CN111412936B - Full-digital orthogonal phase shift pulse COTDR sensing device and method - Google Patents
Full-digital orthogonal phase shift pulse COTDR sensing device and method Download PDFInfo
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
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- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses a full-digital orthogonal phase shift pulse COTDR sensing device, which is characterized by comprising a light source (1), a 1x2 optical fiber coupler (2), a digital modulation signal generating device (3), a frequency shift pulse modulator (4), an erbium-doped optical fiber amplifier (5), an optical fiber circulator (6), a sensing optical fiber (7), a 2x2 optical fiber coupler (8), a photoelectric balance detector (9), a signal acquisition device (10) and a signal processing device (11). The phase difference is linearly related to the stress of the optical fiber, and distortion of a sensing result caused by nonlinear correlation of an interference light intensity signal and the stress is eliminated.
Description
Technical Field
The invention relates to the technical field of coherent optical time domain reflection and the technical field of signal demodulation, in particular to a phase-shift pulse COTDR sensing device and a phase-shift pulse COTDR sensing method.
Background
The Coherent Optical Time Domain Reflectometry (COTDR) sensing technology has wide application and requirements in the aspects of building structure health monitoring, mineral exploration, submarine optical cable monitoring, underwater monitoring and the like. According to the COTDR sensing technology, local reference light and backward Rayleigh scattering light signals injected into an optical fiber are mixed and amplified, and optical phase information of each part of the sensing optical fiber is obtained through demodulation, so that phase changes of each part of the optical fiber caused by external vibration and sound wave signals are detected in real time, and then a vibration source and a sound source are identified and positioned. For example, in the aspect of safety monitoring along an oil and gas pipeline, the COTDR device can monitor the conditions of pipeline leakage points, abnormal vibration and the like in real time through the sensing optical fiber fixed along the pipeline.
The traditional COTDR phase extraction method adopts a 90-degree optical mixer or a 3x3 optical fiber coupler to generate multi-path phase shift signals for phase demodulation, adopts a plurality of sets of photoelectric conversion and data acquisition devices, not only increases the system cost, but also introduces noise due to inconsistent intensity and time delay among the plurality of sets of devices; in another conventional method, all-digital orthogonal phase shift pulses are injected into a sensing optical fiber in sequence at intervals to obtain continuous multi-frame phase shift COTDR signals for phase demodulation, but because multi-frame data is required for demodulation, the sensing response frequency of a system is reduced. .
Disclosure of Invention
The invention aims to provide a full-digital orthogonal phase shift pulse COTDR sensing device and a method, which transmit digital orthogonal phase shift pulses in the same pulse transmission period and construct orthogonal phase COTDR signals, thereby avoiding low sensing response frequency of a system under the condition of only using one set of photoelectric conversion and digital acquisition device, demodulating phase information at each position of a sensing optical fiber and sensing vibration information at each position.
The invention relates to a full-digital orthogonal phase shift pulse COTDR sensing device, which comprises a light source 1, a 1x2 optical fiber coupler 2, a digital modulation signal generating device 3, a frequency shift pulse modulator 4, an erbium-doped optical fiber amplifier 5, an optical fiber circulator 6, a sensing optical fiber 7, a 2x2 optical fiber coupler 8, a photoelectric balance detector 9, a signal acquisition device 10 and a signal processing device 11, wherein the light source 1 is connected with the input end of the 1x2 optical fiber coupler 2, the 1x2 optical fiber coupler 2 is provided with two output ends, one output end is used as a signal light output end, and the output end is sequentially connected with the erbium-doped optical fiber amplifier 5, the optical fiber circulator 6 and the sensing optical fiber 7 respectively; the other output end is used as the output end of the low reference light and is sequentially connected with the input end of the 2 × 2 optical fiber coupler 8, the photoelectric balance detector 9, the signal acquisition device 10 and the signal processing device 11; the other input end of the 2x2 optical fiber coupler 8 is connected with the optical fiber circulator 6; wherein:
the light source 1 emits light with a frequency f0The continuous laser light passes through a 1x2 coupler 2 and is divided into two paths of local reference light and signal light: the signal light is modulated into full-digital quadrature phase-shifted pulses containing light frequencies f by a frequency-shift pulse modulator 4 controlled by a digital modulation signal generating device 30+f1、f0+f2And f0+f3The initial phase is 0 degrees, 0 degrees and 90 degrees respectively, and the width of the all-digital orthogonal phase shift pulse is W; the all-digital orthogonal phase shift pulse is amplified by the erbium-doped optical fiber amplifier 5 and transmitted by the optical fiber circulator 6, is injected into the sensing optical fiber 7 and transmitted along the sensing optical fiber 7, sequentially generates backward Rayleigh scattering at each position of the sensing optical fiber 7 and returns along the sensing optical fiber 7, and the optical frequency f of the all-digital orthogonal phase shift pulse containing the phase information used for demodulating each position of the sensing optical fiber is0+f1、f0+f2And f0+f3The all-digital orthogonal phase shift pulse signals are returned by the optical fiber circulator 6 and then reach the 2 multiplied by 2 optical fiber coupler 8, and are mixed and interfered with local reference light; after the optical signals with three frequencies are respectively mixed and interfered with local reference light in a 2x2 optical fiber coupler, two paths of opposite-phase light intensity signals for weakening common-mode noise are output, received by a photoelectric balance detector 9 and converted into voltage signals, and vibration information of each position in the sensing optical fiber 7 is obtained through a signal acquisition device 10 and a signal processing device 11.
The invention discloses a full-digital orthogonal phase shift pulse COTDR sensing method, which comprises the following steps:
step one, the light source emits light with frequency f0The continuous laser is divided into two paths of local reference light and signal light by a 1x2 optical fiber coupler; the signal light is modulated into full digital phase shift pulse by frequency shift pulse modulator controlled by digital modulation signal generator, and T contains 3 pulse signals with width W in each repetition period, wherein the frequency shift is f1And f3Is sent out simultaneously with a frequency shift of f2Modulated signal interval W0Emitting at a frequency f1、f2And f3Is 0 DEG, 0 DEG and 90 DEG, respectively, wherein f1、f2And f3Satisfy f2-f1＝f3-f2Δ f, which is the difference of the pulse frequency shift; the digital phase-shifted pulses have optical frequencies f0+f1、f0+f2And f0+f3Digital phase-shifted optical pulses of width W and optical frequency f0+f1And f0+f3Are emitted simultaneously with an optical frequency f0+f2Pulse interval W of0Sending out;
secondly, the all-digital phase-shifted light pulses are amplified by an erbium-doped optical fiber amplifier and a circulator in sequence and then injected into the sensing optical fiber, and the digital phase-shifted light pulses respectively generate backward Rayleigh scattering in the sensing optical fiber and return to the optical fiber along with the backward Rayleigh scattering; the optical frequency containing phase information used for demodulating all parts of the sensing optical fiber is f0+f1、f0+f2And f0+f3The optical signals are returned by the circulator and then reach the 2 multiplied by 2 optical fiber coupler to be mixed and interfered with the local reference light;
step three, the frequency is f1、f2And f3Respectively mixed with local reference light in a 2x2 optical fiber coupler, and outputting two opposite-phase light intensity signals S for weakening common-mode noise+、S-Received by the photoelectric balance detector and converted into a voltage signal S:
wherein the content of the first and second substances,
and
phase information at the starting points Z and Z + L of the distance sensing fiber, A1(t)、A2(t)、A3(t) envelopes of the three frequency signals, respectively, t is time,
the distance between two points corresponding to the differential phase is defined as n, the effective refractive index of the optical fiber is defined as n, and the light velocity in vacuum is defined as c;
step four, the central frequency of the voltage signal S passing through is f1、f2And f3Respectively obtaining signals S by digital band-pass filtering1、S2、S3：
S1And S3After envelope elimination, the envelope is respectively processed with S2Digital mixing and low-pass filtering, constructing digital quadrature signals I and Q:
wherein the content of the first and second substances,
the differential phase is in direct proportion to the strain of the sensing optical fiber between Z and Z + L, the constructed digital orthogonal signals I and Q are constructed into signals according to Q + I and I, a complex phase angle is obtained to obtain the differential phase phi (Z), and the vibration information of each position of the sensing optical fiber is obtained by monitoring the change of the differential phase phi (Z) along with the time.
Compared with the prior art, the full-digital orthogonal phase shift pulse COTDR sensing device and the method have the following positive effects:
1. by sending digital orthogonal phase shift pulses in the same pulse transmission period and constructing orthogonal phase COTDR signals, only one set of photoelectric detection and data acquisition device is adopted to realize orthogonal phase demodulation under the condition of avoiding reducing the sensing response frequency of the system;
2. the sensing spatial resolution can be flexibly adjusted according to requirements and the intensity of the return light signal is kept stable by flexibly adjusting the pulse intensity and the pulse width;
3. the phase difference change of each position of the sensing optical fiber is obtained through demodulation, the phase difference is linearly related to the stress of the optical fiber, and the distortion of the sensing result caused by the nonlinear correlation of the interference light intensity signal and the stress is eliminated.
Drawings
FIG. 1 is a schematic structural diagram of an all-digital quadrature phase-shifted pulse COTDR sensing device according to the present invention;
FIG. 2 is a schematic diagram of a modulation signal of the digital modulation signal generating apparatus;
FIG. 3 is a block diagram of a full digital quadrature phase shifted pulse CODDR demodulation algorithm;
reference numerals:
1. the device comprises a light source, 2, 1 multiplied by 2 couplers, 3, a digital modulation signal generating device, 4, a frequency shift pulse modulator, 5, an erbium-doped fiber amplifier, 6, a fiber circulator, 7, a sensing fiber, 8, 2 multiplied by 2 fiber couplers, 9, a photoelectric balance detector, 10, a signal collecting device, 11 and a signal processing device.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and the detailed description.
Fig. 1 is a schematic structural diagram of an all-digital quadrature phase-shifted pulse COTDR sensing device according to the present invention. The device comprises a light source 1, a 1x2 optical fiber coupler 2, a digital modulation signal generating device 3, a frequency shift pulse modulator 4, an erbium-doped optical fiber amplifier 5, an optical fiber circulator 6, a sensing optical fiber 7, a 2x2 optical fiber coupler 8, a photoelectric balance detector 9, a signal collecting device 10 and a signal processing device 11, wherein:
the light source 1 emits light with a frequency f0The continuous laser light passes through a 1x2 coupler 2 and is divided into two paths of local reference light and signal light: the signal light is modulated into full-digital quadrature phase-shifted pulses containing light frequencies f by a frequency-shift pulse modulator 4 controlled by a digital modulation signal generating device 30+f1、f0+f2And f0+f3The initial phase is 0 degrees, 0 degrees and 90 degrees respectively, and the width of the all-digital orthogonal phase shift pulse is W; the all-digital orthogonal phase shift pulse is amplified by the erbium-doped optical fiber amplifier 5 and transmitted by the optical fiber circulator 6, is injected into the sensing optical fiber 7 and transmitted along the sensing optical fiber 7, sequentially generates backward Rayleigh scattering at each position of the sensing optical fiber 7 and returns along the sensing optical fiber 7, and the optical frequency f of the all-digital orthogonal phase shift pulse containing the phase information used for demodulating each position of the sensing optical fiber is0+f1、f0+f2And f0+f3The all-digital orthogonal phase-shifted pulse signals are returned by the optical fiber circulator 6 and then reach the 2x2 optical fiber coupler 8, and are mixed and interfered with the local reference light. After the optical signals with three frequencies are respectively mixed and interfered with local reference light in a 2x2 optical fiber coupler, two paths of opposite-phase light intensity signals for weakening common-mode noise are output, received by a photoelectric balance detector 9 and converted into voltage signals, and vibration information of each position in the sensing optical fiber 7 is obtained through a signal acquisition device 10 and a signal processing device 11.
Wherein:
the light source 1 adopts a narrow linewidth (100 Hz-1 MHz) continuous laser and is used for providing laser output with long coherence length required by a system.
The 1 × 2 optical fiber coupler 2 is configured to divide laser light emitted by the continuous laser into two paths, one path of the laser light passes through the frequency shift pulse modulator to generate signal light, and the other path of the laser light serves as local reference light.
The digital modulation signal generating device 3 generates a modulation signal required by the full-digital quadrature phase shift pulse, and the sampling rate of the modulation signal is 100 MS/s-10 GS/s.
The frequency shift pulse modulator 4 is used for modulating and generating full-digital orthogonal phase shift pulse optical signals, the bandwidth of the pulse signal is 10 MHz-1 GHz, the high-speed modulation requirement is met, and the pulse signal comprises an acousto-optic modulator or a double parallel Mach-Zehnder modulator.
The erbium-doped optical fiber amplifier 5 is used for amplifying signal light generated through modulation, has gain of 10-30 dB, and meets the requirement of long-distance detection.
And the optical fiber circulator 6 is used for inputting the signal light into the sensing optical fiber and inputting the returned signal light into the demodulation optical path.
The sensing optical fiber 7 is used for sensing sound wave vibration signals and transmitting optical signals, and the length is 0.1 km-50 km;
the 2 × 2 optical fiber coupler 8 is used for realizing that coherent detection generates two paths of opposite phase interference light intensity signals, and the input signals are returned rayleigh scattering signal light and local reference light.
The photoelectric balance detector 9 is used for receiving the signal output by the optical mixer and outputting a corresponding digital voltage signal with a bandwidth of 10 MHz-1 GHz.
The signal acquisition device 10 is used for acquiring digital voltage signals output by the photoelectric detector.
The signal processing device 11 is configured to process the acquired digital signals and demodulate phase information of each position of the sensing optical fiber, so as to sense vibration information of each position.
The invention discloses a full-digital orthogonal phase shift pulse COTDR sensing method.A light source emits a frequency f0Is subjected to 1x2 couplingThe device is divided into two paths of light of local reference light and signal light; the signal light is modulated into digital phase-shifted pulse light by a frequency-shift pulse modulator controlled by a digital modulation signal generating device, and the digital phase-shifted pulse light contains light frequencies f0+f1、f0+f2And f0+f3The initial phases are 0 degrees, 0 degrees and 90 degrees respectively, and the widths of the digital phase-shifted optical pulses are W. Fig. 2 is a schematic diagram of a modulation signal of the digital modulation signal generating apparatus. The modulation signal of the digital modulation signal generating device is changed as shown in FIG. 2, and comprises 3 pulse signals with width W in each repetition period T, wherein the frequency shift is f1And f3Is sent out simultaneously with a frequency shift of f2Modulated signal interval W0Emitting at a frequency f1、f2And f3Is 0 DEG, 0 DEG and 90 DEG, respectively, wherein f1、f2And f3Satisfy f2-f1＝f3-f2Δ f is the difference in pulse frequency shift. The full-digital orthogonal phase shift pulse is amplified by the erbium-doped optical fiber amplifier and the circulator in sequence and then is injected into the sensing optical fiber, the pulse signal generates backward Rayleigh scattering in the passing optical fiber, the backward Rayleigh scattering returns along the optical fiber, and the optical frequency containing the phase information at each position of the sensing optical fiber for demodulation is f0+f1、f0+f2And f0+f3And the optical signals are returned by the optical fiber circulator together and then reach the 2 multiplied by 2 optical fiber coupler to be mixed and interfered with the local reference light. The 2x2 optical fiber coupler output light interference signal is received by the balanced detector and converted into the form:
the voltage signal of (a), wherein,
and
phase information at the starting points Z and Z + L of the distance sensing fiber, respectively.
Processing the signal according to the block diagram of the full-digital orthogonal phase shift pulse COTDR demodulation algorithm shown in figure 3, and obtaining the signal through a digital band-pass filter
And
S1and S3After envelope elimination, the envelope is respectively processed with S2Digital mixing and low pass filtering to construct a digital quadrature signal
And
wherein the content of the first and second substances,
is a differential phase, and is proportional to the strain of the sensing fiber between Z and Z + L. And constructing a signal according to Q + i.I, solving a complex phase angle to obtain a differential phase phi (Z), and further monitoring the time variation of the differential phase phi (Z) to obtain vibration information of each position of the sensing optical fiber.
Wherein each frequency shift amount f of the all-digital phase-shifted pulse generated by modulation1、f2、f3Using 10 MHz-1 GHz, f1、f2And f3Satisfy f2-f1＝f3-f2Setting the frequency difference delta f as 10 MHz-500 MHz; the pulse width W is 5 ns-500 ns, and the pulse interval W 05 ns-500 ns is adopted, and the interval W between pulses 05 ns-500 ns is used.
Claims (2)
1. A full-digital orthogonal phase shift pulse COTDR sensing device is characterized by comprising a light source (1), a 1x2 optical fiber coupler (2), a digital modulation signal generating device (3), a frequency shift pulse modulator (4), an erbium-doped optical fiber amplifier (5), an optical fiber circulator (6), a sensing optical fiber (7), a 2x2 optical fiber coupler (8), a photoelectric balance detector (9), a signal acquisition device (10) and a signal processing device (11), wherein the light source (1) is connected with the input end of the 1x2 optical fiber coupler (2), the 1x2 optical fiber coupler (2) is provided with two output ends, one output end is used as a signal light output end, and the erbium-doped optical fiber amplifier (5), the optical fiber circulator (6) and the sensing optical fiber (7) are sequentially and respectively connected; the other output end is used as a local reference light output end and is sequentially connected with the input end of the 2x2 optical fiber coupler (8), the photoelectric balance detector (9), the signal acquisition device (10) and the signal processing device (11); the other input end of the 2x2 optical fiber coupler (8) is connected with the optical fiber circulator (6); wherein:
the frequency of the light emitted by the light source (1) is f0The continuous laser light passes through a 1x2 optical fiber coupler (2) and is divided into two paths of local reference light and signal light: the signal light is modulated into full digital quadrature phase shift pulses through a frequency shift pulse modulator (4) controlled by a digital modulation signal generating device (3), and contains light frequencies f0+f1、f0+f2And f0+f3The all-digital orthogonal phase shift pulse with the initial phase of 0 degree, 0 degree and 90 degrees and the width of W; the all-digital orthogonal phase shift pulse is amplified by an erbium-doped optical fiber amplifier (5) and transmitted by an optical fiber circulator (6), is injected into a sensing optical fiber (7) and transmitted along the sensing optical fiber (7), generates backward Rayleigh scattering in turn at each part of the sensing optical fiber (7) and returns along the sensing optical fiber (7), and the optical frequency containing phase information of each part of the sensing optical fiber is f0+f1、f0+f2And f0+f3The all-digital orthogonal phase shift pulse signals are returned together through the optical fiber circulator (6) and then reach the 2 multiplied by 2 optical fiber coupler (8) to be mixed and interfered with local reference light; the optical signals with three frequencies are respectively mixed and interfered with local reference light in a 2x2 optical fiber coupler (8), two paths of opposite-phase light intensity signals for weakening common-mode noise are output, are received by a photoelectric balance detector (9) and are converted into voltage signals, and vibration information of each position in the sensing optical fiber (7) is obtained through a signal acquisition device (10) and a signal processing device (11).
2. A full-digital orthogonal phase-shift pulse COTDR sensing method is characterized by comprising the following steps:
step one, the light source emits light with frequency f0The continuous laser is divided into two paths of local reference light and signal light by a 1x2 optical fiber coupler; the signal light is modulated into full digital phase shift pulse by frequency shift pulse modulator controlled by digital modulation signal generator, and each repetition period T contains 3 pulse signals with width W, wherein the frequency shift is f1And f3Is sent out simultaneously with a frequency shift of f2Modulated signal interval W0Emitting at a frequency f1、f2And f3Is 0 DEG, 0 DEG and 90 DEG, respectively, wherein f1、f2And f3Satisfy f2-f1＝f3-f2Δ f, which is the difference of the pulse frequency shift; the digital phase-shifted pulses have optical frequencies f0+f1、f0+f2And f0+f3Digital phase-shifted optical pulses of width W and optical frequency f0+f1And f0+f3Are emitted simultaneously with an optical frequency f0+f2Pulse interval W of0Sending out;
secondly, the all-digital phase-shifted light pulses are amplified by an erbium-doped optical fiber amplifier and a circulator in sequence and then injected into the sensing optical fiber, and the digital phase-shifted light pulses respectively generate backward Rayleigh scattering in the sensing optical fiber and return to the optical fiber along with the backward Rayleigh scattering; the optical frequency containing phase information used for demodulating all parts of the sensing optical fiber is f0+f1、f0+f2And f0+f3The optical signals are returned by the circulator and then reach the 2 multiplied by 2 optical fiber coupler to be mixed and interfered with the local reference light;
step three, the frequency is f1、f2And f3Respectively mixed with local reference light in a 2x2 optical fiber coupler, and outputting two opposite-phase light intensity signals S for weakening common-mode noise+、S-Received by the photoelectric balance detector and converted into a voltage signal S:
wherein the content of the first and second substances,
and
phase information at the starting points Z and Z + L of the distance sensing fiber, A1(t)、A2(t)、A3(t) envelopes of the three frequency signals, respectively, t is time,
the distance between two points corresponding to the differential phase is defined as n, the effective refractive index of the optical fiber is defined as n, and the light velocity in vacuum is defined as c;
step four, the central frequency of the voltage signal S passing through is f1、f2And f3Respectively obtaining signals S by digital band-pass filtering1、S2、S3：
S1And S3After envelope elimination, the envelope is respectively processed with S2Digital mixing and low-pass filtering, constructing digital quadrature signals I and Q:
wherein the content of the first and second substances,
the differential phase is in direct proportion to the strain of the sensing optical fiber between Z and Z + L, the constructed digital orthogonal signals I and Q are constructed into signals according to Q + I and I, a complex phase angle is obtained to obtain the differential phase phi (Z), and the vibration information of each position of the sensing optical fiber is obtained by monitoring the change of the differential phase phi (Z) along with the time.
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