A time-frequency shared coherent optical fiber communication and sensing integrated system

Abstract

This invention discloses a time-frequency coherent optical fiber communication and sensing integrated system. The entire system includes a narrow-linewidth laser, an optical fiber coupler, a polarization controller, an IQ modulator, a coherent sensing signal generator, an optical fiber amplifier, an optical fiber circulator, optical fiber, a local oscillator, a high-speed coherent receiver, a communication data acquisition and processing module, a high-sensitivity coherent receiver, and a sensing data acquisition and processing module. The transmitted signal and the sensing detection signal are fused to form a time-frequency coherent signal, and the coherent sensing optical signal is generated by the same laser and modulator. The transmission and sensing performance of the system can be flexibly adjusted by regulating the power ratio of the transmitted signal and the sensing detection signal. The transmitted signal is detected at the remote end using a high-speed coherent receiver, and the sensing signal is obtained at the local end using zero-difference coherent detection. This invention features a highly integrated system that is simple, easy to implement, and easy to adjust; it has high spectral efficiency; and it offers flexible communication and sensing adjustments with good performance.

Description

Technical Field

[0001] This invention pertains to optical fiber communication and distributed optical fiber acoustic sensing technology, and particularly relates to a time-frequency coherent optical fiber communication and sensing integrated system. Background Technology

[0002] Over the past few decades, with the rapid development of big data, cloud computing, the Internet of Things, the Industrial Internet, and digital transformation, fiber optic communication networks have experienced explosive growth. Currently, fiber optic communication networks are ubiquitous, and data transmission using only optical networks is no longer sufficient to meet current needs; there is an urgent need to develop more new functions for these massive optical networks. Distributed fiber optic sensing technology has received widespread attention and extensive research due to its advantages such as high sensitivity, resistance to electromagnetic interference, and long-distance fully distributed measurement. Among the many distributed fiber optic sensing technologies, phase-sensitive optical time-domain reflectometry (OTDR) has found excellent applications and received positive 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, and distributed acoustic detection.

[0003] In fact, fiber optic sensing systems and fiber optic communication systems share many similarities. They utilize many of the same components (lasers, modulators, detectors), and especially the same transmission media (single-mode fiber, multi-mode fiber, etc.). Furthermore, many technologies from 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 is highly compatible with fiber optic communication, and distributed fiber optic sensing technology can be easily integrated into existing optical communication networks.

[0004] Based on this, a few researchers have conducted research on integrated communication and sensing systems, integrating phase-sensitive optical time-domain reflectometry (PTZ) technology into existing fiber optic networks and achieving field testing. However, most current integration schemes employ wavelength division multiplexing (WDM) and frequency division multiplexing (FDM). These integration methods only share the physical medium (optical fiber) and are essentially still two independent systems, thus suffering from low integration density, system complexity, and low transmission efficiency. In addition, a small number of time-frequency shared fiber optic sensing integrated systems can improve the integration density and transmission sensing efficiency of the integrated system. However, the communication part of current time-frequency multiplexing fiber optic sensing integrated systems mainly focuses on optical signal amplitude modulation. Relying solely on modulation in a single amplitude dimension makes it difficult to achieve high-spectral-efficiency, high-speed transmission, which is also a crucial area requiring breakthroughs. Currently, there are no good technical means to improve the integration density of fiber optic communication and sensing integrated systems and obtain more compact, higher-spectral-efficiency fiber optic sensing integrated systems. Summary of the Invention

[0005] In view of the high complexity and low efficiency of existing integrated systems, the purpose of this invention is to provide a simple, compact and efficient time-frequency coherent fiber optic sensing integrated system, which solves the shortcomings of existing integrated systems in practical applications, such as low spectrum efficiency, limited sensing distance and capacity.

[0006] The present invention discloses a time-frequency coherent optical fiber communication and sensing integrated system, the specific structure of which is as follows:

[0007] The continuous light output from the narrow-linewidth laser is split into two paths after passing through a 90:10 fiber coupler. 90% of the continuous light from the upper branch is regulated by a polarization controller and then used by an IQ modulator driven by an integrated sensing signal generator to produce an integrated sensing optical signal. This integrated optical signal output from the IQ modulator is then amplified by an fiber amplifier to adjust its power to an appropriate value before being injected into the test fiber via a fiber circulator. The optical signal output from the far end of the fiber is coupled with the continuous light output from the local oscillator and injected into a high-speed coherent receiver for conversion into an electrical signal. This electrical signal is acquired by a communication data acquisition module and transmitted to a communication data processing module for further signal processing. The backscattered Rayleigh light generated by the fiber is output from port 3 of the fiber circulator. The output scattered light is coupled with the continuous light output from the 10% branch of the fiber coupler and injected into a high-sensitivity coherent receiver for photoelectric conversion. The electrical signal output from the high-sensitivity coherent receiver is acquired by a sensor data acquisition module and transmitted to a sensor data processing module for post-processing.

[0008] Furthermore, in this invention, the transmission signal and the sensing detection signal are fused to form a time-frequency integrated signal, and the same laser and a modulator generate a sensing integrated optical signal. The transmission and sensing performance of the system can be flexibly adjusted by adjusting the power ratio of the transmission signal and the sensing detection signal. The transmission signal is obtained by a high-speed coherent receiver at the remote end, and the sensing signal is obtained by zero-difference coherent detection at the local end.

[0009] Integrated signal transmitter:

[0010] The expression X of the integrated signal generated in the digital domain ISAC (t) is:

[0011] X ISAC (t)=[X(t)+γ]exp(jkπt 2 (1)

[0012] In the formula, Let A(t) be the baseband signal to be transmitted, and let A(t) be the amplitude of the baseband signal. γ is the phase of the baseband signal, γ is the sensing signal coefficient, and k is the chirp rate of the linear frequency modulated signal, k = B / T p B is the bandwidth of the frequency modulation signal, T p It is the repetition period of the frequency modulation signal, and T pIt must be greater than 2n g L / c, where L is the length of the sensing fiber in the system, and n g is the refractive index of the fiber group, and c is the speed of light in a vacuum.

[0013] The aforementioned integrated inductive signal is generated in the digital domain, then used by a generator to produce an integrated electrical signal, which is then applied to an IQ modulator to generate an integrated optical signal E. ISAC (t):

[0014] E ISAC (t)=X ISAC (t)exp(jω c t)=[X(t)+γ]expj(ω c t+kπt 2 (2)

[0015] In the formula, ω c ω is the angular frequency of the optical carrier wave.

[0016] Communication receiver:

[0017] E ISAC (t) after transmission through optical fiber, it is connected to the local oscillator laser E LO (t) Coupling E at the far end LO (t)=A L exp(jω c t), and a coherent receiver is used to convert it into an electrical signal. The expression for the real / imaginary part of the electrical signal is:

[0018]

[0019] In the formula, is the conversion coefficient of the photodetector, Re|·| represents taking the real part of the signal, and Im|·| represents taking the imaginary part of the signal.

[0020] The real and imaginary parts in equation (3) are synthesized and transformed to recover the complex signal E. rec (t):

[0021]

[0022] The first part of the above formula is the transmitted signal, and the second part is the sensing signal.

[0023] The transmitted signal is recovered at the receiving end using a synchronous chirp cancellation algorithm.

[0024]

[0025] in,

[0026]

[0027] in, It is a cross-correlation operator, c(t) = exp(jkπt) 2 ) is the chirped matched signal, n is the cross-correlation result of the transmitted signal and , 2γM represents the cross-correlation value of the sensing signal and , and n << 2γM, M is the number of digital signal points participating in the cross-correlation operation.

[0028] The signal synchronization position t0 and the sensing signal coefficient γ are obtained through equation (6). max Then, the chirp factor and sensor signal components in the received signal are eliminated to obtain the demodulated transmission signal X. rec (t) is:

[0029]

[0030] Sensor receiver:

[0031] As shown in formula (2), the integrated optical signal E ISAC (t) contains both a transmission signal and a sensing signal. The integrated signal generates backscattered Rayleigh light during fiber optic transmission. The sensing signal is a periodic, known signal, and its corresponding Rayleigh scattered light E is obtained at the sensing receiver. RBS (t); At the sensor receiver, the light source signal from the transmitter is used as the local oscillator E. sL (t)=exp(jω c t) is coupled to the scattered light and fed into a highly sensitive coherent receiver to obtain the sensing electrical signal i. sI (t) and i sQ (t), combining the two into a complex signal, we get:

[0032]

[0033] in, The sensitivity of the sensing coherent receiver is given by s, where * represents the convolution operator. SEN h(t) is the equivalent sensing signal after the optical signal is recovered through photoelectric conversion, and h(t) is the Rayleigh scattering impulse response of the optical fiber.

[0034] The above expression is:

[0035]

[0036] In the formula, a(t) is a random number distributed by Rayleigh. α is a uniformly distributed random number, and α is the transmission attenuation coefficient of the optical fiber.

[0037] Generate a value in the digital domain that is the same as s. SEN The matched filter corresponding to (t) and the scattered signal E re (t) Perform cross-correlation operation to recover the sensing signal, and the demodulated signal is:

[0038]

[0039] Where R(t) is the equivalent pulse obtained by cross-correlation operation, and its expression is:

[0040]

[0041] The beneficial technical effects of this invention are as follows:

[0042] 1. The system is simple, using only a single-wavelength narrow-linewidth laser as the light source. The system is highly integrated, simple, easy to implement, and easy to adjust.

[0043] 2. The system uses a digital integrated sensing signal and an IQ modulator to generate an integrated sensing optical signal. The signal modulation is simple and efficient, and the communication and sensing adjustment are flexible and perform well.

[0044] 3. The sensing signals generated by the system utilize the advantage of the large bandwidth of the communication modulator, enabling higher resolution sensing.

[0045] 4. The entire system adopts a time-frequency sharing method to realize an integrated communication and sensing system, which has high spectrum efficiency.

[0046] 5. The entire system can flexibly adjust the communication and distributed sensing performance by adjusting the power ratio and bandwidth ratio of the sensing signal and the communication signal, which greatly improves the system's flexibility, covers more application scenarios, and has better flexibility for different application scenarios. Attached Figure Description

[0047] Figure 1 This is a structural diagram of the coherent optical fiber communication and sensing integrated system for time and frequency sharing according to the present invention.

[0048] Figure 2 The simulation results of the communication (200 Gbit / s 16QAM signal) and sensing (DAS) over an 80 km range are shown in the figure. Here, a is the chirp factor synchronization curve under different signal-to-noise ratio conditions; b and c are the constellation diagram distributions under signal-to-noise ratios of 27.2 dB and 29.2 dB, respectively. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0050] The present invention provides a time-frequency coherent optical fiber communication and sensing integrated system, the structure of which is as follows: Figure 1 As shown, specifically:

[0051] The continuous light output from the narrow linewidth laser 1 is split into two paths after passing through a 90:10 fiber coupler 2. The 90% continuous light in the upper branch is regulated by the polarization controller 3 and then driven by the IQ modulator 4 and the integrated sensing signal generator 5 to generate an integrated sensing optical signal. The integrated optical signal output by the IQ modulator 4 is adjusted to an appropriate value by the fiber amplifier 6 and then injected into the test fiber 8 through the fiber circulator 7. The optical signal output from the far end of the fiber is coupled with the continuous light output from the local oscillator 9 and injected into the high-speed coherent receiver 10 to be converted into an electrical signal. The electrical signal is collected by the communication data acquisition module 11 and transmitted to the communication data processing module 12 for subsequent signal processing. The backscattered Rayleigh light generated by the fiber 8 is output through port 3 of the fiber circulator 7. The output scattered light is coupled with the continuous light output from the 10% branch of the fiber coupler 2 and injected into the high-sensitivity coherent receiver 13 for photoelectric conversion. The electrical signal output by the high-sensitivity coherent receiver 13 is collected by the sensor data acquisition module 14 and transmitted to the sensor data processing module 15 for post-processing.

[0052] In practice, the integrated sensing signal needs to be combined with digital domain signals, the time-frequency response characteristics of IQ modulators, and bias control for joint optimization to achieve better performance in generating integrated sensing optical signals. The sensing signal bandwidth is about 1 GHz (corresponding to an inherent spatial resolution of 0.1 m), and the period of the sweep frequency signal must be greater than the fiber length.

[0053] In practice, the electrical bandwidth of the high-speed coherent receiver 10 needs to be greater than the analog bandwidth of the modulated signal generated by the communication signal generator (this value is related to the roll-off factor of the shaping filter); for example, a 50 Gbaud signal has an analog bandwidth of 27.5 GHz after being shaped by a roll-off factor of 0.1.

[0054] In practice, the electrical bandwidth of a high-sensitivity coherent receiver needs to be greater than the bandwidth of the sensing signal. For example, if the sensing signal bandwidth is 1 GHz, then the detector bandwidth of the coherent receiver needs to be greater than 1 GHz.

[0055] Furthermore, the system uses a single light source to generate a communication and sensing integrated signal with a shared time and frequency channel. Based on this signal, data transmission and environmental parameter sensing are realized simultaneously. The transmission and sensing performance of the integrated system can be flexibly adjusted by adjusting the power ratio of the communication and sensing signals.

[0056] Furthermore, the integrated signal transmitted in the system is generated in the digital domain and modulated by a single IQ modulator, while simultaneously transmitting communication signals and probe light as a distributed optical fiber sensor.

[0057] Furthermore, the system communication signals and distributed sensing signals are detected and demodulated at the remote and local ends, respectively.

[0058] Furthermore, the system's communication signal detection method is the same as that of a single coherent optical communication system, requiring no additional auxiliary equipment for receiving communication signals. The system's communication signal demodulation method differs from that of a single coherent optical communication system, but only the demodulation digital processing algorithm needs modification.

[0059] Furthermore, the distributed sensing signals in the system are acquired using coherent detection, and only the Rayleigh scattering signal corresponding to the sensing signal in the integrated signal is retained during signal detection.

[0060] Furthermore, the sensing signals in the system can not only achieve distributed sensing, but also assist in eliminating the relative phase noise between the transmitting and receiving lasers in communication signal detection and demodulation, thereby improving communication performance and achieving communication enhancement.

[0061] In this invention, the transmitting optical path uses a narrow-linewidth light source as the carrier for generating the integrated optical signal. The digitally generated integrated signal for the coherent system is loaded onto this optical carrier via an IQ modulator to generate a sensing integrated optical signal. The communication receiving end (remote end) uses a local oscillator laser and a high-speed coherent receiver to convert the optical signal into an electrical signal. The sensing receiving end (local end) uses the transmitting light source as the local oscillator laser and uses homodyne coherent detection to obtain the sensing signal. The principle is analyzed as follows:

[0062] Integrated signal transmitter:

[0063] The expression X of the integrated signal generated in the digital domain ISAC (t) is:

[0064] X ISAC (t)=[X(t)+γ]exp(jkπt 2 (1)

[0065] In the formula, Let A(t) be the baseband signal to be transmitted, and let A(t) be the amplitude of the baseband signal. γ is the phase of the baseband signal, γ is the sensing signal coefficient, and k is the chirp rate of the linear frequency modulated signal, k = B / T p B is the bandwidth of the frequency modulation signal, T p It is the repetition period of the frequency modulation signal, and T p It must be greater than 2n g L / c, where L is the length of the sensing fiber in the system, and n g is the refractive index of the fiber group, and c is the speed of light in a vacuum.

[0066] The aforementioned integrated inductive signal is generated in the digital domain, then used by a generator to produce an integrated electrical signal, which is then applied to an IQ modulator to generate an integrated optical signal E. ISAC (t):

[0067] EISAC (t)=X ISAC (t)exp(jω c t)=[X(t)+γ]expj(ω c t+kπt 2 (2)

[0068] In the formula, ω c ω is the angular frequency of the optical carrier wave.

[0069] Communication receiver:

[0070] E ISAC (t) after transmission through optical fiber, it is connected to the local oscillator laser E LO (t) Coupling E at the far end LO (t)=A L exp(jω c t), and a coherent receiver is used to convert it into an electrical signal. The expression for the real / imaginary part of the electrical signal is:

[0071]

[0072] In the formula, is the conversion coefficient of the photodetector, Re|·| represents taking the real part of the signal, and Im|·| represents taking the imaginary part of the signal.

[0073] The real and imaginary parts in equation (3) are synthesized and transformed to recover the complex signal E. rec (t):

[0074]

[0075] The first part of the above formula is the transmitted signal, and the second part is the sensing signal.

[0076] The transmitted signal is recovered at the receiving end using a synchronous chirp cancellation algorithm.

[0077]

[0078] in,

[0079]

[0080] in, It is a cross-correlation operator, c(t) = exp(jkπt) 2 ) is the chirped matched signal, n is the cross-correlation result of the transmitted signal and , 2γM represents the cross-correlation value of the sensing signal and , and n << 2γM, M is the number of digital signal points participating in the cross-correlation operation.

[0081] The signal synchronization position t0 and the sensing signal coefficient γ are obtained through equation (6). maxThen, the chirp factor and sensor signal components in the received signal are eliminated to obtain the demodulated transmission signal X. rec (t) is:

[0082]

[0083] Sensor receiver:

[0084] As shown in formula (2), the integrated optical signal E ISAC (t) contains both a transmission signal and a sensing signal. The integrated signal generates backscattered Rayleigh light during fiber optic transmission. The sensing signal is a periodic, known signal, and its corresponding Rayleigh scattered light E is obtained at the sensing receiver. RBS (t); At the sensor receiver, the light source signal from the transmitter is used as the local oscillator E. sL (t)=exp(jω c t) is coupled to the scattered light and fed into a highly sensitive coherent receiver to obtain the sensing electrical signal i. sI (t) and i sQ (t), combining the two into a complex signal, we get:

[0085]

[0086] in, The sensitivity of the sensing coherent receiver is given by s, where * represents the convolution operator. SEN h(t) is the equivalent sensing signal after the optical signal is recovered through photoelectric conversion, and h(t) is the Rayleigh scattering impulse response of the optical fiber.

[0087] The above expression is:

[0088]

[0089] In the formula, a(t) is a random number distributed by Rayleigh. α is a uniformly distributed random number, and α is the transmission attenuation coefficient of the optical fiber.

[0090] Generate a value in the digital domain that is the same as s. SEN The matched filter corresponding to (t) and the scattered signal E re (t) Perform cross-correlation operation to recover the sensing signal, and the demodulated signal is:

[0091]

[0092] Where R(t) is the equivalent pulse obtained by cross-correlation operation, and its expression is:

[0093]

[0094] In summary, the above analysis shows that the proposed time-frequency coherent integrated system can effectively transmit communication signals and simultaneously restore the stability of the fiber optic link. Therefore, the theoretical analysis demonstrates that the present invention is feasible in principle.

[0095] Figure 2 The figure shows the simulation results for the transmission performance and DAS sensing performance of this invention, with an 80 km fiber optic cable and a rate of 112 Gbit / s (16QAM). Figure 2 (a) shows the chirp factor synchronization curves under different signal-to-noise ratio conditions. The chirp factor synchronization performance of 24.4dB signal-to-noise ratio, 27.2dB and 29.2dB is comparable. Figure 2 (b) and Figure 2 (c) shows the constellation diagram distributions at signal-to-noise ratios of 27.2 dB and 29.2 dB, respectively, which are comparable to those of traditional coherent communication.

[0096] In summary, the present invention has the following advantages:

[0097] (1) The system is simple, using only a single-wavelength laser as the light source. The system is highly integrated, simple, easy to implement and easy to adjust. (2) The entire system uses a time-frequency integrated signal to realize an integrated communication and sensing system with high spectral efficiency. (3) The entire system can flexibly adjust the communication and distributed acoustic wave sensing performance of the system by simply adjusting the power ratio and bandwidth ratio of the communication signal and the sensing signal, which improves the flexibility of the system and covers more application scenarios.

Claims

1. A time and frequency shared coherent fiber-optic communication and sensing integrated system, characterized by, The specific structure is as follows: The continuous light output from the narrow linewidth laser (1) is split into two paths after passing through a 90:10 fiber coupler (2). 90% of the continuous light in the upper branch is adjusted by a polarization controller (3) and then driven by an IQ modulator (4) and an integrated sensing signal generator (5) to generate an integrated sensing optical signal. The integrated optical signal output from the IQ modulator (4) is then adjusted to an appropriate value by an fiber amplifier (6) and injected into the test fiber (8) through a fiber circulator (7). The optical signal output from the far end of the fiber is coupled with the continuous light output from the local oscillator (9) and then injected into a high-speed coherent receiver. (10) is converted into an electrical signal, which is collected by the communication data acquisition module (11) and transmitted to the communication data processing module (12) for subsequent signal processing; the backscattered Rayleigh light generated by the optical fiber (8) is output through the 3 port of the optical fiber circulator (7), and the output scattered light and the continuous light output from the 10% branch of the optical fiber coupler (2) are coupled and injected into the high-sensitivity coherent receiver (13) for photoelectric conversion. The electrical signal output by the high-sensitivity coherent receiver (13) is collected by the sensor data acquisition module (14) and transmitted to the sensor data processing module (15) for post-processing; The transmission signal and the sensing signal are fused to form a time-frequency integrated signal, and the same laser and modulator generate a sensing integrated optical signal. The transmission and sensing performance of the system can be flexibly adjusted by adjusting the power ratio of the transmission signal and the sensing signal. The transmission signal is obtained by a high-speed coherent receiver at the remote end, and the sensing signal is obtained by zero-difference coherent detection at the local end. Integrated signal transmitter: Expression of an integrated signal generated in the digital domain is: （1） In the formula, The baseband signal to be transmitted. The amplitude of the baseband signal. It is the phase of the baseband signal. It is the coefficient of the sensor detection signal. It is the chirp rate of the linear frequency modulated signal. , It is the bandwidth of the frequency modulation signal. It is the repetition period of the frequency modulation signal, and Must be greater than , It is the length of the sensing fiber in the system. It is the group refractive index of the optical fiber. It is the speed of light in a vacuum; The aforementioned integrated inductive signal is generated in the digital domain, then used by a generator to produce an integrated electrical signal, which is then applied to an IQ modulator to generate an integrated optical signal. : （2） In the formula, is the angular frequency of the optical carrier; Communication receiver: After transmission through the optical fiber and mixing with the local laser Coupling at the far end and converting it into an electrical signal using a coherent receiver, the real and imaginary parts of the electrical signal are expressed as: （3） wherein is the conversion factor of the photodetector, denotes taking the real part of the signal, denotes taking the imaginary part of the signal; combining real and imaginary parts of equation (3) to recover the complex signal : （4） The first part of the above formula is the transmitted signal, and the second part is the sensing signal; The transmitted signal is recovered at the receiving end using a synchronous chirp cancellation algorithm. （5） in, （6） in, It is a cross-correlation operator. It is a chirped matched signal, and n is the cross-correlation result of the transmitted signal and . This represents the cross-correlation value between the sensing signal and , and M is the number of digital signal points participating in the cross-correlation operation; The signal synchronization position is obtained by equation (6) and the sensing signal coefficient After that, the chirp factor and the sensing signal component in the received signal are eliminated, so as to obtain the demodulated transmission signal is: （7） Sensor receiver: As shown in formula (2), the integrated optical signal The integrated signal comprises both transmission and sensing signals. During fiber optic transmission, the integrated signal generates backscattered Rayleigh light. The sensing signal is a periodic, known signal, and its corresponding Rayleigh scattering is acquired at the sensing receiver. At the sensor receiver, the light source signal from the transmitter is used as the local oscillator. The scattered light is coupled into a highly sensitive coherent receiver to obtain the sensing electrical signal. and Combining the two into a complex signal, we get: （8） in, For the sensitivity of the sensing coherent receiver, For convolution operators, This is the equivalent sensing signal after the optical signal has been recovered through photoelectric conversion. This represents the Rayleigh scattering impulse response of an optical fiber. The above expression is: （9） wherein is a random number following a Rayleigh distribution, is a random number following a uniform distribution, is the transmission attenuation coefficient of the optical fiber; A signal corresponding to the is correlated with the scattered signal The sensing signal is recovered by correlation operation, and the demodulated signal is （10） wherein is the equivalent impulse obtained from the cross-correlation operation, expressed as: （11）。

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