Optical fiber sensing integrated system based on phase coding optical carrier

Abstract

The invention discloses an optical fiber sensing integrated system based on a phase coding optical carrier. The optical fiber sensing integrated system is composed of an optical path detection part and a circuit demodulation part. The whole system is composed of a continuous wave laser, an optical fiber coupler, an acousto-optic modulator, a multi-phase coding generator, a polarization controller, an intensity modulator, a communication signal generator, an optical fiber amplifier, a dispersion compensation module, an optical fiber circulator, an optical fiber, a photoelectric detector, a data acquisition module, a data processing module and a high-sensitivity coherent receiver. The system is simple, only one single-wavelength laser is adopted as a light source, and the system is highly integrated, simple, easy to implement and easy to adjust; the whole system adopts a common time frequency integrated signal to realize a communication sensing integrated system, and has high spectrum efficiency; the whole system can flexibly adjust the system communication and distributed sound wave sensing performance only by adjusting the carrier signal power ratio, the flexibility of the system is improved, and more application scenes are covered.

Description

Technical Field

[0001] The present invention belongs to the field of distributed fiber optic acoustic sensing technology, and particularly relates to an optical fiber communication and sensing integrated system based on a phase-coded optical carrier. Background Art

[0002] In the past few decades, with the rapid development of big data, cloud computing, Internet of Things, industrial Internet, digital transformation, etc., fiber optic communication networks have grown explosively. Currently, fiber optic communication networks have become ubiquitous, and using only optical networks for data transmission can no longer meet current needs. There is an urgent need to develop more new functions for the huge optical network. Distributed fiber optic sensing technology has received extensive attention and a large amount of research due to its high sensitivity, electromagnetic interference resistance, long-distance fully distributed measurement, etc. Among many distributed fiber optic sensing technologies, phase-sensitive optical time domain reflectometry has good applications and obtained good feedback in fields such as oil and gas pipelines, structural health monitoring, high-speed rail speed measurement and positioning, high-speed rail perimeter protection, earthquake monitoring, distributed acoustic wave detection, etc.

[0003] In fact, fiber optic sensing systems and fiber optic communication systems have high similarity, and many of the devices they use (lasers, modulators, detectors) are the same, especially the same transmission medium (single-mode fiber, multi-mode fiber, etc.). In addition, many technologies in fiber optic communication are also applied to distributed fiber optic sensing to improve the performance of fiber optic sensing systems. Therefore, distributed fiber optic sensing and fiber optic communication have strong compatibility, and it is easy to integrate distributed fiber optic sensing technology into existing optical communication networks.

[0004] Based on this, a few researchers have carried out research on communication and sensing integrated systems, integrated phase-sensitive optical time domain reflectometry into existing fiber optic networks, and achieved field tests. However, current integration schemes all adopt wavelength division multiplexing and frequency division multiplexing methods. These integration methods only share the physical medium (fiber optic), and are still two independent systems in essence. Therefore, they have disadvantages such as low integration degree, complex system, and low transmission efficiency. In order to improve the integration degree of the integrated system and the transmission and sensing efficiency, it is necessary to break through this limiting condition. Currently, there are no corresponding technical means for improving the integration degree of fiber optic communication and sensing integrated systems and obtaining a more compact and efficient system. Summary of the Invention

[0005] In view of the disadvantages of high complexity and low efficiency of existing integrated systems, as well as the deficiencies in practical applications. The present invention provides a simple, compact, and high-efficiency optical fiber communication and sensing integrated system based on a phase-coded optical carrier.

[0006] An optical fiber communication and sensing integrated system based on a phase-coded optical carrier of the present invention generates a transmission optical signal and a sensing detection optical signal from the same laser. By adjusting the modulation power of the transmission signal, the transmission performance and sensing performance of the system are changed. At the remote end, direct detection (a single detector) is used to obtain the transmission signal, and at the local end, heterodyne coherent detection is used to obtain the sensing signal. The specific structure of the system is as follows:

[0007] The continuous light output by the narrow-linewidth continuous-wave laser is divided into two paths after passing through a 90:10 fiber coupler. 90% of the continuous light in the upper branch is injected into the acousto-optic modulator. The acousto-optic modulator is driven by a multi-phase coded radio frequency signal (the carrier is the frequency shift of the acousto-optic modulator) generated by a multi-phase coding generator to generate a phase-coded optical carrier. The light output by the acousto-optic modulator is injected into the intensity modulator after the polarization state is adjusted by a polarization controller. The intensity modulator is driven by a transmission signal generated by a communication signal generator. The optical signal output by the intensity modulator compensates for the optical power loss through an optical fiber amplifier, and then a dispersion compensation module is used to eliminate the influence of optical fiber dispersion on the transmission coding. Then, it is injected into the transmission optical fiber through an optical fiber circulator. The optical signal output at the remote end of the optical fiber is converted into an electrical signal by a photodetector, and the electrical signal is collected by a data acquisition module and transmitted to a data processing module for subsequent signal processing. The backward Rayleigh scattered light generated by the optical fiber is output through port 3 of the circulator. The output scattered light and the continuous light output from the 10% output arm of the fiber coupler are coupled and injected into a high-sensitivity coherent receiver for optoelectronic conversion. The electrical signal output by the high-sensitivity coherent receiver is collected by a data acquisition module and transmitted to the data processing module for post-processing.

[0008] Further, the system uses a single light source to generate a communication and sensing integrated signal with the same carrier frequency, and simultaneously realizes data transmission and environmental parameter perception based on this signal. The transmission and sensing performance of the integrated system can be flexibly adjusted by adjusting the carrier signal power ratio.

[0009] Further, the system uses the phase-coded optical carrier as both the optical carrier of the pulse amplitude modulation transmission signal and the detection light of the distributed optical fiber sensing.

[0010] Further, the communication signal and the distributed sensing signal of the system are detected and demodulated at the remote end and the local end respectively.

[0011] Further, the distributed sensing signal in the system uses heterodyne coherent detection to obtain the signal, and only the Rayleigh scattering signal corresponding to the phase-coded optical carrier is retained in the signal detection.

[0012] The present invention has the following beneficial technical effects compared with the prior art.

[0013] 1. The system is simple. The system only uses a single-wavelength laser as the light source, and the system is highly integrated, simple, easy to implement, and easy to adjust.

[0014] 2. The system uses phase encoding and an acousto-optic modulator to generate multi-phase optical carriers, with high modulation efficiency, low optical power loss, no need for additional optical amplification, higher optical signal-to-noise ratio of the optical carriers, and better communication and sensing performance.

[0015] 3. The phase-encoded carrier adopted by the system has a better main-to-side lobe power ratio than the frequency-modulated carrier, enabling higher-resolution sensing.

[0016] 4. The entire system uses a spectrum sharing method to implement a communication and sensing integrated system, with high spectral efficiency.

[0017] 5. The entire system can flexibly adjust the system communication and distributed sensing performance by adjusting the carrier sideband power ratio, greatly improving the flexibility of the system, covering more application scenarios, and having better flexibility for different application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 FIG. is a structural diagram of the fiber optic communication and sensing integrated system based on phase-encoded optical carriers of the present invention.

[0019] Figure 2 FIG. shows the simulation results of the communication (56 Gbit / s PAM4 signal) and sensing (DAS) of the present invention at a communication and sensing distance of 10 km, where: a) Bit error rate response curves under different signal-to-noise ratio conditions; b) DAS sensing sensitivity distribution curves at a spatial resolution of 7 m. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The present invention will be further described in detail below with reference to the drawings and specific implementation methods.

[0021] The structure of an optical fiber communication and sensing integrated system based on phase-encoded optical carriers of the present invention is as Figure 1 shown, and it consists of two parts: an optical path and an electrical circuit. The specific structure is as follows:

[0022] The continuous light output by the narrow linewidth continuous wave laser 1 is divided into two paths after passing through the 90:10 fiber coupler 2. 90% of the continuous light in the upper branch is injected into the acousto-optic modulator 3. The acousto-optic modulator 3 is driven by the multi-phase coded radio frequency signal generated by the multi-phase coding generator 4 to generate a phase-coded optical carrier. The light output by the acousto-optic modulator 3 is injected into the intensity modulator 6 after the polarization state is adjusted by the polarization controller 5. The intensity modulator 6 is driven by the transmission signal generated by the communication signal generator 7. The optical signal output by the intensity modulator 6 compensates for the optical power loss through the fiber amplifier 8, and then the dispersion compensation module 9 is used to eliminate the influence of fiber dispersion on the transmission coding. Then it is injected into the transmission fiber 11 through the fiber circulator 10. The optical signal output at the far end of the fiber is converted into an electrical signal by the photodetector 12, and the electrical signal is collected by the data acquisition module 13 and transmitted to the data processing module 14 for subsequent signal processing. The backward Rayleigh scattered light generated by the fiber 11 is output from port 3 of the circulator 10. The output scattered light and the continuous light output from the 10% output arm of the fiber coupler 2 are coupled and injected into the high-sensitivity coherent receiver 15 for optoelectronic conversion. The electrical signal output by the high-sensitivity coherent receiver 15 is collected by the data acquisition module 16 and transmitted to the data processing module 17 for post-processing.

[0023] For the fiber communication and sensing integrated system based on phase-coded optical carrier of the present invention, the optical path uses a multi-phase phase-coded optical carrier to replace the traditional single-frequency optical carrier. This phase-coded optical carrier serves as both the carrier of the transmission signal and the detection light of the distributed fiber sensing system. The far-end transmission signal uses direct detection to convert the optical signal into an electrical signal, and the local end uses heterodyne coherent detection to obtain the sensing signal. The principle analysis is as follows:

[0024] The multi-phase coding generator generates a coding waveform and modulates it onto the acousto-optic modulator. The expression of the generated phase-coded optical carrier is:

[0025]

[0026] In the formula, E0 is the amplitude of the optical carrier, f c is the optical output frequency of the light source, f A is the frequency shift value of the acousto-optic modulator, is the multi-phase coding signal, and the repetition period of the multi-phase coding is T p must be greater than 2n g L / c, where L is the fiber distance. The code width τ of the multi-phase coding determines the sensing spatial resolution of the system.

[0027] The transmission signal is loaded onto the generated phase-coded optical carrier. The expression of the integrated optical signal to be transmitted is:

[0028]

[0029] Among them, \(x(t)\) is the modulation phase generated corresponding to the transmission signal, which is equal to \(\pi V X (t) / V π , \(V X (t)\) is the signal voltage, \(V π \) is the half-wave voltage of the modulator, \) is the bias phase, which is determined by the voltage value loaded on the modulator. Usually, the transmission signal is converted into an electrical signal by direct detection at the far end, and the expression of the electrical signal is:

[0030]

[0031] In the above formula, \) is the conversion coefficient of the photodetector. The integrated communication and sensing signal using phase-encoded optical carrier has the same detection and demodulation methods as the traditional amplitude modulation transmission.

[0032] The integrated optical signal \(E isac (t)\) will generate backward Rayleigh scattered light during fiber optic transmission. After demodulation, the vibration signal of the fiber optic link can be restored, and the expression of the Rayleigh scattered light is:

[0033]

[0034] Formula (2) Amplitude expression related to the communication signal can be expanded by Taylor series to decompose the integrated signal into a carrier component and a signal component:

[0035]

[0036] By demodulating the backward Rayleigh scattered light generated by the carrier component \(E c (t)\), the sensing signal of the fiber optic link can be restored. The sensing signal corresponding to the carrier obtained by coherent detection is:

[0037]

[0038] Among them,

[0039]

[0040] Generate a matched filter corresponding to \(s dc (t)\) in the digital domain and perform a cross-correlation operation with the scattered signal \(I R (t)\) to restore the sensing signal. The demodulated signal is:

[0041]

[0042] From the above analysis, it can be seen that the effective sensing signal of the optical fiber link can be extracted by using the scattered signal of the phase-coded optical carrier. In summary, the above theoretical analysis proves that the present invention is feasible in principle.

[0043] In implementation, the polyphase coding needs to be optimized to match the spectral response characteristics of the acousto-optic modulator. The bandwidth of the coded signal is about 50 MHz (corresponding to a spatial resolution of 2 m), and the period of the coded signal is determined by the fiber length.

[0044] In implementation, the electrical domain bandwidth of the photodetector 12 needs to be greater than the analog bandwidth of the modulation signal generated by the communication signal generator (this value is related to the roll-off factor of the shaping filter); for example: after a 28 Gbaud signal passes through a shaping filter with a roll-off factor of 0.1, the analog bandwidth is 15.5 GHz.

[0045] In implementation, the electrical domain bandwidth of the high-sensitivity coherent receiver 15 is jointly determined by the bandwidth of the phase-coded optical carrier and the frequency shift of the acousto-optic modulator. For example, if the phase-coded optical bandwidth is 0.5 GHz and the acousto-optic modulator frequency shift is 0.2 GHz, then the detector bandwidth needs to be greater than 0.7 GHz.

[0046] Figure 2 This is the simulation result of the transmission performance and DAS sensing performance of the present invention. As shown in the figure, it is the simulation result with a 10-kilometer optical fiber and a rate of 56 Gbit / s. Figure 2 (a) is the bit error rate response curve under different signal-to-noise ratio conditions. When the signal-to-noise ratio ≥ 16 dB, there is no bit error in transmission. Figure 2 (b) is the DAS phase noise distribution (i.e., the system sensitivity distribution) at a spatial resolution of 7 m.

Claims

1. An optical fiber communication and sensing integrated system based on a phase-coded optical carrier, characterized in that The transmitted optical signal and the sensing detection optical signal are generated by the same laser. By adjusting the modulation power of the transmitted signal, the transmission performance and sensing performance of the system are changed. At the far end, the transmitted signal is obtained by direct detection, and at the local end, the sensing signal is obtained by heterodyne coherent detection; The specific structure of its system is as follows: The continuous light output by the narrow linewidth continuous wave laser (1) is divided into two paths after passing through the 90:10 optical fiber coupler (2). 90% of the continuous light in the upper branch is injected into the acousto-optic modulator (3). The acousto-optic modulator (3) is driven by the multi-phase coded radio frequency signal generated by the multi-phase coding generator (4) to generate a phase-coded optical carrier. The light output by the acousto-optic modulator (3) is injected into the intensity modulator (6) after the polarization state is adjusted by the polarization controller (5). The intensity modulator (6) is driven by the transmission signal generated by the communication signal generator (7). The optical signal output by the intensity modulator (6) compensates for the optical power loss through the optical fiber amplifier (8), and then the dispersion compensation module (9) is used to eliminate the influence of optical fiber dispersion on the transmission coding. Then, it is injected into the transmission optical fiber (11) through the optical fiber circulator (10). The optical signal output at the far end of the optical fiber is converted into an electrical signal by the photodetector (12). The electrical signal is collected by the data acquisition module (13) and transmitted to the data processing module (14) for subsequent signal processing; The backward Rayleigh scattered light generated by the optical fiber (11) is output from port 3 of the circulator (10). The output scattered light and the continuous light output from the 10% output arm of the optical fiber coupler (2) are coupled and injected into the high-sensitivity coherent receiver (15) for optoelectronic conversion. The electrical signal output by the high-sensitivity coherent receiver (15) is collected by the data acquisition module (16) and transmitted to the data processing module (17) for post-processing.

2. The fiber-optic communication and sensing integrated system based on a phase-coded optical carrier according to claim 1, wherein The system uses a single light source to generate a communication and sensing integrated signal with the same carrier frequency, and simultaneously realizes data transmission and environmental parameter perception based on this signal. The transmission and sensing performance of the integrated system can be flexibly adjusted by adjusting the carrier signal power ratio.

3. The fiber-optic communication and sensing integrated system based on a phase-coded optical carrier according to claim 1, characterized in that The system uses the phase-coded optical carrier as both the optical carrier of the pulse amplitude modulation transmission signal and the detection optical signal of the distributed optical fiber sensing.

4. The fiber-optic communication and sensing integrated system based on a phase-coded optical carrier according to claim 1, wherein The communication signal and the distributed sensing signal of the system are detected and demodulated at the far end and the local end respectively.

5. The fiber-optic communication and sensing integrated system based on a phase-coded optical carrier according to claim 4, wherein In the system, the distributed sensing signal is obtained by heterodyne coherent detection, and only the Rayleigh scattering signal corresponding to the phase-coded optical carrier is retained in the signal detection.

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