CN113670352A

CN113670352A - Low-cost quasi-distributed physical quantity measuring method, device and system

Info

Publication number: CN113670352A
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: 2021-11-19
Anticipated expiration: 2040-05-15
Also published as: CN113670352B

Abstract

The application discloses a low-cost quasi-distributed physical quantity measuring method, which measures the physical quantity change of an object to be measured through a fiber grating array coupled to the object to be measured. According to the optical fiber grating array sensor spectrum measuring device, the vertical cavity surface reflection laser is applied to the quasi-distributed physical quantity measuring device based on direct intensity detection, the wavelength tuning of each waveband is realized by applying current modulation to the vertical cavity surface reflection laser at different temperatures, and meanwhile, the laser wavelength monitoring unit is utilized to determine the splicing position of each waveband signal so as to obtain the optical fiber grating array sensor spectrum of the whole waveband. 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, and each fiber grating generally has a strong reflectivity and different central wavelengths. The fiber grating array in this form is a quasi-distributed fiber sensor because the fiber gratings on the sensor are distributed over spatially discrete locations. When in use, the sensor is generally positioned at a measured object, and can sense physical quantities such as temperature or strain of the measured object at different positions. The change in physical quantity causes the center wavelength of the grating to shift. There are many methods for demodulating fiber grating arrays used for sensing, including FP filter method, tunable light source method, broadband light source wavelength division multiplexing method, etc. (1 jongqinghua, research based on FBG sensing signal demodulation technology, 2006, yanshan university 2 courage wave, research on fiber grating sensing characteristics and multi-point multiplexing technology, 2012, harbourne industrial university). The purpose of each method is to obtain the offset of the central wavelength of the grating at different positions on the fiber grating array, and further obtain the information of the measured physical quantity.

A fiber grating array physical quantity measuring method based on direct intensity detection) and a device using a narrow-linewidth tunable laser as a system light source require that the central wavelengths of all gratings on a detected fiber grating array have a certain interval and ensure that the central wavelengths of the gratings with adjacent central wavelengths do not coincide after the external physical quantity change occurs, that is, each grating has an 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 sensor and the bandwidth occupied by each grating. The bandwidth occupied by each grating is directly related to the measured physical quantity range. The above characteristics are similar to the broadband light source wavelength division multiplexing and demodulation method, but the measurement accuracy and spectral resolution of the fiber grating array physical quantity measurement method based on direct intensity detection are higher because the spectrum of the grating under specific light wavelength is acquired point by point. In order to further improve the multiplexing number and the measurement range and resolution in the demodulation device and method, a tunable light source with a wider tuning range and a measurement system with higher spectral resolution are required. The existing fiber grating array physical quantity measuring device and method based on direct intensity detection adopts a tunable light source such as a DBR laser, and for the fiber grating array demodulating device adopting the laser, stepping scanning is generally adopted, for example, 1pm of each stepping triggers one-time acquisition, and the fiber grating array spectrum information of the whole wave band is recovered through the stepping scanning and acquisition of the whole wave band ([1] Torawei, Sujian, Jiangcalthough, Wubo, Shenyong. However, the tuning range of the method is limited (the tuning range of the DBR laser is about 15 nm) and because step scanning is adopted, the original sampling point of the spectrum is also 1pm in step amount, and the resolution of the original spectrum is limited, namely the resolution of the measured physical quantity is limited.

A vertical cavity surface reflection laser (VCSEL) based laser is one type of semiconductor laser, the wavelength of which can be continuously tuned with current or temperature, and the sensitivity of temperature and current tuning is high. While having a larger tuning range compared to distributed feedback lasers (DFB). Taking a vertical cavity surface reflection laser RC32xxx1-PFAmt of the Korean Raycan company as an example, the wavelength is changed by about 0.1nm when the temperature is changed by 1 ℃, and the tuning range is generally lower than 5 nm. On the other hand, wavelength tuning by laser drive current tuning is usually around 0.5nm per mA of wavelength conversion below the nominal safety current (Altabas J A, Izquirdo D, Lazaro J A, et al. Chirp-based direct phase modulation of VCSELs for cost-effective transducers [ J ]. Optics drivers, 2017,42(3): 583-. In addition, the cost price of a VCSEL laser single chip is generally dozens of dollars, and the VCSEL laser single chip is extremely low in cost compared with an external cavity laser, and is suitable for large-scale popularization.

The invention applies a 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 measuring 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, including the steps of: sequentially carrying out current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the starting temperature to the ending temperature to obtain laser output from the starting wavelength to the ending wavelength; wherein the current tuning is configured to: the initial wavelength in current tuning at one of the discrete temperature values is smaller than the termination wavelength in current tuning at an adjacent and lower temperature value at the temperature value so that the output lasers at the adjacent temperature states are partially overlapped on the spectrum; synchronously acquiring a measurement state absolute wavelength monitoring signal containing 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 grating array for the laser output; determining a splicing point of the direct intensity detection signal in the measurement state according to the absolute wavelength information; removing overlapped areas except the splicing point in the measurement state direct intensity detection signal according to the splicing point to form a spliced measurement state direct intensity detection signal; solving the positions of the peak values of different fiber grating spectrums of the fiber 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 measuring state according to the position of the peak value; and comparing the central wavelength with the initial central wavelength of each grating to obtain the central wavelength variation, thereby 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 through a fiber grating array coupled to the object to be measured, including: a vertical cavity surface reflection laser configured to sequentially current-tune the vertical cavity surface reflection laser at a plurality of discrete temperature values from an initial temperature to a termination temperature to obtain a laser output from an initial wavelength to a termination wavelength; a direct intensity detection unit comprising a fiber coupler or a circulator for directing light into the fiber grating array and a photodetector coupled to the circulator, the detection unit being configured to direct the laser output into the fiber grating array and 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; the acquisition unit is 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 splicing point of the direct intensity detection signal according to the absolute wavelength information; removing overlapped areas except the splicing point in the direct intensity detection signal according to the splicing point to form a spliced direct intensity detection signal; solving the positions of the peak values of different fiber grating spectrums of the fiber 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 the central wavelength variation, thereby 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 invention applies the vertical cavity surface reflection laser to a quasi-distributed physical quantity measuring device based on direct intensity detection, realizes the wavelength tuning of each wave band by applying current modulation to the vertical cavity surface reflection laser at different temperatures, and simultaneously determines the splicing position of each wave band signal by using a laser wavelength monitoring unit so as to obtain the spectrum of the fiber grating array sensor of the whole wave band.

Drawings

FIG. 1 is a schematic view of a VCSEL structure according to some embodiments of the present application;

in fig. 1: reference numeral 44 denotes a thermoelectric cooler, 45 denotes a thermistor, 2 denotes a vertical cavity surface reflection laser, and 46 denotes a laser diode.

FIG. 2 is a diagram of a quasi-distributed physical quantity 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 drive current terminal, 25 is a current drive unit, 26 is a temperature control unit, 1 is a control unit, 26 is a temperature control unit, 3 is a first optical fiber coupler, 4 is an optical fiber grating array sensor, 12 is a second optical fiber coupler, 23 is a delay optical 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 rotator mirror, 14 is a second faraday rotator mirror, 40 is a closed-loop power control unit, and 5 is an optical 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 the first fiber grating, 82 is the second fiber grating, 83 is the third fiber grating, and 84 is the fourth fiber grating

FIG. 4 is a graph of a spectrum of a fiber grating array sensor in accordance with some embodiments of the present application.

FIG. 5 is a diagram of a quasi-distributed physical quantity measurement device with an electro-optic phase-locked loop in accordance with 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 denotes a semiconductor optical amplifier, 92 denotes a tenth coupler, 93 denotes a fourth photodetector, and 94 denotes a comparator. Filter 95, operational amplifier 96 and current driver 97.

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

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

in fig. 8, 70 is the sampling point position corresponding to the signal splicing position of MC11, 71 is the sampling point position corresponding to the signal splicing position of MC12, 72 is the signal of MC11, 73 is the signal of MC12, 74 is the signal of MA11, 75 is the signal of MA12, and 77 is the signal of MC 1112.

FIG. 9 illustrates absolute wavelength values corresponding to absorption peaks in a hydrogen cyanide chamber, according to some embodiments of the present disclosure.

Detailed Description

The method and the device for measuring the quasi-distributed physical quantity based on the vertical cavity surface reflection laser, which are provided by the application, use 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 drive current tuning under each temperature gradient, and the output laser of each laser is multiplexed and spliced on the wavelength, which is equivalent to the expansion of the sweep frequency or wavelength tuning range of the light source of the quasi-distributed physical quantity measuring device. Meanwhile, the magnitude of the driving current simultaneously influences the optical power output by the laser, and in order to obtain laser output with stable power, a closed-loop power control unit taking a semiconductor optical amplifier as a core is added behind the laser. 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 wavelength of each vertical cavity surface reflection laser can realize gapless coverage. After the full-wave-band laser output is obtained, the laser is injected into a quasi-distributed physical quantity measuring system, and the high-speed and high-resolution quasi-distributed physical quantity measurement of the sensing optical fiber is realized by observing the relative spectral movement of a reference state and a measurement state. The invention will be described in more detail below.

FIG. 1 is a schematic diagram of a typical VCSEL structure. In general, the vcsel 43 has a thermoelectric cooler 44 for heating or cooling that can be controlled by current and a thermistor 45 whose resistance changes with temperature. For the VCSEL model RC32xxx1-PFAmt from Raycan, Korea, the VCSEL output wavelength is responsive to both temperature and current. The threshold current is 2mA, the maximum working current is 14mA, and the output wavelength change is about 6nm under the condition of 14mA of the current changing from 2 mA. If the laser is manufactured in the same batch, the output center wavelength of the laser at a certain driving current and temperature, such as 7mA and 15 degrees, should be equal or deviate less than 0.5 nm. At a fixed drive current, the temperature value changes from 10 degrees to 50 degrees, with an output wavelength variation of about 5 nm.

The parameters of the vertical cavity surface reflection laser used when the measuring device is introduced later are as follows:

(1) the driving current is 2mA, the output wavelength of the vertical cavity surface reflection laser is 1530nm under the temperature of 10 ℃.

(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 5 nm.

(3) The temperature tuning coefficient is 0.1 nm/degree centigrade, and the temperature gradient is set to 10 degrees and 50 degrees;

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

Fig. 3 is a schematic diagram of a fiber grating array sensor, which is composed of a plurality of fiber gratings with a certain reflectivity, which are engraved at different positions on an optical fiber, and each fiber grating has a different central wavelength, and the central wavelengths do not overlap with each other after a physical quantity change occurs; the fiber sensor 4 shown in fig. 2 has ten fiber gratings with 20% reflectivity, the central wavelengths of the gratings increase from left to right, and the central wavelength interval between adjacent gratings is 2nm and the spatial 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 1538 nm. These are determined during the writing of the fiber grating array (depending on the writing parameters and subject to ambient temperature stress, etc.). When the fiber grating array of sensors 2 is connected to the structure to be measured, the fiber gratings at different positions sense a physical quantity of the structure to be measured, such as temperature or strain or other physical quantity that may cause strain or temperature change in the optical fiber, and the shift of the center wavelength occurs. For example, as shown in fig. 4, the horizontal axis of the spectrum of the fiber grating array is a wavelength or an optical frequency, gratings with different spatial positions are respectively located at different wavelengths, the spectrum of each grating is a peak similar to a parabola, and the position corresponds to a nominal center wavelength or a reference center wavelength, that is, a center wavelength under a known reference strain or temperature, and then if the grating has an effect of a physical quantity change, the center wavelength will shift, and the shift amount is solved to obtain a change amount of the physical quantity, such as temperature or strain, and if the original reference center wavelength is known, an absolute quantity of the physical quantity will also be solved.

Fig. 5 shows a quasi-distributed physical quantity measuring device, in which the thermoelectric cooler 35 of the vcsel 2 is connected to the laser temperature control terminal 28, and applying a control signal to the thermoelectric cooler 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 vcsel 2. The current drive unit 25 is used to provide a drive current signal to the VCSEL for wavelength tuning the VCSEL, which is applied to a 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 the 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 purpose of stable output power; the output laser beam passing through the closed loop power control unit 40 is split into 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 the 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, including determining a splicing position of each band signal to complete signal splicing; for calculating quasi-distributed physical quantities. The data processing unit 31 is a unit such as a CPU, an FPGA, or a DSP of a computer that can perform an operation.

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

The control unit 1 is used for the time sequence 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 is a computer CPU or an embedded FPGA, an ARM and the like.

To achieve gapless tuning and spectral coverage, a first wavelength in the current tuning at one of the discrete temperature values is smaller than a second wavelength in the current tuning at an adjacent and lower one of the discrete temperature values such that the output lasers at adjacent temperature states partially overlap spectrally.

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 is adjusted from a start current of 2mA to a stop current of 12mA, and the first vertical cavity surface reflection laser of the vertical cavity surface reflection laser 2 is driven for wavelength tuning under the first current driving signal CDS1, and the first vertical cavity surface reflection laser is tuned from 1530nm to 1535 nm. At the same time, the control unit 1 controls the acquisition unit 19 to acquire the signal MA11 output from the wavelength monitoring unit 20, the signal MB11 output from the auxiliary interferometer unit 21, and the signal MC11 output from the main interferometer unit 22, and stores the data in the storage unit 31. Next, the control unit 1 applies the second temperature control signal TCS2 to the temperature control unit 26 to control the vertical cavity surface reflection laser 2 to 50 degrees. The control unit 1 controls the current driving unit 25 to output the second current driving signal CDS2, the first current driving signal CDS2 is adjusted from the start current 2mA to the end current 12mA, the vertical cavity surface reflection laser 2 is driven for wavelength tuning under the second current driving signal CDS2, and the vertical cavity surface reflection laser is tuned from 1534nm to 1539 nm. During 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, and the signal MC12 output by the main path interferometer unit 22, and stores data in the storage unit 31.

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

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

The acquired original signals output by the main path interferometer unit 22 are sequentially arranged in the access waveband sequence as follows: MC11(1530-1535nm) MC12(1534-1539 nm).

The wavelength band is defined as the spectral range covered by the wavelength tuning of the VCSEL under current modulation applied by the VCSEL at a certain temperature. The parenthesis above indicates the wavelength range, i.e., band, of the laser output. It can be seen that the collected signal has two wave bands, and adjacent wave bands have wavelength overlap, and the wavelength overlap region is 1 nm. Two bands need to be spliced and combined to form a complete signal without overlapping. The process of determining the splicing positions of the signals of the auxiliary interferometer unit and the main path interferometer unit in adjacent wavelength bands by using the signals of the wavelength monitoring unit is needed.

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

Referring to fig. 8, the absorption peak position of the hydrogen cyanide cell is used as a wavelength monitoring unit to determine the process of splicing the signal with the splice point position. The MC11 (72 in FIG. 7) and MC12 (73 in FIG. 8) signals are used as examples. For hydrogen cyanide cell transmission signals, MA11 (74 in FIG. 8) and MA12 (75 in FIG. 8) are at wavelength positions

R20(1530.30668nm), R19(1530.78615), R18(1531.27537), R17(1531.77430), R16(1532.28298) show absorption peaks, and MC11 has a wavelength position R16(1532.28298)

R15(1532.80139nm), R14(1533.32954) and R13(1533.86745) have absorption peak peaks. Thus can use

R16(1532.28298) as splice wavelength location. Then, the MC11 discards the data following the sampling point (70 in fig. 6) corresponding to the wavelength position, and the MC12 discards the data preceding the sampling point (71 in fig. 8) corresponding to the wavelength position. The newly obtained main path interferometer output signal of the two adjacent segments is the spliced MC1112 signal (77 in fig. 8).

And completing splicing of signals of other adjacent wave bands in the same way, wherein all spliced wave bands are sequentially arranged from small to large according to the wavelength to form spliced relative wavelength monitoring unit signals, and the spliced direct intensity detection signals.

And then carrying out nonlinear correction on the spliced direct intensity detection signal through the spliced relative wavelength monitoring unit signal. Since the tuning of the laser wavelength by current tuning is non-linear, i.e. the output optical frequency or wavelength does not increase linearly with time, if each output signal is sampled at a fixed sampling rate, the sampling points are not equidistant from the optical frequency, which deteriorates the spatial resolution of the sensing or measuring system. The above-mentioned 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 manners: the relative wavelength monitoring unit signal may be acquired by the acquisition unit 19 with a fixed sampling rate in synchronization with other signals, and then the data processing unit may perform a non-linear correction on the direct intensity detection signal or the wavelength monitoring signal. The method comprises the steps of performing Hilbert expansion on signals of the relative wavelength monitoring unit, performing phase deconvolution, then performing equal division on the phase, for example, performing equal division according to pi radian, obtaining corresponding sampling points, then performing resampling on the direct intensity detection signal and the wavelength monitoring signal by using the sampling points, wherein the resampled direct intensity detection signal and the resampled wavelength monitoring signal are signals with nonlinear correction. In addition, the method also has the realization forms of non-uniform Fourier transform, a deskew filter, PNC phase compensation and the like which use a post software processing mode to correct nonlinearity. In addition, the sinusoidal signal output by the relative wavelength monitoring unit can be used as the clock of the acquisition unit 19, and the clock can be used as the acquisition clock of the direct intensity detection signal and the wavelength monitoring signal to acquire the two paths. In addition, the nonlinear correction can also be performed by adopting the photoelectric phase-locked loop technology. In view of the existing prior art, this part will not be described in detail. The relevant literature can see (1. Dingzhuang, several methods for improving OFDR performance proposed and verified, 2013, Tianjin university. 2.Fan, X., Y. Koshikiya and F. Ito, Phase-noise-compensated Optical Frequency dependent Optical signals, 2007.32(22) p.32273. Sweet-wave interference for Distributed measurement Applications 4.Song, J.et. Main, Long-Range High Resolution test and tuning application 4. Sound, J.P. J.8. J., 17(18):15991-15999.). And recording the spliced direct strength detection signal with the corrected nonlinearity as a final direct strength detection signal, and taking the final direct strength detection signal as the input quantity of the quasi-distributed parameter demodulation program.

When the nonlinear correction is performed by the above-described photoelectric phase-locked loop technique (documents 6 and 7), the measuring apparatus has a structure as shown in fig. 3. The phase-locked loop unit comprises a reference source 81, a multiplication phase discriminator 82, a loop filter 83, an integrator 84 and an adder 85; the auxiliary interferometer output signal, which contains the laser tuning nonlinearity, is compared with the signal set by reference source 81 (typically the sinusoidal signal of the signal generator) in a multiplying phase detector 82. The frequency error signal is input to the loop filter 83 and then to 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 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 32 is configured to determine the splicing position of each path of 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; calculating quasi-distributed physical quantity

Fig. 6 shows a semiconductor optical amplifier and a closed loop power stabilizing unit thereof, which includes: a semiconductor optical amplifier 91 which can apply different gains to the laser power injected into the semiconductor optical amplifier by changing the drive current thereon; a photodetector 93 for converting the optical signal into an electrical signal proportional to the optical power; a comparator 94 for comparing the measured light intensity signal 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 the closed-loop control loop, and the remaining 90% is injected as output light into the rear measurement optical path as measurement device signal light. It can be seen that the closed loop power control unit 40 stabilizes the input light at a certain power setting. A related introduction to semiconductor optical amplifiers can be found in [1]]https://www.thorlabs.de/newgrouppage9.cfmobjectgroup_id＝3901

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

Since 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 collected in the first external state and stored in the memory of the computer, and the second external state, which is described below, represents a measurement state, with respect to the first reference state, the fiber grating array sensor may have the effect of a physical quantity change. The measurement process of the quasi-distributed physical quantity based on the vertical cavity surface reflection laser is as follows:

step 1, obtaining signals of each wave band wavelength monitoring unit in a reference state in an external first state, wherein the signals of each wave band wavelength monitoring unit in the reference state are directly intensity detection signals relative to the signals of the wavelength monitoring unit;

step 2, obtaining signals of the wavelength monitoring unit of each wave band in the measurement state in a second external state, wherein the signals of the wavelength monitoring unit of each wave band in the measurement state are opposite to the signals of the wavelength monitoring unit, and the signals of direct intensity detection of each wave band in the measurement state are obtained;

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

and 5, resolving the quasi-distributed physical quantity: calculating the positions of the peak values of different fiber grating spectrums of the fiber grating array according to the final reference state direct intensity detection signal and the final measurement state direct intensity detection signal; 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 central wavelengths of the reference state grating spectrum and the measurement state grating spectrum corresponds to the physical quantity change on the grating; .

The physical quantity to be measured may be strain, or temperature, or other physical quantity that may cause a strain or temperature change in the optical fiber. These physical quantities and spectral offsets typically differ by a factor (sensitivity) or, for greater accuracy, by a polynomial function, or may be scaled experimentally to obtain a coefficient value.

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

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

In this application, an absolute wavelength monitoring signal refers to a signal provided by an absolute wavelength monitoring unit or units having the same or substantially the same function; relative wavelength monitoring signal refers to a signal provided by a relative wavelength monitoring unit or units 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, a fiber grating with known central wavelength or a spectrometer or a wavelength meter capable of directly obtaining the wavelength. The above description is only a preferred embodiment of the present invention, and these embodiments are based on different implementations of the present invention, and the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. The invention may also be implemented by the following disclosed examples:

1. a low-cost quasi-distributed physical quantity measuring method measures physical quantity change of an object to be measured through a fiber grating array coupled to the object to be measured, and is characterized by comprising the following steps of:

sequentially carrying out current tuning on the vertical cavity surface reflection laser at a plurality of discrete temperature values from the starting temperature to the ending temperature to obtain laser output from the starting wavelength to the ending wavelength; wherein the current tuning is configured to: the initial wavelength in current tuning at one of the discrete temperature values is smaller than the termination wavelength in current tuning at an adjacent and lower temperature value at the temperature value so that the output lasers at the adjacent temperature states are partially overlapped on the spectrum;

synchronously acquiring a measurement state absolute wavelength monitoring signal containing 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 grating array for the laser output;

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

removing overlapped areas except the splicing point in the measurement state direct intensity detection signal according to the splicing point to form a spliced measurement state direct intensity detection signal;

solving the positions of the peak values of different fiber grating spectrums of the fiber 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 measuring state according to the position of the peak value;

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

2. The method of example 1, wherein: further comprises

Providing relative wavelength monitoring signals of the vertical cavity surface reflection laser;

in the measurement state, synchronously acquiring a measurement state absolute wavelength monitoring signal containing 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 grating array to the laser output;

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

determining equal optical frequency interval sampling points of the direct intensity detection signals in the measurement state 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 a resampled spliced measurement state direct intensity detection signal which is used for solving the positions of the peak values of different fiber grating spectrums of the fiber grating array.

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

the initial central wavelengths of different fiber gratings on the fiber grating array are stored in advance or obtained by the following method:

synchronously acquiring 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 acquiring a reference state direct intensity detection signal of the fiber grating array for the laser output;

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

removing overlapped areas except the splicing point in the reference state direct intensity detection signal according to the splicing point to form a spliced reference state direct intensity detection signal;

solving the positions of the peak values of different fiber grating spectrums of the fiber grating array based on the spliced reference state direct intensity detection signal;

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

4. The method of example 3, wherein:

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

5. The method of example 1, wherein: the output wavelength of the VCSEL increases with increasing drive current and with increasing operating temperature.

6. The method of any of the above examples, wherein: the change in physical quantity may include temperature, or strain, or other physical quantity that may cause a strain or temperature change in the optical fiber.

7. The method of any of the above examples, wherein: the original spectrum resolution of the fiber grating array is equal to the equal optical frequency interval value.

8. The method of any of the above examples, wherein: the nonlinear correction comprises: using the relative wavelength monitoring unit signal as an external clock of the acquisition card to trigger the synchronous acquisition of the direct intensity detection signal; or synchronously acquiring a relative wavelength monitoring unit signal and a 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 an equal optical frequency interval; or the nonlinear correction is realized by adopting an electro-optic phase-locked loop.

9. The method of any of the above examples, wherein: the current tuning is configured such that a starting wavelength in the current tuning at one of the discrete temperature values is smaller than an ending wavelength in the current tuning at an adjacent and lower temperature value at that temperature value to cause the output lasers at adjacent temperature states to partially overlap spectrally.

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, the apparatus comprising:

a vertical cavity surface reflection laser configured to sequentially current-tune the vertical cavity surface reflection laser at a plurality of discrete temperature values from an initial temperature to a termination temperature to obtain a laser output from an initial wavelength to a termination wavelength;

a direct intensity detection unit comprising a fiber coupler or a circulator for directing light into the fiber grating array and a photodetector coupled to the circulator, the detection unit being configured to direct the laser output into the fiber grating array and 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;

the acquisition unit is 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 splicing point of the direct intensity detection signal according to the absolute wavelength information;

removing overlapped areas except the splicing point in the direct intensity detection signal according to the splicing point to form a spliced direct intensity detection signal;

solving the positions of the peak values of different fiber grating spectrums of the fiber 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 the central wavelength variation, thereby obtaining the physical quantity variation on each fiber grating.

11. The apparatus of example 10, wherein:

further comprising 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 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 grating array for the laser output;

the data processing unit is configured to:

obtaining the central 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 central wavelength of the measurement state with the central wavelength of the respective reference state of the grating to obtain the central wavelength variation, thereby obtaining the physical quantity variation on each fiber grating.

12. The apparatus according to example 10 or 11, characterized in that:

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 not including the physical quantity change, and a reference state direct intensity detection signal of the fiber grating array for the laser output;

the data processing unit is further configured to:

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

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

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

14. The apparatus of 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 physical quantity calculation result to be measured and storing the initial central wavelength of each grating.

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

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

17. The apparatus of any of the above examples, wherein: the laser also includes a closed-loop power control unit for adjusting the optical power of the laser output of the VCSEL to provide laser light having a stable optical power.

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

19. The apparatus of 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, a fiber grating with known central wavelength or a spectrometer or a wavelength meter capable of directly obtaining the wavelength.

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

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

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

a photodetector for converting a received optical signal into a light 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 of any of the above examples, wherein: still include the photoelectricity phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; and comparing the signal output by the relative wavelength monitoring unit with the reference source in the multiplication phase discriminator. The frequency error is input into a loop filter and then enters an integrator, and an output signal is synthesized with an initial current driving signal of the laser provided by a control unit through an adder and then 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 path of 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; the quasi-distributed physical quantities are resolved.

23. The apparatus of any of the above examples, wherein: the current tuning is configured such that a starting wavelength in the current tuning at one of the discrete temperature values is smaller than an ending wavelength in the current tuning at an adjacent and lower temperature value at that temperature value to cause the output lasers at adjacent temperature states to partially overlap spectrally.

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, the system comprising:

a data processing unit configured to:

and comparing the central wavelength with the initial central wavelength of each grating to obtain the central wavelength variation, thereby 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 according to example 24 or 25, characterized in that:

the data processing unit is further configured to:

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

28. The system of 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 physical quantity calculation result to be measured and storing the initial central wavelength of each grating.

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

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

31. The system of any of the above examples, wherein: the laser also includes a closed-loop power control unit for adjusting the optical power of the laser output of the VCSEL to provide laser light having a stable optical power.

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

33. The system of 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, a fiber grating with known central wavelength or a spectrometer or a wavelength meter capable of directly obtaining the wavelength.

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

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

36. The system of any of the above examples, wherein: still include the photoelectricity phase-locked loop unit: the device comprises a reference source, a multiplication phase discriminator, a loop filter, an integrator and an adder; and comparing the signal output by the relative wavelength monitoring unit with the reference source in the multiplication phase discriminator. The frequency error is input into a loop filter and then enters an integrator, and an output signal is synthesized with an initial current driving signal of the laser provided by a control unit through an adder and then 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 path of 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; the quasi-distributed physical quantities are resolved.

37. The system of any of the above examples, wherein: the current tuning is configured such that a starting wavelength in the current tuning at one of the discrete temperature values is smaller than an ending wavelength in the current tuning at an adjacent and lower temperature value at that temperature value to cause the output lasers at adjacent temperature states to partially overlap spectrally.

Claims

2. The method of claim 1, wherein: further comprises

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

4. The method of claim 3, wherein:

5. 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, the apparatus comprising:

a data processing unit configured to:

6. The apparatus of claim 5, wherein:

the data processing unit is configured to:

7. The apparatus according to claim 5 or 6, characterized in that:

the data processing unit is further configured to:

8. The apparatus of any preceding claim, wherein:

9. The apparatus of any preceding claim, 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 physical quantity calculation result to be measured and storing the initial central wavelength of each grating.

10. 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, the system comprising:

a data processing unit configured to: