AU2020102296A4 - A distributed optical fiber sensing system based on heterodyne detection technology - Google Patents
A distributed optical fiber sensing system based on heterodyne detection technology Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- 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
Specification Abstract
The invention discloses a distributed optical fiber sensing system based on
heterodyne detection technology, and belongs to the field of optical fiber
5 sensing. Comprising: Laser light source (1), first coupler (2), acousto-optic
frequency shifter (3), second coupler (4), electro-optic modulator (5), optical
isolator (6), optical fiber amplifier (7), circulator (8), fiber grating (9), sensing
optical fiber (10), third coupler (11), 900 optical mixer (12), fourth coupler (13),
fifth coupler (14), sixth coupler (15), first balanced photodetector (16), second
0 balanced photodetector (17), first low-pass filter (18), a second low-pass filter
(19), data acquisition card (20), signal processor (21) and pulse generator (22).
Advantages are: Low cost, high reliability, strong real-time monitoring ability
and long monitoring distance, ability to realize the restoration and positioning of
vibration and sound signals, and broad application prospects.
1/1
22 b
9 10
b b
1 2 b3 a 4 b' 5 6 7 8 c
a b
I I1 12 c a 14 16 18 "
13 2 0
a15 17 c 19
Figure 1
1, (t f+ Q(t fAmplitude
Arc tan i(t)/ Q(t LPF Phase
Figure 2
STE + LOTE
signal STE a C sTE -LOTE
local oscillator LOTE b S
TE .LOTE
d STE jLO TE
Figure 3
Description
1/1
22 b
9 10 b b 1 2 b3 a 4 b' 5 6 7 8 c a b I I1 12 c a 14 16 18
" 13 20 a15 17 c 19
Figure 1
1, (tf+ Q(t fAmplitude
Arc tan i(t)/ Q(t LPF Phase
Figure 2
STE + LOTE
signal STE a C sTE -LOTE
b S TE .LOTE local oscillator LOTE d STE jLO TE
Figure 3
A Distributed Optical Fiber Sensing System Based on Heterodyne Detection Technology
Technical Field The invention relates to the technical field of optical fiber sensing field, in particular to a distributed optical fiber sound sensing and positioning system, expecially refers to a distributed optical fiber sensing system based on heterodyne detection technology.
Background Technology Currently, distributed optical fiber vibration sensors mainly include interferometric sensors and backscattering sensors. Interferometric sensors mainly include Sagnac interferometer, Mach-Zehnder interferometer (MZI) and Michelson interferometer (MI), which have made great contributions to the large-scale monitoring of optical fiber vibration sensors. Backscattering sensors use the polarization, light intensity, frequency shift and phase changes of backscattered light to measure external physical quantities. It mainly includes phase sensitive optical time domain reflectometer (p-OTDR), polarized light time domain reflectometer (P-OTDR) and phase sensitive optical frequency domain reflectometer (p-OFDR). Among them, <p-OTDR is suitable for distributed vibration or sound sensing with long distance and high spatial resolution, and has obvious advantages in perimeter security, seismic exploration and pipeline monitoring. However, when external vibration or sound acts on a certain position of the sensing fiber, the fiber at this position will be affected by external stress or strain, which will cause the change of fiber length and refractive index, and then cause the phase change of the backscattered light during transmission. Therefore, the external vibration or sound can be measured by detecting the phase change. In the field of coherent Rayleigh scattering distributed optical fiber sensing technology, the random frequency drift of acousto-optic modulator will occur in the working process, leading to introduction of uncertain interference terms in the demodulation process and impact to the demodulation accuracy. In addition, in order to effectively detect heterodyne signals, high-speed data acquisition equipment (sampling rate of GS/s level) is needed. Therefore, dynamic signal monitoring requires high photoelectric response rate and efficient data processing methods, and real-time and fast signal processing is a great challenge. Therefore, in order to solve the above mentioned technical bottleneck and build a high-performance optical fiber sensing network system, the need of a new distributed optical fiber sensing system based on heterodyne detection technology is a urgent problem technical personnel in this field are facing.
Content of the Invention In view of this problem, this invention provides a distributed optical fiber sensing system based on heterodyne detection technology, which solves the technical problems of the influence of frequency drift of acousto-optic frequency shifter on subsequent signal demodulation and the real-time acquisition and processing of large signals. In order to achieve the above purpose, the invention adopts the following technical scheme: A distributed optical fiber sensing system based on heterodyne detection technology, comprising: Laser light source (1), first coupler (2), acousto-optic frequency shifter (3), second coupler (4), electro-optic modulator (5), optical isolator (6), optical fiber amplifier (7), circulator (8), fiber grating (9), sensing optical fiber (10), third coupler (11), 900 optical mixer (12), fourth coupler (13), fifth coupler (14), sixth coupler (15), first balanced photodetector (16), second balanced photodetector (17), first low-pass filter (18), a second low-pass filter
(19), data acquisition card (20), signal processor (21) and pulse generator (22); its characteristics and optical path structure are as follows: The laser light source (1) emits a continuous light, which is divided into two optical signals A1/A2 through the first coupler (2), and Al is divided into B1/B2 through the second coupler (4) by the acousto-optic frequency shifter (3). B Ipasses through the electro-optic modulator (5) and the optical isolator (6) to ensure one-way transmission, reducing the influence of Rayleigh scattered light on the laser light source (1). After that, it is transmitted to the fiber amplifier (7) for amplification, and then enters the fiber grating (9) through the circulator (8) for filtering the pulse optical signal; The A2 passing through the first coupler (2) is divided into C1/C2 through the third coupler (11), and the C1 is used to generate orthogonal signals with the same frequency shift as that of the acousto-optic frequency shifter (3) through the 90-degree optical mixer (12) and is transmitted to the fifth coupler (14); C2 is transmitted to the fourth coupler (13) as the reference light of the distributed optical fiber sensing system; The B2 divided by the second coupler (4) passes through the 90-degree optical mixer (12) to generate difference frequency orthogonal signals and transmit them to the sixth coupler (15); At the same time, the sensing fiber (10) senses the external vibration signal and returns Rayleigh backscattered light carrying the external vibration signal, which is transmitted to the fourth coupler (13) through the circulator (8). At this time, the fourth coupler (13) divides the signal light carrying the external vibration information returned by the circulator (8) and the third coupler (11) into two reference lights for beat frequency, one of which is transmitted to the fifth coupler (14) and transmits the signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the first balanced photodetector (16) through two paths to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the first low-pass filter (18), filter out high-frequency items and direct-current items in the electrical signals output by the first balanced photodetector (16), and transmit them to the data acquisition card (20); The other path divided by the fourth coupler (13) transmits signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the second balanced photodetector (17) through the sixth coupler (15) to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the second low-pass filter (19), filter out high-frequency items and direct-current items in the electrical signals output by the second balanced photodetector (17), and transmit them to the data acquisition card (20); At this time, the data acquisition card (20) divides the electrical signals collected by the first low-pass filter (18) and the second low-pass filter (19) into two paths, one of which is fed back to trigger signal collection in the pulse generator (22) and the other of which is used to modulate the electro-optical modulator (5) to generate pulsed optical signals. The signals are transmitted to the signal processor (21) through the other path of the data acquisition card (20) for signal processing and analysis to obtain the phase and amplitude information of the external vibration signals. The electro-optical modulator (5) is used for modulating continuous light into pulse light. The continuous light source with narrow linewidth is a narrow linewidth external cavity semiconductor. The acousto-optic frequency shifter (3) is used for introducing a continuous frequency shift on the basis of the original optical frequency. The electro-optical modulator (5) is used for modulating continuous light into pulse light. The fiber amplifier (7) is an erbium-doped fiber amplifier.
The pulse generator (22) is used for generating pulse signals with certain pulse width and repetition frequency. The pulse generator (22) is used for generating pulse signals with certain pulse width and repetition frequency. A detection method of distributed optical fiber sensing system based on heterodyne detection technology is characterized by using a distributed optical fiber sensing system based on heterodyne detection technology, which comprises the following steps: Step 1: sense external vibration signals by using a sensing optical fiber (10); Step 2: turn on the laser light source, and the sensing optical fiber (10) returns an external vibration signal;
Step 3: record the output signal light information Q (t) of the first low-pass filter (18) and the output reference light informationI(t) of the second low-pass filter (19) through the data acquisition card (20).
Step 4: Substitute the recorded output signal light information Q (t) and
output reference light information I(t) into I(t)2+Q(t) and Arctan[I(t)/Q (t)] to obtain the amplitude information and phase of the
external vibration signal.
The expression Q (t)= A cos[#s(t)+#0] of the output signal light
information Q (t) and the expression I (t)=Asin[#(t)+#1] of the output reference light information I (t).
Calculate the output informationI(t) and the output information Q(t)
through I(t) 2 +Q(t) 2 to obtain amplitude information A; calculate the output
information I (t) and the output information Q(t) through
ArctanI(t)/Q (t)] to obtain phase Ot)+1.
According to the above technical scheme, compared with the prior art, this invention discloses a distributed optical fiber sensing system based on heterodyne detection technology, which adopts coherent receiving and orthogonal demodulation technology to extract orthogonal components on the optical path, thereby realizing the measurement of distributed optical fiber vibration or acoustic signals, effectively reducing the computation of orthogonal demodulation algorithm, overcoming the influence of frequency instability of modulator on demodulation results, and realizing the dynamic measurement of large phase signals. Compared with the existing distributed optical fiber vibration measurement technology, it has the advantages of low cost, high reliability, strong real-time monitoring ability and long monitoring distance, and can realize the restoration and positioning of vibration and sound signals. It has great application potential in the fields of long-distance natural gas/oil pipeline safety monitoring and resource exploration.
Description of Figures In order to explain the technical scheme in the embodiment of this invention or in the prior art more clearly, the figures used in the embodiment or the description of the prior art will be briefly introduced below. Obviously, the figures in the following description are only the embodiments of the this invention, and other drawings can be obtained according to the provided drawings for ordinary technicians in the field without providing creative labor. Fig. 1 is a schematic structural diagram of a heterodyne interferometric optical fiber sensing time division multiplexing system provided by the this invention.
Fig. 2 is a schematic diagram of the principle of the orthogonal
demodulation algorithm of the present invention;
Fig. 3 is a schematic diagram of the principle of the 90-degree optical
mixer of the present invention.
In the figure: 1. Laser light source; 2. The first coupler; 3. Acousto-optic frequency shifter; 4. The second coupler; 5. Electro-optic modulator; 6. Optical isolator; 7. Fiber amplifier; 8. Circulator; 9. Fiber grating; 10. Sensing fiber; 11. The third coupler; 12. 90-degree optical mixer; 13. The fourth coupler; 14. The fifth coupler; 15. The sixth coupler; 16. The first balanced photodetector; 17. The second balanced photodetector; 18. The first low-pass filter; 19. The second low-pass filter; 20. Data acquisition card; 21. Signal processor; 22. Pulse generator.
Detailed description of the invention The technical scheme in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of those of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention. Embodiment 1 of the present invention discloses a distributed optical fiber sensing system based on the heterodyne detection technology, which comprises: A laser light source (1), a first coupler (2), an acousto-optic frequency shifter (3), a second coupler (4), an electro-optic modulator (5), an optical isolator (6), a fiber amplifier (7), a circulator (8), a fiber grating (9), a sensing fiber (10), a third coupler (11), a 90-degree optical mixer (12), a fourth coupler (13), a fifth coupler (14), a sixth coupler (15), a first balanced photodetector (16), a second balanced photodetector (17), a first low-pass filter (18), a second low-pass filter (19), a data acquisition card (20), a signal processor (21), and a pulse generator (22); it is characterized in that the optical path structure is as follows: The laser light source (1) emits a continuous light, which is divided into two optical signals A1/A2 through the first coupler (2), and Al is divided into B1/B2 through the second coupler (4) by the acousto-optic frequency shifter (3). B1 passes through the electro-optic modulator (5) and the optical isolator (6) to ensure one-way transmission, reducing the influence of Rayleigh scattered light on the laser light source (1). After that, it is transmitted to the fiber amplifier (7) for amplification, and then enters the fiber grating (9) through the circulator (8) for filtering the pulse optical signal; The A2 passing through the first coupler (2) is divided into C1/C2 through the third coupler (11), and the C1 is used to generate orthogonal signals with the same frequency shift as that of the acousto-optic frequency shifter (3) through the 90-degree optical mixer (12) and is transmitted to the fifth coupler (14); C2 is transmitted to the fourth coupler (13) as the reference light of the distributed optical fiber sensing system; The B2 divided by the second coupler (4) passes through the 90-degree optical mixer (12) to generate difference frequency orthogonal signals and transmit them to the sixth coupler (15); At the same time, the sensing fiber (10) senses the external vibration signal and returns Rayleigh backscattered light carrying the external vibration signal, which is transmitted to the fourth coupler (13) through the circulator (8). At this time, the fourth coupler (13) divides the signal light carrying the external vibration information returned by the circulator (8) and the third coupler (11) into two reference lights for beat frequency, one of which is transmitted to the fifth coupler (14) and transmits the signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the first balanced photodetector (16) through two paths to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the first low-pass filter (18), filter out high-frequency items and direct-current items in the electrical signals output by the first balanced photodetector (16), and transmit them to the data acquisition card (20);
The other path divided by the fourth coupler (13) transmits signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the second balanced photodetector (17) through the sixth coupler (15) to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the second low-pass filter (19), filter out high-frequency items and direct-current items in the electrical signals output by the second balanced photodetector (17), and transmit them to the data acquisition card (20); At this time, the data acquisition card (20) divides the electrical signals o collected by the first low-pass filter (18) and the second low-pass filter (19) into two paths, one of which is fed back to trigger signal collection in the pulse generator (22) and the other of which is used to modulate the electro-optical modulator (5) to generate pulsed optical signals. The signals are transmitted to the signal processor (21) through the other path of the data acquisition card (20) for signal processing and analysis to obtain the phase and amplitude information of the external vibration signals. The electro-optical modulator (5) is used for modulating continuous light into pulse light. The continuous light source with narrow linewidth is a narrow linewidth external cavity semiconductor. The acousto-optic frequency shifter (3) is used for introducing a continuous frequency shift on the basis of the original optical frequency. The electro-optical modulator (5) is used for modulating continuous light into pulse light. The fiber amplifier (7) is an erbium-doped fiber amplifier. The pulse generator (22) is used to generate a pulse signal with a certain pulse width and repetition frequency. The pulse generator (22) is used to generate a pulse signal with a certain pulse width and repetition frequency.
Embodiment 2 of the present invention discloses a distributed optical fiber sensing system based on the heterodyne detection technology, which comprises: The laser light source (1), with its output laser beam being divided into three parts, of which one is used to provide continuous laser to the electro-optic modulator (5) to generate a pulse laser which then enters the sensing fiber through the circulator (8) to carry external vibration information; the second one is used for the reference light of the distributed optical fiber sensing system; and the third one is used to generate a pair of orthogonal signals with the same frequency shift frequency as that of the electro-optic modulator (5). The first coupler (2), with its input port a being connected with the input port of the laser light source (1), and output port b being connected with the acousto-optic frequency shifter (3) to introduce a continuous frequency shift based on the original optical frequency; its output port c is connected with the input port a of the third coupler (11) to generate a pair of orthogonal signals with the same frequency shift as the electro-optic modulator 5 and a reference light of the distributed optical fiber sensing system. The acousto-optic frequency shifter (3), whose input port is connected with the output port b of the first coupler (2), is used for introducing a continuous frequency shift on the basis of the original optical frequency. The second coupler (4), with its input port a being connected with the output port of the acousto-optic frequency shifter (3), and output ports b and c being respectively connected with the input port a of the electro-optic modulator (5) and the input port b of the fourth coupler (13). The electro-optic modulator (5), with its input port a being connected with the output port b of the second coupler (4) and its input port b being connected with the output port a of the pulse generator (22), is used for modulating the continuous laser output by the laser light source (1) into pulse laser. The optical isolator (6), the input port of which is connected with the output port of the electro-optic modulator (5), is used for unidirectionally transmitting the periodically repeated pulse light, and reducing the influence of Rayleigh backscattered light in the optical fiber on the laser light source (1). The erbium-doped fiber amplifier (7), whose input port is connected with the output port of the optical isolator (6), is used for amplifying the optical power of the periodically repeated pulse light, and the amplified pulse light signal is output to the fiber grating (9) through the circulator (8). The circulator (8), the input port a of which is connected with the output port of the erbium-doped fiber amplifier (7), is used for outputting the pulse optical signal amplified by the erbium-doped fiber amplifier (7) to the fiber grating (9). The fiber grating (9), whose input port is connected with the output port b of the circulator (8), is used for filtering the pulse optical signal. The sensing fiber (10), the input port of which is connected with the output port c of the circulator (8), is used for sensing external vibration signals and returning Rayleigh backscattered light carrying the external vibration signals. The third coupler (11), the input port a of which is connected with the output port c of the first coupler (2), for dividing the continuous light output by the first coupler (2) into two parts, one of which is used for subsequent generation of orthogonal signals with the same frequency shift frequency as that of the acousto-optic frequency shifter 3, and the other of which is used as the reference light of distributed optical fiber sensing system. The 90-degree optical mixer (12), whose input ports a and b are respectively connected with the output port b of the third coupler (11) and the output port c of the second coupler (4), is used to generate orthogonal signals with the same frequency shift frequency as that of the acousto-optic frequency shifter 3. The 90-degree optical mixer (12) actually outputs four signals, i.e., a pair of sum frequency orthogonal signals and a pair of difference frequency orthogonal signals. In this patent, the two difference frequency orthogonal signals are taken as the output ports c and d of the 90 optical mixer (12).
The fourth coupler (13), whose input ports a and b are respectively connected with the output port d of the circulator (8) and the output port c of the third coupler (11) respectively, is used to beat the signal light carrying the external vibration information returned by the circulator (8) and the reference light branched off by the third coupler. The fifth coupler (14), whose input ports a and b are respectively connected with the output port c of the 90-degree optical mixer (12) and the output port c of the fourth coupler (13), is used to beat the signal carrying the external vibration information with one of the orthogonal signals. The sixth coupler (15), whose input ports a and b are respectively connected with the output port d of the fourth coupler (13) and the output port d of the 90-degree optical mixer (12), is used to beat the signal carrying the external vibration information with one of the orthogonal signals. The first balanced photodetector (16), whose input ports a and b are connected with the output ports c and d of the fifth coupler (14) respectively, is used for detecting two heterodyne optical signals and converting the optical signals into electrical signals for output. The second balanced photodetector (17), whose input ports a and b are connected with the output ports c and d of the sixth coupler (15) respectively, is used for detecting two heterodyne optical signals and converting the optical signals into electrical signals for output. The first low-pass filter (18), the input port of which is connected with the output port of the first balanced photodetector (16), is used for filtering out high-frequency items and direct-current items in the electrical signal output by the first balanced photodetector (16). The second low-pass filter (19), the input port of which is connected with the output port of the second balanced photodetector (17), is used for filtering out high-frequency items and direct-current items in the electrical signal output by the second balanced photodetector (17).
The data acquisition card (20), with its input ports a and b being connected with the first low-pass filter (18) and the second low-pass filter (19) respectively, for collecting the electrical signals output by the first low-pass filter (18) and the second low-pass filter (19), and its trigger input port c being connected with the output port b of the pulse generator (22) for receiving the trigger pulse output by the pulse generator (22) to trigger a data collection by the data acquisition card (20) for the signal processor (21) to process. The signal processor (21), the input port of which is connected with the output port d of the data acquisition card (20), is used for recombining the o collected mutually orthogonal time series electrical signals and obtaining the phase information of the Rayleigh backscattered light signal in the sensing fiber (10) through an arctangent phase demodulation algorithm and a filtering algorithm. The pulse generator (22), the two output ports a and b of which are connected with the input port b of the electro-optical modulator (5) and the trigger input port c of the acquisition card (20) respectively, is used for generating pulse signals with certain pulse width and repetition frequency, one of which is used for modulating the electro-optical modulator (5) to generate pulse optical signals, and the other is used for triggering the data acquisition card (20) to collect data. Embodiment 3 of the present invention discloses a detection method of distributed optical fiber sensing system based on the heterodyne detection technology, which comprises the following steps: Firstly, the laser light source is turned on, and the optical signal is transmitted according to Embodiment 1 and the device shown in Figure 1; secondly, the sensing fiber (10) senses the external vibration signal, and then returns the Rayleigh backscattered light carrying the external vibration signal, which is transmitted to the fourth coupler (13) as shown in Figure 1. The fourth coupler (13) carries the external vibration signal to beat the frequency and transmits the signal to the photodetector, converting the optical signal into an electrical signal and outputting it to the data acquisition card (20) for recording through the low-pass filter. the first low-pass filter (18) generates the signal light information Q (t)=Acos[#s(t)+#], and the second low-pass filter 19) generates the reference light information (t)=Asi[#(t)+#]. Calculate I (t) and Q (t) by I(t)2+Q(t 2 to get the amplitude information A , and calculate I (t) and Q (t) by Arctan[I (t)/Q (t)] to get the phase #t)+#0
Embodiment 4 of the present invention discloses a detection method of distributed optical fiber sensing system based on the heterodyne detection technology. The signal light and reference light at the two output ports of the
first low-pass filter (18) and the second low-pass filter (19) areQ(t) and I(t), respectively, and the expression is as follows:
Q (t) = A cos[#s(t) +#1] I (t)= A sin[#(t)+#1]
The phase #P)+#1 and amplitude information A of the external vibration signal can be obtained by performing the operations shown in Fig. 2
with the above-mentioned Q (t) and I (t). The various embodiments in this Specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant part can be found in the description of the method. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention should not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.
Claims (1)
1. A distributed optical fiber sensing system based on heterodyne detection technology, comprising: Laser light source (1), first coupler (2), acousto-optic frequency shifter (3), second coupler (4), electro-optic modulator (5), optical isolator (6), optical fiber amplifier (7), circulator (8), fiber grating (9), sensing optical fiber (10), third coupler (11), 900 optical mixer (12), fourth coupler (13), fifth coupler (14), sixth coupler (15), first balanced photodetector (16), second balanced photodetector (17), first low-pass filter (18), a second low-pass filter (19), data acquisition card (20), signal processor (21) and pulse generator (22); its characteristics and optical path structure are as follows: The laser light source (1) emits a continuous light, which is divided into two optical signals A1/A2 through the first coupler (2), and Al is divided into B1/B2 through the second coupler (4) by the acousto-optic frequency shifter (3). B Ipasses through the electro-optic modulator (5) and the optical isolator (6) to ensure one-way transmission, reducing the influence of Rayleigh scattered light on the laser light source (1). After that, it is transmitted to the fiber amplifier (7) for amplification, and then enters the fiber grating (9) through the circulator (8) for filtering the pulse optical signal; The A2 path passing through the first coupler (2) is divided into C1/C2 paths through the third coupler (11), and the C1 path is used to generate orthogonal signals with the same frequency shift as that of the acousto-optic frequency shifter (3) through the 90-degree optical mixer (12) and is transmitted to the fifth coupler (14); C2 is transmitted to the fourth coupler (13) as the reference light of the distributed optical fiber sensing system; The B2 path divided by the second coupler (4) passes through the -degree optical mixer (12) to generate difference frequency orthogonal signals and transmit them to the sixth coupler (15);
At the same time, the sensing fiber (10) senses the external vibration signal and returns Rayleigh backscattered light carrying the external vibration signal, which is transmitted to the fourth coupler (13) through the circulator (8). At this time, the fourth coupler (13) divides the signal light carrying the external vibration information returned by the circulator (8) and the third coupler (11) into two reference lights for beat frequency, one of which is transmitted to the fifth coupler (14) and transmits the signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the first balanced photodetector (16) through two paths to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the first low-pass filter (18), filter out high-frequency items and direct-current items in the electrical signals output by the first balanced photodetector (16), and transmit them to the data acquisition card (20); The other path divided by the fourth coupler (13) transmits signal carrying external vibration information and one path of beat frequency in the orthogonal signal to the second balanced photodetector (17) through the sixth coupler (15) to detect two paths of heterodyne optical signals, convert the optical signals into electrical signals, output them to the second low-pass filter (19), filter out high-frequency items and direct-current items in the electrical signals output by the second balanced photodetector (17), and transmit them to the data acquisition card (20); At this time, the data acquisition card (20) divides the electrical signals collected by the first low-pass filter (18) and the second low-pass filter (19) into two paths, one of which is fed back to trigger signal collection in the pulse generator (22) and the other of which is used to modulate the electro-optical modulator (5) to generate pulsed optical signals. The signals are transmitted to the signal processor (21) through the other path of the data acquisition card (20) for signal processing and analysis to obtain the phase and amplitude information of the external vibration signals.
2, A distributed optical fiber sensing system based on heterodyne detection technology described by claim 1 and its characteristics are: The laser light source (1) is a continuous light source with narrow line width. 3, A distributed optical fiber sensing system based on heterodyne detection technology described by claim 2 and its characteristics are: The continuous light source with narrow linewidth is a narrow linewidth external cavity semiconductor. 4, A distributed optical fiber sensing system based on heterodyne detection technology described by claim 1 and its characteristics are: The acousto-optic frequency shifter (3) is used for introducing a continuous frequency shift on the basis of the original optical frequency. 5, A distributed optical fiber sensing system based on heterodyne detection technology described by claim 1 and its characteristics are: The electro-optical modulator (5) is used for modulating continuous light into pulse light.
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| CN114152327A (en) * | 2021-12-13 | 2022-03-08 | 中国科学院光电技术研究所 | Vibration detection method based on cavity ring-down technology |
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| CN113390441B (en) * | 2021-06-01 | 2023-07-21 | 重庆邮电大学 | Refractive index change sensing device and measuring method |
| CN113447112A (en) * | 2021-06-18 | 2021-09-28 | 天津大学 | Reflected light-based high-frequency vibration sensing system and high-frequency signal demodulation method |
| CN113624322B (en) * | 2021-08-02 | 2023-06-09 | 太原理工大学 | High-speed railway contact net trouble optical fiber detection device |
| CN114623920B (en) * | 2022-03-15 | 2023-01-10 | 北京航空航天大学 | phi-OTDR type distributed optical fiber acoustic wave sensing system and signal demodulation method |
| CN114894227A (en) * | 2022-07-15 | 2022-08-12 | 安徽至博光电科技股份有限公司 | Optical fiber sensing integrated optical chip and system thereof |
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| CN104457960B (en) * | 2014-12-11 | 2017-05-24 | 中国科学院半导体研究所 | Distributed optical fiber sensing system based on coherent reception technology |
| EA035577B1 (en) * | 2014-12-23 | 2020-07-09 | Эни С.П.А. | Reflectometric vibration measurement system and relative method for monitoring multiphase flows |
| US9958605B2 (en) * | 2015-12-01 | 2018-05-01 | Rhode Island Board Of Education, State Of Rhode Island And Providence Plantations | Weak reflection terahertz fiber optic devices for distributed sensing applications |
| US20190003879A1 (en) * | 2015-12-08 | 2019-01-03 | Hawk Measurement Systems Pty. Ltd. | Improved optical fiber sensing system |
| CN107976248B (en) * | 2016-10-25 | 2019-09-13 | 北京大学 | It can be realized the distributed optical fiber sensing system and its measurement method of all phase demodulation |
| CN106679790B (en) * | 2016-12-05 | 2023-04-21 | 华南理工大学 | Cross-correlation demodulation method for improving sensitivity of distributed optical fiber vibration sensing |
| CN207280479U (en) * | 2017-08-30 | 2018-04-27 | 中国电子科技集团公司第三十四研究所 | A kind of φ-OTDR quadrature phase demodulation systems |
| CN108489598A (en) * | 2018-05-21 | 2018-09-04 | 浙江杰昆科技有限公司 | Phase sensitive optical time domain reflectometer phase simulates coherent demodulation system and method |
| CN109459126B (en) * | 2018-09-21 | 2020-12-29 | 南京法艾博光电科技有限公司 | Distributed optical fiber vibration sensing device and method for reducing detection dead zone probability |
| CN109323750B (en) * | 2018-11-14 | 2021-08-06 | 武汉理工光科股份有限公司 | Distributed optical fiber vibration sensing system and phase demodulation method |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114152327A (en) * | 2021-12-13 | 2022-03-08 | 中国科学院光电技术研究所 | Vibration detection method based on cavity ring-down technology |
| CN114152327B (en) * | 2021-12-13 | 2023-12-22 | 中国科学院光电技术研究所 | Vibration detection method based on cavity ring-down technology |
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| CN111289089A (en) | 2020-06-16 |
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