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WO2011140915A1 - 一种探测脉冲的产生方法和相干光时域反射仪 - Google Patents

一种探测脉冲的产生方法和相干光时域反射仪 Download PDF

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Publication number
WO2011140915A1
WO2011140915A1 PCT/CN2011/073376 CN2011073376W WO2011140915A1 WO 2011140915 A1 WO2011140915 A1 WO 2011140915A1 CN 2011073376 W CN2011073376 W CN 2011073376W WO 2011140915 A1 WO2011140915 A1 WO 2011140915A1
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Prior art keywords
signal
pulse
pulse signal
continuous
optical
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PCT/CN2011/073376
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English (en)
French (fr)
Inventor
冯志勇
邱少锋
韦逸嘉
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华为技术有限公司
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Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to EP11780136.5A priority Critical patent/EP2589948B1/en
Priority to BR112013000068-6A priority patent/BR112013000068B1/pt
Publication of WO2011140915A1 publication Critical patent/WO2011140915A1/zh
Priority to US13/728,686 priority patent/US8831422B2/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
    • H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
    • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
    • G01M11/3127—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using multiple or wavelength variable input source

Definitions

  • the invention relates to a method for generating a detection pulse and a coherent optical time domain reflectometer.
  • the application is submitted to the Chinese Patent Office on June 30, 2010, and the application number is 201010219146.7, and the name is "a detection pulse generation method and coherent light”.
  • the present invention relates to the field of communication transmission, and more particularly to a method for generating a detection pulse and a coherent optical time domain reflectometer.
  • COTDR Coherent Optical Time Domain Reflectometer
  • OTDR Fiber optic Time Domain Reflectometer
  • Both OTDR and COTDR periodically transmit a detection pulse to the fiber.
  • the detection pulse will have Rayleigh scattering at each point in the fiber.
  • COTDR and OTDR will receive the Rayleigh scattering signal from the optical signal scattered from the fiber. Analysis based on Rayleigh scatter signals enables fiber fault location.
  • COTDR has the advantages of long positioning distance.
  • the COTDR is required to have a narrow line width, and the line width is usually required. ⁇ ⁇ within the scope.
  • the Rayleigh scattering signal scattered by each point in the fiber has the same frequency, and the Rayleigh scattering signal scattered by some points will destructively interfere when reaching the OTDR or COTDR.
  • the constructive interference makes the Rayleigh scatter signal exhibit a noise-like characteristic, that is, it has a certain randomness. This kind of noise is called coherent fading noise.
  • Coherent fading noise can cause COTDR and OTDR to fail to resolve fiber faults, so optical faults cannot be accurately located. Therefore, some means are needed to reduce this noise-like characteristic to improve the resolution and positioning accuracy of COTDR and OTDR for fiber faults.
  • a technique for directly reducing the coherent fading noise of an OTDR system by directly changing a shape of a laser driving pulse which specifically generates a slowly varying modulated pulse to drive a pulse modulator to modulate a laser through a driving control circuit. Control, so that the detection pulse output by the laser contains light waves of various frequency components to achieve the purpose of reducing coherent fading noise.
  • the above prior art may cause a frequency broadening of the output light wave of the light source, and does not meet the requirements of the COTDR for the narrow line width of the light source.
  • the resolution and positioning accuracy of the COTDR for the fiber failure cannot be improved. It will degrade the performance of COTDR.
  • the present invention provides a coherent optical time domain reflectometer comprising: a control unit, a driving unit, a continuous optical laser, and a detection pulse generating unit;
  • the control unit is configured to generate a first pulse signal and a second pulse signal with the same period T, the second pulse signal lags behind the first pulse signal, and the first pulse signal and the second pulse signal
  • T ⁇ t+2L/C
  • t is the light source adjustment time of the continuous optical laser
  • L is the length of the fiber to be detected
  • C is the propagation speed of the light wave in the optical fiber
  • the driving unit is configured to generate a frequency change driving signal according to the first pulse signal; and the continuous optical laser is configured to generate continuous light with a constant frequency variation spectrum width under the driving of the frequency variation driving signal;
  • the detection pulse generating unit is configured to modulate the continuous light according to the second pulse signal to generate a detection pulse.
  • the invention also provides a method for generating a detection pulse, comprising:
  • the continuous light is modulated according to the second pulse signal to obtain a detection pulse.
  • the frequency is controlled such that each detection pulse contains light waves of a single frequency component, and the different detection pulses contain different wavelengths of light waves, instead of causing the detection pulses output by the continuous light laser to contain light waves of different frequency components, by controlling the first pulse
  • the periodic dry light time domain of the signal and the second pulse signal transmits the next detection pulse, thereby avoiding the superposition of scattering and/or optical signals corresponding to different detection pulses, thereby not only effectively reducing the coherent fading noise At the same time, it does not lead to the broadening of the frequency of the light wave output by the continuous optical laser, which greatly improves the resolution and positioning accuracy of the coherent optical time domain reflectometer for the fiber fault.
  • FIG. 1 is a structural diagram of a coherent optical time domain reflectometer according to Embodiment 1 of the present invention.
  • FIG. 2 is a schematic diagram of a principle of generating a detection pulse according to an embodiment of the present invention
  • FIG. 3 is a structural diagram of a coherent optical time domain reflectometer according to Embodiment 2 of the present invention.
  • FIG. 4 is a structural diagram of a coherent optical time domain reflectometer according to Embodiment 3 of the present invention
  • FIG. 6 is a schematic diagram of continuous optical frequency variation according to an embodiment of the present invention
  • FIG. 8 is a method for generating a detection pulse according to an embodiment of the present invention
  • Schematic diagram of the process
  • Embodiments of the present invention provide a coherent optical time domain reflectometer, the structure of which is illustrated in FIG. 1.
  • the apparatus includes: a control unit 10, a driving unit 11, a continuous optical laser 12, and a detection pulse generating unit 13.
  • the control unit 10 is configured to generate a first pulse signal and a second pulse signal having the same period T, and the second pulse signal lags behind the first pulse signal.
  • the control unit 10 When the control unit 10 generates the first pulse signal and the second pulse signal, it is also possible to specifically control the period T ⁇ t + 2L/C of the first pulse signal and the second pulse signal.
  • L is the length of the fiber to be detected
  • C is the propagation speed of the light wave in the fiber
  • t is the light source adjustment time of the continuous light laser.
  • the light source adjustment time is the time it takes for the laser to go from stable output of one frequency of light to stable output of light of another frequency, which is an inherent description parameter for each laser.
  • the control unit 10 can specifically control the second pulse signal to lag behind the first pulse signal by at least one t when generating the two pulse signals.
  • the driving unit 11 is configured to generate a frequency change driving signal according to the first pulse signal. Since the frequency change drive signal is the frequency of the continuous light applied to the laser to control the output of the laser, the frequency of the continuous light output by the laser can be made different as long as the frequency change drive signals are different. Therefore, the driving unit 11 can regularly change the frequency variation of the output under the trigger of the first pulse signal.
  • the drive signal for example, can change the frequency change drive signal of its output linearly or linearly. Of course, the driving unit 11 can also randomly change the frequency change driving signal of its output under the trigger of the first pulse signal.
  • the continuous light laser 12 outputs continuous light having a constant frequency spectrum width under the control of the frequency change drive signal generated by the drive unit 11.
  • the frequency change driving signal is changed under the trigger of the first pulse signal, that is, the pulse of the first pulse signal is detected, the frequency change driving signal generated under the trigger of the previous pulse is changed, and the changed frequency change is maintained.
  • the drive signal is unchanged until the next pulse of the first pulse signal arrives. Therefore, in one cycle of the first pulse signal, the frequency of the continuous light output by the continuous optical laser 12 in a steady state is single and the spectrum width is constant, and corresponding to the different periods of the first pulse signal, the output of the continuous optical laser The frequency of continuous light is different.
  • the frequency change drive signal changes the frequency of the continuous light output from the continuous light laser 12 by changing the temperature of the continuous light laser 12, the current/voltage of the drive circuit of the continuous light laser 12, the length of the cavity, and the like.
  • the probe pulse generating unit 13 modulates the continuous light output from the continuous light laser 12 based on the second pulse signal generated by the control unit 10 to generate a probe pulse.
  • the detection pulse generating unit 13 modulates the continuous light, it can take a simple OOK (ON-OFF Keying) modulation mode, and the second pulse signal determines the time of light and no light in one modulation period. , or the time of high optical power and low optical power.
  • OOK ON-OFF Keying
  • the timing relationship between the first pulse signal generated by the control unit 10 and the second pulse signal is as shown in FIG. In Fig. 2, the second pulse signal is just one time t lags behind the first pulse signal. In other embodiments, the second pulse signal may lag behind the first pulse signal for more than one time.
  • the continuous optical laser 12 is based on the driving unit.
  • the resulting frequency change drive signal changes the frequency at which it outputs continuous light. Since the frequency change driving signal is applied to the continuous optical laser 12, the continuous optical laser 12 cannot be brought to a stable output state immediately, and the light source adjustment time t is required to stably output the corresponding frequency under a certain frequency change driving signal. Continuous light. During the light source adjustment time t, the continuous optical laser 12 is in an unstable output state, and the frequency of the continuous light outputted at each moment is uncertain, and the output continuous light contains a plurality of frequency components, as shown by the stripe lattice in FIG.
  • the continuous light output by the continuous light laser 12 includes a plurality of Frequency component; After the light source adjustment time t, the continuous optical laser 12 has reached a stable output state, and the continuous light output is a single frequency component and the frequency is stable until a different frequency change is applied to the continuous light.
  • the continuous optical laser 12 enters the unstable output state again on the laser 12. As shown in FIG. 2, when the first pulse of the first pulse signal comes, the continuous optical laser 12 starts to change the frequency of the continuous light output. After adjusting the time t by a light source, the frequency of the continuous light output is stable. Flu up until the second pulse of the first pulse signal arrives. It should be noted that the frequency fl of the continuous light is determined by the frequency change driving signal applied to the continuous optical laser 12. The magnitude of the frequency change driving signal determines the frequency of the continuous light of the continuous optical laser in the stable output state.
  • the second pulse signal is specifically for controlling the detection pulse generating unit 13 to perform OOK modulation on the continuous light output from the continuous light laser 12, and the waveform of the detection pulse generated by the detection pulse generating unit 13 is the same as the waveform of the second pulse signal. Since the second pulse signal lags behind the first pulse signal by a light source adjustment time t, the unstable output period of the continuous light laser 12 is just avoided, and the detected pulse obtained at this time is a light wave of a single frequency component, as shown in FIG.
  • the first pulse of the second pulse signal corresponds to a detection pulse of frequency f, the second pulse corresponds to a detection pulse with a frequency of £, and the third pulse corresponds to a detection of a frequency of ⁇ . pulse.
  • Another embodiment of the present invention provides a coherent optical time domain reflectometer, the structure of which is shown in FIG. 3. Compared with the coherent optical time domain reflectometer of the structure shown in FIG. 1, the difference is that the control unit 10 includes A pulse generating subunit 101 and a second pulse generating subunit 102.
  • the first pulse generating subunit 101 generates a first pulse signal, and inputs the first pulse signal into the driving unit 11; the second pulse generating subunit 102 generates a second pulse signal, and supplies the second pulse signal to the detecting Pulse generating unit 13.
  • Another coherent optical time domain reflectometer provided by the embodiment of the present invention has a structure as shown in FIG. 4, which is different from the coherent optical time domain reflectometer of the structure shown in FIG. 1 in that: the control unit 10 includes a pulse.
  • the subunit 103, the branch subunit 104, and the delay subunit 105 are generated.
  • the pulse generating subunit 103 generates a first pulse signal and inputs it to the branching subunit 104.
  • the branching subunit 104 divides the first pulse signal into two paths, one of which is directly input to the driving unit 11, and the other of which is input to the delaying subunit. 105.
  • the delay pulse unit 105 delays the first pulse signal to obtain a second pulse signal and supplies it to the probe pulse generating unit 13.
  • Another coherent optical time domain reflectometer provided by the embodiment of the present invention has a structure as shown in FIG. 5, which is different from the coherent optical time domain reflectometer of the structure shown in FIG. 1 in that: the driving unit 11 includes Count A unit 111 and a digital to analog converter 112.
  • the counting unit 111 performs pulse counting on the first pulse signal, and the digital-to-analog converter 112 performs digital-to-analog conversion on the counting result of the counting unit 111 to obtain an analog signal, that is, a frequency change driving signal.
  • the counting unit 111 can be implemented by using a counter, such as a quaternary counter, an octal counter, a hexadecimal counter, etc., which is not specifically limited in this application.
  • the counting unit 111 is implemented by a hexadecimal counter, and the counting unit 111 outputs a total of 16 results of 0, 1, 2, .
  • the digital-to-analog converter 112 converts the above 16 kinds of values into analog signals, and can perform linear conversion during conversion, for example, multiplying each result by a fixed analog quantity, in which case the signal output from the digital-to-analog converter 112 is
  • the digital-to-analog converter 112 can also take a nonlinear conversion when performing digital-to-analog conversion.
  • the digital signal output by the counting unit can be converted into an analog signal that changes in a sinusoidal or cosine manner.
  • the continuous optical laser 12 outputs continuous light under the control of the frequency change drive signal.
  • the filter to be detected includes a filter, it is necessary to consider whether the frequency of the continuous light is located to be detected. Within the bandwidth of the filter on the fiber path, if the frequency of the continuous light is outside the bandwidth of the line filter on the path of the fiber to be detected, the detection pulse will be filtered out as noise by the line filter and failure detection will not be possible. Therefore, the frequency change drive number outputted by the driving unit 11 needs to control the continuous optical laser 12 such that the frequency of the continuous light outputted by it is varied within the bandwidth of the line filter, as shown in FIG. 6, where B is the fiber to be detected.
  • the line filter bandwidth of the path, f is the intrinsic center frequency of the continuous optical laser 13, that is, the center frequency of the continuous light output by the continuous optical laser without any modulation.
  • the line filter bandwidth B is determined according to the filter specification on the path of the fiber to be detected. For example, there are multiple filters on the path of the fiber to be detected, and the intersection of the bandwidths of the multiple filters is the bandwidth of the line filter B. .
  • Another coherent optical time domain reflectometer provided by the embodiment of the present invention has a structure as shown in FIG. 7. Compared with the coherent optical time domain reflectometer of the structure shown in FIG. 1, the difference is that the coherent receiver is further included. 14 and signal processing unit 15.
  • the coherent optical time domain reflectometer continuous light output by the continuous optical laser 12 Also provided as a local oscillator to the coherent receiver 14, the coherent receiver 14 receives the optical signal scattered and/or reflected back from the detected fiber, and the reflected or scattered optical signal and the continuous light output by the continuous optical laser 12 The coherent reception is converted into an electrical signal, and the signal processing unit 15 performs signal processing on the electrical signal to obtain a Rayleigh scattering signal and/or an end surface reflection signal.
  • the optical signal transmitted by the coherent optical time domain reflectometer will generate Rayleigh scattering signal when Raypoint scattering occurs at various points of the fiber, and end surface reflection will occur at the fiber fusion joint, joint, fiber breakage, etc. signal.
  • the optical signal received by the coherent optical time domain reflectometer includes not only the Rayleigh scattering signal but also due to various noises. Or end-reflecting signals, including various noises.
  • the structure coherent optical time domain reflectometer shown in Figs. 3, 4 and 5 may further include a coherent receiver 114 and a signal processing unit 15.
  • the control unit can pass FPGA (Field Programmable Gate Array) or CPLD (Complex Programmable Logic). Device, complex programmable logic device) or DSP (Digital Signal Processor) generates digital signals in a digital logic. Of course, the control unit can also generate pulse signals through circuits composed of analog devices.
  • the counting unit referred to in FIG. 5 can also implement the counting function by digital logic through FPGA, CPLD, DSP, etc., and can also implement the counting function through the analog device.
  • the frequency of the light is controlled such that each of the detection pulses contains light waves of a single frequency component, and the frequencies of the light waves contained by the different detection pulses are not the same, instead of causing the detection pulses output by the continuous light laser to contain light waves of different frequency components, by controlling The period of a pulse signal and the second pulse signal T ⁇ t+2L/C, such that the scatter and/or reflected light signal corresponding to one detection pulse returns to the coherent optical time domain before transmitting the next detection pulse, thereby avoiding Superposition of scattering and/or optical signals corresponding to different detection pulses, therefore, not only can effectively reduce the coherent fading noise, but also does not cause the frequency of the light wave output by the continuous optical laser to broaden, greatly improving the coherent light.
  • the resolution and positioning accuracy of the domain reflector for fiber failure Control in the coherent optical time domain reflectometer provided by this embodiment
  • the second pulse signal generated by the one-time unit is delayed by the at least one light source adjustment time t of the first pulse signal, so that the detection pulse generation unit modulates the continuous light outputted by the continuous light laser in a stable output state to generate a detection pulse.
  • the coherent fading noise is further reduced, and the performance of the coherent optical time domain is improved.
  • the embodiment of the invention further provides a method for generating a detection pulse, and the flow thereof is as shown in FIG. 8, which includes:
  • Step S601 generating a first pulse signal and a second pulse signal having the same period T, the second pulse signal is delayed by the first pulse signal, and the period of the first pulse signal and the second pulse signal is T ⁇ t + 2L/C.
  • L is the length of the fiber to be detected
  • C is the propagation speed of the light wave in the fiber
  • t is the light source adjustment time of the continuous light laser.
  • the light source adjustment time is the time it takes for the laser to go from stable output of one frequency of light to stable output of light of another frequency, which is an inherent description parameter for each laser.
  • the generated first pulse signal is a source for controlling the frequency of the continuous light output of the continuous optical laser in the coherent optical time domain reflectometer, and the generated second pulse signal is used for the coherent optical time domain reflectometer.
  • the continuous light output from the medium continuous laser is modulated to generate a detection pulse.
  • the first pulse signal and the second pulse signal may be respectively generated by two independent pulse sources, or the first pulse signal may be generated first by one pulse source, and then the first pulse signal is divided into two paths.
  • the second pulse signal can be obtained after one of the paths has passed a predetermined delay.
  • the specific control second pulse signal may be specifically controlled to lag behind the first pulse signal by at least one ⁇
  • Step S602 Generate a frequency change driving signal according to the first pulse signal.
  • the frequency change drive signal generated in this step is controlled by applying a continuous light laser to the frequency at which continuous light is output. As long as the frequency change drive signal is different, the frequency of the continuous light output by the laser can be made different. Therefore, each time a pulse of the first pulse signal is received, the frequency change drive signal of the current output is changed, and the frequency change drive signal of the output can be changed regularly, for example, the frequency change drive signal can be linearly or sinusoidally changed or Linear zigzag changes; the frequency change drive signal of the output can also be randomly changed.
  • the step may further include:
  • Pulse counting the first pulse signal performing digital-to-analog conversion on the result of the pulse counting - - Rate change drive signal.
  • these results can be converted into frequency-variant driving signals that change regularly, or these results can be converted into randomly varying frequency-changing driving signals.
  • the frequency change driving signal changes regularly, the frequency of the continuous light output by the continuous optical laser will also show a regular change under the driving of the frequency change driving signal; when the frequency change driving signal changes randomly, the corresponding The frequency of the continuous light output by the continuous optical laser driven by the frequency change drive signal will also vary randomly.
  • Step S603 driving the continuous optical laser according to the frequency change driving signal, so that the continuous optical laser generates continuous light whose frequency variation spectral width remains unchanged.
  • the frequency change driving signal is changed under the trigger of the first pulse signal, that is, the pulse of the first pulse signal is detected, the frequency change driving signal generated under the trigger of the previous pulse is changed, and the changed frequency change is maintained.
  • the drive signal is unchanged until the next pulse of the first pulse signal arrives. Therefore, in one cycle of the first pulse signal, the frequency of the continuous light output by the continuous light laser in a steady state is single and the spectrum width is constant, and the continuous optical laser output is continuous corresponding to different periods of the first pulse signal. The frequency of light is different again.
  • the frequency change drive signal changes the frequency of the continuous light output by the laser by changing the temperature of the laser, the current/voltage of the drive circuit of the laser, the length of the cavity, and the like.
  • the continuous optical laser output is driven by a specific frequency varying drive signal, and the frequency of the continuous light output by the continuous optical laser changes linearly in a zigzag or sinusoidal manner, as shown in FIG.
  • Step S604 Modulating the continuous light according to the second pulse signal to obtain a detection pulse.
  • the second pulse signal determines the time of light and no light in one modulation period, or high optical power and low light. Power time.
  • the detection pulse generated in the embodiment of the present invention is coupled to the optical fiber to be detected to implement fault detection. Therefore, when there is a filter on the path of the fiber to be detected, it is necessary to consider whether the frequency of the continuous light generated by the continuous optical laser is located on the path of the fiber to be detected. Within the bandwidth of the filter, if the frequency of the continuous light is outside the bandwidth of the line filter on the fiber path to be detected, the detection pulse is filtered out as noise by the line filter and failure detection is not possible. Therefore, step 603 can also be implemented in a specific implementation. - - When the continuous optical laser is driven by the frequency change driving signal, the frequency of the continuous light output by the continuous optical laser is specifically controlled in the interval [f+B/2, fB/2], as shown in Fig.
  • the line filter bandwidth of the path, f is the inherent center frequency of the continuous optical laser, that is, the center frequency of the continuous light output by the continuous optical laser without any modulation.
  • the line filter bandwidth B is determined according to the filter specification on the path of the fiber to be detected. For example, there are multiple filters on the path of the fiber to be detected, and the intersection of the bandwidths of the multiple filters is the bandwidth of the line filter B. .
  • the method for generating a detection pulse signal may further include: dividing a portion of the continuous light generated in step S603, and separating the portion of the continuous light and the optical signal scattered or reflected from the optical fiber. Performing coherent reception to obtain an electrical signal; performing signal processing on the electrical signal to obtain a Rayleigh scattering signal and/or an end surface reflection signal.
  • each detection pulse when the detection pulse is generated, since the frequency of the continuous light output from the continuous light laser is controlled, each detection pulse contains light waves of a single frequency component, and the frequencies of the light waves included in the different detection pulses are different, instead of
  • the detecting pulse outputted by the continuous optical laser includes light waves of different frequency components, and by controlling the period t+2L/C of the first pulse signal and the second pulse signal, the scattered and/or reflected optical signals corresponding to one detecting pulse are returned to the coherent
  • the next detection pulse is sent after the optical time domain instrument, thereby avoiding the superposition of scattering and/or optical signals corresponding to different detection pulses, thereby not only effectively reducing the coherent fading noise, but also not causing the continuous optical laser.
  • the frequency of the output light wave is broadened.

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Abstract

本发明涉及通信传输领域，尤其涉及一种探测脉冲的产生方法和相干光时域反射仪。所述相干光时域反射仪包括：控制单元，用于产生周期T相同的第一脉冲信号和第二脉冲信号，所述第二脉冲信号滞后于所述第一脉冲信号，且所述第一脉冲信号和第二脉冲信号的周期T≧t+2L/C；驱动单元，用于根据所述第一脉冲信号产生频率变化驱动信号；连续光激光器，用于在所述频率变化驱动信号的驱动下，产生频率变化频谱宽度不变的连续光；探测脉冲产生单元，用于根据所述第二脉冲信号对所述连续光进行调制产生探测脉冲。本发明实施例提供的相干光时域反射仪具有较高的光纤故障分辨率和定位准确度。

Description

一 一 一种探测脉沖的产生方法和相干光时域反射仪 本申请要求于 2010 年 6 月 30 日提交中国专利局、 申请号为 201010219146.7、名称为 "一种探测脉冲的产生方法和相干光时域反射仪"的中 国专利申请的优先权， 其全部内容通过引用结合在本申请中。
技术领域
本发明涉及通信传输领域， 尤其涉及一种探测脉冲的产生方法和相干光 时域反射仪。
背景技术
COTDR ( Coherent Optical Time Domain Reflectometer, 相干光时 i或反射 仪）和 OTDR通常用于对光纤光缆线路故障 （比如， 断纤）进行定位。 OTDR 和 COTDR均是通过周期性地向光纤中发送探测脉冲， 探测脉冲在光纤中各点 会发生瑞利散射， COTDR和 OTDR再接收从光纤中散射回来的光信号中提取 瑞利散射信号， 然后根据瑞利散射信号进行分析实现光纤故障定位。 COTDR 相比于普通的 OTDR, 具有定位距离长等优点， 但是， 由于是釆用相干技术对 瑞利散射信号进行接收处理， 因此， 要求 COTDR的光源线宽很窄， 通常要求 其线宽在 ΙΟΚΗζ ~ ΙΟΟΚΗζ的范围内。
由于探测脉冲的光波频率成分单一， 光纤中各点散射回来的瑞利散射信 号的频率相同，也就会导致某些点散射回来的瑞利散射信号在到达 OTDR或者 COTDR时会发生相消干涉或者相长干涉， 也就使得瑞利散射信号会体现出类 噪声特性， 即具有一定的随机性， 这种噪声称之为相干衰落噪声。 相干衰落 噪声会造成 COTDR和 OTDR无法分辨光纤故障， 从而就不能对光纤故障进行 准确定位。 因此， 需要通过某种手段以减弱这种类噪声特性， 以提高 COTDR 和 OTDR对光纤故障分辨率和定位准确度。
现有技术中提供了一种直接利用改变激光器驱动脉冲形状的技术降低 OTDR系统的相干衰落噪声的方案，其具体为通过一个驱动控制电路产生一个 緩变调制脉冲去驱动脉冲调制器对激光器进行调制控制， 使得激光器输出的 探测脉冲包含各种不同频率成份的光波， 达到减小相干衰落噪声的目的。
但是， 上述现有技术会导致光源输出光波的频语展宽， 不符合 COTDR对 光源窄线宽的要求， 当其应用于 COTDR时， 不仅不能提高 COTDR对光纤故障 的分辨率和定位准确度， 还会劣化 COTDR的工作性能。
发明内容 - - 本发明提供一种相干光时域反射仪， 其包括： 控制单元、 驱动单元、 连 续光激光器和探测脉冲产生单元；
所述控制单元， 用于产生周期 T相同的第一脉冲信号和第二脉冲信号， 所 述第二脉冲信号滞后于所述第一脉冲信号， 且所述第一脉冲信号和第二脉冲 信号的周期 T ^t+2L/C, t为所述连续光激光器的光源调整时间， L为待探测光 纤的长度， C为光波在光纤中的传播速度；
所述驱动单元， 用于根据所述第一脉冲信号产生频率变化驱动信号； 所述连续光激光器， 用于在所述频率变化驱动信号的驱动下， 产生频率 变化频谱宽度不变的连续光；
所述探测脉冲产生单元， 用于根据所述第二脉冲信号对所述连续光进行 调制产生探测脉冲。
本发明还提供一种探测脉冲的产生方法， 包括：
产生周期 T相同的第一脉冲信号和第二脉冲信号， 所述第二脉冲信号滞后 于所述第一脉冲信号， 且所述第一脉冲信号和第二脉冲信号的周期 t+2L/C, t为连续光激光器的光源调整时间， L为待探测光纤的长度， C为光 波在光纤中的传播速度；
根据所述第一脉冲信号产生频率变化驱动信号；
用所述频率变化驱动信号驱动所述连续光激光器， 使得所述连续光激光 器产生频率变化频谱宽度不变的连续光；
根据所述第二脉冲信号对所述连续光进行调制， 得到探测脉冲。 频率进行控制， 使得每一个探测脉冲包含单一频率成份的光波， 而不同探测 脉冲包含的光波的频率不相同， 而不是使得连续光激光器输出的探测脉冲包 含不同频率成份的光波， 通过控制第一脉冲信号和第二脉冲信号的周期 干光时域仪后才发送下一个探测脉冲， 从而避免了不同探测脉冲对应的散射 和 /或光信号之间发生叠加， 因此， 不仅能有效的降低相干衰落噪声， 同时又 不会导致连续光激光器输出的光波的频语展宽， 极大地提高了相干光时域反 射仪对光纤故障的分辨率和定位准确度。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案， 下面将实施 - - 例中所需要使用的附图作简单地介绍， 显而易见地， 下面描述中的附图仅仅 是本发明的一些实施例， 对于本领域普通技术人员来讲， 在不付出创造性劳 动的前提下， 还可以根据这些附图获得其他的附图。
图 1为本发明实施例一提供的相干光时域反射仪的结构图；
图 2为本发明实施例中探测脉冲产生原理示意图；
图 3为本发明实施例二提供的相干光时域反射仪的结构图；
图 4为本发明实施例三提供的相干光时域反射仪的结构图； 图 6为本发明实施例中连续光频率变化示意图； 图 8为本发明实施例提供的一种探测脉冲的产生方法的流程示意图。
具体实施方式
下面将结合本发明实施例中的附图， 对本发明实施例中的技术方案进行 清楚、 完整地描述， 显然， 所描述的实施例仅仅是本发明一部分实施例， 而 不是全部的实施例。 基于本发明中的实施例， 本领域普通技术人员在没有作 出创造性老童前提下所获得的所有其它实施例， 都属于本发明保护的范围。
本发明实施例提供一种相干光时域反射仪， 其结构如图 1所述， 该装置包 括： 控制单元 10, 驱动单元 11 , 连续光激光器 12, 探测脉冲产生单元 13。
控制单元 10, 用于产生周期 T相同的第一脉冲信号和第二脉冲信号， 第二 脉冲信号滞后于第一脉冲信号。
控制单元 10产生第一脉冲信号和第二脉冲信号时， 还可以具体控制第一 脉冲信号和第二脉冲信号的周期 T ^t + 2L/C。 其中， L为待探测光纤的长度， C为光波在光纤中的传播速度， t为连续光激光器的光源调整时间。 光源调整 时间为激光器从稳定输出一种频率的光到稳定输出另一种频率的光所经历的 时间， 是每个激光器固有的描述参数。
其中， 控制单元 10在产生这两个脉冲信号时， 还可以具体控制第二脉冲 信号滞后于第一脉冲信号至少一个 t。
驱动单元 11 , 用于根据第一脉冲信号产生频率变化驱动信号。 由于频率 变化驱动信号是施加在激光器上控制激光器输出的连续光的频率的， 所以只 要频率变化驱动信号不同， 就能使得激光器输出的连续光的频率不同。 因此， 驱动单元 11在第一脉冲信号的触发下， 可以有规律地改变其输出的频率变化 一 一 驱动信号， 例如， 可以线性递增或者线性递减地改变其输出的频率变化驱动 信号。 当然， 驱动单元 11在第一脉冲信号的触发下， 也可以随机地改变其输 出的频率变化驱动信号。
连续光激光器 12, 在驱动单元 11产生的频率变化驱动信号的控制下， 输 出频率变化频谱宽度不变的连续光。
由于频率变化驱动信号是在第一脉冲信号的触发下进行改变的， 即检测 到一个第一脉冲信号的脉冲， 就改变上一个脉冲触发下产生的频率变化驱动 信号， 并保持改变后的频率变化驱动信号不变直到第一脉冲信号的下一个脉 冲到来。 因此， 在第一脉冲信号的一个周期内， 连续光激光器 12在稳定状态 下输出的连续光的频率是单一的且频谱宽度不变， 而对应第一脉冲信号的不 同周期， 连续光激光器输出的连续光的频率又是不一样的。
其中， 频率变化驱动信号通过改变连续光激光器 12的温度、 连续光激光 器 12的驱动电路的电流 /电压、 谐振腔长度等方式， 使得连续光激光器 12输出 的连续光的频率发生变化。
探测脉冲产生单元 13 , 根据控制单元 10产生的第二脉冲信号对连续光激 光器 12输出的连续光进行调制产生探测脉冲。 探测脉冲产生单元 13对连续光 即进行调制时， 可以釆取简单的 OOK ( ON-OFF Keying , 通断键控）调制方 式， 由第二脉冲信号决定一个调制周期内有光和无光的时间， 或者高光功率 和低光功率的时间。 一步的说明。
控制单元 10产生的第一脉冲信号是和第二脉冲信号的时序关系如图 2所 示。 在图 2中， 第二脉冲信号是刚好滞后于第一脉冲信号一个 t的时间， 在其它 的实施例中第二脉冲信号滞后于第一脉冲信号的时间可以大于一个
第一脉冲信号的每个脉冲到来的时刻， 连续光激光器 12就根据驱动单元
11产生的频率变化驱动信号改变其输出连续光的频率。 由于频率变化驱动信 号施加到连续光激光器 12上时， 并不能使得连续光激光器 12立刻达到稳定输 出状态， 需要经过光源调整时间 t才能稳定地输出在某一特定频率变化驱动信 号下所对应频率的连续光。 在光源调整时间 t内， 连续光激光器 12处于不稳定 输出状态， 其各个时刻输出的连续光的频率是不确定的， 且输出的连续光包 含多种频率成份， 如图 2中条紋格表示连续光激光器 12输出的连续光包含多种 频率成份； 经过光源调整时间 t后， 连续光激光器 12就已经达到了稳定输出状 态， 此时输出的连续光是单一频率成份的且频率稳定， 直到有一个不同的频 率变化驱动信号施加到连续光激光器 12上时连续光激光器 12才又进入不稳定 输出状态。 如图 2所示， 第一脉冲信号的第一个脉冲到来时， 连续光激光器 12 就开始改变其输出连续光的频率， 经过一个光源调整时间 t后， 其输出的连续 光的频率一直稳定在 fl上直到第一脉冲信号的第二个脉冲到来。 需要说明的 是， 连续光的频率 fl是由施加在连续光激光器 12上的频率变化驱动信号确定 的， 频率变化驱动信号的值大小决定了连续光激光器在稳定输出状态下的连 续光的频率。
第二脉冲信号具体是用来控制探测脉冲产生单元 13对连续光激光器 12输 出的连续光进行 OOK调制， 探测脉冲产生单元 13产生的探测脉冲的波形就和 第二脉冲信号的波形相同。 由于第二脉冲信号滞后于第一脉冲信号一个光源 调整时间 t, 所以刚好避开了连续光激光器 12不稳定输出时期， 此时得到的探 测脉冲是单一频率成份的光波， 如图 2中所示， 第二脉冲信号的第一个脉冲对 应得到的是频率为 fl的探测脉冲，第二个脉冲对应得到的是频率为 £2的探测脉 冲， 第三个脉冲对应得到的是频率为 β的探测脉冲。
本发明实施例提供了又一种相干光时域反射仪， 其结构如图 3所示， 与图 1所示结构的相干光时域反射仪相比， 不同之处在于： 控制单元 10包括第一脉 冲产生子单元 101和第二脉冲产生子单元 102。
第一脉冲产生子单元 101产生第一脉冲信号， 并将该第一脉冲信号输入到 驱动单元 11中； 第二脉冲产生子单元 102产生第二脉冲信号， 并将该第二脉冲 信号提供给探测脉冲产生单元 13。
本发明实施例提供的另一种相干光时域反射仪， 其结构如图 4所示， 与图 1所示结构的相干光时域反射仪相比， 不同之处在于： 控制单元 10包括脉冲产 生子单元 103、 分路子单元 104和延时子单元 105。
脉冲产生子单元 103产生第一脉冲信号并将其输入到分路子单元 104, 分 路子单元 104将该第一脉冲信号分成两路， 一路直接输入到驱动单元 11 , 另一 路输入到延时子单元 105 , 延时子单元 105该第一脉冲信号进行延时得到第二 脉冲信号并将其提供给探测脉冲产生单元 13。
本发明实施例提供的再一种相干光时域反射仪， 其结构如图 5所示， 与图 1所示结构的相干光时域反射仪相比， 其不同之处在于： 驱动单元 11包括计数 一 一 单元 111和数模转换器 112。
计数单元 111对第一脉冲信号进行脉冲计数， 数模转换器 112对计数单元 111的计数结果进行数模转换得到模拟信号 , 即频率变化驱动信号。
计数单元 111可以釆用计数器来实现， 比如 4进制计数器、 8进制计数器， 16进制计数器等， 本申请不做具体限定。 例如在一实施例中， 计数单元 111釆 用 16进制计数器实现， 计数单元 111输出 0、 1、 2... 15共 16种结果。 数模转换 器 112对将上述 16种数值转换为模拟信号， 转换时可以釆取线性转换， 例如将 每种结果乘以一个固定的模拟量， 此种情况下数模转换器 112输出的信号就呈 线性变化； 数模转换器 112在进行数模转换时还可以釆取非线性转换， 例如， 可以将计数单元输出的数字信号转换为呈正弦状或者余弦状变化的模拟信 号。
当数模转换器 112输出的频率变化驱动信号呈线性变化或者正弦状变化 或者余弦状变化时， 在频率变化驱动信号控制下连续光激光器 12输出连续光
12输出的连续光进行调制产生探测脉冲， 该探测脉冲需要耦合进待探测光纤， 以实现故障探测， 因此， 当待探测光纤路径上包含有滤波器时， 需要考虑连 续光的频率是否位于待探测光纤路径上滤波器的带宽范围之内， 如果连续光 的频率位于待探测光纤路径上线路滤波器的带宽范围之外， 探测脉冲就会作 为噪声被线路滤波器所滤除而无法实现故障探测。 故驱动单元 11输出的频率 变化驱动号需要控制连续光激光器 12, 使得其输出的连续光的频率是在线路 滤波器的带宽范围之内变化， 如图 6所示， 其中 B为待探测光纤所在路径的线 路滤波器带宽， f为连续光激光器 13的固有中心频率， 也就是连续光激光器在 不做任何调制时输出的连续光的中心频率。线路滤波器带宽 B是依据待探测光 纤所在路径上的滤波器规格来确定的， 例如待探测光纤所在路径上有多个滤 波器， 取这多个滤波器带宽的交集为线路滤波器的带宽 B。 示结构的相干光时域反射仪中的驱动单元的实现结构。
本发明实施例提供的又一种相干光时域反射仪， 其结构如图 7所示， 与图 1所示结构的相干光时域反射仪相比， 其不同之处在于还包括相干接收机 14和 信号处理单元 15。 在该相干光时域反射仪中， 连续光激光器 12输出的连续光 还作为本振光提供给相干接收机 14 , 相干接收机 14接收所探测光纤中散射和 / 或反射回来的光信号， 并将该反射或散射回来的光信号和连续光激光器 12输 出的连续光进行相干接收转换为电信号， 信号处理单元 15对该电信号进行信 号处理， 以获取瑞利散射信号和 /或端面反射信号。 探测脉冲期间， 相干光时 域反射仪发送的光信号在途径光纤各点时会发生瑞利散射形成瑞利散射信 号， 在光纤熔接处、 连接处、 断纤处等会发生端面反射形成端面反射信号。 瑞利散射信号和端面反射信号在沿光纤向相干时域反射仪传播的过程中， 由 于各种噪声的影响， 相干光时域反射仪接收到的光信号中不仅包含了瑞利散 射信号和 /或端面反射信号， 还包括了各种噪声。 因此， 需要在利用信号处理 单元 15对相干接收机 14得到的电信号进行处理， 从中提取瑞利散射信号和 /或 端面反射信号， 以便后续根据提取的瑞利散射信号和 /或端面反射信号对光纤 状态进行分析。 其中， 相干接收机 14和信号处理单元 15的详细工作过程均是 现有现有技术， 本申请中不做赘述。
需要说明的是， 图 3、 图 4和图 5所示结构相干光时域反射仪还可以包括相 干接收机 114和信号处理单元 15。
在图 1、 图 3、 图 4、 图 5和图 7所示结构的相干光时域反射仪中， 控制单元 可以通过 FPGA ( Field Programmable Gate Array, 现场可编程门阵列）或者 CPLD ( Complex Programmable Logic Device, 复杂可编程逻辑器件）或者 DSP ( Digital Signal Processor, 数字信号处理器）以数字逻辑的方式来产生脉冲信 号， 当然控制单元也可以通过模拟器件组成的电路来产生脉冲信号。 在图 5中 所涉及到的计数单元同样可以通过 FPGA、 CPLD , DSP等以数字逻辑的方式 实现计数功能， 也可以通过模拟器件来实现计数功能。 光的频率进行控制， 使得每一个探测脉冲包含单一频率成份的光波， 而不同 探测脉冲包含的光波的频率不相同， 而不是使得连续光激光器输出的探测脉 冲包含不同频率成份的光波，通过控制第一脉冲信号和第二脉冲信号的周期 T ≥ t+2L/C , 使得一个探测脉冲对应的散射和 /或反射的光信号回到相干光时域 仪后才发送下一个探测脉冲， 从而避免了不同探测脉冲对应的散射和 /或光信 号之间发生叠加， 因此， 不仅能有效的降低相干衰落噪声， 同时又不会导致 连续光激光器输出的光波的频语展宽， 极大地提高了相干光时域反射仪对光 纤故障的分辨率和定位准确度。 当本实施例提供的相干光时域反射仪中的控 一 一 制单元产生的第二脉冲信号滞后于第一脉冲信号至少一个光源调整时间 t时， 从而使得探测脉冲产生单元是对连续光激光器处于稳定输出状态下输出的连 续光进行调制产生探测脉冲， 就进一步降低了相干衰落噪声， 提高了相干光 时域仪的性能。 本发明实施例还提供了一种产生探测脉冲的方法， 其流程如图 8所示， 包 括：
步骤 S601 : 产生周期 T相同的第一脉冲信号和第二脉冲信号， 第二脉冲信 号滞后于第一脉冲信号， 且第一脉冲信号和第二脉冲信号的周期 T ^t + 2L/C。 其中， L为待探测光纤的长度， C为光波在光纤中的传播速度， t为连续光激光 器的光源调整时间。 光源调整时间为激光器从稳定输出一种频率的光到稳定 输出另一种频率的光所经历的时间， 是每个激光器固有的描述参数。
在本步骤中， 产生的第一脉冲信号是对相干光时域反射仪中的连续光激 光器输出连续光的频率进行控制的源头， 产生的第二脉冲信号是用来对相干 光时域反射仪中连续光激光器输出的连续光进行调制控制以产生探测脉冲。
在本步骤中， 可以由两个独立的脉冲源分别产生第一脉冲信号和第二脉 冲信号， 也可以由一个脉冲源先产生第一脉冲信号， 然后再将该第一脉冲信 号分成两路， 其中一路经过一个预定的延时后就可以得到第二脉冲信号。
由于当一个信号施加到连续光激光器上对其输出连续光的频率进行调整 控制时， 连续光激光器需要经过一段时间才能达到稳定输出状态。 因此， 在 该步骤中还可以具体控制具体控制第二脉冲信号滞后于第一脉冲信号至少一 个^
步骤 S602: 根据第一脉冲信号产生频率变化驱动信号。
本步骤中产生的频率变化驱动信号是施加连续光激光器上对其输出连续 光的频率进行控制的， 只要频率变化驱动信号不同， 就能使得激光器输出的 连续光的频率不同。 因此， 每收到第一脉冲信号的一个脉冲， 就改变当前输 出的频率变化驱动信号， 可以有规律地改变输出的频率变化驱动信号， 例如， 可以使得频率变化驱动信号呈线性或者正弦状变化或者线性锯齿状变化； 也 可以随机地改变输出的频率变化驱动信号。
在一种具体实施例中， 本步骤还可以具体包括：
对第一脉冲信号进行脉冲计数； 对脉冲计数的结果进行数模转换得到频 - - 率变化驱动信号。
在对脉冲计数的结果进行数模转换时， 可以将这些结果转换成呈规律性 变化的频率变化驱动信号， 也可以将这些结果转换成随机变化的频率变化驱 动信号。 当频率变化驱动信号呈规律性变化时， 相应的在该频率变化驱动信 号的驱动下连续光激光器输出的连续光的频率也将呈现规律性变化； 当频率 变化驱动信号随机变化时， 相应的在该频率变化驱动信号的驱动下连续光激 光器输出的连续光的频率也将随机变化。
步骤 S603 : 根据频率变化驱动信号驱动连续光激光器， 使得连续光激光 器产生频率变化频谱宽度保持不变的连续光。
由于频率变化驱动信号是在第一脉冲信号的触发下进行改变的， 即检测 到一个第一脉冲信号的脉冲， 就改变上一个脉冲触发下产生的频率变化驱动 信号， 并保持改变后的频率变化驱动信号不变直到第一脉冲信号的下一个脉 冲到来。 因此， 在第一脉冲信号的一个周期内， 连续光激光器在稳定状态下 输出的连续光的频率是单一的且频谱宽度不变， 而对应第一脉冲信号的不同 周期， 连续光激光器输出的连续光的频率又是不一样的。
在本步骤中， 频率变化驱动信号通过改变激光器的温度、 激光器的驱动 电路的电流 /电压、 谐振腔长度等方式， 使得激光器输出的连续光的频率发生 变化。
在一具体的实施例中， 连续光激光器输出在一具体的频率变化驱动信号 的驱动下， 连续光激光器输出的连续光的频率呈线性锯齿状或者正弦状变化， 如图 6所示。
步骤 S604: 根据所述第二脉冲信号对所述连续光进行调制， 得到探测脉 冲。
在本步骤中， 根据第二脉冲信号对连续光进行调制时， 可以釆取简单的 OOK调制方式， 又第二脉冲信号决定一个调制周期内有光和无光的时间， 或 者高光功率和低光功率的时间。
本发明实施例中产生的探测脉冲耦合进待探测光纤实现故障探测， 因此， 当待探测光纤路径上有滤波器时， 需要考虑连续光激光器产生的连续光的频 率是否位于待探测光纤路径上线路滤波器的带宽范围之内， 如果连续光的频 率位于待探测光纤路径上线路滤波器的带宽范围之外， 探测脉冲就会作为噪 声被线路滤波器所滤除而无法实现故障探测。 故步骤 603在具体实现时还可以 - - 通过频率变化驱动信号在驱动连续光激光器时， 具体控制连续光激光器输出 连续光的频率位于区间 [f+B/2,f-B/2] , 如图 6所示， 其中 B为待探测光纤所在路 径的线路滤波器带宽， f为连续光激光器的固有中心频率， 也就是连续光激光 器在不做任何调制时输出的连续光的中心频率。线路滤波器带宽 B是依据待探 测光纤所在路径上的滤波器规格来确定的， 例如待探测光纤所在路径上有多 个滤波器， 取这多个滤波器带宽的交集为线路滤波器的带宽 B。
本发明实施例中提供的探测脉冲信号的产生方法， 还可以进一步包括： 从步骤 S603中产生的连续光分出一部分， 将分出的该部分连续光和从光纤中 散射或反射回来的光信号进行相干接收， 得到电信号； 对该电信号进行信号 处理， 获取瑞利散射信号和 /或端面反射信号。
本发明实施例产生探测脉冲时， 由于是对连续光激光器输出连续光的频 率进行控制， 使得每一个探测脉冲包含单一频率成份的光波， 而不同探测脉 冲包含的光波的频率不相同， 而不是使得连续光激光器输出的探测脉冲包含 不同频率成份的光波， 通过控制第一脉冲信号和第二脉冲信号的周期 t+2L/C , 使得一个探测脉冲对应的散射和 /或反射的光信号回到相干光时域仪 后才发送下一个探测脉冲， 从而避免了不同探测脉冲对应的散射和 /或光信号 之间发生叠加， 因此， 不仅能有效的降低相干衰落噪声， 同时又不会导致连 续光激光器输出的光波的频语展宽。 当本实施例提供的的第二脉冲信号滞后 于第一脉冲信号至少一个光源调整时间 t时， 从而使得是对连续光激光器处于 衰落噪声。
以上所述， 仅为本发明较佳的具体实施方式， 但本发明的保护范围并不 局限于此， 任何熟悉本技术领域的技术人员在本发明揭露的技术范围内， 可 轻易想到的变化或替换， 都应涵盖在本发明的保护范围之内。 因此， 本发明 的保护范围应该以权利要求书的保护范围为准。

Claims

权 利 要 求
1、 一种相干光时域反射仪， 其特征在于， 包括： 控制单元、 驱动单元、 连续光激光器和探测脉冲产生单元；
所述控制单元， 用于产生周期 T相同的第一脉冲信号和第二脉冲信号， 所 述第二脉冲信号滞后于所述第一脉冲信号， 且所述第一脉冲信号和第二脉冲 信号的周期 T ^t+2L/C, t为所述连续光激光器的光源调整时间， L为待探测光 纤的长度， C为光波在光纤中的传播速度；
所述驱动单元， 用于根据所述第一脉冲信号产生频率变化驱动信号； 所述连续光激光器， 用于在所述频率变化驱动信号的驱动下， 产生频率 变化频谱宽度不变的连续光；
所述探测脉冲产生单元， 用于根据所述第二脉冲信号对所述连续光进行 调制产生探测脉冲。
2、 如权利要求 1所述的相干光时域反射仪， 其特征在于， 所述第二脉冲 信号滞后于所述第一脉冲信号至少一个 t。
3、 如权利要求 1所述的相干光时域反射仪， 其特征在于， 所述控制单元 具体包括：
第一脉冲产生子单元， 用于产生所述第一脉冲信号；
第二脉冲产生子单元， 用于产生所述第二脉冲信号。
4、 如权利要求 1所述的相干光时域反射仪， 其特征在于， 所述控制单元 具体包括：
脉冲产生子单元， 用于产生所述第一脉冲信号；
分路子单元， 用于将所述第一脉冲信号分成两路；
延时子单元， 用于对所述分路子单元得到的所述两路中的一路进行延时， 得到所述第二脉冲信号。
5、 如权利要求 1至 4任一项所述的相干光时域反射仪， 其特征在于， 所述 驱动单元包括：
计数单元， 用于对所述第一脉冲信号进行脉冲计数；
数模转换器， 用于对将所述计数单元的计数结果进行数模转换得到所述 频率变化驱动信号。
6、 如权利要求 5所述的相干光时域反射仪， 其特征在于， 还进一步包括： 相干接收机， 用于接收光纤中散射和 /或反射回来的光信号， 并将其与所 述连续光器产生的所述连续光进行相干得到电信号；
信号处理单元， 用于对所述电信号进行信号处理， 获取瑞利散射信号和 / 或端面反射信号。
7、 一种探测脉冲的产生方法， 其特征在于， 所述方法包括：
产生周期 T相同的第一脉冲信号和第二脉冲信号， 所述第二脉冲信号滞后 于所述第一脉冲信号， 且所述第一脉冲信号和第二脉冲信号的周期 t+2L/C, t为连续光激光器的光源调整时间， L为待探测光纤的长度， C为光 波在光纤中的传播速度；
根据所述第一脉冲信号产生频率变化驱动信号；
用所述频率变化驱动信号驱动所述连续光激光器， 使得所述连续光激光 器产生频率变化频谱宽度不变的连续光；
根据所述第二脉冲信号对所述连续光进行调制， 得到探测脉冲。
8、 如权利要求 7所述的方法， 其特征在于， 所述第二脉冲信号具体滞后 于所述第一脉冲信号至少一个^
9、 如权利要求 7所述的方法， 其特征在于， 所述根据所述频率变化驱动 信号驱动所述连续光激光器， 使得所述连续光激光器产生频率变化频谱宽度 保持不变的连续光具体包括：
根据所述频率变化驱动信号驱动连续光激光器， 使得所述连续光激光器 产生频率呈线性锯齿状或者正弦状变化， 且频谱宽度保持不变的连续光。
10、 如权利要求 7所述的方法， 其特征在于， 所述连续光激光器产生的所 述连续光的频率为位于区间 [f+B/2,f-B/2] ,所述 f为所述连续光激光器的固有中 心频率， 所述 B为待探测光纤路径中的线路滤波器带宽。
11、 如权利要求 7至 10任一项所述的方法， 其特征在于， 所述根据所述第 一脉冲信号产生频率变化驱动信号具体包括：
对所述第一脉冲信号进行脉冲计数；
对脉冲计数的结果进行数模转换得到频率变化驱动信号。
12、 如权利要求 11所述的方法， 其特征在于， 所述方法还进一步包括： 接收光纤中散射和 /或反射回来的光信号；
从所述连续光激光器产生的连续光中分出一部分和所述光纤中散射回来 的散射和 /或反射回来的光信号进行相干， 得到电信号； 对所述电信号进行信号处理， 获取瑞利散射信号和 /或端面反射信号。
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