CN113670352B

CN113670352B - Low-cost quasi-distributed physical quantity measuring method, device and system

Info

Publication number: CN113670352B
Application number: CN202010418018.9A
Authority: CN
Inventors: 武湛君; 赵士元
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2020-05-15
Filing date: 2020-05-15
Publication date: 2024-02-27
Anticipated expiration: 2040-05-15
Also published as: CN113670352A

Abstract

The application discloses a low-cost quasi-distributed physical quantity measuring method, which is used for measuring physical quantity change of an object to be measured through a fiber grating array coupled with the object to be measured. The vertical cavity surface reflection laser is applied to a quasi-distributed physical quantity measuring device based on direct intensity detection, wavelength tuning of each wave band is achieved by applying current modulation to the vertical cavity surface reflection laser at different temperatures, and meanwhile, the laser wavelength monitoring unit is used for determining signal splicing positions of each wave band so as to obtain the spectrum of the fiber bragg grating array sensor of the whole wave band. The application also discloses a corresponding device and a corresponding system.

Description

Low-cost quasi-distributed physical quantity measuring method, device and system

Technical Field

The invention belongs to the technical field of optical fiber sensing, and particularly relates to a low-cost quasi-distributed physical quantity measuring method, device and system.

Background

The fiber grating array is a fiber sensor in which fiber gratings are written on one fiber one by one, each fiber grating generally has a relatively strong reflectivity, and the center wavelengths are different. The fiber grating array with the form is a quasi-distributed fiber sensor because the fiber gratings on the sensor are distributed on the space discrete positions. The sensor is generally positioned at the measured object when in use, and can sense the physical quantities such as temperature or strain at different positions of the measured object. The change in the physical quantity causes the center wavelength of the grating to shift. There are various fiber grating array demodulation methods for sensing, including FP filter method, tunable light source method, broadband light source wavelength division multiplexing method, etc. (1 Wang Qinghua, research based on FBG sensing signal demodulation technique, 2006, university of Yanshan 2's brave wave, fiber grating sensing characteristic and multipoint multiplexing technique research, 2012, harbine industrial university). The purpose of the various methods is to obtain the offset of the central wavelength of gratings at different positions on the fiber grating array, so as to obtain the information of the measured physical quantity.

The fiber grating array physical quantity measuring method based on direct intensity detection) and the device use a narrow linewidth tunable laser as a system light source, require that the center wavelengths of all gratings on the fiber grating array to be measured have a certain interval and ensure that the center wavelengths of the gratings with adjacent center wavelengths are not coincident after the external physical quantity change, namely each grating has independent bandwidth. The total tuning bandwidth (tuning range) of the tunable light source determines the maximum number of fiber gratings that can be multiplexed on a single fiber optic sensor and the bandwidth occupied by each grating. The bandwidth occupied by each grating is directly related to the range of the physical quantity to be measured. The above characteristics and the broadband light source wavelength division multiplexing and demodulation method are very similar, but because the spectrum of the grating under a specific light wavelength is acquired point by point, the measurement accuracy and the spectrum resolution of the fiber grating array physical quantity measurement method based on direct intensity detection are higher. In order to further increase the multiplexing number and measurement range and resolution in the demodulation apparatus and method, a tunable light source is required to have a wider tuning range and a measurement system is required to have a higher spectral resolution. The prior fiber grating array physical quantity measuring device and method based on direct intensity detection adopts a tunable light source such as a DBR laser, for the fiber grating array demodulation device adopting the laser, generally, step scanning is carried out, such as one acquisition is triggered every step of 1pm, and the fiber grating array spectral information of the whole wave band is recovered through step scanning and acquisition in the whole wave band ([ 1] Cui Wei, su Jianjia, jiang Peipei, wu Bo, shen Yonghang, a high-resolution multiplexing fiber grating wavelength demodulation system based on a tunable semiconductor laser [ J ]. Photon theory, 2016,45 (07): 65-7[2] Chu Jiliang, and a fiber grating wavelength demodulation system error analysis and instrumentation research based on the tunable laser [ D ]. Tianjin university, 2018 ]. However, the tuning range of the method is limited (the tuning range of the DBR laser is about 15 nm), and because the method is step-by-step scanning, the original sampling point of the spectrum is also 1pm, and the resolution of the measured physical quantity is limited by limiting the original spectrum resolution.

Vertical cavity surface reflecting lasers (VCSELs) are one type of semiconductor lasers, the wavelength of which can be tuned continuously with current or temperature, and the sensitivity of both temperature and current tuning is high. The tuning range is larger compared to distributed feedback lasers (DFBs). Taking the vertical cavity surface reflection laser RC32xxx1-PFAmt of Raycan company in korea as an example, the tuning range is generally lower than 5nm when the temperature changes by about 1 degree celsius and the wavelength changes by about 0.1 nm. On the other hand, wavelength tuning by laser drive current tuning is typically achieved by a wavelength conversion per mA of about 0.5nm below the nominal safe current (Altabas J A, izquierdo D, lazaro J A, et al Chirp-based direct phase modulation of VCSELs for cost-effective transceivers [ J ]. Optics letters,2017,42 (3): 583-586.). In addition, the single-chip cost price of the VCSEL is generally tens of dollars, and the cost is extremely low compared with that of an external cavity type laser, so that the VCSEL is suitable for large-scale popularization.

The invention applies the vertical cavity surface reflection laser to a quasi-distributed sensing system based on direct intensity detection, and researches a low-cost quasi-distributed physical quantity measuring method, device and system based on the vertical cavity surface reflection laser.

Disclosure of Invention

Some embodiments of the present application provide a low-cost quasi-distributed physical quantity measurement method for measuring a physical quantity change of an object to be measured through a fiber grating array coupled to the object to be measured, comprising the steps of: sequentially performing current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the initial temperature to the final temperature to obtain laser output from the initial wavelength to the final wavelength; wherein the current tuning is configured to: the start wavelength in current tuning at one of the discrete temperature values is less than the end wavelength in current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state; synchronously acquiring a measurement state absolute wavelength monitoring signal containing the absolute wavelength information of the laser output in a measurement state comprising the physical quantity change, and a measurement state direct intensity detection signal of the fiber bragg grating array for the laser output; determining the splicing point of the measured direct intensity detection signal according to the absolute wavelength information; removing overlapping areas except the splicing points in the measured direct intensity detection signals according to the splicing points to form spliced measured direct intensity detection signals; solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array based on the spliced measurement state direct intensity detection signals; obtaining the central wavelength of different fiber gratings of the fiber grating array in the measurement state according to the position of the peak value; and comparing the central wavelength with the initial central wavelength of each grating to obtain a central wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

Some embodiments of the present application provide a low-cost quasi-distributed physical quantity measuring apparatus for measuring a physical quantity change of an object to be measured by a fiber grating array coupled to the object to be measured, comprising: the vertical cavity surface reflection laser is configured to sequentially perform current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the initial temperature to the final temperature to obtain laser output from the initial wavelength to the final wavelength; a direct intensity detection unit comprising a fiber coupler or circulator for introducing light into the fiber grating array, and a photodetector coupled to the circulator, the detection unit configured to introduce the laser output into the fiber grating array and to convert reflected light of the fiber grating array into a direct intensity detection signal; an absolute wavelength monitoring unit configured to receive the laser output and provide a laser output wavelength monitoring signal containing absolute wavelength information of the laser output; an acquisition unit configured to synchronously acquire an absolute wavelength monitoring signal containing absolute wavelength information of the laser output, and a direct intensity detection signal of the fiber grating array for the laser output; and a data processing unit configured to: determining a splice point of the direct intensity detection signal according to the absolute wavelength information; removing overlapping areas except the splicing points in the direct intensity detection signals according to the splicing points to form spliced direct intensity detection signals; solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array based on the spliced direct intensity detection signals; obtaining the central wavelength of different fiber gratings of the fiber grating array in the physical state according to the position of the peak value; and comparing the central wavelength with the initial central wavelength of each grating to obtain a central wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

Some embodiments of the present application also provide systems including the apparatus.

The invention has the beneficial effects that: the method and the device have the advantages of low cost and high measurement precision.

Drawings

FIG. 1 is a schematic diagram of a vertical cavity surface reflecting laser according to some embodiments of the present application;

in fig. 1: 44 is a thermoelectric cooler, 45 is a thermistor, 2 is a vertical cavity surface reflecting laser, and 46 is a laser diode.

FIG. 2 is a quasi-distributed physical measurement device without an electro-optic phase locked loop according to some embodiments of the present application;

in fig. 2: 28 is a laser temperature control terminal, 27 is a laser diode driving current terminal, 25 is a current driving unit, 26 is a temperature control unit, 1 is a control unit, 26 is a temperature control unit, 3 is a first fiber coupler, 4 is a fiber grating array sensor, 12 is a second fiber coupler, 23 is a delay fiber, 20 is a wavelength monitoring unit, 21 is a relative wavelength monitoring unit, 22 is a direct intensity detection unit, 19 is an acquisition unit, 18 is a first photoelectric detector, 15 is a second photoelectric detector, 7 is a third photoelectric detector, 31 is a storage unit, 32 is a data processing unit, 13 is a first Faraday rotary mirror, 14 is a second Faraday rotary mirror, 40 is a closed loop power control unit, and 5 is a fiber circulator.

FIG. 3 is a schematic diagram of a fiber grating array according to some embodiments of the present application;

in fig. 3, 81 is a first fiber grating, 82 is a second fiber grating, 83 is a third fiber grating, and 84 is a fourth fiber grating

FIG. 4 is a spectrum of a fiber optic grating array sensor according to some embodiments of the present application.

FIG. 5 is a block diagram of a quasi-distributed physical quantity measurement device with an electro-optic phase locked loop according to some embodiments of the present application

FIG. 6 is a schematic diagram of a semiconductor optical amplifier and its closed loop optical power control according to some embodiments of the present application;

in fig. 6, 91 is a semiconductor optical amplifier, 92 is a tenth coupler, 93 is a fourth photodetector, and 94 is a comparator. 95 is a filter, 96 is an operational amplifier, and 97 is a current driver.

FIG. 7 is a hydrogen cyanide gas cell absorption spectrum according to some embodiments of the present application;

FIG. 8 is a schematic diagram of splice point determination of adjacent band direct intensity detection unit signals according to some embodiments of the present application;

in fig. 8, 70 is a sampling point position corresponding to the MC11 signal splicing position, 71 is a sampling point position corresponding to the MC12 signal splicing position, 72 is the MC11 signal, 73 is the MC12 signal, 74 is the MA11 signal, 75 is the MA12 signal, and 77 is the MC1112 signal.

FIG. 9 is an absolute wavelength value corresponding to absorption peaks of a hydrogen cyanide chamber according to some embodiments of the present application.

Detailed Description

The method and the device for measuring the quasi-distributed physical quantity based on the vertical cavity surface reflection laser take the vertical cavity surface reflection laser as a system light source. In the invention, the tuning of the output wavelength of the laser diode on the vertical cavity surface reflection laser is controlled by applying the driving current tuning under each temperature gradient, and the output laser of each laser is multiplexed and spliced on the wavelength, which is equivalent to expanding the sweep frequency or wavelength tuning range of the light source of the quasi-distributed physical measurement device. At the same time, the magnitude of the driving current affects the optical power output by the laser, because a closed-loop power control unit with a semiconductor optical amplifier as a core is added behind the laser in order to obtain stable laser output. In addition, the wavelength monitoring unit is used for determining the splicing position of the tuning process of the adjacent wavelength lasers, so that the wavelengths of the reflection lasers of the vertical cavity surfaces can be covered without intervals. After the full-band laser output is obtained, the laser is injected into a quasi-distributed physical quantity measuring system, and the quasi-distributed physical quantity measurement of the sensing optical fiber with high speed and high resolution is realized by examining the relative spectral movement of a reference state and a measurement state. Specific details of the invention are set forth below.

FIG. 1 is a schematic diagram of a typical vertical cavity surface reflecting laser. Typically, the vertical cavity surface reflecting laser 43 has a thermoelectric cooler 44 for heating or cooling, which can be controlled by electric current, and a thermistor 45 whose resistance varies with temperature. The output wavelength of the vertical cavity surface reflection laser is responsive to both temperature and current in the case of the RC32xxx1-PFAmt model of Raycan corporation in korea. The threshold current is 2mA, the maximum working current is 14mA, and the output wavelength change is about 6nm under the condition that the current is changed from 14mA of 2 mA. If the lasers are produced in the same batch, the output center wavelength of the lasers should be equal or less than 0.5nm at a certain driving current and temperature, e.g., 7ma,15 degrees. At a fixed driving current, the temperature value is changed from 10 degrees to 50 degrees, and the output wavelength is changed to about 5nm.

The vertical cavity surface reflection laser parameters selected in the later description of the measuring device are:

(1) The driving current is 2mA, and the output wavelength of the vertical cavity surface reflection laser is 1530nm at the temperature of 10 degrees.

(2) The current tuning coefficient is 0.5nm/mA, the current tuning is sawtooth wave, the initial driving current is 2mA, the final driving current is 12mA, and therefore the current tuning range is 5nm.

(3) The temperature tuning coefficient is 0.1 nm/DEG C, and the temperature gradient is set to be 10 ℃ and 50 ℃;

(4) The driving current is 2mA, and the output wavelength of the vertical cavity surface reflection laser is 1534nm at the temperature of 50 degrees.

FIG. 3 is a schematic diagram of a fiber grating array sensor, which is composed of a plurality of fiber gratings with certain reflectivity engraved at different positions on an optical fiber, wherein the fiber gratings respectively have different center wavelengths and the center wavelengths are not overlapped after the physical quantity change; the optical fiber sensor 4 shown in fig. 2 has ten optical fiber gratings with reflectivity of 20%, the central wavelengths of the gratings increase from left to right, the central wavelength interval between adjacent gratings is 2nm, and the space interval is 1 meter. The center wavelength of the first fiber grating 81 is 1532nm, the center wavelength of the second fiber grating 82 is 1534nm, the center wavelength of the third fiber grating 83 is 1536nm, and the center wavelength of the fourth fiber grating 84 is 1538nm. These are determined at the time of writing the fiber grating array (depending on the writing parameters and affected by the environmental temperature stress, etc.). When the array of sensors 2 is connected to the structure to be measured, the fiber gratings at different positions sense physical quantities of the structure to be measured, such as temperature or strain, or other physical quantities that can cause strain or temperature change in the optical fiber, and shift the center wavelength occurs. As shown in fig. 4, the spectrum of the fiber grating array is shown, the horizontal axis is wavelength or optical frequency, the gratings with different spatial positions are also respectively located on different wavelengths, the spectrum of each grating is a parabolic peak, the position corresponds to the nominal center wavelength or the reference center wavelength, that is, the center wavelength under the known reference strain or temperature, if the grating has the effect of physical quantity change, the center wavelength will shift, the shift can be calculated to obtain the change quantity of the physical quantity such as temperature or strain, and if the original reference center wavelength is known, the absolute quantity of the physical quantity can be solved.

Fig. 5 shows a quasi-distributed physical measurement device, in which the pin of the thermoelectric cooler 35 on the vertical cavity surface reflection laser 2 is a laser temperature control terminal 28, and the application of a control signal to the terminal 28 can change the current passing through the thermoelectric cooler 35, and this control signal is also in the form of current, so as to change the temperature of the vertical cavity surface reflection laser 2. The current drive unit 25 is used to provide a drive current signal for the vertical cavity surface reflecting laser for wavelength tuning of the vertical cavity surface reflecting laser, which signal is applied to the drive current terminal 27 for the laser diode. The tuned laser output obtained in the process of current tuning of the vertical cavity surface reflection laser 2 is coupled into a closed loop power control unit 40 to adjust the optical power of the output laser of the vertical cavity surface reflection laser 2 in real time so as to achieve the aim of stable output power; the output laser beam split through the closed loop power control unit 40 enters the absolute wavelength monitoring unit 20, the relative wavelength monitoring unit 21 and the direct intensity detection unit 22; wherein the direct intensity detection unit 22 comprises an optical fiber sensor 4;

the acquisition unit 19 acquires signals of the absolute wavelength monitoring unit 20, the relative wavelength monitoring block 21 and the direct intensity detection unit 22;

The data processing unit 31 is configured to process the data in the storage unit 32, and includes determining a splicing position of each band signal, so as to complete signal splicing; for calculating quasi-distributed physical quantities. The data processing unit 31 is a unit that can perform operations such as a CPU, FPGA, DSP, or the like of a computer.

The storage unit 32 stores the collected relative wavelength monitor unit signals of each wavelength band, the direct intensity detection signals, the original signals of the wavelength monitor units, and the splice positions of the laser output optical signals obtained after the data processing of the data processing unit 31, the spliced relative wavelength monitor unit signals, the spliced direct intensity detection signals, the final relative wavelength monitor unit signals, the final direct intensity detection signals, and the storage of the quasi-distributed physical quantity calculation results. The storage unit 32 is a hard disk of a computer, a memory, a DRAM of an embedded device, or the like.

The control unit 1 is used for timing control of the current driving unit 24, the temperature control unit 26, the electrical channel switching unit 25 and the acquisition unit 19. The control unit 1 may be a computer CPU or an embedded FPGA, ARM, etc.

To achieve gapless tuning and spectral coverage, a first wavelength in current tuning at one of the discrete temperature values is less than a second wavelength in current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

As shown in fig. 5, the control unit 1 applies a first temperature control signal TCS1 to the temperature control unit 26, and the temperature control unit 26 is connected to the laser temperature control terminal 28 of the vertical cavity surface reflection laser 2 to control the vertical cavity surface reflection laser 2 to 10 degrees. The control unit 1 controls the current driving unit 25 to output a first current driving signal CDS1, the first current driving signal CDS1 tunes from the starting current 2mA to the ending current 12mA, and under the first current driving signal CDS1, the first vertical cavity surface reflection laser in the vertical cavity surface reflection laser 2 is driven to perform wavelength tuning, and the first vertical cavity surface reflection laser is tuned from 1530nm to 1535nm. At the same time, the control unit 1 controls the acquisition unit 19 to acquire the signal MA11 output by the wavelength monitoring unit 20, the signal MB11 output by the auxiliary interferometer unit 21, the signal MC11 output by the main interferometer unit 22, and the data stored in the storage unit 31. Next, the control unit 1 applies a second temperature control signal TCS2 to the temperature control unit 26 to control the vertical cavity surface reflecting laser 2 to 50 degrees. The control unit 1 controls the current driving unit 25 to output a second current driving signal CDS2, the first current driving signal CDS2 is tuned from the start current 2mA to the end current 12mA, and under the second current driving signal CDS2, the vertical cavity surface reflection laser 2 is driven to perform wavelength tuning, and the vertical cavity surface reflection laser is tuned from 1534nm to 1539nm. In the tuning process, the control unit 1 controls the acquisition unit 19 to acquire the signal MA12 output by the wavelength monitoring unit 20, the signal MB12 output by the auxiliary interferometer unit 21, the signal MC12 output by the main interferometer unit 22, and the data are stored in the storage unit 31.

The above-mentioned collected original signals output by the wavelength monitoring unit 20 are sequentially arranged according to the access band sequence: MA11 (1530-1535 nm) MA12 (1534-1539 nm).

The original signals output by the collected auxiliary interferometer unit 21 are sequentially arranged according to the access band sequence: MB11 (1530-1535 nm) MB12 (1534-1539 nm).

The original signals output by the main interferometer unit 22 are sequentially arranged according to the access band sequence: MC11 (1530-1535 nm) MC12 (1534-1539 nm).

The band is defined as the spectral range covered by wavelength tuning under current modulation applied by a vertical facet reflective laser at a certain temperature. The brackets above refer to the wavelength range of the laser output, i.e. the meaning of the wavelength band. It can be seen that the collected signals have two wavebands in total, and the adjacent wavebands have wavelength overlapping, and the wavelength overlapping area is 1nm. The two bands need to be spliced and combined to form a complete signal without overlap. A process of determining splice locations of the auxiliary interferometer unit and the main interferometer unit signals in wavelength adjacent bands using the wavelength monitoring unit signals is required.

The absolute wavelength monitoring unit 20 measures the wavelength by a device such as a spectrometer or a wavemeter, and reads the wavelength as the laser wavelength, and only any point in the overlapping area needs to be selected at this time, preferably, a point in the middle of the overlapping area can be selected as the splicing position. The absolute wavelength monitoring unit 20 may also be a gas molecular cell, such as a hydrogen cyanide molecular cell, an acetylene molecular cell, etc., which may have a characteristic absorption line. The characteristic spectrum of the hydrogen cyanide molecular gas cell is shown in FIG. 7 and is used as the reference of the wavelength of the C band (1530 to 1565 nm). The absolute wavelength corresponding thereto is shown in fig. 9.

As shown in fig. 8, the process of splicing the splice point position and the signal is determined by using the absorption peak position of the hydrogen cyanide gas chamber as a wavelength monitoring unit. Taking the MC11 (72 in fig. 7) and MC12 (73 in fig. 8) signals as an example. MA11 (74 in FIG. 8) and MA12 (75 in FIG. 8) are at wavelength positions for the hydrogen cyanide chamber transmission signal

R20 (1530.30668 nm) R19 (1530.78615), R18 (1531.27537) R17 (1531.77430) R16 (1532.28298) having an absorption peak, MC11 at the wavelength position R16 (1532.28298)

R15 (1532.80139 nm) R14 (1533.32954) and R13 (1533.86745) have an absorption peak. Thus can be used

R16 (1532.28298) as the splice wavelength location. Then, the MC11 discards the data at the rear of the sampling point (70 in fig. 6) corresponding to the wavelength position, and the MC12 discards the data at the front of the sampling point (71 in fig. 8) corresponding to the wavelength position. The newly obtained main interferometer output signals of two adjacent sections are the spliced MC1112 signals (77 in FIG. 8).

And the signals of other adjacent wave bands are spliced in the same way, all the spliced wave bands are sequentially arranged from small to large according to the wavelength to form the signal of the spliced relative wavelength monitoring unit, and the signal is directly detected in intensity after splicing.

And then nonlinear correction is carried out on the spliced direct intensity detection signal through the spliced relative wavelength monitoring unit signal. Since the laser wavelength tuning by current tuning has nonlinearity, i.e. the output optical frequency or wavelength does not increase linearly with time, when the individual output signals are sampled with a fixed sampling rate, the sampling points are not equally spaced, which worsens the spatial resolution of the sensing or measuring system. The method for performing nonlinear correction on the measurement state direct intensity detection signal and the measurement state wavelength monitoring signal by using the relative wavelength monitoring unit signal has several different implementation modes: the relative wavelength monitoring unit signal may be acquired with a fixed sampling rate in synchronization with the other signals with the acquisition unit 19, and then non-linear correction of the direct intensity detection signal or the wavelength monitoring signal may be performed in the data processing unit. The method comprises the steps of performing Hilbert expansion on a relative wavelength monitoring unit signal, performing phase unwrapping, equally dividing the phase, such as equally dividing according to pi radians, to obtain corresponding sampling points, and resampling a direct intensity detection signal and a wavelength monitoring signal by using the sampling points, wherein the resampled direct intensity detection signal and the resampled wavelength monitoring signal are nonlinear signals. In addition, there are implementations of non-uniform fourier transforms, deskew filters, PNC phase compensation, etc. that correct for non-linearities with post-software processing. In addition, the sine signal output by the relative wavelength monitoring unit can be used as a clock of the acquisition unit 19, and the clock can be used as an acquisition clock of the direct intensity detection signal and the wavelength monitoring signal to acquire the two paths. In addition, nonlinear correction can be performed by adopting an optoelectronic phase-locked loop technology. This section will not be described in detail in view of the existing prior art. Relevant literature can be found (1. Ding Zhenyang, proposal and validation of several methods of improving OFDR performance, 2013, tianjin university 2.Fan, X., Y.Koshikiya and F.Ito, phase-noise-compensated optical frequency Domain reflectometry with measurement range beyond laser coherence length realized using concatenative reference methods optics letters,2007.32 (22): p.3223.sweet-wavelength Interferometric Interrogation of Fiber Rayleigh Scatter for Distributed Sensing Applications 4.Song, J., et al, long-Range High Spatial Resolution Distributed Temperature and Strain Sensing Based on Optical Frequency-Domain reflectometry.IEEE Photonics Journal,2014.6 (3): p.1-8.5. Zhang Hao, current-tuned semiconductor laser absolute distance measurement technology research, 2016, harbin university 15, 6.Satyan N,Vasilyev A,Rakuljic G,et al.Precise control of broadband frequency chirps using optoelectronic feedback.Optics express,2009,17 (18): 15991-15999). The direct intensity detection signal after the nonlinear splicing is corrected is recorded as a final direct intensity detection signal and is used as the input quantity of a quasi-distributed parameter demodulation program.

If nonlinear correction is performed using the photoelectric phase locked loop technique described above (the above-described documents 6 and 7), the measuring device will have a structure as shown in fig. 3. The phase-locked loop unit comprises a reference source 81, a multiplicative phase detector 82, a loop filter 83, an integrator 84 and an adder 85; the auxiliary interferometer output signal, including the laser tuning nonlinearity, is compared to a signal set by a reference source 81 (typically a sinusoidal signal of a signal generator) in a multiplicative phase detector 82. The frequency error signal is input to the loop filter 83 and then enters the integrator 84, and the output signal is synthesized with the initial current drive signal of the laser supplied from the control unit 1 by the adder 85 and then input to the current drive unit 24 of the laser, and the drive current value under tuning is corrected in real time.

At this time, the acquisition unit 19 acquires the direct intensity detection unit output signal and the absolute wavelength monitoring unit output signal at a fixed frequency, and the data processing unit 32 is configured to determine the splice position of each signal; intercepting and splicing the direct light intensity detection unit signal and the absolute wavelength monitoring unit signal to obtain a final direct light intensity detection unit signal and a final absolute wavelength monitoring unit signal; resolving quasi-distributed physical quantities

Fig. 6 shows a semiconductor optical amplifier and a closed loop power stabilizing unit thereof, which comprises: the semiconductor optical amplifier 91 can apply different gains to the laser power injected thereto by changing the driving current thereon; a photodetector 93 for converting the optical signal into an electrical signal proportional to the optical power; comparator 94 for comparing the measured valueComparing the light intensity signal of (2) with a set value to obtain an error signal; the voltage signal obtained by filtering and amplifying the error signal output from the comparator 94 is input to the current driver 97 as a current drive signal. The tenth coupler splits 10% of the light into a closed loop control loop, and the remaining 90% is injected as output light into the rear measuring light path as measuring device signal light. It can be seen that the closed loop power control unit 40 stabilizes the input light at a certain power set. For a related description of semiconductor optical amplifiers, see [ [1 ]]https://www.thorlabs.de/newgrouppage9.cfmobjectgroup_id＝3901

[2]https://courses.cit.cornell.edu/ece533/Lectures/handout9.pdf]

In view of the fact that the quasi-distributed physical quantity measurement or sensing based on direct light intensity detection is a relative measurement, it is first necessary to determine a reference state signal, which is acquired in a first external state and stored in a computer memory, and a second external state, which is described below, represents a measured state, and the fiber grating array sensor may have a physical quantity change effect with respect to the first reference state. The quasi-distributed physical quantity measurement process based on the vertical cavity surface reflection laser is as follows:

Step 1, obtaining reference state each wave band wavelength monitoring unit signals in an external first state, wherein the reference state each wave band wavelength monitoring unit signals are relative to the wavelength monitoring unit signals, and the reference state each wave band wavelength monitoring unit signals are direct intensity detection signals;

step 2, obtaining the wavelength monitoring unit signals of each wave band in the measuring state under the second external state, wherein the waves of each wave band in the measuring state are relative to the wavelength monitoring unit signals, and the direct intensity detection signals of each wave band in the measuring state are obtained;

step 3, determining splicing positions of adjacent wave bands according to the signals of the wavelength monitoring units to obtain reference state spliced direct intensity detection signals, reference state spliced relative wavelength monitoring unit signals, measurement state spliced direct intensity detection signals and measurement state spliced direct intensity detection signals;

step 4, respectively utilizing the reference state spliced relative wavelength monitoring unit signal and the measurement state spliced relative wavelength monitoring unit signal to carry out nonlinear correction on the reference state spliced direct intensity detection signal and the measurement state spliced direct intensity detection signal, so as to obtain a final reference state direct intensity detection signal and a final measurement state direct intensity detection signal;

Step 5, quasi-distributed physical quantity calculation: according to the final reference state direct intensity detection signal and the final measurement state direct intensity detection signal, the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array are obtained; obtaining the central wavelength of different fiber gratings of the fiber grating array in the physical state according to the peak position, wherein the difference value of the spectral central wavelengths of the reference state and the measured state gratings corresponds to the physical quantity change on the gratings; .

The measured physical quantity may be strain, or temperature, or other physical quantity that may cause the fiber to strain or change in temperature. The physical quantities and the shift of the spectrum are generally different by a coefficient (sensitivity) or conform to the relation of polynomial functions for more accuracy, or coefficient values can be obtained through calibration experiments.

It should be understood that in some embodiments of the present invention, the non-linearity correction is not necessary, and the measurement method of the present invention may be implemented without non-linearity correction. The reference state information, e.g. the spectrum of the reference state, in some embodiments of the invention may be pre-stored as a reference signal or may be obtained by real-time measurements as described in the above embodiments.

It should be appreciated that the respective initial center wavelengths of the fiber gratings are pre-stored or obtained by the methods set forth in the above embodiments.

In this application, an absolute wavelength monitoring signal refers to a signal provided by an absolute wavelength monitoring unit or a unit having the same or substantially the same function; the relative wavelength monitoring signal refers to a signal provided by a relative wavelength monitoring unit or a unit having the same or substantially the same function; the direct intensity detection signal refers to a signal provided by a direct intensity detection unit or a unit having the same or substantially the same function.

The absolute wavelength monitoring unit obtains an absolute wavelength value output by the laser, and comprises an air chamber for outputting a characteristic signal, and a fiber bragg grating with a known central wavelength or a spectrometer or a wavemeter with a wavelength can be directly obtained. In the foregoing, the present invention is merely preferred embodiments, which are based on different implementations of the overall concept of the invention, and the protection scope of the invention is not limited thereto, and any changes or substitutions easily come within the technical scope of the present invention as those skilled in the art should not fall within the protection scope of the present invention. The invention can also be realized by the examples disclosed below:

1. A low-cost quasi-distributed physical quantity measuring method for measuring physical quantity change of an object to be measured by a fiber grating array coupled to the object to be measured, comprising the steps of:

sequentially performing current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the initial temperature to the final temperature to obtain laser output from the initial wavelength to the final wavelength; wherein the current tuning is configured to: the start wavelength in current tuning at one of the discrete temperature values is less than the end wavelength in current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state;

synchronously acquiring a measurement state absolute wavelength monitoring signal containing the absolute wavelength information of the laser output in a measurement state comprising the physical quantity change, and a measurement state direct intensity detection signal of the fiber bragg grating array for the laser output;

determining the splicing point of the measured direct intensity detection signal according to the absolute wavelength information;

removing overlapping areas except the splicing points in the measured direct intensity detection signals according to the splicing points to form spliced measured direct intensity detection signals;

Solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array based on the spliced measurement state direct intensity detection signals;

obtaining the central wavelength of different fiber gratings on the fiber grating array in the measurement state according to the position of the peak value;

and comparing the central wavelength in the measurement state with the initial central wavelengths of different fiber gratings on the fiber grating array to obtain a central wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

2. The method according to example 1, characterized by: further comprises

Providing a relative wavelength monitoring signal of the vertical cavity surface reflective laser;

synchronously collecting measurement state absolute wavelength monitoring signals containing absolute wavelength information of the laser output, measurement state relative wavelength monitoring signals of the laser output and measurement state direct intensity detection signals of the fiber bragg grating array on the laser output in the measurement state;

removing overlapping areas except the splicing points in the measurement state relative wavelength monitoring signals according to the splicing points to form spliced measurement state relative wavelength monitoring signals;

determining equal optical frequency interval sampling points of the measurement state direct intensity detection signals by using the spliced measurement state relative wavelength monitoring signals, and calibrating equal optical frequency interval values of the equal optical frequency interval sampling points by using the measurement state absolute wavelength monitoring signals;

And resampling the spliced measurement state direct intensity detection signal by using the equal optical frequency interval sampling points to obtain the resampled spliced measurement state direct intensity detection signal which is used for solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array.

3. The method according to example 1 or 2, characterized in that:

the initial center wavelength of each of different fiber gratings on the fiber grating array is stored in advance or obtained by the following method:

synchronously acquiring reference state absolute wavelength monitoring signals containing absolute wavelength information of the laser output in a reference state which does not comprise the physical quantity change, and directly detecting intensity signals of the fiber bragg grating array on the reference state of the laser output;

determining a splice point of the reference state direct intensity detection signal according to the absolute wavelength information;

removing overlapping areas except the splicing points in the reference state direct intensity detection signals according to the splicing points to form spliced reference state direct intensity detection signals;

solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array based on the spliced reference state direct intensity detection signals;

And obtaining the center wavelength of different fiber gratings of the fiber grating array in the reference state, namely the initial center wavelength, according to the position of the peak value.

4. The method according to example 3, characterized in that:

synchronously collecting reference state absolute wavelength monitoring signals containing absolute wavelength information of the laser output, reference state relative wavelength monitoring signals of the laser output and reference state direct intensity detection signals of the fiber bragg grating array on the laser output in the reference state; removing overlapping areas except the splicing points in the reference state relative wavelength monitoring signals according to the splicing points to form spliced reference state relative wavelength monitoring signals; determining an equal optical frequency interval sampling point by using the spliced reference state relative wavelength monitoring signal, and calibrating an equal optical frequency interval value in a tuning wavelength range by using the reference state absolute wavelength monitoring signal; resampling the spliced reference state direct intensity detection signal by using the equal optical frequency interval sampling points to obtain the resampled reference state spliced direct intensity detection signal which is used for solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array.

5. The method according to example 1, characterized by: the output wavelength of the vertical cavity surface reflection laser increases with the increase of the driving current and with the increase of the working temperature.

6. The method according to any of the above examples, characterized by: the physical quantity changes include temperature, or strain, or other physical quantity that may cause the fiber to strain or change in temperature.

7. The method according to any of the above examples, characterized by: the original spectral resolution of the fiber bragg grating array is equal to the equal optical frequency interval value.

8. The method according to any of the above examples, characterized by: the nonlinear correction includes: the relative wavelength monitoring unit signal is used as an external clock of the acquisition card to trigger synchronous acquisition of the direct intensity detection signal; or, synchronously collecting the relative wavelength monitoring unit signal and the direct intensity detection signal by using an internal clock with a fixed sampling rate, estimating the phase of the output signal of the laser according to the relative wavelength monitoring unit signal, and performing nonlinear compensation, such as resampling, on the direct intensity detection signal so that the direct intensity detection signal has equal optical frequency intervals; or a photoelectric phase-locked loop is adopted to realize nonlinear correction.

9. The method according to any of the above examples, characterized by: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

10. A low-cost quasi-distributed physical quantity measuring apparatus for measuring a physical quantity change of an object to be measured by a fiber grating array coupled to the object to be measured, comprising:

the vertical cavity surface reflection laser is configured to sequentially perform current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the initial temperature to the final temperature to obtain laser output from the initial wavelength to the final wavelength;

a direct intensity detection unit comprising a fiber coupler or circulator for introducing light into the fiber grating array, and a photodetector coupled to the circulator, the detection unit configured to introduce the laser output into the fiber grating array and to convert reflected light of the fiber grating array into a direct intensity detection signal;

An absolute wavelength monitoring unit configured to receive the laser output and provide a laser output wavelength monitoring signal containing absolute wavelength information of the laser output;

an acquisition unit configured to synchronously acquire an absolute wavelength monitoring signal containing absolute wavelength information of the laser output, and a direct intensity detection signal of the fiber grating array for the laser output; and

a data processing unit configured to:

determining a splice point of the direct intensity detection signal according to the absolute wavelength information;

removing overlapping areas except the splicing points in the direct intensity detection signals according to the splicing points to form spliced direct intensity detection signals;

solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array based on the spliced direct intensity detection signals;

obtaining the central wavelength of different fiber gratings of the fiber grating array in the physical state according to the position of the peak value;

and comparing the central wavelength with the initial central wavelength of each grating in each fiber grating array to obtain a central wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

11. The apparatus of example 10, wherein:

the laser light source further comprises a relative wavelength monitoring unit configured to provide a relative wavelength monitoring signal of the laser output;

the acquisition unit is configured to synchronously acquire a measurement state absolute wavelength monitoring signal containing the absolute wavelength information of the laser output, a measurement state relative wavelength monitoring signal of the laser output, and a measurement state direct intensity detection signal of the fiber bragg grating array for the laser output;

the data processing unit is configured to:

obtaining the center wavelength of different fiber gratings of the fiber grating array in the reference state according to the position of the peak value;

and comparing the measured state center wavelength with the center wavelength of each reference state of the grating to obtain a center wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

12. The apparatus of example 10 or 11, wherein:

the acquisition unit is further configured to synchronously acquire a reference state absolute wavelength monitoring signal containing absolute wavelength information of the laser output in a reference state which does not include the physical quantity change, and a reference state direct intensity detection signal of the fiber bragg grating array for the laser output;

the data processing unit is further configured to:

13. The apparatus according to any of the above examples, wherein:

The acquisition unit is configured to synchronously acquire reference state absolute wavelength monitoring signals containing absolute wavelength information of the laser output in the reference state, reference state relative wavelength monitoring signals of the laser output and reference state direct intensity detection signals of the fiber bragg grating array for the laser output;

the data processing unit is configured to remove overlapping areas except the splicing points in the reference state relative wavelength monitoring signals according to the splicing points to form spliced reference state relative wavelength monitoring signals; determining an equal optical frequency interval sampling point by using the spliced reference state relative wavelength monitoring signal, and calibrating an equal optical frequency interval value in a tuning wavelength range by using the reference state absolute wavelength monitoring signal; resampling the spliced reference state direct intensity detection signal by using the equal optical frequency interval sampling points to obtain the resampled reference state spliced direct intensity detection signal which is used for solving the positions of peaks of different fiber bragg grating spectrums of the fiber bragg grating array.

14. The apparatus according to any of the above examples, wherein: the device also comprises a storage unit which is used for storing the original sampling data of each unit of each wave band, storing the calculation result of the measured physical quantity and storing the initial center wavelength of each grating.

15. The apparatus according to any of the above examples, wherein: the laser also comprises a current driving unit for providing a driving current signal for the vertical cavity surface reflection laser.

16. The apparatus according to any of the above examples, wherein: the laser diode laser also comprises a temperature control unit for providing a control signal of the working temperature for the laser diode in the vertical cavity surface reflection laser.

17. The apparatus according to any of the above examples, wherein: a closed loop power control unit is also included for adjusting the optical power of the laser output of the vertical facet reflective laser to provide a laser with a stable optical power.

18. The apparatus according to any of the above examples, wherein: the laser output of the vertical cavity surface reflection laser is respectively injected into a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit through a beam splitting coupler, and an acquisition unit acquires respective output signals of the three units.

19. The apparatus according to any of the above examples, wherein: the absolute wavelength monitoring unit obtains an absolute wavelength value output by the laser, and comprises an air chamber for outputting a characteristic signal, and a fiber bragg grating with a known central wavelength or a spectrometer or a wavemeter with a wavelength can be directly obtained.

20. The apparatus according to any of the above examples, wherein: the relative wavelength monitoring unit comprises a fiber interferometer with a fixed optical path difference and a Mach-Zehnder structure or a Michael Sun Jiegou structure, or an FP etalon or a fiber ring resonator structure.

21. The apparatus according to any of the above examples, wherein: the closed loop power control unit includes:

a semiconductor optical amplifier configured to apply a function of different gains to laser power injected to the semiconductor optical amplifier by changing a driving current thereon;

a photodetector for converting the received optical signal into an optical intensity signal proportional to the optical power;

the comparator is used for comparing the measured light intensity signal with a set value to obtain an error signal; and

and the actuator is used for converting the error signal into a current driving signal, and the current driving signal is used for driving the semiconductor optical amplifier so as to change the gain of the semiconductor optical amplifier in real time.

22. The apparatus according to any of the above examples, wherein: the device further comprises an optoelectronic phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; the signal output by the relative wavelength monitoring unit is compared with a reference source in a multiplicative phase detector. The frequency error is input into a loop filter, then enters an integrator, and the output signal and an initial current driving signal of the laser provided by the control unit are synthesized through an adder and then are input into a current driving unit of the laser. At the moment, the acquisition unit acquires the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit at a fixed frequency, and the data processing unit is configured to determine the splicing position of each signal; intercepting and splicing the direct light intensity detection unit signal and the absolute wavelength monitoring unit signal to obtain a final direct light intensity detection unit signal and a final absolute wavelength monitoring unit signal; and resolving the quasi-distributed physical quantity.

23. The apparatus according to any of the above examples, wherein: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

24. A low cost quasi-distributed physical quantity measuring system for measuring a physical quantity change of an object to be measured by a fiber grating array coupled to the object to be measured, the system comprising:

a data processing unit configured to:

and comparing the central wavelength with the initial central wavelength of each grating to obtain a central wavelength variation, and further obtaining the physical quantity variation on each fiber grating.

25. The system of example 24, wherein:

the data processing unit is configured to:

26. The system of example 24 or 25, wherein:

the data processing unit is further configured to:

27. The system according to any of the above examples, wherein:

28. The system according to any of the above examples, wherein: the device also comprises a storage unit which is used for storing the original sampling data of each unit of each wave band, storing the calculation result of the measured physical quantity and storing the initial center wavelength of each grating.

29. The system according to any of the above examples, wherein: the laser also comprises a current driving unit for providing a driving current signal for the vertical cavity surface reflection laser.

30. The system according to any of the above examples, wherein: the laser diode laser also comprises a temperature control unit for providing a control signal of the working temperature for the laser diode in the vertical cavity surface reflection laser.

31. The system according to any of the above examples, wherein: a closed loop power control unit is also included for adjusting the optical power of the laser output of the vertical facet reflective laser to provide a laser with a stable optical power.

32. The system according to any of the above examples, wherein: the laser output of the vertical cavity surface reflection laser is respectively injected into a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit through a beam splitting coupler, and an acquisition unit acquires respective output signals of the three units.

33. The system according to any of the above examples, wherein: the absolute wavelength monitoring unit obtains an absolute wavelength value output by the laser, and comprises an air chamber for outputting a characteristic signal, and a fiber bragg grating with a known central wavelength or a spectrometer or a wavemeter with a wavelength can be directly obtained.

34. The system according to any of the above examples, wherein: the relative wavelength monitoring unit comprises a fiber interferometer with a fixed optical path difference and a Mach-Zehnder structure or a Michael Sun Jiegou structure, or an FP etalon or a fiber ring resonator structure.

35. The system according to any of the above examples, wherein: the closed loop power control unit includes:

36. The system according to any of the above examples, wherein: the device further comprises an optoelectronic phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; the signal output by the relative wavelength monitoring unit is compared with a reference source in a multiplicative phase detector. The frequency error is input into a loop filter, then enters an integrator, and the output signal and an initial current driving signal of the laser provided by the control unit are synthesized through an adder and then are input into a current driving unit of the laser. At the moment, the acquisition unit acquires the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit at a fixed frequency, and the data processing unit is configured to determine the splicing position of each signal; intercepting and splicing the direct light intensity detection unit signal and the absolute wavelength monitoring unit signal to obtain a final direct light intensity detection unit signal and a final absolute wavelength monitoring unit signal; and resolving the quasi-distributed physical quantity.

37. The system according to any of the above examples, wherein: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

Claims

2. The method according to claim 1, characterized in that: further comprises

3. The method according to claim 1 or 2, characterized in that:

4. A method according to claim 3, characterized in that:

5. The method according to claim 1, characterized in that: the output wavelength of the vertical cavity surface reflection laser increases with the increase of the driving current and with the increase of the working temperature.

6. The method according to claim 1, characterized in that: the physical quantity changes include temperature, or strain, or other physical quantity that may cause the fiber to strain or change in temperature.

7. The method according to claim 2 or 4, characterized in that: the original spectral resolution of the fiber bragg grating array is equal to the equal optical frequency interval value.

8. The method according to claim 1, characterized in that: the relative wavelength monitoring unit signal is used as an external clock of the acquisition card to trigger synchronous acquisition of the direct intensity detection signal; or, synchronously collecting the relative wavelength monitoring unit signal and the direct intensity detection signal by using an internal clock with a fixed sampling rate, estimating the phase of the output signal of the laser according to the relative wavelength monitoring unit signal, and performing nonlinear compensation, such as resampling, on the direct intensity detection signal so that the direct intensity detection signal has equal optical frequency intervals; or a photoelectric phase-locked loop is adopted to realize nonlinear correction.

9. The method according to claim 1, characterized in that: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

a data processing unit configured to:

obtaining the center wavelengths of different fiber gratings of the fiber grating array according to the position of the peak value;

11. The apparatus according to claim 10, wherein:

the data processing unit is configured to:

determining a splicing point of the reference state direct intensity detection signal according to the absolute wavelength information;

12. The apparatus according to claim 11, wherein:

the data processing unit is further configured to:

13. The apparatus according to claim 11 or 12, characterized in that:

14. The apparatus according to claim 10, wherein: the device also comprises a storage unit which is used for storing the original sampling data of each unit of each wave band, storing the calculation result of the measured physical quantity and storing the initial center wavelength of each grating.

15. The apparatus according to claim 10, wherein: the laser also comprises a current driving unit for providing a driving current signal for the vertical cavity surface reflection laser.

16. The apparatus according to claim 10, wherein: the laser diode also comprises a temperature control unit for providing a control signal of the working temperature for the laser diode in the vertical cavity surface reflection laser.

17. The apparatus according to claim 10, wherein: a closed loop power control unit is also included for adjusting the optical power of the laser output of the vertical facet reflective laser to provide a laser with a stable optical power.

18. The apparatus according to claim 10, wherein: the laser output of the vertical cavity surface reflection laser is respectively injected into a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit through a beam splitting coupler, and an acquisition unit acquires respective output signals of the three units.

19. The apparatus according to claim 10, wherein: the absolute wavelength monitoring unit obtains an absolute wavelength value output by the laser, and comprises an air chamber for outputting a characteristic signal, and a fiber bragg grating with a known central wavelength or a spectrometer or a wavemeter with a wavelength can be directly obtained.

20. The apparatus as claimed in claim 11 or 18, wherein: the relative wavelength monitoring unit comprises a fiber optic interferometer with a fixed optical path difference, which is a Mach-Zehnder structure or a Michael Sun Jiegou structure, or an FP etalon or a fiber ring resonator structure.

21. The apparatus as claimed in claim 17, wherein: the closed loop power control unit includes:

22. The apparatus according to claim 10, wherein: the device further comprises an optoelectronic phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; comparing the signal output by the relative wavelength monitoring unit with a reference source in a multiplication phase discriminator; the frequency error is input into a loop filter, then enters an integrator, and the output signal and an initial current driving signal of the laser provided by the control unit are synthesized through an adder and then are input into a current driving unit of the laser; at the moment, the acquisition unit acquires the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit at a fixed frequency, and the data processing unit is configured to determine the splicing position of each signal; intercepting and splicing the direct light intensity detection unit signal and the absolute wavelength monitoring unit signal to obtain a final direct light intensity detection unit signal and a final absolute wavelength monitoring unit signal;

And resolving the quasi-distributed physical quantity.

23. The apparatus according to claim 10, wherein: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.

a data processing unit configured to:

25. The system according to claim 24, wherein:

the data processing unit is configured to:

26. The system according to claim 25, wherein:

the data processing unit is further configured to:

27. The system as claimed in claim 25 or 26, wherein:

28. The system according to claim 24, wherein: the device also comprises a storage unit which is used for storing the original sampling data of each unit of each wave band, storing the calculation result of the measured physical quantity and storing the initial center wavelength of each grating.

29. The system according to claim 24, wherein: the laser also comprises a current driving unit for providing a driving current signal for the vertical cavity surface reflection laser.

30. The system according to claim 24, wherein: the laser diode also comprises a temperature control unit for providing a control signal of the working temperature for the laser diode in the vertical cavity surface reflection laser.

31. The system according to claim 24, wherein: a closed loop power control unit is also included for adjusting the optical power of the laser output of the vertical facet reflective laser to provide a laser with a stable optical power.

32. The system according to claim 24, wherein: the laser output of the vertical cavity surface reflection laser is respectively injected into a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit through a beam splitting coupler, and an acquisition unit acquires respective output signals of the three units.

33. The system according to claim 24, wherein: the absolute wavelength monitoring unit obtains an absolute wavelength value output by the laser, and comprises an air chamber for outputting a characteristic signal, and a fiber bragg grating with a known central wavelength or a spectrometer or a wavemeter with a wavelength can be directly obtained.

34. The system according to claim 25 or 32, wherein: the relative wavelength monitoring unit comprises a fiber optic interferometer with a fixed optical path difference, which is a Mach-Zehnder structure or a Michael Sun Jiegou structure, or an FP etalon or a fiber ring resonator structure.

35. The system according to claim 31, wherein: the closed loop power control unit includes:

36. The system according to claim 24, wherein: the device further comprises an optoelectronic phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; comparing the signal output by the relative wavelength monitoring unit with a reference source in a multiplication phase discriminator; the frequency error is input into a loop filter, then enters an integrator, and the output signal and an initial current driving signal of the laser provided by the control unit are synthesized through an adder and then are input into a current driving unit of the laser; at the moment, the acquisition unit acquires the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit at a fixed frequency, and the data processing unit is configured to determine the splicing position of each signal; intercepting and splicing the direct light intensity detection unit signal and the absolute wavelength monitoring unit signal to obtain a final direct light intensity detection unit signal and a final absolute wavelength monitoring unit signal;

And resolving the quasi-distributed physical quantity.

37. The system according to claim 24, wherein: the current tuning is configured such that a start wavelength in the current tuning at one of the discrete temperature values is less than a stop wavelength in the current tuning at an adjacent and lower temperature value to spectrally overlap the output laser light at the adjacent temperature state.