Fiber-based quasi-distributed flexible optoelectronic sensing system

Abstract

The application relates to a quasi-distributed flexible photoelectric sensing system based on an optical fiber, and relates to the field of distributed optical fiber sensing. The system comprises a fiber core, a cladding, a coating layer, an electro-optical conversion module group and a demodulation system; the fiber core, the cladding and the coating layer form an optical fiber structure; the light output end of the electro-optical conversion module is opposite to the position of the fiber core; the fiber core comprises at least two groups of 45-degree fiber grating arrays; and the signal receiving end of the demodulation system is opposite to the output end position of the fiber core. After the electro-optical conversion module receives sensor parameters, the converted light signals pass through the corresponding 45-degree fiber grating arrays, are transmitted through the fiber core and are sent to the demodulation system, so that the sensor reading is obtained. Through the combination of the electro-optical conversion module, the 45-degree fiber grating arrays and the demodulation system, sensing measurement is realized by using a single optical fiber, and the problems of poor sensitivity during multi-physical quantity detection of the existing distributed optical fiber sensing system, complex demodulation devices and algorithms and susceptibility to interference are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of distributed optical fiber sensing, in particular to a quasi-distributed flexible optical fiber sensing system. BACKGROUND

[0002] Optical fiber sensing technology is an all-optical sensing technology with optical fiber as a sensing unit. Compared with a pure electrical sensing system, it has a series of unique advantages such as small size, high sensitivity, low cost, anti-electromagnetic interference, resistance to high temperature and high pressure, easy long-distance sensing and large-scale networking. Among them, distributed optical fiber sensing technology or quasi-distributed optical fiber sensing technology can realize continuous measurement of environmental parameters on the entire optical fiber length or multiple serial detection points.

[0003] The present stage research more distributed optical fiber sensing technology can be divided into based on the principle of interference distributed optical fiber sensing technology and based on the principle of backscattering distributed optical fiber sensing technology. The core device of the distributed optical fiber sensing technology based on the principle of interference is interferometer, mainly including Michelson fiber interferometer, Mach-Zehnder fiber interferometer, Sagnac fiber interferometer and their combination, this kind of distributed optical fiber sensor has the advantages of high sensitivity, but it is easy to be disturbed, the detection range is short, the positioning algorithm is complex and it faces the problems of strain and temperature monitoring mutual interference. According to the scattering type, the distributed optical fiber sensing technology based on the principle of backscattering can be divided into Rayleigh scattering, Raman scattering and Brillouin scattering. Rayleigh scattering carries the loss information along the line of optical fiber, although the OTDR, Φ-OTDR and other products based on Rayleigh scattering have accurate positioning, but they need to be averaged several times to improve the signal-to-noise ratio, and the measurement frequency and accuracy of the system are difficult to improve; Raman scattering carries the temperature information of each part of the optical fiber, which is suitable for temperature detection, but it is rarely used in the field of strain and gas molecule detection, and the spontaneous Raman scattering energy is low, and the transmission distance is limited; Brillouin scattering can continuously measure the temperature and strain of each point along the optical fiber, but the spontaneous Brillouin scattering energy is also low, and the transmission distance is limited, so it is necessary to inject pump light and probe light at both ends of the optical fiber, which requires high equipment and complex demodulation algorithm. The wavelength drift based on FBG is another common distributed optical fiber sensing technology, the reflection center wavelength of FBG is modulated by external parameters such as strain and temperature, the detection capability is not affected by factors such as light source power fluctuation, light bending loss, and detector aging, but it faces the problems of strain and temperature sensing interference, and the demodulation equipment is large in size and expensive, and cannot be directly applied to gas molecule sensing, environmental humidity sensing, gas flow rate sensing and other fields. Some new distributed optical fiber sensing technology or quasi-distributed optical fiber sensing technology has also been proposed. In 2019, Arnaldo G. Leal-Junior proposed a quasi-distributed polymer optical fiber sensor based on intensity change in Optics and Laser Technology, in which the light source is coupled into the polymer optical fiber from the side, each light source is connected with a sensor, and sensing is realized through time division multiplexing, which realizes quasi-distributed optical fiber sensing, but it faces the problems of low sensitivity, complex device, limited transmission distance and so on.

[0004] In summary, the existing distributed optical fiber sensing technology based on the principle of interference and the distributed optical fiber sensing technology based on the principle of backscattering have certain deficiencies in one or more aspects of multi-physical quantity detection and demodulation, transmission distance, detection accuracy, equipment cost and operation difficulty, and the stability of the light source is high, and the detected physical quantity is mainly temperature, strain and sound wave, which cannot be directly applied to gas molecule sensing, environmental humidity sensing, gas flow rate sensing and other fields. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art, and provides a quasi-distributed flexible optical-electric sensing system based on optical fiber, which constructs light conversion structure on the surface of the optical fiber to solve the problems of poor sensitivity, complex demodulation device and algorithm, and easy interference when detecting multiple physical quantities in the existing distributed optical fiber sensing system. The system comprises:

[0006] The system comprises a fiber core, a cladding, a coating layer, an electro-optical conversion module group, and a demodulation system.

[0007] The fiber core, the cladding, and the coating layer form a single-mode optical fiber structure.

[0008] The electro-optical conversion module group comprises at least one electro-optical conversion module, the electro-optical conversion module is located inside the cladding, and the light output end of the electro-optical conversion module is opposite to the position of the fiber core, and the electrical signal of the electro-optical conversion module is used to represent the sensor reading;

[0009] The fiber core comprises at least two groups of 45-degree fiber grating arrays, and the number and position of the 45-degree fiber grating arrays are opposite to the position of the light output end of the electro-optical conversion module.

[0010] The signal receiving end of the demodulation system is opposite to the output end position of the fiber core.

[0011] In an optional embodiment, the electro-optical conversion module comprises an electrical sensor, a P-metal contact layer, a P-distributed Bragg reflector (DBR), a quantum well active region, an oxide layer, an N-DBR, a substrate, and an N-metal contact layer.

[0012] The electrical sensor, the P-metal contact layer, the P-DBR, the quantum well active region, the oxide layer, the N-DBR, and the substrate are sequentially distributed.

[0013] The substrate is in contact with the N-metal contact layer.

[0014] The electrical sensor is connected to the N-metal contact layer.

[0015] In an optional embodiment, the electrical sensor is modified to the surface of the cladding by curved surface printing.

[0016] The electrical sensor, the P-metal contact layer, the P-DBR, the quantum well active region, the oxide layer, the N-DBR, the substrate, and the N-metal contact layer are modified to the cladding by evaporation.

[0017] In an optional embodiment, the wavelength of the laser emitted by the electro-optical conversion module matches the radiation center wavelength of the corresponding 45-degree fiber grating array.

[0018] In an optional embodiment, the 45-degree fiber grating array is prepared by using a hydrogen-loaded sensitization method.

[0019] In an optional embodiment, the electro-optical conversion module is connected in series with the 45-degree fiber grating array.

[0020] In an optional embodiment, the demodulation system comprises a wavelength demodulation module, an intensity detection module, and a signal processing module.

[0021] The wavelength demodulation module is connected with the intensity detection module, and the intensity detection module is connected with the signal processing module.

[0022] The technical scheme provided by the present application has at least the following beneficial effects:

[0023] By arranging the electro-optical conversion module outside the single-mode fiber structure and arranging the 45-degree fiber grating array inside the single-mode fiber structure, the light signal converted by the electro-optical conversion module after receiving the sensor parameter is transmitted through the fiber core after passing through the corresponding 45-degree fiber grating array and is sent to the demodulation system to obtain the sensor reading. By combining the electro-optical conversion module, the 45-degree fiber grating array, and the demodulation system, the single-sensor fiber is used to realize quasi-distributed sensing measurement, and the problems of poor sensitivity, complex demodulation device and algorithm, and susceptibility to interference in the existing distributed fiber sensing system are solved. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0025] Figure 1 A structure diagram of a quasi-distributed flexible photoelectric sensing system based on an optical fiber is shown.

[0026] Figure 2 A structure diagram of an electro-optical conversion module is shown.

[0027] Figure 3 A principle diagram of a DBR is shown.

[0028] Figure 4 A principle diagram of another DBR is shown.

[0029] Figure 5A schematic diagram of the structure of a demodulation system provided in an exemplary embodiment of this application is shown. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] Figure 1 This illustration shows a schematic diagram of a fiber-optic-based quasi-distributed flexible photoelectric sensing system provided in an exemplary embodiment of this application. Please refer to [the provided text]. Figure 1 The system includes a fiber core 1, a cladding 2, a coating layer 3, an electro-optic conversion module group, and a demodulation system 6. The fiber core 1, cladding 2, and coating layer 3 constitute a single-mode fiber structure. The electro-optic conversion module group includes at least one electro-optic conversion module 4, located inside the cladding, with its optical output end opposite to the fiber core 1. The electrical signal from the electro-optic conversion module 4 is used to characterize sensor readings. The fiber core includes at least two sets of 45-degree fiber Bragg grating arrays 4, the number and position of which are opposite to the optical output end of the electro-optic conversion module 4. The signal receiving end of the demodulation system 6 is opposite to the output end of the fiber core 1.

[0032] In the embodiments of this application, the fiber core is an optical fiber for optical transmission, and the cladding and coating are structures superimposed on the outside of the fiber core. Through the superposition design of the cladding and coating on the outside of the fiber core, the fiber core, cladding and coating form a single-mode optical fiber structure.

[0033] In this embodiment, the electro-optic conversion module group includes at least two electro-optic conversion modules. The electro-optic conversion modules are used to sense changes in external physical quantities and add the information of changes in external physical quantities to the laser wavelength and power.

[0034] In this embodiment, a 45-degree grating array is used to fold the optical path, so that the laser sent by the electro-optic conversion module is coupled into the fiber core and transmitted to the demodulation system through the fiber core. The demodulation system analyzes the information to determine the sensing information corresponding to the electrical signal in the optical signal sent by the electro-optic conversion module.

[0035] In summary, the system provided by the embodiment of the application sets the electro-optical conversion module outside the single-mode optical fiber structure and correspondingly sets the 45-degree fiber grating array inside, so that the light signal converted by the electro-optical conversion module after receiving the sensor parameter is transmitted through the fiber core after passing through the corresponding 45-degree fiber grating array and is sent to the demodulation system to obtain the sensor reading. Through the combination of the electro-optical conversion module, the 45-degree fiber grating array and the demodulation system, the single-sensor optical fiber realizes quasi-distributed sensing measurement, and solves the problems of poor sensitivity, complex demodulation device and algorithm and easy interference in the multi-physical quantity detection of the existing distributed optical fiber sensing system.

[0036] In an optional embodiment, referring to Figure 2 The electro-optical conversion module includes an electrical sensor 7, a P-metal contact layer 8, a P-distributed Bragg reflection (DBR) 9, a quantum well active region 10, an oxidation layer 11, an N-DBR 12, a substrate 13 and an N-metal contact layer 14. The electrical sensor 7, the P-metal contact layer 8, the P-DBR 9, the quantum well active region 10, the oxidation layer 11, the N-DBR 12 and the substrate 13 are sequentially distributed; the substrate 13 is in contact with the N-metal contact layer 14; and the electrical sensor 7 is connected to the N-metal contact layer 14.

[0037] In the embodiment of the application, the electrical sensor is implemented as a precision electrical sensor, which is a passive device. Optionally, the precision electrical sensor can be implemented as at least one of a gas sensor, a strain sensor and a temperature sensor. Under the stimulation of external physical quantities such as gas molecule concentration and gas flow rate, an electric current signal can be generated, and the precision electrical sensor forms a good ohmic contact with the P-metal contact layer and the N-metal contact layer to load the electric current signal; the P-DBR and the N-DBR are P-type and N-type distributed Bragg reflection mirrors, respectively, and have high reflectivity for light of a specific wavelength to form a laser resonant cavity; the multi-quantum well active region can form laser output under the action of the pump current and the distributed Bragg reflection mirror; and the oxidation layer can control the spot size.

[0038] In an optional embodiment, the electrical sensor is modified to the cladding surface by a curved surface printing method; and the electrical sensor, the P-metal contact layer, the P-DBR, the quantum well active region, the oxidation layer, the substrate and the N-metal contact layer are modified to the cladding by an evaporation method.

[0039] In the embodiment of the application, the specific way of modifying the electrical sensor to the optical fiber includes the following steps:

[0040] S1.1 stripping the cladding layer of the single mode fiber, cleaning the fiber facet, and vacuum depositing a ring-shaped N-metal contact layer. In this embodiment, the N-metal contact layer is Au, 0.2 μm thick, and a photoresist-deposition-acetone stripping procedure is used to form a ring-shaped electrode to control the shape and size of the laser spot.

[0041] S1.2 depositing a substrate layer on the Au electrode using metal organic chemical vapor deposition (MOCVD). In this embodiment, the substrate layer is GaAs, 50 μm thick.

[0042] S1.3 depositing an N-DBR layer using MOCVD. In this embodiment, the high and low refractive index layers are Al0.88Ga0.12As, 10 μm thick, with an optical thickness of one quarter of the wavelength.

[0043] S1.4 depositing an oxide layer using MOCVD. In this embodiment, the material is AlxOy, 0.2 μm thick.

[0044] S1.5 depositing a multiple quantum well active region using MOCVD. In this embodiment, the material is In0.19Ga0.81As, 0.2 μm thick, with a single quantum well thickness of 8 nm.

[0045] S1.6 depositing a P-DBR layer using MOCVD. In this embodiment, the high and low refractive index layers are Al0.88Ga0.12As, 5 μm thick, with an optical thickness of one quarter of the wavelength.

[0046] S1.7 vacuum depositing a P-metal contact layer. In this embodiment, the P-metal contact layer is Au, 0.2 μm thick.

[0047] S1.8 attaching a precision electrical sensor to the fiber facet using a curved surface printing technique to form a good ohmic contact between the precision electrical sensor and the metal contact layer.

[0048] In an alternative embodiment, the laser wavelength emitted by the electro-optical conversion module matches the center wavelength of the corresponding 45° fiber grating array.

[0049] In the embodiments of the present application, the DBR is a multi-layer reflective film, and the basic principle is equal inclination interference, i.e., as shown in FIG. 1, parallel light emitted by a light source is all converged at infinity after being reflected by a parallel plate, or is converged on a focal plane by a lens, resulting in equal inclination interference. Figure 3

[0050] Figure 3 ​In the formula, n0 and n1 are the refractive indexes of the plate and the surrounding medium respectively, N is the foot of the perpendicular line from C to AD, the optical path lengths from N and C to the lens focal plane P are equal. The plate thickness is h, the incident angle and the refractive angle are θ1 and θ2 respectively, the optical path difference Δ and the phase difference δ are shown in the following formula 1 and formula 2:

[0051] Formula 1: Δ = n (AB + BC) - n0AN

[0052] Formula 2:

[0053] In the formula, π is the constant of the circular ratio, λ is the wavelength of the incident laser, and n is the refractive index of the medium.

[0054] In the case that the reflectivity of the parallel band is high, the reflected light of the subsequent three levels and the driver cannot be ignored, and the reflectivity of the parallel band is combined with the reflectivity of the other bands Figure 4 In the process, the parallel band multi-beam interference rate can be expressed as the following formula 3:

[0055] Formula 3:

[0056] In the formula, r1 and r2 are the reflection coefficients of the light on the two surfaces of the film, and the calculation method is shown in the following formula 4:

[0057] Formula 4:

[0058] In combination with Figure 4 In formula 4, n0 is the refractive index of the space medium where the incident light is located, and n is the refractive index of the film.

[0059] When the optical thickness of the optical film is one-quarter of the wavelength, in the case of a half-wave mutation, the phase difference can be expressed as the following formula 5:

[0060] Formula 5:

[0061] At this time, the single-layer film, that is, the multi-plate interference reflectivity is shown in the following formula 6:

[0062] Formula 6:

[0063] Therefore, when the optical thickness of the optical film is one-quarter of the wavelength, each film layer satisfies the interference constructive condition, so that the incident light obtains strong reflection on each film layer, and after several layers of reflection, the incident light is almost completely reflected back to form a resonant cavity with high reflectivity, and has the function of selecting the output laser wavelength.

[0064] In an alternative embodiment, the 45-degree fiber grating array is prepared in a "hydrogen-loaded" sensitization manner.

[0065] In the embodiments of the present application, the 45-degree tilted fiber Bragg grating is used for energy coupling. According to the radiation mode theory, the 45-degree tilted fiber Bragg grating can radiate the light along the fiber axis out of the fiber perpendicularly. Due to the reversibility of the light path, the laser light perpendicular to the fiber can also be coupled into the fiber.

[0066] The principle of hydrogen-loaded sensitization is to place the fiber in high-pressure (2-76 MPa) hydrogen at a certain temperature (20-75 ℃) to make the hydrogen molecules penetrate and diffuse into the fiber, thereby enhancing the absorption of ultraviolet light by the fiber and further increasing the change in the core refractive index. The mask plate is a special optical device, and the base material thereof is usually quartz glass. There is a precise periodic structure on the surface thereof, which is made by etching process. The fiber is etched by using different orders of diffracted light interference.

[0067] In the embodiments of the present application, the main steps of hydrogen-loaded sensitization are as follows:

[0068] S2.1 hydrogen loading treatment is performed on the single-mode fiber.

[0069] S2.2 the optical path is built, and the mask plate is rotated in the direction perpendicular to the fiber so as to form an angle of 33.7 degrees with the fiber axis, because the grating tilt angle and the mask plate tilt angle satisfy the following formula 7:

[0070] Formula 7:

[0071] wherein θ G is the grating tilt angle, n uv is the refractive index of the fiber under ultraviolet light, and θ M is the tilt angle of the mask plate. Therefore, for the 45-degree tilted fiber Bragg grating, the tilt angle of the mask plate during preparation is about 33.7 degrees.

[0072] S2.3 the position of the single-mode fiber where the 45-degree tilted fiber Bragg grating needs to be written is determined, the coating layer is removed, and the alcohol is used for cleaning.

[0073] S2.4 ultraviolet exposure is performed to write the 45-degree tilted fiber Bragg grating, and the radiated light perpendicular to the fiber axis and the transmission light along the fiber axis are monitored in real time until the performance is optimal.

[0074] S2.5 annealing treatment is performed to remove the unreacted hydrogen molecules and stabilize the chemical bonds.

[0075] S2.6 performance test is performed on the 45-degree tilted fiber Bragg grating after the annealing treatment, and the finished 45-degree tilted fiber Bragg grating capable of radiating the set wavelength at a high efficiency is selected.

[0076] In an optional embodiment, the electro-optical conversion module is connected in series with the 45-degree fiber grating array. In this case, the output laser of the electro-optical conversion module is reasonably used and distributed with the radiation bandwidth and wavelength interval of the 45-degree fiber grating, so that the utilization of the spectrum can be improved and the series number can be increased.

[0077] The precision electrical sensors of the different electro-optical conversion modules in series can detect different physical quantities, and the change information of the different physical quantities can be loaded on the laser of different wavelengths to realize multifunctional sensing of a single microstructured optical fiber. The different electro-optical conversion modules emit laser of different wavelengths, and the positions of the electro-optical conversion modules in the optical fiber installation process are recorded in advance to determine the positions of the physical quantities that change.

[0078] In an optional embodiment, please refer to Figure 5 The demodulation system includes a wavelength demodulation module 61, an intensity detection module 62, and a signal processing module 63. The wavelength demodulation module is connected with the intensity detection module, and the intensity detection module is connected with the signal processing module. When the laser is transmitted to the demodulation system, the laser of different wavelengths is separated by the wavelength demodulation module, the intensity of each laser of different wavelengths is detected by the intensity detection module, and the original physical quantity can be sensed by the signal processing module in combination with the known transmission loss.

[0079] In summary, the system provided in the embodiments of the present application sets the electro-optical conversion module outside the single-mode optical fiber structure and correspondingly sets the 45-degree fiber grating array inside, so that the optical signal converted by the electro-optical conversion module after receiving the sensor parameter is transmitted through the fiber core after passing through the corresponding 45-degree fiber grating array and is sent to the demodulation system to obtain the sensor reading. Through the combination of the electro-optical conversion module, the 45-degree fiber grating array, and the demodulation system, the quasi-distributed sensing measurement is realized by using a single sensing optical fiber, and the problems of poor sensitivity, complex demodulation device and algorithm, and easy interference in the multi-physical quantity detection of the existing distributed optical fiber sensing system are solved.

[0080] The system provided in the embodiments of the present application is modified to the side surface of the optical fiber by the curved surface printing method, has a certain bending ability, has good mechanical properties, is a flexible structure, and solves the technical problem of poor mechanical properties of the existing electrical sensing system.

[0081] The system provided in the embodiments of the present application is a passive device outside the demodulation device, does not need to be powered, does not depend on external auxiliary equipment, and has good consistency and stability.

[0082] The system provided by the embodiment of the application can couple laser into a fiber core to propagate by a 45-degree inclined fiber grating, has small loss, and can realize long-distance sensing; different electro-optical conversion modules emit laser of different wavelengths, and the positions of the electro-optical conversion modules in the fiber installation process are recorded in advance to determine the positions of the physical quantities that change. The technical problems that the existing electrical sensing system is susceptible to electromagnetic interference and the transmission distance is limited are solved.

[0083] The above is only an optional embodiment of the application and is not used to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A quasi-distributed flexible optoelectronic sensing system based on optical fiber, characterized in that, The system comprises a fiber core, a cladding, a coating layer, an electro-optical conversion module group and a demodulation system. The fiber core, the cladding and the coating layer constitute a single-mode fiber structure. The electro-optical conversion module group comprises at least two electro-optical conversion modules. The fiber core comprises at least two 45-degree fiber grating arrays, the number of the 45-degree fiber grating arrays corresponding to the number of the electro-optical conversion modules, the fiber grating arrays being located at the side of the output position of the electro-optical conversion modules. The electro-optical conversion modules are located on the surface of the cladding, and the electrical signals of the electro-optical conversion modules are used to represent sensor readings. The signal receiving end of the demodulation system is opposite to the output position of the fiber core. The electro-optical conversion module comprises an electrical sensor, a P-metal contact layer, a P-DBR, a quantum well active region, an oxide layer, an N-DBR, a substrate and an N-metal contact layer. The electrical sensor, the P-metal contact layer, the P-DBR, the quantum well active region, the oxide layer, the N-DBR, the substrate and the N-metal contact layer are sequentially distributed. The substrate is in contact with the N-metal contact layer. The electrical sensor is connected to the N-metal contact layer.

2. The fiber-based quasi-distributed flexible optoelectronic sensing system of claim 1, wherein, The electrical sensor is modified to the surface of the cladding by curved surface printing. The preparation process of the P-metal contact layer, the P-DBR, the quantum well active region, the oxide layer, the N-DBR, the substrate and the N-metal contact layer is evaporation.

3. The fiber-based quasi-distributed flexible optoelectronic sensing system of claim 1, wherein, The wavelength of the laser emitted by the electro-optical conversion module matches the incident central wavelength of the corresponding 45-degree fiber grating array.

4. The fiber optic-based quasi-distributed flexible optoelectronic sensing system of claim 1, wherein, The 45-degree fiber grating array is prepared by using a "hydrogen-loaded" sensitization method.

5. The fiber optic-based quasi-distributed flexible optoelectronic sensing system of claim 1, wherein, The electro-optical conversion module and the 45-degree fiber grating array are correspondingly connected in series.

6. The fiber optic-based quasi-distributed flexible optoelectronic sensing system of claim 1, wherein, The demodulation system comprises a wavelength demodulation module, an intensity detection module and a signal processing module. The wavelength demodulation module is connected to the intensity detection module, and the intensity detection module is connected to the signal processing module.

Images