Cavity optomechanical mems acceleration sensor based on reservoir cavity light enhancement

Abstract

The application discloses a kind of cavity optomechanics MEMS acceleration sensors based on reserve pool cavity light enhancement, including double-cavity sensing unit and optical detection unit, wherein, double-cavity sensing unit includes spring oscillator structure, MEMS concave mirror and MEMS plane mirror that are sequentially spaced apart and arranged in parallel, spring oscillator structure includes mass block, suspension beam and outer frame, mass block and MEMS concave mirror form the flat concave F-P cavity of sensing action between, MEMS concave mirror and MEMS plane mirror form reserve F-P cavity between, reserve F-P cavity and flat concave F-P cavity are matched in anti-resonance state;Optical detection unit includes modulation light path, transmission light path and photoelectric detection component.The application is based on traditional sensing F-P cavity, build parameter matching reserve F-P cavity, can effectively improve the quality factor of sensor, and can realize higher quality factor under relatively lower reflectivity, effectively reduce the difficulty and cost of device manufacturing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of acceleration sensors, and more particularly relates to a cavity optomechanics MEMS acceleration sensor based on light enhancement of a reservoir cavity. BACKGROUND

[0002] An acceleration sensor is an instrument for measuring the acceleration of a moving object, and has been deeply researched and widely applied in many fields, such as inertial navigation, earthquake monitoring, resource exploration, consumer electronics, etc. Traditional piezoresistive and capacitive MEMS acceleration sensors are approaching the performance limit, and compared with them, a cavity optomechanics MEMS acceleration sensor based on a Fabry-Perot resonant cavity (F-P cavity) has the advantages of high sensitivity, high resolution, strong anti-electromagnetic interference ability, miniaturization, simple structure and easy processing, etc., and is a research direction of the next generation of high-precision acceleration sensors, and has great development potential.

[0003] However, the cavity optomechanics MEMS acceleration sensor currently faces some problems in improving the quality factor (Q value) of the cavity: the cavity Q value mainly depends on the cavity length and the reflectivity of the reflecting surface, on the one hand, the cavity optomechanics device with small size is difficult to effectively improve the cavity Q value and the light force coupling efficiency by increasing the cavity length; on the other hand, the surface roughness of the cavity optomechanics device manufactured by the MEMS process is difficult to prepare a high-reflectivity cavity mirror. Therefore, in order to improve the performance of the cavity optomechanics acceleration sensor, a method capable of effectively improving the Q value of the cavity optomechanics device needs to be explored. SUMMARY

[0004] In view of the defects of the prior art, the purpose of the application is to provide a cavity optomechanics MEMS acceleration sensor based on light enhancement of a reservoir cavity, which can effectively improve the quality factor of the sensor by building a parameter-matched reservoir F-P cavity on the basis of a traditional F-P sensing cavity, and can realize a high quality factor at a relatively low reflectivity, thereby effectively reducing the difficulty and cost of device manufacturing.

[0005] To achieve the above purpose, the application provides a cavity optomechanics MEMS acceleration sensor based on light enhancement of a reservoir cavity, which comprises a double-cavity sensing unit and an optical detection unit, the double-cavity sensing unit comprises a spring oscillator structure, a MEMS concave mirror and a MEMS plane mirror which are sequentially and spacedly arranged in parallel, the spring oscillator structure comprises a mass block, a suspension beam and an outer frame, the mass block is connected to the outer frame through the suspension beam, a flat-concave type F-P cavity for sensing action is formed between the mass block and the MEMS concave mirror, a reservoir F-P cavity is formed between the MEMS concave mirror and the MEMS plane mirror, and the reservoir F-P cavity and the flat-concave type F-P cavity are matched in an anti-resonance state; the optical detection unit comprises a modulation light path, a transmission light path and a photoelectric detection component.

[0006] The modulation optical path is used to modulate the incident 1550nm laser wavelength, so that the laser wavelength is detuned and locked at the operating point on one side of the resonance peak; the transmission optical path is used to transmit the laser with the determined wavelength to the dual-cavity sensing unit; the dual-cavity sensing unit is used to convert the external acceleration excitation into the displacement of the mass block, and to perform multi-beam interference through a plano-concave FP cavity, and then send the reflected light carrying the acceleration information to the photoelectric detection component through the transmission optical path for acceleration measurement.

[0007] In one embodiment, the side of the spring oscillator structure facing the MEMS concave mirror and the side of the MEMS plane mirror facing the MEMS concave mirror are both coated with a reflective film with a reflectivity of R1, and the concave surface of the MEMS concave mirror facing the spring oscillator structure is coated with a reflective film with a reflectivity of R2.

[0008] Wherein, the reserve FP cavity and the plano-concave FP cavity are matched in an anti-resonance state to satisfy:

[0009] R2 = 4R1 / (1+R1) 2

[0010] L1 / L2 = 1 / 2

[0011] In the formula, L1 is the cavity length of the plano-concave FP cavity; L2 is the cavity length of the reserve FP cavity.

[0012] In one embodiment, the side of the MEMS planar mirror away from the MEMS concave mirror is coated with an anti-reflection film.

[0013] In one embodiment, the MEMS concave mirror is etched using an isotropic wet etching process to create a hemispherical concave cavity with a certain aspect ratio on a single-crystal silicon wafer.

[0014] In one embodiment, the ratio of the hemispherical depth to the radius of curvature of the hemispherical concave cavity is 0.47 to 0.53, wherein the depth is 290 to 310 μm and the radius of curvature is 590 to 610 μm.

[0015] In one embodiment, the surface of the mass block of the spring oscillator structure, the MEMS concave mirror, and the MEMS plane mirror are all made of SiN. x Photonic crystal reflective film fabricated from thin films.

[0016] In one embodiment, the spring oscillator structure is manufactured using SOI silicon MEMS technology, and a suspension beam is fabricated in the device layer of the SOI structure to maintain the out-of-plane movement of the mass block.

[0017] In one embodiment, a suspended beam structure with symmetrical distribution on both sides is fabricated using a dual-layer SOI bonding process.

[0018] In one embodiment, the modulation optical path employs a laser, an electro-optic modulator, and an optical attenuator; the transmission optical path employs a fiber optic circulator and an optical collimator; and the photoelectric detection component employs a photodetector.

[0019] In one embodiment, the optical detection unit further includes a spectrometer for real-time detection of the laser wavelength modulated by the electro-optic modulator.

[0020] Overall, the above technical solutions described in this invention have the following advantages compared with the prior art: (1) Based on the traditional sensing FP cavity, a parameter-matched reserve FP cavity dual-cavity structure is built. The reserve FP cavity can effectively improve the quality factor of the sensor cavity, thereby improving the sensitivity of the accelerometer; (2) The dual-cavity structure designed in this invention can achieve a higher quality factor under relatively low reflectivity, which helps to reduce the difficulty and cost of device manufacturing; (3) The dual-cavity structure designed in this invention is manufactured and packaged by MEMS process, has a small size, can be mass-produced, and can meet the needs of more application scenarios. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of a dual-cavity sensing unit in a cavity optomechanical MEMS accelerometer provided in an embodiment of the present invention;

[0022] Figure 2 This is a simulation diagram showing how the dual-cavity sensing unit provided by the present invention improves the quality factor of the sensing FP cavity;

[0023] Figure 3 This is a schematic diagram of the principle of optical interferometry measurement performed by the sensing FP cavity in the dual-cavity sensing unit provided by the present invention;

[0024] Figure 4 This is a schematic diagram of the optical testing principle of the optical detection unit in the dual-cavity sensing unit provided by the present invention.

[0025] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1 is a spring oscillator structure, 101 is a mass block, 102 is a suspension beam, 103 is an outer frame, 2 is a MEMS concave cavity, 3 is a MEMS plane mirror, 4 is a mounting fixture, 6 is a two-dimensional photonic crystal reflective film, 7 is an antireflection film, 8 is a reservoir cavity Q-value curve, 9 is a sensing cavity Q-value curve, 10 is an enhanced sensing FP cavity Q-value curve, 11 is a laser wavelength, 12 is a sensing FP cavity resonance peak, 13 is a resonance peak frequency shift under external acceleration excitation, 14 is the operating point of optical detection, 15 is a 1550nm single-frequency laser, 16 is an electro-optic modulator, 17 is a spectrometer, 18 is an fiber optic attenuator, 19 is a fiber optic circulator, 20 is a fiber optic collimator, 21 is a dual-cavity sensing unit, 22 is a photodetector, and 23 is a signal acquisition end. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] Figure 1 This is a schematic diagram of a cavity optical dynamics MEMS accelerometer based on cavity optical enhancement of a reservoir, according to an embodiment of the present invention. Figure 1 As shown, the cavity optomechanical MEMS accelerometer includes a dual-cavity sensing unit and an optical detection unit.

[0028] In this embodiment, the dual-cavity sensing unit consists of three mirrors placed in parallel, namely, a spring oscillator structure 1, a MEMS concave mirror 2, and a MEMS plane mirror 3 arranged in parallel at intervals. The spring oscillator structure 1 and the MEMS plane mirror 3 constitute the two end mirrors in the dual-cavity sensing unit, and the MEMS concave mirror 2 constitutes the middle mirror in the dual-cavity sensing unit.

[0029] The spring oscillator structure 1 includes a mass block 101, a suspension beam 102 and an outer frame 103. The mass block 101 is connected to the outer frame 103 through the suspension beam 102. The mass block 101 and the MEMS concave mirror 2 form a plano-concave FP cavity for sensing (also called a sensing FP cavity). The MEMS concave mirror 2 and the MEMS plane mirror 3 form a reserve FP cavity.

[0030] In this configuration, the reserve FP cavity and the sensing FP cavity are matched in an anti-resonant state. According to the theory of light interference, when the reserve FP cavity and the sensing FP cavity are matched in an anti-resonant state, the light dissipated from the sensing FP cavity will be pumped back into the sensing FP cavity from the reserve FP cavity. This reduces the number of photons escaping from the sensing FP cavity, thereby increasing the number of round trips of photons within the sensing FP cavity and improving the quality factor of the sensing FP cavity. Specifically, the anti-resonant matching of the reserve FP cavity and the plano-concave FP cavity should satisfy the following:

[0031] R2 = 4R1 / (1+R1) 2

[0032] L1 / L2 = 1 / 2

[0033] In the formula, R1 is the reflectivity of the two end mirrors, that is, the reflectivity of the side of the spring oscillator structure 1 facing the MEMS concave mirror 2 and the side of the MEMS plane mirror 3 facing the MEMS concave mirror 2; R2 is the reflectivity of the middle mirror, that is, the reflectivity of the concave surface of the MEMS concave mirror 2 facing the concave surface of the spring oscillator structure 1; L1 is the cavity length of the plano-concave FP cavity; L2 is the cavity length of the reserve FP cavity.

[0034] Anti-resonance requires that the cavity lengths of the sensing FP cavity and the reserve FP cavity satisfy a 1:2 ratio, and a high-quality-factor sensing FP cavity can be achieved with only a single high-reflectivity intermediate mirror R2. Furthermore, the reserve FP cavity can improve the quality factor of the sensing cavity by 1 to 2 orders of magnitude. Figure 2 As shown, this can effectively improve the sensitivity of the accelerometer.

[0035] The optical detection unit includes a modulation optical path, a transmission optical path, and a photoelectric detection component.

[0036] The principle of acceleration measurement provided in this embodiment based on cavity optical enhancement of the reservoir-based MEMS accelerometer is as follows: the modulation optical path is used to modulate the incident 1550nm laser wavelength, so that the 1550nm laser is detuned and locked at the operating point on one side of the resonance peak; the transmission optical path is used to transmit the laser with the determined wavelength to the dual-cavity sensing unit; the dual-cavity sensing unit is used to convert the external acceleration excitation into the displacement of the mass block, and to perform multi-beam interference through a plano-concave FP cavity, and then send the reflected light carrying the acceleration information to the photoelectric detection component through the transmission optical path for acceleration measurement.

[0037] It should be noted that the reflected light carrying acceleration information mentioned in this embodiment actually refers to the output light intensity of the dual-cavity sensing unit. Under external acceleration excitation, the resonant peak will generate a frequency shift. Since the laser wavelength is fixed, the output light intensity will change, and the photoelectric detection component will complete the measurement of external acceleration based on this light intensity change.

[0038] The cavity optomechanical MEMS accelerometer based on cavity optical enhancement provided in this embodiment builds a parameter-matched dual-cavity structure with a reservoir FP cavity on the basis of the traditional sensing FP cavity. The reservoir FP cavity can effectively improve the quality factor of the sensor cavity, thereby improving the sensitivity of the accelerometer. In addition, the dual-cavity structure used in this embodiment can achieve a high quality factor with relatively low reflectivity, which helps to reduce the difficulty and cost of device manufacturing.

[0039] The structure and principle of the cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement provided by the present invention will be described in detail below with reference to specific embodiments:

[0040] like Figure 1 As shown, the dual-cavity sensing unit in the cavity optomechanical MEMS accelerometer provided in this embodiment consists of a spring oscillator structure 1, a MEMS concave cavity 2, and a MEMS plane mirror 3. The mass block 101 and the MEMS concave mirror 2 form a sensing FP cavity, and the MEMS concave mirror 2 and the MEMS plane mirror 3 form a reserve FP cavity.

[0041] The spring oscillator structure 1 consists of a mass block 101, a suspension beam 102, and an outer frame 103. The mass block 101 is connected to the outer frame 103 via the suspension beam 102, allowing the mass block 101 to move in the out-of-plane direction. This converts external acceleration excitation into displacement of the mass block, which is then measured through multi-beam interference of the sensing FP cavity. The inner surface of the dual-cavity sensing unit is coated with an anti-reflection film 6, and the light guide end face is coated with an anti-reflection film 7 to facilitate light input into the sensing FP cavity. The entire dual-cavity structure and the fiber collimator 20 are fixed on the mounting fixture 4. The fiber collimator 20 is used to collimate the sensing light into the FP cavity.

[0042] Figure 2 The simulation diagram shows how the dual-cavity sensing unit improves the quality factor of the sensing cavity. The Q-value curves of the storage FP cavity (8) and the sensing FP cavity (9) are shown. Under the anti-resonant coupling condition, the light dissipated from the sensing FP cavity will be pumped back into the sensing FP cavity, effectively improving the quality factor of the sensing FP cavity (10).

[0043] Figure 3 This is a schematic diagram illustrating the principle of optical interferometry measurement using the sensing FP cavity in a dual-cavity sensing unit. During the sensing process, an interference resonance peak near 1550nm is selected, and the laser wavelength 11 is detuned and locked to the operating point 14 on one side of the resonance peak 12. When external acceleration excitation occurs, the spring oscillator structure 1 undergoes out-of-plane motion, changing the cavity length of the FP cavity. When the laser frequency is detuned and locked at the optical microcavity resonant frequency, the intracavity interference conditions change accordingly, leading to a change in reflection or transmission intensity. Through this sensing mechanism, the acceleration along the sensitive axis is converted into the displacement of the mechanical oscillator, which is then read out through optical detection, thereby achieving optical detection of the acceleration signal.

[0044] Figure 4 This is a schematic diagram of the optical testing principle of the optical detection unit. A 1550nm single-frequency laser 15 serves as the sensing light source. An electro-optic modulator 16 can adjust the wavelength of the laser in the optical path within a small range, facilitating laser wavelength detuning to lock the cavity resonance peak. A spectrometer 17 is used to detect the wavelength of light in the optical path in real time. An optical fiber attenuator 18 is used to adjust the light intensity in the optical path. An optical fiber circulator 19 and an optical fiber collimator 20 together incident light onto the dual-cavity sensing unit for sensing and collect reflected light carrying acceleration information, which is then sent to a photodetector 22 and recorded and analyzed through a signal acquisition terminal 23.

[0045] In one embodiment, the MEMS concave cavity 2 can be etched on a single-crystal silicon wafer using a MEMS isotropic wet etching process to form a hemispherical concave cavity with a certain aspect ratio.

[0046] In this embodiment, the hemispherical cavity can increase the ability to confine the light field and improve sensing sensitivity. Furthermore, it reduces the requirement for parallel mounting of the two end mirrors of the FP cavity. Specifically, the ratio of the depth to the radius of curvature of the hemispherical cavity should be approximately 0.5 (0.47–0.53), with a depth of approximately 300 μm (290–310 μm) and a radius of curvature of approximately 600 μm (590–610 μm). This design can maintain beam waist matching between the MEMS concave mirror and the MEMS planar mirror even with large manufacturing errors.

[0047] In one embodiment, the antireflection film 6 is made of SiN x The two-dimensional photonic crystal reflective film prepared by thin film can achieve high reflectivity of light at a wavelength of 1550nm.

[0048] In one embodiment, the spring oscillator structure 1 connects the outer frame 103 and the mass block 101 via several suspended beams 102. The entire structure can be fabricated using SOI silicon wafer MEMS technology. The suspended beams are fabricated within the device layer of the SOI structure, enabling the mass block to maintain out-of-plane movement. The SOI structure is a three-layer structure: a thinner device layer, an intermediate oxide layer, and a thicker substrate layer. Preferably, a symmetrically distributed suspended beam structure is fabricated using a dual-wafer SOI bonding process, which increases the modal suppression ratio of the spring oscillator structure 1.

[0049] Overall, the above technical solutions described in this invention have the following advantages compared with the prior art: (1) Based on the traditional sensing FP cavity, a parameter-matched reserve FP cavity dual-cavity structure is built. The reserve FP cavity can effectively improve the quality factor of the sensor cavity, thereby improving the sensitivity of the accelerometer; (2) The dual-cavity structure designed in this invention can achieve a higher quality factor under relatively low reflectivity, which helps to reduce the difficulty and cost of device manufacturing; (3) The dual-cavity structure designed in this invention is manufactured and packaged by MEMS process, has a small size, can be mass-produced, and can meet the needs of more application scenarios.

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cavity optical dynamics MEMS accelerometer based on reservoir-based cavity optical enhancement, characterized in that, The device includes a dual-cavity sensing unit and an optical detection unit. The dual-cavity sensing unit comprises a spring oscillator structure, a MEMS concave mirror, and a MEMS plane mirror arranged in parallel at intervals. The spring oscillator structure includes a mass block, a suspension beam, and an outer frame. The mass block is connected to the outer frame through the suspension beam. The mass block and the MEMS concave mirror form a plano-concave FP cavity for sensing. The MEMS concave mirror and the MEMS plane mirror form a reserve FP cavity. The reserve FP cavity and the plano-concave FP cavity are matched in an anti-resonance state. The optical detection unit includes a modulation optical path, a transmission optical path, and a photoelectric detection component. The modulation optical path is used to modulate the incident 1500nm laser wavelength, so that the laser wavelength is detuned and locked at the operating point on one side of the resonance peak; the transmission optical path is used to transmit the laser with the determined wavelength to the dual-cavity sensing unit; the dual-cavity sensing unit is used to convert the external acceleration excitation into the displacement of the mass block, and to perform multi-beam interference through a plano-concave FP cavity, and then send the reflected light carrying the acceleration information to the photoelectric detection component through the transmission optical path for acceleration measurement.

2. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 1, characterized in that, The side of the spring oscillator structure facing the MEMS concave mirror and the side of the MEMS plane mirror facing the MEMS concave mirror are both coated with a reflective film with a reflectivity of R1, and the concave surface of the MEMS concave mirror facing the spring oscillator structure is coated with a reflective film with a reflectivity of R2. Wherein, the reserve FP cavity and the plano-concave FP cavity are matched in an anti-resonance state to satisfy: R2=4R1 / (1+R1) 2 L1 / L2 = 1 / 2 In the formula, L1 is the cavity length of the plano-concave FP cavity; L2 is the cavity length of the reserve FP cavity.

3. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 2, characterized in that, The side of the MEMS plane mirror away from the MEMS concave mirror is coated with an anti-reflection film.

4. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 2, characterized in that, The MEMS concave mirror is etched using an isotropic wet etching process to create a hemispherical concave cavity with a certain aspect ratio on a single-crystal silicon wafer.

5. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 4, characterized in that, The ratio of the hemispherical depth to the radius of curvature of the hemispherical concave cavity is 0.47 to 0.53, wherein the depth is 290 to 310 μm and the radius of curvature is 590 to 610 μm.

6. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 2, characterized in that, The surface of the mass block, the MEMS concave mirror, and the MEMS plane mirror of the spring oscillator structure are all made of SiN. x Photonic crystal reflective film fabricated from thin film.

7. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 2, characterized in that, The spring oscillator structure is manufactured using SOI silicon wafer MEMS technology. A suspended beam is fabricated in the device layer of the SOI structure to maintain the out-of-plane movement of the mass block.

8. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 7, characterized in that, A suspended beam structure with symmetrical distribution on both sides was fabricated using a dual-layer SOI bonding process.

9. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 2, characterized in that, The modulation optical path employs a laser, an electro-optic modulator, and an optical attenuator; the transmission optical path employs an optical fiber circulator and an optical collimator; and the photoelectric detection component employs a photodetector.

10. The cavity optical dynamics MEMS accelerometer based on reservoir cavity optical enhancement according to claim 9, characterized in that, The optical detection unit also includes a spectrometer, which is used to detect the laser wavelength modulated by the electro-optic modulator in real time.

Images