural frequency that conforms to the design value.

[0094] In this embodiment, a physical model of the reflector assembly 20 was prepared according to steps 101-104. The residual biaxial stress σ of the thin film system was measured to be 247.6 ± 0.2 MPa, the resonant mode n of the thin film system in the x-axis direction was 1, and the resonant mode m of the thin film system in the y-axis direction was measured to be 1. Substituting these values ​​into formula (2), the natural frequency of the working mirror surface was calculated to be 199.71 kHz. The working frequency of the alternating voltage excitation power supply 206 was set to 199.71 kHz and applied to the two electrodes of the annular piezoelectric sheet 2031. This drove the deformable mirror body 201 of the deformable reflector to resonate and deform. By adjusting the amplitude of the driving voltage, the central deformation of the deformable mirror body was changed, thereby achieving the control of the focal length of the deformable reflector. In this embodiment, the zoom range of the deformable reflector is from 98 ± 2 mm to positive infinity or from negative infinity to -98 ± 2 mm.

[0095] This embodiment also utilizes the correspondence between the central deformation of the working mirror surface and the amplitude of the driving voltage measured by an interferometer, as follows: Figure 6 As shown in (a), it can be seen that the central deformation of the working mirror is basically proportional to the amplitude of the driving voltage. Substituting the measured central deformation of the working mirror as the value of 'a' into formula (1), the relationship between the focal length of the working mirror and the amplitude of the driving voltage can be obtained as follows: Figure 6 As shown in (b).

[0096] like Figure 7 As shown, the deformable mirror 1 is horizontally positioned. A 15mW laser generator 2 (wavelength 633nm) generates a parallel light source, which is vertically irradiated onto the working mirror surface of the mirror assembly 20. The reflected light from the working mirror surface is reflected a second time onto the CCD 4 (Charge-coupled Device, image sensor) by a 45-degree beam splitter 3. The CCD 4 is horizontally moved to obtain the change in the propagation light field of the reflected light. The distance between the CCD 4 and the beam splitter 3, and the distance between the beam splitter 3 and the working mirror surface are measured. The sum of these two distances is the focal length of the deformable mirror 1. The specific focal length measurement is as follows: Figure 6 As shown by the square icon in (b), comparing the measured and calculated values, it can be seen that the actual focal length adjustment effect of the deformable mirror is basically consistent with the theoretical calculation.

[0097] In addition, such as Figure 8 As shown in (a) to (f), this embodiment also utilizes a laser interferometer and a two-dimensional moving platform to obtain the three-dimensional morphology of the working mirror surface under driving voltage amplitudes of 0.1V, 2V, 4V, 6V, 8V, and 10V. It can be seen from the figures that when the driving voltage amplitude is low, such as... Figure 8 As shown in (a), the deformable mirror exhibits a linear resonance mode, with its working mirror surface undergoing a simple parabolic deformation; as the amplitude of the driving voltage increases, as... Figure 8 (b)~ Figure 8 As shown in (f), the working mirror enters a nonlinear resonance mode, and the deformation of the working mirror transforms into a concentric ring deformation similar to a Fresnel lens. Furthermore, as the driving voltage amplitude increases, the number of concentric rings increases, and the central deformation of the working mirror increases. Combined with... Figure 6 (b) shows that the focal length measurement of the deformable mirror under different driving voltage amplitudes indicates that the concentric annular deformation focusing effect of this Fresnel-like lens surface is similar to that of a traditional parabolic deformation. Based on the working mirror surface operating in a nonlinear resonance mode, the focal length control effect of the deformable mirror provided in this embodiment is consistent with the theoretical calculation, further demonstrating that the deformable mirror provided in this embodiment has good focal length control accuracy.

[0098] It should be noted that any reference numerals placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In claims that enumerate several means, several of these means may be embodied by the same hardware. The use of the terms first, second, third, etc., is merely for convenience of expression and does not indicate any order. These terms can be understood as part of the component names.

[0099] Furthermore, it should be noted that in the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0100] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims should be interpreted to include both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, then this invention should also include these modifications and variations.

Claims

1. A deformable mirror based on ultrasonic resonance driving, characterized in that, The deformable mirror includes a vacuum cavity and a mirror assembly fixedly arranged in the vacuum cavity, the mirror assembly includes a deformable mirror body capable of resonant deformation under external driving force, and the vacuum cavity is provided with a light-transmitting window allowing incident light and reflected light of the deformable mirror body to pass through. The mirror assembly further includes a driving member and a support member, the support member is provided with a hollow structure formed by a hollow part in the middle of the support member, and the hollow part penetrates through the upper end surface and the lower end surface of the support member; the upper end surface of the support member is fixedly connected to the side of the deformable mirror body away from the reflecting surface thereof, and the lower end surface of the support member is fixedly connected to the driving member. The cross section of the hollow part near the upper end surface is centrally axisymmetric. The driving member is a ring-shaped piezoelectric sheet, the first end surface of the ring-shaped piezoelectric sheet is fixedly connected to the lower end surface of the support member, and the second end surface of the ring-shaped piezoelectric sheet is fixedly connected to the inner wall of the vacuum cavity; the inner cavity of the ring-shaped piezoelectric sheet is in communication with the hollow part of the support member, and a ventilation channel is arranged between the second end surface of the ring-shaped piezoelectric sheet and the inner wall of the vacuum cavity, the ventilation channel being in communication with the inner cavity of the ring-shaped piezoelectric sheet and the internal space of the vacuum cavity outside the ring-shaped piezoelectric sheet. The two electrodes of the ring-shaped piezoelectric sheet are arranged on the first end surface and the second end surface of the ring-shaped piezoelectric sheet respectively, and the two electrodes of the ring-shaped piezoelectric sheet are connected to an alternating voltage excitation power source through wires. With the continuous increase of the amplitude of the alternating voltage output by the alternating voltage excitation power source, the edge region of the deformable mirror body appears concentric ring-shaped deformation of the Fresnel lens mirror surface. The cross section of the hollow part near the upper end surface is a square, and the side length of the square is 0.5mm-1.5mm. The thickness of the deformable mirror body is 75-260nm.

2. The deformable mirror of claim 1, wherein, The air pressure in the vacuum cavity is not greater than 2mbar.

3. The deformable mirror of claim 1, wherein, The light-transmitting window includes any one of a sapphire window, a diamond window and an optical coating window.

4. The deformable mirror of claim 1, wherein, The deformable mirror body includes an elastic deformation layer and a reflecting layer, the elastic deformation layer is fixedly connected to the reflecting layer, and the side of the elastic deformation layer away from the reflecting layer is fixedly connected to the upper end surface of the support member.

5. The deformable mirror of claim 4, wherein, The elastic deformation layer includes one or more of a silicon nitride film, a silicon carbide film, a boron nitride film and a boron carbon nitride film.

6. The deformable mirror of claim 4, wherein, The reflecting layer is a metal reflecting layer, and the material of the metal reflecting layer is any one of gold, silver, copper and aluminum. The thickness of the reflecting layer is 25-60nm.

7. The deformable mirror according to claim 4, wherein The elastic deformation layer is a silicon nitride film layer, and the silicon nitride film layer is deposited on the upper end surface of the support member based on PECVD technology; The material of the support member is silicon, and the hollow part of the support member is etched based on a wet etching technology; The reflecting layer is a gold film layer, and the gold film layer is evaporated on the side of the silicon nitride film away from the support member based on EBPVD technology.

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