A double-channel parallel FPI composite optical fiber temperature and salinity synchronous measurement sensor and method

Abstract

The application discloses a kind of double-channel parallel FPI composite optical fiber temperature salt synchronous measurement sensor and method, belong to marine environment monitoring technical field, the sensor includes light source, light path guiding module, sensor probe and spectral detection module;Sensor probe is connected by single-mode optical fiber, mode control optical fiber, side hole optical fiber and single-mode optical fiber in sequence, two micropores are equipped on side hole optical fiber, respectively constitute temperature sensing cavity and salinity sensing cavity;Sensor probe receives optical signal, after mode excitation, transmission to side hole optical fiber, generate multiple interference signals in probe and superimposed to generate composite interference spectrum;Wherein, two sensing cavities are reflected interference modulation to optical signal, so that temperature and salinity modulation component are contained in multiple interference signals;Spectral detection module receives returned composite interference spectrum and resolves, obtains temperature parameter and salinity parameter, by implementation the application, temperature salt cross talk can be effectively inhibited, and the precision of temperature and salinity parameter synchronous measurement under marine environment is improved.

Description

Technical Field

[0001] This application relates to the field of marine environmental monitoring technology, and in particular to a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor and method. Background Technology

[0002] Ocean temperature and salinity are core parameters describing the physical properties of seawater, and their accurate and synchronous measurement plays a fundamental supporting role in ocean circulation research, climate prediction, underwater navigation, and marine resource development. Because temperature and salinity parameters exhibit complex dynamic changes in the marine environment, and the two often occur simultaneously, sensors need to possess both high sensitivity and good parameter decoupling capabilities to achieve accurate and synchronous acquisition of temperature and salinity.

[0003] Currently, the mainstream technologies in the field of ocean temperature and salinity monitoring mainly include three categories: electrical sensors, fiber Bragg grating (FBG) sensors, and interferometric fiber optic sensors. Electrical sensor technology is mature, but it suffers from problems such as complex power supply, susceptibility to electromagnetic interference, and poor corrosion resistance, making it difficult to meet the needs of long-term, remote, and large-scale network monitoring. While FBG-based sensing schemes have solved the electromagnetic interference problem to some extent, their salinity sensitivity is generally low, making it difficult to support high-precision measurement requirements. Furthermore, the coating layer of the sensitive material is prone to aging and peeling, leading to significant temperature and salinity crosstalk. Even with temperature compensation using bare fiber gratings, coupling interference cannot be completely eliminated. To pursue higher sensitivity, researchers have turned to interferometric fiber optic sensors, especially sensing schemes based on Fabry-Perot interferometers. These sensors utilize changes in the cavity length or refractive index of a single interferometer cavity to induce spectral shifts, achieving parameter detection with improved sensitivity compared to FBG schemes. However, existing interferometric schemes still have the following technical bottlenecks: the sensitivity of a single interferometric cavity structure has an inherent upper limit; when a single cavity is used to respond to temperature and salinity parameters simultaneously, the temperature and salinity signals are completely coupled in the same interference spectrum; even with algorithm demodulation, crosstalk still exists; the two interference signals interfere with each other in the optical path; the demodulation complexity is high, resulting in limited measurement accuracy and stability.

[0004] In summary, the biggest drawback of existing technologies is that the sensing structure of current interferometric fiber optic temperature and salinity sensors cannot achieve physically isolated dual-channel parallel measurement, making it difficult to acquire temperature and salinity parameters synchronously and with low crosstalk in high-precision monitoring of the marine environment. Therefore, there is an urgent need for a fiber optic sensing solution that can achieve physical isolation between temperature and salinity channels and support high-sensitivity synchronous measurement to improve the measurement accuracy of temperature and salinity parameters in the marine environment. Summary of the Invention

[0005] This application provides a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor and method, aiming to solve the technical problem that existing interferometric fiber optic temperature and salinity sensors cannot achieve physically isolated dual-channel parallel measurement due to the inability of the sensing structure, which makes it difficult to synchronously and with low crosstalk acquire temperature and salinity parameters in high-precision monitoring of the marine environment, and to achieve high-sensitivity synchronous measurement and effective decoupling of temperature and salinity parameters.

[0006] In a first aspect, this application provides a dual-channel parallel FPI composite fiber temperature and salinity synchronous measurement sensor, the sensor comprising: a light source, an optical path guiding module, a sensor probe, and a spectral detection module; wherein, the sensor probe is composed of a first single-mode fiber, a mode control fiber, a side-hole fiber, and a second single-mode fiber connected in sequence, and the side-hole fiber is provided with two physically isolated micro-holes, which respectively constitute a temperature sensing cavity and a salinity sensing cavity. The sensor probe is used to receive the optical signal transmitted by the optical path guiding module, and to excite the input optical signal through the mode modulation fiber; the excited optical signal is transmitted to the side-hole fiber so that the excited optical signal generates a multi-path interference signal in the sensor probe; the multi-path interference signals are superimposed to generate a composite interference spectrum; wherein, the temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal so that the multi-path interference signal contains a temperature modulation component and a salinity modulation component; The spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters.

[0007] This application establishes two physically isolated micropores to form independent temperature and salinity sensing cavities. The temperature sensing cavity responds only to temperature changes and modulates the corresponding interference signal, while the salinity sensing cavity responds only to salinity changes and modulates the corresponding interference signal. This achieves physical separation of temperature and salinity signals at their physical source, fundamentally solving the crosstalk problem of temperature-salinity signal coupling in traditional sensors. By generating multiple interference signals within the sensor probe and superimposing them to form a composite interference spectrum, and by performing reflection interference modulation on the optical signal through the temperature and salinity sensing cavities respectively, the multiple interference signals carry temperature and salinity information respectively. This allows the optical signals caused by temperature and salinity changes to be concentrated in the composite spectrum, achieving synchronous measurement of temperature and salinity parameters. Compared to a single interference cavity structure, the superposition of multiple signals amplifies the spectral shift caused by temperature and salinity changes, thereby improving measurement accuracy. The composite interference spectrum is solved by a spectral detection module, directly separating and outputting temperature and salinity parameters from the composite signal, completing the full conversion from optical signal to temperature and salinity information. Meanwhile, the all-fiber fusion splicing structure eliminates the need for discrete optical components in the sensor, resulting in excellent structural stability and environmental adaptability, ensuring stable optical signal entry into the sensing area. Compared to existing sensors that rely on a single interference cavity or sensitive material coating, this application fundamentally solves the temperature and salinity crosstalk problem through a physically isolated dual-channel parallel FPI structure. Furthermore, the superposition of multiple interference signals improves measurement accuracy, achieving high-precision synchronous measurement of temperature and salinity parameters.

[0008] Furthermore, the excited optical signal generates multiple interference signals within the sensor probe, including: The sensor probe is equipped with four reflective surfaces, namely the first reflective surface, the second reflective surface, the third reflective surface and the fourth reflective surface; The first reflecting surface is the splice surface between the first single-mode fiber and the mode-controlled fiber; The second reflective surface is the fusion splice surface of the mode-tuning fiber and the side-hole fiber; The third reflective surface is the inner surface of the micropore; The fourth reflective surface is the fusion splice surface between the side-hole optical fiber and the second single-mode optical fiber; When the optical signal propagates within the sensor probe, it is reflected at the first, second, third, and fourth reflecting surfaces, generating multi-path interference signals.

[0009] By explicitly setting four reflective surfaces inside the sensor probe, definite optical boundary conditions are provided for the generation of multi-path interference signals, enabling the light signal to be reflected at multiple preset positions when propagating inside the sensor probe, thus laying the structural foundation for the formation of composite interference spectra.

[0010] Furthermore, the multi-channel interference signal includes: The first interference signal formed by the reflected light from the first reflecting surface and the second reflecting surface; The second interference signal formed by the reflected light from the third reflecting surface and the fourth reflecting surface; The third interference signal formed by the reflected light from the second reflecting surface and the fourth reflecting surface; The first interference signal, the second interference signal, and the third interference signal are superimposed to form the composite interference spectrum. By specifically defining the composition of the three interference signals, the interference signals generated by different combinations of reflective surfaces can each carry different physical information, providing identifiable basic signal units for the subsequent separation of temperature and salinity signals from the composite spectrum; by superimposing the three interference signals to form a composite interference spectrum, the fusion of multiple signals is realized, making the final spectrum contain richer environmental parameter information.

[0011] Furthermore, the third reflecting surface includes the inner surfaces of the two micro-holes, and the reflected light between the two micro-holes and the fourth reflecting surface together forms the second interference signal.

[0012] The second interference signal is formed by the reflected light between the inner surfaces of the two micro-holes and the fourth reflecting surface. This solves the problem of how the temperature sensing cavity and the salinity sensing cavity can cooperate to carry information at the signal level, even though they are physically independent. Temperature modulation and salinity modulation are applied to the same interference signal, which maintains the physical isolation of the two cavities and realizes the superposition of temperature and salinity information in the same signal. This provides a feasibility at the signal level for decoupling temperature and salinity parameters through mathematical methods, while avoiding the problem of the spectrum being too complex and difficult to analyze due to too many signal paths.

[0013] Furthermore, the spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters, including: The composite interference spectrum was analyzed to obtain a spectrum diagram; At least two characteristic frequencies are extracted from the spectrum, the at least two characteristic frequencies including a second characteristic frequency and a third characteristic frequency; wherein the second characteristic frequency corresponds to a second interference signal, and the third characteristic frequency corresponds to a third interference signal.

[0014] By extracting characteristic frequencies from the composite interference spectrum, at least a second characteristic frequency corresponding to the temperature sensing cavity and the salinity sensing cavity is obtained. This enables the extraction of characteristic signals carrying temperature and salinity information from the complex composite spectrum, transforming the original spectral data into frequency parameters with clear physical meaning and reducing the computational complexity of subsequent data processing. By determining the characteristic frequencies, a correspondence between optical signals and physical parameters is established, providing directly processable basic data for subsequent quantitative calculations.

[0015] Furthermore, the spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters, and also includes: Obtain the second and third reference frequencies of the sensor in its initial state; The second offset is obtained based on the difference between the second characteristic frequency and the second reference frequency; The third offset is obtained based on the difference between the third characteristic frequency and the third reference frequency; Based on the pre-stored sensitivity matrix, matrix operations are performed on the second offset and the third offset to obtain the temperature change and salinity change.

[0016] By acquiring the reference frequency of the sensor in its initial state and calculating the difference between the current characteristic frequency and the reference frequency to obtain the offset, the influence of sensor structural differences, light source fluctuations, and environmental background on the measurement results is eliminated, improving the accuracy and repeatability of the measurement. By pre-storing a sensitivity matrix containing four response coefficients, the response characteristics of the temperature sensing cavity and the salinity sensing cavity to temperature and salinity are described. By performing matrix operations on the offset, quantitative decoupling calculation of temperature and salinity signals is realized, outputting the temperature change and salinity change, completing the accurate quantitative conversion from optical signal to physical parameter, and solving the signal separation problem in the simultaneous measurement of multiple parameters.

[0017] Furthermore, the temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal, so that the multi-channel interference signal includes a temperature modulation component and a salinity modulation component, including: The temperature sensing cavity is filled with thermo-optical material; The refractive index of the thermo-optical material in the temperature sensing cavity is determined based on the current temperature of the solution being measured. Based on the refractive index of the thermo-optical material, the excited optical signal is subjected to reflection interference modulation to generate a temperature-modulated interference signal component.

[0018] By filling the temperature sensing cavity with thermo-optical material, temperature changes can be directly converted into changes in the refractive index of the thermo-optical material, thereby altering the optical path difference of the interference signal and achieving a specific response of the temperature signal at the optical level. The generation of temperature-modulated interference signal components provides a clear signal source for subsequent extraction of temperature information from composite signals.

[0019] Furthermore, the temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal, so that the multi-channel interference signal includes a temperature modulation component and a salinity modulation component, and further includes: The salinity sensing cavity has an open structure; The refractive index of the salinity sensing cavity is determined based on the salinity of the solution being measured. Based on the refractive index of the salinity sensing cavity, the excited optical signal is subjected to reflection interference modulation to generate a salinity-modulated interference signal component. The temperature-modulated interference signal component and the salinity-modulated interference signal component are superimposed on the second interference signal.

[0020] By setting the salinity sensing cavity as an open structure, the measured solution can directly enter the micropore. Changes in solution salinity directly cause changes in refractive index, eliminating the response delay caused by the coating layer of the sensitive material and improving the dynamic response speed of salinity measurement. By superimposing the temperature modulation component and the salinity modulation component into the second interference signal, the same physical signal can simultaneously carry dual information of temperature and salinity, which not only ensures efficient signal transmission, but also provides a composite information basis for subsequent decoupling.

[0021] Furthermore, the side-hole optical fiber is provided with two physically isolated micro-holes, which respectively constitute a temperature sensing cavity and a salinity sensing cavity, specifically: The two physically isolated micropores are formed using femtosecond laser processing and have a symmetrical structure.

[0022] By using femtosecond lasers to process the side-hole fiber, two physically isolated micro-holes with a symmetrical structure are obtained, ensuring that the two sensing cavities have the same optical boundary conditions. This guarantees that the temperature cavity and salinity cavity have similar reflection characteristics in the optical path, facilitating subsequent signal processing and parameter calibration. Femtosecond laser processing can achieve sub-micron level processing accuracy, ensuring that the size, shape, and position of the micro-holes meet design requirements. Furthermore, femtosecond laser processing requires no subsequent processing, avoiding contamination or structural damage that may be introduced by methods such as chemical etching.

[0023] Furthermore, the step of exciting the input optical signal through the mode-controlled optical fiber and transmitting the excited optical signal to the side-hole optical fiber specifically involves: The optical signal is excited by the mode-controlled optical fiber to generate an excited optical signal containing multiple transmission modes. The excited optical signal is coupled and output to the side-hole optical fiber.

[0024] By using mode-controlled optical fibers to excite optical signals in multiple modes, a single-mode optical signal can be expanded into an optical field distribution containing multiple transmission modes, thus enriching the information carried by the optical signal. When the multi-mode optical field propagates within the side-hole optical fiber, it can generate richer interference effects at multiple reflecting surfaces, enhancing the intensity and clarity of the interference signal. The excited optical signal is effectively coupled to the side-hole optical fiber, ensuring that the mode-enhanced optical signal can fully enter the sensing area and play its role.

[0025] Secondly, this application provides a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement method, the method being applicable to a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor as described in the first aspect, the method comprising: Transmit the optical signal to the sensor probe; The optical signal is excited by the mode modulation fiber inside the sensor probe, and the excited optical signal is transmitted to the side hole fiber inside the sensor probe. The excited optical signal is reflected at multiple reflective surfaces within the sensor probe, generating multi-path interference signals. The multi-path interference signals are superimposed to generate a composite interference spectrum. The two physically isolated micro-holes on the side-hole optical fiber serve as a temperature sensing cavity and a salinity sensing cavity, respectively, to perform reflection interference modulation on the excited optical signal, so that the multi-path interference signal contains temperature modulation components and salinity modulation components. The composite interference spectrum is returned to the spectral detection module; the spectral detection module then calculates the composite interference spectrum to obtain temperature and salinity parameters.

[0026] This application solves the crosstalk problem caused by the coupling of temperature and salinity signals in traditional sensors by setting two physically isolated micropores on the side-hole optical fiber to form independent temperature and salinity sensing cavities. This achieves physical separation of temperature and salinity signals at the source. By using mode-controlled optical fiber to excite the optical signal and generate multiple interference signals at multiple reflective surfaces to form a composite interference spectrum, the changes in optical signal caused by temperature and salinity changes are amplified, improving measurement accuracy. By setting the salinity sensing cavity as an open structure, the measured solution can directly enter the micropore without the need for an indirect response from the sensitive material coating layer, shortening the salinity measurement response time. At the same time, the all-fiber fusion splicing structure gives the sensor good vibration resistance and corrosion resistance, and the femtosecond laser processing of the micropores avoids complex coating processes, reducing the difficulty and cost of fabrication. Attached Figure Description

[0027] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the structure of one embodiment of the dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor provided in this application; Figure 2 This is a schematic diagram of a sensor probe structure according to one embodiment of the present application; Figure 3 This is a schematic flowchart of an embodiment of the dual-channel parallel FPI composite fiber optic synchronous temperature and salinity measurement method provided in this application. Labeling Explanation: 100, Light Source; 200, Optical Path Guiding Module; 300, Sensor Probe; 400, Spectral Detection Module; 310, First Single-Mode Fiber; 320, Mode Control Fiber; 330, Side-Hole Fiber; 340, Second Single-Mode Fiber; 331, Temperature Sensing Cavity; 332, Salinity Sensing Cavity. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0033] In marine environmental monitoring, achieving high-precision synchronous measurement of temperature and salinity is a core foundation for assessing the marine environment. However, existing sensors generally suffer from bottlenecks such as signal crosstalk and insufficient sensitivity during synchronous measurement: electrical sensors are susceptible to interference and have poor corrosion resistance; FBG sensors have low sensitivity and severe crosstalk; single-cavity FPI cannot completely decouple signals; and SPR is difficult to scale up due to its complex manufacturing process and high cost. Therefore, how to suppress crosstalk at the source and simultaneously improve measurement accuracy and response speed under stable and low-cost conditions has become a key challenge in the development of current marine monitoring technologies. To address this, this application proposes a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor. Through a physically isolated dual-cavity structure and a multi-channel interference signal superposition mechanism, it eliminates temperature and salinity crosstalk at the source, achieving high-sensitivity synchronous measurement.

[0034] Please refer to Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of the structure of one embodiment of the dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor provided in this application. Figure 2 This is a schematic diagram of a sensor probe structure according to an embodiment of this application. To address the technical problem of limited measurement accuracy in existing temperature and salinity sensors due to signal crosstalk, an embodiment of this application provides a dual-channel parallel FPI composite fiber optic synchronous temperature and salinity measurement sensor, comprising: a light source 100, an optical path guiding module 200, a sensor probe 300, and a spectral detection module 400. The specific connection relationships and functions of each module are as follows: The sensor probe 300 is composed of a first single-mode fiber 310, a mode-tuning fiber 320, a side-hole fiber 330, and a second single-mode fiber 340 connected in sequence. The side-hole fiber 330 has two physically isolated micro-holes, which respectively form a temperature sensing cavity 331 and a salinity sensing cavity 332. The sensor probe 300 is used to receive the optical signal transmitted by the optical path guiding module 200 and to excite the input optical signal through the mode modulation fiber 320; the excited optical signal is transmitted to the side hole fiber 330 so that the excited optical signal generates multiple interference signals in the sensor probe 300; the multiple interference signals are superimposed to generate a composite interference spectrum; wherein, the temperature sensing cavity 331 and the salinity sensing cavity 332 respectively perform reflection interference modulation on the excited optical signal so that the multiple interference signals contain temperature modulation components and salinity modulation components. The spectral detection module 400 is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters.

[0035] The optical path guiding module enables unidirectional transmission of optical signals, preventing reflected light from interfering with the light source and detection system. The temperature and salinity sensing cavities respectively perform reflection interference modulation on the excited optical signals. This means that the two micro-apertures act as independent Fabry-Perot interference cavities, changing the optical path difference through variations in the refractive index of their internal media, thereby modulating the optical signal passing through the cavity. Reflection interference modulation refers to the reflection of the optical signal at the inner surface of the micro-aperture, interfering with reflected light from other reflective surfaces. Changes in the interference signal reflect changes in environmental parameters. The temperature and salinity modulation components are superimposed on the multi-path interference signals, collectively forming a composite interference spectrum carrying temperature and salinity information.

[0036] In one embodiment, the light source is an ASE broadband light source with an output wavelength range of 1520~1620nm and power stability ≤±0.1dB, providing a stable incident light basis for interferometric measurements; the optical path guiding module uses an optical fiber circulator with unidirectional conduction characteristics at ports 1→2→3, insertion loss ≤0.5dB, and isolation ≥60dB, to avoid interference from reflected light to the light source and detection system, ensuring the purity of the optical signal; the spectral detection module uses a spectral analyzer with a wavelength resolution ≤0.01nm, a spectral acquisition rate ≥10Hz, and fast Fourier transform analysis function, used to receive the interferometric spectrum and analyze the temperature and salinity characteristic signals; The first and second single-mode fibers are SMF-28e type single-mode fibers with a diameter of 125μm and a numerical aperture of 0.14, used to achieve low-loss input and output of optical signals and ensure optical coupling stability. The mode modulation fiber is a multimode fiber with a length of 1mm, a diameter of 125μm, and a numerical aperture of 0.22, used to excite multiple transmission modes and provide a rich optical field basis for interference. The side-hole fiber is 180μm long and 125μm in diameter, with two micro-holes formed by femtosecond laser processing. The micro-hole dimensions are 100μm in length, 10~16μm in depth, and 30μm in width, used to ensure the structural consistency and independence of the two sensing cavities.

[0037] Specifically, in some embodiments, the excited optical signal generates multiple interference signals within the sensor probe 300, including: The sensor probe 300 has four reflective surfaces, namely the first reflective surface, the second reflective surface, the third reflective surface and the fourth reflective surface; The first reflecting surface is the splice surface of the first single-mode fiber 310 and the mode-tuning fiber 320. The second reflective surface is the fusion splice surface of the mode-controlled fiber 320 and the side-hole fiber 330. The third reflecting surface is the inner surface of the micropore; The fourth reflecting surface is the fusion splice surface between the side-hole fiber 330 and the second single-mode fiber 340; When the light signal propagates within the sensor probe 300, it is reflected at the first, second, third, and fourth reflecting surfaces, generating multiple interference signals.

[0038] Here, the reflecting surface refers to the physical interface formed at the junction of different media in the optical fiber, which enables part of the incident light to undergo Fresnel reflection. In this embodiment, the four reflecting surfaces are as follows: First reflecting surface M1: The splice surface of the first single-mode fiber and the mode-controlled fiber. Due to the difference in the core diameter and numerical aperture of the two fibers, the refractive index is discontinuous at this interface, forming the first reflection point. Second reflective surface M2: The splice surface between the mode-controlled fiber and the side-hole fiber. The material and structural differences between the two fibers cause a second reflection point to be formed at this interface. The third reflecting surface M3: the inner surface of the micro-hole on the side-hole optical fiber, that is, the interface between the optical fiber material and the medium inside the micro-hole. Due to the difference in refractive index between the optical fiber material and the medium inside the hole, a strong reflecting surface is formed. The fourth reflecting surface M4 is the fusion splice surface between the side-hole fiber and the second single-mode fiber, serving as the last reflection point before the optical signal is output.

[0039] Specifically, in some embodiments, the multiple interference signals in the sensor probe 300 include: The first interference signal formed by the reflected light from the first reflecting surface and the second reflecting surface; The second interference signal is formed by the reflected light from the third and fourth reflecting surfaces; The third interference signal is formed by the reflected light from the second and fourth reflecting surfaces; The first, second, and third interference signals are superimposed to form a composite interference spectrum.

[0040] Interference signals refer to the constructive or destructive interference that occurs when two coherent beams of light meet in space due to their different optical path differences, resulting in alternating bright and dark interference fringes. In the spectral domain, interference signals exhibit periodic fluctuations in intensity that vary with wavelength. Reflected light pairs with different optical path differences produce interference signals of different frequencies.

[0041] For specific implementation details, please refer to [the relevant documentation / reference]. Figure 2 The schematic diagram of the sensor probe structure shown illustrates the specific process by which the excited optical signal propagates within the sensor probe and generates multi-channel interference signals: Step S301: The excited optical signal is incident on the first reflective surface M1 through the first single-mode fiber, and the first reflection occurs at the first reflective surface M1. The reflected light propagates to the left and returns to the first single-mode fiber. At the same time, most of the optical signal is transmitted through the first reflective surface M1 and enters the mode control optical cable.

[0042] Step S302: The transmitted light propagates within the mode-tuning optical cable to the second reflecting surface M2, where it undergoes a second reflection. The reflected light propagates to the left and returns to the mode-tuning optical fiber. Simultaneously, most of the optical signal is transmitted through the second reflecting surface M2 and enters the side-hole optical fiber.

[0043] Step S303: The optical signal entering the side-hole fiber continues to propagate to the right within the fiber, encountering the inner surfaces of two micro-apertures (i.e., the third reflecting surface M3) and the fourth reflecting surface M4 in sequence. Due to the structural symmetry of the two micro-apertures, the optical signal is reflected at both inner surfaces, and the two reflected beams propagate back to the left respectively; finally, the remaining optical signal propagates to the fourth reflecting surface M4 and is reflected, with the reflected beam propagating back to the left.

[0044] The multiple reflected beams superimpose as they propagate to the left within the sensor probe, forming a multi-path interference signal. Specifically: The reflected light from the first reflecting surface M1 and the second reflecting surface M2 forms a first interference signal due to the difference in path length; The reflected light from the inner surfaces of the two micro-holes (i.e., the third reflecting surface M3) and the fourth reflecting surface M4 respectively forms two interference signals with similar frequencies. These two signals are regarded as integral components of the second interference signal in subsequent processing. The reflected light from the second reflecting surface M2 and the fourth reflecting surface M4 forms a third interference signal.

[0045] Through the above process, the optical signal is reflected multiple times at the four reflective surfaces inside the sensor probe, generating three interference signals with different optical path differences, which are superimposed to form a composite interference spectrum.

[0046] Specifically, in some embodiments, in the sensor probe 300, the third reflecting surface includes the inner surfaces of two micro-holes, and the inner surfaces of the two micro-holes together with the reflected light between the fourth reflecting surface form a second interference signal.

[0047] In this embodiment, the third reflecting surface is not a single reflecting surface, but a group of reflecting surfaces composed of two physically isolated micro-pore inner surfaces. Since the two micro-pores are processed by femtosecond laser to form a symmetrical structure, their size, shape, and position are highly consistent. Therefore, the inner surfaces of the two micro-pores have similar optical properties as reflecting surfaces.

[0048] In one embodiment, the inner surfaces of the two micro-holes are respectively part of the third reflective surface. When the excited light signal propagates to the two micro-holes, it is reflected on the inner surfaces of the two micro-holes respectively. The two reflected lights interfere with the reflected light of the fourth reflective surface. Since the two micro-holes are close in position and have symmetrical structure, the frequencies of the two interference signals are similar, and they are superimposed on the spectrum to form a second interference signal.

[0049] In the specific implementation, when the excited optical signal propagates to the right within the side-aperture fiber, it first reaches the positions of the two microapertures. Partial reflection occurs at the inner surface of the first microaperture, and the reflected light propagates to the left; partial reflection also occurs at the inner surface of the second microaperture, and the reflected light propagates to the left. Because the two microapertures are close to each other... In actual measurements, due to the resolution limitations of the spectral detection module, the two interference signals with similar frequencies cannot be distinguished as two independent frequency peaks in the spectrum after Fast Fourier Transform (FFT). Instead, they superimpose to form a broadened frequency peak. Therefore, in the signal processing model, the interference signals from the two micro-apertures are considered together as a component of the second interference signal.

[0050] Specifically, in some embodiments, the spectral detection module 400 is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters, including: Spectral analysis was performed on the composite interference spectrum to obtain the spectrum diagram; At least two characteristic frequencies are extracted from the spectrum, including a second characteristic frequency and a third characteristic frequency; wherein the second characteristic frequency corresponds to the second interference signal and the third characteristic frequency corresponds to the third interference signal.

[0051] In this context, the characteristic frequency refers to the frequency value corresponding to the peak value appearing in the spectrum after the composite interference spectrum has undergone a fast Fourier transform. In this embodiment, the composite interference spectrum is composed of three interference signals with different optical path differences superimposed on each other, and each interference signal corresponds to a characteristic frequency peak in the spectrum. The magnitude of the characteristic frequency is proportional to the optical path difference of the interference signals; the larger the optical path difference, the higher the characteristic frequency.

[0052] In an optional embodiment, the spectral detection module continuously acquires the composite interference spectrum I(λ) returned by the optical path guiding module at a rate of ≥10Hz. In this embodiment, the spectral detection module uses a spectrometer with a wavelength resolution ≤0.01nm to ensure that the acquired spectral data has sufficient precision for subsequent analysis. The acquired composite interference spectrum I(λ) is represented as a discrete data sequence of light intensity varying with wavelength.

[0053] The spectral detection module performs a Fast Fourier Transform (FFT) on the acquired composite interference spectrum I(λ), transforming the spectrum from the wavelength domain to the spatial frequency domain to obtain a spectrogram. The mathematical expression for the FFT transform is: , in, f The spatial frequency, in nm⁻¹ or μm⁻¹, represents the number of periods of interference fringes per unit wavelength; For the corresponding frequency f The amplitude value.

[0054] In the spectrum, since the three interference signals have different optical path differences, they correspond to peak values ​​at different frequency positions. Specifically, the first interference signal (formed by the first reflecting surface M1 and the second reflecting surface M2) corresponds to the lowest frequency peak, which is denoted as the first characteristic frequency. f 1; The second interference signal (formed by the third reflecting surface M3 and the fourth reflecting surface M4) corresponds to a peak value in the middle of the frequency range. However, due to the presence of the two micro-apertures, this peak value usually appears as a broadened peak, and its center frequency is denoted as the second characteristic frequency. f 2; The peak value of the highest frequency corresponding to the third interference signal (formed by the second reflecting surface M2 and the fourth reflecting surface M4) is denoted as the third characteristic frequency f3.

[0055] Of the three characteristic frequencies mentioned above, the first characteristic frequency is... Determined by its pure photonic structure (mode-controlled fiber), its optical path is minimally affected by temperature and does not respond to changes in salinity. It remains largely unaffected by changes in seawater salinity and is primarily used to monitor common-mode interference such as fluctuations in light source power and changes in optical path loss, providing a self-test benchmark and error correction reference for the system. In actual measurements, The stability of the system can be used to determine its operating status and, when necessary, to adjust it. and Normalization correction is performed to eliminate the impact of common-mode interference on measurement accuracy.

[0056] Second characteristic frequency The optical path difference between the two micro-apertures and the fourth reflecting surface is determined by the optical path difference. Since the two micro-apertures are respectively filled with thermo-optical material (temperature sensing) and directly vented with seawater (salinity sensing), therefore... Simultaneously modulated by temperature and salinity, it is the main signal of the overall salt information of the carrier. Changes in temperature and salinity will cause changes in the refractive index of the medium within the micropores, thus leading to... An offset occurs, and this offset is the core input for subsequent temperature and salinity calculations.

[0057] Third characteristic frequency Due to the length and refractive index of the side-hole fiber itself, the side-hole fiber exhibits a thermo-optical effect, therefore It is sensitive to temperature changes, but because the side-hole fiber material (pure quartz) is unresponsive to salinity, It is largely insensitive to changes in salinity. Therefore, Primarily used as a temperature parameter signal, its offset reflects temperature changes, providing a second independent equation for decoupling temperature and salinity.

[0058] During the temperature and salinity calculation process, the spectral detection module extracts the second characteristic frequency. and third characteristic frequency As the primary parameter, combined with a pre-calibrated sensitivity matrix, matrix operations can be performed to simultaneously obtain the temperature and salinity changes. First characteristic frequency. Although it does not directly participate in the solution, it can be used as a reference signal to improve the long-term stability and anti-interference capability of the system.

[0059] Specifically, in some embodiments, the spectral detection module 400 is used to receive the composite interference spectrum returned by the optical path guiding module 200, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters, and also includes: Acquire the second and third reference frequencies of the sensor in its initial state; The second offset is obtained based on the difference between the second characteristic frequency and the second reference frequency; The third offset is obtained based on the difference between the third characteristic frequency and the third reference frequency; Based on the pre-stored sensitivity matrix, matrix operations are performed on the second and third offsets to obtain the temperature change and salinity change.

[0060] The reference frequency refers to the characteristic frequency value measured by the sensor under known initial conditions. In this embodiment, the initial state is typically chosen as a standard marine environment. Under this condition, the spectral detection module extracts the characteristic frequencies from the acquired composite interferometric spectrum, and the obtained reference frequency of the corresponding signal serves as the reference zero point for subsequent measurements, used to eliminate the influence of structural differences in the sensor itself and environmental background. The offset refers to the change in the characteristic frequency relative to the reference frequency under the current measurement state; the magnitude of the offset directly reflects the degree of change in temperature and salinity. In this embodiment, the sensitivity matrix refers to the mathematical model of the response characteristics of the characteristic frequency to changes in temperature and salinity.

[0061] In one embodiment, the sensor is placed at a known temperature before its first use or during periodic calibration. and salinity In a standard marine environment (e.g., standard seawater), the light source and spectral detection module are activated to acquire the composite interference spectrum at this time. Frequency domain transformation and characteristic frequency extraction are then performed to obtain the reference frequency of the corresponding interference signal. The reference frequency is stored in the non-volatile memory of the spectral detection module as a reference for subsequent measurements.

[0062] During the actual measurement process, the spectral detection module performs a frequency domain transformation on the currently acquired composite interference spectrum to obtain the second characteristic frequency under the current state. and third characteristic frequency Retrieve the second reference frequency from memory. and the third reference frequency The offset is calculated by comparing it with the current feature frequency. Second offset , Third offset , The offsets mentioned above are signed real numbers; positive values ​​indicate an increase in frequency, and negative values ​​indicate a decrease in frequency.

[0063] Retrieve the pre-stored sensitivity matrix K from memory. This matrix can be obtained through the following experimental calibration: Temperature calibration: Maintain constant salinity ( ), change temperature Measure the second characteristic frequency offset at different temperatures and the third characteristic frequency offset Obtained through linear fitting and ; Salinity calibration: Maintain a constant temperature ( ), change salinity Measured at different salinity levels and Obtained through linear fitting and .

[0064] According to the definition of the sensitivity matrix, the offset and the temperature-salinity change satisfy the following linear relationship: , in The change in temperature This represents the change in salinity.

[0065] The above system of equations can be written in matrix form: , Record , , These are the sensitivity coefficients of the second characteristic frequency to temperature and salinity (units: nm⁻¹ / °C, nm⁻¹ / %o), respectively. , These are the sensitivity coefficients of the third characteristic frequency to temperature and salinity, respectively. This matrix was obtained through experimental calibration and is pre-stored in the memory of the spectral detection module. Regarding the sensitivity matrix... Find the inverse to obtain the inverse matrix. The change in temperature and salinity can be calculated using the following formula: , The specific expression for the inverse matrix is: , After unfolding, we get: , The calculated and As the final output, if absolute temperature and salinity values ​​are required, they can be calculated based on the initial calibration values: .

[0066] Specifically, in some embodiments, the temperature sensing cavity 331 and the salinity sensing cavity 332 respectively perform reflection interference modulation on the excited optical signal, so that the multi-path interference signal includes a temperature modulation component and a salinity modulation component, including: The temperature sensing cavity 331 is filled with thermo-optical material; The refractive index of the thermo-optical material in the temperature sensing cavity 331 is determined based on the current temperature of the solution being measured. Based on the refractive index of the thermo-optical material, the excited optical signal is subjected to reflection interference modulation to generate a temperature-modulated interference signal component.

[0067] Femtosecond laser processing refers to the use of pulse widths in the femtosecond (10⁻¹) range. 5 Femtosecond lasers are a technology that uses ultrashort pulse lasers on the order of seconds to process materials. Femtosecond lasers have extremely high instantaneous power density and extremely short processing times, enabling cold processing with sub-micron precision. The heat-affected zone during processing is minimal, avoiding defects such as material melting and cracking, making them particularly suitable for the micro-processing of brittle materials such as optical fibers.

[0068] A symmetrical structure refers to two micro-apertures that are highly consistent in geometric dimensions, shape, and positional distribution. In this embodiment, the symmetrical structure includes, but is not limited to, the two micro-apertures having the same length, width, and depth, and being symmetrically distributed with respect to the axis of the side-aperture optical fiber. The symmetrical structure design ensures that the temperature sensing cavity and the salinity sensing cavity have the same optical boundary conditions and similar optical field distribution characteristics.

[0069] Physical isolation refers to the separation of two microcavities by a solid material consisting of side-hole optical fibers, preventing them from communicating and forming independent microcavity structures. This physical isolation ensures the optical and fluid independence of the temperature sensing cavity and the salinity sensing cavity, avoiding mutual interference between them.

[0070] In one embodiment, the temperature sensing cavity is filled with UV adhesive (model: NOA65) with a refractive index that varies with temperature by a coefficient of 1.8 × 10⁻⁻. 4 The temperature is ℃, and the cavity length changes linearly with temperature. When the temperature of the seawater being measured changes, the refractive index of the UV adhesive changes accordingly, causing a change in the optical path difference of the optical signal passing through the temperature sensing cavity, which in turn modulates the interference signal and generates a temperature-modulated interference signal component.

[0071] Specifically, in some embodiments, the temperature sensing cavity 331 and the salinity sensing cavity 332 respectively perform reflection interference modulation on the excited optical signal, so that the multi-path interference signal includes a temperature modulation component and a salinity modulation component, and further includes: The salinity sensing cavity 332 has an open structure; The refractive index of the salinity sensing cavity 332 is determined based on the salinity of the solution being measured. Based on the refractive index of the salinity sensing cavity 332, the excited optical signal is subjected to reflection interference modulation to generate a salinity-modulated interference signal component. The temperature-modulated interference signal component and the salinity-modulated interference signal component are superimposed on the second interference signal.

[0072] In one embodiment, the salinity sensing cavity is an open structure, directly vented with a marine salt solution. When the salinity of seawater changes, the refractive index of the seawater changes linearly, and the amount of refractive index change is linearly related to the salinity. This causes a change in the optical path difference of the optical signal passing through the salinity sensing cavity, thereby modulating the interference signal and generating a salinity-modulated interference signal component. This salinity-modulated component and the temperature-modulated component are superimposed on the second interference signal.

[0073] Specifically, in some embodiments, the side-hole optical fiber 330 has two physically isolated micro-holes, which respectively constitute a temperature sensing cavity 331 and a salinity sensing cavity 332, as follows: The two physically isolated micropores are formed using femtosecond laser processing and have a symmetrical structure.

[0074] In actual operation, the two micro-holes on the side-hole fiber are formed by femtosecond laser processing with submicron precision. The micro-hole size is precisely controlled to be 100μm in length, 10~16μm in depth, and 30μm in width. The two micro-holes are symmetrical to ensure that the temperature sensing cavity and the salinity sensing cavity have consistent optical characteristics and physical isolation.

[0075] Specifically, in some embodiments, the input optical signal is excited by a mode-controlled optical fiber, and the excited optical signal is transmitted to the side-hole optical fiber, as follows: The optical signal is excited by mode modulation fiber to generate an excited optical signal containing multiple transmission modes. The excited optical signal is coupled and output to the side hole optical fiber.

[0076] In one embodiment, the mode modulation fiber is a 1 mm long multimode fiber with a numerical aperture of 0.22. When an optical signal enters the mode modulation fiber from the first single-mode fiber, due to the intermode interference effect of the multimode fiber, the single-mode optical signal is excited to include TE. 01 Model, TM 01 The multimode interference optical field with multiple transmission modes provides an optical field basis for generating rich multi-path interference signals in the side-hole fiber.

[0077] Please refer to Figure 3 , Figure 3 This is a flowchart illustrating an embodiment of the dual-channel parallel FPI composite fiber optic synchronous temperature and salinity measurement method provided in this application, including steps S1 to S4, each step of which is detailed below: Step S1: Transmit the optical signal to the sensor probe; Step S2: The optical signal is excited by the mode modulation fiber inside the sensor probe, and the excited optical signal is transmitted to the side hole fiber inside the sensor probe. Step S3: The excited light signal is reflected at multiple reflective surfaces in the sensor probe, generating multi-path interference signals; the multi-path interference signals are superimposed to generate a composite interference spectrum; wherein, the two physically isolated micro-holes on the side-hole fiber serve as temperature sensing cavity and salinity sensing cavity, respectively, and perform reflection interference modulation on the excited light signal so that the multi-path interference signal contains temperature modulation components and salinity modulation components. Step S4: Return the composite interference spectrum to the spectral detection module; use the spectral detection module to solve the composite interference spectrum to obtain the temperature and salinity parameters.

[0078] It is understood that the above method embodiments correspond to the sensor embodiments of this application, and are applicable to the dual-channel parallel FPI composite fiber temperature and salinity synchronous measurement sensor provided in any of the above embodiments of this application.

[0079] For ease of description and brevity, the embodiments of the method in this application include all the implementation methods described in the above-described dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor embodiments, and will not be repeated here.

[0080] The above are preferred embodiments of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor, characterized in that, The sensor includes: a light source, an optical path guiding module, a sensor probe, and a spectral detection module; wherein, the sensor probe is composed of a first single-mode fiber, a mode control fiber, a side-hole fiber, and a second single-mode fiber connected in sequence; the side-hole fiber has two physically isolated micro-holes, which respectively form a temperature sensing cavity and a salinity sensing cavity. The sensor probe is used to receive the optical signal transmitted by the optical path guiding module, and to excite the input optical signal through the mode modulation fiber; the excited optical signal is transmitted to the side-hole fiber so that the excited optical signal generates a multi-path interference signal in the sensor probe; the multi-path interference signals are superimposed to generate a composite interference spectrum; wherein, the temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal so that the multi-path interference signal contains a temperature modulation component and a salinity modulation component; The spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters.

2. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 1, characterized in that, The excited optical signal generates multiple interference signals within the sensor probe, including: The sensor probe is equipped with four reflective surfaces, namely the first reflective surface, the second reflective surface, the third reflective surface and the fourth reflective surface; The first reflecting surface is the splice surface between the first single-mode fiber and the mode-controlled fiber; The second reflective surface is the fusion splice surface of the mode-tuning fiber and the side-hole fiber; The third reflective surface is the inner surface of the micropore; The fourth reflective surface is the fusion splice surface between the side-hole optical fiber and the second single-mode optical fiber; When the optical signal propagates within the sensor probe, it is reflected at the first, second, third, and fourth reflecting surfaces, generating multi-path interference signals.

3. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 2, characterized in that, The multi-channel interference signal includes: The first interference signal formed by the reflected light from the first reflecting surface and the second reflecting surface; The second interference signal formed by the reflected light from the third reflecting surface and the fourth reflecting surface; The third interference signal formed by the reflected light from the second reflecting surface and the fourth reflecting surface; The first interference signal, the second interference signal, and the third interference signal are superimposed to form the composite interference spectrum.

4. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 2 or 3, characterized in that, The third reflecting surface includes the inner surfaces of the two micro-holes, and the reflected light between the inner surfaces of the two micro-holes and the fourth reflecting surface together forms the second interference signal.

5. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 1, characterized in that, The spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature parameters and salinity parameters, including: The composite interference spectrum was analyzed to obtain a spectrum diagram; At least two characteristic frequencies are extracted from the spectrum, the at least two characteristic frequencies including a second characteristic frequency and a third characteristic frequency; wherein the second characteristic frequency corresponds to a second interference signal, and the third characteristic frequency corresponds to a third interference signal.

6. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 5, characterized in that, The spectral detection module is used to receive the composite interference spectrum returned by the optical path guiding module, and to solve the composite interference spectrum to obtain temperature and salinity parameters. It also includes: Obtain the second and third reference frequencies of the sensor in its initial state; The second offset is obtained based on the difference between the second characteristic frequency and the second reference frequency; The third offset is obtained based on the difference between the third characteristic frequency and the third reference frequency; Based on the pre-stored sensitivity matrix, matrix operations are performed on the second offset and the third offset to obtain the temperature change and salinity change.

7. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 1, characterized in that, The temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal, so that the multi-channel interference signal includes a temperature modulation component and a salinity modulation component, including: The temperature sensing cavity is filled with thermo-optical material; The refractive index of the thermo-optical material in the temperature sensing cavity is determined based on the current temperature of the solution being measured. Based on the refractive index of the thermo-optical material, the excited optical signal is subjected to reflection interference modulation to generate a temperature-modulated interference signal component.

8. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 7, characterized in that, The temperature sensing cavity and the salinity sensing cavity respectively perform reflection interference modulation on the excited optical signal, so that the multi-channel interference signal includes a temperature modulation component and a salinity modulation component, and further includes: The salinity sensing cavity has an open structure; The refractive index of the salinity sensing cavity is determined based on the salinity of the solution being measured. Based on the refractive index of the salinity sensing cavity, the excited optical signal is subjected to reflection interference modulation to generate a salinity-modulated interference signal component. The temperature-modulated interference signal component and the salinity-modulated interference signal component are superimposed on the second interference signal.

9. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 1, characterized in that, The side-hole optical fiber has two physically isolated micro-holes, which respectively form a temperature sensing cavity and a salinity sensing cavity, as follows: The two physically isolated micropores are formed using femtosecond laser processing and have a symmetrical structure.

10. The dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor according to claim 1, characterized in that, The process of exciting the input optical signal through the mode-controlled optical fiber and transmitting the excited optical signal to the side-hole optical fiber specifically involves: The optical signal is excited by the mode-controlled optical fiber to generate an excited optical signal containing multiple transmission modes. The excited optical signal is coupled and output to the side-hole optical fiber.

11. A method for synchronous measurement of temperature and salinity using a dual-channel parallel FPI composite optical fiber, characterized in that, The method is applicable to a dual-channel parallel FPI composite fiber optic temperature and salinity synchronous measurement sensor as described in any one of claims 1-10, and the method includes: Transmit the optical signal to the sensor probe; The optical signal is excited by the mode modulation fiber inside the sensor probe, and the excited optical signal is transmitted to the side hole fiber inside the sensor probe. The excited optical signal is reflected at multiple reflective surfaces within the sensor probe, generating multi-path interference signals. The multi-path interference signals are superimposed to generate a composite interference spectrum. The two physically isolated micro-holes on the side-hole optical fiber serve as a temperature sensing cavity and a salinity sensing cavity, respectively, to perform reflection interference modulation on the excited optical signal, so that the multi-path interference signal contains temperature modulation components and salinity modulation components. The composite interference spectrum is returned to the spectral detection module; the spectral detection module then calculates the composite interference spectrum to obtain temperature and salinity parameters.

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