Apparatus for suppressing coherent rayleigh interference

Abstract

The embodiment of the present application provides a coherent Rayleigh interference suppression device, which comprises a signal offset device, a first filter and a second filter; the signal offset device is used for causing frequency offset of a passing signal; and the first filter and the second filter are used for filtering signal noise generated based on coherent Rayleigh interference. The coherent Rayleigh interference suppression device provided by the embodiment of the present application adds a signal offset device in a bidirectional MZI and adds a filter at a receiving end, suppresses coherent Rayleigh interference in a frequency shift manner, reduces intensity noise superimposed due to coherent Rayleigh scattering noise, and increases correctness and robustness of a system, so that the device can be applied to long-distance sensing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, in particular to a coherent Rayleigh interference suppression device. BACKGROUND

[0002] The optical fiber fingerprint takes optical fiber as the transmission medium, has the advantages of small volume, light weight, easy bending, small loss, anti-electromagnetic interference, good anti-radiation performance, etc., and can realize the acoustic information sensing function based on the submarine optical and electrical composite cable (hereinafter referred to as submarine cable). The submarine cable monitoring prototype based on the interference type optical fiber fingerprint technology can greatly improve the sensing sensitivity and frequency response range of the submarine cable to the acoustic vibration in the surrounding environment, can identify the wideband weak signals such as ship engine, anchor lifting machine, net lifting machine and underwater exploration operation which endanger the safety of the submarine cable, and can realize the wide range of dangerous event prediction and judgment of the submarine cable in the water. At the same time, the submarine cable near the ship anchor throwing, fishing net dragging and other events can be accurately positioned and warned, so as to reduce the risk of external damage to the submarine cable and improve the power supply reliability.

[0003] The submarine cable monitor based on the interference type optical fiber fingerprint technology can be classified into intensity type, polarization type, phase interference type and the like according to the principle, wherein the phase interference type is most widely applied due to its high sensitivity and high measurement accuracy. According to the structure and principle of the measuring device, the phase interference type can be divided into Michelson type, Mach-Zehnder type, Fabry-Perot type and Sagnac type. However, in the interference of the traditional bidirectional symmetrical Mach-Zehnder interferometer (MZI), due to the coherence of Rayleigh backscattering signal and sensing signal, the intensity noise will be superimposed after interference, resulting in incorrect demodulation position. Moreover, the Rayleigh backscattering light accumulates with the length of the optical fiber, and when the bidirectional symmetrical MZI is applied to long distance sensing, the intensity noise superimposed by the Rayleigh backscattering light will be stronger, increasing the uncertainty of demodulation. SUMMARY

[0004] The present application provides a coherent Rayleigh interference suppression device to solve the technical problem of low position demodulation accuracy caused by coherent Rayleigh interference in the prior art.

[0005] To solve the above technical problems, the present application provides a coherent Rayleigh interference suppression device, which comprises:

[0006] A signal offset device, a first filter and a second filter;

[0007] The first end of the signal offset device is connected with the second end of the first circulator, and the second end of the signal offset device is connected with the first end of the second coupler;

[0008] The first end of the first filter is connected to the first end of the first photodetector, and the second end of the first filter is connected to the first end of the acquisition card.

[0009] The first end of the second filter is connected to the first end of the second photodetector, and the second end of the second filter is connected to the second end of the acquisition card.

[0010] The signal offset device is used to cause the frequency offset of the passing signal.

[0011] The first filter and the second filter are used to filter the signal noise generated based on coherent Rayleigh interference.

[0012] In some embodiments, further comprising a first coupler;

[0013] The first end of the first coupler is connected to the laser emitter, the second end of the first coupler is connected to the first end of the second circulator, and the third end of the first coupler is connected to the first end of the first circulator.

[0014] In some embodiments, further comprising:

[0015] The third end of the first circulator is connected to the second end of the first photodetector.

[0016] The third end of the second circulator is connected to the second end of the second photodetector.

[0017] In some embodiments, further comprising:

[0018] A first optical fiber arranged between the second coupler and the third coupler.

[0019] A second optical fiber arranged between the second coupler and the third coupler.

[0020] In some embodiments, further comprising a third optical fiber:

[0021] The third optical fiber is arranged between the third coupler and the second circulator.

[0022] In some embodiments, the signal offset device is an acousto-optic modulator or an IQ modulator.

[0023] In some embodiments, further comprising a driving device;

[0024] The driving device is connected to the third end of the signal offset device.

[0025] In some embodiments, the first filter is a low-pass filter or a digital filter.

[0026] The second filter is a low-pass filter or a digital filter.

[0027] In some embodiments, further comprising:

[0028] The frequency offset range of the signal offset device is 20MHz to 400MHz.

[0029] In some embodiments, further comprising:

[0030] The frequency offset of the signal offset device is 100MHz.

[0031] The coherent Rayleigh interference suppression device provided by the embodiments of the present application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses coherent Rayleigh interference through frequency shifting, reduces the intensity noise superimposed due to coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that it can be applied to long-distance sensing. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present application or prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0033] Figure 1 is a structural schematic diagram of a conventional bidirectional symmetric MZI provided by the embodiments of the present application;

[0034] Figure 2 is a structural schematic diagram of a coherent Rayleigh interference suppression device provided by the embodiments of the present application. DETAILED DESCRIPTION

[0035] At present, based on the principle of symmetric Mach-Zehnder interferometer (MZI), the monitoring and early warning of submarine cable acoustic information can be realized. Based on the time difference between the arrival time of the uplink light and the downlink light at the external vibration position, the two channels of the acquisition card collect the electrical signals of the two photodetectors, so that the position of the vibration can be accurately located by calculating the time difference of the interference signals detected by the two detection units, thereby realizing the positioning of the external vibration. However, due to the coherence of Rayleigh backscattering signal and sensing signal, the intensity noise will be superimposed after interference, resulting in incorrect demodulation position; the Rayleigh backscattering light accumulates with the length of the optical fiber, and when the bidirectional symmetric MZI is applied to long-distance sensing, the intensity noise superimposed by the Rayleigh backscattering light will be stronger, increasing the uncertainty of demodulation.

[0036] The conventional bidirectional symmetric MZI interference cannot meet the demand of stable and accurate positioning of the external vibration position. Based on this, the present application provides a coherent Rayleigh interference suppression device to solve the technical problem of low position demodulation accuracy in the prior art.

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Figure 1 This is a schematic diagram of the structure of a conventional bidirectional symmetrical MZI provided in the embodiments of this application, such as... Figure 1 As shown, the main principle of this technology is as follows: Coupler 1 splits the output beam of the semiconductor laser (LD) into two beams, which are transmitted in two single-mode optical fibers respectively. The upper beam is transmitted through coupler 2 in fiber 1 and fiber 2 respectively, and then combined by coupler 3, causing interference. After passing through fiber 3, the change in interference light intensity is detected at photodetector 2. Similarly, photodetector 1 can detect the change in interference light intensity after the lower beam is split and combined. Therefore, external vibration is monitored by detecting the change in light intensity. Since the upper and lower beams arrive at the external vibration location at different times, the two channels of the acquisition card collect the electrical signals of the two photodetectors. Therefore, by calculating the time difference between the two detection units detecting the interference signal, the location of the vibration can be accurately located, thereby realizing the localization of external vibration.

[0039] In a traditional symmetrical MZI interferometer, the two interferometers share the same optical path but propagate in opposite directions. Photodetector 1 detects the counter-clockwise transmitted sensing signal. and The photodetector 2 detects the clockwise transmitted sensing signal by observing the change in interference light intensity. and The change in interference light intensity. According to Figure 1 In the fiber optic interference structure, the AC component of the light intensity output by the two photodetectors can be expressed as:

[0040]

[0041]

[0042] in and They are respectively and of

[0043] amplitude, The phase change is due to vibration, and τ is the signal delay related to the vibration position. I in equations (1) and (2) 上 and I 下The cross-correlation is performed to find a peak point of the cross-correlation function, and the time delay τ of the signal can be mapped, so that the position of the external disturbance can be calculated.

[0044] However, Rayleigh backscattered light will be generated when the sensing signal light is transmitted at different positions of the optical fiber, such as the clockwise-transmitted sensing signal and generates counterclockwise-transmitted Rayleigh backscattered light and and vice versa. Therefore, the counterclockwise-transmitted Rayleigh backscattered light and has the same frequency as the counterclockwise-transmitted effective sensing signal and coherent Rayleigh interference is generated, and it is difficult to calculate the position of the external disturbance signal. The following formula takes the counterclockwise-transmitted Rayleigh backscattered light and and the counterclockwise-transmitted effective sensing signal and as an example:

[0045]

[0046] where R is the Rayleigh scattering coefficient of the optical fiber, is the phase difference between the Rayleigh backscattered signal and the effective sensing signal, is the phase difference between the two Rayleigh scattering signals. As can be seen from formula (3), in addition to the effective interference signal of the first term, Rayleigh backscattering will introduce coherent Rayleigh interference, which superimposes intensity noise on the effective interference signal, thereby increasing the uncertainty of demodulation.

[0047] Figure 2 is a structural schematic diagram of a coherent Rayleigh interference suppression device provided by an embodiment of the application, as Figure 2 indicated, the application provides a coherent Rayleigh interference suppression device, comprising:

[0048] a signal offset device, a first filter and a second filter;

[0049] The first end of the signal offset device is connected to the second end of the first circulator, and the second end of the signal offset device is connected to the first end of the second coupler.

[0050] The first end of the first filter is connected to the first end of the first photodetector, and the second end of the first filter is connected to the first end of the acquisition card.

[0051] The first end of the second filter is connected with the first end of the second photodetector, and the second end of the second filter is connected with the second end of the acquisition card.

[0052] The signal offset device is used for frequency offset of the passing signal.

[0053] The first filter and the second filter are used for filtering signal noise generated based on coherent Rayleigh interference.

[0054] Specifically, the signal offset device is added in the structure of the bidirectional MZI, and the first filter and the second filter are added in the receiving end. And The frequency of the clockwise transmission sensing signal And is offset by the signal offset device, and the frequency of the counterclockwise transmission Rayleigh backscattering light And is also offset, and the frequency offset of the effective sensing signal And

[0055] transmitted counterclockwise is 0 MHz, and the frequency offsets of the two are different. In this case, the beat frequency components of the Rayleigh backscattering signal and the effective sensing signal can be filtered out by the filters in the receiving end. The first coupler is coupler 1, the first circulator is circulator 1, the second circulator is circulator 2, the first photodetector is photodetector 1, and the second photodetector is photodetector 2.

[0056] For example, an acousto-optic modulator (AOM) and its matching drive are added in the structure of the bidirectional MZI, and a low-pass filter is added in the receiving end.

[0057] For another example, an IO modulator and its matching drive are added in the structure of the bidirectional MZI, and a digital filter is added in the receiving end.

[0058] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI, adds a filter in the receiving end, suppresses coherent Rayleigh interference by frequency offset, reduces intensity noise superimposed due to coherent Rayleigh scattering noise, and increases correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0059] In some embodiments, the first coupler is further connected with a laser emitter.

[0060] Specifically, the coupler 1 is connected with the semiconductor laser, the coupler 1 divides the output light beam of the semiconductor laser into two beams, which are transmitted in the upper path and the lower path single-mode optical fibers respectively. Because the upper path light and the lower path light reach the external vibration position at different times, the two channels of the acquisition card acquire the electrical signals of the two photodetectors, so that the position of the vibration can be accurately located by calculating the time difference of the interference signals detected by the two detection units, so that the positioning of the external vibration is realized.

[0061] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0062] In some embodiments, further comprising:

[0063] The third end of the first circulator is connected with the second end of the first photodetector;

[0064] The third end of the second circulator is connected with the second end of the second photodetector.

[0065] Specifically, the first end of the circulator 1 is connected with the third end of the coupler 1, the second end of the circulator 1 is connected with the first end of the signal offset device, and the third end of the circulator 1 is connected with the second end of the photodetector 1. The first end of the circulator 2 is connected with the second end of the coupler 1, the second end of the circulator 2 is connected with the first end of the optical fiber 3, and the third end of the circulator 2 is connected with the second end of the photodetector 2.

[0066] Further, the output light beams divided into two beams by the coupler 1 are transmitted in two paths of single-mode optical fibers through the circulator 1 and the circulator 2.

[0067] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0068] In some embodiments, further comprising:

[0069] A first optical fiber arranged between the second coupler and the third coupler;

[0070] A second optical fiber arranged between the second coupler and the third coupler.

[0071] Specifically, the first end of the optical fiber 1 is connected with the second end of the coupler 2, and the second end of the optical fiber 1 is connected with the second end of the coupler 3. The first end of the optical fiber 2 is connected with the third end of the coupler 2, and the second end of the optical fiber 2 is connected with the third end of the coupler 3. The first optical fiber is the optical fiber 1, and the second optical fiber is the optical fiber 2.

[0072] Further, the uplink light is transmitted in the optical fiber 1 and the optical fiber 2 through the coupler 2 respectively, and then interferes after being combined by the coupler 3, and the change of the interference light intensity is detected at the photodetector 2 after passing through the optical fiber 3; similarly, the change of the interference light intensity after the downlink light is split and then combined can be detected at the photodetector 1, so that the external vibration is monitored by detecting the change of the light intensity.

[0073] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0074] In some embodiments, a third optical fiber is further included:

[0075] The third optical fiber is arranged between the third coupler and the second circulator.

[0076] Specifically, the first end of the optical fiber 3 is connected with the first end of the coupler 3, and the second end of the optical fiber 3 is connected with the second end of the circulator 2. The third optical fiber is the optical fiber 3.

[0077] Further, the uplink light is transmitted in the optical fiber 1 and the optical fiber 2 through the coupler 2 respectively, and then interferes after being combined by the coupler 3, and the change of the interference light intensity is detected at the photodetector 2 after passing through the optical fiber 3; similarly, the change of the interference light intensity after the downlink light is split and then combined can be detected at the photodetector 1, so that the external vibration is monitored by detecting the change of the light intensity.

[0078] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0079] In some embodiments, the signal offset device is an acousto-optic modulator or an IQ modulator.

[0080] Specifically, the signal offset device is used for causing the passing signal to have a frequency offset, and can be an acousto-optic modulator, an IQ modulator, or other devices that can have the same effect.

[0081] For example, the structure of the bidirectional MZI is added with an acousto-optic modulator and its matching drive, and a low-pass filter is added at the receiving end.

[0082] For example, the structure of the bidirectional MZI is added with an IO modulator and its matching drive, and a digital filter is added at the receiving end.

[0083] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI, adds a filter at the receiving end, suppresses coherent Rayleigh interference in a frequency shift manner, reduces intensity noise superimposed due to coherent Rayleigh scattering noise, and increases correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0084] In some embodiments, the device further comprises a driving device;

[0085] The driving device is connected to the third end of the signal offset device.

[0086] Specifically, in the case of using an acousto-optic modulator, the acousto-optic modulator is configured with a corresponding driving device.

[0087] For example, the structure of the bidirectional MZI is added with an acousto-optic modulator and its matching drive, and a low-pass filter is added at the receiving end.

[0088] The coherent Rayleigh interference suppression device provided by the embodiment of the application adds a signal offset device in the bidirectional MZI, adds a filter at the receiving end, suppresses coherent Rayleigh interference in a frequency shift manner, reduces intensity noise superimposed due to coherent Rayleigh scattering noise, and increases correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0089] In some embodiments, the first filter is a low-pass filter or a digital filter;

[0090] The second filter is a low-pass filter or a digital filter.

[0091] Specifically, the filter added at the receiving end is used for filtering signal noise generated based on coherent Rayleigh interference, and can be a low-pass filter, a digital filter, or other devices that can have the same effect.

[0092] For example, the structure of the bidirectional MZI is added with an acousto-optic modulator and its matching drive, and a low-pass filter is added at the receiving end.

[0093] For example, the structure of the bidirectional MZI is added with an IO modulator and its matching drive, and a digital filter is added at the receiving end.

[0094] The coherent Rayleigh interference suppression device provided in the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0095] In some embodiments, further comprising:

[0096] The frequency offset range of the signal offset device is 20MHz to 400MHz.

[0097] Specifically, considering that the frequency shift range of a general acousto-optic modulator is above 0MHz to 100MHz, the bandwidth of the effective signal in the embodiment of the application is below 10MHz. The frequency offset range of the signal offset device can be selected as 20MHz to 400MHz.

[0098] The coherent Rayleigh interference suppression device provided in the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0099] In some embodiments, further comprising:

[0100] The frequency offset of the signal offset device is 100MHz.

[0101] Specifically, considering that the frequency shift range of a general acousto-optic modulator is above 0MHz to 100MHz, the bandwidth of the effective signal in the embodiment of the application is below 10MHz. The frequency offset range of the signal offset device can be selected as 100MHz.

[0102] The coherent Rayleigh interference suppression device provided in the embodiment of the application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference in the form of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0103] The method in the above embodiment is further described below with specific examples.

[0104] Taking the frequency offset of the acousto-optic modulator as 100MHz as an example.

[0105] After adding the acousto-optic modulator and its matching drive, the clockwise transmission of the sensing signal and The frequency offset of the Rayleigh backscattering light transmitted in the counterclockwise direction is 100 MHz after the frequency shift by the AOM and The frequency offset of the effective sensing signal transmitted in the counterclockwise direction is 0 MHz, and the frequency offsets of the two are different, so formula (3) is rewritten as:

[0106]

[0107] where Δf is the frequency offset of the AOM, and the frequency offset is taken as 100 MHz in the following Figure 2 After that, a low-pass filter is added to filter out the high-frequency component at Δf, and formula (4) is rewritten as:

[0108]

[0109] As shown in formula (5), the beat frequency component of the Rayleigh backscattering signal and the effective sensing signal can be filtered out. As can be seen from the comparison between formula (5) and formula (1), although there is still interference between the Rayleigh backscattering signals, the interference can be ignored due to the small Rayleigh scattering coefficient R of the optical fiber.

[0110] The coherent Rayleigh interference suppression device provided by the embodiments of the present application adds a signal offset device in the bidirectional MZI and adds a filter at the receiving end, suppresses the coherent Rayleigh interference by means of frequency shift, reduces the intensity noise superimposed due to the coherent Rayleigh scattering noise, and increases the correctness and robustness of the system, so that the device can be applied to long-distance sensing.

[0111] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.​​

Claims

1. A device for suppressing coherent Rayleigh interference, characterized in that, include: Signal offset device, first filter and second filter; The first end of the signal offset device is connected to the second end of the first circulator, and the second end of the signal offset device is connected to the first end of the second coupler. The first end of the first filter is connected to the first end of the first photodetector, and the second end of the first filter is connected to the first end of the data acquisition card. The first end of the second filter is connected to the first end of the second photodetector, and the second end of the second filter is connected to the second end of the acquisition card; The signal offset device is used to offset the frequency of the passing signal; The first filter and the second filter are used to filter signal noise generated based on coherent Rayleigh interference; Also includes: A first coupler, the first end of which is connected to a laser emitter, the second end of which is connected to the first end of a second circulator, and the third end of which is connected to the first end of the first circulator; A first optical fiber disposed between the second coupler and the third coupler; A second optical fiber disposed between the second coupler and the third coupler; The third optical fiber is disposed between the third coupler and the second circulator; The third end of the first circulator is connected to the second end of the first photodetector; The third end of the second circulator is connected to the second end of the second photodetector.

2. The device for suppressing coherent Rayleigh interference according to claim 1, characterized in that, The signal offset device is an acousto-optic modulator or an IQ modulator.

3. The device for suppressing coherent Rayleigh interference according to claim 2, characterized in that, It also includes a drive unit; The driving device is connected to the third end of the signal offset device.

4. The device for suppressing coherent Rayleigh interference according to claim 1, characterized in that, The first filter is a low-pass filter or a digital filter; The second filter is a low-pass filter or a digital filter.

5. The device for suppressing coherent Rayleigh interference according to claim 1, characterized in that, Also includes: The frequency offset range of the signal offset device is from 20MHz to 400MHz.

6. The device for suppressing coherent Rayleigh interference according to claim 1, characterized in that, Also includes: The frequency offset of the signal offset device is 100MHz.

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