Three-axis optical fiber acceleration sensor based on silicon optical microstructure

Abstract

The invention discloses a three-axis optical fiber acceleration sensor based on a silicon optical microstructure, which is characterized in that detection light rays are distributed to three mutually orthogonal detection light paths, the detection light rays are incident to three mutually orthogonal side surfaces in a reflective mass block by utilizing silicon-based micromirrors in the light paths respectively, and the surface reflectivity of the mass block is calculated by utilizing gradient distribution of the surface reflectivity of the mass block. The optical power of the reflected light is mapped according to the position of the reflection point, then the reflected light is fed back to the optical fiber through the coupling assembly, and the change condition of the position of the reflection point is determined according to the recognition result of the power state of the reflected light, so that the displacement of the mass block in each direction is accurately detected, and the corresponding acceleration is calculated. According to the three-axis optical fiber acceleration sensor provided by the invention, high-linearity and three-axis simultaneous measurement can be realized on a single optical fiber or a small number of optical fibers; only optical fiber connection is adopted, the system is suitable for a long-distance distributed detection scene, centralized demodulation can be realized, and the power consumption of terminal equipment is reduced; the LED lamp is simple in structure and easy to manufacture in batches.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology and microelectromechanical systems (MEMS) technology, and particularly relates to a triaxial fiber optic accelerometer based on silicon photonic microstructures. Background Technology

[0002] Existing fiber optic accelerometers mainly include fiber Bragg grating (FBG) type and FP interferometer type. Among them, FBG type sensors require a precise wavelength demodulation device, and the structure on which they achieve triaxial measurement is complex, resulting in high operating costs. FP interferometer type sensors, on the other hand, have high requirements for light source coherence and environmental stability, and require complex algorithms to implement demodulation algorithms and temperature compensation to obtain accurate sensing data.

[0003] If traditional electrical MEMS accelerometers are used for detection, they rely on capacitance, resistance, or piezoelectric signals for readout. Therefore, wired connections typically require dedicated multi-core copper cables for power supply and signal transmission, resulting in short transmission distances, thick wiring, and high costs. When using wireless connections for data exchange, battery power is required at the sensing device, and these batteries need to be replaced periodically. Wireless transmission is also susceptible to electromagnetic interference. Therefore, under current technology, electrical MEMS accelerometers, whether using wired or wireless data transmission, are unsuitable for distributed deployments over distances of several kilometers or even tens of kilometers.

[0004] Existing electrical MEMS accelerometers are inferior to fiber optic accelerometers in terms of lifespan, passive intrinsic safety, electromagnetic interference resistance, high transmission speed, lightning protection, multi-point distributed measurement, and signal security. Furthermore, existing fiber optic accelerometers are limited by the detection and demodulation requirements of their optical signals, necessitating complex algorithms and detection structures to achieve accurate acceleration detection.

[0005] There is an urgent need for an inertial measurement unit that is suitable for structural health monitoring scenarios such as bridges, tunnels, rail transit, oil and gas pipelines, wind turbines, wind turbine blades, and conveyor belts, can be deployed over long distances, has a lifespan of more than 30 years, is passively intrinsically safe, is resistant to electromagnetic interference, has a fast signal transmission speed, does not attract lightning, and is suitable for multi-point distribution. Summary of the Invention

[0006] The problem this invention aims to solve is to provide a triaxial fiber optic accelerometer that utilizes silicon-based microstructures and optical sensing coding principles, overcoming the shortcomings of existing fiber optic accelerometers such as complex wavelength modulation, high requirements for environmental stability, and complex structure.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a triaxial fiber optic accelerometer based on a silicon photonics microstructure, comprising: a coupling component disposed in a silicon substrate, which is externally connected to an optical fiber and internally distributes the detection light provided by the optical fiber into three mutually orthogonal detection optical paths; each detection optical path is respectively provided with: a silicon micromirror, which receives one of the detection light rays, incident it onto one side surface of a reflective mass block, and receives the reflected light rays from the reflective mass block, and feeds the reflected light rays back to the optical fiber through the coupling component; the reflective mass block is elastically supported inside the sensor, and a monotonically changing reflectivity gradient distribution is provided on its mutually orthogonal surfaces along the incident direction of the detection light rays on that side.

[0008] Optionally, as described above, a triaxial fiber optic accelerometer based on a silicon photonic microstructure, wherein the silicon-based micromirror is disposed in a silicon substrate and has a gold-plated reflective surface, the reflective surface adjusting the reflection angle of the sensor relative to the reflective mass in response to a voltage electrostatic field.

[0009] Optionally, as described above, the triaxial fiber optic accelerometer based on silicon photonic microstructures, wherein the reflective mass block is a cubic structure, which is elastically connected to the silicon substrate of the sensor through an elastic cantilever or support beam, suspended and held in the sensor, and can be displaced relative to the silicon substrate around it as the sensor rotates.

[0010] Optionally, in the triaxial fiber optic accelerometer based on silicon photonic microstructures as described above, the reflective mass block constructs a gradient-distributed continuous reflectivity region by setting a multilayer dielectric coating on its surface, or by gradually adjusting the thickness of a metal thin film on its surface, or by micro / nano structures on its surface, or a combination of the above methods.

[0011] Optionally, as described above, the triaxial fiber optic accelerometer based on silicon photonic microstructures has a reflectivity gradient ranging from 10% to 90% on the surface of the reflective mass block.

[0012] Optionally, in the triaxial fiber optic accelerometer based on silicon photonic microstructures as described above, the silicon micromirrors corresponding to each detection optical path oscillate synchronously at a preset frequency and open at different time period windows to incident the detection light onto the surface of the reflective mass block. By utilizing the reflectivity of the reflected light spot on the surface of the reflective mass block, a corresponding displacement-power component is superimposed on the reflected light. Combined with the period window of the detection fiber, a detection signal of acceleration in the reflection direction is formed.

[0013] Optionally, as described above, a triaxial fiber optic accelerometer based on a silicon photonics microstructure, wherein the optical fiber feeds back the sensor's detection signal to the silicon photonics module, and the silicon photonics module feeds back the detection signal to a corresponding processing unit. The silicon photonics module includes: an optical fiber connector for connecting the optical fiber; a circulator with a unidirectional optical path switch, a laser connected to a first port, an optical fiber connector connected to a second port, and a photodetector connected to a third port; the laser feeds detection light into the optical fiber through the circulator and the optical fiber connector; the reflected light detected by the sensor is received through the optical fiber connector, and relayed by the circulator to the photodetector to extract the corresponding detection signal.

[0014] Optionally, in the triaxial fiber optic accelerometer based on silicon photonic microstructures as described above, the reflective mass block has its reflective regions on each of its mutually orthogonal surfaces divided into at least 4096 equal-spaced cells. In each cell, the reflectivity of the reflective mass block surface structure is arranged to increase or decrease gradually in a linear gradient distribution within the range of 10% to 90% of the reflection intensity.

[0015] Optionally, as described in any of the above-mentioned three-axis fiber optic accelerometers based on silicon photonics microstructures, wherein the acceleration detected by the three-axis fiber optic accelerometer in any direction is: ,in, The axial direction representing acceleration, for The optical power of the reflected echo in the axial direction for The optical power of the detection ray incident along the axial direction. These are factory calibration constants, determined based on the measurement results of the total optical coupling efficiency and loss of the detection optical path. Beneficial effects

[0016] The triaxial fiber optic accelerometer based on silicon photonics microstructures provided in this application utilizes three synchronously operating silicon-based MEMS micromirrors to open or close three optical paths at a fixed rhythm, distributing the detection light into three mutually orthogonal detection optical paths. The silicon-based micromirrors in each optical path incident the detection light onto three mutually orthogonal surfaces of a reflective mass block. By utilizing the gradient distribution of the reflectivity of the mass block surface and the displacement of the mass block caused by acceleration in each direction of the sensor, a linear mapping is achieved between the position of the reflection point and the echo power of the reflected light. The reflected light is then fed back to the optical fiber through a coupling component. Based on the identification result of the power state of the reflected light, the change in the position of the reflection point is determined, thereby accurately detecting the displacement of the mass block in each direction and calculating its corresponding acceleration. The triaxial fiber optic accelerometer provided in this application can achieve high linearity and simultaneous triaxial measurement on a single or a small number of optical fibers. It uses only optical fiber connections, making it suitable for long-distance distributed detection scenarios. It can also be centrally demodulated, reducing the power consumption of terminal equipment. This application has a simple structure, is easy to demodulate, can achieve triaxial acceleration measurement over long distances via optical fiber connections, has no electromagnetic interference, does not attract lightning, and is easy to mass-produce. Attached Figure Description

[0017] The following detailed description, in conjunction with the accompanying drawings and embodiments of the present invention, is as follows: Figure 1 This is a schematic diagram of the structure of the triaxial fiber optic accelerometer based on silicon photonics microstructure provided by the present invention. Figure 2 A schematic diagram illustrating the connection method of the triaxial fiber optic accelerometer based on silicon photonics microstructure provided by the present invention; Figure 3 This is a schematic diagram of the demodulation laser module of the triaxial fiber optic accelerometer in this application. Figure 4 This is a schematic diagram illustrating the detection principle of the triaxial fiber optic accelerometer based on silicon photonics microstructure provided by the present invention. Figure 5 This is a schematic diagram illustrating the implementation method of electrostatically driven micromirrors based on silicon photonic microstructures provided by the present invention. Detailed Implementation

[0018] This embodiment provides a novel triaxial fiber optic accelerometer based on silicon photonics microstructures. It performs power mapping on the reflection points of a line by constructing a reflectivity gradient structure on three mutually orthogonal surfaces of a reflective mass block, thereby superimposing the real-time position state of the mass block on the reflected light and realizing the calculation of its acceleration.

[0019] See Figure 1 As shown, this application provides a triaxial fiber optic accelerometer based on a silicon photonics microstructure, which includes components disposed in a silicon substrate: The coupling component connects to the external optical fiber and distributes the detection light provided by the multimode optical fiber to three mutually orthogonal detection optical paths. In the sensor provided in this application, the optical fiber can be flexibly selected as single-mode optical fiber or multimode optical fiber according to the setting requirements. However, for cost-sensitive scenarios or scenarios that require long-distance detection deployment, single-mode optical fiber is usually preferred to realize the transmission of detection optical signal. This application specifies that the three detection optical paths corresponding to the three axes in the silicon substrate are each set separately: A silicon-based micromirror receives one of the detection beams, directs it onto one side surface of a reflective mass, receives the reflected beam from the reflective mass, and feeds the reflected beam back into an optical fiber via a coupling component. The reflective mass block is elastically supported inside the sensor, and a monotonically varying reflectivity gradient distribution is set on its mutually orthogonal surfaces along the incident direction of the detection light on that side.

[0020] Therefore, in the sensing structure of this application, the silicon-based micromirrors corresponding to each detection optical path oscillate synchronously at a preset frequency, opening at different time period windows to incident detection light onto the surface of the reflective mass block. Utilizing the reflectivity of the location of the reflected light spot on the surface of the reflective mass block, a corresponding displacement-power component is superimposed on the reflected light. Combined with the periodic window of the detection fiber, this forms a detection signal of acceleration in the reflection direction. Thus, the system can directly determine which of the three axes the current signal corresponds to based on the time period of the received reflected signal, determine the position of the reflected light spot on the reflective mass block surface based on the power intensity of the reflected signal, and calculate the magnitude of the acceleration in the detection direction corresponding to that axis based on the change in position over time.

[0021] The above calculation process for optical signals and acceleration in different directions can be achieved through... Figure 2 The demodulation unit shown implements this functionality. This demodulation unit can connect to several triaxial fiber optic accelerometers based on silicon photonics microstructures simultaneously via a multi-core communication optical cable, as shown on the right side of the diagram. By sending corresponding detection beams to each sensor individually or simultaneously, it achieves real-time detection of acceleration changes at different sensor installation locations. This detection system can simultaneously achieve real-time sensing and detection over long distances and from multiple ends using a single optical cable. It is low-cost, easy to engineer, and the right side shows a stand-alone fiber optic silicon photonic accelerometer connected to the multi-core communication optical cable. The aforementioned data processing and controller unit can flexibly communicate with the server or third-party platform via wired or wireless means, enabling real-time calculation and analysis of acceleration at different detection locations within the computer room. Engineering optical cables typically have 4 to 288 cores, with prices generally ranging from 1 to 10 yuan per meter. Taking a 288-core cable as an example, the average cost per meter of fiber is approximately 0.03 yuan, offering a significant cost advantage compared to traditional electrical signal-based sensing methods. Furthermore, this advantage increases with longer detection distances and the increased number of sensors required.

[0022] To achieve feeding into the aforementioned different optical axes and demodulating the reflected light to process the acceleration information carried therein, this application typically refers to... Figure 3 The structure shown incorporates a silicon photonics module, which, while emitting detection light, processes the detection signal from the sensor fed back via single-mode or multimode fiber to extract the acceleration information expressed therein. This silicon photonics module includes: Fiber optic connectors, of which SC fiber optic connectors may be used, are used to connect optical fibers; A circulator with a unidirectional optical path switch, a laser connected to the first port, an optical fiber connector connected to the second port, and a photodetector connected to the third port; The laser feeds detection light into the optical fiber through a circulator and an optical fiber connector; The reflected light detected by the sensor is received through an optical fiber connector, relayed by a circulator to a photodetector to extract the corresponding detection signal, and supplied to the conditioning and control unit. The reflection power of the reflected signal is identified and calculated accordingly to obtain acceleration data matching the change in the position of the reflected light spot.

[0023] In the aforementioned silicon photonics module, the laser and modulation control interact to determine the emission wavelength of the detection light received from the sensor and match it with the reflected wavelength received by the device. The laser feeds the detection light of the corresponding wavelength unidirectionally through a circulator into the optical connector, feeding the light into the corresponding sensor, and then through the sensor's internal structure to the corresponding position on the surface of the reflective mass block. Because the cubic mass block is elastically connected to the silicon substrate of the sensor only through spring structures such as elastic cantilever or support beams, it is held in a suspended posture within the sensor. Therefore, it can be driven by gravity in real time, displacing relative to the surrounding silicon substrate according to the rotation of the sensor. The incident light in the sensor will be incident at different positions with different reflectivity due to the rotation of the mass block. Due to the gradient setting of the reflectivity of the mass block surface, it will absorb a portion of the incident light and reflect a corresponding proportion of optical power. Thus, the intensity of the reflected detection light can reflect the position of the reflection point on the mass block surface according to the magnitude of the optical power, thereby detecting acceleration and rotation state by the change in reflection position per unit period. The reflected light from the superimposed reflected light power enters the silicon photonics module through the fiber optic connector, and reaches the photodetector through unidirectional transmission via the circulator. By extracting the reflected light that matches the wavelength of the current incident laser, and by demodulating and calculating the changes in its optical power intensity, real-time acceleration data can be obtained.

[0024] The following specific example illustrates the specific correspondence between the surface reflectivity gradient distribution of the mass block and the detection light in this application, in order to explain the specific demodulation and calculation process of the reflected light in this application.

[0025] In this embodiment, the internal structure of the silicon photonics module is as follows: Figure 3 As shown. The left side of the silicon photonics module feeds back the corresponding data signal of the detected reflected light to the data processing and controller for demodulation and calculation. The right side of the silicon photonics module... Figure 2 The single-mode or multimode optical fiber shown connects each optical core in the fiber to a separate optical fiber, such as... Figure 1 The sensor unit shown is fixed at the corresponding coordinate position of the target detection to realize real-time detection of triaxial acceleration at different detection positions.

[0026] Each of the aforementioned silicon photonic sensors can employ the following internal optical structure: Figure 4 The scheme shown uses modern silicon photonics technology to form highly integrated small mass blocks inside each sensing unit, and encodes the reflectivity at different positions on its surface to superimpose the position information of the reflection point into the reflected light.

[0027] The novel triaxial fiber optic accelerometer based on silicon photonics microstructures provided in this embodiment may include: 1. At least one single-mode optical fiber is used to transmit the laser modulation signal to the sensor and the triaxial echo signal back to the demodulation end; 2. A coupling assembly connected to the single-mode optical fiber, used to direct the incident light at a predetermined ratio. Figure 4 The optical paths shown are distributed to three optical paths, X, Y, and Z, and the echo light from the three optical paths is combined back into the single-mode fiber. 3. Three silicon-based MEMS micromirrors are arranged between the coupling component and the reflective mass. These micromirrors may employ gold-plated reflective surfaces, adjusting their reflection angle relative to the reflective mass in response to a voltage electrostatic field. The point-type fiber optic silicon optical accelerometer on the right is a passive sensor that requires no power supply in the field.

[0028] This silicon-based MEMS micromirror first converts the light energy fed by the optical fiber into electrical energy through a silicon photodetector embedded in the silicon substrate. This electrical energy is then supplied to corresponding boost and control circuits to realize a cyclic fixed-frequency scanning drive unit controlled by a preset detection cycle. The periodically changing electrostatic force generated by this unit induces movement in the micromirror structure, causing displacement of the micromirror assembly. This mechanical movement of the micromirror alters the optical path of the incident light fed by the optical fiber, periodically reflecting the incident light to the corresponding surface of the mass block. The reflected light from the mass block is then transmitted back to the optical fiber via a coupler, thus transmitting the detection signal. The silicon-based MEMS micromirror preferably uses an electrostatic drive method because the circuit units required for the photoelectric conversion and electrostatic drive can be integrated into the chip, seamlessly integrating with other components in the silicon substrate. These drivers generate relatively small electrostatic forces, resulting in low power consumption and less susceptibility to external electromagnetic influences.

[0029] Thus, they correspond to the X-axis optical path, Y-axis optical path, and Z-axis optical path, respectively. The three micromirrors swing synchronously at a fixed frequency under the drive of the control circuit, which is used to open or close the corresponding optical path within their respective predetermined time windows. 4. A reflective mass block, which is elastically connected to the silicon substrate through an elastic cantilever or support beam, and can undergo small displacements relative to the silicon substrate in three mutually orthogonal directions of X, Y, and Z. The above-mentioned elastic structure corresponds to an equivalent spring stiffness in each direction of the mass block. In this reflective mass block, at least three mutually orthogonal surfaces are respectively set Figure 4 The reflectivity gradient structure is used to encode the optical power of reflected light in the plane by taking these three surfaces as the X, Y and Z surfaces respectively and utilizing the monotonic change of their reflectivity along their respective coordinate directions.

[0030] The reflectivity gradient distribution can be achieved by depositing a multilayer dielectric coating on the surface, gradually adjusting the thickness of the metal thin film on the surface, using micro / nano structures on the surface, or a combination of the above methods, to construct a corresponding continuous gradient reflectivity region. In the reflective mass block, the reflective region of each mutually orthogonal surface can be equally divided into at least 4096 small cells. Within each cell, the reflectivity of the reflective mass block surface structure increases or decreases linearly within a reflectivity intensity range of 10% to 90%. The step size of this reflectivity gradient change can be set according to the reflectivity level or the width of the mass block.

[0031] On each surface, the reflectivity function along the corresponding coordinate direction s Within the working region, it can be approximated as linear: in The initial reflectivity of this axis. This represents the reflectivity gradient along the axis.

[0032] The reflectivity gradient can be designed to vary from 10% to 90%, and can be achieved through micro-gradation of the process to achieve 2¹² (4096 levels) or 2¹ 6 The effective resolution is 65,536 levels. The more levels of resolution, the higher the accuracy of acceleration detection in this application.

[0033] Since the reflective mass can be equivalent to a mass-spring system in every coordinate direction, taking the X-axis as an example, its dynamic equation is: in, For the equivalent mass in the X direction, For the equivalent stiffness in the X direction, The damping coefficient is... Let X be the linear acceleration in the X direction. Under low-frequency or static operating conditions, the inertial force and spring force can be approximated as being in balance, and the damping effect can be neglected, resulting in: in Let g be the X-axis acceleration. ≈9.81 m / s^2 is the gravitational acceleration constant.

[0034] Similarly, on the Y and Z axes: Therefore, the X, Y, and Z optical paths of the sensor can project the incident light from the corresponding micromirrors onto the X, Y, and Z surfaces of the mass block, respectively, and couple the reflected light rays with different reflected light powers back to the single-mode fiber through the original optical path. Thus, through the photodetector and data processing unit at the demodulation end, under the condition of known micromirror open-circuit rhythm, the change in echo light power is extracted in a split axis, and the acceleration values ​​in the X, Y, and Z directions are calculated according to the pre-calibrated sensitivity coefficient.

[0035] The specific calculation process takes the displacement of the mass block along a certain axis as an example: the gradient encoding surface of the corresponding reflectivity is translated as a whole in that direction, which is equivalent to a change in the coordinates of the light spot on the reflectivity gradient. Taking the X-axis as an example, the position of the light spot under no acceleration is... The reflectance is: Acceleration in the X direction Under the action, the mass block is displaced Then, the position of the light spot changed The corresponding reflectance is: It can be seen that within the working range, there is a linear relationship between reflectivity and acceleration.

[0036] Similarly, the results for the Y and Z directions are as follows: Based on the above mapping relationship, this application can obtain the optical power incident on the X-plane of the mass block as: At that time, the total optical coupling efficiency and loss coefficient corresponding to the optical path on that axis are: In this case, the echo power is: Substituting the above formula, we get: in It can be determined as a fixed factory-calibrated constant by measuring the total optical coupling efficiency and loss of the optical path.

[0037] Therefore, by measuring the echo power, the X-axis acceleration can be directly calculated: The same applies to the Y and Z axes: .

[0038] Therefore, the linear correspondence between the acceleration component in any axial direction and the echo power can be obtained as follows: ,in, The axial direction representing acceleration, for The optical power of the reflected echo in the axial direction for The optical power of the detection ray incident along the axial direction. These are the factory calibration constants. Therefore, by calculating the intensity of the reflected light signal through the processing unit, real-time acceleration data in all directions on the sensor side are obtained.

[0039] The structure and principle of a single triaxial sensor are illustrated below with another embodiment.

[0040] In the sensor provided in this embodiment, each sensing axis corresponds to a silicon-based MEMS micromirror. The micromirror is driven by electrostatic force, with its surface oscillating relative to the silicon substrate around a torsion beam. The driving frequency can be set to 4kHz or other fixed frequencies. The three micromirrors operate synchronously under the drive of a control circuit, and their operation includes, but is not limited to: In its simplest form, it acts as a switch in its respective optical path, maintaining a certain angle within a certain time window to ensure that the light beam stably illuminates the corresponding coding surface, thereby measuring the axis. Alternatively, it can also vibrate slightly within the window in a small sine or square wave manner to achieve phase-locked amplification or self-test calibration.

[0041] Regardless of the control method used, the driving power of the micromirror can be obtained through the photoelectric conversion unit in the sensor: a small portion of the incident light power is allocated to the photodiode, which is then boosted by the circuit to power the electrostatic drive electrode, without the need for an external power supply.

[0042] In this application, the micromirror can be electrostatically driven, inducing microstructure movement by applying electrostatic force. This electrostatic force is generated from charged components (typically...). Figure 5 The electrostatic driver (ESD) generates an attractive or repulsive force between the electrodes and the movable mirror (as shown), causing the micromirror structure to shift or deflect at an angle, thus achieving the mechanical movement required for light reflection. This ESD driver can be integrated into a chip, seamlessly integrating with other components, and the electrostatic forces generated by these drivers are relatively small, resulting in low power consumption.

[0043] After connecting the silicon photonics module and multi-point sensing device to the demodulation end respectively, the feeding and detection of light can be realized. Specifically, this embodiment can construct a silicon photonics module with the following units using silicon photonics integration technology: 1. 1550nm laser and modulation control circuit; 2. Silicon-based circulators or waveguide couplers are used to separate the outgoing and returning light. 3. Multi-channel photodetector array; 4. Interface circuit for connecting to external data processing and controllers.

[0044] Each silicon photonics module constructed based on the above units can be connected to multiple triaxial fiber optic accelerometers via multi-core optical cables for engineering communication, enabling multi-channel series or parallel deployment. With fiber optic attenuation of approximately 0.2 dB / km, long-distance deployment over distances of several kilometers or even tens of kilometers is possible.

[0045] The triaxial fiber optic accelerometer connected to the end of the fiber optic cable provides the detection light fed into the corresponding optical path through the fiber optic connector and the 1×3 coupling assembly 2. The silicon-based triaxial MEMS structure 3 in the optical path is based on a reflective mass block 31, an elastic support beam 32, an X-axis micromirror 33, a Y-axis micromirror 34, and a Z-axis micromirror 35. Through small lenses or folding mirrors 4 on the three optical paths, the incident light is adjusted and the return light is coupled. Because the reflectivity gradient distribution is unidirectionally arranged on the reflective mass block, in situations such as Figure 2 On the reflective mass block 31, which has an approximate cubic structure, its three mutually orthogonal surfaces can be defined as the X-plane, Y-plane, and Z-plane, respectively. The mass block is suspended from the silicon substrate by four or more elastic support beams 32, thereby achieving a slight translation relative to the silicon substrate in the X, Y, and Z directions as the orientation of the detection position changes.

[0046] Taking the X-plane as an example, a reflectivity gradient film is etched or deposited on the X-axis, so that the reflectivity changes approximately linearly from R_{x,min} to R_{x,max} in the working region; similar gradient films are formed on the Y-plane and Z-plane along the corresponding axes, respectively.

[0047] The optical path and measurement principle of each axis can be found in the following references. Figure 3 As shown, the optical signal in single-mode fiber 1 is split off by a 1×3 coupling component 2 to form an X-axis incident light X1. The incident light is collimated by a small lens 4 and then incident on an X-axis micromirror 33. The micromirror reflects the beam and projects it onto the X-plane of the mass block. The reflected light X2 returns along the original path, is coupled back into the single-mode fiber via the X-axis micromirror 33 and the 1×3 coupling component 2, and is then transmitted to the demodulation end.

[0048] During normal operation, the X-axis micromirror 33 oscillates periodically at a fixed frequency (e.g., 4kHz) under the drive of the control circuit. Its sweep angle range is designed to be a small angle interval to ensure that the spot always falls within the linear working area of ​​the X-plane. A brief self-test window can also be set within one cycle to calibrate the zero-point drift.

[0049] The mass block is subjected to external acceleration in the X direction Effect, its displacement From the formula Given. Due to the existence of a reflectivity gradient on the X-plane. The coordinates of the light spot on the surface shift along with the mass block, directly causing the reflectivity obtained by the silicon photonics module to change from... Change to Both conditions are met: The echo power is: Therefore, the demodulation end can determine the demodulation value based on the measured data. Obtained using factory calibration and It can be obtained in real time .

[0050] The optical paths along the Y and Z axes are similar to those along the X axis. Y-axis micromirror 34 and Z-axis micromirror 35 are used to control the beam's illumination of the Y and Z surfaces of the mass block, respectively. The corresponding reflectivity gradient functions are... , The relationships between echo power and acceleration are as follows: This allows for the calculation of acceleration data along the corresponding axes.

[0051] In this embodiment, the three micromirrors can be driven synchronously at the same frequency, or they can be time-division multiplexed in different phase windows to facilitate the demodulation end to process them separately according to time slices.

[0052] The reflectivity grading structure of the mass block surface in this application is described below with reference to another embodiment: In this embodiment, the reflectivity gradient film achieves discrete gradation through discrete control of the thickness of multiple dielectric films. The effective length of the X-plane is divided into 4096 equidistant cells, with the reflectivity of each cell increasing linearly within the range of 10% to 90%. Similarly, the Y-plane and Z-plane can use the same or different numbers of gradations. Because the reflectivity gradation is sufficiently fine, combined with the size and displacement range of the light spot, it can still be considered as an approximately linear gradient overall; at the same time, the gradation characteristics can also be used to achieve absolute position encoding when needed.

[0053] Therefore, this application can utilize the built-in light source, circulator, photodetector, and signal processing circuitry of the silicon photonics module at the demodulation end to achieve the output of the detected light and the reception of its reflected light. The light source outputs continuous or pulsed laser light, which is sent to the sensor via optical fiber. The echo light signal is recorded separately by a three-channel photodetector or by time-division sampling.

[0054] When the sensor leaves the factory, an acceleration of ±1g is applied, and the optical power of each axis in different directions is measured. Then, using a pre-calibrated linear fitting relationship, a correspondence between the reflected light power and the acceleration can be established based on the power variation of the reflected light. In actual use, the acceleration value corresponding to each direction can be obtained by substituting the measured values ​​into the linear formula.

[0055] The sensor structure implemented by the above embodiments can be used in a multi-point distributed triaxial monitoring system.

[0056] like Figure 4 As shown, three silicon-based MEMS micromirrors operate via electrostatic force at frequencies ranging from 1 kHz to 20 kHz, working synchronously at the same frequency. Each micromirror oscillates in a small-amplitude sinusoidal manner within its respective time window. This oscillation, achieved through lock-in amplification, maximizes the optical signal before filtering out background noise, thereby suppressing Gaussian random noise and improving the signal-to-noise ratio of the echo optical power measurement. The sensor internally incorporates a photoelectric conversion circuit to convert a portion of the incident light power into electrical energy to electrostatically drive the silicon-based MEMS micromirrors.

[0057] by Figure 5 Taking the MEMS micromirror driving system shown as an example: MEMS micromirrors (also known as "micromirrors" or "scanning mirrors") are optical MEMS devices that can drive micromechanical structures with electrical signals to precisely deflect, modulate, open, close, and phase-control light beams, exhibiting extremely high response speeds. MEMS micromirrors can be driven by electrostatic, electromagnetic, piezoelectric, and electrothermal methods.

[0058] Electrostatic actuators induce movement of microstructures within a micromirror by applying electrostatic forces. These forces arise from attractive or repulsive forces between charged components (typically electrodes and movable mirrors), causing displacement and achieving the desired mechanical motion. Electrostatic actuators are favored because they can be integrated onto a chip, seamlessly integrating with other components. These actuators generate relatively small electrostatic forces, resulting in low power consumption.

[0059] Figure 5In the driving system described in the example, the electrostatic force driving the micromirror to deflect is achieved by the upper and lower driving electrodes acting on a movable plate formed by the middle mirror surface. The electrostatic force acting on the micromirror approximately satisfies... Therefore, when it is necessary to adjust its "positive / negative direction", high voltage bias can usually be used. This is achieved through superimposed differential control. Specifically: This driving system can apply a fixed bias to the micromirror surface (or common electrode):

[0060] Then, the electrodes on its left and right sides output respectively: This way you can pass The electrostatic torque is approximately the same as... A proportional driving coefficient enables effective adjustment of its deflection angle and position. This driving method offers better linearity and bidirectional control, fully meeting the driving requirements of this application.

[0061] In this embodiment, several triaxial fiber optic accelerometers are connected in series to a single silicon photonics demodulation module via a multi-core optical fiber cable for engineering communication. The silicon photonics demodulation module includes a laser, an optical coupler, a photodetector, and a data processing unit. The multi-core optical fiber cable is used for optical signal transmission between the silicon photonics demodulation module and the multiple triaxial fiber optic accelerometers. Each sensor corresponds to one core of the optical fiber, or shares a core and multiplexes it in wavelength / timing. By appropriately setting the laser power, optical path allocation ratio, and demodulation time window, synchronous monitoring of hundreds of triaxial measurement points can be achieved. This is suitable for large-scale structural health monitoring scenarios such as long bridges, dams, and subway tunnels.

[0062] In summary, the triaxial fiber optic accelerometer provided in this application has the following advantages: 1. The triaxial integration constructs a reflectivity gradient on three orthogonal surfaces of the same reflective mass block and uses three micromirrors to realize three optical paths, enabling triaxial acceleration measurement to be completed on a single core or a few optical fibers, with a compact structure.

[0063] 2. Linear intensity encoding simplifies demodulation. By utilizing the linear relationship between mass block displacement and reflectivity gradient, the echo power and acceleration are approximately linear. The demodulation end only needs to perform intensity measurement and linear calculation, eliminating the need for complex interferometric phase demodulation or wavelength tracking, significantly reducing system cost and complexity.

[0064] 3. Long-distance passive sensing. Except for the low-power photoelectric conversion circuit, the sensor does not require an external power supply. All signals are transmitted through optical fiber, making it suitable for long-distance, multi-point distributed deployment and insensitive to electromagnetic interference.

[0065] 4. High sensitivity and high resolution gradation. The reflectivity gradient film can be designed with a large dynamic range of 10% to 90%, and the resolution of 4096 to 65536 levels can be achieved through processing. When combined with a high-precision photodetector, high sensitivity and high resolution acceleration measurement can be achieved.

[0066] 5. Good process compatibility. The mass block, elastic support, and micromirrors can all be fabricated using silicon-based MEMS technology, making them easy to integrate with silicon waveguides, integrated photodetectors, and other devices on the same chip or in the same package, offering excellent manufacturability and cost advantages.

[0067] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A triaxial fiber optic accelerometer based on silicon photonics microstructures, characterized in that, Including those set in the silicon substrate: The coupling component connects to the optical fiber externally and distributes the detection light provided by the optical fiber into three mutually orthogonal detection optical paths internally. Each detection optical path is configured separately: A silicon-based micromirror receives one of the detection beams, directs it onto one side surface of a reflective mass, receives the reflected beam from the reflective mass, and feeds the reflected beam back into an optical fiber via a coupling component. The reflective mass block is elastically supported inside the sensor, and a monotonically varying reflectivity gradient distribution is set on its mutually orthogonal surfaces along the incident direction of the detection light on that side.

2. The triaxial fiber optic accelerometer based on silicon photonics microstructure as described in claim 1, characterized in that, The silicon-based micromirror is disposed in a silicon substrate and has a gold-plated reflective surface. The reflective surface adjusts the reflection angle relative to the reflective mass block in response to a voltage electrostatic field.

3. The triaxial fiber optic accelerometer based on silicon photonics microstructures as described in claim 1, characterized in that, The reflective mass block has a cubic structure and is elastically connected to the silicon substrate of the sensor through an elastic cantilever or support beam. It is suspended and held in the sensor and can move relative to the silicon substrate around it as the sensor rotates.

4. The triaxial fiber optic accelerometer based on silicon photonics microstructure as described in claim 3, characterized in that, The reflective mass block constructs a gradient-distributed continuous reflectivity region by setting a multilayer dielectric coating on its surface, or by gradually adjusting the thickness of the metal thin film on its surface, or by using micro-nano structures on its surface, or a combination of the above methods.

5. The triaxial fiber optic accelerometer based on silicon photonics microstructure as described in claim 4, characterized in that, The reflectivity gradient of the surface of the reflective mass block ranges from 10% to 90%.

6. The triaxial fiber optic accelerometer based on silicon photonics microstructure as described in claim 2, characterized in that, Each silicon-based micromirror corresponding to the detection optical path oscillates synchronously at a preset frequency and opens at different time period windows, so that the detection light is incident on the surface of the reflective mass block. By utilizing the reflectivity of the reflected light spot on the surface of the reflective mass block, the corresponding displacement-power component is superimposed on the reflected light. Combined with the period window of the detection optical fiber, a detection signal of acceleration in the reflection direction is formed.

7. The triaxial fiber optic accelerometer based on silicon photonic microstructures as described in claims 1-6, characterized in that, The optical fiber feeds back the sensor's detection signal to the silicon photonics module, and the silicon photonics module then feeds back the detection signal to the corresponding processing unit. The silicon photonics module includes: Fiber optic connectors are used to connect optical fibers; A circulator with a unidirectional optical path switch, a laser connected to the first port, an optical fiber connector connected to the second port, and a photodetector connected to the third port; The laser feeds detection light into the optical fiber through a circulator and an optical fiber connector; The reflected light detected by the sensor is received through an optical fiber connector and relayed by a circulator to a photodetector to extract the corresponding detection signal.

8. The triaxial fiber optic accelerometer based on silicon photonics microstructure as described in claim 5, characterized in that, In the reflective mass block, the reflective area of ​​each mutually orthogonal side surface is divided into at least 4096 equal-distance cells, and in each cell, the reflectivity of the reflective mass block surface structure is set to increase or decrease in a linear gradient distribution within the range of 10% to 90% of the reflection intensity.

9. The triaxial fiber optic accelerometer based on silicon photonic microstructures as described in claims 1-8, characterized in that, The acceleration detected by the triaxial fiber optic accelerometer in any direction is ,in, The axial direction representing acceleration, for The optical power of the reflected echo in the axial direction for The optical power of the detection ray incident along the axial direction. These are the factory calibration constants.

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