Optical wave phase measurement method and device based on single sideband modulation and coherent detection
Patent Information
- Application Number
- CN202611319152.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-28
- Publication Date
- 2026-10-09
AI Technical Summary
但是激光具有超高的频率，直接测量激光的相位变化是难以实现的
本发明通过单边带调制将激光的高频相位平移到低频调制波相位，再通过相干检测和数字信号处理提取相位差；双光路外差相干探测架构，相比传统干涉条纹方法，本发明不再受限于干涉条纹的非线性，提高了灵敏度和准确度；同时，本发明中误差在两束光（测量光和参考光）中具有互易性，通过双通道差分探测可以有效消除或减弱共模误差（如激光器频率漂移、环境温度变化等），提高了系统稳定性及精确性。
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Figure CN122881890A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of laser precision measurement technology, specifically to a method and apparatus for measuring optical wave phase based on single-sideband modulation and coherent detection. Background Technology
[0002] In precision distance-related measurements, changes in the phase of light waves are often used to indirectly measure changes in time, ultimately yielding changes in distance. For example, the Michelson interferometer essentially measures the phase difference of a laser beam; this phase difference corresponds to a time difference, which is then multiplied by the speed of light to obtain the distance change. However, lasers have extremely high frequencies, making direct measurement of their phase changes difficult.
[0003] In high-precision laser measurement applications, laser interferometry is often used for high-precision distance measurement, such as the Michelson interferometer mentioned above. It splits a beam of light into two beams, which travel through different paths. One beam passes through the material being measured, while the other serves as the interference beam. The length change of the target is measured by observing the interference fringes. However, the laser interference fringe method has nonlinearity, which limits further improvement in accuracy. For example, interferometric fiber optic gyroscopes have this problem.
[0004] This invention proposes a method for accurately measuring laser phase changes and improving measurement accuracy and stability, which can be applied to high-precision laser measurements, such as those involving minute displacements in fiber optic gyroscopes, machine tools, and lithography machines. Summary of the Invention
[0005] To address the above problems, this invention provides a method and apparatus for measuring optical wave phase based on single-sideband modulation and coherent detection.
[0006] In a first aspect, this application provides an optical phase measurement method based on single-sideband modulation and coherent detection, comprising: The laser emitted by the continuous wave laser source is divided into local oscillator light and signal light; The local oscillator light is split into two beams, which are respectively connected to the measurement signal optical mixer and the reference signal optical mixer; The signal light is modulated by an external modulator using a single-sideband modulator. The external modulator modulates a low-frequency signal acquired from an external source onto the signal light to obtain a single-sideband modulated signal. The single-sideband modulated signal is divided into measurement light and reference light; The measurement light is emitted to the medium under test via an optical transmitting antenna. After being phase-shifted by the medium under test, it is received by an optical receiving antenna. The measurement light received by the optical receiving antenna and the local oscillator light are coherently detected in the measurement signal optical mixer to recover the measurement signal. The reference light and the local oscillator light are coherently detected in the reference signal optical mixer to recover the reference signal; The measured signal and the reference signal are converted into digital signals to calculate the phase difference between the measured signal and the reference signal, and the changes in the measured medium are determined based on the phase difference.
[0007] Furthermore, the single-sideband modulator is a DD-MZM modulator. The DD-MZM modulator uses a 90° electrical phase shifter to split the low-frequency signal into two signals with the same amplitude and a 90° phase difference. The two signals are used to drive the upper and lower arms of the DD-MZM modulator in a push-pull manner to obtain a single-sideband modulated signal by suppressing the sideband.
[0008] Furthermore, in the step of converting the measurement signal and the reference signal into digital signals to calculate the phase difference between the measurement signal and the reference signal, and determining the change of the measured medium based on the phase difference, the measurement signal and the reference signal are converted into digital signals, and a fast Fourier transform is performed on the converted measurement signal and the reference signal to output the phase difference.
[0009] Furthermore, in the step of transmitting the measurement light to the medium under test via an optical transmitting antenna, receiving the light after phase shifting by the medium under test via an optical receiving antenna, and performing coherent detection of the received measurement light and the local oscillator light in the measurement signal optical mixer to recover the measurement signal, the phase difference is related to the phase shift between the reflected light of the measurement light through the medium under test and the reference light.
[0010] Furthermore, the method is used for angular velocity measurement of a fiber optic gyroscope, wherein the measured medium is the fiber optic loop in the fiber optic gyroscope. The step of converting the measured signal and the reference signal into digital signals to calculate the phase difference between the measured signal and the reference signal, and determining the change of the measured medium based on the phase difference, includes: determining the phase change of the fiber optic loop caused by the Sagnac effect based on the phase difference, and then calculating the angular velocity of the fiber optic gyroscope.
[0011] Furthermore, the fiber optic ring is a bi-fiber optic ring, with the forward fiber of the bi-fiber optic ring connected to the measurement light and the reverse fiber of the bi-fiber optic ring connected to the reference light, in order to counteract the influence of temperature changes on the measured value.
[0012] Furthermore, the beam splitter is a polarization beam splitter, and the fiber ring uses polarization-maintaining fiber.
[0013] Furthermore, the method is used for dual-frequency laser interferometry, where the measured medium is a moving object, and the measuring light is coherently detected with the local oscillator light after being reflected by the moving object, and the velocity or displacement of the object is calculated based on the Doppler principle.
[0014] On the other hand, the present invention provides an optical phase measurement device based on single-sideband modulation and coherent detection, comprising: a continuous wave laser source, a beam splitter, a single-sideband modulator, an optical transmitting antenna, an optical receiving antenna, a measurement signal optical mixer, a reference signal optical mixer, and a signal processing module; A continuous wave laser source, used to emit laser light; The beam splitter includes: a first beam splitter for splitting the laser into a local oscillator beam and a signal beam; a second beam splitter for splitting a single-sideband modulated signal into a measurement beam and a reference beam; and a third beam splitter for splitting the local oscillator beam into two beams and connecting them to the measurement beam signal mixer and the reference beam signal mixer, respectively. A single-sideband modulator is used to modulate the signal light with a single sideband, modulating the low-frequency signal onto the light wave to obtain a single-sideband modulated signal. An optical transmitting antenna is used to transmit measurement light to the medium being measured; An optical receiving antenna is used to receive measurement light after it has passed through the medium being measured. A measurement signal optical mixer is used to coherently detect the received measurement light and the local oscillator light to recover the measurement signal; A reference signal optical mixer is used to coherently detect the reference light and the local oscillator light to recover the reference signal; The signal processing module is used to calculate the phase difference between the measurement signal and the reference signal, and to determine the optical phase change caused by the measured medium based on the phase difference.
[0015] Furthermore, the signal processing module includes an analog-to-digital conversion unit and a digital signal processing unit. The analog-to-digital conversion unit is used to convert the measured signal and the reference signal into digital signals, and the digital signal processing unit is used to extract the phase difference between the measured signal and the reference signal using a fast Fourier transform.
[0016] The beneficial effects of this invention are: This invention shifts the high-frequency phase of the laser to the low-frequency modulated wave phase using single-sideband modulation, and then extracts the phase difference through coherent detection and digital signal processing. The dual-path heterodyne coherent detection architecture, compared to traditional interference fringe methods, is no longer limited by the nonlinearity of interference fringes, thus improving sensitivity and accuracy. Furthermore, the errors in this invention are reciprocal between the two beams (measurement beam and reference beam), and dual-channel differential detection can effectively eliminate or reduce common-mode errors (such as laser frequency drift, ambient temperature changes, etc.), improving system stability and accuracy. Attached Figure Description
[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention, and are not intended to limit the present invention.
[0018] Figure 1 This is a schematic diagram of the optical wave phase measurement method of the present invention; Figure 2 This is a flowchart of the optical wave phase measurement method of the present invention; Figure 3 This is a schematic diagram of the structure of the present invention applied to a fiber optic gyroscope; Figure 4 This is a schematic diagram of the structure of the present invention applied to a dual-frequency laser interferometer. Detailed Implementation
[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0021] like Figure 1-2 As shown, this invention provides a method for measuring the phase of an optical wave based on single-sideband modulation and coherent detection, comprising the following steps: S1: The laser emitted from the continuous-wave laser source is split into a local oscillator beam and a signal beam. The continuous-wave laser source emits laser light, which is split into two beams by the first beam splitter: one beam serves as the local oscillator beam, and the other serves as the signal beam. ;in, The angular velocity of the laser source signal. The amplitude of the laser source signal.
[0022] S2: The local oscillator light is split into two beams, which are respectively connected to the measurement signal optical mixer and the reference signal optical mixer. The local oscillator light is split into two beams again by a second beam splitter, which are respectively connected to the reference signal optical mixer and the measurement signal optical mixer, serving as the local oscillator input for coherent detection.
[0023] S3: The signal light is subjected to single-sideband modulation (SSB) via an external modulator. The external modulator modulates an externally acquired low-frequency signal onto the signal light, resulting in a single-sideband modulated signal. The signal light is subjected to SSB modulation via the external modulator to obtain a low-frequency sine wave. Modulated onto the light wave (where, For the amplitude of the modulated signal, (For the modulated signal angular velocity), this invention uses a DD-MZM as a single-sideband modulator. The DD-MZM modulator locks the phase difference of the upper and lower arm optical signals to 90°. Before the modulated electrical signal is applied to the two RF electrodes of the MZM, it first passes through a 90° electrical phase shifter, splitting into two signals with the same amplitude but a phase difference of 90° (π / 2). These two signals then drive the upper and lower arms of the MZM in a push-pull manner, obtaining a single-sideband modulated signal by suppressing the sidebands. The modulated optical signal is:
[0024] in, This represents the amplitude of the modulated optical signal.
[0025] S4: The single-sideband modulated signal is split into a measurement beam and a reference beam. The modulated single-sideband signal is split into two beams using a beam splitter: one beam is used as the measurement beam, and the other beam is used as the reference beam.
[0026] S5: The measurement light is emitted to the medium under test via an optical transmitting antenna. After being phase-shifted by the medium under test, it is received by an optical receiving antenna. The measurement light received by the optical receiving antenna and the local oscillator light are coherently detected in the measurement signal optical mixer to recover the measurement signal. The measurement light is emitted to the medium under test via an optical transmitting antenna. Due to propagation delay, a phase shift occurs as it passes through the medium under test. Finally, it is received by the optical receiving antenna and then used as one input to the measurement signal optical mixer. When the signal light is emitted from the modulator, its signal is: When the signal reaches the mixer after passing through the optical transmitter, the measured medium, and the optical receiver, neglecting losses, the time elapsed... Arrival at the detector, The phase change caused by time is The signal becomes: This signal is related to the local oscillator light. Conduct coherent detection; among which, This refers to the phase of the local oscillator light reaching the mixer.
[0027] According to the square law formula for laser detection, the current is: I =
[0028] It generates three parts: a DC term, a frequency doubling term, and a difference frequency term. Considering the physical efficiency of the detector, the frequency doubling term, being high-frequency, will be filtered out. Simultaneously, after DC blocking, only the difference frequency term remains; ultimately, the measurement signal is obtained. = ;in, For conversion efficiency, The amplitude of the radio frequency signal is recovered after coherent detection of the measured signal.
[0029] S6: The reference light and the local oscillator light undergo coherent detection in the reference signal optical mixer to recover the reference signal. The reference light is directly input to the reference signal optical mixer without passing through the measured medium, and undergoes coherent detection with the local oscillator light. The reference signal is obtained similarly. = ,in, The amplitude of the radio frequency signal is recovered after coherent detection of the reference signal.
[0030] S7: Convert the measured signal and the reference signal into digital signals to calculate the phase difference between the measured signal and the reference signal, and determine the change in the measured medium based on the phase difference. After the measured signal and the reference signal are converted into digital signals, the phase difference between the measured signal and the reference signal is calculated: Of these, only It changes with the medium being measured. , , It is a fixed value, so according to It can determine the changes in the measured medium.
[0031] In this embodiment, when calculating the phase difference, digital signal processing algorithms such as Fast Fourier Transform (FFT) can be used to perform spectral analysis on the sampled measurement signal and reference signal, extract the phase information at the low-frequency modulation frequency, and then calculate the phase difference between the two.
[0032] This invention shifts the laser frequency to a new frequency of laser frequency + modulation frequency through single-sideband modulation, and then converts the phase difference in the optical frequency domain to a low-frequency electrical signal domain through coherent beat frequency with the local oscillator. This transforms the high-frequency phase change of the laser, which was originally difficult to measure directly, into a low-frequency electrical signal phase change that is easy to measure, thereby achieving high-precision phase measurement while avoiding the nonlinearity problem in the traditional interference fringe method.
[0033] In addition, this application also provides an optical phase measurement device based on single-sideband modulation and coherent detection, including: a continuous wave laser source, a single-sideband modulator, a beam splitter, an optical transmitting antenna, an optical receiving antenna, a measurement signal optical mixer, a reference signal optical mixer, and a signal processing module; A continuous wave laser source is used to emit laser light. In this embodiment, the laser source can be a DFB laser (distributed feedback laser) or other types of continuous wave lasers. A single-sideband modulator is used to modulate the signal light with a single-sideband modulator, modulating the low-frequency signal onto the light wave to obtain a single-sideband modulated signal. In this embodiment, DD-MZM is used as the single-sideband modulator, emphasizing the use of single-sideband modulation to generate new frequencies, and is not limited to a specific type of single-sideband modulator. The beam splitter includes: a first beam splitter for splitting the laser into a local oscillator beam and a signal beam; a second beam splitter for splitting a single-sideband modulated signal into a measurement beam and a reference beam; and a third beam splitter for splitting the local oscillator beam into two beams and connecting them to the measurement beam signal mixer and the reference beam signal mixer, respectively. An optical transmitting antenna is used to transmit measurement light to the medium under test; an optical receiving antenna is used to receive the measurement light after it has passed through the medium under test; the output of the optical receiving antenna is connected to the measurement light input of the measurement light signal mixer. A measurement signal optical mixer is used to coherently detect the received measurement light and the local oscillator light to recover the measurement signal; in this embodiment, the measurement signal optical mixer is a 90° optical mixer, used to output in-phase components and quadrature electrical signals; A reference signal optical mixer is used to coherently detect the reference light and the local oscillator light to recover the reference signal; in this embodiment, the reference signal optical mixer is a 90° optical mixer, used to output in-phase and quadrature component electrical signals. The signal processing module is used to calculate the phase difference between the measured signal and the reference signal, and to determine the optical phase change caused by the measured medium based on the phase difference. The signal processing module includes an analog-to-digital conversion unit and a digital signal processing unit. The analog-to-digital conversion unit is used to convert the measured signal and the reference signal into digital signals, and the digital signal processing unit is used to extract the phase difference between the measured signal and the reference signal using a fast Fourier transform (FFT).
[0034] like Figure 3 As shown, in one embodiment, the method of the present invention can be applied to the angular velocity measurement of a fiber optic gyroscope, wherein the measured medium is the fiber optic loop in the fiber optic gyroscope. The step of converting the measured signal and the reference signal into digital signals to calculate the phase difference between the measured signal and the reference signal, and determining the change of the measured medium based on the phase difference, includes: determining the phase change of the fiber optic loop caused by the Sagnac effect based on the phase difference, and then calculating the angular velocity of the fiber optic gyroscope.
[0035] In this embodiment, the laser source emits continuous laser light, which is split into local oscillator light and signal light by the first beam splitter. The signal light, after being modulated by a single-sideband modulator, is split into measurement light and reference light by the second beam splitter. The measurement light enters the CW (forward fiber) optical path of the fiber optic ring, carries a Sagnac phase shift after passing through the fiber optic ring, and undergoes coherent detection with the split local oscillator light in the measurement signal light mixer to recover the measurement signal. The reference light can be directly connected to the reference light mixer (without passing through the fiber optic ring), or it can be connected to the CCW (reverse fiber) optical path of the fiber optic ring before entering the reference light mixer. When the reference light also passes through the reverse optical path of the fiber optic ring, the fiber optic ring adopts a two-wire fiber optic ring system—that is, two fibers are wound in the same fiber optic ring, serving as the forward (CW) and reverse (CCW) optical paths respectively. With the measurement light passing through the forward fiber optic ring and the reference light passing through the reverse fiber optic ring, the impact of ambient temperature changes on the forward and reverse fiber optic rings is consistent, effectively offsetting the influence of temperature changes on the measured values and solving the problem of zero drift in interferometric fiber optic gyroscopes. After the optical signals from the forward and reverse fiber loops are coherently detected with the local oscillator light, the modulated wave is recovered. The phase difference between the two modulated waves is then calculated, and the angular velocity of the gyroscope is calculated accordingly.
[0036] For the beam splitter, since the fiber optic gyroscope is a high-precision device with high polarization requirements, the beam splitter in this embodiment is a polarization beam splitter, and the optical fiber is a polarization-maintaining fiber to ensure the stability of the polarization state of the optical signal and improve the measurement accuracy.
[0037] Compared to traditional interferometric fiber optic gyroscopes, this embodiment uses coherent detection to directly recover the phase of the low-frequency modulation signal, avoiding errors caused by nonlinearity of interference fringes. It eliminates the need for complex closed-loop phase modulation control and Y-waveguide integrated optical modulators, thus reducing costs.
[0038] For multi-axis gyroscopes, traditional interferometric fiber optic gyroscopes require a complete optical path for each axis (light source, fiber coupler, Y-waveguide integrated optical modulator, fiber optic loop, and photodetector). The Y-waveguide is expensive, resulting in a high overall cost. However, using the measurement method of this invention, multiple axes can share a light source and reference signal measurement data. Only one fiber optic loop and coherent detection module are needed for each axis, effectively simplifying the complexity of multi-axis gyroscopes and reducing cost and size.
[0039] like Figure 4 As shown, in one embodiment, the method of the present invention can be applied to dual-frequency laser interferometry, wherein the measured medium is a moving object, the measuring light is reflected by the moving object and coherently detected with the local oscillator light, and the velocity or displacement of the object is calculated based on the Doppler principle.
[0040] In this embodiment, the laser emits a frequency of The continuous laser beam is split into a measurement beam and a reference beam by a beam splitter. The measurement beam is then modulated by a single-sideband modulation, transforming the optical signal into... That is, generating a second frequency laser through single-sideband modulation. The modulated signal is then split by a beam splitter, with one beam emitted through an optical transmitting antenna. After being reflected by the object being measured, it is received by an optical receiving antenna. If the reflecting object is moving, according to the Doppler principle, the received signal will exhibit a frequency change depending on the direction of movement. The final received signal has a frequency of [frequency value missing]. After the received signal undergoes coherent detection with the local oscillator light, the measured signal and the local oscillator light generate a beat frequency signal, thus obtaining the radio frequency difference signal. , This indicates whether the motion is towards or away from each other. Similarly, the reference signal and the local oscillator light undergo coherent detection after passing through a mixer to obtain the radio frequency difference signal. Finally passed get ,according to Calculate the velocity of the object; if the motion of the reflecting object is a small displacement, then the frequency difference is the phase difference. ,according to The minute movements were calculated.
[0041] Compared to existing laser dual-frequency interferometers, the second frequency in this embodiment can be obtained through single-sideband modulation, which allows for easy adjustment of the electrical signal frequency to modify the dual-frequency difference, thereby covering the measurement range of object motion from low speed to high speed and providing strong anti-interference capability.
[0042] The measurement method and device provided by this invention can be widely used in precision measurement fields such as fiber optic gyroscopes, dual-frequency interferometers, laser ranging, laser velocimetry, and atmospheric vacuum measurement. They are characterized by low cost, small size, and high reliability, and have good industrial applicability and market prospects.
[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.
Claims
1. A method for measuring the phase of an optical wave based on single-sideband modulation and coherent detection, characterized in that, Includes the following steps: The laser emitted by the continuous wave laser source is divided into local oscillator light and signal light; The local oscillator light is split into two beams, which are respectively connected to the measurement signal optical mixer and the reference signal optical mixer; The signal light is modulated by an external modulator using a single-sideband modulator. The external modulator modulates a low-frequency signal acquired from an external source onto the signal light to obtain a single-sideband modulated signal. The single-sideband modulated signal is divided into measurement light and reference light; The measurement light is emitted to the medium under test via an optical transmitting antenna. After being phase-shifted by the medium under test, it is received by an optical receiving antenna. The measurement light received by the optical receiving antenna and the local oscillator light are coherently detected in the measurement signal optical mixer to recover the measurement signal. The reference light and the local oscillator light are coherently detected in the reference signal optical mixer to recover the reference signal; The measured signal and the reference signal are converted into digital signals to calculate the phase difference between the measured signal and the reference signal, and the changes in the measured medium are determined based on the phase difference.
2. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 1, characterized in that, The single-sideband modulator is a DD-MZM modulator. The DD-MZM modulator divides the low-frequency signal into two signals with the same amplitude and a 90° phase difference through a 90° electrical phase shifter. The two signals are used to drive the upper and lower arms of the DD-MZM modulator in a push-pull manner to obtain a single-sideband modulated signal by suppressing the sideband.
3. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 1, characterized in that, In the step of converting the measured signal and the reference signal into digital signals, calculating the phase difference between the measured signal and the reference signal, and determining the change in the measured medium based on the phase difference, The measured signal and the reference signal are converted into digital signals, and a fast Fourier transform is performed on the converted measured signal and the reference signal to output the phase difference.
4. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 1, characterized in that, The measurement light is emitted to the medium under test via an optical transmitting antenna. After being phase-shifted by the medium under test, it is received by an optical receiving antenna. The optical receiving antenna performs coherent detection of the received measurement light and the local oscillator light in the measurement signal optical mixer to recover the measurement signal. The phase difference is related to the phase shift between the measured light reflected from the medium under test and the reference light.
5. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 1, characterized in that, The method is used for angular velocity measurement of a fiber optic gyroscope, where the measured medium is the fiber optic loop in the gyroscope. The steps include converting the measured signal and the reference signal into digital signals, calculating the phase difference between the measured signal and the reference signal, and determining the changes in the measured medium based on the phase difference: The phase change of the fiber optic ring caused by the Sagnac effect is determined based on the phase difference, and then the angular velocity of the fiber optic gyroscope is calculated.
6. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 5, characterized in that, The fiber optic ring is a bi-wire fiber optic ring. The forward fiber of the bi-wire fiber optic ring is connected to the measurement light, and the reverse fiber of the bi-wire fiber optic ring is connected to the reference light to counteract the influence of temperature changes on the measured value.
7. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 5 or 6, characterized in that, The fiber optic ring uses polarization-maintaining fiber.
8. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 1, characterized in that, The method is used for dual-frequency laser interferometry, where the measured medium is a moving object, and the measuring light is coherently detected with the local oscillator light after being reflected by the moving object. The velocity or displacement of the object is calculated based on the Doppler principle.
9. An optical phase measurement device based on single-sideband modulation and coherent detection, employing the method described in any one of claims 1-8, characterized in that, include: Continuous wave laser source, beam splitter, single-sideband modulator, optical transmitting antenna, optical receiving antenna, measurement signal optical mixer, reference signal optical mixer, and signal processing module; A continuous wave laser source, used to emit laser light; The beam splitter includes: a first beam splitter for splitting the laser into a local oscillator beam and a signal beam; a second beam splitter for splitting a single-sideband modulated signal into a measurement beam and a reference beam; and a third beam splitter for splitting the local oscillator beam into two beams and connecting them to the measurement beam signal mixer and the reference beam signal mixer, respectively. A single-sideband modulator is used to modulate the signal light with a single sideband, modulating the low-frequency signal onto the light wave to obtain a single-sideband modulated signal. An optical transmitting antenna is used to transmit measurement light to the medium being measured; An optical receiving antenna is used to receive measurement light after it has passed through the medium being measured. A measurement signal optical mixer is used to coherently detect the received measurement light and the local oscillator light to recover the measurement signal; A reference signal optical mixer is used to coherently detect the reference light and the local oscillator light to recover the reference signal; The signal processing module is used to calculate the phase difference between the measurement signal and the reference signal, and to determine the optical phase change caused by the measured medium based on the phase difference.
10. The optical phase measurement method based on single-sideband modulation and coherent detection according to claim 9, characterized in that, The signal processing module includes an analog-to-digital conversion unit and a digital signal processing unit. The analog-to-digital conversion unit is used to convert the measured signal and the reference signal into digital signals, and the digital signal processing unit is used to extract the phase difference between the measured signal and the reference signal using a fast Fourier transform.