Dual-parameter simultaneous detection method and system based on tunable laser sparse sampling

Abstract

The application discloses a kind of based on tunable laser sparse sampling dual-parameter simultaneous detection method and system, it is related to optical fiber sensing technical field.The method includes: based on two to be detected parameters preparation two interferometers;According to the free spectral range of interferometer, the sweep interval of tunable laser is determined;Two interferometers are inserted into the liquid to be detected, and sparse sampling is carried out using sensing device, to obtain two sparse interference spectra corresponding to two interferometers;Two sparse interference spectra are fitted respectively, to obtain two interference spectra;According to the interference spectrum, the amount of interference spectrum translation is determined, and then the change amount of two to be detected parameters relative to their respective calibration value is determined;Calibration value is added to change amount to obtain the measurement value of two to be detected parameters.The application improves the detection accuracy and sensitivity of optical fiber sensing system, and realizes dual-parameter synchronous measurement, provides a new type of sensing solution with simplified structure and excellent performance for marine environment monitoring.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a method and system for simultaneous detection of two parameters based on sparse sampling of a tunable laser. Background Technology

[0002] Fiber optic sensors, using optical fibers as their basic carrier, offer advantages such as compact structure, resistance to electromagnetic interference, low cost, small size, and easy reusability. They enable real-time, efficient, rapid, in-situ, and large-scale continuous monitoring of environmental parameters. In recent years, fiber optic sensors based on the optical vernier effect have received widespread attention in the field of simultaneous dual-parameter measurement. The vernier effect amplifies minute changes in external physical quantities through the interaction of two interference spectra with similar but different free spectral ranges, achieving high-resolution measurement. It offers advantages such as high sensitivity, non-contact measurement, and multi-parameter measurement.

[0003] Existing systems for dual-parameter measurement based on the vernier effect typically employ a main interferometer and an auxiliary interferometer scheme, such as one auxiliary interferometer and two sensing interferometers, with a spectrometer used for detection. This approach has several drawbacks: First, the introduction of the auxiliary interferometer not only increases the complexity of the system structure but also requires it to be located far from the sensing unit and in a stable environment to avoid external interference affecting the stability of the vernier envelope. Second, once the auxiliary interferometer is determined, the system's final sensitivity is also fixed, making it difficult to flexibly adjust the amplification factor. Furthermore, systems using broadband light sources and spectrometers result in higher sensing system costs, and the spectrometer directly measures the mixed interferometric spectrum of multiple interferometers, requiring complex data processing to obtain the vernier interferometric spectrum. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a method and system for simultaneous detection of two parameters based on sparse sampling of a tunable laser.

[0005] According to one aspect of the present invention, a method for simultaneous detection of two parameters based on sparse sampling of a tunable laser is proposed, the method comprising:

[0006] The first and second interferometers were prepared based on two parameters to be detected.

[0007] The sweep interval of the tunable laser is determined based on the free spectral ranges of the first and second interferometers;

[0008] One end of the first interferometer and the second interferometer are inserted into the liquid to be tested. The two parameters to be tested in the liquid to be tested are sparsely sampled using a sensing device containing a tunable laser, the first interferometer and the second interferometer, to obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer.

[0009] The first sparse interference spectrum and the second sparse interference spectrum are fitted respectively to obtain the first interference spectrum and the second interference spectrum;

[0010] The first and second interference spectrum shifts relative to the calibration interference spectrum envelope of the parameter to be detected are determined based on the first and second interference spectra, respectively.

[0011] The changes of the two parameters to be detected relative to their respective calibration values ​​are determined based on the first and second interference spectrum shifts.

[0012] The changes of the two parameters to be detected relative to their respective calibration values ​​are added to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

[0013] Furthermore, the two parameters to be detected are temperature and salinity; the first interferometer is made by sequentially fusing a single-mode optical fiber and a hollow optical fiber with one end filled with polydimethylsiloxane material; the second interferometer is made by staggered fusing of three single-mode optical fibers.

[0014] Furthermore, the sweep frequency interval of the tunable laser is determined based on the free spectral ranges of the first and second interferometers as follows:

[0015] SI=FSR1+ Or SI = FSR2+ ;

[0016] In the formula, SI represents the sweep interval of the tunable laser; FSR1 represents the free spectral range of the first interferometer; and FSR2 represents the free spectral range of the second interferometer. The difference between the sweep interval of the tunable laser and the free spectral range FSR1 of the first interferometer; This is the difference between the sweep interval of the tunable laser and the free spectral range FSR2 of the second interferometer; , The value ranges from 0.01 to 0.5, and the unit is nm.

[0017] Furthermore, the formulas for calculating the free spectral range of the first and second interferometers are as follows:

[0018] ;

[0019] In the formula, This indicates the sweep wavelength of the tunable laser; and These are the refractive indices of the intracavity media of the first and second interferometers, respectively. and These are the cavity lengths of the first and second interferometers, respectively.

[0020] Furthermore, the sensing device includes a tunable laser, a coupler, a first fiber optic circulator, a second fiber optic circulator, a first interferometer, a second interferometer, and an optical power meter; wherein, the output end of the tunable laser is connected to the input end of the coupler, the three output ends of the coupler are respectively connected to the first channel of the optical power meter, the first port of the first fiber optic circulator, and the first port of the second fiber optic circulator; the third port of the first fiber optic circulator and the third port of the second fiber optic circulator are respectively connected to one end of the first interferometer and the second interferometer; the second port of the first fiber optic circulator and the second port of the second fiber optic circulator are respectively connected to the second channel and the third channel of the optical power meter.

[0021] Furthermore, the step of using a sensing device comprising a tunable laser, a first interferometer, and a second interferometer to perform sparse sampling of two parameters to be detected in the liquid to be detected, and obtaining the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer, includes: the laser emitted by the tunable laser is split into three paths by a coupler, one of which is directly connected to the first channel of the optical power meter to monitor the intensity fluctuation of the light source in real time; the other two paths enter the first interferometer and the second interferometer respectively through the first fiber optic circulator and the second fiber optic circulator; the optical signals returned by the first interferometer and the second interferometer enter the second channel and the third channel of the optical power meter respectively through the first fiber optic circulator and the second fiber optic circulator; and the optical power meter collects the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer.

[0022] Furthermore, determining the changes of the two parameters to be detected relative to their respective calibration values ​​based on the first and second interference spectrum shifts includes calculating the changes using the following formula:

[0023] ;

[0024] ;

[0025] In the formula, Δλ1 and Δλ2 represent the first and second interference spectrum shifts, respectively; ΔT and ΔS represent the changes in temperature and salinity relative to the calibration values, respectively. and These are the temperature sensitivity and salinity sensitivity corresponding to the first interference spectrum, respectively. and These are the temperature sensitivity and salinity sensitivity corresponding to the second interference spectrum, respectively.

[0026] Furthermore, the temperature sensitivity corresponding to the first interference spectrum is M1 times the temperature sensitivity obtained by the sensing device through dense temperature sampling, and the expression for M1 is:

[0027] ;

[0028] The salinity sensitivity corresponding to the second interference spectrum is M² times the salinity sensitivity obtained by the sensing device through dense sampling of salinity. The expression for M² is:

[0029] .

[0030] According to another aspect of the present invention, a dual-parameter simultaneous detection system based on sparse sampling of a tunable laser is proposed, the system being used to implement the dual-parameter simultaneous detection method based on sparse sampling of a tunable laser described above; the system includes a sensing device and a signal processing module;

[0031] The sensing device is used to sparsely sample two parameters of the liquid to be tested, and obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer. The sensing device includes a tunable laser, a first interferometer, and a second interferometer. The frequency sweep interval of the tunable laser is determined according to the free spectral range of the first interferometer and the second interferometer. The first interferometer and the second interferometer are prepared based on the two parameters to be tested.

[0032] The signal processing module is used to fit the first sparse interference spectrum and the second sparse interference spectrum to obtain the first interference spectrum and the second interference spectrum, respectively; based on the first interference spectrum and the second interference spectrum, determine the first interference spectrum shift and the second interference spectrum shift relative to the calibration interference spectrum envelope corresponding to the parameter to be detected, respectively; based on the first interference spectrum shift and the second interference spectrum shift, determine the change of the two parameters to be detected relative to their respective calibration values; add the change of the two parameters to be detected relative to their respective calibration values ​​to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

[0033] The beneficial technical effects of this invention are:

[0034] This invention proposes a method and system for simultaneous detection of two parameters based on sparse sampling of a tunable laser, which has the following advantages: 1) No auxiliary interferometer is required; only two sensing interferometers are needed to achieve dual-parameter measurement, and the sensor structure is relatively simple; 2) Only sparse sampling of a tunable laser is needed to obtain the vernier envelope spectra of the two sensing interferometers, and the vernier amplification can be flexibly adjusted by controlling the sparse sampling interval; 3) The optical power meter detection method not only greatly reduces the cost of the sensing system, but also allows the optical power meter to use different channels to detect the vernier envelope spectra of the two sensing interferometers separately, so that the two spectra do not interfere with each other; 4) Dual-parameter measurement can be achieved by establishing a two-dimensional matrix of the change of the peak (or valley) wavelength of the two vernier envelope spectra with the dual parameters.

[0035] This invention combines the advantages of sparse sampling technology and fiber optic sensing technology, and utilizes the amplification effect of vernier-like effect to not only improve the detection accuracy and sensitivity of fiber optic sensing system, but also realize the synchronous measurement of dual parameters, providing a new sensing solution with simplified structure and excellent performance for marine environmental monitoring. Attached Figure Description

[0036] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. Several embodiments of the invention are illustrated in the drawings by way of example and not limitation, wherein:

[0037] Figure 1 This is a flowchart of a dual-parameter simultaneous detection method based on sparse sampling of a tunable laser, as described in an embodiment of the present invention.

[0038] Figure 2 This is a schematic diagram of the sensor head structure in an embodiment of the present invention; wherein (a) corresponds to the first interferometer; and (b) corresponds to the second interferometer.

[0039] Figure 3 This is a schematic diagram of the sensing device in an embodiment of the present invention;

[0040] Figure 4 These are the interferometric spectra of two FPI sensors during dense sampling in this embodiment of the invention; where (a) corresponds to the first interferometer; and (b) corresponds to the second interferometer.

[0041] Figure 5 This refers to the first interferometer spectrum corresponding to sparse sampling at different sampling intervals in this embodiment of the invention; where (a) corresponds to sampling interval SI1≈FSR1; and (b) corresponds to sampling interval SI2. FSR1 Sampling interval SI1;

[0042] Figure 6 These are the second interferometric spectra corresponding to the second interferometer under sparse sampling at different sampling intervals in this embodiment of the invention; where (a) corresponds to sampling interval SI1≈FSR2; and (b) corresponds to sampling interval SI2. FSR2 Sampling interval SI1;

[0043] Figure 7 This is the sparse sampling interferometric spectrum corresponding to the first interferometer in this embodiment of the invention. Temperature and salinity calibration values ​​and measured values; where (a) corresponds to the calibration value; (b) corresponds to the measured value;

[0044] Figure 8 This is the sparse sampling interferometric spectrum corresponding to the second interferometer in this embodiment of the invention. Temperature and salinity calibration values ​​and measured values; where (a) corresponds to the calibration value; and (b) corresponds to the measured value. Detailed Implementation

[0045] The principles and spirit of the invention will now be described with reference to several exemplary embodiments. It should be understood that these embodiments are given merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way. Rather, these embodiments are provided to make this disclosure more thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0046] This invention aims to address the following problems in existing technologies: Firstly, systems for dual-parameter measurement are complex in structure and have low integration; secondly, the auxiliary interferometer must be located far from the sensing unit and placed in a stable environment to avoid external interference affecting the stability of the vernier envelope. Thirdly, once the auxiliary interferometer is determined, the final sensitivity of the system is also fixed, making flexible adjustment difficult. Furthermore, existing systems generally use broadband light sources and spectrometers as light sources and detectors, resulting in excessively high sensing system costs. Spectrometers directly measure the mixed interference spectrum of multiple interferometers, which has a complex shape and cannot intuitively reflect changes in the measured parameter. Multi-step signal processing is required for demodulation, which not only easily introduces additional errors but also affects system performance. To address these problems, this invention proposes a novel dual-parameter simultaneous sensing method and system based on sparse sampling using a tunable laser. The sensor designed in this invention uses only two sensing interferometers, eliminating the need for additional auxiliary interferometers. By flexibly adjusting the sampling interval of the tunable laser to approximate the free spectral range of the two interferometers, a vernier-like effect is generated in the spectrum. Under sparse sampling conditions, the optical power meter obtains the sparse sampling interference spectra of the two interferometers respectively. The peak (or valley) wavelengths of the two interferometers drift with the changes of the two parameters to be measured. By establishing a two-dimensional matrix equation between the peak (or valley) wavelengths of the two interference spectra and the two parameters to be measured, and solving the relationship matrix, the synchronous measurement of the two parameters can be realized.

[0047] This invention proposes a method for simultaneous detection of two parameters based on sparse sampling of a tunable laser, such as... Figure 1 As shown, the method includes:

[0048] S1. Prepare a first interferometer 4 and a second interferometer 6 based on two parameters to be detected;

[0049] S2. Determine the sweep interval of the tunable laser 1 based on the free spectral range of the first interferometer 4 and the second interferometer 6.

[0050] S3. Insert one end of the first interferometer 4 and the second interferometer 6 into the liquid to be tested, and use a sensing device including the tunable laser 1, the first interferometer 4 and the second interferometer 6 to perform sparse sampling of the two parameters to be tested in the liquid to be tested, and obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer.

[0051] S4. Fit the first sparse interference spectrum and the second sparse interference spectrum respectively to obtain the first interference spectrum and the second interference spectrum;

[0052] S5. Based on the first interference spectrum and the second interference spectrum, determine the first interference spectrum shift and the second interference spectrum shift relative to the calibration interference spectrum envelope corresponding to the parameter to be detected, respectively.

[0053] S6. Determine the changes of the two parameters to be detected relative to their respective calibration values ​​based on the first interference spectrum shift and the second interference spectrum shift.

[0054] S7. Add the changes of the two parameters to be detected relative to their respective calibration values ​​to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

[0055] The method begins with S1. In S1, a first interferometer 4 and a second interferometer 6 are prepared based on two parameters to be detected.

[0056] According to an embodiment of the present invention, the two parameters to be detected are temperature and salinity, but other parameters may also be used. Corresponding to temperature, the first interferometer 4 (i.e., sensing cavity FP1) is formed by sequentially fusing a single-mode fiber (SMF) and a hollow-core fiber (HCF) filled with polydimethylsiloxane (PDMS) material at one end; PDMS is temperature-sensitive. As an example, the single-mode fiber has a diameter of 125 micrometers and a core diameter of 8-10 micrometers; the hollow-core fiber has an outer diameter of 125 micrometers and an inner diameter of 50 micrometers. Corresponding to salinity, the second interferometer 6 (i.e., sensing cavity FP2) is formed by staggered fusing of three single-mode fibers, with a stagger of 273-275.5 micrometers. Examples of the fabrication of the first interferometer 4 and the second interferometer 6 are as follows... Figure 2 As shown.

[0057] Then, in S2, the sweep interval of the tunable laser 1 is determined based on the free spectral range of the first interferometer 4 and the second interferometer 6.

[0058] According to an embodiment of the present invention, the free spectral ranges of the first interferometer 4 and the second interferometer 6 can be expressed as:

[0059] (1)

[0060] In the formula, This represents the sweep wavelength of the tunable laser 1; and These are the refractive indices of the intracavity media of the first interferometer 4 and the second interferometer 6, respectively. and These are the cavity lengths of the first interferometer 4 and the second interferometer 6, respectively.

[0061] As can be seen from the above, with the sweep wavelength... As the wavelength increases, the free spectral range of FP1 and FP2 gradually increases, but within the wavelength tuning range of the tunable laser (TLS)1, FSR1 and FSR2 can be approximated as constants.

[0062] Based on the free spectral ranges (FSR1 and FSR2) of the first interferometer 4 and the second interferometer 6, the sweep interval of the tunable laser 1 is determined as follows:

[0063] The original interference spectrum of FP1 is sparsely sampled, and the sampling interval (i.e., the sweep interval of tunable laser 1) is SI = FSR1 + ,in The difference between the sweep interval of the tunable laser 1 and the free spectral range FSR1 of the first interferometer 4 is given by: sparse sampling of the original interference spectrum of FP2, with the sampling interval (i.e., the sweep interval of the tunable laser 1) being SI = FSR2 + ... ,in The difference between the sweep interval of the tunable laser 1 and the free spectral range FSR2 of the second interferometer 6; where, , The value range is 0.01-0.5 (unit: nm).

[0064] Then, in S3, one end of the first interferometer 4 and the second interferometer 6 are inserted into the liquid to be tested. The two parameters to be tested in the liquid to be tested are sparsely sampled using a sensing device including the tunable laser 1, the first interferometer 4 and the second interferometer 6, so as to obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer.

[0065] According to embodiments of the present invention, the sensing device is as follows: Figure 3As shown, its structure includes a tunable laser 1, a coupler 2, a first interferometer 4, a second interferometer 6, a first fiber optic circulator 3, a second fiber optic circulator 5, and an optical power meter 7. The output of the tunable laser 1 is connected to the input of the coupler 2. The three outputs of the coupler 2 are respectively connected to the first channel 7-1 of the optical power meter 7, the first port 3-1 of the first fiber optic circulator 3, and the first port 5-1 of the second fiber optic circulator 5. The third port 3-3 of the first fiber optic circulator 3 and the third port 5-3 of the second fiber optic circulator 5 are respectively connected to one end of the first interferometer 4 and the second interferometer 6. The second port 3-2 of the first fiber optic circulator 3 and the second port 5-2 of the second fiber optic circulator 5 are respectively connected to the second channel 7-2 and the third channel 7-3 of the optical power meter 7.

[0066] The sensing device operates as follows: The light emitted by the tunable laser 1 is first split into three paths by the coupler 2. One path is directly connected to the first channel 7-1 of the optical power meter 7 to monitor the intensity fluctuations of the laser source in real time, thereby reducing the influence of the unstable intensity of the light source on the interference spectrum of the two interferometers. The other two paths are transmitted to two interferometers with different structures, the first interferometer 4 and the second interferometer 6, through the first port 3-1 and the third port 3-3 of the first fiber optic circulator 3 and the first port 5-1 and the third port 5-3 of the second fiber optic circulator 5, respectively. The reflected light generated by the two interferometers returns through the second port 3-2 of the first fiber optic circulator 3 and the second port 5-2 of the second fiber optic circulator 5, respectively, and is finally received by the second channel 7-2 and the third channel 7-3 of the optical power meter 7. The optical power meter 7 collects the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer 4 and the second interferometer 6. As an example, the wavelength range of the tunable laser 1 is 1525nm-1565nm, and the sampling interval is 0.01nm.

[0067] Specifically, the incident light emitted by the tunable laser 1 is split by the coupler 2 and then transmitted to the first interferometer 4 and the second interferometer 6 via the first fiber optic circulator 3 and the second fiber optic circulator 5, respectively. The light undergoes multiple reflections between these interferometers, forming a typical two-beam interference signal, which is finally received by the optical power meter 7. For dense sampling, the interference spectra of the first interferometer 4 and the second interferometer 6 are expressed as follows:

[0068] (2)

[0069] (3)

[0070] Wherein, I1 and I2 are the light intensities of the two reflected beams of the first interferometer 4, and I3 and I4 are the light intensities of the two reflected beams of the second interferometer 6.

[0071] Substituting equation (1) into equations (2) and (3), the light intensity of the interference signal can be further expressed as:

[0072] (4)

[0073] (5)

[0074] As can be seen from equations (4) and (5), the interference spectra of FP1 and FP2 are periodic, with spectral periods of FSR1 and FSR2.

[0075] When the tunable laser 1 is densely sampled, that is, when the frequency sweep interval of the TLS is much smaller than the free spectral range of the FPI, the interference signal measured by the sensing device is the complete interference spectrum of the FPI; when the tunable laser 1 is sparsely sampled, that is, when the frequency sweep interval of the TLS is close to the free spectral range of the FPI, the interference signal measured by the sensing device is not the complete interference spectrum of the FPI.

[0076] Specifically, the original interferometric spectrum of FP1 is sparsely sampled with a sampling interval of SI = FSR1 + The wavelength of the m-th sampling point is = +mSI, where If the wavelength of the first sampling point is represented, then... Sparse sampling interferometric spectrum at Represented as:

[0077] (6)

[0078] Equation (6) shows that the interference intensity at sparse sampling points is still a periodic function, and specifically a periodic function of m, with the corresponding wavelength period (free spectral range) being:

[0079] (7)

[0080] Where M1 is the magnification, that is, the free spectral range of the sparsely sampled interference spectrum of FP1 is M1 times the free spectral range of FP1 when densely sampled. The magnification M1 can be expressed as:

[0081] (8)

[0082] From equation (8), it can be seen that the temperature sensitivity of FP1 after sparse sampling (producing a vernier-like effect) is M1 times that of FP1 during dense sampling (without a vernier-like effect). It is worth noting that, because FSR1 increases with increasing wavelength, ... It also increases with increasing wavelength.

[0083] Similarly, when sparsely sampling the original interferometric spectrum of FP2, its free spectral range... and magnification for:

[0084] (9)

[0085] in, This represents the ratio of the free spectral range measured by FP2 under sparse sampling to the free spectral range of FP1 under dense sampling. It also indicates that the salinity sensitivity of FP2 after sparse sampling (producing a vernier-like effect) is equal to the salinity sensitivity of FP2 under dense sampling (without a vernier-like effect). times.

[0086] Then, in S4, the first sparse interference spectrum and the second sparse interference spectrum are fitted respectively to obtain the first interference spectrum and the second interference spectrum; in S5, the first interference spectrum shift and the second interference spectrum shift relative to the calibration interference spectrum envelope corresponding to the parameter to be detected are determined according to the first interference spectrum and the second interference spectrum.

[0087] According to an embodiment of the present invention, the signal light collected by the optical power meter is the interference spectrum of each of the two interferometers. During the signal processing stage, only cubic spline interpolation is needed in the software to fit the sampling points, thus reconstructing the densely sampled or sparsely sampled interference spectrum corresponding to each of the two parameters with high precision. Then, by comparing the translation between the reconstructed sparsely sampled interference spectrum (i.e., the first interference spectrum and the second interference spectrum) and the experimental calibration spectrum (i.e., the envelope of the calibration interference spectrum corresponding to the parameter to be detected) (the translation of the first interference spectrum and the translation of the second interference spectrum), a response relationship matrix between the interference spectrum translation and the two parameters to be measured can be established.

[0088] Then, in S6, the changes of the two parameters to be detected relative to their respective calibration values ​​are determined based on the first and second interference spectrum shifts; in S7, the changes of the two parameters to be detected relative to their respective calibration values ​​are added to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

[0089] According to an embodiment of the present invention, when temperature and salinity (two parameters to be measured) change, the sparse sampling interference spectrum... and The first interference spectrum shift Δλ1 and the second interference spectrum shift Δλ2 are expressed as follows:

[0090] (10)

[0091] The corresponding matrix equation can be expressed as:

[0092] (11)

[0093] Where Δλ1 and Δλ2 are sparse sampling interferometric spectra, respectively. and The shift of the interference spectrum envelope relative to the calibration value; ΔT and ΔS represent the changes in temperature and salinity relative to their calibration values ​​(T0, S0), respectively. and Sparse sampling interferometry spectrum The temperature sensitivity and salinity sensitivity are constants that can be measured experimentally. and Sparse sampling interferometry spectrum The temperature sensitivity and salinity sensitivity are constants that can be measured experimentally.

[0094] Then, the temperature T and salinity S to be measured can be obtained by solving the matrix equation:

[0095] (12)

[0096] The processes described in S4 to S7 are implemented using computer software.

[0097] Figure 4 The image shows the interference spectrum of two FPI sensors when the laser is densely sampled (SI = 0.01 nm). To improve the sensitivity of a single FPI sensor, the sampling interval of the tunable laser is flexibly controlled to approach the free spectral ranges (FSR1 and FSR2) of the two FPI sensors, thereby generating a vernier-like effect in the spectrum, such as... Figure 5 , Figure 6 As shown in the figure, SI1 and SI2 both represent the sampling interval. When the external temperature and salinity change, the sparse sampling interference spectra of both FPI sensors show significant drift, such as... Figure 7 , Figure 8 As shown.

[0098] In summary, this invention combines the advantages of sparse sampling technology and fiber optic sensing technology, and utilizes the amplification effect of vernier-like effect to not only improve the detection accuracy and sensitivity of the fiber optic sensing system, but also realize the synchronous measurement of dual parameters, providing a new sensing solution with simplified structure and excellent performance for marine environmental monitoring.

[0099] This invention also proposes a dual-parameter simultaneous detection system based on sparse sampling of a tunable laser. The system is used to implement the dual-parameter simultaneous detection method based on sparse sampling of a tunable laser described in the above embodiments. The system includes a sensing device and a signal processing module.

[0100] The sensing device is used to sparsely sample two parameters of the liquid to be tested, and obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer. The sensing device includes a tunable laser 1, a first interferometer 4 and a second interferometer 6. The frequency sweep interval of the tunable laser 1 is determined according to the free spectral range of the first interferometer 4 and the second interferometer 6. The first interferometer 4 and the second interferometer 6 are prepared based on the two parameters to be tested.

[0101] The signal processing module is used to fit the first sparse interference spectrum and the second sparse interference spectrum to obtain the first interference spectrum and the second interference spectrum, respectively; based on the first interference spectrum and the second interference spectrum, determine the first interference spectrum shift and the second interference spectrum shift relative to the calibration interference spectrum envelope corresponding to the parameter to be detected, respectively; based on the first interference spectrum shift and the second interference spectrum shift, determine the change of the two parameters to be detected relative to their respective calibration values; add the change of the two parameters to be detected relative to their respective calibration values ​​to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

[0102] Other aspects of the dual-parameter simultaneous detection system based on tunable laser sparse sampling described in the embodiments of the present invention can be found in the dual-parameter simultaneous detection method based on tunable laser sparse sampling described in the foregoing embodiments, and will not be elaborated further here.

[0103] While the spirit and principles of the invention have been described with reference to several specific embodiments, it should be understood that the invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A method for simultaneous detection of two parameters based on sparse sampling of a tunable laser, characterized in that, include: A first interferometer (4) and a second interferometer (6) are prepared based on two parameters to be detected; the two parameters to be detected are temperature and salinity. The first interferometer (4) is made by sequentially fusing a single-mode fiber and a hollow fiber with one end filled with polydimethylsiloxane material; the second interferometer (6) is made by staggered fusing of three single-mode fibers. The frequency sweep interval of the tunable laser (1) is determined based on the free spectral range of the first interferometer (4) and the second interferometer (6) as follows: SI = FSR1 + or SI = FSR2 + ; In the formula, SI represents the frequency sweep interval of the tunable laser (1); FSR1 represents the free spectral range of the first interferometer (4); and FSR2 represents the free spectral range of the second interferometer (6). The difference between the sweep interval of the tunable laser (1) and the free spectral range FSR1 of the first interferometer (4); The difference between the sweep interval of the tunable laser (1) and the free spectral range FSR2 of the second interferometer (6); , The value range is 0.01-0.5, and the unit is nm; wherein, the calculation formula for the free spectral range of the first interferometer (4) and the second interferometer (6) is: ； In the formula, The sweep wavelength of the tunable laser (1) is indicated; and The refractive indices of the intracavity medium of the first interferometer (4) and the second interferometer (6) are respectively. and The cavity lengths of the first interferometer (4) and the second interferometer (6) are respectively; One end of the first interferometer (4) and the second interferometer (6) are inserted into the liquid to be tested. A sensing device comprising a tunable laser (1), the first interferometer (4), and the second interferometer (6) is used to perform sparse sampling of two parameters of the liquid to be tested, obtaining the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first and second interferometers. The sensing device includes a tunable laser (1), a coupler (2), a first fiber optic circulator (3), a second fiber optic circulator (5), the first interferometer (4), the second interferometer (6), and an optical power meter (7). The output end of the tunable laser (1) is connected to the coupler (2). The input terminal of the coupler (2) is connected to the first channel (7-1) of the optical power meter (7), the port 1 (3-1) of the first fiber optic circulator (3), and the port 1 (5-1) of the second fiber optic circulator (5), respectively; the port 3 (3-3) of the first fiber optic circulator (3) and the port 3 (5-3) of the second fiber optic circulator (5) are connected to one end of the first interferometer (4) and the second interferometer (6), respectively; the port 2 (3-2) of the first fiber optic circulator (3) and the port 2 (5-2) of the second fiber optic circulator (5) are connected to the second channel (7-2) and the third channel (7-3) of the optical power meter (7), respectively. The first sparse interference spectrum and the second sparse interference spectrum are fitted respectively to obtain the first interference spectrum and the second interference spectrum; The first and second interference spectrum shifts relative to the calibration interference spectrum envelope of the parameter to be detected are determined based on the first and second interference spectra, respectively. The changes of the two parameters to be detected relative to their respective calibration values ​​are determined based on the first and second interference spectrum shifts. The changes of the two parameters to be detected relative to their respective calibration values ​​are added to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

2. The method for simultaneous detection of two parameters based on sparse sampling of a tunable laser according to claim 1, characterized in that, The method of using a sensing device including a tunable laser (1), a first interferometer (4), and a second interferometer (6) to perform sparse sampling of two parameters to be detected in the liquid to be detected, and to obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer, includes: the laser emitted by the tunable laser (1) is split into three paths by a coupler (2), one of which is directly connected to the first channel (7-1) of the optical power meter (7) to monitor the intensity fluctuation of the light source in real time; the other two paths are respectively connected to the first interferometer (4) and the second interferometer (6) through the first fiber optic circulator (3) and the second fiber optic circulator (5); the optical signals returned by the first interferometer (4) and the second interferometer (6) are respectively connected to the second channel (7-2) and the third channel (7-3) of the optical power meter (7) through the first fiber optic circulator (3) and the second fiber optic circulator (5); the optical power meter (7) collects the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer (4) and the second interferometer (6).

3. The method for simultaneous detection of two parameters based on sparse sampling of a tunable laser according to claim 1, characterized in that, The determination of the changes of the two parameters to be detected relative to their respective calibration values ​​based on the first and second interferometric spectrum shifts includes calculating the changes using the following formula: ； ； In the formula, Δλ1 and Δλ2 represent the first and second interference spectrum shifts, respectively; ΔT and ΔS represent the changes in temperature and salinity relative to the calibration values, respectively. and These are the temperature sensitivity and salinity sensitivity corresponding to the first interference spectrum, respectively. and These are the temperature sensitivity and salinity sensitivity corresponding to the second interference spectrum, respectively.

4. The method for simultaneous detection of two parameters based on sparse sampling of a tunable laser according to claim 3, characterized in that, The temperature sensitivity corresponding to the first interference spectrum is M1 times the temperature sensitivity obtained by the sensing device through dense temperature sampling, where M1 is expressed as: ； The salinity sensitivity corresponding to the second interference spectrum is M² times the salinity sensitivity obtained by the sensing device through dense sampling of salinity. The expression for M² is: 。 5. A dual-parameter simultaneous detection system based on sparse sampling of a tunable laser, characterized in that, The system is used to implement the dual-parameter simultaneous detection method based on sparse sampling of a tunable laser, as described in any one of claims 1-4; the system includes a sensing device and a signal processing module; wherein... The sensing device is used to perform sparse sampling of two parameters to be detected in the liquid to be tested, and to obtain the first sparse interference spectrum and the second sparse interference spectrum corresponding to the first interferometer and the second interferometer; the sensing device includes a tunable laser (1), a first interferometer (4) and a second interferometer (6), the frequency sweep interval of the tunable laser (1) is determined according to the free spectral range of the first interferometer (4) and the second interferometer (6); the first interferometer (4) and the second interferometer (6) are prepared based on the two parameters to be detected; The signal processing module is used to fit the first sparse interference spectrum and the second sparse interference spectrum to obtain the first interference spectrum and the second interference spectrum, respectively; based on the first interference spectrum and the second interference spectrum, determine the first interference spectrum shift and the second interference spectrum shift relative to the calibration interference spectrum envelope corresponding to the parameter to be detected, respectively; based on the first interference spectrum shift and the second interference spectrum shift, determine the change of the two parameters to be detected relative to their respective calibration values; add the change of the two parameters to be detected relative to their respective calibration values ​​to their respective calibration values ​​to obtain the measured values ​​of the two parameters to be detected.

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