Single-ended BOTDA (Brillouin Optical Time Domain Analysis) multi-parameter simultaneous measurement method and device

Abstract

The invention discloses a single-ended BOTDA (Brillouin Optical Time Domain Analysis) multi-parameter simultaneous measurement method and a single-ended BOTDA multi-parameter simultaneous measurement device, and relates to the technical field of measurement. Wherein backward Rayleigh scattering light generated by continuous light in different modes in the few-mode optical fiber is used as detection light, sensing pulse light in different modes is used as pump light, and the detection light and the pump light in each mode generate intramode and intermode stimulated Brillouin scattering effect; then a photon lantern is used as a demultiplexer to extract detection light signals of each linear polarization mode, a photoelectric detector is used for detection, and finally temperature, strain and bending values are analyzed according to different characteristics of Brillouin frequency shift of each mode and corresponding coefficients of each physical quantity. According to the single-ended BOTDA multi-parameter simultaneous measurement method and device, the structure is simple, application is convenient, detection can still be carried out when optical fibers are broken, and multi-parameter simultaneous measurement with the high signal-to-noise ratio can be achieved.

Description

Technical Field

[0001] The invention relates to the field of measurement technology, and in particular to a single-ended BOTDA multi-parameter simultaneous measurement method and device. Background Art

[0002] Distributed fiber optic sensing technology based on Brillouin optical time domain analysis can realize continuous monitoring of parameters such as temperature, strain, bending, etc., and has the advantages of high reliability, anti-electromagnetic interference, long distance, high spatial resolution and high measurement accuracy. It is widely used in the fields of electricity, petroleum, aviation and health status monitoring of large structures.

[0003] The double-ended BOTDA system needs to inject the pump light and the probe light that propagate in opposite directions at both ends of the optical fiber. When the frequency difference between the pump light and the probe light is the Brillouin frequency shift, stimulated Brillouin scattering will occur in the sensing optical fiber. The Brillouin frequency shift is determined by measuring the center frequency of the Brillouin scattering spectrum, and then the information of the measured physical quantity is obtained. However, in actual engineering applications, it is inconvenient to use due to its complex system structure and difficult construction. Compared with the double-ended BOTDA, the single-ended BOTDA still has the ability to detect when the optical fiber is broken, and its single-ended working mode is more convenient to use in actual engineering.

[0004] For standard single-mode optical fiber, since BFS is sensitive to both temperature and strain, there is a cross-sensitivity problem, and it can only measure a single physical quantity, and it is difficult to achieve simultaneous measurement of two or more physical quantities. The commonly used solution at present is to lay a reference optical fiber, one optical fiber is embedded in the structure to detect the combined effects of strain and temperature, while keeping the other reference optical fiber loose, only detecting temperature or strain, so as to distinguish temperature from strain; however, in practical applications, there are difficulties in laying optical fibers and it is difficult to achieve consistent optical fiber length. Another solution is to use hybrid physical effects, such as a combination of Raman scattering and Brillouin scattering to measure temperature and strain simultaneously, but the high noise caused by spontaneous Raman scattering is considered to be the main limiting factor for the use of hybrid sensing solutions. In addition, there are special waveguide structures such as polarization-maintaining fiber, non-zero dispersion-shifted fiber, annular hyperbolic tangent fiber and multi-core fiber to achieve simultaneous measurement of multiple parameters, but they are expensive and not suitable for long-distance sensing.

[0005] Therefore, there is an urgent need for a method and device with a simple structure, easy application, and capable of simultaneously measuring multiple physical quantities. Summary of the invention

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions: a single-ended BOTDA multi-parameter simultaneous measurement method, using a narrow linewidth laser to output two optical signals with unchanged polarization states through a polarization-maintaining coupler, one continuous light with a changed frequency output through a continuous light module, and one pulse light with a high extinction ratio output through a pulse light module. The synthetic optical signal formed after the two optical signals are coupled is incident from one end of the few-mode optical fiber after passing through a circulator and a photon lantern, and the different modes of back-Rayleigh scattered light generated by the continuous light in the few-mode optical fiber are used as detection light, and the different modes of pulse light are used as pump light. The pump light and the detection light of different modes undergo stimulated Brillouin scattering in the few-mode optical fiber; the photon lantern extracts the detection light carrying Brillouin scattering information of each mode, and detects it using a photodetector. By demodulating the Brillouin frequency shift of different modes in the detection light, the simultaneous measurement of multiple physical quantities can be achieved.

[0007] Preferably, the different modes are linear polarization modes extracted in the few-mode optical fiber by using the photon lantern as a mode multiplexer or demultiplexer.

[0008] Preferably, the simultaneous measurement of the multiple physical quantities is determined based on the number of modes in the detection light. Each linear polarization mode has a different response to the Brillouin frequency shift of physical quantities such as temperature, strain, and bending. By solving the sensitivity of each linear polarization mode to different physical quantities and establishing a sensitivity matrix, simultaneous analysis of multiple physical quantities can be achieved.

[0009] A single-ended BOTDA multi-parameter simultaneous measurement device includes a narrow linewidth laser, a polarization-maintaining coupler, a microwave generator, a first electro-optic modulator, a pulse signal source, a second electro-optic modulator, a first erbium-doped fiber amplifier, a first grating filter, a first polarization scrambler, a second erbium-doped fiber amplifier, a second grating filter, a second polarization scrambler, an optical coupler, a first optical circulator, a second optical circulator, a third optical circulator, a photon lantern, a few-mode fiber, an optical filter, a photodetector, a data acquisition card, and a computer. The narrow linewidth laser outputs two continuous lights with unchanged polarization states through the polarization-maintaining coupler, the first continuous light is connected to the optical coupler after passing through a continuous light module, and the second continuous light is connected to the optical coupler. The coupler output is connected to the first optical port of the first optical circulator, the second optical circulator, and the third optical circulator, the second optical port of the optical circulator is connected to the few-mode fiber through the photon lantern, and the third optical port of the optical circulator is connected to the computer through the optical filter, the photodetector, and the data acquisition card in sequence.

[0010] Preferably, the few-mode optical fiber is the optical fiber to be tested, and physical quantities such as temperature, strain, bending, etc. are all applied to the few-mode optical fiber.

[0011] Preferably, the photon lantern is a bidirectional input-output device, with multiple single-mode optical fibers at one end and a single few-mode optical fiber at the other end, and the number of obtainable linear polarization modes is determined by the number of input ports of the photon lantern.

[0012] Preferably, the continuous optical module is composed of a microwave generator, a first electro-optical modulator, a first erbium-doped fiber amplifier, a first grating filter and a first polarization scrambler. The microwave generator drives the first electro-optical modulator to perform double-sideband modulation of the first optical signal output by the polarization-maintaining coupler with suppressed carrier, and the output frequency component is ν0±ν m The continuous light is amplified by the first erbium-doped fiber amplifier and filtered by the first grating filter to filter out the carrier and spontaneous emission noise, and then the polarization state is disturbed by the first polarization scrambler to reduce polarization fading.

[0013] The ν m is the microwave generator frequency, which is approximately the Brillouin frequency shift value of the few-mode fiber, and ν0 is the center frequency of the narrow-linewidth laser.

[0014] Preferably, the pulse light module is composed of a pulse signal source, a second electro-optical modulator, a second erbium-doped fiber amplifier, a second grating filter and a second polarization scrambler. The pulse signal source drives the second electro-optical modulator to perform pulse modulation on the second optical signal output by the polarization-maintaining coupler, and outputs a pulse light with a frequency component ν0. After the signal is amplified by the second erbium-doped fiber amplifier and filtered by the second grating filter, the spontaneous radiation noise is filtered out, and then the polarization state is disturbed by the second polarization scrambler to reduce polarization fading.

[0015] Preferably, the grating filter is composed of a circulator and a fiber Bragg grating, and can be replaced by other types of fiber filters.

[0016] The present invention provides a single-ended BOTDA multi-parameter simultaneous measurement method and device, which has the following beneficial effects:

[0017] Physical quantity measurement is achieved by detecting the Brillouin frequency shifts of different modes in few-mode optical fibers, and simultaneous measurement of multiple physical quantities is achieved based on the different responsiveness of Brillouin frequency shifts of different modes to different physical quantities. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the composition of the measuring device of the present invention;

[0019] Figure 2 This is a schematic diagram of the structure of a photon lantern;

[0020] Figure 3 This is a schematic diagram of the SBS process in few-mode optical fibers;

[0021] The reference numerals in the figure represent: LD, narrow linewidth laser; PMC, polarization-maintaining coupler; MG, microwave generator; EOM1, first electro-optic modulator; PG, pulse signal source; EOM2, second electro-optic modulator; EDFA1, first erbium-doped fiber amplifier; FBG1, first grating filter; PS1, first polarization scrambler; EDFA2, second erbium-doped fiber amplifier; FBG2, second grating filter; PS2, second polarization scrambler; CO, optical coupler; OC1, first optical circulator; OC2, second optical circulator; OC3, third optical circulator; PL, photon lantern; FMF, few-mode fiber; CO2, second coupler; OF, optical filter; PD, photodetector; DAQ, data acquisition card; PC, computer. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0023] The first embodiment, as Figures 1 to 3 As shown, the present invention provides a technical solution: a single-ended BOTDA multi-parameter simultaneous measurement method and device, a narrow linewidth laser LD is used as a laser source, and its output optical signal is divided into two paths after passing through a polarization-maintaining coupler PMC: the first optical signal is driven by a microwave generator MG to achieve double-sideband modulation of the suppressed carrier by the first electro-optical modulator EOM1, and the output frequency is ν0±ν m The microwave modulated continuous light is then amplified by the first erbium-doped fiber amplifier EDFA1, and then the carrier and spontaneous radiation noise are filtered out by the first grating filter FBG1, and the polarization state is disturbed by the first polarization scrambler PS1; the second optical signal is pulse modulated by the second electro-optical modulator EOM2 driven by the pulse signal source PG to generate a sensing pulse light with a center frequency of ν0, and then amplified by the second erbium-doped fiber amplifier EDFA2, and then the spontaneous radiation noise is filtered out by the second grating filter FBG2, and the polarization state is disturbed by the second polarization scrambler PS2; the first and second modulated optical signals are coupled by the optical coupler CO to output a sensing pulse light with a center frequency of ν0 and a frequency of ν0±ν mThe synthesized optical signal of microwave modulated continuous light; the synthesized light enters the three single-mode fiber ports of the photon lantern PL through the first optical circulator OC1, the second optical circulator OC2, and the third optical circulator OC3 respectively, at which time mode conversion occurs, and the converted mode enters the few-mode fiber FMF through a single few-mode fiber port of PL; at this time, the back-Rayleigh scattered light (i.e., ν0±ν m The ν0 frequency component) is used as the detection light to produce stimulated Brillouin scattering with the sensing pulse (i.e., the ν0 frequency component) as the pump light; the detection light carrying the stimulated Brillouin scattering information returns to the PL, and the detection lights of different modes are respectively extracted from the three single-mode optical fiber ports, and the upper sideband of the detection light is filtered out by the optical filter OF, and then enters the photodetector PD for detection, and then the data is collected by the data acquisition card DAQ, and processed by the data processing unit in the computer PC. According to the sensitivity matrix of each physical quantity in different modes, distributed multi-parameter simultaneous measurement is realized.

[0024] The few-mode optical fiber in the present invention can transmit a limited number of orthogonal modes, has a larger core diameter and a higher SBS threshold, and can realize sensing measurements such as temperature, strain, and bending. By utilizing the interaction between its different optical modes and acoustic modes, it can overcome the problem of multi-parameter cross-sensitivity and realize simultaneous measurement of multiple parameters.

[0025] The single-ended BOTDA structure refers to the situation where the synthetic optical signal is injected into the sensing fiber from the same end of the optical fiber with a frequency of ν0±ν m The Rayleigh scattered light generated by the microwave modulated continuous light in the few-mode fiber is used as the probe light and the pulse light is used as the pump light. The two undergo stimulated Brillouin scattering, and there is no need to inject the probe light and the pump light from the two ends of the optical fiber respectively.

[0026] The schematic diagram of the structure of the photon lantern is as follows: Figure 2 As shown in the figure, the conversion process from the high-order mode to the fundamental mode with phase matching is shown in the figure. The two ends of the structure are a three-port single-mode fiber and a single-port few-mode fiber. The three-port single-mode fiber can transmit LP 01 LP 11a and LP 11b Three linear polarization modes.

[0027] It should be noted that Figure 1 and Figure 2 All use three-port photon lanterns, suitable for two-mode, four-mode, etc. including LP 01 LP 11a and LP 11b Three linear polarization modes of few-mode optical fiber; however, the present invention includes but is not limited to the use of three-port photon lanterns, and can also use photon lanterns with more ports, such as six-port photon lanterns that can transmit LP 01 LP11a LP 11b LP 21a LP 21b and LP 02 Six linear polarization modes.

[0028] The few-mode optical fiber may include LP 01 LP 11a and LP 11b Any type of few-mode fiber with three linear polarization modes.

[0029] The first electro-optic modulator EOM1 is driven by a microwave generator MG to generate a first-order sideband optical signal with a suppressed carrier. The frequency of the microwave generator MG is v m It is approximately the Brillouin frequency shift value of the few-mode fiber; the second electro-optic modulator EOM2 is driven by the pulse signal source PG to generate a sensing pulse light; the two together constitute a synthetic optical signal.

[0030] After the synthesized optical signal enters the few-mode fiber, the microwave modulated continuous light will generate multiple modes of backscattered Rayleigh light as the probe light, and the pulse light will excite multiple modes as the pump light. The probe light and pump light of different modes will cause intra-mode and inter-mode stimulated Brillouin scattering in the few-mode fiber, such as Figure 3 shown.

[0031] The generated intra-mode and inter-mode stimulated Brillouin scattering spectra will be superimposed, and the Brillouin scattering spectrum of each linear polarization mode will be extracted separately through the photon lantern.

[0032] The Brillouin scattering spectrum of each mode basically conforms to the Lorentz line shape, and the Brillouin frequency shift of each mode can be obtained through Lorentz fitting.

[0033] The Brillouin frequency shift of each mode can be expressed as

[0034]

[0035] Where n eff1 and n eff2 is the effective refractive index of the probe light and the pump light, λ1 and λ2 are the wavelengths of the probe light and the pump light, V A is the speed of sound in few-mode fiber.

[0036] The first polarization scrambler PS1 and the second polarization scrambler PS2 are used for scrambling the polarization states of the microwave modulated continuous light and the pulse light branches respectively, so as to reduce the influence of polarization fading and polarization state mismatch on the Brillouin scattering signal.

[0037] Photon lanterns can convert high-order modes into low-order modes, but the physical quantity information such as temperature or strain contained therein will be retained, and the temperature and strain information can be extracted by separating the Brillouin scattering spectrum of each mode.

[0038] The different effective refractive indices of different modes in few-mode optical fibers lead to different Brillouin frequency shifts of different modes, so different modes also respond differently to various physical quantities. In order to measure multiple physical quantities simultaneously, at least three optical modes with different sensitivities to each physical quantity are required.

[0039] For any three optical modes, the relationship matrix between their Brillouin frequency shift and the changes in various physical quantities can be expressed as

[0040]

[0041] where vV B1 、V B2 and V B3 They are the Brillouin frequency shifts of the three modes, C vT , C vε and C vd are the response coefficients of the Brillouin frequency shift to temperature, strain, and bending, respectively.

[0042] The three-port photon lantern used above to extract the three optical modes is only for the description of a specific embodiment, but the present invention is not limited to the above embodiment. The use of multiple optical modes, changing the mode multiplexer and demultiplexer, and the optical fiber type will not deviate from the protection scope of the present invention.

[0043] It should be noted that higher-order modes may be more sensitive to changes in physical quantities, that is, the combination of low-order modes and high-order modes can better distinguish different physical quantities.

[0044] The optical filter OF is placed before the photodetector PD to filter out unnecessary carrier waves with a frequency of ν0 and a frequency of ν0+ν. m The anti-Stokes component of the detection light forms the only part with frequency ν0-ν that carries the stimulated Brillouin scattering information. m of the detection light.

[0045] Note that the present invention includes but is not limited to using the back-Rayleigh scattered light generated by microwave modulated continuous light as the probe light to produce stimulated Brillouin scattering with the pump light, and also covers using the Fresnel reflected light generated at the end of the few-mode optical fiber as the probe light to produce stimulated Brillouin scattering with the pump light. Both schemes can achieve non-destructive, single-ended structure multi-parameter simultaneous measurement.

[0046] The present invention includes but is not limited to demodulating various physical quantities using a linear polarization mode, and also includes demodulating various physical quantities using a vector mode.

[0047] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A single-ended BOTDA multi-parameter simultaneous measurement method, characterized in that: A narrow linewidth laser is used to output two optical signals through a polarization-maintaining coupler. One optical signal is a continuous light with a changed frequency output through a continuous optical module, and the other optical signal is a pulse light with a high extinction ratio output through a pulse optical module. The synthesized optical signal formed by coupling the two optical signals through the optical coupler is incident from one end of the few-mode optical fiber after passing through the circulator and the photon lantern. The different modes of back-scattered Rayleigh light generated by the continuous light in the few-mode optical fiber are used as the detection light, and the different modes of pulsed light are used as the pump light. The pump light and the detection light of different modes undergo stimulated Brillouin scattering in the few-mode optical fiber. The photon lantern extracts the detection light carrying Brillouin scattering information of each mode, filters it through an optical filter and then detects it with a photodetector. The Brillouin frequency shift of different modes in the detection light is stored on a data acquisition card and demodulated by a computer, which can achieve simultaneous measurement of multiple physical quantities.

2. A single-ended BOTDA multi-parameter simultaneous measurement device, characterized in that: It includes a narrow linewidth laser, a polarization-maintaining coupler, a microwave modulated continuous optical module composed of a microwave generator, a first electro-optical modulator, a first erbium-doped fiber amplifier, a first grating filter, and a first polarization scrambler, a pulse optical module composed of a pulse signal source, a second electro-optical modulator, a second erbium-doped fiber amplifier, a second grating filter, and a second polarization scrambler, an optical coupler, a first optical circulator, a second optical circulator, a third optical circulator, a photon lantern, a few-mode optical fiber, an optical filter, a photodetector, a data acquisition card, and a computer; The narrow linewidth laser outputs two paths of continuous light with unchanged polarization state through a polarization-maintaining coupler, the first path of continuous light is connected to an optical coupler after passing through a continuous light module, and the second path of continuous light is connected to an optical coupler; The coupler output is connected to the first optical ports of the first optical circulator, the second optical circulator and the third optical circulator. The second optical port of the optical circulator is connected to the few-mode optical fiber via a photon lantern. The third optical port of the optical circulator is connected to the computer via an optical filter, a photoelectric detector and a data acquisition card in sequence.

3. A single-ended BOTDA multi-parameter simultaneous measurement device according to claim 2, characterized in that: The continuous optical module drives the first electro-optic modulator by a microwave generator to perform double-sideband modulation with suppressed carrier on the first optical signal output by the polarization-maintaining coupler, and the output frequency component is ν0±ν m The continuous light is amplified by the first erbium-doped fiber amplifier and filtered by the first grating filter to filter out the carrier and spontaneous emission noise, and then the polarization state is disturbed by the first polarization scrambler to reduce polarization fading; The ν m is the frequency of the microwave generator, approximately the Brillouin frequency shift value of the few-mode fiber, and ν0 is the center frequency of the narrow-linewidth laser.

4. A single-ended BOTDA multi-parameter simultaneous measurement device according to claim 2, characterized in that: The pulse light module drives the second electro-optic modulator by a pulse signal source to pulse modulate the second optical signal output by the polarization-maintaining coupler, and outputs a pulse light with a frequency component of . The signal is amplified by the second erbium-doped fiber amplifier and filtered by the second grating filter to filter out spontaneous radiation noise, and then the polarization state is disturbed by the second polarization scrambler to reduce polarization fading.

5. The single-ended BOTDA multi-parameter simultaneous measurement device according to claim 2, characterized in that: The photon lantern can convert high-order modes into low-order modes, but the physical quantity information such as temperature or strain contained therein will be retained, and the temperature and strain information can be extracted by separating the Brillouin scattering spectrum of each mode.

6. A single-ended BOTDA multi-parameter simultaneous measurement device according to claim 2, characterized in that: The optical filter OF is placed before the photodetector PD to filter out unnecessary carrier waves with a frequency of ν0 and a frequency of ν0+ν m The anti-Stokes component of the detection light forms the only part with frequency ν0-ν that carries the stimulated Brillouin scattering information. m of the detection light.

7. The single-ended BOTDA multi-parameter simultaneous measurement device according to claim 2, characterized in that: After the synthesized optical signal enters the few-mode optical fiber, the microwave modulated continuous light will generate multiple modes of backscattered Rayleigh light as detection light, and the pulse light will excite multiple modes as pump light. The detection light and pump light of different modes will undergo intra-mode and inter-mode stimulated Brillouin scattering in the few-mode optical fiber.

8. The single-ended BOTDA multi-parameter simultaneous measurement device according to claim 7, characterized in that: Different effective refractive indexes of different modes in the few-mode optical fiber lead to different Brillouin frequency shifts of different modes, so different modes also respond differently to various physical quantities. In order to measure multiple physical quantities simultaneously, at least three optical modes with different sensitivities to the physical quantities are required.

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