CN118836911A - Physical quantity measuring method and device for optical fiber grating array spectrum detection - Google Patents
Physical quantity measuring method and device for optical fiber grating array spectrum detection Download PDFInfo
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- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35383—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using multiple sensor devices using multiplexing techniques
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Abstract
本发明公开了一种光纤光栅阵列光谱探测的物理量测量方法及装置，属于光纤传感相关技术领域，基于外腔激光器与直接强度探测实现光纤光栅阵列的物理量测量，其采用一种等光频间隔采样的方式获取光栅阵列的光谱，进而实现光纤光栅阵列的波长解调与准分布式物理量测量，获得了大范围访问带宽，使得可以复用更多数量的光纤光栅，提高了单个光纤光栅可探测到的物理量测量的量程；同时以更密的等光频采样点恢复了光纤光栅阵列传感器的反射光谱，提高了物理量的分辨力与解调精度。
The present invention discloses a physical quantity measurement method and device for optical fiber grating array spectrum detection, which belongs to the technical field related to optical fiber sensing. The physical quantity measurement of the optical fiber grating array is realized based on an external cavity laser and direct intensity detection. The spectrum of the grating array is acquired by an equal optical frequency interval sampling method, so as to realize wavelength demodulation and quasi-distributed physical quantity measurement of the optical fiber grating array, obtain a wide range of access bandwidth, make it possible to multiplex a larger number of optical fiber gratings, and improve the range of physical quantity measurement that can be detected by a single optical fiber grating; at the same time, the reflection spectrum of the optical fiber grating array sensor is restored with denser equal optical frequency sampling points, and the resolution and demodulation accuracy of the physical quantity are improved.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a physical quantity measuring method and device for optical fiber grating array spectrum detection.
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. (Wang Qinghua, research based on FBG sensing signal demodulation technology, 2006, yan Shanda), research on brave wave generation, fiber grating sensing characteristics and multipoint multiplexing technology, 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.
In the method and the device for measuring the physical quantity of the fiber bragg grating array based on direct intensity detection, a narrow linewidth tunable laser is used as a system light source, the central wavelengths of all gratings on the fiber bragg grating array to be measured are required to have a certain interval, and the fact that the central wavelengths of the gratings with adjacent central wavelengths are not coincident after the external physical quantity change is acted is ensured, 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, and for the fiber grating array demodulation device adopting the laser, the device generally adopts step scanning, such as triggering one acquisition per step of 1pm, and the spectral information of the fiber grating array in the whole wave band is recovered through step scanning and acquisition in the whole wave band. 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.
Disclosure of Invention
The invention provides a physical quantity measuring method and a device for optical fiber grating array spectrum detection, which are characterized in that an external cavity laser is used as a light source of an optical fiber grating array demodulation device, and an equal optical frequency interval sampling mode is adopted to acquire the spectrum of a grating array, so that the wavelength demodulation and quasi-distributed physical quantity measurement of the optical fiber grating array are realized.
The specific technical scheme provided by the invention is as follows:
in a first aspect, the present invention provides a method for measuring physical quantity of spectral detection of an optical fiber grating array, including:
Starting wavelength tuning of an external cavity type tuning laser to enable the wavelength to be continuously scanned from the initial wavelength 1520nm to the final wavelength 1570nm, and respectively connecting the split laser to a fiber grating array sensor, an absolute wavelength monitoring unit and a relative wavelength monitoring unit;
Synchronously acquiring an output signal of the direct intensity detection unit, an output signal of the absolute wavelength monitoring unit and an output signal of the relative wavelength monitoring unit at a fixed sampling rate of 100 MSa/s;
The method comprises the steps of selecting an output signal of an absolute wavelength monitoring unit as a starting wavelength position, intercepting and retaining the subsequent data at the starting wavelength position by using an output signal of a direct intensity detection unit and an output signal of a relative wavelength monitoring unit which are synchronously acquired, so as to obtain an output signal of the direct intensity detection unit and an output signal of the relative wavelength monitoring unit with known wavelengths;
Calculating the number of rising edge zero crossing points of sinusoidal signals of output signals of the relative wavelength monitoring units corresponding to the absorption peaks R26 and the absorption peaks P27 of the hydrogen cyanide molecular air chamber, and dividing the wavelength difference between the two absorption peaks by the number of the rising edge zero crossing points to obtain an optical frequency interval value corresponding to each period of the relative wavelength monitoring units in the range;
resampling the output signal of the direct intensity detection unit by utilizing the rising edge zero crossing point position of each sinusoidal signal to obtain a final direct intensity detection unit signal;
And (3) obtaining the positions of the peaks of the spectrums of the different fiber gratings of the fiber grating array to obtain the center wavelengths of the different fiber gratings of the fiber grating array in the physical state, and further obtaining the physical quantity change of each fiber grating.
Optionally, resampling the output signal of the direct intensity detection unit by using the rising edge zero crossing point position of each sinusoidal signal to obtain a final direct intensity detection unit signal includes:
And determining equal-light-frequency interval sampling points according to the rising edge zero crossing points of each sinusoidal signal, finding out the position serial numbers in the direct intensity detection unit signals and the data of the same positions of the equal-light-frequency interval sampling points according to the equal-light-frequency interval sampling points, and rearranging the data in sequence to form a group of new data to obtain the final direct intensity detection unit signals.
In a second aspect, the present invention further provides a physical quantity measurement method for spectral detection of an optical fiber grating array, including:
starting wavelength tuning of the external cavity tuning laser to scan the wavelength from the initial wavelength 1520nm to the final wavelength 1570nm, and respectively connecting the split laser to a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit;
The sine signal output by the relative wavelength monitoring unit is used as an external clock to trigger and collect the output signal of the direct light intensity detection unit and the output signal of the absolute wavelength monitoring unit;
Calculating the number of sampling points of the output signal of the direct intensity detection unit corresponding to the absorption peak R26 and the absorption peak P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of sampling points to obtain the optical frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit in the range;
Selecting an output signal of an absolute wavelength monitoring unit as a starting wavelength position, intercepting the acquired output signal of a direct light intensity detection unit at the starting wavelength position, and reserving the subsequent data to obtain a spectrum of a final fiber bragg grating array sensor;
the spectrum of the fiber bragg grating array sensor is a plurality of peaks at different wavelength positions, each peak corresponds to the central wavelength of the fiber bragg grating at a specific space position, the positions of the peaks of the fiber bragg grating array spectra of different fiber bragg gratings are obtained, the central wavelengths of the fiber bragg grating array different fiber bragg gratings in the physical state are obtained, and then the physical quantity change of each fiber bragg grating is obtained.
Optionally, the external cavity tuning laser is provided with a Littrow or Littman structure.
Optionally, the relative wavelength monitoring unit includes at least one of a mach-zehnder structure with a fixed optical path difference, a michael Sun Jiegou fiber interferometer, and a fiber ring resonator structure.
In a third aspect, the present invention provides a physical quantity measuring device for spectral detection of an optical fiber grating array, comprising:
The scanning unit is used for starting wavelength tuning of the external cavity type tuning laser to enable the wavelength to be continuously scanned from the initial wavelength 1520nm to the final wavelength 1570nm, and the laser is respectively connected to the fiber grating array sensor, the absolute wavelength monitoring unit and the relative wavelength monitoring unit after being split;
The acquisition unit is used for synchronously acquiring the output signal of the direct intensity detection unit, the output signal of the absolute wavelength monitoring unit and the output signal of the relative wavelength monitoring unit at a fixed sampling rate of 100 MSa/s;
the intercepting unit is used for selecting the output signal of the absolute wavelength monitoring unit as a starting wavelength position, intercepting the output signal of the synchronously acquired direct intensity detection unit and the output signal of the relative wavelength monitoring unit at the starting wavelength position and reserving the subsequent data to obtain the output signal of the direct intensity detection unit with known wavelength and the output signal of the relative wavelength monitoring unit;
The calculation unit is used for calculating the number of rising edge zero crossing points of the sinusoidal signals of the output signals of the relative wavelength monitoring units corresponding to the absorption peaks R26 and the absorption peaks P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of the rising edge zero crossing points to obtain an optical frequency interval value corresponding to each period of the relative wavelength monitoring units in the range;
the resampling unit is used for resampling the output signal of the direct intensity detection unit by utilizing the rising edge zero crossing point position of each sinusoidal signal to obtain a final direct intensity detection unit signal;
The processing unit is used for obtaining the positions of the peaks of the spectrums of the different fiber gratings of the fiber grating array to obtain the central wavelengths of the different fiber gratings of the fiber grating array in the physical state, and further obtaining the physical quantity change of each fiber grating.
Optionally, the resampling unit is specifically configured to:
And determining equal-light-frequency interval sampling points according to the rising edge zero crossing points of each sinusoidal signal, finding out the position serial numbers in the direct intensity detection unit signals and the data of the same positions of the equal-light-frequency interval sampling points according to the equal-light-frequency interval sampling points, and rearranging the data in sequence to form a group of new data to obtain the final direct intensity detection unit signals.
In a fourth aspect, the present invention provides a physical quantity measuring device for spectral detection of an optical fiber grating array, comprising:
The scanning unit is used for starting wavelength tuning of the external cavity type tuning laser to scan the wavelength from the initial wavelength 1520nm to the final wavelength 1570nm, and the laser is respectively connected to the direct intensity detection unit, the absolute wavelength monitoring unit and the relative wavelength monitoring unit after being split;
the acquisition unit is used for triggering and acquiring the output signal of the direct light intensity detection unit and the output signal of the absolute wavelength monitoring unit by taking the sine signal output by the relative wavelength monitoring unit as an external clock;
The calculation unit is used for calculating the number of sampling points of the output signal of the direct intensity detection unit corresponding to the absorption peak R26 and the absorption peak P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of sampling points to obtain the optical frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit in the range;
The intercepting unit is used for selecting the output signal of the absolute wavelength monitoring unit as a starting wavelength position, intercepting the acquired output signal of the direct light intensity detecting unit at the starting wavelength position, and reserving the subsequent data to obtain the spectrum of the final fiber bragg grating array sensor;
The processing unit is used for obtaining the positions of the peaks of the optical fiber grating spectrums of the optical fiber grating array sensor, obtaining the central wavelengths of the optical fiber gratings of the optical fiber grating array under the physical state, and further obtaining the physical quantity change of each optical fiber grating.
Optionally, the external cavity tuning laser is provided with a Littrow or Littman structure.
Optionally, the relative wavelength monitoring unit includes at least one of a mach-zehnder structure with a fixed optical path difference, a michael Sun Jiegou fiber interferometer, and a fiber ring resonator structure.
The beneficial effects of the invention are as follows:
The embodiment of the invention provides a physical quantity measuring method and a physical quantity measuring device for optical fiber grating array spectrum detection, which are used for realizing physical quantity measurement of the optical fiber grating array based on an external cavity laser and direct intensity detection, acquiring the spectrum of the optical fiber grating array in an equal optical frequency interval sampling mode, further realizing wavelength demodulation and quasi-distributed physical quantity measurement of the optical fiber grating array, obtaining a large-range access bandwidth, multiplexing a plurality of optical fiber gratings and improving the measuring range of the physical quantity measurement which can be detected by a single optical fiber grating; and meanwhile, the reflection spectrum of the fiber bragg grating array sensor is recovered by using denser equal-optical-frequency sampling points, and the resolution and demodulation precision of physical quantity are improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a fiber grating array physical quantity sensing device based on continuous scanning of an external cavity laser according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a fiber grating array according to an embodiment of the present invention;
FIG. 3 is a schematic representation of a hydrogen cyanide chamber transmission spectrum signal according to an embodiment of the invention;
FIG. 4 is a schematic diagram of an FP etalon output signal according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a transmission spectrum signal of an optical fiber ring resonator according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The following describes a physical quantity measurement method and device for optical fiber grating array spectrum detection in detail with reference to fig. 1 to 5. In fig. 1, 11 is an external cavity type tuning laser, 12 is a first optical fiber coupler, 13 is a second optical fiber coupler, 14 is a delay optical fiber, 15 is a first faraday rotation mirror, 16 is a second faraday rotation mirror, 17 is a second photoelectric detector, 19 is an acquisition unit, 20 is a storage unit, 9 is a data processing unit, 2 is an optical fiber circulator, 18 is a third photoelectric detector, 1 is a relative wavelength monitoring unit, 4 is an optical fiber grating array sensor, 5 is a measured structure, 8 is a control unit, 3 is an absolute wavelength monitoring unit, 6 is a hydrogen cyanide molecular air chamber, 7 is a first photoelectric detector, and 10 is a direct intensity detection unit. In fig. 2, 31 is a first fiber grating, 32 is a second fiber grating, 33 is a third fiber grating, 34 is a seventh fiber grating, and 35 is an eighth fiber grating.
The external cavity type tuning laser adopted by the embodiment of the invention has a Littrow or Littman structure, can continuously tune the wavelength in a wide range, can cover the wavelength range required by the fiber grating array, and outputs narrow linewidth laser. Continuously tunable refers to continuous variation of wavelength without mode hops, unlike step-wise wavelength tuning. The light source is used as a light source of the fiber grating array distributed physical quantity measuring device. And recording the reflection spectrum information of the fiber bragg grating array during laser wavelength scanning to obtain the reflection spectrum information of each fiber bragg grating in the whole tuning range, further obtaining the center wavelength of the fiber bragg grating at each spatial position of the fiber bragg grating array, and calculating the measured physical quantity according to the wavelength movement amount of the center wavelength. Because the time-sampled signal is recorded in the time domain, and the tunable laser has some nonlinearity in the wavelength tuning process (nonlinear sources include nonlinearity in mechanical tuning and a nonlinear relationship between wavelength and optical frequency), that is, the optical frequency does not increase linearly with time, the spectral signal corresponding to the sampling point is not an equal optical frequency interval if an equal time interval is used. In addition, consideration needs to be given to how to increase the sampling point density so that the spectrum sampling interval is smaller to improve the spectrum resolution of the demodulation system, which is important for improving the resolution of the final measured physical quantity.
Referring to the schematic diagram of the fiber grating array shown in fig. 2, the fiber grating array is composed of a plurality of fiber gratings with certain reflectivity which are engraved at different positions on the optical fiber, and the fiber gratings respectively have different center wavelengths and do not overlap with each other after the physical quantity change; the fiber sensor 36 shown in fig. 2 has ten fiber gratings each having a reflectivity of 20%, increasing the center wavelength of the grating from left to right, and the center wavelength spacing between adjacent gratings is 5nm, and the spatial spacing is 1 meter. The center wavelength of the first fiber grating 31 is 1520nm, the center wavelength of the second fiber grating 32 is 1525nm, the center wavelength of the third fiber grating 33 is 1530nm, and so on, the center wavelength of the seventh fiber grating 34 is 1560nm, and the center wavelength of the eighth fiber grating 35 is 1565nm. 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 fiber grating array sensor 4 is connected with the measured structure 5, the fiber gratings at different positions sense the physical quantities of the measured structure, such as temperature or strain, and when the physical quantities change, the change of the physical quantities can be calculated by detecting the movement of the center wavelength of the fiber grating in the state, i.e. the measured state, relative to the initial state, i.e. the reference state, i.e. the center wavelength without the physical quantity change.
According to the physical quantity measuring method and device for optical fiber grating array spectrum detection, the spectrum of the grating array is acquired in the mode of equal optical frequency interval sampling, so that the wavelength demodulation and quasi-distributed physical quantity measurement of the optical fiber grating array are realized, a large-range access bandwidth is obtained, a plurality of optical fiber gratings can be multiplexed, and the measuring range of the physical quantity detectable by a single optical fiber grating is improved; and meanwhile, the reflection spectrum of the fiber bragg grating array sensor is recovered by using denser equal-optical-frequency sampling points, so that spectrum demodulation errors caused by tuning nonlinearity of a tuning laser can be suppressed to a certain extent, the measurement precision and the measurement resolution are improved, and the resolution and the demodulation precision of physical quantities are improved. The light frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit in the range is obtained by calculating the number of sampling points of the output signal of the direct intensity detection unit corresponding to the absorption peak R26 and the absorption peak P27 of the hydrogen cyanide molecular gas chamber and dividing the wavelength difference value between the two absorption peaks by the number of sampling points, and accordingly the accuracy of the light frequency is ensured.
Fig. 1 is a fiber bragg grating array physical measurement device based on continuous scanning of an external cavity laser, which comprises an external cavity tuning laser 11 and a fiber bragg grating array sensor 4 with a structure shown in fig. 2, and also comprises the following units:
The relative wavelength monitoring unit 1 is used for monitoring the relative change of the output optical frequency or wavelength of the external cavity type tunable laser 11. The relative wavelength monitor unit 1 can generate a periodic signal at certain optical frequency values, and the structure capable of realizing the function comprises an optical fiber interferometer with a fixed optical path difference and a Mach-Zehnder structure or a Michael Sun Jiegou, namely a structure consisting of devices with the reference numbers of 13-17 shown in fig. 1. The output signal of the relative wavelength monitoring unit 1 is a sinusoidal signal, and one sinusoidal signal theoretically corresponds to a wavelength interval (the central wavelength of the swept laser, n is the refractive index in the optical fiber, and L is the optical path difference of the interferometer), so that it can be seen that the optical frequency interval depends on the optical path difference of two arms of the interferometer, that is, the length of the delay optical fiber 14. However, since the tunable laser tuning has nonlinear effects, the period of the sinusoidal signal varies if the sinusoidal signal is sampled with a clock having a fixed sampling rate. Based on this, there are two sampling modes: one is to collect the output signal of the direct intensity detection unit 10, the output signal of the absolute wavelength monitoring unit 3 and the output signal of the relative wavelength monitoring unit 1 simultaneously at a fixed sampling rate. The other is to directly use the signal output by the relative wavelength monitoring unit 1 as the external clock of the acquisition unit, and the periodic signal triggers the acquisition of the output signal of the direct intensity detection unit 22 and the output signal of the absolute wavelength monitoring unit 3.
The sine signal output by the wavelength monitoring unit 3 directly corresponds to the phase of the output signal of the light source, so that the interferometer can track the wavelength or the phase of the laser output by the tuning laser, and the phase change condition of the optical signal can be obtained after the sine signal Hilbert is unfolded, and the output signal can also be used as the signal of the wavelength tracking. Then, according to the spread signal, each interval of 2pi or pi phase can be set as an equal optical frequency interval position, and the position is utilized to resample the direct intensity detection unit signal, so as to obtain the direct intensity detection unit signal with a known optical frequency interval value. In addition, the rising edge zero crossing point can also be directly used as the equal optical frequency interval position, and the position can be used for resampling the direct intensity detection unit signal.
The relative wavelength monitoring unit 1 may also be an FP etalon or an optical fiber ring resonator, fig. 4 is a signal of a tuned optical signal passing through the FP etalon, and for an FP etalon with high coherence, its output signal has a sharp comb-like periodic signal, and its optical frequency interval is the free spectral range of the FP etalon, and is related to its cavity length and refractive index. Fig. 5 is a typical fiber ring resonator output signal having a signal similar to the FP etalon output, with a sharp peak signal, and with a free spectral range (FSR on fig. 5) related to the internal fiber length. For the relative wavelength monitoring units under the two configurations, under the condition of adopting a fixed sampling rate sampling mode, the peak position of the signal is used as an equal optical frequency interval position, and the position is utilized to resample the direct intensity detection unit signal, so as to obtain the direct intensity detection unit signal with a known optical frequency interval value. When this signal is used as an external clock to trigger the acquisition of the output signal of the direct intensity detection unit 22, the output signal of the absolute wavelength monitoring unit 3, it should be that the acquisition unit 19 triggers the acquisition once every time a rising edge signal is received.
The absolute wavelength monitoring unit 3 is used for monitoring the wavelength output value of the external cavity type tunable laser 11, calibrating the wavelength value of the relative wavelength monitoring unit and determining the equidistant optical frequency value. The absolute wavelength monitoring unit 3 can obtain the absolute wavelength value output by the laser, and the absolute wavelength value comprises a gas chamber for outputting a characteristic signal, such as a hydrogen cyanide molecular gas chamber or an acetylene molecular gas chamber. The implementation shown in fig. 1 is a hydrogen cyanide molecular gas cell 6 that can output a characteristic signal, whose absorption spectrum is shown in fig. 3 as being absorbed at a specific traceable wavelength location. The different absorption peaks correspond to different wavelength values, the smallest absorption peak is R26 (1527.63342 nm) and the largest absorption peak is P27 (1564.44519 nm). The light passing through the hydrogen cyanide molecular gas cell 6 is detected by the first photodetector 7, collected by one collection channel of the collection unit 19, and transferred to the storage unit 20. The acquisition unit 19 may be a multichannel oscilloscope or an acquisition card.
The absolute wavelength monitoring unit 3 may also be a device for directly measuring the wavelength, such as a spectrometer or a wavemeter, where the reading is the laser wavelength. In general, the two devices have a larger wavelength measurement range than the gas molecular air chamber, and meanwhile, unlike the gas molecular air chamber, the wavelength value of the laser to be measured can be given at any position in the range instead of the wavelength value of the traceable source corresponding to the absorption peak position. Although the periodic signal output by the relative wavelength monitoring unit 1 can theoretically have a numerical relation with the optical frequency, in practice, due to an error existing in the arm length difference (i.e., the length of the delay fiber 14 in fig. 1) and nonlinearity existing in the laser tuning, the numerical relation is not accurate, so that the absolute wavelength monitoring unit 3 needs to be used to calibrate the optical frequency interval value corresponding to the periodic signal output by the relative wavelength monitoring unit 1.
The acquisition unit 19 is configured to acquire a signal output by the absolute wavelength monitoring unit 3 or a reading thereof, acquire an output signal of the relative wavelength monitoring unit 1, and acquire an output signal of the direct intensity detection unit 10. On the acquisition clock source, the on-chip clock can be selected to sample at a fixed sampling rate, and the external signal source can trigger acquisition every cycle or every rising edge signal. And the control unit 8 is used for timing control of the external cavity type tunable laser 11 and the acquisition unit 19. May be an FPGA or a computer.
The embodiment of the invention provides a physical quantity measuring method of fiber bragg grating array spectrum detection based on a fiber bragg grating array physical quantity measuring device based on continuous scanning of an external cavity laser shown in fig. 1, which comprises the following steps:
Step 101: starting wavelength tuning of an external cavity type tuning laser to enable the wavelength to be continuously scanned from the initial wavelength 1520nm to the final wavelength 1570nm, and respectively connecting the split laser to a fiber grating array sensor, an absolute wavelength monitoring unit and a relative wavelength monitoring unit;
step 102: synchronously acquiring an output signal of the direct intensity detection unit, an output signal of the absolute wavelength monitoring unit and an output signal of the relative wavelength monitoring unit at a fixed sampling rate of 100 MSa/s;
Step 103: the method comprises the steps of selecting an output signal of an absolute wavelength monitoring unit as a starting wavelength position, intercepting and retaining the subsequent data at the starting wavelength position by using an output signal of a direct intensity detection unit and an output signal of a relative wavelength monitoring unit which are synchronously acquired, so as to obtain an output signal of the direct intensity detection unit and an output signal of the relative wavelength monitoring unit with known wavelengths;
Specifically, the output signal of the absolute wavelength monitoring unit 3, that is, the absorption peak R26 of the hydrogen cyanide molecular gas chamber 6 is selected as the initial wavelength position, and the absolute wavelength of the position is 1527.63342nm. The output signal of the direct intensity detection unit 22 and the output signal of the relative wavelength monitoring unit 1 which are synchronously collected are intercepted at the position of the sampling point, and the subsequent data are reserved, so that the output signal of the direct intensity detection unit 22 and the output signal of the relative wavelength monitoring unit 1 with known wavelengths are obtained.
Step 104: calculating the number of rising edge zero crossing points of sinusoidal signals of output signals of the relative wavelength monitoring units corresponding to the absorption peaks R26 and the absorption peaks P27 of the hydrogen cyanide molecular air chamber, and dividing the wavelength difference between the two absorption peaks by the number of the rising edge zero crossing points to obtain an optical frequency interval value corresponding to each period of the relative wavelength monitoring units in the range;
Specifically, the number of rising edge zero crossing points of the sinusoidal signal of the output signal of the relative wavelength monitoring unit 1 corresponding to the absorption peak R26 (1527.63342 nm) and the absorption peak P27 (1564.44519 nm) of the hydrogen cyanide molecular gas chamber 6 is calculated, and the light frequency interval value corresponding to each period of the relative wavelength monitoring unit 1 in the range is obtained by dividing the wavelength difference between the two absorption peaks by the number of rising edge zero crossing points.
Step 105: resampling the output signal of the direct intensity detection unit by utilizing the rising edge zero crossing point position of each sinusoidal signal to obtain a final direct intensity detection unit signal;
Specifically, resampling the direct intensity detection unit signal obtained in step 103 by using the equal-light-frequency interval sampling points (that is, rising edge zero crossing points of each sinusoidal signal) determined in step 104, finding out the position serial number in the direct intensity detection unit signal and the data of the same position of the equal-light-frequency interval sampling points in the resampling process, and rearranging the data to form a group of new data in sequence to obtain a final direct intensity detection unit signal, wherein the output signal of the final direct intensity detection unit 22 has a known starting point wavelength, and the light-frequency interval of adjacent points is known, that is, the spectrum of the accurate final fiber bragg grating array sensor is obtained; the first to eighth fiber gratings on the fiber grating array sensor 4 may be covered by the measuring device and used for demodulation, taking into consideration the start wavelength and the end wavelength determined by the absorption peak and the occupied bandwidth of each grating due to its physical quantity measuring range. If a spectrometer or a wavemeter is used as the absolute wavelength monitoring unit, a larger number of accessible gratings and wavelength range can be covered.
Step 106: and (3) obtaining the positions of the peaks of the spectrums of the different fiber gratings of the fiber grating array to obtain the center wavelengths of the different fiber gratings of the fiber grating array in the physical state, and further obtaining the physical quantity change of each fiber grating.
Based on similar inventive concept, the embodiment of the invention also provides another physical quantity measuring method based on fiber bragg grating array spectrum detection of the fiber bragg grating array physical quantity measuring device based on continuous scanning of the external cavity laser shown in fig. 1, which comprises the following steps:
Step 201: starting wavelength tuning of the external cavity tuning laser to scan the wavelength from the initial wavelength 1520nm to the final wavelength 1570nm, and respectively connecting the split laser to a direct intensity detection unit, an absolute wavelength monitoring unit and a relative wavelength monitoring unit;
Step 202: the sine signal output by the relative wavelength monitoring unit is used as an external clock to trigger and collect the output signal of the direct light intensity detection unit and the output signal of the absolute wavelength monitoring unit;
Step 203: calculating the number of sampling points of the output signal of the direct intensity detection unit corresponding to the absorption peak R26 and the absorption peak P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of sampling points to obtain the optical frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit in the range;
Specifically, the number of sampling points of the output signal of the direct intensity detection unit 22 corresponding to the absorption peak R26 (1527.63342 nm) and the absorption peak P27 (1564.44519 nm) of the hydrogen cyanide molecular gas chamber 6 is calculated, and the light frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit 22 and the output signal of the absolute wavelength monitoring unit 3 in the range is obtained by dividing the wavelength difference between the two absorption peaks by the number of sampling points.
Step 204: selecting an output signal of an absolute wavelength monitoring unit as a starting wavelength position, intercepting the acquired output signal of a direct light intensity detection unit at the starting wavelength position, and reserving the subsequent data to obtain a spectrum of a final fiber bragg grating array sensor;
The output signal of the absolute wavelength monitoring unit 3 is selected as a starting wavelength position, that is, the absorption peak R26 of the hydrogen cyanide molecular gas chamber 6 is selected as a starting wavelength position, and the absolute wavelength of the starting wavelength position is 1527.63342nm. Intercepting the collected output signal of the direct intensity detection unit 22 at the position of the sampling point, and reserving the subsequent data, wherein the output signal of the final direct intensity detection unit 22 has known starting point wavelength, and the optical frequency interval of the adjacent points is known, namely, the spectrum of the accurate final fiber bragg grating array sensor is obtained; the first to eighth fiber gratings on the fiber grating array sensor 4 may be covered by the measuring device and used for demodulation, taking into consideration the start wavelength and the end wavelength determined by the absorption peak and the occupied bandwidth of each grating due to its physical quantity measuring range. If a spectrometer or a wavemeter is used as the absolute wavelength monitoring unit, a larger number of accessible gratings and wavelength range can be covered.
Step 205: the spectrum of the fiber bragg grating array sensor is a plurality of peaks at different wavelength positions, each peak corresponds to the central wavelength of the fiber bragg grating at a specific space position, the positions of the peaks of the fiber bragg grating array spectra of different fiber bragg gratings are obtained, the central wavelengths of the fiber bragg grating array different fiber bragg gratings in the physical state are obtained, and then the physical quantity change of each fiber bragg grating is obtained.
The physical quantity change of the embodiment of the present invention includes, but is not limited to, temperature, strain, or other physical quantity that can cause the optical fiber to be strained or changed in temperature.
Based on the same inventive concept, the present embodiment further provides a physical quantity measuring device for optical fiber grating array spectrum detection, including:
The scanning unit is used for starting wavelength tuning of the external cavity type tuning laser to enable the wavelength to be continuously scanned from the initial wavelength 1520nm to the final wavelength 1570nm, and the laser is respectively connected to the fiber grating array sensor, the absolute wavelength monitoring unit and the relative wavelength monitoring unit after being split;
The acquisition unit is used for synchronously acquiring the output signal of the direct intensity detection unit, the output signal of the absolute wavelength monitoring unit and the output signal of the relative wavelength monitoring unit at a fixed sampling rate of 100 MSa/s;
the intercepting unit is used for selecting the output signal of the absolute wavelength monitoring unit as a starting wavelength position, intercepting the output signal of the synchronously acquired direct intensity detection unit and the output signal of the relative wavelength monitoring unit at the starting wavelength position and reserving the subsequent data to obtain the output signal of the direct intensity detection unit with known wavelength and the output signal of the relative wavelength monitoring unit;
The calculation unit is used for calculating the number of rising edge zero crossing points of the sinusoidal signals of the output signals of the relative wavelength monitoring units corresponding to the absorption peaks R26 and the absorption peaks P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of the rising edge zero crossing points to obtain an optical frequency interval value corresponding to each period of the relative wavelength monitoring units in the range;
the resampling unit is used for resampling the output signal of the direct intensity detection unit by utilizing the rising edge zero crossing point position of each sinusoidal signal to obtain a final direct intensity detection unit signal;
The processing unit is used for obtaining the positions of the peaks of the spectrums of the different fiber gratings of the fiber grating array to obtain the central wavelengths of the different fiber gratings of the fiber grating array in the physical state, and further obtaining the physical quantity change of each fiber grating.
Optionally, the resampling unit is specifically configured to:
And determining equal-light-frequency interval sampling points according to the rising edge zero crossing points of each sinusoidal signal, finding out the position serial numbers in the direct intensity detection unit signals and the data of the same positions of the equal-light-frequency interval sampling points according to the equal-light-frequency interval sampling points, and rearranging the data in sequence to form a group of new data to obtain the final direct intensity detection unit signals.
Based on the same inventive concept, the present embodiment also provides another physical quantity measuring device for optical fiber grating array spectrum detection, including:
The scanning unit is used for starting wavelength tuning of the external cavity type tuning laser to scan the wavelength from the initial wavelength 1520nm to the final wavelength 1570nm, and the laser is respectively connected to the direct intensity detection unit, the absolute wavelength monitoring unit and the relative wavelength monitoring unit after being split;
the acquisition unit is used for triggering and acquiring the output signal of the direct light intensity detection unit and the output signal of the absolute wavelength monitoring unit by taking the sine signal output by the relative wavelength monitoring unit as an external clock;
The calculation unit is used for calculating the number of sampling points of the output signal of the direct intensity detection unit corresponding to the absorption peak R26 and the absorption peak P27 of the hydrogen cyanide molecular gas chamber, and dividing the wavelength difference between the two absorption peaks by the number of sampling points to obtain the optical frequency interval value corresponding to the adjacent sampling points of the output signal of the direct intensity detection unit and the output signal of the absolute wavelength monitoring unit in the range;
The intercepting unit is used for selecting the output signal of the absolute wavelength monitoring unit as a starting wavelength position, intercepting the acquired output signal of the direct light intensity detecting unit at the starting wavelength position, and reserving the subsequent data to obtain the spectrum of the final fiber bragg grating array sensor;
The processing unit is used for obtaining the positions of the peaks of the optical fiber grating spectrums of the optical fiber grating array sensor, obtaining the central wavelengths of the optical fiber gratings of the optical fiber grating array under the physical state, and further obtaining the physical quantity change of each optical fiber grating.
Optionally, the external cavity tuning laser is provided with a Littrow or Littman structure.
Optionally, the relative wavelength monitoring unit includes at least one of a mach-zehnder structure with a fixed optical path difference, a michael Sun Jiegou fiber interferometer, and a fiber ring resonator structure.
The embodiment of the invention provides a physical quantity measuring method and a physical quantity measuring device for optical fiber grating array spectrum detection, which are used for realizing physical quantity measurement of the optical fiber grating array based on an external cavity laser and direct intensity detection, acquiring the spectrum of the optical fiber grating array in an equal optical frequency interval sampling mode, further realizing wavelength demodulation and quasi-distributed physical quantity measurement of the optical fiber grating array, obtaining a large-range access bandwidth, multiplexing a plurality of optical fiber gratings and improving the measuring range of the physical quantity measurement which can be detected by a single optical fiber grating; and meanwhile, the reflection spectrum of the fiber bragg grating array sensor is recovered by using denser equal-optical-frequency sampling points, and the resolution and demodulation precision of physical quantity are improved.
It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present invention without departing from the spirit or scope of the embodiments of the invention. Thus, if such modifications and variations of the embodiments of the present invention fall within the scope of the claims and the equivalents thereof, the present invention is also intended to include such modifications and variations.
Claims (10)
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| WO2024077503A1 (en) * | 2022-10-09 | 2024-04-18 | 广东感芯激光科技有限公司 | Interferometer absolute-displacement demodulation system and method using gas absorption spectrum as reference |
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| KR20050025760A (en) * | 2003-09-08 | 2005-03-14 | 도남시스템주식회사 | Fiber bragg grating sensor system |
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