Multi-core grating sensor and manufacturing method therefor, and permafrost monitoring method

Abstract

The present invention relates to the technical field of optical fiber sensing. Disclosed are a multi-core grating sensor and a manufacturing method therefor, and a permafrost monitoring method. The multi-core grating sensor comprises a multi-core optical fiber grating, a strain gauge structure, and a demodulator, and the multi-core optical fiber grating comprises four uniformly and symmetrically distributed single-mode optical fibers, a cladding layer wrapping the four single-mode optical fibers, and a coating layer located between the single-mode optical fibers and the cladding layer; the strain gauge structure is attached to the outside of the multi-core optical fiber grating by means of glue bonding; and the demodulator is used for monitoring the dynamic change of the wavelength of the multi-core optical fiber grating, the demodulator comprises a broadband light source and a spectrum analyzer, an incident end of the multi-core optical fiber grating is connected to the broadband light source by means of the single-mode optical fibers, and an exit end thereof is connected to the spectrum analyzer by means of the single-mode optical fibers. Also disclosed in the present invention is a permafrost monitoring method. By means of comprehensive analysis and demodulation of fiber core wavelength variation amounts of a plurality of single-mode optical fibers on a single multi-core optical fiber grating, simultaneous measurement of multiple parameters is achieved, and the permafrost monitoring accuracy is improved.

Description

A multi-core optical grating sensor, a manufacturing method thereof and a frozen soil monitoring method TECHNICAL FIELD

[0001] The present application relates to the technical field of frozen soil monitoring, and particularly relates to a multi-core optical grating sensor, a manufacturing method thereof and a frozen soil monitoring method. BACKGROUND

[0002] Optical fiber sensors have many advantages such as simple structure, good environmental resistance, anti-electromagnetic interference, long-distance monitoring, and the like, and have been widely applied to many fields such as structural health state monitoring, power system safety monitoring, oil and gas resource exploration and exploitation, and national defense.

[0003] At present, the conventional single-core optical fiber grating sensor has been very mature in the research of manufacturing process and engineering application. However, in the monitoring of the strain of a more complex frozen soil structure, more sensors are needed to measure the multi-dimensional structural strain, so that the system structure is complex and inconvenient for engineering application.

[0004] Since the frozen soil layer is mostly located in the highland or severe cold zone in the northwest and northeast of China, the environment is harsh and unstable. The conventional frozen soil monitoring system has low sensitivity, redundant sensors, high false alarm rate and is easily affected by the environment, so that the traditional multi-sensor integrated system is prone to failure of the electronic sensor in the extreme environment, which increases a lot of uncertainty for the frozen soil monitoring, and the sensing unit does not have integration, and the measurement accuracy and difficulty are increased.

[0005] SUMMARY

[0006] The present application provides a multi-core optical grating sensor, a manufacturing method thereof and a frozen soil monitoring method, to solve the technical problems of poor integration, low measurement accuracy and great difficulty of the sensor used in the existing frozen soil monitoring process.

[0007] To solve the above problems, the first purpose of the present application is to provide a multi-core optical grating sensor, comprising:

[0008] The multi-core optical fiber grating comprises four uniformly and symmetrically distributed single-mode optical fibers, a cladding wrapped outside the four single-mode optical fibers, and a coating layer between the single-mode optical fibers and the cladding, and the four single-mode optical fibers are respectively a first optical fiber FBG1, a second optical fiber FBG2, a third optical fiber FBG3 and a fourth optical fiber FBG4.

[0009] When the multi-core fiber grating is bent and strained by the internal structure of the frozen soil, the core center wavelengths of the first fiber FBG1, the second fiber FBG2, the third fiber FBG3 and the fourth fiber FBG4 have different strain response rules to measure the bending radius vector R' and the bending direction angle θ of the multi-core fiber grating in the frozen soil.

[0010] A strain gauge structure is attached to the outside of the multi-core fiber grating by adhesive bonding.

[0011] A demodulator is used to monitor the wavelength dynamic change of the multi-core fiber grating, which includes a broadband light source and a spectrum analyzer, the incident end of the multi-core fiber grating is connected to the broadband light source through a single-mode fiber, and the emitting end of the multi-core fiber grating is connected to the spectrum analyzer through a single-mode fiber.

[0012] Preferably, the calculation expressions of the bending radius vector R' and the bending direction angle θ of the multi-core fiber grating are respectively:

[0013] Wherein: R' represents the bending radius vector of the fiber, R x ' represents the decomposition vector of the fiber in the 0° orientation, R y ' represents the decomposition vector of the fiber in the 270° orientation, K FBG1 is the reflection wavelength bending sensitivity of the first fiber FBG1 bending to the 0° orientation, K FBG2 is the reflection wavelength bending sensitivity of the second fiber FBG2 bending to the 90° orientation, Δλ FBG13 is the wavelength difference between the first fiber FBG1 and the third fiber FBG3, Δλ FBG24 is the wavelength difference between the second fiber FBG2 and the fourth fiber FBG4.

[0014] Preferably, the core center wavelength of the single-mode fiber is 1520-1620 nm, the reflectivity is > 90%, the 3dB bandwidth is ≤ 0.3 nm, and the side mode suppression ratio is > 10 dB.

[0015] Preferably, the diameter of the cladding is 150-240 μm, and the diameter of the coating layer is 200-300 μm.

[0016] Preferably, the channel number of the demodulator is 4-32 channels, the monitoring wavelength range is C+L band, the wavelength demodulation resolution is ≤ 10 pm, and the sampling frequency is ≤ 4 khz.

[0017] Preferably, the core spacing between the first optical fiber FBG1, the second optical fiber FBG2, the third optical fiber FBG3 and the fourth optical fiber FBG4 is 50-80 mu m.

[0018] Preferably, the strain gauge structure is made of stainless steel material.

[0019] The second object of the present application is to provide a multi-core optical grating sensor manufacturing method based on the multi-core optical grating sensor as described above, the manufacturing method comprising:

[0020] Step S 10 : Based on the femtosecond laser exposure method, a multi-core fiber grating is exposed and formed on a multi-core optical fiber;

[0021] Step S 20 : Place the multi-core fiber grating on the customized strain gauge structure;

[0022] Step S 30 : Apply a pre-stress F to both ends of the multi-core fiber grating, and use 353ND glue to glue and heat for a time T to fix, and finally encapsulate to complete the multi-core grating sensor.

[0023] Preferably, in step S 10 , in the femtosecond laser exposure method, a femtosecond laser with a wavelength of 1030 nm imported from Lithuania is used, the output wavelength of the frequency doubling module of the femtosecond laser is 515 nm, the pulse width of the femtosecond laser is 250 fs-8 ps, the single pulse energy is greater than 40 mu j, and the numerical aperture of the microscope objective is 1.42 and the working distance is 20 mm.

[0024] The third object of the present application is to provide a frozen soil monitoring method based on a multi-core grating sensor, which uses the multi-core grating sensor as described above, and the frozen soil monitoring method comprises:

[0025] Step S 100 : A plurality of multi-core grating sensors are longitudinally linearly connected in series, and transversely connected in parallel to form an array network;

[0026] Step S 200 : Each multi-core grating sensor in the array network is calibrated, and the change of the reflection wavelength drift of the multi-core fiber grating with the bending direction under a constant bending curvature is measured respectively;

[0027] Step S 300 : Fix the array network on the inner wall of the inclinometer in the frozen soil layer, and then pre-bury;

[0028] Step S 400When the slope body gradually changes the tiny displacement, the multi-core fiber grating in each multi-core grating sensor has different wavelength change amounts;

[0029] Step S 500 Data is transmitted to the data center through the wireless transmission system;

[0030] Step S 600 The demodulator cooperates with the AI fusion deep operation method to operate and demodulate the real-time data to obtain the permafrost layer distribution, ice content and permafrost thawing orientation trend data of the current position;

[0031] Step S 700 Simulation is performed through the digital twin visualization platform;

[0032] Step S 800 The geographic information is displayed in a three-dimensional holographic manner.

[0033] Compared with the prior art, the present application has obvious advantages and beneficial effects, which are embodied in the following aspects:

[0034] The multi-core grating sensor in the present application is composed of a multi-core fiber grating, a strain gauge structure and a demodulator, the multi-core fiber grating is exposed and formed on a multi-core fiber by a femtosecond laser exposure method, the multi-core fiber grating is placed on a customized strain gauge structure, a pre-stress is applied to both ends of the multi-core fiber grating, the multi-core fiber grating is glued with 353ND glue and fixed by heating for a period of time, and finally the multi-core grating sensor is packaged and manufactured. The inside of each multi-core fiber grating has a first optical fiber FBG 1, a second optical fiber FBG 2, a third optical fiber FBG 3 and a fourth optical fiber FBG 4, and they are distributed in geometric symmetry on the fiber cross section of the multi-core fiber grating, so that the bending response of the reflection wavelengths of the first optical fiber FBG 1 and the third optical fiber FBG 3 and the second optical fiber FBG 2 and the fourth optical fiber FBG 4 is different. Therefore, based on the single multi-core fiber grating array, a multi-parameter multi-core grating sensor is packaged, a plurality of multi-core grating sensors are networked to form a complete permafrost monitoring network system, the optical fiber gratings at a plurality of points are demodulated as a whole, and through comprehensive analysis and demodulation of the wavelength change amounts of the several fiber core gratings, the permafrost layer temperature, permafrost thawing strain, soil ice content and thawing displacement orientation can be accurately detected in real time. Through comprehensive analysis and demodulation of the wavelength change amounts of the several fiber core gratings on the single multi-core grating sensor, the permafrost layer temperature, permafrost thawing strain, soil ice content and thawing displacement orientation can be measured simultaneously on the single multi-core grating sensor, which has high measurement physical parameter sensitivity and high integration, and solves the problems of low sensitivity, redundant sensors, high false alarm rate, easy environmental influence and high technical threshold in the conventional permafrost monitoring system. BRIEF DESCRIPTION OF DRAWINGS

[0035] Fig. 1 is a structural schematic diagram of a multi-core fiber grating and a multi-core grating sensor in an embodiment of the present application;

[0036] Fig. 2 is a structural schematic diagram of a multi-core fiber grating encapsulated in a strain gauge structure in an embodiment of the present application;

[0037] Fig. 3 is a structural schematic diagram of a multi-core grating sensor fixed on the inner wall of a borehole inclinometer in a frozen soil layer in an embodiment of the present application;

[0038] Fig. 4 is a structural schematic diagram of a multi-core grating sensor combined as an array network through longitudinal linear series and horizontal parallel combination in an embodiment of the present application;

[0039] Fig. 5 is a flow schematic diagram of a fiber automatic processing system in an embodiment of the present application;

[0040] Fig. 6 is a decomposition schematic diagram of a fiber bending radius vector R' in an embodiment of the present application;

[0041] Fig. 7 is a curve schematic diagram of a change of a reflection wavelength drift of each multi-core fiber grating with a bending direction under a constant bending curvature in an embodiment of the present application;

[0042] Fig. 8 is a curve schematic diagram of a change of a multi-core fiber grating reflection wavelength drift with a bending curvature when the bending direction is constant in an embodiment of the present application;

[0043] Fig. 9 is a curve schematic diagram of a change of a multi-core fiber grating reflection wavelength with temperature when the bending direction is constant in an embodiment of the present application;

[0044] Fig. 10 is a flow schematic diagram of a multi-core grating sensor manufacturing method in an embodiment of the present application;

[0045] Fig. 11 is a flow schematic diagram of a frozen soil monitoring method based on a multi-core grating sensor in an embodiment of the present application.

[0046] Legend of reference signs:

[0047] 100 - multi-core grating sensor;

[0048] 1 - multi-core fiber grating; 11 - single-mode optical fiber; 12 - cladding; 13 - coating layer;

[0049] 2 - strain gauge structure. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0051] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, motion condition, etc. between components in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directional indications will also change accordingly.

[0052] In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes, for example, "A and / or B" includes A scheme, or B scheme, or A and B simultaneously meet the scheme. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of the ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application.

[0053] Optical fibers can be used as sensors to measure strain, temperature, pressure and other parameters, which are by changing the optical fiber so that the parameter to be measured modulates the light intensity, phase, polarization, wavelength or through time, etc. through the optical fiber.

[0054] The traditional way of monitoring frozen soil is through manual operation, which needs to be done once a day. Influenced by many factors such as geographical location and weather, it not only causes great waste in manpower, material resources and other aspects, but also has poor reliability in data collection.

[0055] The frozen soil layer is mostly in the northwest and northeast plateau or severe cold zone of China, and the environment is harsh and unstable. The conventional frozen soil monitoring system has low sensitivity, redundant sensors, high false alarm rate and is easily affected by the environment, so that the sensor integration system is easy to fail in the extreme environment, which increases a lot of uncertainty for frozen soil monitoring, and the sensor unit does not have integration, and the measurement accuracy and difficulty are increased.

[0056] To solve the above technical problems, as shown in FIGS. 1-9, embodiments of the present application provide a multi-core optical grating sensor 100, which comprises a multi-core optical fiber grating 1, a strain gauge structure 2 and a demodulator, wherein:

[0057] The multi-core fiber grating 1 includes four single-mode optical fibers 11, a cladding 12 and a coating layer 13, the four single-mode optical fibers 11 are respectively a first optical fiber FBG1, a second optical fiber FBG2, a third optical fiber FBG3 and a fourth optical fiber FBG4, and the first optical fiber FBG1, the second optical fiber FBG2, the third optical fiber FBG3 and the fourth optical fiber FBG4 are uniformly and symmetrically distributed; the cladding 12 is wrapped outside the four single-mode optical fibers 11, and the coating layer 13 is located between the single-mode optical fibers 11 and the cladding 12; when the multi-core fiber grating 1 is installed in the frozen soil and a bending strain is generated in the internal structure of the frozen soil, the core center wavelengths of the first optical fiber FBG1, the second optical fiber FBG2, the third optical fiber FBG3 and the fourth optical fiber FBG4 have different strain response rules, so as to measure the bending radius vector R' and the bending direction angle θ of the bending strain generated in the multi-core fiber grating 1 in the frozen soil.

[0058] The strain gauge structure 2 is attached to the outside of the multi-core fiber grating 1 by means of gluing; the demodulator is used for monitoring the wavelength dynamic change of the multi-core fiber grating 1, and in the embodiment, the demodulator includes a broadband light source and a spectrum analyzer, the incident end of the multi-core fiber grating 1 is connected with the broadband light source through a single-mode optical fiber, and the emergent end of the multi-core fiber grating 1 is connected with the spectrum analyzer through a single-mode optical fiber.

[0059] Specifically, since each multi-core grating sensor 100 has a multi-core fiber grating 1 inside, and each multi-core fiber grating 1 has a first optical fiber FBG1, a second optical fiber FBG2, a third optical fiber FBG3 and a fourth optical fiber FBG4 inside, and is geometrically symmetrically distributed on the fiber cross section of the multi-core fiber grating 1, therefore, the bending responses of the reflection wavelengths of the first optical fiber FBG1 and the third optical fiber FBG3 and the second optical fiber FBG2 and the fourth optical fiber FBG4 are different.

[0060] Further, the calculation expressions of the bending radius vector R' and the bending direction angle θ of the bending strain generated by the multi-core fiber grating 1 are respectively:

[0061] Specifically, as shown in FIG. 6, the bending radius R caused by vibration changes, which is the size of the frozen soil melting trend, θ is the stress direction, which is the direction of the frozen soil melting, and the bending radius vector R' can be orthogonally decomposed into R x and R' y When the multi-core grating sensor 100 is installed in the frozen soil layer, and the measured object in the frozen soil layer bends to the θ direction, the wavelength drifts of the first optical fiber FBG1 and the second optical fiber FBG2 observed by the spectrum analyzer are respectively Δλ FBG1 and Δλ FBG2 , K FBG1 is the reflection wavelength bending sensitivity of the first optical fiber FBG1 bending to the 0° direction (i.e. the +y direction), KFBG2 The wavelength bending sensitivity of the second fiber FBG2 when bending in the 90° orientation (i.e. +x direction) is Δλ2= K2R2, where K2= 0.000 1 nm-1, and R2= 0.5 m.

[0062] wherein R' represents the bending radius vector of the fiber, R x ' represents the decomposition vector of the fiber in the 0° orientation, R y ' represents the decomposition vector of the fiber in the 270° orientation, Δλ FBG1 is the wavelength shift of the first fiber FBG1 observed by the spectrum analyzer, Δλ FBG2 is the wavelength shift of the second fiber FBG2 observed by the spectrum analyzer, K FBG1 is the wavelength bending sensitivity of the first fiber FBG1 when bending in the 0° orientation, K FBG2 is the wavelength bending sensitivity of the second fiber FBG2 when bending in the 90° orientation, Δλ FBG13 is the wavelength difference between the first fiber FBG1 and the third fiber FBG3, Δλ FBG24 is the wavelength difference between the second fiber FBG2 and the fourth fiber FBG4.

[0063] Further, the single-mode fiber 11 has a core center wavelength of 1520 nm-1620 nm, a reflectivity of >90%, a 3dB bandwidth of ≤0.3 nm, and a side mode suppression ratio of >10 dB.

[0064] Further, the cladding 12 has a diameter of 150-240 μm, and the coating layer 13 has a diameter of 200-300 μm. In a preferred embodiment, the multi-core fiber grating 1 has a cladding diameter of 240 μm, a coating diameter of 300 μm, the single-mode fiber 11 has a core center wavelength of 1552 nm, a 3dB bandwidth of 0.3 nm, a side mode suppression ratio of 11 dB, and a reflectivity of 91%.

[0065] Further, the core spacing between the first fiber FBG1, the second fiber FBG2, the third fiber FBG3, and the fourth fiber FBG4 in the single-mode fiber 11 is 50-80 μm.

[0066] Specifically, referring to FIGS. 1 and 2, in the embodiment of the present application, the multi-core fiber grating 1 has four cores, and the material of the multi-core fiber grating is silica quartz material, and the core spacing is 80 μm.

[0067] Further, a demodulator is used to monitor the wavelength dynamic change of the multi-core fiber grating 1, wherein the demodulator has 4-32 channels, monitors the C+L wavelength range, has a wavelength demodulation resolution of ≤10 pm, and has a sampling frequency of ≤4 khz.

[0068] In a preferred embodiment, the demodulator is a fiber grating demodulator, which can monitor the wavelength dynamic change of the multi-core fiber grating 1. The specific channel number is 4-32 channels, the detection wavelength range is C+L band, the wavelength demodulation resolution is ≤10pm, and the sampling frequency is ≤4khz.

[0069] As shown in FIG. 9, the center wavelength of the first optical fiber FBG1 changes linearly with the change of temperature. That is, by monitoring the wavelength change of the first optical fiber FBG1, the real-time change of the permafrost temperature can be analyzed, that is, the permafrost temperature.

[0070] Wherein: λ FBG1 is the center wavelength of the first optical fiber FBG1, ε is the strain generated on the first optical fiber FBG1 by the vibration and bending of the core, P e is the fiber photoelastic coefficient, ξ f is the fiber thermal photoelastic coefficient; ΔT is the real-time change of the permafrost temperature.

[0071] Therefore, by using the multi-core grating sensor 100, the real environment of permafrost monitoring can be accurately simulated, including the position, temperature, ice content, melting direction and other parameters of the permafrost layer, which can help the operator better understand and analyze the real situation of the actual permafrost layer.

[0072] Referring to FIG. 10, the embodiment of the application further provides a manufacturing method of a multi-core grating sensor, which comprises the following steps:

[0073] Step S 10 : Based on the femtosecond laser exposure method, a multi-core fiber grating 1 is formed on a multi-core optical fiber by exposure;

[0074] Step S 20 : The multi-core fiber grating 1 is placed on a customized strain gauge structure 2.

[0075] Step S 30 : A pre-stress F is applied to both ends of the multi-core fiber grating 1, 353ND glue is used for gluing, and a heating time T is used for fixing, so that the multi-core grating sensor 100 is finally packaged and manufactured.

[0076] In step S 30 , preferably, the size of the pre-stress F is 0.5-5N, and the heating time T is preferably 60 minutes.

[0077] Thus, based on the single multicore fiber grating 1 encapsulated into the multi-parameter multicore grating sensor 100, the multi-core grating sensors 100 are networked to form an array network to build a complete frozen soil monitoring network system, the multi-core fiber gratings 1 of multiple points are overall demodulated, and through comprehensive analysis and demodulation of wavelength change amounts of several fiber core gratings, the frozen soil layer temperature, frozen soil melting strain, soil ice content and melting displacement direction can be accurately detected in real time.

[0078] Further, in step S 10 Among them, the writing platform used based on femtosecond laser exposure includes a femtosecond laser output system for forming a laser path in sequence, a laser for emitting laser;

[0079] A laser energy control system for monitoring and adjusting the power of the laser;

[0080] A light field regulation system for adjusting the frequency of the laser and increasing the spot size to compress the beam divergence angle;

[0081] An automatic focusing real-time imaging system for filtering stray light and outputting laser;

[0082] A precision displacement control system provided at the output end of the automatic focusing real-time imaging system, the precision displacement control system for carrying the optical fiber to be processed;

[0083] An optical fiber automatic processing system for completing the writing of the grating.

[0084] Specifically, please refer to the writing platform shown in Figure 5, in the embodiment of the present application, the writing platform includes a femtosecond laser output system, a laser energy control system, a light field regulation system, an automatic focusing real-time imaging system, a precision displacement control system and an optical fiber automatic processing system, wherein the writing process of the writing platform is as follows:

[0085] The jig is used to fix the processed multicore optical fiber on the precision displacement control system, and the axis direction of the multicore optical fiber is adjusted to be horizontal, and the multicore optical fiber is positioned by the automatic focusing real-time imaging system;

[0086] The jig is moved by the precision displacement control system, so that the processed multicore optical fiber is located below the automatic focusing real-time imaging system;

[0087] The Z-axis of the precision displacement control system is controlled to move, so that the upper surface of the multicore optical fiber can be clearly imaged in the CCD camera, and the scale z1 of the Z-axis at this time is recorded. The Z-axis is controlled to continue to move downward, so that the lower surface of the optical fiber is clearly imaged in the CCD camera, and the scale z2 of the Z-axis at this time is recorded. The middle position of the scales z1 and z2 is the focal point position of laser processing;

[0088] The laser is emitted by a femtosecond laser output system, and the wavelength of the emitted laser is preferably 1030 mm, and the pulse width is 250 fs-8 ps; the laser sequentially passes through a laser energy control system, an optical field regulation system, and an automatic focusing real-time imaging system, and finally irradiates on a multi-core optical fiber to be processed; wherein the laser energy control system is used for monitoring and adjusting the power of the laser; the optical field regulation system is used for adjusting the frequency of the laser and increasing the spot size to compress the beam divergence angle, and further reducing the focused spot size; the automatic focusing real-time imaging system is used for filtering stray light and outputting the laser; in this process, the power of the laser output is monitored in real time by the laser energy control system, and compensation is made according to the fluctuation of the laser power.

[0089] In addition, the laser passes through the optical field regulation system and enters the automatic focusing real-time imaging system, which in this embodiment is composed of a variable diaphragm and a focusing objective lens; the variable diaphragm can filter out stray light at the edge of the light beam by adjusting the incident aperture to improve the grating writing effect; the incident light beam is focused by the focusing objective lens and then emitted into the inside of the optical fiber to be processed.

[0090] Further, in step S 10 Among them, the femtosecond laser output system includes a femtosecond laser and a microscopic immersion objective lens, wherein:

[0091] In the femtosecond laser exposure method, a femtosecond laser imported from Lithuania with a wavelength of 1030 nm is used, the output wavelength of the frequency doubling module of the femtosecond laser is 515 nm, the pulse width of the femtosecond laser is 250 fs-8 ps, the single pulse energy is greater than 40 μj, the numerical aperture of the microscopic objective lens is 1.42, and the working distance is 20 mm.

[0092] Specifically, in the embodiment of the present application, based on the high-performance 1030 nm femtosecond laser imported from Lithuania, the frequency doubling module outputs 515 nm, the pulse width is 250 fs-8 ps adjustable, and the single pulse energy is greater than 40 μj.

[0093] A 60x Olympus near-infrared achromatic microscopic immersion objective lens with a numerical aperture of 1.42 and a working distance of 20 mm is used, and the laser passes through the laser transmission and energy control system, the optical field regulation system, the automatic focusing and real-time imaging system, the precision motion control system, and the optical fiber automatic processing system to prepare a four-core fiber grating.

[0094] Specifically, in the embodiment of the present application, in step S 30 Among them, the multi-core fiber grating 1 is placed on a customized strain gauge structure 2, and a pre-stress of 4.53 N is applied to both ends of the multi-core fiber grating 1, and the 353ND glue is heated for 60 min for fixation, and finally a multi-core grating sensor 100 is completed.

[0095] Referring to FIG. 11, another embodiment of the present application provides a frozen soil monitoring method based on a multi-core optical grating sensor, which adopts the multi-core optical grating sensor 100, and the frozen soil monitoring method comprises the following steps:

[0096] Step S 100 : a plurality of multi-core optical grating sensors 100 are collected through longitudinal linear series and combined in array network in transverse parallel;

[0097] Specifically in the embodiment of the present application, the number of the multi-core optical grating sensors 100 is 100, and the 100 multi-core optical grating sensors 100 are combined in series and parallel to form an array network.

[0098] Step S 200 : each multi-core optical grating sensor 100 is calibrated, and the change of the reflection wavelength drift of the multi-core fiber grating 1 in the multi-core optical grating sensor 100 with the bending direction under a constant bending curvature is measured respectively;

[0099] As shown in FIGS. 7 and 8, each multi-core optical grating sensor 100 is calibrated, and the change of the reflection wavelength drift of each multi-core fiber grating 1 (the first fiber FBG1, the second fiber FBG2, the third fiber FBG3 and the fourth fiber FBG4) in the multi-core optical grating sensor 100 with the bending direction under a constant bending curvature is measured respectively. Under a constant bending curvature, the change of the reflection wavelength drift of the multi-core fiber grating 1 with the bending direction presents an approximate sine and cosine function relationship. When the multi-core fiber grating 1 is bent to different directions, the bending sensitivity is different, that is, the bending sensitivity of the multi-core fiber grating 1 has strong bending direction correlation.

[0100] Step S 300 : the multi-core optical grating sensor 100 is fixed on the inner wall of the inclinometer in the frozen soil layer, and then pre-buried;

[0101] As shown in FIG. 3, the multi-core optical grating sensor 100 is fixed in the frozen soil layer through the inclinometer, the wavelength change of the multi-core fiber grating 1 is monitored according to the real-time change of the temperature of the frozen soil layer, the real environment of the frozen soil monitoring is accurately simulated, the real environment of the frozen soil layer includes the position, temperature, ice content, melting direction and other parameters of the frozen soil layer, and then the real situation of the frozen soil layer is obtained.

[0102] Step S 400 : when the slope body has a gradual small displacement, the multi-core fiber grating 1 in each multi-core optical grating sensor 100 has different wavelength change amounts;

[0103] Step S 500 : the data is transmitted to the data center through a wireless transmission system;

[0104] Step S 600 : The demodulator cooperates with the AI fusion depth operation method to demodulate the real-time data to obtain the permafrost layer distribution, ice content, and permafrost thawing orientation trend data of the current position.

[0105] In this step, a large amount of data can be demodulated and calculated through AI data operation.

[0106] Step S 700 : Simulation is performed through the digital twin visualization platform.

[0107] In this step, the digital twin visualization platform includes function modules such as three-dimensional modeling, three-dimensional rendering, three-dimensional scene interaction, and space GIS fusion. Through digital definition and modeling of the composition, characteristics, functions, and performance of each physical entity of each application scenario business unit, the organic fusion of virtual reality technology, space GIS technology, and simulation technology is realized.

[0108] The digital twin visualization platform performs holographic display of geographic information in a three-dimensional manner, and performs scene switching interaction through voice and touch screen modes, and provides early warning, mining, and analysis of abnormal indicators, and provides auxiliary decision support.

[0109] Step S 800 : Holographic display of geographic information in a three-dimensional manner.

[0110] In this step, holographic display of geographic information in a three-dimensional manner is performed, and scene switching interaction is performed through voice and touch screen modes, and early warning, mining, and analysis of abnormal indicators are performed, and auxiliary decision support is provided.

[0111] It should be particularly noted that according to the requirements, the system first studies the interaction function of VR, and then uses ActiveX technology to encapsulate the VR-based measurement and control interface into a standardized control embedded in the configuration software, to realize seamless linking and dynamic data exchange between physical permafrost and virtual permafrost, and finally realize remote monitoring.

[0112] The permafrost monitoring system based on virtual manufacturing realizes virtual human-computer interaction through modeling simulation technology and software development technology, and realizes real-time simulation through the use of geometric modeling, physical modeling, motion modeling, behavior modeling, interactive mapping, and model segmentation.

[0113] The system realizes the construction and simulation of a virtual scene through the combination of software and hardware design. The design of the virtual scene includes visualization, data processing, and user interaction.

[0114] Although the present disclosure has been disclosed with reference to the above embodiments, the scope of the present disclosure is not limited to the above embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present disclosure.

Claims

1. A multicore optical grating sensor, characterized by, The application relates to a multi-core fiber grating sensor and a monitoring method thereof. The multi-core fiber grating (1) comprises four uniformly and symmetrically distributed single-mode optical fibers (11), a cladding (12) wrapped outside the four single-mode optical fibers (11), and a coating layer (13) between the single-mode optical fibers (11) and the cladding (12), wherein the four single-mode optical fibers (11) are respectively a first optical fiber FBG1, a second optical fiber FBG2, a third optical fiber FBG3 and a fourth optical fiber FBG4. When the multi-core fiber grating (1) is bent and strained due to the internal structure of frozen soil, the core center wavelengths of the first optical fiber FBG1, the second optical fiber FBG2, the third optical fiber FBG3 and the fourth optical fiber FBG4 have different strain response rules, so as to measure the bending radius vector R' and the bending direction angle theta of the multi-core fiber grating (1) in the frozen soil. A strain gauge structure (2) is attached to the outside of the multi-core fiber grating (1) by means of adhesion. A demodulator is used for monitoring the wavelength dynamic change of the multi-core fiber grating (1), the demodulator comprises a broadband light source and a spectrum analyzer, the incident end of the multi-core fiber grating (1) is connected with the broadband light source through a single-mode optical fiber, and the emitting end of the multi-core fiber grating (1) is connected with the spectrum analyzer through a single-mode optical fiber.

2. The multicore optical raster sensor according to claim 1, characterized in that, The calculation expression of the bending radius vector R' and the bending direction angle θ of the bending strain generated by the multicore fiber grating (1) are respectively: wherein: R' represents the bending radius vector of the optical fiber, R x K' represents the decomposition vector of the optical fiber in the 0° orientation, R y K" represents the decomposition vector of the optical fiber in the 270° orientation, K FBG1 is the reflection wavelength bending sensitivity of the first optical fiber FBG1 when bent in the 0° orientation, K FBG2 is the reflection wavelength bending sensitivity of the second optical fiber FBG2 when bent in the 90° orientation, Δλ FBG13 is the wavelength difference between the first optical fiber FBG1 and the third optical fiber FBG3, Δλ FBG24 is the wavelength difference between the second optical fiber FBG2 and the fourth optical fiber FBG4.

3. The multicore optical raster sensor of claim 1, wherein, The core center wavelength of the single-mode optical fiber (11) is 1520nm-1620nm, the reflectivity is greater than 90%, the 3dB bandwidth is less than or equal to 0.3nm, and the side mode suppression ratio is greater than 10dB.

4. The multicore optical raster sensor of claim 1, wherein, The diameter of the cladding (12) is 150-240mu m, and the diameter of the coating layer (13) is 200-300mu m.

5. The multicore optical raster sensor of claim 1, wherein, The channel number of the demodulator is 4-32 channels, the monitoring wavelength range is C+L waveband, the wavelength demodulation resolution is less than or equal to 10pm, and the sampling frequency is less than or equal to 4khz.

6. The multicore optical raster sensor of claim 1, wherein, The core spacing between the first optical fiber FBG1, the second optical fiber FBG2, the third optical fiber FBG3 and the fourth optical fiber FBG4 is 50-80mu m.

7. The multicore optical raster sensor of claim 1, wherein, The strain gauge structure (2) is made of stainless steel material.

8. A method of fabricating a multicore optical grating sensor, the method comprising: The application further discloses a manufacturing method of the multi-core fiber grating sensor. Step S 10 : A multi-core fiber grating (1) is formed by exposing a multi-core fiber based on a femtosecond laser exposure method. Step S 20 : Placing the multicore fiber grating (1) on a custom strain gauge structure (2); Step S 30 : Apply pre-stress F at both ends of the multi-core fiber grating (1), and fix it by using 353ND glue and heating for time T. Finally, the multi-core grating sensor is completed by packaging.

9. The method of fabricating a multicore optical grating sensor of claim 8, wherein: In step S 10 Among them, in the femtosecond laser exposure method, a femtosecond laser with a wavelength of 1030nm imported from Lithuania is used, the output wavelength of the frequency doubling module of the femtosecond laser is 515nm, the pulse width of the femtosecond laser is 250fs-8ps, the single pulse energy is greater than 40μj, the numerical aperture of the microscope objective is 1.42, and the working distance is 20mm.

10. A method for monitoring frozen ground based on a multi-core optical grating sensor, using the multi-core optical grating sensor according to any one of claims 1-7, characterized in that, The application further discloses a monitoring method of the frozen soil. The application further discloses a monitoring method of the frozen soil. Step S 100 : The multiple multi-core optical grating sensors are collected by longitudinal linear series and combined as an array network in transverse parallel. Step S 200 : Each multi-core fiber grating sensor in the array network is calibrated, and the change of the reflection wavelength shift of the multi-core fiber grating (1) with the bending direction under a constant bending curvature is measured respectively; Step S 300 : Fix the array network on the inner wall of the inclinometer tube inside the frozen soil layer, and then pre-bury; Step S 400 : When the slope body has a gradual small displacement, the multi-core fiber grating (1) in each multi-core optical grating sensor has different wavelength change amounts; Step S 500 : transmitting the data to the data center through the wireless transmission system; Step S 600 : The demodulator cooperates with the AI fusion deep operation method to operate and demodulate the real-time data to obtain the permafrost layer distribution, ice content, and permafrost thaw orientation trend data of the current position. Step S 700 : Simulate by digital twin visualization platform; Step S 800 : The holographic display of geographic information is performed in a three-dimensional manner.

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