Large-dynamic-range micro-optical accelerometer

Abstract

The invention provides a large dynamic range micro-optical accelerometer. The accelerometer is composed of an optical transceiver module, a beam splitting and combining module, an MEMS sensitive unit and a packaging substrate, the optical transceiver module is composed of a laser and a plurality of detectors, the beam splitting module is composed of a diffraction grating, the MEMS sensitive unit is composed of a spring-mass block with a reflector, and the packaging substrate is composed of an upper substrate, a lower substrate and a supporting substrate. According to the invention, the detection of multiple diffraction orders of the micro-optical accelerometer is realized, the dynamic range of the system is improved by using high-order diffraction light, and the acceleration measurement with high precision and large dynamic range is realized.

Description

Technical Field

[0001] The present application relates to the technical field of micro-opto-electromechanical systems and acceleration sensors (micro-inertial measurement), and in particular to a large dynamic range micro-optical accelerometer that utilizes high-order diffracted light to achieve high-precision large dynamic range acceleration measurement. Background Art

[0002] Due to the limitations of traditional electrical measurement methods, conventional piezoresistive and capacitive MEMS have encountered bottlenecks in measurement sensitivity and noise, and cannot meet the needs of application fields such as high-precision inertial navigation. In recent years, optical MEMS (micro-optical) accelerometers based on optical detection and MEMS technology are gradually coming into people's view. MEMS process technology provides a good process foundation for the implementation of micro-optical accelerometers. On the other hand, optical detection schemes use optical detection methods such as light intensity, frequency, phase, and near-field effects to achieve displacement detection of sensitive units, which can provide better displacement detection resolution than traditional electrical detection schemes. Micro-optical accelerometers have a series of advantages such as miniaturization, high precision, and anti-electromagnetic interference. With the further development of photonic integrated design and technology, micro-optical accelerometers will become the representative of a new generation of high-precision accelerometers.

[0003] In recent years, research institutions at home and abroad have begun to conduct some research on micro-optical accelerometers. In 2008, NA Hall et al. from Sandia National Laboratory in the United States proposed a new optical micro-accelerometer structure, which uses a VCSEL laser source to excite a grating connected to a spring-mass block, and measures the grating displacement and acceleration caused by acceleration by detecting the intensity of the grating reflected light. The acceleration detection accuracy can theoretically reach In 2017, Lu Qianbo and others from Zhejiang University proposed a micro-optical accelerometer based on a grating interferometer cavity and optimized the sensor structure to achieve a noise of In 2019, Gao Shan et al. from Beijing University of Aeronautics and Astronautics conducted theoretical modeling of a micro-grating accelerometer based on a Gaussian beam and increased the size of the spring-mass block to achieve The noise floor and zero bias stability of 3.1ug. Traditional micro-optical accelerometers have high displacement and acceleration sensitivity, but due to the periodic changes in the interference fringes, the linear range is small, so the dynamic range is small in the open-loop case. The interferometric measurement of the above-mentioned schemes only utilizes the ±1st order diffraction. Although it can achieve high measurement accuracy, the measurement range is only a few mg. With the continuous improvement of the performance requirements of micromechanical accelerometers, there is an urgent need for inertial navigation-grade micro-accelerometers with high precision and large dynamic range, that is, zero bias stability better than 1ug and dynamic range greater than ±1g.

[0004] However, the dynamic range of the micro-optical accelerometer in the prior art is relatively small and cannot meet the demand. Summary of the invention

[0005] In response to the defects or improvement needs of the prior art, the present invention application proposes a micro-optical accelerometer that utilizes high-order diffraction light detection to achieve high-precision and large dynamic range, thereby solving the problem of small dynamic range of micro-optical accelerometers in the prior art.

[0006] The present invention provides a large dynamic range micro-optical accelerometer, comprising an optical transceiver module (1), a beam splitting and combining module (2), a MEMS sensitive unit (3) and a packaging substrate (7); the optical transceiver module (1) comprises a laser (4), a ±1-level detector group (5) and a ±3-level detector group (6); the packaging substrate (7) comprises an upper substrate (8), a supporting substrate (9) and a lower substrate (10); the MEMS sensitive unit (3) comprises a spring-mass block structure with a reflector, the reflector is located in the central area of ​​the upper surface of the spring-mass block, and moves out of the plane with the spring-mass block structure.

[0007] More specifically, the positions of the ±1-level detector group and the ±3-level detector group of the optical transceiver module are symmetrically distributed relative to the position of the laser. The laser emitted downward by the laser passes through the grating interferometer cavity and then symmetrically returns to the target surfaces of the ±1-level detector group and the ±3-level detector group, thereby realizing large dynamic range displacement detection of the grating interferometer cavity length.

[0008] More specifically, the beam splitting and combining module includes a diffraction grating, which is made of a silicon wafer by etching linear grooves with uniform intervals to split and combine laser beams.

[0009] More specifically, the laser, ±1-level detector group and ±3-level detector group are mounted on the lower surface of the upper substrate to ensure that they are on the same plane; the beam splitting and combining module and the MEMS sensitive unit are mounted on the upper surface of the lower substrate; the supporting substrate ensures the spacing and parallelism between the optical transceiver module and the beam splitting and combining module, so that the multi-order diffraction light emitted from the beam splitting and combining module can accurately enter the target center of the ±1-level detector group and the ±3-level detector group.

[0010] More specifically, the laser is a vertical cavity surface emitting laser, the power may be 0.1 to 1 mW, and the wavelength is 850 nm.

[0011] More specifically, the ±1-level detector group 5 and the ±3-level detector group 6 may be low-noise silicon photodiodes.

[0012] More specifically, when the collimated coherent laser is vertically incident on the upper surface of the diffraction grating, the grating acts as a beam splitter, part of the light will be reflected, and the other part of the light will be transmitted through the grating and incident on the reflector; the grating will also play a diffraction role, and the reflected and transmitted diffraction light beams both contain a series of orders, which may include 0th order, ±1st order, ±3rd order, and more orders, depending on the grating constant; among them, the transmitted series of diffraction light beams will return to the grating after being reflected by the reflector, and will be split and diffracted again on the surface of the grating.

[0013] More specifically, when the grating and the reflector remain strictly parallel, a series of diffracted light beams that are reflected by the semi-transparent and semi-reflective grating for the first time will share the same optical path with a series of diffracted light beams that are transmitted after passing through the grating for the second time, and the corresponding diffraction order light beams will be coherently superimposed or destructive in the far field to form a series of interference spots; the positions of these interference spots remain fixed and are only related to the wavelength of the incident light and the grating constant, while their intensity will be modulated by the distance between the grating and the reflector.

[0014] More specifically, when external acceleration acts on the MEMS sensitive unit, the spring-mass block of the MEMS sensitive unit will produce a corresponding displacement along the sensitive axis due to the inertial force, thereby causing the distance between the MEMS sensitive unit and the diffraction grating, that is, the length of the micro-nano optical cavity to change. Multiple groups of larger-order detectors with fixed positions can be used to detect more different orders of light intensities, thereby achieving a larger range of detected light intensity.

[0015] More specifically, the distance between the diffraction grating and the spring-mass block will vary with the direction of the input acceleration. Therefore, the variable Δd of the cavity length of the micro-nano optical cavity is a vector. When the direction of the external input acceleration is consistent with the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd is positive, and the cavity length composed of the grating and the sensitive spring-mass block becomes d=(d0+Δd)>d0.

[0016] When the direction of the external input acceleration is opposite to the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd at this time can be defined as negative, and the cavity length composed of the grating and the sensitive spring-mass block at this time becomes d = (d0 + Δd) <d0;

[0017] The functional relationship between each level of light intensity and acceleration is:

[0018]

[0019] Where Γ is a constant.

[0020] The working principle of a micro-optical accelerometer capable of detecting multiple diffraction orders proposed in the present invention application is described as follows: the incident coherent collimated laser beam is incident on the surface of the diffraction grating, and the diffraction grating plays a dual role of splitting and diffraction. One path directly produces reflective diffraction to form 0-order, ±1-order and ±3-order reflective diffraction light; the other path passes through the diffraction grating to reach the reflector surface formed by the MEMS sensitive unit, and after reflection, passes through the diffraction grating again, and then produces transmissive diffraction to form 0-order, ±1-order and ±3-order transmissive diffraction light. The two diffraction beams of corresponding orders interfere in the far field, and the phase corresponding to the interference light is related to the spacing between the grating and the reflector composed of the spring-mass block, so the intensity is modulated but the position of the interference light does not change.

[0021] When external acceleration acts on the MEMS sensitive unit, the spring-mass block of the MEMS sensitive unit will produce a corresponding displacement along the sensitive axis due to the inertial force, which will cause the distance between the MEMS sensitive unit and the diffraction grating, that is, the length of the micro-nano optical cavity, to change. Therefore, multiple groups of fixed-position detectors can be used to detect light intensities of different orders. The combination of different diffraction order light intensity detection can achieve a larger detection light intensity range, and ultimately achieve high-precision acceleration measurement with a large dynamic range.

[0022] The beneficial effects of the present invention are:

[0023] (1) A micro-optical accelerometer with a large dynamic range is realized by using high-order diffraction light. Since the intensity of high-order diffraction is proportional to the intensity of low-order diffraction, the interferometric measurement method combining ±1st and ±3rd order diffraction can theoretically improve the dynamic range of the system. The positive and negative diffraction differences can suppress common-mode noise at the same time. The results show that, with other conditions unchanged, the dynamic range of the accelerometer with the addition of ±3rd order diffraction detection can be increased by 9 times.

[0024] (2) An open-loop system and a laser are used to achieve acceleration measurement with a large dynamic range. On the one hand, an open-loop system is used. Using preamplifiers with different fixed gain coefficients, the intensities of the ±1st and ±3rd order diffraction detection lights can be set to the optimal detection intensity where the detector is close to saturation, thereby reducing system noise and simplifying the structure compared to the open-loop system; on the other hand, the ±1st and ±3rd order diffraction detection lights are both emitted by the same laser, and after differentiation, common mode noise can be better eliminated, further improving system sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a structural schematic diagram of the accelerometer of the present invention;

[0027] Figure 2 It is a schematic diagram of the working principle of the accelerometer of the present invention;

[0028] Figure 3 is the relationship between the first and third order outgoing light intensity and the input acceleration;

[0029] Figure 4 It is the diffraction spots of different diffraction orders and the diffraction intensity diagram of different orders.

[0030] Figure numerals: 1-optical transceiver module, 2-beam splitting and combining module, 3-MEMS sensitive unit, 4-laser, 5-±1 level detector group, 6-±3 level detector group, 7-packaging substrate, 8-upper substrate, 9-support substrate, 10-lower substrate. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0032] In the description of the present application, it should be noted that, unless otherwise specified and limited, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element 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 application. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0033] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0034] The present invention proposes a micro-optical accelerometer capable of realizing detection of multiple diffraction orders as shown in the attached figure. Figure 1 As shown, the accelerometer is composed of an optical transceiver module 1, a beam splitter and combiner module 2, a MEMS sensitive unit 3 and a packaging substrate 7;

[0035] The optical transceiver module 1 is composed of a laser 4, a ±1-level detector group 5, and a ±3-level detector group 6; the positions of the ±1-level detector group and the ±3-level detector group are symmetrically distributed relative to the position of the laser, and the laser emitted downward by the laser passes through the grating interferometer cavity and is symmetrically split and returned to the target surfaces of multiple ±1-level detector groups and ±3-level detector groups, thereby realizing high-precision and large dynamic range displacement detection of the cavity length of the grating interferometer cavity;

[0036] The MEMS sensitive unit 3 is composed of a spring-mass block structure with a reflector, and the reflector is located in the central area of ​​the upper surface of the spring-mass block and moves out of the plane with the spring-mass block structure;

[0037] The beam splitting and combining module 2 is composed of a diffraction grating, which is realized by etching uniformly spaced linear grooves on a silicon wafer to achieve the functions of laser beam splitting and combining;

[0038] The packaging substrate 7 is composed of an upper substrate 8, a supporting substrate 9 and a lower substrate 10. The laser 4, the ±1-level detector group 5 and the ±3-level detector group 6 are mounted on the lower surface of the upper substrate 8 to ensure that they are on the same plane; the combination of the beam splitting and combining module 2 and the MEMS sensitive unit 3 is mounted on the upper surface of the lower substrate 10; the supporting substrate 9 ensures the spacing and parallelism between the optical transceiver module 1 and the beam splitting and combining module 2, so that the multi-order diffracted light emitted from the beam splitting and combining module 2 is accurately incident on the target center of the ±1-level detector group 5 and the ±3-level detector group 6.

[0039] An example of the laser 4 may be a vertical cavity surface emitting laser (VCSEL), the power may be 0.1-1 mW, the wavelength may be 850 nm. The laser generates a stable, single longitudinal mode output laser, and the electro-optical conversion efficiency may be above 30%, which can help achieve ultra-low power consumption of the system.

[0040] Furthermore, the laser provides high-quality TEM00 spatial mode output and a mode field diameter close to the diffraction limit, which can improve the contrast of the diffracted light returned to the ±1-level detector group 5 and the ±3-level detector group 6, thereby improving the detection sensitivity of the accelerometer.

[0041] The ±1-level detector group 5 and the ±3-level detector group 6 can be low-noise silicon photodiodes (PDs), which have low voltage and current noise levels, so that the system noise can be close to the shot noise limit. The two symmetrically distributed detector chips form a first-level differential detection structure, which can remove the common-mode noise of the laser, such as relative intensity noise (RIN). It is worth noting that more detector groups can be used to detect higher-order diffraction light intensities, further improving the dynamic range of the system.

[0042] The packaging substrate 7 is composed of an upper substrate 8, a supporting substrate 9 and a lower substrate 10. The substrate material is usually an aluminum nitride substrate, and the substrates are connected by gold-gold bonding or gluing.

[0043] Figure 2 This is a schematic diagram of the working principle of the accelerometer of this application. When the collimated coherent laser is incident vertically on the upper surface of the diffraction grating, the grating will first act as a beam splitter, and part of the light will be reflected, while the other part of the light will be transmitted through the grating and incident on the reflector. The grating will also play a diffraction role. The reflected and transmitted diffraction beams both contain a series of orders, which may include 0th order, ±1st order, ±3rd order, and more orders, depending on the grating constant. Among them, the series of diffraction beams that are transmitted will return to the grating after being reflected by the reflector, and will be split and diffracted again on the surface of the grating.

[0044] When the grating and the reflector are kept strictly parallel, a series of diffracted light beams reflected by the semi-transparent and semi-reflective grating for the first time will share the same optical path with a series of diffracted light beams transmitted after passing through the grating for the second time, so that the corresponding diffracted order light beams will coherently superimpose or destruct in the far field, forming a series of interference spots. The positions of these interference spots are only related to the wavelength of the incident light and the grating constant, so they will remain fixed, and their intensity will be modulated by the distance between the grating and the reflector. The grating and the reflector form a spacing-phase sensitive micro-nano grating interference cavity, referred to as a micro-nano optical cavity. The grating and the reflector are equivalent to the two plates in the Michelson interferometer. The spacing-phase sensitive micro-nano grating interference cavity not only has the advantage of the Michelson interferometer in achieving high-precision displacement detection, but also avoids the introduction of complex alignment and calibration problems because no spectroscopic elements are required.

[0045] When external acceleration acts on the MEMS sensitive unit, the spring-mass block of the MEMS sensitive unit will produce a corresponding displacement along the sensitive axis due to the inertial force, which will cause the distance between the MEMS sensitive unit and the diffraction grating, that is, the length of the micro-nano optical cavity, to change. Therefore, multiple groups of fixed-position detectors can be used to detect light intensities of different orders. The combination of different diffraction order light intensity detection can achieve a larger detection light intensity range, and ultimately achieve high-precision acceleration measurement with a large dynamic range.

[0046] like Figure 3 The figure shows the relationship between the first and third order output light intensities and the input acceleration. The distance between the diffraction grating and the spring-mass block will vary with the direction of the input acceleration. Therefore, the variable Δd of the cavity length of the micro-nano optical cavity is directional and can be positive or negative, and is a vector. When the direction of the external input acceleration is consistent with the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd at this time can be defined as positive, and the cavity length composed of the grating and the sensitive spring-mass block at this time becomes d=(d0+Δd)>d0;

[0047] When the direction of the external input acceleration is opposite to the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd at this time can be defined as negative, and the cavity length composed of the grating and the sensitive spring-mass block at this time becomes d = (d0 + Δd) <d0。

[0048] The functional relationship between each level of light intensity and acceleration is:

[0049]

[0050]

[0051] Where Γ is a constant.

[0052] From the above formula, we can know that the intensity of each order of light is in a periodic cosine function relationship with the external acceleration. Therefore, the magnitude of the input acceleration can be obtained by detecting the light intensity. The results show that, with other conditions unchanged, the dynamic range of the accelerometer with the addition of ±3rd order diffraction detection can be increased by 9 times. Furthermore, if higher-order diffraction light such as ±5th and ±7th orders is included in the detection, the dynamic range of the system can be further improved.

[0053] like Figure 4 The figure shows the diffraction spots of different diffraction orders and the diffraction intensity diagrams of different orders. The period of the grating is set to 4um. The system is modeled and analyzed using the non-sequential analysis tool of the commercial optical design software. The detection light energy of 0, ±1, and ±3 energy levels is isolated and analyzed. It can be seen that the energy distribution conforms to the proportional relationship of theoretical analysis. Therefore, the use of high-order diffraction order detection can effectively improve the dynamic range of the system.

[0054] Although the present invention has been disclosed as above with preferred embodiments, the embodiments are not intended to limit the present invention. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the content defined by the claims of the present application.

Claims

1. A large dynamic range micro-optical accelerometer, characterized in that: The invention comprises an optical transceiver module (1), a beam splitting and combining module (2), a MEMS sensitive unit (3) and a packaging substrate (7); the optical transceiver module (1) comprises a laser (4), a ±1-level detector group (5) and a ±3-level detector group (6); the packaging substrate (7) comprises an upper substrate (8), a supporting substrate (9) and a lower substrate (10); the MEMS sensitive unit (3) comprises a spring-mass block structure with a reflector, the reflector is located in the central area of ​​the upper surface of the spring-mass block and moves out of the plane along with the spring-mass block structure.

2. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: The positions of the ±1-level detector group and the ±3-level detector group of the optical transceiver module are symmetrically distributed relative to the position of the laser. The laser emitted downward by the laser passes through the grating interferometer cavity and then symmetrically returns to the target surfaces of the ±1-level detector group and the ±3-level detector group, thereby realizing large dynamic range displacement detection of the grating interferometer cavity length.

3. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: The beam splitting and combining module includes a diffraction grating, which is made by etching evenly spaced linear grooves on a silicon wafer to split and combine the laser beams.

4. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: The laser, ±1-level detector group and ±3-level detector group are mounted on the lower surface of the upper substrate to ensure that they are on the same plane; the beam splitting and combining module and the MEMS sensitive unit are mounted on the upper surface of the lower substrate; the supporting substrate ensures the spacing and parallelism between the optical transceiver module and the beam splitting and combining module, so that the multi-order diffraction light emitted from the beam splitting and combining module can accurately enter the target center of the ±1-level detector group and the ±3-level detector group.

5. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: The laser is a vertical cavity surface emitting laser, the power may be 0.1 to 1 mW, and the wavelength may be 850 nm.

6. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: The ±1-level detector group 5 and the ±3-level detector group 6 may be low-noise silicon photodiodes.

7. The large dynamic range micro-optical accelerometer according to claim 1, characterized in that: When the collimated coherent laser is vertically incident on the upper surface of the diffraction grating, the grating acts as a beam splitter. Part of the light will be reflected, and the other part will be transmitted through the grating and incident on the reflector. The grating will also play a diffraction role. The reflected and transmitted diffraction beams contain a series of orders, which may include 0th order, ±1st order, ±3rd order, and more orders according to the grating constant. Among them, the transmitted series of diffraction beams will return to the grating after being reflected by the reflector, and will be split and diffracted again on the surface of the grating.

8. The large dynamic range micro-optical accelerometer according to claim 7, characterized in that: When external acceleration acts on the MEMS sensitive unit, the spring-mass block of the MEMS sensitive unit will produce a corresponding displacement along the sensitive axis due to the inertial force, which will cause the distance between the MEMS sensitive unit and the diffraction grating, that is, the length of the micro-nano optical cavity to change. Multiple groups of larger-order detectors with fixed positions can be used to detect more different orders of light intensities, thereby achieving a larger range of detected light intensity.

9. The large dynamic range micro-optical accelerometer according to claim 7, characterized in that: The distance between the diffraction grating and the spring-mass block will vary with the direction of the input acceleration. Therefore, the variable Δd of the cavity length of the micro-nano optical cavity is a vector. When the direction of the external input acceleration is consistent with the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd is positive, and the cavity length composed of the grating and the sensitive spring-mass block becomes d=(d0+Δd)>d0. When the direction of the external input acceleration is opposite to the direction of the inherent gravitational acceleration of the sensitive spring-mass block itself, the cavity length change Δd at this time can be defined as negative, and the cavity length composed of the grating and the sensitive spring-mass block at this time becomes d = (d0 + Δd) <d0; The functional relationship between each level of light intensity and acceleration is: Where Γ is a constant.

Images