A distance-gated anti-interference optical frequency domain reflectometry distributed measurement device and method

Abstract

The application discloses a kind of distance gating anti-interference optical frequency domain reflection distributed measuring device and method, its device includes frequency-sweeping laser light source, first optical coupler, Mach-Zehnder modulator, circulator, detection optical fiber, polarization controller, second optical coupler, balanced photodetector and data measurement unit.Wherein, Mach-Zehnder modulator is configured as using pseudo-random spread spectrum coding technology to the input probe light is BPSK modulation.Through the above device and method, the application successfully solves the contradiction between long distance measurement and fast frequency sweep in traditional OFDR difficult to obtain.

Description

Technical Field

[0001] The present invention relates to the field of distributed optical fiber sensing and measurement technology, and more particularly to a distance-gated, anti-disturbance optical frequency domain reflection distributed measurement device and method. Background Art

[0002] Compared to traditional optical time-domain reflectometry, Optical Frequency Domain Reflectometry (OFDR) uses a linearly swept frequency-modulated continuous-wave laser signal to detect fiber links. The echo signal in the fiber is coherently mixed with the local oscillator signal and received. The frequency of the beat signal after coherent mixing is proportional to the delay difference of the echo signal relative to the local oscillator. Therefore, the spectrum of the beat signal can intuitively reflect the reflection and scattering conditions at different locations in the fiber. Thanks to its measurement mechanism, OFDR has high sensitivity and high-precision spatial positioning capabilities. It not only provides high spatial resolution and signal-to-noise ratio, but also has the potential for long-distance measurement. It can more accurately distinguish the location and nature of different disturbances and is widely used in medium- and short-distance optical network maintenance and distributed fiber sensing.

[0003] In recent years, with the increasing demand for applications such as infrastructure health monitoring and perimeter security, OFDR's potential in long-distance measurement and high spatial resolution has gradually attracted attention and become a research hotspot. High spatial resolution can accurately locate cracks, faults, or external intrusions in underground or submarine oil and gas pipelines. It also plays an important role in the safety monitoring of critical infrastructure such as bridges and railways, broadening the application prospects of OFDR in these scenarios requiring long-distance, high spatial resolution measurements.

[0004] However, in actual measurement scenarios, optical fibers are susceptible to environmental influences (such as mechanical vibration and acoustic noise), which can cause changes in the fiber's state. Especially when conducting long-distance measurements, a long sweep cycle (i.e., one OFDR measurement cycle) is often required to meet the requirement that the sweep cycle (i.e., one OFDR measurement cycle) be significantly longer than the fiber's round-trip delay. This makes it difficult to ensure that the fiber is unaffected by environmental changes during the measurement cycle. This degrades the spatial resolution of the OFDR trace and limits the maximum measurement distance range.

[0005] To enhance OFDR's resistance to environmental disturbances such as mechanical vibration and acoustic noise, increasing the frequency sweep speed is an effective approach. On the one hand, faster frequency sweeps result in larger beat signals. According to the Nyquist sampling theorem, higher beat frequencies require higher sampling rates. Consequently, as fiber length increases, the required sampling rate also increases, making real-time signal processing more difficult.

[0006] To address this issue, researchers have proposed an OFDR measurement technique based on bandpass filtering. This technique uses bandpass filters to divide the received beat signal into N distinct bandwidths, then downconverts each of these bandwidths to baseband through mixing. This reduces the required sampling rate by a factor proportional to the number of bandwidths divided. However, simultaneously measuring N bandwidths requires at least N-1 bandpass filters and corresponding mixers, along with a corresponding number of low-pass filters and analog-to-digital converters, adding to the receiver's complexity and system overhead. Furthermore, if a measurement cycle exceeds one sweep cycle—that is, encompasses multiple sweep cycles—it becomes impossible to distinguish between reflections from different sweep cycles, representing different distances. This leads to multi-cycle range ambiguity, and therefore typically only one sweep cycle can be included in a single measurement cycle. Given this limitation, and to meet the required round-trip delay for optical fiber propagation, long-distance measurements require a longer single sweep cycle, exacerbating the impact of environmental disturbances within the measurement cycle. Current bandpass filtering-based techniques also struggle to resolve this range ambiguity. Summary of the Invention

[0007] Aiming at the influence and degradation of environmental disturbance on measurement performance under long sweep period, and in order to overcome the contradiction between long distance measurement and fast sweep, the present invention proposes a distance-gated anti-disturbance optical frequency domain reflection distributed measurement device and method.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] On one hand, the present invention discloses a range-gated, anti-disturbance optical frequency domain reflectometry distributed measurement device. In one embodiment, the device includes a swept-frequency laser light source. The swept-frequency laser light generated by the swept-frequency laser light source is divided into two beams by a first optical coupler, one of which is input into a Mach-Zehnder modulator as a probe light, and the other is input into a polarization controller as a local oscillator light.

[0010] The Mach-Zehnder modulator is configured to perform BPSK modulation on the input probe light using a pseudo-random spread spectrum coding technique, the BPSK-modulated probe light is input to the input port of the circulator, the forward output port of the circulator is connected to a single-mode optical fiber, and the isolation port of the circulator is connected to an input end of the second optical coupler;

[0011] The polarization controller is configured to adjust the polarization state of the input local oscillation light, and the adjusted local oscillation light is input into the other input end of the second optical coupler;

[0012] The output end of the second optical coupler is connected to the balanced photodetector and the data measurement unit in sequence.

[0013] Preferably, in the above embodiment, the sweep frequency range of the sweep frequency laser is 100 MHz, and the sweep frequency time T sweep =10μs.

[0014] Preferably, in the above embodiment, the first optical coupler comprises a 90:10 optical coupler, and of the two swept laser beams, 90% is used as detection light and 10% is used as local oscillator light.

[0015] Preferably, in the above embodiment, the Mach-Zehnder modulator performs BPSK modulation on the input detection light by using a pseudo-random spread spectrum coding technology through a signal generator and an MZM bias controller connected thereto.

[0016] Preferably, in the above embodiment, the Mach-Zehnder modulator includes an MX-LN-05 electro-optical intensity modulator.

[0017] Preferably, in the above embodiment, the data measurement unit includes a data acquisition module and a data distance gating module; wherein, the data measurement unit is used to convert the analog beat frequency electrical signal output by the balanced photodetector into a digital electrical signal; the data distance gating module is used to decode the converted digital electrical signal and use the decoded digital electrical signal to realize distance measurement.

[0018] Another aspect of the present invention discloses a distance-gated anti-disturbance optical frequency domain reflectometry distributed measurement method, which is characterized by comprising the following steps:

[0019] Step 1: Use the pseudo-random code sequence p(t) to drive the MZM to implement BPSK modulation on the probe light. The pseudo-random code sequence p(t) is a maximum length m-code sequence:

[0020] S0=cos(2π(υ0+f0)t+πγt 2 )p(t),

[0021] Wherein, υ0 represents the optical frequency, f0 represents the initial sweep frequency of the probe light, γ represents the sweep speed of the probe light, and p(t) represents the m-code sequence signal;

[0022] Step 2: Obtain the time domain beat signal S after the BPSK modulated detection light and the local oscillator light interfere with each other i :

[0023]

[0024] Among them, τ ij represents the time delay corresponding to each Rayleigh scattering point of a single-mode optical fiber; i represents the i-th optical fiber segment selected by the pseudo-random code sequence, and j represents the j-th Rayleigh scattering point in the optical fiber segment;

[0025] Step 3: Use the delayed pseudo-random code sequence Real-time decoding of the corresponding optical fiber section:

[0026]

[0027] Step 4: Perform Fourier transform on the decoded fiber segment to obtain the corresponding fiber segment spectrum:

[0028]

[0029] Step 5: Splice all the optical fiber segment spectra to obtain a complete optical fiber trace.

[0030] Furthermore, in the above method, the pseudo-random code sequence further includes a Gray code sequence, an A1 code sequence or an A2 code sequence.

[0031] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a range-gated anti-disturbance optical frequency domain reflectometry distributed measurement device and method, which has the following beneficial effects:

[0032] The present invention uses OFDR measurement with a short sweep period, which has a fast sweep speed and effectively enhances the resistance to environmental disturbances and acoustic noise.

[0033] The present invention successfully resolves the contradiction between long-distance measurement and fast frequency sweep in traditional OFDR. Therefore, the measurement distance is no longer limited by the frequency sweep period, thereby realizing long-distance measurement. At the same time, the required sampling rate can be reduced, reducing hardware pressure.

[0034] The present invention can simultaneously demodulate different distance segments during long-distance measurement, thereby increasing the real-time performance of the system and improving the efficiency and flexibility of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0036] Figure 1 This is a structural schematic diagram of the distance-gated anti-disturbance optical frequency domain reflection distributed measurement device provided by the present invention.

[0037] Figure 2 This is a flow chart of the distance-gated anti-disturbance optical frequency domain reflection distributed measurement method provided by the present invention.

[0038] Figure 3This is a schematic diagram of the principle of the distance-gated anti-disturbance optical frequency domain reflection distributed measurement method provided by the present invention.

[0039] Figure 4 The spectrum diagram of the distance-gated anti-disturbance optical frequency domain reflection distributed measurement device measured at different distances of 4km optical fiber provided by the embodiment of the present invention, wherein Figure 4 (a) Spectrum diagram showing the optical fiber segment with a gating distance of 0-1 km; Figure 4 (b) shows the spectrum of the optical fiber segment with a gating distance of 1-2 km; Figure 4 (c) shows the spectrum of the optical fiber segment with a gating distance of 2-3 km; Figure 4 (d) shows the spectrum of the optical fiber segment with a selection distance of 3-4 km. In the figure, the horizontal axis represents the frequency value of each frequency component in the signal, and the vertical axis represents the intensity or amplitude of each frequency component in the signal.

[0040] Figure 5 This is a comparison diagram of the energy spectra of the range-gated anti-disturbance optical frequency domain reflection distributed measurement method provided by the embodiment of the present invention and the traditional slow-scan optical frequency distributed measurement method, where Figure 5 (a) The energy spectrum obtained by measuring 4 km of optical fiber according to the present invention; Figure 5 (b) The energy spectrum obtained by measuring 4 km of optical fiber using traditional slow-scan OFDR. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0042] The embodiment of the present invention first discloses a distance-gated anti-disturbance optical frequency domain reflection distributed measurement device, such as Figure 1 As shown, it includes a swept laser light source 1, a first optical coupler 2, a Mach-Zehnder modulator (MZM) 3, a signal generator 4, an MZM bias controller 5, a circulator 6, a detection fiber 7, a polarization controller 8, a second optical coupler 9, a balanced photodetector 10, a data acquisition module 11 and a data range selection module 12.

[0043] In the above-mentioned distance-gated anti-disturbance optical frequency domain reflection distributed measurement device, the swept laser light source 1 is used to provide the device with a swept laser light source as a detection light and a local oscillator light. The swept laser generated by the swept laser light source 1 is divided into two beams through the first optical coupler 2, one of which is input into the Mach-Zehnder modulator 3 as the detection light, and the other is input into the polarization controller 8 as the local oscillator light.

[0044] In the embodiment of the present invention, the swept laser light source 1 generates a linear frequency modulated continuous wave. In a specific embodiment, the sweep range of the swept laser light source 1 is 100 MHz, and the sweep period T is 100 MHz. sweep = 10μs. Under these sweep parameters, using conventional OFDR measurement methods, the maximum measurable fiber length is 1km, corresponding to a maximum beat frequency of 100MHz. If the length exceeds 1km, distance ambiguity will occur. To address the distance ambiguity issue, the present invention proposes a distance gating technique that combines coding discrimination. It should be noted that in the present invention, the sweep parameters of the swept laser light source 1 are not fixed and can be used according to specific requirements.

[0045] In the embodiment of the present invention, the swept laser emitted by the swept laser light source 1 is split by the first optical coupler 2. Specifically, the first optical coupler 2 can select a 90:10 optical coupler, in which 90% of the swept laser after splitting is used as detection light and 10% is used as local oscillator light.

[0046] In Mach-Zehnder modulator 3, a pseudo-random noise (PRN) code sequence of a certain length is input into the RF port of Mach-Zehnder modulator 3, thereby performing phase modulation of the probe light between 0 and π, i.e., BPSK modulation. The BPSK-modulated probe light is connected to port a (input port) of circulator 6 (a three-port polarization-maintaining fiber circulator) via the output of Mach-Zehnder modulator 3. Port b (input port) of circulator 6 is connected to detection fiber 7. The coded signal (BPSK-modulated probe light) output from port b (forward output port) of circulator 6 divides detection fiber 7 into segments 1, 2, ..., N. The probe light generates backscattering in detection fiber 7, and the scattered echo light signal is input to one input port of a second optical coupler 9 via port c (isolation port) of circulator 6.

[0047] The Mach-Zehnder modulator 3 can use the MX-LN-05 electro-optical intensity modulator or other types of MZM. The MX-LN-05 electro-optical intensity modulator can modulate the swept-frequency laser with a bandwidth of 5 GHz in the 1550 nm band. The half-wave voltage V π About 3.5v.

[0048] The local oscillator light obtained by splitting the swept laser through the first optical coupler 2 is input into the polarization controller 8. The polarization state of the local oscillator light is polarized by the polarization controller 8 so that the polarization state of the local oscillator path matches that of the detection path. The local oscillator light after polarization adjustment is input into the other input end of the second optical coupler 9.

[0049] In the second optical coupler 9, the polarization-adjusted local oscillator light and the echo light signal in the detection optical fiber are combined to form a delayed interference light signal, and the delayed interference light signal is input into the balanced photodetector 10. Specifically, the second optical coupler 9 can select a 50:50 optical coupler.

[0050] The balanced photodetector 10 is connected to the output end of the second optical coupler 9 , converts the delayed interference optical signal into a beat frequency electrical signal, and inputs the beat frequency electrical signal into the data acquisition module 11 .

[0051] The balanced photodetector 10 of the present invention converts optical signals into electrical signals. Specifically, the balanced photodetector 10 can convert delayed interferometric optical signals in the 800-1700nm wavelength range and a 3dB bandwidth of DC-200MHz. Alternatively, the balanced photodetector 10 can be replaced with another dual-balanced detector that meets system performance requirements.

[0052] In the embodiment of the present invention, the detection optical fiber 7 may be a common single-mode optical fiber, or other special light, such as FBG optical fiber (fiber grating).

[0053] The data acquisition module 11 is used to sample the beat frequency electrical signal. The sampling frequency of the data acquisition module 11 only needs to meet the signal sampling requirements of each optical fiber section, that is, the sampling frequency is greater than twice the maximum beat frequency corresponding to each optical fiber section.

[0054] In the present invention, the data acquisition module 11 needs to convert the analog electrical signal into a digital signal before sampling the beat frequency signal. The sampling frequency of the data acquisition module can be set to 400 MHz, or other parameters can be used according to specific needs.

[0055] The output end of the data acquisition module 11 is connected to the input end of the data distance gating module 12. The data distance gating module 12 is used to process and analyze the sampled beat frequency electrical signal, perform distance domain splicing on N segments of beat frequency electrical signals, and obtain the complete optical frequency domain reflection beat frequency signal spectrum of the detection optical fiber 7.

[0056] It should be noted that the data distance gating module 12 can be a software demodulator capable of achieving distance gating of the complete optical frequency domain reflection beat signal of the detection optical fiber 7, or it can be a hardware-based demodulator. Specifically, software demodulation of distance gating refers to demodulating the beat signal after conversion by an analog-to-digital converter using software in a computer or host computer. For example, after acquiring the beat signal through an oscilloscope, programming software such as MATLAB or Python is used in the host computer to demodulate the different fiber segments of the beat signal to pass the corresponding coded signal. Hardware demodulation refers to demodulating the different fiber segments of the beat signal using a hardware module capable of signal phase demodulation, such as a field programmable gate array (FPGA).

[0057] In an embodiment of the present invention, the pseudo-random noise (PRN) code sequence used by the Mach-Zehnder modulator 3 for BPSK modulation is provided by a signal generator 4 connected thereto. The signal generator 4 is capable of sending a PRN code sequence consisting of digital 1 and -1 codes, where -1 corresponds to a modulation phase 0 in BPSK modulation and 1 corresponds to a modulation phase π in BPSK modulation.

[0058] In the present invention, the signal generator is mainly used to realize the generation of pseudo-random noise code sequence. The pseudo-random noise (PRN) code sequence generated in the present invention can adopt maximum length sequence (Maximal length sequences, m code sequence), Gray code sequence, A1 code sequence, A2 code sequence, etc.

[0059] Specifically, when the pseudo-random noise sequence generated by the signal generator is an m-code sequence, the autocorrelation of the m-code sequence is equivalent to the code length and is determined by the bit depth of the code. Its autocorrelation coefficient is 2 n -1, the mutual correlation coefficient is -1. In this embodiment, the code length l of the m code sequence is 2 8 -1, chip period T chip The sweep period T of the swept laser light source 1 sweep Correspondingly, in this embodiment, T chip =T sweep =10μs. When the optical fiber segment length of the distance gate is 1km, through the autocorrelation characteristics of the m code combined with the BPSK coding technology, the maximum measurement length is extended to: l*T chip *d = 255 km, where d is the length of the optical fiber segment.

[0060] Optionally, a faster m-code sequence can be used according to specific needs to divide the detection fiber into smaller units to further reduce the sampling rate (i.e., by using a shorter chip period T chip To divide the detection fiber into shorter sections, and then combine the relationship between OFDR distance and frequency to collect the detection signal at a lower sampling rate), such as setting the chip period of the m code to Where M is a positive integer. However, the sampling frequency should be greater than twice the maximum beat frequency corresponding to each fiber segment.

[0061] Optionally, since the autocorrelation coefficient of the m code is 2 n -1, the mutual correlation coefficient is -1, and the inter-code crosstalk is limited by the length of the m-code; therefore, a longer m-code sequence or an m-code pattern with better correlation can be used according to specific needs to further suppress the inter-code crosstalk.

[0062] In the embodiment of the present invention, the Mach-Zehnder modulator 3 is further connected to an MZM bias controller 5, which is used to provide a bias voltage V for the Mach-Zehnder modulator 3. B , which is equal to the MZM half-wave voltage V π , that is, to maintain the bias of the Mach-Zehnder modulator MZM in the null working mode.

[0063] When the Mach-Zehnder modulator has an ideal extinction ratio, the output optical power should be zero in Null mode. Specifically, in Null mode, if no drive signal is input to the Mach-Zehnder modulator (i.e., the voltages on the two arms of the Mach-Zehnder modulator are the same), the light waves in the two output arms of the Mach-Zehnder modulator cancel each other out, resulting in no optical power at the output end, and the output optical power is zero.

[0064] In the embodiment of the present invention, the Mach-Zehnder modulator uses a pseudo-random noise (PRN) code sequence for modulation. In order to prevent the operating point of the Mach-Zehnder modulator 3 from deviating from the null operating mode and thus maintaining the initial state of the output optical power at zero, the input PRN code is required to have no DC bias (i.e., the average voltage of the PRN code sequence input to the Mach-Zehnder modulator is zero); at the same time, the peak-to-peak voltage is less than 2V. π (That is, the maximum voltage change of the driving signal will not exceed twice the MZM half-wave voltage. This ensures that the Mach-Zehnder modulator will not exceed its linear operating area during the entire modulation process, thereby avoiding nonlinear effects and ensuring modulation quality).

[0065] The present invention also provides a distance-gated anti-disturbance optical frequency domain reflection measurement method, comprising the following steps:

[0066] First, the swept-frequency laser light source is divided into detection light and local oscillator light through the first fiber coupler. The detection light passes through the Mach-Zehnder modulator (MZM). The MZM bias controller maintains the Mach-Zehnder modulator (MZM) in the Null point working mode and uses the input pseudo-random noise code sequence to drive the Mach-Zehnder modulator to perform BPSK modulation on the input continuous detection light.

[0067] During BPSK modulation, a pseudo-random noise code sequence (PRN code sequence) of -1 corresponds to a modulation phase of 0, and a PRN code sequence of 1 corresponds to a modulation phase of π.

[0068] Second, the BPSK-modulated probe light signal is injected into a single-mode optical fiber serving as the detection fiber through a circulator. The single-mode optical fiber is divided into segments 1, 2, ..., N by the probe light modulated with a pseudo-random noise code sequence. Simultaneously, the probe light generates post-Rayleigh scattering in the single-mode optical fiber.

[0069] Third, the Rayleigh scattered light signal reflected back from the single-mode optical fiber is combined with the local oscillator light to form a delayed interference light signal, which then enters the balanced photodetector for heterodyne reception and converts the light signal into a beat frequency electrical signal.

[0070] Fourth, the beat frequency electrical signal output by the balanced detector is collected using a data acquisition module. The sampling frequency of the data acquisition module only needs to be greater than twice the maximum beat frequency corresponding to the first optical fiber section.

[0071] Fifth, generate the PRN code sequence corresponding to the delay of the optical fiber segment, that is, delay the PRN code sequence by τ1, τ2..., τ N , decode the beat frequency electrical signal output by the balanced photodetector. τ1, τ2…, τ N These correspond to the round-trip time of the detection light signal traveling through fiber sections 1, 2, ..., N, respectively.

[0072] Sixth, use the PRN code sequence after a specific delay to decode the fiber section corresponding to the delay, Fourier transform to obtain the corresponding fiber section spectrum, and then splice the various fiber sections to obtain the complete fiber length trace.

[0073] The length of the single-mode optical fiber used as the detection optical fiber in the above embodiment is 4 km.

[0074] Combine Figure 2-Figure 3 The specific implementation steps of the distance-gated anti-disturbance optical frequency domain reflection measurement method disclosed in the present invention are as follows:

[0075] S1. Use a pseudo-random noise code sequence p(t) to drive a Mach-Zehnder modulator to perform BPSK (Binary Phase Shift Keying) modulation on the probe light. In this embodiment, the pseudo-random noise code sequence uses a maximum length m code sequence:

[0076] S0=cos(2π(υ0+f0)t+πγt 2 )p(t),

[0077] Wherein, υ0 represents the optical frequency of the probe light, f0 represents the initial sweep frequency of the swept laser light source, γ represents the sweep speed of the swept laser light source, and p(t) represents the m-code sequence signal;

[0078] S2, collect the time domain beat frequency signal S after interfering with the local oscillator light i :

[0079]

[0080] Among them, τ ijrepresents the time delay corresponding to each Rayleigh scattering point of the single-mode optical fiber; i represents the i-th fiber section selected by the m code sequence, and j represents the j-th Rayleigh scattering point in the fiber section.

[0081] S3, using the m code sequence with a specific delay real-time decoding of the specific fiber section i to obtain time-domain data of the corresponding optical signal on the specific fiber section i:

[0082]

[0083] S4, Fourier transforming the time-domain data of each fiber section i to obtain the corresponding fiber section spectrum:

[0084]

[0085] Figure 4 The frequency spectrum graphs of different distances obtained by selecting 4km single-mode optical fiber are shown in the following figures, wherein Figure 4 (a) represents the frequency spectrum graph of the fiber section with a selected distance of 0-1km; Figure 4 (b) represents the frequency spectrum graph of the fiber section with a selected distance of 1-2km; Figure 4 (c) represents the frequency spectrum graph of the fiber section with a selected distance of 2-3km; Figure 4 (d) represents the frequency spectrum graph of the fiber section with a selected distance of 3-4km; in the figures, the abscissa represents the frequency value of each frequency component in the signal, and the ordinate represents the intensity or amplitude of each frequency component in the signal.

[0086] S5, splicing the fiber section spectra of all fiber sections i to obtain the complete optical frequency domain reflection beat frequency signal spectrum.

[0087] In the above measurement method, the m code as a pseudo-random noise code sequence is input through a signal generator and drives the MZM (Mach-Zehnder modulator), thereby realizing BPSK modulation on the probe light signal. Then, in subsequent decoding, the m code signal is used to decode the beat frequency signal, and after a specific delay of the m code sequence, the decoding of the specific single-mode fiber section can be realized.

[0088] In the above embodiment of the application, the single-mode optical fiber as the detection optical fiber is divided into equal-length sections, which can realize long-distance measurement and successfully solve the contradiction between long-distance measurement and fast frequency sweeping in OFDR.

[0089] In order to verify the superiority of the application, Figure 5A comparison chart of the energy spectra of the range-gated anti-disturbance optical frequency domain reflection distributed measurement method and the traditional slow-scanning optical frequency distributed measurement method is given. Figure 5 (a) The energy spectrum obtained by measuring 4 km of optical fiber according to the present invention; Figure 5 (b) The energy spectrum obtained by measuring 4 km of optical fiber using traditional slow-scan OFDR.

[0090] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0091] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A range-gated, anti-disturbance optical frequency domain reflectometry distributed measurement device, characterized in that: It includes a swept-frequency laser light source, wherein the swept-frequency laser generated by the swept-frequency laser light source is divided into two beams through a first optical coupler, one beam is input into a Mach-Zehnder modulator as a detection light, and the other beam is input into a polarization controller as a local oscillator light; The Mach-Zehnder modulator is configured to perform BPSK modulation on the input probe light using a pseudo-random spread spectrum coding technique. The BPSK-modulated probe light is input to the input port of the circulator. The forward output port of the circulator is connected to the detection optical fiber. The isolation port of the circulator is connected to an input end of a second optical coupler. The coded signal output by the forward output port of the circulator divides the detection optical fiber into 1, 2, ..., N segments. The Mach-Zehnder modulator, through a signal generator and an MZM bias controller connected thereto, performs BPSK modulation on the input probe light using the pseudo-random spread spectrum coding technique. The polarization controller is configured to adjust the polarization state of the input local oscillation light, and the adjusted local oscillation light is input into the other input end of the second optical coupler; The output end of the second optical coupler is connected to the balanced photodetector and the data measurement unit in sequence; The data measurement unit includes a data acquisition module and a data distance gating module; wherein, the data measurement unit is used to convert the analog beat frequency electrical signal output by the balanced photodetector into a digital electrical signal; the data distance gating module is used to decode the converted digital electrical signal and use the decoded digital electrical signal to achieve distance measurement; specifically, the data distance gating module performs distance domain splicing on N segments of beat frequency electrical signals to obtain the complete optical frequency domain reflection beat frequency signal spectrum of the detection optical fiber.

2. The distance-gated anti-disturbance optical frequency domain reflectometry distributed measurement device according to claim 1, characterized in that: The sweep range of the swept laser light source is 100 MHz, and the sweep time T sweep =10μs.

3. The range-gated anti-disturbance optical frequency domain reflectometry distributed measurement device according to claim 1, characterized in that: The first optical coupler comprises a 90:10 optical coupler, and of the two swept-frequency laser beams, 90% is used as detection light and 10% is used as local oscillator light.

4. The distance-gated anti-disturbance optical frequency domain reflectometry distributed measurement device according to claim 1, characterized in that: The Mach-Zehnder modulator includes an MX-LN-05 electro-optical intensity modulator.

5. The distance-gated, anti-disturbance optical frequency domain reflectometry distributed measurement method according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Use the pseudo-random code sequence p(t) to drive the MZM to implement BPSK modulation on the probe light. The pseudo-random code sequence p(t) is a maximum length m-code sequence: S0=cos(2π(υ0+f0)t+πγt 2 )p(t), Wherein, υ0 represents the optical frequency, f0 represents the initial sweep frequency of the probe light, γ represents the sweep speed of the probe light, and p(t) represents the m-code sequence signal; Step 2: Obtain the time domain beat signal S after the BPSK modulated detection light and the local oscillator light interfere with each other i : Among them, τ ij represents the time delay corresponding to each Rayleigh scattering point of a single-mode optical fiber; i represents the i-th optical fiber segment selected by the pseudo-random code sequence, and j represents the j-th Rayleigh scattering point in the optical fiber segment; Step 3: Use the delayed pseudo-random code sequence Real-time decoding of the corresponding optical fiber section: Where, T chip Indicates the chip period; Step 4: Perform Fourier transform on the decoded fiber segment to obtain the corresponding fiber segment spectrum: Step 5: Splice all the optical fiber segment spectra to obtain a complete optical fiber trace.

6. The range-gated anti-disturbance optical frequency domain reflectometry distributed measurement method according to claim 5, characterized in that: The pseudo-random code sequence also includes a Gray code sequence, an A1 code sequence or an A2 code sequence.

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