A wavelength-tuned MOEMS displacement sensor, displacement detection method and apparatus

Abstract

The application provides a wavelength-tunable MOEMS displacement sensor, a displacement detection method and device, the MOEMS displacement sensor comprising: a light source, a collimating lens, a light splitting prism, a grating and a MEMS mirror arranged in sequence along an optical path; the sensor further comprising a first light detector, a second light detector, a third light detector and a signal processing unit; the first light detector is arranged on a reference light beam exit path of the light splitting prism and used for collecting a reference light signal; the second light detector is arranged on a converging path of interference light beams generated after the grating interference cavity acts and used for collecting an interference signal; the third light detector is arranged at an ambient light receiving position of the sensor and used for collecting an ambient light signal; the signal processing unit is used for background compensation of the interference signal according to the ambient light signal, and normalization processing of the compensated interference signal according to the reference light signal, so as to obtain a corrected signal, and calculating a displacement measurement value according to the corrected signal.

Description

Technical Field

[0001] This invention relates to the field of displacement measurement technology, specifically to a wavelength-tuned MOEMS displacement sensor, displacement detection method, and device. Background Technology

[0002] Displacement measurement is a fundamental technology in the field of precision metrology, with widespread demand in scientific research such as photoacoustic spectroscopy and optical force measurement, as well as industrial applications such as high-precision positioning and automated control. Currently, displacement sensing technologies are mainly divided into two categories: electrical methods and optical methods. Electrical methods, including capacitive, inductive, and eddy current sensors, have the advantages of simple structure and easy integration, but their measurement accuracy and resistance to electromagnetic interference are relatively limited. Optical methods, such as laser interferometers and grating interferometers, have become the preferred solution for ultra-precision displacement measurement due to their advantages of non-contact measurement, high resolution, and large bandwidth.

[0003] However, traditional optical displacement sensors generally suffer from large size and low integration. This is mainly due to two reasons: first, they require discrete optical components, such as light sources, lenses, beam splitters, and mirrors, to construct complex optical paths, demanding precise alignment between components; second, the miniaturization of high-performance light sources and detectors is insufficient. Taking a typical Michelson interferometer as an example, its optical path requires multiple discrete optical adjustment mounts, resulting in a large system size and complex debugging, making it difficult to meet the miniaturization requirements of portable devices and embedded systems.

[0004] To address the aforementioned issues, researchers have proposed various integrated displacement sensing schemes based on micro-opto-electro-mechanical systems (MOEMS) in recent years. For example, Chinese patent application CN114001661A discloses an optical interferometric integrated micro-displacement sensing structure. This structure incorporates optical interferometric detection through grating coupling, using a drivable grating to add phase modulation to the interference signal, thus achieving integrated detection of micro-displacement. While this scheme has made some progress in integration, the displacement control accuracy of its drivable grating is significantly affected by driving voltage drift and ambient temperature changes. Deviations exist between the actual added phase modulation and the set value, impacting measurement stability. Furthermore, existing optical interferometric sensors typically employ an approximate linear demodulation method; when the static operating point is shifted due to interference, the measurement sensitivity and linearity decrease significantly.

[0005] Chinese patent application CN119958429A discloses a miniaturized integrated precision grating vortex interferometry displacement sensor. Its structure includes a laser diode chip, an integrated phase-modulated micro / nano metasurface, a beam splitter, a grating structure, and a photodetector array. Its core innovation lies in using a micro / nano metasurface for phase modulation, replacing the traditional bulk optical modulator and significantly reducing the system size. Simultaneously, the use of vortex interferometry improves its resistance to environmental interference. This approach represents the latest development direction for integrated optical displacement sensors; however, it still has the following limitations: First, the phase modulation depth and rate of the micro / nano metasurface are limited by the design and material properties of the metasurface structure, making it difficult to achieve large-scale, high-rate phase scanning. Second, the vortex interferometry principle requires complex signal demodulation algorithms and high data processing capabilities. Third, the high process complexity and relatively high manufacturing cost hinder large-scale application.

[0006] Furthermore, a common problem exists in existing technologies: the lack of an effective monitoring and compensation mechanism for light source wavelength drift. Traditional interferometric displacement sensors typically use fixed-wavelength laser sources. In practical applications, the laser's wavelength drift can occur due to fluctuations in injected current or changes in ambient temperature, leading to nonlinear changes in the interference signal and introducing measurement errors. Some existing technologies attempt to use tunable laser sources to extend the measurement range, but these typically only employ a single photodetector, which cannot distinguish the effects of light source wavelength drift and ambient light interference on the measurement signal. When there are changes in background light or light source wavelength drift in the measurement environment, the measurement results from a single detector cannot accurately reflect the true displacement, limiting the sensor's application in complex working conditions.

[0007] Therefore, how to improve the ability of optical displacement sensors to suppress wavelength drift and environmental interference while maintaining high integration, and to achieve high stability and high precision displacement measurement, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0008] In view of this, this application proposes a wavelength-tuned MOEMS displacement sensor, displacement detection method and device to achieve real-time suppression of light source wavelength drift, light intensity fluctuation and ambient light interference, thereby improving the sensor's measurement accuracy, stability and environmental adaptability.

[0009] Specifically, this application is implemented through the following technical solution:

[0010] According to a first aspect of the embodiments of this specification, a wavelength-tuned MOEMS displacement sensor is provided, comprising:

[0011] A light source, a collimating lens, a beam splitter, a grating, and a MEMS mirror are arranged sequentially along the optical path. The initial light beam emitted by the light source is collimated by the collimating lens to form a parallel beam that is incident on the beam splitter. The beam splitter divides the parallel beam into a measurement beam and a reference beam. The measurement beam is incident on the grating and enters the grating interference cavity formed by the grating and the MEMS mirror.

[0012] The MOEMS displacement sensor further includes a first photodetector, a second photodetector, a third photodetector, and a signal processing unit; wherein:

[0013] The first photodetector is positioned on the exit path of the reference beam of the beam splitter and is used to collect the reference light signal;

[0014] The second photodetector is positioned on the converging path of the interference beam generated after the grating interference cavity is activated, and is used to collect interference signals;

[0015] The third photodetector is located at the ambient light receiving position of the MOEMS displacement sensor and is used to collect ambient light signals;

[0016] The signal processing unit is connected to the first photodetector, the second photodetector, and the third photodetector, respectively, and is used to perform background compensation on the interference signal according to the ambient light signal, and to normalize the compensated interference signal according to the reference light signal to obtain a corrected signal, and to calculate the displacement measurement value according to the corrected signal.

[0017] According to a second aspect of the embodiments of this specification, a displacement detection method based on a MOEMS displacement sensor is provided, wherein the MOEMS displacement sensor is the MOEMS displacement sensor described in the first aspect, and the displacement detection method includes the following steps:

[0018] Step S1: Control the light source to emit a light beam to obtain the reference light signal collected by the first photodetector, the interference signal collected by the second photodetector, and the ambient light signal collected by the third photodetector;

[0019] Step S2: Perform background compensation on the interference signal based on the ambient light signal, and normalize the compensated interference signal based on the reference light signal to obtain the corrected signal;

[0020] Step S3: Calculate the displacement measurement value based on the correction signal.

[0021] According to a third aspect of the embodiments of this specification, a displacement detection device based on a MOEMS displacement sensor is provided, wherein the MOEMS displacement sensor is the MOEMS displacement sensor described in the first aspect, and the displacement detection device includes:

[0022] A light source control module is used to control the light source to emit a light beam in order to obtain a reference light signal collected by the first photodetector, an interference signal collected by the second photodetector, and an ambient light signal collected by the third photodetector.

[0023] The signal correction module is used to perform background compensation on the interference signal based on the ambient light signal, and to normalize the compensated interference signal based on the reference light signal to obtain the corrected signal.

[0024] The displacement calculation module is used to calculate the displacement measurement value based on the correction signal.

[0025] The embodiments of this application have at least the following technical effects:

[0026] First, by setting up a first photodetector to monitor the wavelength drift and intensity fluctuation of the light source in real time, and combining it with the normalization processing of the signal processing unit, the effect of light source instability on the measurement results is effectively eliminated, and the measurement accuracy and stability are significantly improved.

[0027] Second, this application implements a method that collects ambient light signals by setting a third photodetector, performs background compensation on the interference signals, eliminates ambient light interference, and enhances the sensor's adaptability under complex working conditions.

[0028] Third, this application adopts an integrated optical path design, integrating the light source, collimating lens, beam splitter prism, grating, MEMS mirror and photodetector on the same optical platform. The structure is compact and the size is small, making it easy to realize system integration and engineering applications. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Some specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings indicate the same or similar parts or components. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0030] Figure 1 This is a schematic diagram of the optical path structure of a wavelength-tuned MOEMS displacement sensor, as shown in an exemplary embodiment of this application.

[0031] Figure 2 This is a schematic diagram illustrating the principle of a grating interference cavity according to an exemplary embodiment of this application;

[0032] Figure 3This is a LIV characteristic curve of a laser shown in an exemplary embodiment of this application;

[0033] Figure 4 This is a schematic diagram illustrating a current-tuned wavelength according to an exemplary embodiment of this application;

[0034] Figure 5 This is a schematic diagram illustrating the periodicity of an interference signal under wavelength tuning, as shown in an exemplary embodiment of this application.

[0035] Figure 6 This is a spectrum of a semiconductor laser under a 5mA drive current, as illustrated in an exemplary embodiment of this application.

[0036] Figure 7 This is a schematic diagram illustrating the working state of three photodetectors in an exemplary embodiment of this application;

[0037] Figure 8 This is a schematic diagram illustrating a current-tuned phase modulation principle according to an exemplary embodiment of this application;

[0038] Figure 9 This is a schematic flowchart illustrating a displacement detection method based on a MOEMS displacement sensor, as shown in an exemplary embodiment of this application.

[0039] Figure 10 This is a block diagram illustrating a displacement detection device based on a MOEMS displacement sensor, as shown in an exemplary embodiment of this application. Detailed Implementation

[0040] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0041] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0042] The embodiments described in this specification will now be described in detail.

[0043] This application provides a wavelength-tuned MOEMS displacement sensor, such as... Figure 1 As shown, the MOEMS displacement sensor includes: a light source 1, a collimating lens 2, a beam splitter 6, a grating 7, and a MEMS reflector 8 arranged sequentially along the optical path.

[0044] The collimating lens 2 is positioned in the light emission direction of the light source 1, and the beam splitter 6 is located on the light emission side of the collimating lens 2.

[0045] The light beam emitted by the light source 1 is collimated by the collimating lens 2 to form a parallel beam that is incident on the beam splitter 6. The beam splitter 6 splits the parallel beam into a measurement beam and a reference beam. The measurement beam is incident on the grating 7 and enters the interference cavity formed by the grating 7 and the MEMS mirror 8.

[0046] In practical applications, the beam splitter 6 can divide the parallel beam into a measurement beam and a reference beam according to a preset ratio, such as dividing it into a 90% measurement beam and a 10% reference beam.

[0047] refer to Figure 7 When the measurement beam is incident on the grating 7, part of the light is directly diffracted and reflected by the grating strips, forming a multi-order diffracted beam; the other part of the light passes through the gaps in the grating and diffracts to the MEMS mirror 8, is reflected by the MEMS mirror 8 and returns, passing through the surface of the grating 7 again to form a multi-order diffracted beam. The diffracted beams of the same order in these two parts of reflected light interfere with each other, forming an interference beam.

[0048] In some possible implementations of this embodiment, the light source is a vertical cavity surface-emitting laser.

[0049] In this embodiment, the MOEMS displacement sensor further includes a first photodetector 3, a second photodetector 4, and a third photodetector 5. In this embodiment, three photodetectors are positioned above and below the grating 7 and to the right of the beam splitter 6. The three photodetectors respectively detect the coherent interference light reflected by the grating and MEMS mirror and the light from the upper and lower sides, as well as the reference light from one side of the beam splitter 6. Specifically:

[0050] The first photodetector 3 is positioned on the reference beam exit path of the beam splitter 6 to collect reference light signals in order to monitor the wavelength changes and intensity fluctuations of the light source in real time.

[0051] The second photodetector 4 is positioned on the converging path of the interference beam generated after the interference cavity is activated, and is used to collect interference signals;

[0052] The third photodetector 5 is located at the ambient light receiving position of the MOEMS displacement sensor and is used to collect ambient light signals.

[0053] In some possible implementations of this embodiment, the first photodetector, the second photodetector, and the third photodetector are photodiodes.

[0054] For example, such as Figure 3 As shown, the vertical-cavity surface-emitting laser has an output power of 2mW and a center wavelength of 850nm, and is driven by a constant power circuit to maintain stable output light intensity. The photodiode has a photosensitive area of ​​φ0.1mm, a spectral response range of 320~1000nm, and a typical dark current of 1pA under a 2V reverse bias voltage, exhibiting low noise and high sensitivity.

[0055] The MOEMS displacement sensor in this embodiment also includes a signal processing unit. The signal processing unit is connected to a first photodetector, a second photodetector, and a third photodetector, respectively. It is used to perform background compensation on the interference signal based on the ambient light signal to eliminate interference from ambient background noise, and to normalize the compensated interference signal based on a reference light signal to obtain a corrected signal, thereby eliminating measurement errors caused by light source wavelength drift and intensity fluctuations. Finally, it calculates the displacement measurement value based on the corrected signal to improve the accuracy of the displacement measurement results.

[0056] like Figure 2 As shown, when the measurement beam is incident on grating 7, part of the light is directly diffracted and reflected by the grating strips, forming a multi-order diffracted beam; another part of the light passes through the grating gaps and diffracts to the MEMS mirror, is reflected back by the MEMS mirror, and then passes through the grating surface again to form a multi-order diffracted beam. The diffracted beams of the same order in these two reflected beams interfere, forming an interference beam. The intensity of this interference beam is related to the period of the grating and the distance between the grating and the MEMS mirror; when the distance changes, the intensity of the interference beam changes accordingly.

[0057] Therefore, when using the MOEMS displacement sensor of this embodiment for displacement measurement, the MEMS reflector is attached to the surface of the object being measured. When the object undergoes slight movement, vibration, or deformation, the reflector will move synchronously with the object, causing a change in the optical path difference of the incident light. The reflector moves synchronously with the object, causing a change in the optical path difference between the emitted light and the reflected light. By detecting the amount of change in the optical path difference, the actual displacement change of the object can be determined.

[0058] In some embodiments, the signal processing unit includes:

[0059] A differential circuit is used to remove the ambient light signal from the reference optical signal and the interference signal, respectively.

[0060] The division circuit is used to divide the interference signal after removing the ambient light signal by the reference light signal after removing the ambient light signal to obtain the ratio signal;

[0061] The multiplication circuit is used to multiply the ratio signal by the average output light intensity of the light source and output a correction signal.

[0062] In some embodiments, the light source is a current-tunable laser to change the output wavelength by adjusting the injection current.

[0063] The MOEMS displacement sensor in this embodiment also includes:

[0064] A wavelength tuning unit, connected to the light source, is used to modulate the injected current of the light source so that the output wavelength of the light source changes periodically.

[0065] A lock-in amplifier, whose signal input terminal receives the correction signal and whose reference input terminal receives a reference signal with the same modulation frequency as the injected current, is used to coherently demodulate the correction signal and output a displacement-related DC signal.

[0066] The signal processing unit is used to calculate the displacement measurement value based on the DC signal output by the lock-in amplifier.

[0067] The MOEMS displacement sensor provided in this application embodiment is based on the grating interferometer cavity sensing principle, combined with wavelength tuning technology and a three-detector collaborative compensation mechanism to achieve high-precision displacement measurement.

[0068] To more clearly illustrate the working principle of the MOEMS displacement sensor and the theoretical basis of its signal processing method, the measurement model of the sensor is derived below using grating interferometry theory. This theoretical analysis reveals the functional relationship between the interference signal intensity and the measured displacement, and quantitatively explains the influence mechanism of light source wavelength drift, light intensity fluctuation, and ambient stray light on measurement accuracy, thus providing theoretical support for the three-detector collaborative compensation scheme proposed in this application.

[0069] When the period of the grating and the length of the grating interference cavity are large enough to meet the application requirements, the complex amplitude can be expressed by scalar diffraction theory as follows:

[0070] (1)

[0071] In this formula, The complex amplitude of the diffraction signal. It is the laser source wave vector. It is a normalization constant. It is the transfer function of the grating. ,in and These are the incident angle and the diffraction angle, respectively. It is the transfer function of the grating over one period. It is the period of the grating, and N is the total number of periods of the grating.

[0072] The transfer function F of the grating over one period can be expressed as:

[0073] (2)

[0074] In formula (2) , The initial cavity length between the grating and the mirror. These are displacement measurements. This is the new distance between the mirror and the grating after the object has moved.

[0075] When the light beam is incident perpendicularly to the grating, we have ,and Then it can be deduced that... Combined with incident complex amplitude The complex amplitude of diffraction within one period can be rewritten as:

[0076] (3)

[0077] The intensities of different interference diffraction orders can be obtained from the following formula:

[0078] (4)

[0079] Therefore, the expression for the intensity of the nth-order interference diffraction can be derived:

[0080] (5)

[0081] Let be the incident light intensity. This equation shows the relationship between the shift of the interference diffraction order and the intensity. From this equation, we can derive... The function relating intensity and displacement in order-order interferometric diffraction is as follows:

[0082] (6)

[0083] (7)

[0084] (8)

[0085] In practical applications, to improve resolution, the effects of environmental noise and intensity fluctuations of the laser source itself must be considered. For example, The detected interference signal, The cavity length is calculated. Based on formula (7), the following conclusion can be drawn:

[0086] (9)

[0087] like To achieve the ideal input light intensity, For ideal light intensity detection. If the displacement remains constant, then and All are constants. If we consider the fluctuations in the laser source, the intensity of the light after the laser source fluctuations is... ,and Fluctuations will lead to The fluctuation can be represented as In addition, there is ambient stray light from other optical components. Too and Factors that cause fluctuations. It is generally considered a constant, however, and All are variables, affected by random fluctuations caused by environmental conditions and the laser source itself. The calculated displacement error can be expressed as:

[0088] (10)

[0089] To minimize displacement error, the following measures should be taken: Correction measures, but due to fluctuation components It is not suitable to use it directly as a normalization benchmark, therefore a correction factor is introduced. Using total incident light intensity Perform normalization correction so that the corrected signal satisfies:

[0090] (11)

[0091] In the MOEMS displacement sensor of this embodiment, since a beam-splitting prism is set in front of the grating interference cavity as a beam splitter, a portion of the incident laser enters the grating interference cavity and is detected by the second photodetector, abbreviated as Exemplary .

[0092] Another portion of the incident laser is detected by the first photodetector, abbreviated as... .because and From the same laser source, therefore and Proportional. Therefore It can be represented as M is the scaling factor of the optical path.

[0093] The third light detector detects ambient light, abbreviated as... Under experimental conditions, the three photodetectors were tightly fixed together to ensure they were under the same lighting conditions, meaning... .

[0094] The MOEMS displacement sensor in this embodiment also includes a signal conditioning circuit, which first modulates the interference signal... and reference optical signal Subtract ambient light respectively To reduce the impact of ambient light, the two signals are then fed into a divider. Under the given assumptions, the signal processed by the differencer and divider can be expressed as:

[0095] (12)

[0096] In some embodiments, the reference signal for the spectral dispersion is also processed by a filtering circuit and an averaging circuit to obtain the value of the input intensity.

[0097] The signal conditioning circuit obtains the corrected signal through a multiplier: .in, The average value of the light intensity fluctuation component of the light source is obtained by low-pass filtering or moving average processing of the light intensity signal of the reference optical path after subtracting ambient light, which characterizes the slow power drift of the light source caused by factors such as temperature, driving current or aging.

[0098] Divide the corrected signal by the signal The correction coefficient can be obtained. for:

[0099] (13)

[0100] If the number of experimental samples is large enough, then The assumption is then satisfied, that is to say It is obvious. When the scaling factor M is adjusted to 1, the expression for the revised signal is as follows:

[0101]

[0102]

[0103] (14)

[0104] Substituting the correction signal into equation (10), the theoretical displacement error can be obtained as follows:

[0105] (15)

[0106] Due to system and environment, light intensity and The fluctuations change synchronously, therefore it can be approximated as follows:

[0107] (16)

[0108] Thus, it can be deduced that Approximately equal to 0.

[0109] The above theoretical derivation shows that, under ideal conditions, as shown in formulas (6) to (8), the interference signal intensity and the measured displacement satisfy a definite cosine or sine function relationship. However, in actual measurements, the intensity fluctuation of the laser source... and ambient stray light This will directly lead to distortion of the interference signal, thereby introducing displacement measurement error as shown in formula (10). Traditional single detector schemes cannot distinguish between useful signals and interference components. However, this application sets up three photodetectors to collect interference signals, reference light signals and ambient light signals respectively, and introduces correction coefficients for differential normalization processing. Theoretically, the displacement error can be reduced to near zero, proving that the MOEMS displacement sensor of this application can significantly improve measurement accuracy.

[0110] Traditional grating interference cavities typically use piezoelectric ceramics (PZT) to drive the grating or mirror, causing periodic minute changes in the cavity length, thereby modulating the phase of the interference light and facilitating the extraction of weak displacement signals by a lock-in amplifier.

[0111] Unlike traditional solutions, such as Figure 8 As shown, this embodiment achieves phase modulation by periodically modulating the injected current into the laser and using wavelength tuning, with a sinusoidal modulation wavelength output from the tunable laser. Phase modulation of the grating interference cavity is achieved by introducing phase changes through altering the laser wavelength. The waveform generator outputs the modulation signal, simultaneously driving the laser wavelength tuning unit and the lock-in amplifier to ensure synchronization between the modulation and the reference signal. Figure 4 This refers to the wavelengths corresponding to this laser in the 2mA-6mA range. Figure 5 This is a schematic diagram of the periodicity of the interference signal. Figure 6 This is the spectral distribution corresponding to 5 mA.

[0112] Wavelength sinusoidal modulation with time can be expressed as:

[0113] (17)

[0114] in, The center wavelength of the laser. For wavelength modulation amplitude, The angular frequency of the modulated waveform.

[0115] The total phase of the grating interference cavity is determined by both the cavity length and the wavelength.

[0116] (18)

[0117] Under the small modulation amplitude approximation, the additional phase introduced by wavelength modulation can be expressed as:

[0118] (19)

[0119] Where D is the phase modulation depth of the wavelength modulation, satisfying .

[0120] The intensity of the first order diffracted light in an interference diffraction order can be described as follows:

[0121] (20)

[0122] Using Bessel series expansion and trigonometric function transformations, formula (20) can be rewritten as:

[0123] (twenty one)

[0124] Collected by the second photodetector After the signal is processed by the signal conditioning circuit, a correction signal is generated. Due to circuit noise and environmental interference during the actual detection process, the correction signal sent to the lock-in amplifier is superimposed with narrowband Gaussian noise, which can be described as:

[0125] (twenty two)

[0126] Where S is the responsivity of the second photodetector, and Ω is the gain of the signal conditioning circuit in the frequency band. Within, the power spectral density of n(t) is equivalent to Narrowband noise can be decomposed into n(t), where and They are two independent low-frequency stationary random processes.

[0127] because The signal contains noise and is an AC signal, which cannot be directly used for displacement demodulation; therefore, a reference signal is required. A synchronization reference is provided for coherent extraction. The reference signal sent to the lock-in amplifier is... , where R is the amplitude of the reference signal. This reference signal Generated by the system modulation drive circuit or local oscillator signal source, it has the same frequency and origin as the modulation frequency of the signal under test. The purpose is to enable the lock-in amplifier to sensitively extract only the component to be measured that is in phase and frequency with the reference signal, suppress incoherent noise, and thus achieve high signal-to-noise ratio detection of weak signals and pass them through the lock-in amplifier.

[0128] Under certain conditions, the output signal of the lock-in amplifier For composite signals:

[0129] (twenty three)

[0130] Because of the low-pass filter in the lock-in amplifier, if the displacement remains constant and the cutoff frequency of the low-pass filter is appropriate, the output voltage will be a DC signal:

[0131] (twenty four)

[0132] Due to ideal incident light intensity The signal will drift with fluctuations in light source intensity, temperature changes, and operating conditions, and cannot be directly used as a stable parameter for displacement demodulation. Based on the three-detector intensity compensation principle mentioned above, in order to eliminate measurement errors caused by fluctuations in light source intensity and interference from ambient light, differential normalization processing is performed on the measured signals from the three detectors.

[0133] In this embodiment, the corrected signal after ambient light removal and reference light normalization can accurately reflect the proportional relationship between the interference signal after removing environmental interference and the real-time intensity of the light source, and is independent of incident light intensity fluctuations. Therefore, the corrected signal of this embodiment replaces the one in formula (24). This yields the compensated output signal after eliminating intensity disturbances.

[0134] (25)

[0135] When the total system gain coefficient is , When the function is a first-order Bessel function of the first kind with D as the independent variable, the simplified relationship between the final output and the displacement is:

[0136] (26)

[0137] By performing inverse trigonometric function operations on formula (26), the displacement measurement formula can be directly solved as follows:

[0138] (27)

[0139] In summary, the embodiments of this application, by introducing current-tuned wavelength technology and combining a three-detector collaborative compensation mechanism with phase modulation technology, effectively suppress system noise, improve the signal-to-noise ratio and measurement accuracy of the displacement sensor, and obtain highly accurate displacement measurement values. In other words, the technical solution of this application achieves at least the following technical effects:

[0140] First, by setting up a first photodetector to monitor the wavelength drift and intensity fluctuation of the light source in real time, combined with the normalization processing of the signal processing module, the influence of light source instability on the measurement results is effectively eliminated, and the measurement accuracy and stability are significantly improved.

[0141] Second, by setting up a third photodetector to collect ambient light signals and performing background compensation on the interference signals, ambient light interference is eliminated, enhancing the sensor's adaptability under complex working conditions.

[0142] Third, by using a wavelength-tunable laser as the light source, interference signals are acquired through wavelength periodic modulation scanning, and the data is fused with lock-in amplification signal processing technology, which can further identify and eliminate the inherent errors of the optical system and achieve high-precision displacement measurement.

[0143] Fourth, it adopts an integrated optical path design, integrating the light source, collimating lens, beam splitter prism, grating, MEMS mirror and photodetector on the same optical platform. It has a compact structure and small size, making it easy to achieve system integration and engineering applications.

[0144] This application also provides a displacement detection method based on a MOEMS displacement sensor. The structure and function of the MOEMS displacement sensor can be referred to in the previous related embodiments, and will not be repeated here. Figure 9 This is a schematic flowchart illustrating a displacement detection method based on a MOEMS displacement sensor, as shown in an exemplary embodiment of this application. Figure 9 As shown, the displacement detection method of this embodiment includes at least the following steps:

[0145] Step S1: Control the light source to emit a light beam to obtain the reference light signal collected by the first photodetector, the interference signal collected by the second photodetector, and the ambient light signal collected by the third photodetector;

[0146] Step S2: Perform background compensation on the interference signal based on the ambient light signal, and normalize the compensated interference signal based on the reference light signal to obtain the corrected signal;

[0147] Step S3: Calculate the displacement measurement value based on the correction signal.

[0148] In some embodiments, the light source is a current-tunable laser, and step S1 includes:

[0149] The injected current of the light source is modulated so that the output wavelength of the light source changes periodically;

[0150] Step S3 includes:

[0151] Based on a reference signal with the same modulation frequency as the injected current, the correction signal is coherently demodulated by a lock-in amplifier to output a displacement-related DC signal; the displacement measurement value is calculated based on the DC signal output by the lock-in amplifier.

[0152] In some embodiments, step S2 includes:

[0153] The ambient light signal is removed from the reference light signal and the interference signal respectively; the interference signal after removing the ambient light signal is divided by the reference light signal after removing the ambient light signal to obtain a ratio signal; the ratio signal is multiplied by the average output light intensity of the light source to obtain a correction signal.

[0154] In some embodiments, the MEMS mirror is attached to the surface of the object being measured during displacement detection.

[0155] This application also provides a displacement detection device based on a MOEMS displacement sensor. The structure and function of the MOEMS displacement sensor can be referred to in the previous related embodiments, and will not be repeated here. Figure 10 This is a block diagram illustrating a displacement detection device based on a MOEMS displacement sensor, as shown in an exemplary embodiment of this application. Figure 10 As shown, the MOEMS displacement detection device in this embodiment includes: a light source control module 101, a signal correction module 102, and a displacement calculation module 103;

[0156] The light source control module 101 is used to control the light source to emit a light beam in order to obtain a reference light signal collected by the first photodetector, an interference signal collected by the second photodetector, and an ambient light signal collected by the third photodetector.

[0157] The signal correction module 102 is used to perform background compensation on the interference signal based on the ambient light signal, and to normalize the compensated interference signal based on the reference light signal to obtain the corrected signal.

[0158] The displacement calculation module 103 is used to calculate the displacement measurement value based on the correction signal.

[0159] In some embodiments, the light source is a current-tunable laser, and the light source control module 101 is used to modulate the injection current of the light source so that the output wavelength of the light source changes periodically.

[0160] The displacement calculation module 103 is used to perform coherent demodulation of the correction signal through a lock-in amplifier based on a reference signal with the same modulation frequency as the injected current, and output a DC signal related to the displacement; and calculate the displacement measurement value based on the DC signal output by the lock-in amplifier.

[0161] In some embodiments, the signal correction module 102 is configured to remove the ambient light signal from the reference light signal and the interference signal respectively; divide the interference signal after removing the ambient light signal by the reference light signal after removing the ambient light signal to obtain a ratio signal; and multiply the ratio signal by the average output light intensity of the light source to obtain a correction signal.

[0162] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to in the description of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this application according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0163] Similarly, although the operations are depicted in a specific order in the accompanying drawings, this should not be construed as requiring these operations to be performed in the specific order shown or sequentially, or requiring all illustrated operations to be performed to achieve the desired result. In some cases, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system modules and components in the above embodiments should not be construed as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0164] Thus, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired result. Furthermore, the processes depicted in the drawings are not necessarily shown in a specific order or sequence to achieve the desired result. In some implementations, multitasking and parallel processing may be advantageous.

[0165] It should be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0166] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A wavelength-tunable MOEMS displacement sensor, characterized in that, include: A light source, a collimating lens, a beam splitter, a grating, and a MEMS mirror are arranged sequentially along the optical path. The light beam emitted by the light source is collimated by the collimating lens to form a parallel beam that is incident on the beam splitter. The beam splitter splits the parallel beam into a measurement beam and a reference beam. The measurement beam is incident on the grating and enters the grating interference cavity formed by the grating and the MEMS mirror. The MOEMS displacement sensor further includes a first photodetector, a second photodetector, a third photodetector, and a signal processing unit; wherein: The first photodetector is positioned on the exit path of the reference beam of the beam splitter and is used to collect the reference light signal; The second photodetector is positioned on the converging path of the interference beam generated after the grating interference cavity is activated, and is used to collect interference signals; The third photodetector is located at the ambient light receiving position of the MOEMS displacement sensor and is used to collect ambient light signals; The signal processing unit is connected to the first photodetector, the second photodetector, and the third photodetector, respectively, and is used to perform background compensation on the interference signal according to the ambient light signal, and to normalize the compensated interference signal according to the reference light signal to obtain a corrected signal, and to calculate the displacement measurement value according to the corrected signal.

2. The MOEMS displacement sensor according to claim 1, characterized in that, The light source is a current-tunable laser, and the MOEMS displacement sensor also includes: A wavelength tuning unit, connected to the light source, is used to modulate the injected current of the light source so that the output wavelength of the light source changes periodically. A lock-in amplifier, whose signal input terminal receives the correction signal and whose reference input terminal receives a reference signal with the same modulation frequency as the injected current, is used to coherently demodulate the correction signal and output a displacement-related DC signal. The signal processing unit is used to calculate the displacement measurement value based on the DC signal output by the lock-in amplifier.

3. The MOEMS displacement sensor according to claim 2, characterized in that, The displacement measurement value is calculated using the following formula: ； in, The center wavelength of the current-tunable laser is given. The DC signal output by the lock-in amplifier. This is the gain coefficient. The interference signal is collected by the second photodetector. The ambient light signal collected by the third photodetector. The reference light signal collected by the first photodetector. The gain of the signal conditioning circuit is used to condition the interference signal into the corrected signal. The amplitude of the reference signal, The responsivity of the second photodetector. Let D be a first-order Bessel function of the first kind with D as the independent variable, where D is the phase modulation depth. The initial cavity length between the grating and the mirror. The number of interference fringes, These are displacement measurements.

4. The MOEMS displacement sensor according to claim 1, characterized in that, The signal processing unit includes: A differential circuit is used to remove the ambient light signal from the reference optical signal and the interference signal, respectively. The division circuit is used to divide the interference signal after removing the ambient light signal by the reference light signal after removing the ambient light signal to obtain the ratio signal; The multiplication circuit is used to multiply the ratio signal by the average output light intensity of the light source and output a correction signal.

5. The MOEMS displacement sensor according to claim 4, characterized in that, The expression for the corrected signal is as follows: ； in, The interference signal is collected by the second photodetector. The ambient light signal collected by the third photodetector. The reference light signal collected by the first photodetector. The intensity of the incident light. This represents the average value of the light intensity fluctuation component of the light source.

6. A displacement detection method based on a MOEMS displacement sensor, characterized in that, The MOEMS displacement sensor is the displacement sensor according to any one of claims 1 to 5, and the displacement detection method includes the following steps: Step S1: Control the light source to emit a light beam to obtain the reference light signal collected by the first photodetector, the interference signal collected by the second photodetector, and the ambient light signal collected by the third photodetector; Step S2: Perform background compensation on the interference signal based on the ambient light signal, and normalize the compensated interference signal based on the reference light signal to obtain the corrected signal; Step S3: Calculate the displacement measurement value based on the correction signal.

7. The method according to claim 6, characterized in that, The light source is a current-tunable laser, and step S1 includes: The injected current of the light source is modulated so that the output wavelength of the light source changes periodically; Step S3 includes: Based on a reference signal with the same modulation frequency as the injected current, the correction signal is coherently demodulated by a lock-in amplifier to output a DC signal related to displacement. The displacement measurement value is calculated based on the DC signal output by the lock-in amplifier.

8. The method according to claim 6, characterized in that, Step S2 includes: Remove the ambient light signal from the reference light signal and the interference signal respectively; The ratio signal is obtained by dividing the interference signal after removing the ambient light signal by the reference light signal after removing the ambient light signal. The correction signal is obtained by multiplying the ratio signal by the average output light intensity of the light source.

9. The method according to any one of claims 6 to 8, characterized in that, During displacement detection, the MEMS mirror is attached to the surface of the object being measured.

10. A displacement detection device based on a MOEMS displacement sensor, characterized in that, The MOEMS displacement sensor is the displacement sensor according to any one of claims 1 to 5, and the device comprises: A light source control module is used to control the light source to emit a light beam in order to obtain a reference light signal collected by the first photodetector, an interference signal collected by the second photodetector, and an ambient light signal collected by the third photodetector. The signal correction module is used to perform background compensation on the interference signal based on the ambient light signal, and to normalize the compensated interference signal based on the reference light signal to obtain the corrected signal. The displacement calculation module is used to calculate the displacement measurement value based on the correction signal.

Images