Interferometric optical fiber sensor distributed system for ocean multi-parameter measurement

Abstract

The utility model discloses an interference type optical fiber sensor distributed system for ocean multi-parameter measurement, and relates to the technical field of distributed optical fiber sensing. The system comprises a tunable laser, a first coupler, a main interferometer, an auxiliary interferometer, an FP type sensing unit and a data acquisition card, the output end of the tunable laser is respectively connected with the input ends of the first coupler and the data acquisition card; the output end of the first coupler is respectively connected with the input ends of the main interferometer and the auxiliary interferometer; the output ends of the main interferometer and the auxiliary interferometer are connected with the input end of the data acquisition card; wherein the main interferometer comprises a circulator, and a port 2 of the circulator is connected with an FP type sensing unit; the number of the FP type sensing units is one or more, and the multiple FP type sensing units are connected in parallel. Each FP type sensing unit comprises a coupler and a sensing cavity. According to the utility model, the problem of multiplexing of a traditional single-point sensor in multi-point sensing is solved, and the reusability and high sensitivity of a sensing system are greatly improved.

Description

Technical Field

[0001] The utility model relates to the technical field of distributed optical fiber sensing, in particular to an interference type optical fiber sensor distributed system for ocean multi-parameter measurement. Background Art

[0002] Distributed fiber optic sensing (DOFS) technology uses optical fiber as a signal transmission medium and sensing unit, and utilizes the changes in parameters such as intensity, phase and polarization state of optical signals in optical fiber under external influences to achieve continuous distributed measurement of external parameters along the optical fiber. This technology has now become an ideal means of non-destructive health monitoring of large facilities in many fields such as energy, electricity, aerospace, communications, transportation and marine inspection. In terms of optical fiber link diagnosis, optical reflectometers are indispensable tools and provide broad application prospects for sensor multiplexing. Among various types of optical reflectometers, optical frequency domain reflectometers (OFDR) stand out because they borrow from the frequency modulated continuous wave (FMCW) technology in radar applications and have excellent spatial resolution. Moreover, OFDR can accurately obtain the link information of the optical fiber under test, so it has received widespread attention and application in optical sensing systems.

[0003] At present, OFDR-based fiber optic sensing relies on the backscattering of optical fibers, including Rayleigh scattering, Brillouin scattering, and Raman scattering. However, the intensity of traditional single-fiber distributed Rayleigh scattering is very weak, which leads to a low signal-to-noise ratio (SNR) in the sensing process, posing a challenge to sensing detection. At the same time, traditional broadband light sources have problems such as low spatial resolution, limited signal strength, and unstable phase information. Therefore, it is difficult for ordinary optical sensors to achieve multi-point sensing parameter monitoring. Moreover, existing fiber optic sensing systems often face nonlinear noise interference when implementing linear frequency scanning, which makes it difficult to accurately distinguish reflected signals, thereby affecting the spatial resolution of the sensor. In addition, in traditional light sources, fiber optic sensors based on the principle of interference have low sensitivity, and the number of sensors multiplexed in the system through frequency division multiplexing technology is also limited. Utility Model Content

[0004] In view of the above problems, the utility model proposes an interferometric optical fiber sensor distributed system for ocean multi-parameter measurement.

[0005] An interferometric optical fiber sensor distributed system for ocean multi-parameter measurement, comprising: a tunable laser 1, a first coupler 2, a main interferometer, an auxiliary interferometer, an FP type sensing unit 13 and a data acquisition card 7;

[0006] The output end of the tunable laser 1 is connected to the input end of the first coupler 2 and the data acquisition card 7 respectively, and the output end of the first coupler 2 is connected to the input end of the main interferometer and the auxiliary interferometer respectively; the output end of the main interferometer and the auxiliary interferometer is connected to the input end of the data acquisition card 7;

[0007] The main interferometer includes a circulator 12 , and two ports of the circulator 12 are connected to the FP type sensor unit 13 .

[0008] Furthermore, the main interferometer also includes a third coupler 8, a polarization controller 9, a circulator 12, a fifth coupler 10, and a balanced detector 11; the input end of the third coupler 8 is connected to the output end of the first coupler 2, the output end of the third coupler 8 is respectively connected to the input end of the polarization controller 9 and port 1 of the circulator 12, port 3 of the circulator 12 is connected to the input end of the fifth coupler 10, the output end of the fifth coupler 10 is connected to the input end of the balanced detector 11, and the output end of the balanced detector 11 is connected to the input end of the data acquisition card 7.

[0009] Furthermore, the auxiliary interferometer includes a second coupler 3, a delay fiber 4, a fourth coupler 5, and a photodetector 6; the input end of the second coupler 3 is connected to the output end of the first coupler 2, the output end of the second coupler 3 is connected to one end of the delay fiber 4, the other end of the delay fiber 4 is connected to the input end of the fourth coupler 5, the output end of the fourth coupler 5 is connected to the input end of the photodetector 6, and the output end of the photodetector 6 is connected to the input end of the data acquisition card 7.

[0010] Furthermore, there are one or more FP-type sensor units 13, and multiple FP-type sensor units 13 are connected in parallel; each FP-type sensor unit 13 includes a coupler and a sensor cavity, and the coupler is a 95:5 1×2 coupler, the 5% output end of the coupler is connected to the sensor cavity, and the 95% output end is connected to the input end of the next FP-type sensor unit 13.

[0011] Furthermore, the sensing cavity is formed by fusion-joining a single-mode optical fiber and a hollow-core optical fiber, and polydimethylsiloxane material is injected into the hollow-core optical fiber.

[0012] Furthermore, the output wavelength of the tunable laser 1 is between 1525nm and 1565nm.

[0013] Further, the first coupler 2 and the third coupler 8 are 1×2 couplers with a ratio of 99:1; the second coupler 3 and the fifth coupler 10 are 1×2 couplers with a ratio of 50:50.

[0014] Furthermore, a 99% output end of the first coupler 2 is connected to an input end of the main interferometer, and a 1% output end is connected to an input end of the auxiliary interferometer.

[0015] Furthermore, a 99% output end of the third coupler 8 is connected to port 1 of the circulator 12 , and a 1% output end is connected to an input end of the polarization controller 9 .

[0016] Furthermore, the wavelength range of the balanced detector 11 is between 800nm ​​and 1700nm; the wavelength range of the photodetector 6 is between 800nm ​​and 1700nm.

[0017] The beneficial technical effects of the utility model are:

[0018] The system proposed in the utility model effectively compensates for nonlinear noise and wavelength drift by introducing an auxiliary interferometer and a plurality of sensitivity-enhanced FP cavities. It not only inherits the advantages of high-precision positioning and perception capabilities of traditional distributed sensors, but also overcomes the problem of multiplexing of traditional single-point sensors in multi-point perception, greatly improving the reusability and high sensitivity of the sensing system, which is of great significance in ocean parameter measurement applications that require a large number of sensing points. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] By reading the detailed description below with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, wherein:

[0020] Figure 1 It is a structural diagram of an interferometric optical fiber sensor distributed system for ocean multi-parameter measurement described in an embodiment of the utility model.

[0021] Figure 2 It is a schematic diagram of the structure of the sensing cavity of the FP type sensing unit 13 in the embodiment of the utility model.

[0022] Figure 3 This is an example diagram of the original beat frequency signal spectrum in the embodiment of the present utility model.

[0023] Figure 4 This is an example diagram of the frequency domain spectrum of the beat frequency signal after applying FFT to the original beat frequency signal in the embodiment of the utility model; wherein the reflection peak appears at a preset position.

[0024] Figure 5 It is an example diagram of the magnification of three pairs of reflection peaks in the embodiment of the utility model.

[0025] Figure 6 This is an example diagram of the interference waveform spectrum of the first FP type sensor unit 13 in the embodiment of the utility model.

[0026] Figure 7 This is an example diagram of the red shift of the interference spectrum of the first FP type sensor unit 13 in the embodiment of the utility model as the temperature increases. DETAILED DESCRIPTION

[0027] The principle and spirit of the present invention will be described below with reference to several exemplary embodiments. It should be understood that these embodiments are provided only to enable those skilled in the art to better understand and implement the present invention, and are not intended to limit the scope of the present invention in any way. On the contrary, these embodiments are provided to make the present disclosure more thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0028] In recent years, fiber optic sensors for ocean monitoring applications have developed rapidly, and a large number of ocean parameter sensing schemes have been proposed. Ocean parameters mainly include seawater temperature, salinity and depth. As an important means of information acquisition, optical sensing units, as a new type of passive sensor device, have demonstrated their advantages of high sensitivity, small size and anti-electromagnetic interference. They have played an important role in many fields, especially in ocean monitoring. Compared with other scattering mechanisms, the reflection of optical sensing units, among which the OFDR of Rayleigh backscattering (RBS) has higher spatial resolution and signal-to-noise ratio.

[0029] Therefore, the utility model proposes an interferometric fiber optic sensor distributed system for ocean multi-parameter measurement. By utilizing the simple structure and easy manufacturing characteristics of FPI optical sensing, the temperature-sensitive FP sensor is combined with the frequency-adjustable continuous wave FMCW measurement technology, which greatly increases the number of multiplexing and can achieve high spatial resolution and high sensitivity ocean parameter perception parameter measurement.

[0030] The present utility model embodiment provides an interferometric optical fiber sensor distributed system for ocean multi-parameter measurement, such as Figure 1 As shown, the system includes: a tunable laser 1, a first coupler 2, a main interferometer, an auxiliary interferometer, an FP type sensor unit 13 and a data acquisition card 7;

[0031] The output end of the tunable laser 1 is connected to the input end of the first coupler 2 and the data acquisition card 7 respectively, and the output end of the first coupler 2 is connected to the input end of the main interferometer and the auxiliary interferometer respectively; the output end of the main interferometer and the auxiliary interferometer is connected to the input end of the data acquisition card 7;

[0032] The main interferometer includes a circulator 12 , and two ports of the circulator 12 are connected to the FP type sensor unit 13 .

[0033] Among them, the main interferometer also includes a third coupler 8, a polarization controller 9, a circulator 12, a fifth coupler 10, and a balanced detector 11; the input end of the third coupler 8 is connected to the output end of the first coupler 2, the output end of the third coupler 8 is respectively connected to the input end of the polarization controller 9 and the port 1 of the circulator 12, the port 3 of the circulator 12 is connected to the input end of the fifth coupler 10, the output end of the fifth coupler 10 is connected to the input end of the balanced detector 11, and the output end of the balanced detector 11 is connected to the input end of the data acquisition card 7.

[0034] The auxiliary interferometer includes a second coupler 3, a delay optical fiber 4, a fourth coupler 5, and a photodetector 6; the input end of the second coupler 3 is connected to the output end of the first coupler 2, the output end of the second coupler 3 is connected to one end of the delay optical fiber 4, the other end of the delay optical fiber 4 is connected to the input end of the fourth coupler 5, the output end of the fourth coupler 5 is connected to the input end of the photodetector 6, and the output end of the photodetector 6 is connected to the input end of the data acquisition card 7.

[0035] There are one or more FP-type sensing units 13, and multiple FP-type sensing units 13 are connected in parallel; each FP-type sensing unit 13 includes a coupler and a sensing cavity, and the coupler is a 95:5 1×2 coupler, the 5% output end of the coupler is connected to the sensing cavity, and the 95% output end is connected to the input end of the next FP-type sensing unit 13. The sensing cavity is fused by a single-mode optical fiber and a hollow-core optical fiber, and polydimethylsiloxane material is injected into the hollow-core optical fiber. The sensing cavity is fused by a single-mode optical fiber and a hollow-core optical fiber, and polydimethylsiloxane material is injected into the hollow-core optical fiber.

[0036] In this embodiment, preferably, the output wavelength of the tunable laser 1 is between 1525nm and 1565nm. The first coupler 2 and the third coupler 8 are 1×2 couplers with a ratio of 99:1; the second coupler 3 and the fifth coupler 10 are 1×2 couplers with a ratio of 50:50. The wavelength range of the balanced detector 11 is between 800nm ​​and 1700nm; the wavelength range of the photodetector 6 is between 800nm ​​and 1700nm. The 99% output end of the first coupler 2 is connected to the input end of the main interferometer, and the 1% output end is connected to the input end of the auxiliary interferometer. The 99% output end of the third coupler 8 is connected to port 1 of the circulator 12, and the 1% output end is connected to the input end of the polarization controller 9.

[0037] According to an embodiment of the utility model, both the main interferometer and the auxiliary interferometer are Mach-Zehnder interferometers (MZI). The system mainly consists of three parts: the first part is the auxiliary interferometer. Generally speaking, it is difficult for the tunable laser (TLS) 1 to achieve ideal linear frequency scanning, and it is often accompanied by nonlinear phase noise, which will reduce the spatial resolution of the system and have a greater impact on the recovery of the spectrum. In order to compensate for the nonlinear phase noise, an auxiliary interferometer is usually added. The interference spectrum is a standard trigonometric function in the frequency domain. The interval between the zero points of the trigonometric function is determined. The auxiliary interferometer can be used to achieve constant frequency and equal interval resampling. In this embodiment, a Mach-Zehnder interferometer (MZI) is used as an auxiliary interferometer, and a certain length of delay fiber provides an optical path difference. The photodetector (PD) 6 is used to convert the sinusoidal beat frequency signal into a TTL clock signal as the sampling clock of the data acquisition card (DAQ) 7. As an example, the data acquisition card (DAQ) 7 can use PCIe8531B, which includes 4 channels, each channel 20M 14 bits.

[0038] The second part is the main interferometer, in which the branch with weaker light intensity is the reference arm, on which a polarization controller (PC) 9 is placed to reduce the polarization effect; the branch with higher light intensity is the signal arm, which is connected to the sensing area through an optical circulator 12.

[0039] The third part is the sensing area, where the optical fibers led out from the 2 ports of the optical circulator 12 are connected in parallel with multiple groups of FP cavity sensors (i.e., FP type sensing units 13), such as Figure 2 As shown in the figure, each set of sensing units is composed of a single-mode optical fiber (SMF) and a hollow-core optical fiber (HCF) filled with PDMS. The interference cavity is a closed cavity, which is sensitive to temperature and can be used to measure seawater temperature. Polydimethylsiloxane (PDMS) is a material that is extremely sensitive to temperature. It will produce thermal expansion and contraction effects when the temperature changes, and has good light transmittance and refractive index. By utilizing the high thermal expansion and high thermo-optical properties of PDMS and combining it with optical fiber, the length of the cavity will change when the environment in which the optical fiber is located changes, which can improve the sensitivity of temperature measurement.

[0040] The preparation process of the sensing system is as follows:

[0041] 1) Trigger channel. A circuit is led out from the tunable laser (TLS) 1 and connected to the trigger channel of the data acquisition card (DAQ) 7, instructing the acquisition card to start working;

[0042] 2) Auxiliary interferometer. It is composed of a certain length of delay fiber 4 and a photodetector (PD) 6. The delay fiber 4 provides an optical path difference, and the photodetector 6 converts the optical signal into an electrical signal, which serves as the sampling clock of the data acquisition card 7;

[0043] 3) Main interferometer. It consists of a polarization controller 9, a circulator (CIR) 12 and a balanced detector (BPD) 11; the polarization controller 9 reduces the light polarization effect, the circulator 12 superimposes all the beat frequency signals, and the balanced detector 11 converts the optical signal into an electrical signal;

[0044] 4) Optical sensing unit. The interferometer (i.e., FP type sensing unit 13) is formed by fusing a single-mode optical fiber with a hollow-core optical fiber, and injecting PDMS into the hollow-core optical fiber to form a sensing cavity, which is sensitive to temperature. As an example, the cavity length of the sensing cavity is 100 nm.

[0045] Specifically, the working principle of the system is as follows: the light beam emitted from the tunable laser source (TLS) 1 passes through the first coupler (OFC) 2 and enters the two interferometers; the weaker light (1%) enters the auxiliary interferometer, and the light beam passes through a certain length of delay optical fiber 4 to form an optical path difference, thereby generating a sinusoidal beat frequency signal, which is converted into a TTL clock signal through a photodetector 6 and serves as an external sampling clock of a data acquisition card (DAQ) 7. The frequency interval of signal sampling is constant, which improves the accuracy and reliability of data acquisition; the stronger light (99%) enters the main interferometer, and a part of the weaker light enters the reference arm A polarization controller (PC) 9 is placed on the reference arm to reduce the polarization effect. Most of the remaining light enters the optical sensing area (i.e., the FP type sensing unit 13) through the 2 ports of the optical circulator 12. After the light beam reaches the sensitive FP cavity at a certain interval, since the time delay τ of the light beam reaching each FP cavity is different, each reflection end face will generate a beat signal with a specific frequency difference. The beat signals of all FP cavities are collected together through the circulator 12 to form a complex system interference spectrum, which is received by the balanced detector (BPD) 11 and converted into electrical signals, and finally received by the data acquisition card (DAQ) 7.

[0046] The tunable laser light source 1 emits incident light with a frequency that changes with time. The weaker part of the light enters the auxiliary interferometer, and the stronger part of the light enters the main interferometer. The light of the main interferometer passes through the circulator 12 and enters the FP type sensor unit 13-FP1, FP2, FP3..., and the reflected light reflected by several FP type sensor units 13 appears as delayed light relative to the reference light. Since the position of each FP type sensor unit 13 is different, the corresponding time delay τ is different. The reflected light from the two end faces of all FP type sensor units 13, and then passes through the circulator 12 and the reference light to form interference light under the action of the coupler, which is converted into an electrical signal by the balanced detector 11 and received by the data acquisition card 7.

[0047] Furthermore, in order to realize the processing of the system spectrum and the spectrum recovery of the optical sensing unit, the system also includes a signal processing module in the computer, that is, the signal data collected by the data acquisition card 7 is imported into the signal processing module in the computer; as an example, the signal processing module can be a software for data processing written based on the LabView development environment.

[0048] The signal processing module processes the collected data in the following way: first, the total beat frequency signal is imported into the software, and the spectrum of the system spectrum is analyzed by fast Fourier transform (FFT) to obtain the position information of each reflective end face. Then, the required reflection peak is selected by sliding window function, and the reflection peak is intercepted and then inverse Fourier transform (IFFT) and bandpass filtering are performed to obtain the wavelength information. Finally, the required spectrum can be demodulated by using the root mean square (RMS) envelope and sinusoidal signal fitting to realize multi-parameter measurement.

[0049] In the main interferometer, the incident light is divided into the reference arm and the sensor arm by the third coupler 8. The electric field intensity expression of the reference arm can be expressed as:

[0050]

[0051] Where E0 is the initial amplitude of the electric field, a is the splitting ratio of the coupler, Represents the electric field phase. For a linear frequency modulated light source, it can be expressed as follows:

[0052]

[0053] Where f0 represents the initial optical frequency of the laser light source, f0=c / λ0, γ represents the frequency sweep rate of the incident light, and t represents time. The reflected light from the sensor arm can be expressed as a frequency sweep signal with a fixed time delay difference from the reference light:

[0054]

[0055] Among them, r m Expressed as the reflectivity of the mth end face of the sensing unit, τ m It is expressed as the time delay of the mth reflection point in the sensor arm, which is given by the formula τ m =2nl m / c is used to describe it, n is the refractive index of the sensing cavity, l m is the difference in length between the reflection point and the reference arm. Therefore, the beat frequency signal after the reference light and the reflected light meet and interfere is:

[0056] I m =[E r (t)+E s (t)][E r (t)+E s(t)]* (4)

[0057] Therefore, the above formula is expanded to calculate and the beat frequency signal of a single reflection end face is obtained, which is simplified and combined to obtain the following formula:

[0058]

[0059] Among them, the beat frequency f b =γτ m , which is proportional to the length of the sensor arm. Finally, the total interference light intensity is:

[0060] I total =I1+I2+I3+I4+......+I m (10)

[0061] The free spectral range of the interferometer based on the Mach-Zehnder principle can be expressed as:

[0062] FSR=λ 2 / nΔL (11)

[0063] Where λ is the central wavelength and ΔL is the difference in length between the reference arm and the sensing arm.

[0064] In the sensing interferometer FPI, due to the weak reflectivity of the two surfaces of the FP cavity, only the double-beam interference of one reflection is considered. The interference envelope spectrum of the reflected light can be expressed as:

[0065]

[0066] Among them, I0 is the incident light intensity value, η is the transmission coefficient of the light in the cavity, and r1 and r2 are the reflection coefficients of the two end faces of the FP cavity respectively.

[0067] When the temperature changes, the translation Δλ1 of the interference spectrum envelope Ien-1 can be expressed as:

[0068]

[0069] Therefore, the change in ambient temperature can be derived from formula (12):

[0070]

[0071] Wherein, ΔT represents the change of temperature relative to the calibration point T0; Δλ1 represents the translation of the interference spectrum envelope Ien-1 relative to the interference spectrum envelope of the calibration point; is the temperature sensitivity of the interference spectrum envelope Ien-1, which is a constant and can be measured experimentally. By solving the above equation, the temperature to be measured T can be obtained as:

[0072] T=T0+ΔT (15)

[0073] Then the number of sensors that can be reused in the system is studied. In the absence of external optical power loss, the reflected end-face optical power of the Nth cascade sensor is:

[0074]

[0075] Among them, P out It represents the optical power reflected from the nth reflection end face to the balanced detector, P in represents the input optical power of the measurement arm, r m represents the reflectivity of the FP cavity (rm of the PDMS cavity = 2%), a n represents the coupling ratio of the nth fiber coupler (in the experiment, a n =5%). According to theoretical analysis, when the optical power of the laser source decays from 1mW to 100nW, the reflection peak of the FP cavity can still be detected. When Pin = 100nW, P out =250rmpW=5pW. In other words, the minimum detectable optical power is less than 5pW. Assuming that the reflected light power of each FP sensor is 5pW and the light source power is 10mW, the maximum multiplexing number can be estimated as Nmax=[(1010rmpW) / (250rm pW)]0.5=6325, which greatly increases the number of multiplexing of the interferometric fiber optic sensor. In addition, the number of multiplexing can be further increased by increasing the light source power.

[0076] The technical effect of the utility model is further verified through experiments. Figure 3 is the original beat frequency signal spectrum, which is a complex interference spectrum formed by the superposition of reflected light from multiple temperature-sensitive FP cavities. In the experiment, three FP cavities were selected for research, at 5m, 6m, and 7m respectively. Then the original interference spectrum was subjected to Fourier transform, spatial domain analysis, window function interception, inverse Fourier transform, and wavelength shift analysis (taking the first FP cavity - FP1), as shown in Figure 1. Figures 4 to 7 As shown, the parameters are measured by the wavelength shift as the temperature changes.

[0077] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims.

Claims

1. An interferometric optical fiber sensor distributed system for ocean multi-parameter measurement, characterized in that: include: A tunable laser (1), a first coupler (2), a main interferometer, an auxiliary interferometer, an FP type sensor unit (13) and a data acquisition card (7); The output end of the tunable laser (1) is respectively connected to the input end of the first coupler (2) and the data acquisition card (7); the output end of the first coupler (2) is respectively connected to the input end of the main interferometer and the auxiliary interferometer; the output end of the main interferometer and the auxiliary interferometer is connected to the input end of the data acquisition card (7); The main interferometer comprises a circulator (12), and two ports of the circulator (12) are connected to the FP type sensor unit (13).

2. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 1, characterized in that: The main interferometer further comprises a third coupler (8), a polarization controller (9), a circulator (12), a fifth coupler (10), and a balanced detector (11); the input end of the third coupler (8) is connected to the output end of the first coupler (2), the output end of the third coupler (8) is respectively connected to the input end of the polarization controller (9) and port 1 of the circulator (12), port 3 of the circulator (12) is connected to the input end of the fifth coupler (10), the output end of the fifth coupler (10) is connected to the input end of the balanced detector (11), and the output end of the balanced detector (11) is connected to the input end of the data acquisition card (7).

3. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 2, characterized in that: The auxiliary interferometer comprises a second coupler (3), a delay optical fiber (4), a fourth coupler (5), and a photodetector (6); the input end of the second coupler (3) is connected to the output end of the first coupler (2), the output end of the second coupler (3) is connected to one end of the delay optical fiber (4), the other end of the delay optical fiber (4) is connected to the input end of the fourth coupler (5), the output end of the fourth coupler (5) is connected to the input end of the photodetector (6), and the output end of the photodetector (6) is connected to the input end of the data acquisition card (7).

4. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 1, characterized in that: There are one or more FP-type sensing units (13), and the multiple FP-type sensing units (13) are connected in parallel; each FP-type sensing unit (13) comprises a coupler and a sensing cavity, the coupler is a 95:5 1×2 coupler, the 5% output end of the coupler is connected to the sensing cavity, and the 95% output end is connected to the input end of the next FP-type sensing unit (13).

5. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 4, characterized in that: The sensing cavity is formed by fusion-joining a single-mode optical fiber and a hollow-core optical fiber, and polydimethylsiloxane material is injected into the hollow-core optical fiber.

6. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 1, characterized in that: The output wavelength of the tunable laser (1) is between 1525nm and 1565nm.

7. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 3, characterized in that: The first coupler (2) and the third coupler (8) are 99:1 1×2 couplers; the second coupler (3) and the fifth coupler (10) are 50:50 1×2 couplers.

8. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 7, characterized in that: The 99% output end of the first coupler (2) is connected to the input end of the main interferometer, and the 1% output end is connected to the input end of the auxiliary interferometer.

9. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 7, characterized in that: The 99% output end of the third coupler (8) is connected to the 1 port of the circulator (12), and the 1% output end is connected to the input end of the polarization controller (9).

10. The interferometric optical fiber sensor distributed system for ocean multi-parameter measurement according to claim 3, characterized in that: The wavelength range of the balanced detector (11) is between 800nm ​​and 1700nm; the wavelength range of the photoelectric detector (6) is between 800nm ​​and 1700nm.

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