Fabry-Perot temperature-depth sensor based on optical fiber ring laser and measuring system

Abstract

The invention relates to the technical field of optical detection and optical fiber sensing, in particular to a Fabry-Perot temperature-depth sensor based on an optical fiber ring laser and a measuring system. The sensor adopts an all-fiber intracavity sensing design, and comprises a composite sensing probe formed by cascading a Fabry-Perot interferometer and a fiber bragg grating, a fiber ring laser cavity and a demodulation unit. The sensor probe is integrally packaged by adopting a three-dimensional photoetching 3D printing technology, the structure is firm, and the size is compact. According to the system, a sensing probe is embedded into a laser cavity, weak signals are amplified by utilizing gain in the cavity, and response signals of an FPI and an FBG are processed in real time based on a multi-parameter matrix algorithm in combination with stable wavelength reference and temperature reference provided by the FBG, so that high-precision synchronous measurement of temperature and hydraulic pressure (depth) and effective decoupling of cross sensitivity are realized. The optical fiber temperature-depth sensor overcomes the problems that a traditional optical fiber temperature-depth sensor is serious in cross sensitivity and poor in environmental adaptability in a complex underwater environment, has the advantages of being high in sensitivity, good in stability, high in anti-interference capacity, convenient to integrate and the like, and is suitable for the fields of ocean observation, deep sea exploration, underwater engineering safety monitoring and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical detection and fiber sensing, and in particular to a Fabry-Perot temperature-depth sensor and measurement system based on a fiber ring laser. BACKGROUND

[0002] The fiber-optic temperature-depth sensor is a sensing tool for synchronous and accurate measurement of temperature and depth information underwater, which can help humans better understand the ocean environment and its change rules. The fiber-optic temperature-depth sensor can assist the ocean observation system to perform hydrological monitoring, deep-sea exploration, and underwater engineering safety warning, etc., which makes it widely concerned in the field of ocean science and engineering. Temperature-depth sensors based on different optical principles and demodulation technologies have been developed and applied to various ocean observation platforms and operation scenarios.

[0003] In 2021, Ming Zhang et al. reported a liquid level sensor based on a reflective long-period fiber grating, which couples the core mode to the cladding mode by using a grating, and a reflective film is coated at the tail end to form a reflective structure. When the sensor is immersed in a liquid with a higher refractive index than the cladding, the cladding mode is transmitted in a leaky form, and its loss increases with the increase of the liquid level. By detecting the change of reflected light power, the liquid level is sensed, and the sensitivity of 0.772 dB / m is measured in a glycerol medium. In 2022, Junda Lao et al. disclosed a fiber Bragg grating pressure sensor packaged with a flange cylinder and PDMS. The external hydraulic pressure is transmitted to the grating through the PDMS elastomer, causing the Bragg wavelength to shift, achieving a sensitivity of 4.417 nm / MPa in the range of 0-30 meters of water pressure. In 2023, Jia Shi et al. further proposed a liquid level detection scheme based on a Fabry-Perot interferometer and in-cavity sensing of a fiber ring laser. By using a polyimide film to sense the hydraulic pressure and change the length of the interference cavity, the laser cavity loss and output power are modulated, achieving a resolution of 1.5 millimeters in the range of 0.6 meters.

[0004] Traditional temperature-depth sensors are mainly based on thermocouple, thermistor or piezoresistive pressure sensing principles, which are susceptible to electromagnetic interference and difficult to work stably in high-pressure, corrosive or long-term water immersion environments. Although fiber-optic temperature-depth sensors have advantages such as electromagnetic interference resistance, corrosion resistance, and long-distance transmission, they also have problems such as temperature and depth cross-sensitivity, complex structure, and expensive demodulation systems. Moreover, existing sensor designs mostly use discrete or rigid packaging, which makes it difficult to integrate with small underwater mobile platforms or flexible monitoring networks. Although distributed fiber-optic sensing technology has the ability to monitor continuously in space, its application in synchronous high-resolution temperature-depth sensing is still not mature, especially in achieving long-term stability and measurement accuracy in deep-sea environments. SUMMARY

[0005] The application aims to overcome the defects of the prior art fiber-optic temperature-depth sensor, such as serious temperature-pressure cross-sensitivity, limited measurement dimension and precision in complex underwater environment, and provide a Fabry-Perot (FPI) temperature-depth sensor and a measurement system based on fiber ring laser (FRL) cavity sensing.

[0006] To achieve the above object, in one aspect, the application provides a fiber-optic temperature-depth sensor based on FPI, comprising: a 500-micron monocrystalline silicon wafer for contacting external pressure and temperature and generating elastic deformation; an embedded single-mode optical fiber forming an FP cavity with the silicon wafer and a resin shell and realizing sensing by causing transmission spectrum shift through silicon deformation; a fiber Bragg grating for realizing stable laser wavelength, serving as a temperature sensor and providing temperature compensation for the FPI to realize decoupling measurement; and a resin shell, which is a hollow structure for integrating the 500-micron monocrystalline silicon wafer, the single-mode optical fiber and the fiber Bragg grating together.

[0007] Further, the 500-micron monocrystalline silicon wafer serves as a sensitive element and realizes high-sensitivity detection of pressure by using its high refractive index uniformity and mechanical stability.

[0008] Further, the resin shell is made of photosensitive resin material by light-curing 3D printing technology. The total length of the shell is set to 15 mm, and the diameters of the internal channels are all 0.8 mm.

[0009] Further, the FPI structure is composed of the 500-micron monocrystalline silicon wafer, the resin shell and the single-mode optical fiber embedded in the resin shell.

[0010] Further, the FPI structure has temperature and pressure sensitivity characteristics, and the transmission spectrum redshift amount has a linear relationship with the size of pressure and temperature.

[0011] Further, the resin shell has a first optical fiber groove and a second optical fiber groove symmetrically distributed, with a depth of 13 mm and a diameter of 0.8 mm, for fixing a single-mode optical fiber and a fiber Bragg grating.

[0012] Further, the length of the FP cavity in the FPI structure is 2 mm, and the inner diameter is 1.6 mm.

[0013] Further, the single-mode optical fiber and the fiber Bragg grating are respectively the F1 port and the F2 port of the fiber temperature-depth sensor.

[0014] Further, the lengths of the single-mode optical fiber and the fiber Bragg grating are respectively 30 cm and 3 cm.

[0015] On the other hand, the present application also provides a measuring system, comprising: a pump light source, a wavelength division multiplexer, an erbium-doped optical fiber, an optical fiber isolator, an optical fiber circulator, an optical fiber temperature-depth sensor, an optical fiber coupler, and an optical spectrum analyzer, for realizing optical signal transmission, interference and demodulation.

[0016] Among them, the relationship between the elements of the measuring system is as follows:

[0017] The light output port A1 port of the pump light source is connected to the B1 port of the wavelength division multiplexer;

[0018] The B2 port of the wavelength division multiplexer is connected to the C1 port of the erbium-doped optical fiber;

[0019] The C2 port of the erbium-doped optical fiber is connected to the D1 port of the optical fiber isolator;

[0020] The D2 port of the optical fiber isolator is connected to the E1 port of the first optical fiber circulator;

[0021] The E2 port of the first optical fiber circulator is connected to the F1 port of the optical fiber temperature-depth sensor;

[0022] The E3 port of the first optical fiber circulator is connected to the G1 port of the second optical fiber circulator;

[0023] The G2 port of the second optical fiber circulator is connected to the F2 port of the optical fiber temperature-depth sensor;

[0024] The G3 port of the second optical fiber circulator is connected to the H1 port of the optical fiber coupler;

[0025] The H2 port of the optical fiber coupler is connected to the I1 port of the optical spectrum analyzer;

[0026] The H3 port of the optical fiber coupler is connected to the B3 port of the wavelength division multiplexer;

[0027] Compared with the prior art, the beneficial effects of the present invention are that the Fabry-Perot depth sensor and measurement system based on the fiber ring laser adopts an all-fiber intracavity sensing design, including: a fiber ring laser, a Fabry-Perot interferometer-fiber Bragg grating composite sensing probe, and a differential demodulation method.

[0028] Furthermore, the fiber ring laser adopts a saturable absorber frequency stabilization structure to output stable laser light, providing a high-quality optical carrier for intrinsically high signal-to-noise ratio sensing.

[0029] Furthermore, the Fabry-Perot interferometer-fiber Bragg grating composite sensing probe is constructed by cascading FPI and FBG, and is integrated and packaged using stereolithography 3D printing technology to form a compact and mechanically stable miniature sensing head.

[0030] Furthermore, the FPI is highly sensitive to both temperature and hydraulic pressure, and its reflection spectrum drifts with changes in external parameters, enabling simultaneous sensing of two parameters.

[0031] Furthermore, the FBG has a clear temperature response characteristic and is insensitive to hydraulic pressure, serving as an intracavity wavelength selector and temperature reference sensor to provide an accurate temperature reference for the system.

[0032] Furthermore, the differential detuning method is based on a multi-parameter matrix algorithm to process the output signals of FPI and FBG in real time, thereby achieving real-time decoupling of temperature and hydraulic pressure and significantly suppressing cross-sensitivity.

[0033] Furthermore, the system's optical path is entirely fiber-optic, with signals transmitted inside the optical fiber, possessing intrinsic characteristics of electromagnetic interference resistance, corrosion resistance, and adaptability to high-pressure environments.

[0034] Furthermore, the present invention also provides a corresponding measurement method, including: laser excitation, intracavity sensing, signal demodulation and parametric inversion, for achieving high-precision and high-stability synchronous monitoring of temperature and water depth. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of an optical fiber temperature and depth sensor provided in an embodiment of the present invention.

[0036] Figure 2 This is a structural block diagram of a fiber optic ring laser-based measurement system provided in an embodiment of the present invention.

[0037] Figure 3 This invention provides a transmission spectrum of a fiber optic ring laser measurement system at different liquid levels (hydraulic).

[0038] Figure 4This invention provides a transmission spectrum of a fiber optic ring laser-based measurement system at different temperatures, as part of an embodiment of the invention.

[0039] Figure 5 This invention provides a fitting graph of the output wavelength variation at different temperatures for a fiber optic ring laser measurement system.

[0040] Figure 6 This invention provides a peak power fitting diagram at different temperatures based on a fiber ring laser measurement system, which is an embodiment of the present invention.

[0041] In the figure: 1. 500-micron single-crystal silicon wafer, 2. resin shell, 3. first fiber slot, 4. second fiber slot, 5. single-mode fiber, 6. fiber Bragg grating. Detailed Implementation

[0042] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0043] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0044] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0045] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] Furthermore, it should be noted that in this invention, the core sensing unit and functional entity of the fiber optic temperature-depth sensor is the composite sensing probe formed by the cascaded Fabry-Perot interferometer and fiber Bragg grating. This composite probe integrates optical elements sensitive to temperature and hydraulic pressure (depth) into one unit, and forms a structurally complete independent sensor device through integrated packaging. Specifically, the Fabry-Perot interferometer serves as a pressure-sensitive unit, and its optical cavity length is modulated by external hydraulic pressure; the fiber Bragg grating serves as a temperature-sensitive unit and wavelength reference, and its Bragg wavelength changes with temperature. The two are optically and structurally integrated to achieve synchronous sensing and signal conversion of temperature and depth information. Therefore, in the context of this invention, the "fiber optic temperature-depth sensor" is structurally and functionally equivalent to the "Fabry-Perot interferometer / fiber Bragg grating composite sensing probe," and the two are different expressions of the same technical entity.

[0047] Please see Figure 1 As shown, this is the Fabry-Perot-based temperature and depth sensor fabricated according to the present invention. The specific fabrication process is as follows:

[0048] Step (1) The resin sensing probe housing is manufactured using stereolithography 3D printing technology. The total length of the housing is 15 mm. Inside, there are two parallel precision fiber slots for fixing single-mode fiber and fiber Bragg grating respectively. The length of the first fiber slot and the second fiber slot is 13 mm, the internal diameter is 0.8 mm, and the length of the FP cavity between the first fiber slot and the single crystal silicon wafer is 2 mm, the internal diameter is 1.6 mm.

[0049] Step (2) A 500-micrometer-thick single-crystal silicon thin film is used as a sensitive film and aligned with the end face of the prefabricated FP cavity. Epoxy resin adhesive is evenly applied to the bonding surface of the two, followed by bonding and curing to form an airtight optical FP interference cavity.

[0050] Step (3) Install the FPI assembly completed in step (2) onto a high-precision triaxial alignment platform. Insert a single-mode fiber into the near end of the housing and precisely guide it into the first fiber slot using the alignment platform. Simultaneously, monitor the reflection spectrum in real time using a spectrometer, and iteratively fine-tune the fiber position until a stable interference spectrum with optimal contrast is obtained. Subsequently, while maintaining the airtightness of the cavity, permanently fix the fiber in the slot using UV-cured epoxy resin.

[0051] Step (4) employs the same alignment, monitoring, and curing process as step (3) to integrate the FBG fiber into the second fiber slot, thereby completing the overall packaging of the cascaded FPI / FBG structure sensing probe. The fiber optic temperature-depth sensor described above is finally fabricated.

[0052] Please see Figure 2The diagram shown is a structural block diagram of a Fabry-Perot depth sensing system based on a fiber ring laser provided by this invention. This system achieves high-precision, synchronous demodulation of temperature and depth (hydraulic) through an intracavity sensing mechanism. It mainly includes: a pump source, a wavelength division multiplexer, erbium-doped fiber (gain medium), a fiber isolator, first and second fiber circulators, a fiber temperature and depth sensor (Fabry-Perot interferometer and fiber Bragg grating composite sensing probe), a fiber coupler, and a spectrometer.

[0053] The connection relationships of the optical components in the system are as follows:

[0054] The output terminal A1 of the pump light source is connected to port B1 of the wavelength division multiplexer, and the signal port B2 of the wavelength division multiplexer is connected to port C1 of the erbium-doped fiber. The other end C2 of the erbium-doped fiber is connected to the input terminal D1 of the fiber optic isolator, and the output terminal D2 of the fiber optic isolator is connected to port E1 of the first fiber optic circulator. Port E2 of the first fiber optic circulator is connected to port F1 of the composite sensing probe. Port E3 of the first fiber optic circulator is connected to port G1 of the second fiber optic circulator. Port G2 of the second fiber optic circulator is connected to port F2 of the composite sensing probe. Port G3 of the second fiber optic circulator is connected to the input terminal H1 of the fiber optic coupler. The two output terminals of the fiber optic coupler are respectively connected to port I1 of the spectrometer and signal return port B3 of the wavelength division multiplexer to form a closed fiber optic ring laser resonator.

[0055] The pump light source is used to generate a pump light signal at the optical output port A1 with a working wavelength of 976nm and send it to the B1 port of the wavelength division multiplexer.

[0056] The wavelength division multiplexer and erbium-doped fiber are used to couple the pump light received at port B1 into the gain medium to achieve stimulated amplification of the optical signal.

[0057] The fiber optic isolator is used to ensure that the amplified optical signal propagates unidirectionally in the direction from D2 to E1 within the ring cavity, and to suppress backscattered light in order to maintain stable laser oscillation.

[0058] The first and second fiber optic circulators work together to guide the optical path and embed the fiber optic temperature and depth sensor (composite sensing probe) as a reflective sensing unit into the laser resonant cavity. Specifically, light from the isolator is introduced through port E1 of the first circulator, outputs from port E2 and is incident on the fiber optic temperature and depth sensor; it is output from port E3 of the first circulator to port G1 of the second circulator, and then incident on the sensing probe a second time through port G2. The light signal reflected back from the sensing probe carries external temperature and hydraulic information and is finally output from port G3 of the second circulator.

[0059] The fiber optic coupler used is a 10:90 fiber optic coupler, which splits the optical signal from the second circulator port 3G3 into a 10% and 90% ratio. 10% of the optical power is coupled to port 11 of the spectrometer for real-time monitoring and demodulation of the output signal; the remaining 90% of the optical power is fed back to port B3 of the wavelength division multiplexer to oscillate within the ring cavity, maintaining a stable laser state.

[0060] The spectrometer is used to receive and demodulate the transmitted light signal from the coupler. Its resolution is not less than 14 pm. It can deduce the temperature and hydraulic parameters by analyzing the intensity and spectral characteristics of the output laser.

[0061] The fiber optic temperature-depth sensor, also known as the composite sensing probe, serves as the core sensing unit, used to simultaneously sense changes in external temperature and hydraulic pressure. Specifically, the Fabry-Perot interferometer is sensitive to both temperature and hydraulic pressure, and its optical cavity length is modulated by both. The fiber Bragg grating is primarily sensitive to temperature, and its wavelength drifts with temperature, providing the system with a stable wavelength reference and direct temperature measurement. The cascaded reflection spectrum changes of both sensors modulate the cavity loss and feedback conditions, thereby converting changes in external parameters into measurable shifts in laser output intensity and wavelength.

[0062] It should be noted that the selection of the above optical components can be adjusted according to actual application requirements, and this embodiment does not impose a unique limitation. For example, the operating wavelength of the pump light source can be in other rare earth ion absorption bands, the splitting ratio of the coupler can be optimized while ensuring sufficient feedback power and output signal-to-noise ratio, and the resolution of the spectrometer can be selected according to the final measurement accuracy requirements.

[0063] On the one hand, as the first sensing element in the sensing probe, the phase matching condition of the resonant wavelength of the FBG is expressed as:

[0064] λ FBG =2 nef Λ

[0065] In the formula, λ FBG n is the resonant wavelength of the fiber grating. off Λ represents the effective refractive index of the fiber core and Λ represents the grating period. Furthermore, the reflected wavelength can be adjusted by changing the grating period.

[0066] Within the sensing probe, the FBG is susceptible to temperature changes but insensitive to pressure changes. Therefore, its temperature sensitivity to temperature changes can be expressed as:

[0067]

[0068] On the other hand, another sensing element in the sensing probe is an FPI (Fiber Optic Injection Pipe), whose interference cavity is formed by the inner surface of a single-crystal silicon diaphragm and the end face of a single-mode fiber. When a light beam is incident on this FPI cavity, it will undergo multiple reflections and refractions between the two reflection interfaces, forming a series of coherent beams with a fixed phase relationship. A constant optical path difference is maintained between adjacent reflected beams. Neglecting half-wave loss, the interference signal intensity can be expressed as:

[0069]

[0070] In the formula, I1 represents the light intensity reflected from the inner surface of the single-crystal silicon wafer. I2 represents the light intensity reflected from the end face of the single-mode optical fiber. eff Let n be the refractive index of the medium inside the FP cavity. c λ is the refractive index of the gas inside the microcavity. L is the length of the FP cavity. FPI φ is the wavelength of the interference light, and φ0 is the initial phase.

[0071] Because FPI is highly sensitive to both hydraulic pressure and temperature, its hydraulic sensitivity and temperature sensitivity under these parameter changes can be expressed as follows:

[0072]

[0073] Since the laser wavelength is determined by the resonant wavelength of the fiber grating, its displacement under temperature change ΔT can be expressed as:

[0074]

[0075] In the formula Δλ laser This represents the shift in the system's resonant wavelength. Since the system's resonant wavelength is determined by the fiber grating, k is... λ las。r-T Defined as k λ FBG-T .

[0076] Since the system's output intensity is modulated by both temperature and hydraulic pressure acting on the FPI, it can be expressed as:

[0077]

[0078] Where ΔI laser This represents the system's output strength. ΔI λ FPI and ΔI λ FBG The values ​​represent the resonant intensity changes under FPI and FBG wavelength shifts, respectively. ΔP and ΔT represent the changes in hydraulic pressure and temperature, respectively.

[0079] Based on the response characteristics of the aforementioned sensing units to different physical quantities, the sensing model of the system described in this invention can be expressed in matrix form, and temperature and hydraulic pressure can be demodulated by solving the following matrix equations:

[0080]

[0081] Please see Figure 3 As shown, it is a transmission spectrum of a fiber optic ring laser measurement system at different liquid levels (corresponding to different hydraulic pressures) provided in an embodiment of the present invention.

[0082] As shown in the figure, as the liquid level gradually increases from 50 mm to 700 mm, the transmission spectrum output by the sensing system changes accordingly. The output power changes periodically with the increase of the liquid level, and the output power sensitivity reaches 2.057 nW / mm.

[0083] Please see Figure 4 As shown, it is a transmission spectrum evolution diagram of a fiber optic ring laser-based measurement system under different temperature conditions provided by an embodiment of the present invention.

[0084] During the process of gradually increasing the temperature from 30℃ to 70℃, the overall shape of the output spectrum remained stable, without any mode jumps or obvious distortions, indicating that the laser operates stably over a wide temperature range and has good temperature adaptability.

[0085] Please see Figure 5 As shown, it is a linear fitting graph of the output wavelength of a fiber ring laser measurement system as a function of temperature, provided by an embodiment of the present invention.

[0086] Experiments showed that the wavelength redshifted with increasing temperature. Linear regression analysis determined the system's temperature sensitivity to be 10 pm / ℃, with a coefficient of determination R0. 2 The value of 0.999 indicates that the fiber Bragg grating plays a stable and accurate role in temperature sensing in the system, with excellent linearity.

[0087] Please see Figure 6 As shown, it is a linear fitting graph of the output power of a fiber ring laser measurement system as a function of temperature, provided by an embodiment of the present invention.

[0088] Data shows that within the temperature range of 30℃ to 70℃, the output power increases approximately linearly with increasing temperature. The fitted data indicates that the power sensitivity to temperature is 11 nW / ℃, and the coefficient of determination R0 is [value missing]. 2 The value is 0.924. This result indicates that the system's output intensity also exhibits a distinguishable response to temperature, providing an important basis for subsequent multi-parameter decoupling.

[0089] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A Fabry-Perot depth sensor based on a fiber ring laser, characterized in that, include: A composite sensing probe, consisting of a Fabry-Perot interferometer and a fiber Bragg grating cascaded, is used to synchronously sense external temperature and hydraulic pressure, and serves as a wavelength selection and feedback unit within the laser cavity. A fiber ring laser is used to provide optical gain and signal amplification for the composite sensing probe and output a laser signal carrying sensing information; a demodulation unit is used to acquire the wavelength and intensity information of the laser signal in real time and decouple the temperature and hydraulic pressure values ​​through multi-parameter matrix operations.

2. The sensor according to claim 1, characterized in that, The interference cavity of the Fabry-Perot interferometer is composed of the inner surface of a single-crystal silicon diaphragm and the end face of a single-mode optical fiber, and it has high sensitivity to both temperature and hydraulic pressure.

3. The sensor according to claim 1, characterized in that, The fiber Bragg grating is temperature sensitive, and its Bragg wavelength provides a stable intracavity wavelength reference and serves as an independent temperature sensing element.

4. The sensor according to claim 1, characterized in that, The encapsulation shell is manufactured using stereolithography 3D printing technology and integrated into a single package. It has a total length of 15 mm and an inner diameter of 0.8 mm. Internally, it contains precision fiber optic slots, 13 mm long and 0.8 mm in inner diameter, for respectively fixing the Fabry-Perot interferometer and the fiber Bragg grating.

5. The sensor according to claim 2, characterized in that, The thickness of the single-crystal silicon film is 500 micrometers.

6. A measurement system for the fiber optic temperature and depth sensor according to any one of claims 1-5, characterized in that, The system includes: a pump source, a wavelength division multiplexer, an erbium-doped fiber gain medium, a fiber isolator, a first fiber circulator, a second fiber circulator, a 10:90 fiber coupler, and a spectrometer. The pump light source is connected to the pump port of the wavelength division multiplexer, and the signal port of the wavelength division multiplexer is sequentially connected to the erbium-doped fiber, the fiber isolator, and the first port of the first fiber circulator. The second port of the first fiber optic circulator is connected to the composite sensing probe, and its third port is connected to the first port of the second fiber optic circulator. The second port of the second fiber optic circulator is connected to the composite sensing probe, and its third port is connected to the input end of the 10:90 fiber optic coupler. The first output of the 10:90 fiber coupler is connected to the spectrometer, and the second output is connected back to the signal return port of the wavelength division multiplexer to form a closed fiber ring laser resonant cavity.

7. The measurement system according to claim 6, characterized in that, The pump light source operates at a wavelength of 976 nanometers, and the spectrometer has a resolution of no less than 14 picometers.

8. A method for measuring temperature depth based on the measurement system according to any one of claims 6-7, characterized in that, Includes the following steps: The fiber ring laser is excited to generate a single longitudinal mode narrow linewidth laser; the composite sensing probe is modulated by external temperature and hydraulic pressure, causing changes in the laser output wavelength and intensity; the wavelength and intensity change signals are acquired in real time by the spectrometer; based on the pre-calibrated sensitivity matrix, the signals are calculated in real time, and the temperature and hydraulic pressure values ​​are output synchronously and independently.

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