CN113390441A - Refractive index change sensing device and measuring method - Google Patents
Refractive index change sensing device and measuring method Download PDFInfo
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Abstract
The invention relates to a refractive index change sensing device and a measuring method, belonging to the field of optical fiber sensing, wherein the device comprises: the device comprises a laser, a carrier suppression double-sideband modulation module, a microwave source, an optical beam splitter, a refractive index sensitive module, a frequency shifter, an optical coupler, a photoelectric detector and a signal acquisition and data processing module. The laser, the carrier-suppression double-sideband modulation module, the optical beam splitter, the refractive index sensitive module, the frequency shifter, the optical coupler and the photoelectric detector are sequentially connected in an optical mode; the carrier-restraining double-sideband modulation module and the microwave source are sequentially connected in a circuit; and the photoelectric detector and the signal acquisition and data processing module are sequentially connected by a circuit. The invention overcomes the defects of low spectrum analysis precision in the existing optical fiber sensing detection technology and the need of a wide-frequency range detection and processing system in the traditional microwave photon sensing detection, and has the advantages of high measurement precision, real-time measurement, only need of a low-frequency detection and processing system and the like.
Description
Technical Field
The invention belongs to the optical fiber sensing technology, and particularly relates to a device and a measuring method based on refractive index change sensing.
Background
The optical fiber sensing technology is the research focus of the research field of the optical fiber technology since the optical fiber technology goes from theory to practice, and the requirements for the sensor are higher and higher along with the continuous development of the scientific technology. The sensitivity, the high accuracy, small become the sensor development direction. The traditional sensor can not meet the requirement gradually due to the defects of electromagnetic interference, high temperature and high voltage resistance and the like, and the optical fiber sensor can be widely applied due to the advantages of electromagnetic interference resistance, low loss, high cost performance, safety and the like. The basic principle of the optical fiber sensing technology is that when light is transmitted in an optical fiber, a physical parameter to be measured (such as temperature, pressure, stress, a magnetic field, an electric field and the like) changes characteristic parameters (such as frequency, phase, wavelength and the like) of the light transmitted in the optical fiber, so that optical properties (such as wavelength, phase, polarization state and the like) of the light in the optical fiber are changed, and the light with the changed optical properties becomes modulated light. And subsequently, the photoelectric detector is connected to the designed link output end through an optical fiber sensor demodulation technology, and the required external physical parameter is demodulated through the output signal of the photoelectric detector.
The simplest and most direct demodulation technology is a demodulation method of a spectrum analyzer, and the principle of the demodulation technology is that the phase change amount of modulated light is directly detected through spectral analysis of the modulated light by the spectrum analyzer, and then the change of an external physical parameter is calculated. Although the method is simple, the spectral analysis accuracy by directly utilizing the spectrometer is not high, and the method is inconvenient to integrate with other systems due to large volume and high price, and is only suitable for occasions such as laboratories and the like. For this purpose, a microwave photon sensing detection technique has been proposed in which an optical signal is converted into an electrical signal by a photodetector and digital signal processing is performed. The basic link consists of five parts, namely a light source, a modulator, a photon processing module, a photoelectric detector and a data processing module. The principle is that light emitted by a light source is sent into a modulator through an optical fiber, so that an external physical parameter and the light emitted by the light source interact in the modulator, and the optical property of the light is changed, namely modulated light. The modulated light enters a photon processing module and the physical parameters are processed in the optical domain. Then the optical signal output by the photon processing module is converted into an electric signal through the photoelectric detector and is sent to the data processing module for digital signal processing. But this detection technique requires the use of a broadband photodetector and processing system.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A refractive index change sensing device and a measuring method are provided. The technical scheme of the invention is as follows:
a refractive index change sensing device, comprising: a laser (1), a carrier suppression double-sideband modulation module (2), a microwave source (3), an optical beam splitter (4), a refractive index sensitive module (5), a frequency shifter (6), an optical coupler (7), a photoelectric detector (8) and a signal acquisition and data processing module (9),
the laser (1), the carrier-suppression double-sideband modulation module (2), the optical beam splitter (4), the refractive index sensitive module (5), the frequency shifter (6), the optical coupler (7) and the photoelectric detector (8) are sequentially optically connected; the carrier suppression double-sideband modulation module (2) and the microwave source (3) are sequentially connected in a circuit; the photoelectric detector (8) and the signal acquisition and data processing module (9) are sequentially connected by a circuit, wherein the output frequency of the laser (1) is f0The light wave enters a carrier-restraining double-sideband modulation module (2), and a microwave source (3) emits light with the frequency f1The microwave signal is loaded on the light wave through a carrier-restraining double-sideband modulation module (2) to generate a frequency f0-f1And f0+f1After the carrier-suppressed double-sideband optical signal output by the carrier-suppressed double-sideband modulation module (2) passes through the optical beam splitter (4)Is divided into two identical branches, namely a branch 1 and a branch 2; in the branch 1, the optical signal for inhibiting the carrier double-sideband passes through the refractive index sensitive module (5), the refractive index sensitive module (5) is used for sensing the refractive index change caused by the change of an external physical parameter, so that the phase difference of the two optical sidebands is changed, and in the branch 2, the optical signal for inhibiting the carrier double-sideband passes through the frequency shifter (6) to generate the frequency fsIs shifted so that the frequency is f0-f1And f0+f1Respectively of optical signals f0+f1+fsAnd f0-f1+fsOptical signals output by the two branches are coupled by an optical coupler (7) and then enter a photoelectric detector (8) to carry out heterodyne detection to output electric signals; the electric signal output by the photoelectric detector (8) is acquired by a signal acquisition and data processing module (9) and is subjected to data processing and analysis to obtain the frequency fsThe signal power p (m).
Furthermore, the carrier double-sideband modulation restraining module (2) can restrain the generation of carrier double-sideband modulation by working at the lowest bias point through a Mach-Zehnder modulator or can restrain the generation of carrier double-sideband modulation by filtering out a central carrier through the combination of an electro-optical modulator and an optical band-stop filter.
Furthermore, the refractive index sensitive module (5) comprises all modules, the refractive index of which can be changed due to the change of external physical parameters to be measured (such as temperature, pressure, stress, magnetic field, electric field, concentration, vibration and the like), and the refractive index change amounts of different light waves are different.
Further, the frequency shift amount f generated by the frequency shifter (6)sIn MHz magnitude, only a photoelectric detection and signal processing system with low frequency bandwidth is needed.
Further, changing external physical parameters to obtain the frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithComprises the following steps:
wherein R is the responsivity of the photodetector; a. the1And A2The optical signal amplitude values of the branch 1 and the branch 2 are respectively; j. the design is a square1(m) is a class of Bessel functions; m is the modulation coefficient of a modulator in the carrier suppression double-sideband modulation module;
is the initial phase difference of branch 1 and branch 2; f. ofsIs the frequency shift amount of the frequency shifter; d (M) is refractive index variation caused by an external physical parameter; lambda [ alpha ]0The wavelength of laser emitted by the laser; f. of1The frequency of the microwave signal emitted by the microwave source; c is the speed of the light wave in vacuum; t is a time parameter.
A refractive index change sensing measurement method based on the device, comprising the steps of:
1) the output frequency of the laser (1) is f0The light wave enters a carrier-restraining double-sideband modulation module (2), and a microwave source (3) emits light with the frequency f1The microwave signal is loaded on the light wave through a carrier-restraining double-sideband modulation module (2) to generate a frequency f0-f1And f0+f1After the optical signal for inhibiting the carrier double-sideband output by the module (2) for inhibiting the carrier double-sideband modulation passes through the optical beam splitter (4), the optical signal for inhibiting the carrier double-sideband is divided into two identical branches, namely a branch 1 and a branch 2;
2) in the branch 1, the optical signal for inhibiting the carrier double-sideband passes through the refractive index sensitive module (5), the refractive index sensitive module (5) is used for sensing the refractive index change caused by the change of an external physical parameter, so that the phase difference of the two optical sidebands is changed, and in the branch 2, the optical signal for inhibiting the carrier double-sideband passes through the frequency shifter (6) to generate the frequency fsIs shifted so that the frequency is f0-f1And f0+f1Respectively of optical signals f0+f1+fsAnd f0-f1+fsOptical signals output by the two branches are coupled by an optical coupler (7) and then enter a photoelectric detector (8) to carry out heterodyne detection to output electric signals;
3) the electric signal output by the photoelectric detector (8) is collected by a signal collecting and data processing module (9) and is analyzed by data processing,obtaining a frequency of fsThe signal power P (M) is changed to obtain the frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwith；
4) And the other conditions are kept unchanged, and the frequency f of the microwave signal emitted by the microwave source (3) is set1If it is zero, repeating the above steps 1-3 to obtain a new frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithout；
5) Constructing a transmission function (ACF) F (M) which is changed along with the external physical parameter M by the ratio of the power functions obtained twicewithout/P(M)withAnd then measuring the ACF value corresponding to the external physical parameter to be measured, and comparing the operation result with the prestored ACF curve parameter to obtain the size of the external physical parameter.
Further, changing the external physical parameter to obtain the frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithThe method specifically comprises the following steps:
power function P (M)withComprises the following steps:
wherein R is the responsivity of the photodetector; a. the1And A2The optical signal amplitude values of the branch 1 and the branch 2 are respectively; j. the design is a square1(m) is a class of Bessel functions; m is the modulation coefficient of a modulator in the carrier suppression double-sideband modulation module;
is the initial phase difference of branch 1 and branch 2; f. ofsIs the frequency shift amount of the frequency shifter; d (M) is the refractive index variation caused by the external physical parameter. Lambda [ alpha ]0The wavelength of laser emitted by the laser; f. of1The frequency of the microwave signal emitted by the microwave source; c is the speed of the light wave in vacuum; t is a time parameter.
Further, said step 4) The method specifically comprises the following steps: the frequency f of the microwave signal emitted by the microwave source (3) is set under the condition that other conditions are kept unchanged1Zero, repeating the above steps 1) -3) to obtain a new frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithoutComprises the following steps:
constructing a transmission function ACF which changes along with the external physical parameter M to be measured according to the ratio of the power functions obtained twice as follows:
only the ACF value corresponding to the external physical parameter to be measured needs to be measured, and the operation result is compared with the pre-stored ACF curve parameter, so that the size of the external physical parameter to be measured is obtained.
The invention has the following advantages and beneficial effects:
the invention relates to a device and a measuring method based on refractive index change sensing, which can realize the measurement of a power attenuation transmission function generated by a large-range external physical parameter through a refractive index sensitive module by adopting a frequency shifter for inhibiting carrier double-sideband modulation signals from respectively passing through the refractive index sensitive module and a tiny frequency shift amount and detecting heterodyne beat frequency of a refractive index change optical signal and a frequency shift optical signal only by detecting a fixed low-frequency component signal, thereby greatly reducing the detection requirement of microwave photon sensing detection.
The invention adopts a frequency shift heterodyne structure, can effectively overcome the problems of frequency drift and jitter of the laser, and realizes high-precision and wide-range external physical parameter measurement by constructing a transmission function. And by varying the microwave signal f emitted by the microwave source1And external physical parameter mapping function curves with different precisions and ranges can be constructed.
Drawings
FIG. 1 is a schematic diagram of the structure of a device for sensing based on refractive index change according to a preferred embodiment of the present invention.
In the figure: 1-laser; 2-a carrier-suppressed double sideband modulation module; 3-a microwave source; 4-an optical beam splitter; 5-a refractive index sensitive module; 6-a frequency shifter; 7-an optical coupler; 8-a photodetector; and 9, a signal acquisition and data processing module.
FIG. 2 is a graph of refractive index variation versus microwave power variation obtained by the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described in detail and clearly with reference to the accompanying drawings. The described embodiments are only some of the embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
the invention provides a sensing device based on refractive index change, which comprises: the device comprises a laser 1, a carrier suppression double-sideband modulation module 2, a microwave source 3, an optical beam splitter 4, a refractive index sensitive module 5, a frequency shifter 6, an optical coupler 7, a photoelectric detector 8 and a signal acquisition and data processing module 9.
The working principle of the sensing device and the measuring method based on the refractive index change is as follows:
the laser 1 has an output frequency f0The light wave enters a carrier-restraining double-sideband modulation module 2, and a microwave source 3 emits light with the frequency f1The microwave signal is loaded on the light wave through the carrier-restraining double-sideband modulation module 2 to generate a frequency f0-f1And f0+f1The carrier-suppressed double-sideband optical signal output by the carrier-suppressed double-sideband modulation module 2 is divided into two identical branches after passing through the optical beam splitter 4, namely a branch 1 and a branch 2; in the branch 1, the optical signal for inhibiting the carrier double-sideband passes through the refractive index sensitive module 5, the refractive index sensitive module 5 is used for sensing the refractive index change caused by the change of the external physical parameter, so that the phase difference of the two optical sidebands is changed, and in the branch 2, the optical signal for inhibiting the carrier double-sideband passes through the frequency shifter 6 to generate the frequency fsIs movedFrequency, so that the frequency is f0-f1And f0+f1Respectively of optical signals f0+f1+fsAnd f0-f1+fsOptical signals output by the two branches are coupled by an optical coupler 7 and enter a photoelectric detector 8 to carry out heterodyne detection to output electric signals; the electric signal output by the photoelectric detector 8 is acquired by the signal acquisition and data processing module 9 and is processed and analyzed to obtain the frequency fsThe signal power p (m). Changing the external physical parameter to obtain the frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M)withComprises the following steps:
wherein R is the responsivity of the photodetector; a. the1And A2The optical signal amplitude values of the branch 1 and the branch 2 are respectively; j. the design is a square1(m) is a class of Bessel functions; m is the modulation coefficient of a modulator in the carrier suppression double-sideband modulation module;
is the initial phase difference of branch 1 and branch 2; f. ofsIs the frequency shift amount of the frequency shifter; d (M) is the refractive index variation caused by the external physical parameter.
The frequency f of the microwave signal emitted by the microwave source 3 is set to be constant under other conditions1If it is zero, repeating the above steps 1-3 to obtain a new acquisition frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M)withoutComprises the following steps:
constructing a transmission function ACF which changes along with the external physical parameter M according to the ratio of the power functions obtained twice as follows:
only the ACF value corresponding to the external physical parameter to be measured needs to be measured, and the operation result is compared with the pre-stored ACF curve parameter, so that the size of the external physical parameter to be measured is obtained.
Examples
FIG. 1 is a schematic diagram of a refractive index change-based sensing device according to the present invention. The optical carrier output by the laser 1 is input into the carrier-restraining double-sideband modulation module 2, the microwave signal emitted by the microwave source 3 is loaded on the optical carrier through the carrier-restraining double-sideband modulation module 2, and the modulated optical carrier output by the carrier-restraining double-sideband modulation module 2 is divided into a branch 1 and a branch 2 through the optical beam splitter 4. In the branch 1, the optical signal of the carrier double sideband is restrained from passing through the refractive index sensitive module 5, and the refractive index sensitive module 5 is used for sensing the refractive index change caused by the change of the external physical parameter, so that the phase difference of the two optical sidebands is changed. In branch 2, the optical signal of the double-sideband with suppressed carrier is generated by a frequency shifter 6 with frequency fsThe frequency shift of (3). The optical signals output by the branch 1 and the branch 2 are coupled by the optical coupler 7 and enter the photoelectric detector 8 for photoelectric conversion. The electric signal output by the photoelectric detector 8 is processed and analyzed by the data acquisition and processing module 9. According to the invention, the frequency of a microwave signal emitted by a microwave source is set to be 16GHz, the FBG grating (the initial refractive index is 1.45) is selected as the refractive index sensitive module, the length is set to be 3mm, the frequency shift amount is set to be 0.1GHz by the frequency shifter, and a relation curve of the microwave power variation and the refractive index variation is obtained through the output of the signal acquisition and data processing module 8, as shown in FIG. 2. The acquired data is fitted to obtain a linear variation curve, whereby as a mapping function, when the power variation is 0.25dB, the corresponding refractive index variation is 0.002. Namely, the function curve constructed by the device based on refractive index change sensing of the invention really accords with a formula under the condition of inhibiting the carrier double-sideband modulation.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The above examples are to be construed as merely illustrative and not limitative of the remainder of the disclosure. After reading the description of the invention, the skilled person can make various changes or modifications to the invention, and these equivalent changes and modifications also fall into the scope of the invention defined by the claims.
Claims (9)
1. A refractive index change sensing device, comprising: a laser (1), a carrier suppression double-sideband modulation module (2), a microwave source (3), an optical beam splitter (4), a refractive index sensitive module (5), a frequency shifter (6), an optical coupler (7), a photoelectric detector (8) and a signal acquisition and data processing module (9),
the laser (1), the carrier-suppression double-sideband modulation module (2), the optical beam splitter (4), the refractive index sensitive module (5), the frequency shifter (6), the optical coupler (7) and the photoelectric detector (8) are sequentially optically connected; the carrier suppression double-sideband modulation module (2) and the microwave source (3) are sequentially connected in a circuit; the photoelectric detector (8) and the signal acquisition and data processing module (9) are sequentially connected by a circuit, wherein the output frequency of the laser (1) is f0The light wave enters a carrier-restraining double-sideband modulation module (2), and a microwave source (3) emits light with the frequency f1The microwave signal is loaded on the light wave through a carrier-restraining double-sideband modulation module (2) to generate a frequency f0-f1And f0+f1After the optical signal for inhibiting the carrier double-sideband output by the module (2) for inhibiting the carrier double-sideband modulation passes through the optical beam splitter (4), the optical signal for inhibiting the carrier double-sideband is divided into two identical branches, namely a branch 1 and a branch 2; in the branch 1, the optical signal for inhibiting the carrier double-sideband passes through the refractive index sensitive module (5), and the refractive index sensitive module (5) is used for sensing the change of the external physical parameterSo that the phase difference between the two optical sidebands is changed, and in the branch 2, the optical signal for inhibiting the carrier double-sideband is generated by a frequency shifter (6) with the frequency fsIs shifted so that the frequency is f0-f1And f0+f1Respectively of optical signals f0+f1+fsAnd f0-f1+fsOptical signals output by the two branches are coupled by an optical coupler (7) and then enter a photoelectric detector (8) to carry out heterodyne detection to output electric signals; the electric signal output by the photoelectric detector (8) is acquired by a signal acquisition and data processing module (9) and is subjected to data processing and analysis to obtain the frequency fsThe signal power p (m).
2. The refractive index change sensing device according to claim 1, wherein the carrier double sideband modulation suppression module (2) is used for suppressing the generation of carrier double sideband modulation by operating a Mach-Zehnder modulator at the lowest bias point or filtering the generation of central carrier by combining an electro-optical modulator and an optical band-stop filter.
3. The refractive index change sensing device according to claim 1, wherein the refractive index sensing module (5) comprises all modules capable of changing refractive index due to the change of external physical parameters to be measured, the external physical parameters to be measured comprise temperature, pressure, stress, magnetic field, electric field, concentration and vibration, and the refractive index change amounts of different light waves are different.
4. A refractive index change sensing device according to claim 3, wherein the frequency shifter (6) generates the frequency shift fsIn MHz magnitude, only a photoelectric detection and signal processing system with low frequency bandwidth is needed.
5. A refractive index change sensing device according to claim 4, wherein the external physical parameter is changed to obtain a frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithComprises the following steps:
wherein R is the responsivity of the photodetector; a. the1And A2The optical signal amplitude values of the branch 1 and the branch 2 are respectively; j. the design is a square1(m) is a class of Bessel functions; m is the modulation coefficient of a modulator in the carrier suppression double-sideband modulation module;
is the initial phase difference of branch 1 and branch 2; f. ofsIs the frequency shift amount of the frequency shifter; d (M) is refractive index variation caused by an external physical parameter; lambda [ alpha ]0The wavelength of laser emitted by the laser; f. of1The frequency of the microwave signal emitted by the microwave source; c is the speed of the light wave in vacuum; t is a time parameter.
6. A refractive index change sensing measurement method based on the device of any one of claims 1 to 5, comprising the steps of:
1) the output frequency of the laser (1) is f0The light wave enters a carrier-restraining double-sideband modulation module (2), and a microwave source (3) emits light with the frequency f1The microwave signal is loaded on the light wave through a carrier-restraining double-sideband modulation module (2) to generate a frequency f0-f1And f0+f1After the optical signal for inhibiting the carrier double-sideband output by the module (2) for inhibiting the carrier double-sideband modulation passes through the optical beam splitter (4), the optical signal for inhibiting the carrier double-sideband is divided into two identical branches, namely a branch 1 and a branch 2;
2) in the branch 1, the optical signal for inhibiting the carrier double-sideband passes through the refractive index sensitive module (5), the refractive index sensitive module (5) is used for sensing the refractive index change caused by the change of an external physical parameter, so that the phase difference of the two optical sidebands is changed, and in the branch 2, the optical signal for inhibiting the carrier double-sideband passes through the frequency shifter (6) to generate the frequency fsIs shifted so that the frequency is f0-f1And f0+f1Respectively of optical signals f0+f1+fsAnd f0-f1+fsOptical signals output by the two branches are coupled by an optical coupler (7) and then enter a photoelectric detector (8) to carry out heterodyne detection to output electric signals;
3) the electric signal output by the photoelectric detector (8) is acquired by a signal acquisition and data processing module (9) and is subjected to data processing and analysis to obtain the frequency fsThe signal power P (M) is changed to obtain the frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwith；
4) And the other conditions are kept unchanged, and the frequency f of the microwave signal emitted by the microwave source (3) is set1Zero, repeating the above steps 1-3) to obtain a new frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithout；
5) Constructing a transmission function (ACF) F (M) which is changed along with the external physical parameter M by the ratio of the power functions obtained twicewithout/P(M)withAnd then measuring the ACF value corresponding to the external physical parameter to be measured, and comparing the operation result with the prestored ACF curve parameter to obtain the size of the external physical parameter.
7. The refractive index change sensing measurement method according to claim 6, wherein the frequency f is obtained by changing an external physical parametersPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithThe method specifically comprises the following steps:
power function P (M)withComprises the following steps:
wherein R is the responsivity of the photodetector; a. the1And A2The optical signal amplitude values of the branch 1 and the branch 2 are respectively; j. the design is a square1(m) is a class of Bessel functions; m is a suppressed carrierModulation coefficients of modulators in the double-sideband modulation module;
is the initial phase difference of branch 1 and branch 2; f. ofsIs the frequency shift amount of the frequency shifter; d (M) is the refractive index variation caused by the external physical parameter. Lambda [ alpha ]0The wavelength of laser emitted by the laser; f. of1The frequency of the microwave signal emitted by the microwave source; c is the speed of the light wave in vacuum; t is a time parameter.
8. The refractive index change sensing measurement method according to claim 6, wherein the step 4) is specifically: the frequency f of the microwave signal emitted by the microwave source (3) is set under the condition that other conditions are kept unchanged1Zero, repeating the above steps 1) -3) to obtain a new frequency fsPower function P (M) of signal power P (M) changing with external physical parameter M to be measuredwithoutComprises the following steps:
constructing a transmission function ACF which changes along with the external physical parameter M to be measured according to the ratio of the power functions obtained twice as follows:
only the ACF value corresponding to the external physical parameter to be measured needs to be measured, and the operation result is compared with the pre-stored ACF curve parameter, so that the size of the external physical parameter to be measured is obtained.
9. The refractive index change sensing-based measurement method according to claim 6, wherein the external physical parameters include temperature, pressure, stress, magnetic field, electric field, concentration, and vibration, and the refractive index change amount is different for different light waves.
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