Range-gated anti-disturbance optical frequency domain reflection distributed measurement device and method

Abstract

The invention discloses a range gating anti-disturbance optical frequency domain reflection distributed measurement device and method. The device comprises a sweep frequency laser light source, a first optical coupler, a Mach-Zehnder modulator, a circulator, a detection optical fiber, a polarization controller, a second optical coupler, a balanced photoelectric detector and a data measurement unit. Wherein the Mach-Zehnder modulator is configured to perform BPSK modulation on the input probe light by using a pseudo-random spread spectrum coding technology. By means of the device and the method, the contradiction that long-distance measurement and fast frequency sweeping are difficult to achieve at the same time in a traditional OFDR is successfully solved.

Description

Technical Field

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

[0002] Compared with the traditional optical time domain reflectometry technology, the optical frequency domain reflectometry (OFDR) technology uses a linearly swept frequency modulated continuous wave laser signal to detect the optical fiber link, and receives the echo signal in the optical fiber by coherent mixing with the local oscillator signal. 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 positions in the optical fiber. Thanks to its measurement mechanism, OFDR has high sensitivity and high-precision spatial positioning capabilities. It can not only provide 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 optical fiber sensing.

[0003] In recent years, with the increasing demand for applications such as infrastructure health monitoring and perimeter security, the potential of OFDR in long-distance measurement and high spatial resolution applications 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, and plays an important role in the safety monitoring of key infrastructure such as bridges and railways, broadening the application prospects of OFDR in these scenarios requiring long-distance and high spatial resolution measurements.

[0004] However, in actual measurement scenarios, optical fibers are easily affected by the complex surrounding environment (such as mechanical vibration, acoustic noise, etc.), causing the state of the optical fiber to change. Especially when performing long-distance measurements, in order to meet the requirement that the sweep cycle (i.e., one measurement cycle of OFDR) is much longer than the round-trip delay of the optical fiber, a longer sweep cycle is often required. Therefore, it is difficult to ensure that the optical fiber is not affected by changes in the complex external environment during the measurement cycle, which will deteriorate the spatial resolution of the OFDR trace and restrict the maximum measurement distance range.

[0005] In order to enhance OFDR's resistance to environmental disturbances such as mechanical vibration and acoustic noise, increasing the frequency sweep speed is an effective method. On the one hand, fast frequency sweeping will lead to larger beat frequency signals. According to the Nyquist sampling theorem, higher beat frequency requires higher sampling rate. Therefore, as the length of the optical fiber increases, the sampling rate requirement also increases accordingly, making real-time signal processing difficult.

[0006] In order to solve this problem, researchers proposed an OFDR measurement technology based on bandpass filtering, which uses bandpass filters to divide the received beat signal into N different bandwidth parts, and then down-converts each independent bandwidth part to baseband through mixing. This means that the required sampling rate can be reduced by a proportional factor equal to the number of divided bandwidths. However, simultaneous measurement of N bandwidth parts requires at least N-1 bandpass filters and corresponding mixers, and needs to be coordinated with a corresponding number of low-pass filters and analog-to-digital conversion, which additionally increases the complexity and system overhead of the receiver. On the other hand, if a measurement cycle exceeds one sweep cycle, that is, it contains multiple sweep cycles, it is impossible to distinguish the reflected signals from different sweep cycles, that is, different distances, resulting in multi-cycle distance ambiguity. Therefore, generally only one sweep cycle can be included in a single measurement cycle. Under this limitation, in order to meet the requirements of the round-trip delay during propagation in the optical fiber, a longer single sweep cycle is required to achieve long-distance measurement, which in turn exacerbates the impact of environmental disturbances on the measurement results during the measurement cycle, and the current technical methods based on bandpass filtering are also difficult to solve the distance ambiguity problem. Summary of the invention

[0007] In view of 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 solution:

[0009] On one hand, the present invention discloses a distance-gated anti-disturbance optical frequency domain reflection distributed measurement device. In one embodiment, the device includes a swept-frequency laser light source. The swept-frequency laser generated by the swept-frequency laser light source is divided into two beams through a first optical coupler, one of which is input into a Mach-Zehnder modulator as a detection 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 detection light using pseudo-random spread spectrum coding technology, the BPSK modulated detection light is input to the input port of the circulator, the forward output port of the circulator is connected to the 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 oscillator light, and the adjusted local oscillator light is input to another 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-frequency 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 implements BPSK modulation of 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 achieve distance measurement.

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

[0019] Step 1: Use a pseudo-random code sequence p(t) to drive the MZM to implement BPSK modulation on the detection 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 frequency sweep of the detection light, γ represents the frequency sweep speed of the detection 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 segment:

[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 also 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 distance-gated anti-disturbance optical frequency domain reflection distributed measurement device and method, which has the following beneficial effects:

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

[0033] The present invention successfully solves the contradiction between long-distance measurement and fast frequency sweep in traditional OFDR, so the measurement distance is no longer limited by the frequency sweep period, thereby realizing long-distance measurement, while reducing the required sampling rate and reducing hardware pressure.

[0034] The present invention can simultaneously demodulate different distance sections 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

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

[0037] Figure 2 A schematic 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 frequency spectrum of the distance-gated anti-disturbance optical frequency domain reflection distributed measurement device provided in the embodiment of the present invention measuring different distances of 4km optical fiber, wherein Figure 4 (a) shows the spectrum of 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) is a spectrum diagram showing a fiber section with a selection distance of 3-4 km; in the diagram, 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 A comparison diagram of the energy spectra of the range-gated anti-disturbance optical frequency domain reflection distributed measurement method provided by an embodiment of the present invention and the traditional slow-scanning optical frequency distributed measurement method, wherein Figure 5 (a) The energy spectrum obtained by measuring 4 km of optical fiber according to the present invention; Figure 5 (b) is the energy spectrum obtained by measuring 4 km optical fiber using traditional slow-scan OFDR. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work 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-frequency 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 optical fiber 7, a polarization controller 8, a second optical coupler 9, a balanced photodetector 10, a data acquisition module 11 and a data distance selection module 12.

[0043] In the above-mentioned distance-gated anti-disturbance optical frequency domain reflection distributed measurement device, the swept-frequency laser light source 1 is used to provide the device with a swept-frequency laser light source as a detection light and a local oscillator light. The swept-frequency laser generated by the swept-frequency laser light source 1 is divided into two beams through a 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 swept laser light source 1 has a sweep range of 100 MHz and a sweep period T. sweep =10μs. Under this scanning parameter, if the traditional OFDR measurement method is used, the maximum measurable fiber length is 1km, and the corresponding maximum beat frequency is 100MHz. If the length exceeds 1km, distance ambiguity will occur. In order to solve the distance ambiguity problem, the present invention proposes a distance gating technology combined with coding distinction. It should be pointed out that in the present invention, the scanning parameters of the swept laser light source 1 are not fixed, and other sweep parameters can also be used according to specific needs.

[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 the Mach-Zehnder modulator 3, a pseudo-random noise (PRN) code sequence of a certain length is input to the radio frequency port of the Mach-Zehnder modulator 3, so as to perform phase modulation of 0 and π on the detection light, i.e., BPSK modulation. The detection light after BPSK modulation is connected to the a port (input port) of the circulator 6 (three-port polarization-maintaining fiber circulator) through the output end of the Mach-Zehnder modulator 3, and the b port (input port) of the circulator 6 is connected to the detection optical fiber 7. The coded signal (BPSK-modulated detection light) output by the b port (forward output port) of the circulator divides the detection optical fiber 7 into 1, 2, ..., N segments, and the detection light generates backward Rayleigh scattering in the detection optical fiber 7. The scattered echo optical signal is input to an input end of the second optical coupler 9 through the c port (isolation port) of the circulator 6.

[0047] Mach-Zehnder modulator 3 can use MX-LN-05 electro-optic intensity modulator or other types of MZM; MX-LN-05 electro-optic intensity modulator can modulate the swept frequency laser with a wavelength of 1550nm and a bandwidth of 5GHz. The half-wave voltage V π It is 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, and the polarization state of the local oscillator light is polarization-adjusted in 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 optical signal in the detection optical fiber are combined to form a delayed interference optical signal, and the delayed interference optical 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 signal into the data acquisition module 11 .

[0051] The balanced photodetector 10 of the present invention is a detector that converts optical signals into electrical signals. The specifically selected balanced photodetector 10 can convert delayed interference optical signals with a wavelength range of 800-1700nm and a 3dB bandwidth of DC-200MHz. In addition, the balanced photodetector 10 can also be replaced by other dual balanced detectors that meet the system performance.

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

[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 requirement 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 selection module 12. The data distance selection 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 demodulation that can realize the distance gating of the complete optical frequency domain reflection beat signal of the detection optical fiber 7, or it can be a hardware-based demodulation. Specifically, the software demodulation of distance gating refers to the demodulation of the beat signal after conversion by the analog-to-digital converter using the software in the computer or the host computer. For example, after the beat signal is collected by an oscilloscope, the programming software such as matlab, python, etc. 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 the demodulation of the different fiber segments of the beat signal using a hardware module that can realize phase demodulation of the signal, 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, and the signal generator 4 is capable of sending a PRN code sequence composed 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] The signal generator in the present invention 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 sequences (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 distance-gated optical fiber segment length 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, d is the length of the optical fiber segment.

[0060] Optionally, a faster m-code sequence can be used according to specific requirements 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, use a lower sampling rate to collect the detection signal), 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, and the MZM bias controller 5 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, maintaining 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 the Null mode; specifically, in the Null working mode, if no driving 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 of the two output arms of the Mach-Zehnder modulator cancel each other out, so there is 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 working point of the Mach-Zehnder modulator 3 from deviating from the null working mode and thus maintaining the initial state of the output optical power being 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 value of the 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 does not exceed its linear operating region 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 optical 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 the BPSK modulation process, -1 of the pseudo-random noise code sequence (PRN code sequence) corresponds to a modulation phase of 0, and 1 of the PRN code sequence corresponds to a modulation phase of π.

[0068] Second, the BPSK modulated detection light signal is injected into the single-mode optical fiber used as the detection optical fiber through a circulator. The single-mode optical fiber is divided into the 1st, 2nd, ..., Nth segments by the detection light with a pseudo-random noise code sequence modulated coding signal. At the same time, the detection light generates post-Rayleigh scattering in the single-mode optical fiber.

[0069] Third, the Rayleigh scattered light signal reflected back by 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 by using a data acquisition module, and 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 a 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 They correspond to the round-trip time of the detection light signal traveling through 1, 2, ..., N optical fiber sections respectively.

[0072] Sixth, use the PRN code sequence after a specific delay to decode the fiber section corresponding to the delay, obtain the corresponding fiber section spectrum through Fourier transform, and then splice each fiber section to obtain a 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] Combination 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:

[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 detection 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] Among them, υ0 represents the optical frequency of the detection 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 ijIt represents the time delay corresponding to each Rayleigh scattering point of the single-mode optical fiber; i represents the i-th optical fiber section selected by the m-code sequence, and j represents the j-th Rayleigh scattering point in the optical fiber section.

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

[0082]

[0083] S4. Perform Fourier transform on the time domain data of each optical fiber segment i to obtain the corresponding optical fiber segment spectrum:

[0084]

[0085] Figure 4 The spectrum diagram of different distances obtained by selecting 4km single-mode optical fiber, where Figure 4 (a) shows the spectrum of 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) is a spectrum diagram showing a fiber section with a selection distance of 3-4 km; in the diagram, 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.

[0086] S5. Splicing the obtained optical fiber segment spectra of all optical fiber segments i to obtain a complete optical frequency domain reflection beat frequency signal spectrum.

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

[0088] In the above embodiment of the present invention, the single-mode optical fiber used as the detection optical fiber is divided into sections of equal length, which can realize long-distance measurement and successfully solve the contradiction between OFDR long-distance measurement and fast frequency sweeping. At the same time, the present invention can use OFDR measurement with a short frequency sweeping period, with a fast frequency sweeping speed, which effectively enhances the resistance to environmental disturbances and acoustic noise.

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

[0090] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0091] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be 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 will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A distance-gated anti-disturbance optical frequency domain reflection distributed measurement device, characterized in that: It comprises a frequency-sweeping laser light source, wherein the frequency-sweeping laser light generated by the frequency-sweeping 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 detection light using a pseudo-random spread spectrum coding technique, the BPSK modulated detection light is input to the input port of the circulator, the forward output port of the circulator is connected to the detection optical fiber, and the isolation port of the circulator is connected to an input end of the second optical coupler; The polarization controller is configured to adjust the polarization state of the input local oscillator light, and the adjusted local oscillator light is input to another 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.

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 sweep laser is 100 MHz, and the sweep time is T sweep =10μs.

3. The distance-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 realizes BPSK modulation of the input detection light by using pseudo-random spread spectrum coding technology through a signal generator and an MZM bias controller connected thereto.

5. 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.

6. The distance-gated anti-disturbance optical frequency domain reflectometry distributed measurement device according to claim 1, characterized in that: 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.

7. A distance-gated anti-disturbance optical frequency domain reflection distributed measurement method, characterized in that: The following steps are involved: Step 1: Use a pseudo-random code sequence p(t) to drive the MZM to implement BPSK modulation on the detection 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 frequency sweep of the detection light, γ represents the frequency sweep speed of the detection 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 segment: 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.

8. The distance-gated anti-disturbance optical frequency domain reflectometry distributed measurement method according to claim 7, 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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