F-p cascade optical fiber sensor and method for measuring seawater temperature and salinity

Abstract

The application discloses a kind of F-P cascade optical fiber sensor and method for measuring seawater temperature and salt, by a kind of F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and demodulator, optical fiber sensing structure and demodulator are connected by single-mode optical fiber, and optical fiber sensing structure is composed of temperature sensing cavity and salinity sensing cavity cascade;Temperature sensing cavity and salinity sensing cavity are isolated by temperature-sensitive material film;The sensing structure designed in the application combines capillary quartz tube and temperature-sensitive material, greatly improves temperature measurement sensitivity;At the same time, based on the principle of temperature compensation, the application realizes the correction to salinity measurement using F-P cascade structure, improves the precision of salinity measurement;The application has simple structure, low manufacturing cost, high precision, and is an effective means to realize high-precision measurement of seawater temperature and salinity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a F-P cascaded optical fiber sensor for measuring seawater temperature and salinity and a method thereof. BACKGROUND

[0002] Temperature and salinity are important parameters for water resource monitoring, environmental protection and marine resource development, and are of great significance to the study of oceanography, hydrology and meteorology, and environmental protection. Seawater temperature and salinity measurement requires a sensor with high sensitivity, simple structure, wide measurement range and stable transmission. Currently, the conductivity-temperature-depth (CTD) sensor has been widely used in the study of oceanography.

[0003] However, the CTD sensor mainly relies on electronic components, which is prone to failure and signal transmission difficulties in harsh marine environments, and has defects such as difficulty in long-distance transmission and high maintenance cost. It cannot meet the future needs of marine stereoscopic observation.

[0004] In recent years, due to the excellent characteristics of optical fiber sensors such as small size, small signal attenuation, strong anti-electromagnetic interference ability, corrosion resistance, low cost and long transmission distance, they are expected to become a new choice for replacing CTD detection systems in marine environments. Fiber grating sensors and fiber Fabry-Perot (F-P) sensors are two mature sensors in the field of optical fiber sensing. Although fiber grating sensors have the advantages of stable structure and easy manufacturing, their temperature measurement sensitivity is low, and it is difficult to measure salinity, making them difficult to be applied in actual measurement process. As an important branch of optical fiber sensors, fiber Fabry-Perot (F-P) sensors have the advantages of simple structure, high detection precision and large measurement dynamic range in addition to the advantages of optical fiber sensors.

[0005] Chinese patent CN202110059378.9 discloses a seawater salinity and temperature dual-parameter sensor based on interference vernier effect. Although this sensor realizes the dual-parameter measurement of seawater temperature and salinity, the preparation process requires the manufacture of a microcavity inside the optical fiber, which is technically difficult. Moreover, the sensor structure is a discrete structure, which cannot meet the demand of high spatial and temporal resolution measurement. Chinese patent CN202121932895.4 discloses a single optical fiber cascaded temperature-depth-salinity sensor. Although the sensing probe realizes the integration of the sensing structure, its temperature sensitivity is low, and the technical conditions in the preparation process are harsh, such as hydrogen-oxygen catalytic bonding technology. Therefore, it is particularly important to realize an optical fiber FP integrated cascaded device with simple structure, multiple measurement parameters, high sensitivity and easy manufacturing.

[0006] For marine survey applications, a single optical fiber cascaded sensor with high sensitivity, simple structure, easy manufacturing, small size and multi-parameter measurement capability has broad application prospects. SUMMARY

[0007] In view of the defects of the prior art, the application designs a F-P cascade optical fiber sensor and method for measuring seawater temperature and salinity.

[0008] A F-P cascade optical fiber sensor for measuring seawater temperature and salinity is composed of a F-P cascade optical fiber sensing structure for measuring seawater temperature and salinity and a demodulator, the optical fiber sensing structure and the demodulator are connected through a single-mode optical fiber, and the optical fiber sensing structure is composed of a temperature sensing cavity and a salinity sensing cavity in cascade.

[0009] The temperature sensing cavity is specifically a single-mode optical fiber core made of silica, a capillary quartz tube is connected outside the core, a temperature-sensitive material film is plated at the end of the capillary quartz tube, and the air cavity between the single-mode optical fiber core and the temperature-sensitive material film is the temperature sensing cavity; the temperature-sensitive material film isolates the temperature sensing cavity from the salinity sensing cavity.

[0010] The capillary quartz tube is connected with a quartz tube outside, the quartz tube is connected with a quartz rod at the end, the inner side end face of the quartz rod is plated with a gold film, and the salinity sensing cavity is between the temperature-sensitive material film and the gold film; the quartz tube wall has a microporous structure.

[0011] The optical fiber sensing structure has four reflecting surfaces of single-mode optical fiber-air end face, air-temperature-sensitive material end face, temperature-sensitive material-seawater end face and gold film end face, wherein the temperature sensing cavity includes the single-mode optical fiber-air end face and the air-temperature-sensitive material end face, and the salinity sensing cavity includes the temperature-sensitive material-seawater end face and the gold film end face; the single-mode optical fiber core end face and the air in the temperature sensing cavity form the single-mode optical fiber-air end face, the air in the temperature sensing cavity and the temperature-sensitive material end face form the air-temperature-sensitive material end face, the temperature-sensitive material end face and the seawater contact surface form the temperature-sensitive material-seawater end face, and the gold film and the seawater contact surface form the gold film end face.

[0012] A method for measuring seawater temperature and salinity is realized by using the above-mentioned F-P cascade optical fiber sensor for measuring seawater temperature and salinity, and specifically includes the following contents:

[0013] The demodulator scans and emits wide spectrum light, which is coupled into the optical fiber sensing structure through an optical fiber; there are four reflecting surfaces in the optical fiber sensing structure, i.e., a single-mode optical fiber-air end face, an air-temperature sensitive material end face, a temperature sensitive material-seawater end face and a gold film end face; the wide spectrum light is reflected by the four reflecting surfaces and then transmitted to the demodulator through an optical fiber to form an interference spectrum signal; then the interference spectrum signal is transmitted to an upper computer, and after band-pass filtering in the upper computer, the temperature sensing cavity spectrum and the salinity sensing cavity spectrum and the center wavelengths of specific resonant peaks corresponding to each spectrum are obtained; the center wavelength moving amounts of the specific resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum under different temperature and salinity environments are calculated; then the seawater temperature and salinity are inversely deduced by using a double-wavelength matrix method; the moving amount is the difference between the center wavelengths of the specific resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum.

[0014] The double-wavelength matrix method is specifically as follows: when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the temperature sensing cavity spectrum will move by different amounts; when the seawater temperature remains unchanged and the seawater salinity changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move by different amounts; when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move by different amounts.

[0015] The double-wavelength matrix of the F-P cascaded optical fiber sensing structure is as follows:

[0016]

[0017] wherein, Δλ K and Δλ P are the moving amounts of the center wavelengths of the resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum; A is the temperature sensitivity of the temperature sensing cavity of the F-P cascaded optical fiber sensing structure, C is the sensitivity of the temperature sensing cavity of the F-P cascaded optical fiber sensing structure to seawater salinity, the temperature sensing cavity is isolated from seawater, and therefore the temperature sensing cavity is not sensitive to salinity, and the sensitivity is 0; B is the sensitivity of the salinity sensing cavity of the F-P cascaded optical fiber sensing structure to seawater temperature, and D is the sensitivity of the salinity sensing cavity of the F-P cascaded optical fiber sensing structure to seawater salinity; the temperature sensitivity is obtained by least square fitting of the center wavelengths of the resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum under different temperatures and the corresponding temperatures; the salinity sensitivity is obtained by least square fitting of the center wavelengths of the resonant peaks corresponding to the salinity sensing cavity spectrum under different salinities and the corresponding salinities; the seawater temperature and salinity are deduced by using matrix operation according to the two center wavelength moving amounts.

[0018] The present application has the following beneficial technical effects:

[0019] The F-P cascade optical fiber sensor and method for measuring seawater temperature and salinity provided by the application cascade a temperature sensing cavity and a salinity sensing cavity on the same optical fiber only by using arc fusion technology, without laser welding or wet etching technology, combine the capillary quartz tube and the temperature sensitive material, form a small volume sensing structure in a normal temperature and pressure environment, can synchronously detect the seawater salinity and temperature, and correct the error through temperature measurement, and the structure is simple, the sensitivity is high, and it is an effective means for realizing the detection of seawater temperature and salinity. Compared with the electrical sensor technology, the optical fiber sensing structure of the application has stable signal transmission and lower cost; compared with the current ocean temperature and salinity sensor, the application has the characteristics of high temperature sensitivity, realizes temperature compensation, and improves the precision of salinity measurement. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the F-P cascade optical fiber sensing structure of the application.

[0021] Figure 2 It is a schematic diagram of the F-P cascade optical fiber sensor using method of the embodiment of the application.

[0022] Figure 3 It is a seawater temperature rising response curve of the F-P cascade optical fiber sensor of the embodiment of the application.

[0023] Figure 4 It is a seawater temperature measurement sensitivity curve of the F-P cascade optical fiber sensor of the embodiment of the application.

[0024] Figure 5 It is a seawater salinity rising response curve of the F-P cascade optical fiber sensor of the embodiment of the application.

[0025] Figure 6 It is a seawater salinity measurement sensitivity curve of the F-P cascade optical fiber sensor of the embodiment of the application. DETAILED DESCRIPTION

[0026] The technical solutions of the application will be further described below in combination with the embodiments and the drawings.

[0027] The capillary quartz tube and the temperature sensitive material are combined to form a temperature sensing cavity with high temperature sensitivity; the temperature sensing cavity sensitive to temperature only and the salinity sensing cavity sensitive to temperature and temperature salinity are cascade processed to realize the simultaneous measurement of seawater temperature and salinity; based on the principle of temperature compensation, the precision of salinity measurement is improved;

[0028] The utility model relates to a kind of F-P cascade optical fiber sensor for measuring seawater temperature and salt, by a kind of F-P cascade optical fiber sensing structure for measuring seawater temperature and salt and demodulator, optical fiber sensing structure and demodulator are connected by single-mode optical fiber, and optical fiber sensing structure is composed of temperature sensing cavity 1 and salinity sensing cavity 2 cascade;A kind of F-P cascade optical fiber sensing structure for measuring seawater temperature and salt, as shown in Figure 1 ;

[0029] Temperature sensing cavity 1 is specifically: single-mode optical fiber core 3 of material is silica, capillary quartz tube 4 is connected outside fiber core 3, temperature-sensitive material film 5 is plated at the end of capillary quartz tube 4, and the air cavity between single-mode optical fiber core 3 and temperature-sensitive material film PDMS film 5 is temperature sensing cavity 1;Temperature-sensitive material film 5 isolates between temperature sensing cavity 1 and salinity sensing cavity 2;

[0030] The PDMS solution of configuration is applied to one end of capillary quartz tube 4, is deposited in thermostat box 100 DEG C for one hour, and PDMS is solidified, then single-mode optical fiber core 3 and the other end of capillary quartz tube 4 coated with PDMS film 5 are fused together using arc fusion technique using optical fiber fusion machine. Temperature sensing cavity 1 is made.

[0031] Capillary quartz tube 4 is connected with quartz tube 6 outside, quartz rod 7 is connected at the end of quartz tube 6, gold film 8 is plated on the inner side end face of quartz rod 7, and temperature-sensitive material film 5 and gold film 8 are salinity sensing cavity 2;There are micropore structures 9 in the wall of quartz tube 6 for the flow of seawater.

[0032] Grinding flat quartz rod 7 is placed in coating instrument to carry out coating, and gold film 8 plated quartz rod is fused on the quartz tube 6 with micropore structure 9 in the wall using arc fusion technique using optical fiber fusion machine, and finally temperature sensing cavity 1 and quartz tube 6 are fused together using arc fusion technique using optical fiber fusion machine, and temperature-sensitive material film and gold film constitute salinity sensing cavity 2, and sensing structure is completed.

[0033] Temperature-sensitive material film 5 is polydimethylsiloxane film (PDMS), and the thickness is 200-500 um;The length of temperature sensing cavity is 40-100 um;The length of salinity sensing cavity is 80-150 um;The thickness of gold film is 40-200 nm;

[0034] The optical fiber sensor has four reflecting surfaces of a single-mode optical fiber-air end face, an air-temperature sensitive material end face, a temperature sensitive material-seawater end face and a gold film end face, wherein the temperature sensing cavity comprises the single-mode optical fiber-air end face and the air-temperature sensitive material end face, the salinity sensing cavity comprises the temperature sensitive material-seawater end face and the gold film end face; the single-mode optical fiber end face and the air in the temperature sensing cavity form the single-mode optical fiber-air end face, the air in the temperature sensing cavity and the temperature sensitive material end face form the air-temperature sensitive material end face, the temperature sensitive material end face and the seawater contact surface form the temperature sensitive material-seawater end face, and the gold film and the seawater contact surface form the gold film end face.

[0035] A method for measuring seawater temperature and salinity, which utilizes an F-P cascade optical fiber sensor for measuring seawater temperature and salinity, as shown in the accompanying drawings, and specifically comprises the following contents. Figure 2

[0036] The demodulator 11 emits wide-spectrum light, which enters the optical fiber sensing structure through the optical fiber; the optical fiber sensing structure 10 has four reflecting surfaces of a single-mode optical fiber-air end face, an air-temperature sensitive material end face, a temperature sensitive material-seawater end face and a gold film end face, the wide-spectrum light forms an interference spectrum signal after being reflected by the four reflecting surfaces, and is transmitted back to the demodulator through the optical fiber; then the interference spectrum signal is transmitted to the host computer 12, and after being processed by band-pass filtering in the host computer, the temperature sensing cavity spectrum and the salinity sensing cavity spectrum and the center wavelengths of the specific resonant peaks corresponding to each spectrum are obtained, the center wavelength moving amounts of the specific resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum under different temperature and salinity environments are calculated, and then the seawater temperature and salinity are inversely deduced by using a double-wavelength matrix method; the moving amount is the difference between the center wavelengths of the specific resonant peaks corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum; the host computer is a computer.

[0037] The double-wavelength matrix method specifically includes that when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the temperature sensing cavity spectrum will move by different amounts; when the seawater temperature remains unchanged and the seawater salinity changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move by different amounts; and when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move by different amounts.

[0038] The double-wavelength matrix of the F-P cascade optical fiber sensing structure is as follows:

[0039]

[0040] Wherein, Δλ K and Δλ P ​respectively, the moving amount of the center wavelength of the corresponding resonance peak of the temperature sensing cavity spectrum and the salinity sensing cavity spectrum; A is the temperature sensitivity of the temperature sensing cavity of the F-P cascaded optical fiber sensing structure, C is the salinity sensitivity of the temperature sensing cavity of the F-P cascaded optical fiber sensing structure to seawater, the temperature sensing cavity is isolated from seawater, and therefore the temperature sensing cavity is not sensitive to salinity, and the sensitivity is 0; B is the temperature sensitivity of the salinity sensing cavity of the F-P cascaded optical fiber sensing structure to seawater, D is the salinity sensitivity of the salinity sensing cavity of the F-P cascaded optical fiber sensing structure to seawater, the temperature sensitivity is obtained by least square fitting of the corresponding resonance peak center wavelength of the temperature sensing cavity spectrum and the salinity sensing cavity spectrum and the corresponding temperature under different temperatures, and the salinity sensitivity is obtained by least square fitting of the corresponding resonance peak center wavelength of the salinity sensing cavity spectrum and the corresponding salinity under different salinities; the temperature and salinity of seawater are obtained by using matrix operation according to the two center wavelength moving amounts.

[0041] Figure 3 It is a seawater temperature measurement response curve of the F-P cascaded optical fiber sensor of the embodiment of the application. The temperature sensing cavity spectrum moving result displayed in the upper computer after the sensing structure undergoes a certain temperature change in seawater.

[0042] Figure 4 It is a seawater temperature measurement sensitivity curve of the F-P cascaded optical fiber sensor of the embodiment of the application. The fitting result of the center wavelength of a specific resonance peak of the temperature sensing cavity spectrum changing with temperature after the sensing structure undergoes multiple temperature changes in seawater.

[0043] Figure 5 It is a seawater salinity measurement response curve of the F-P cascaded optical fiber sensor of the embodiment of the application. The salinity sensing cavity spectrum moving result displayed in the upper computer after the sensing structure undergoes a certain salinity change in seawater.

[0044] Figure 6 It is a seawater salinity measurement sensitivity curve of the F-P cascaded optical fiber sensor of the embodiment of the application. The fitting result of the center wavelength of a specific resonance peak of the salinity sensing cavity spectrum changing with salinity after the sensing structure undergoes multiple salinity changes in seawater. It is shown that the seawater temperature and salinity data obtained by the method have high precision.

Claims

1. A F-P cascade optical fiber sensor for measuring seawater temperature and salinity, characterized in that, The application relates to a F-P cascade optical fiber sensing structure and a demodulator for measuring seawater temperature and salinity. The temperature sensing cavity is a single-mode optical fiber core made of silica, a capillary quartz tube is connected outside the single-mode optical fiber core, a temperature-sensitive material film is plated at the end of the capillary quartz tube, and an air cavity between the single-mode optical fiber core and the temperature-sensitive material film is the temperature sensing cavity; the temperature-sensitive material film isolates the temperature sensing cavity from the salinity sensing cavity; The salinity sensing cavity is that a quartz tube is connected outside the capillary quartz tube, a quartz rod is connected at the end of the quartz tube, a gold film is plated at the inner side end face of the quartz rod, and a salinity sensing cavity is formed between the temperature-sensitive material film and the gold film; the quartz tube wall has a micropore structure; The thickness of the temperature-sensitive material film is 200-500 um; The length of the temperature sensing cavity is 40-100 um; The length of the salinity sensing cavity is 80-150 um; and the thickness of the gold film is 40-200 nm; The optical fiber sensing structure has four reflecting surfaces, namely a single-mode optical fiber-air end face, an air-temperature-sensitive material end face, a temperature-sensitive material-seawater end face and a gold film end face, wherein the temperature sensing cavity comprises the single-mode optical fiber-air end face and the air-temperature-sensitive material end face, the salinity sensing cavity comprises the temperature-sensitive material-seawater end face and the gold film end face; the single-mode optical fiber-air end face is formed by the single-mode optical fiber core end face and the air in the temperature sensing cavity, the air-temperature-sensitive material end face is formed by the air in the temperature sensing cavity and the temperature-sensitive material end face, the temperature-sensitive material-seawater end face is formed by the temperature-sensitive material end face and the seawater contact surface, and the gold film end face is formed by the gold film and the seawater contact surface; The preparation method of the optical fiber sensing structure is as follows: PDMS solution is applied to one end of the capillary quartz tube, the PDMS is stored in a thermostat at 100 DEG C for one hour to solidify, then the single-mode optical fiber core and the other end of the capillary quartz tube coated with the PDMS film are fused together by using an arc fusion technology of a fiber fusion machine to prepare the temperature sensing cavity; The ground and smoothed quartz rod is plated in a film plating instrument, the quartz rod plated with the gold film is fused to the quartz tube with the micropore structure by using the arc fusion technology of the fiber fusion machine, finally the temperature sensing cavity and the quartz tube are fused together by using the arc fusion technology of the fiber fusion machine, the temperature-sensitive material film and the gold film form the salinity sensing cavity, and the sensing structure is prepared.

2. A method for measuring seawater temperature and salinity, using the F-P cascade fiber-optic sensor for measuring seawater temperature and salinity according to claim 1, characterized in that, The application further discloses a preparation method of the optical fiber sensing structure. The demodulator scans and emits wide spectrum light, which enters the optical fiber sensing structure through the optical fiber; there are four reflecting surfaces of single-mode fiber-air end face, air-temperature sensitive material end face, temperature sensitive material-seawater end face and gold film end face in the optical fiber sensing structure, the wide spectrum light is reflected after passing through the four reflecting surfaces, and is transmitted to the demodulator through the optical fiber to form an interference spectrum signal; then the interference spectrum signal is transmitted to the upper computer, after band-pass filtering processing in the upper computer, the temperature sensing cavity spectrum and the salinity sensing cavity spectrum and the center wavelength of the specific resonant peak corresponding to each spectrum are obtained, the center wavelength moving amount of the specific resonant peak corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum under different temperature and salinity environments is calculated, then the seawater temperature and salinity are back calculated by using the double-wavelength matrix method; the moving amount is the difference value of the center wavelength of the specific resonant peak corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum.

3. The method of measuring seawater temperature and salinity according to claim 2, wherein, The double-wavelength matrix method is as follows: when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the temperature sensing cavity spectrum will move in different sizes; when the seawater temperature remains unchanged and the seawater salinity changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move in different sizes; when the seawater salinity remains unchanged and the seawater temperature changes, the center wavelength of the specific resonant peak corresponding to the salinity sensing cavity spectrum will move in different sizes.

4. The method of measuring seawater temperature and salinity according to claim 2, wherein, The double-wavelength matrix of the F-P cascaded optical fiber sensing structure is: ； wherein, and respectively are the moving amount of the specific resonance peak center wavelength corresponding to the temperature sensing cavity spectrum and the salinity sensing cavity spectrum; A is the temperature sensitivity of the temperature sensing cavity of the F-P cascaded fiber sensing structure, C is the sensitivity of the temperature sensing cavity of the F-P cascaded fiber sensing structure to seawater salinity, the temperature sensing cavity is isolated from seawater, so the temperature sensing cavity is not sensitive to salinity, and the sensitivity is 0; B is the sensitivity of the salinity sensing cavity of the F-P cascaded fiber sensing structure to seawater temperature, and D is the sensitivity of the salinity sensing cavity of the F-P cascaded fiber sensing structure to seawater salinity, the temperature sensitivity is obtained by least square fitting of the corresponding resonance peak center wavelength of the temperature sensing cavity spectrum and the salinity sensing cavity spectrum at different temperatures and the corresponding temperature, and the salinity sensitivity is obtained by least square fitting of the corresponding resonance peak center wavelength of the salinity sensing cavity spectrum at different salinities and the corresponding salinity; the temperature and salinity of seawater are obtained by using matrix operation according to the two center wavelength moving amounts.

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