Optical fiber sensing integrated system and optical fiber monitoring system

Abstract

The invention provides an optical fiber communication and sensing integrated system and an optical fiber monitoring system, the optical fiber communication and sensing integrated system comprises a signal sending unit, a communication receiving unit, a sensing receiving unit and a transmission link unit, the signal sending unit is used for generating a communication and sensing integrated waveform and sending the waveform to the communication receiving unit and the sensing receiving unit; the sensing and receiving unit is used for extracting phase information after performing coherent demodulation on the communication and sensing integrated optical signal, and is also used for distinguishing the vibration intensity and frequency of the transmission optical fiber by detecting and analyzing the change of the phase information; and the communication receiving unit is used for converting the communication-sensing integrated optical signal into a communication-sensing integrated electric signal to obtain original communication information. According to the invention, higher transmission rate and spectral efficiency are realized by adopting high-order digital modulation, an El-Mett symmetrical structure is adopted, and the change of an optical fiber link is detected by utilizing the sensing information of a radio frequency component, so that the sensing accuracy is further improved.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technologies, and in particular, to an optical fiber communication and sensing integrated system and an optical fiber monitoring system. Background Art

[0002] Optical fiber communication and optical fiber sensing are two different research directions, and the key technologies required for each are also different. Optical fiber communication mainly relies on optical carriers to carry information, and realizes the information transmission function after modulation and demodulation. Optical fiber sensing mainly relies on the interaction between light and the medium when light travels in the optical fiber, and senses the degree of change of the optical fiber affected by the external environment. For example, by extracting the changes in characteristic signals such as Rayleigh scattering and Brillouin scattering, the changes in the optical fiber are sensed. In recent years, a new optical fiber communication and sensing integrated technology (abbreviation: optical fiber communication and sensing integration) based on optical fiber communication and optical fiber sensing technologies has emerged. It organically combines the two to achieve efficient information transmission and precise sensing. Specifically, optical fiber communication and sensing integration includes two main aspects: using optical fiber as a common transmission medium for communication and sensing to achieve simultaneous transmission and sensing of information; using common technical means of optical fiber communication and optical fiber sensing to achieve simultaneous processing and sensing of information. Optical fiber communication and sensing integration technology has the characteristics of large broadband information capacity, high security, and high reliability. However, the main development modes of existing optical fiber communication and sensing integration technologies are different times, different wavelengths, and different channels. These technologies will waste a large amount of resources, the communication rate is not high enough, and the spectrum utilization rate is relatively low, and true communication and sensing integration has not been achieved. Summary of the Invention

[0003] The inventor found that the latest research progress has been able to achieve optical fiber communication and sensing integration at the same time, the same wavelength, and the same channel. The LFM (Linear Frequency Modulation) signal (linear frequency modulation signal) carrier is used to modulate the PAM4 signal (4-Level Pulse Amplitude Modulation, that is, a four-level pulse amplitude modulation signal), where the PAM4 signal is used to transmit communication information, and the LFM linear frequency modulation signal is used as a sensing signal. However, this method also has certain defects. It can only use signals transmitted in the PAM modulation format, the communication rate is not high enough, and the spectrum utilization rate is relatively low, and it cannot meet the current high-rate and high-capacity transmission requirements.

[0004] In view of the above problems, it is necessary to propose an optical fiber communication and sensing integrated system to solve or partially solve the above problems. The technical solutions proposed by the present invention are as follows:

[0005] In a first aspect, the present invention provides an optical fiber communication and sensing integrated system, including a signal sending unit, a communication receiving unit, a sensing receiving unit, and a transmission link unit, wherein:

[0006] The transmission link unit at least includes a transmission optical fiber and a vibrator. One end of the transmission optical fiber is respectively used to connect to a signal sending unit and a sensing receiving unit. The other end of the transmission optical fiber is also connected to the communication receiving unit and receives the vibration of the vibrator;

[0007] The signal sending unit is used to generate a time-domain RF-OFDM signal with a Hermitian symmetric structure from the original communication information; it is also used to generate an LFM linear frequency modulation signal according to a preset rule, generate a communication and sensing integrated waveform by using the time-domain RF-OFDM signal and the LFM linear frequency modulation signal, and generate a communication and sensing integrated electrical signal and a communication and sensing integrated optical signal based on the communication and sensing integrated waveform and then output them;

[0008] The sensing receiving unit is used to perform coherent demodulation on the received communication and sensing integrated optical signal to extract phase information, and is also used to distinguish the vibration intensity and frequency of the transmission optical fiber by detecting and analyzing the change of the phase information;

[0009] The communication receiving unit is used to convert the received communication and sensing integrated optical signal into a communication and sensing integrated electrical signal to obtain the original communication information.

[0010] Further, the transmission link unit further includes an optical splitter and a circulator. The input end of the optical splitter is connected to the signal sending unit, and the two output ends of the optical splitter are respectively connected to the input end of the circulator and the sensing receiving unit; the two output ends of the circulator are respectively connected to the transmission optical fiber and the sensing receiving unit.

[0011] Further, the signal sending unit generates a time-domain RF-OFDM signal with a Hermitian symmetric structure from the communication information, including:

[0012] Performing digital modulation on the communication information;

[0013] Filling the modulated communication information into a preset OFDM data frame structure according to the Hermitian conjugate matrix structure to obtain OFDM frequency-domain symbols;

[0014] Adding a radio frequency signal RF as a low-frequency DC signal at the zero-bit frequency component of the OFDM frequency-domain symbol, filling 0 bits at the preset low-frequency components, and then performing inverse Fourier transform to obtain the time-domain RF-OFDM signal.

[0015] Further, the signal sending unit is used to generate an LFM linear frequency modulation signal according to a preset rule, including:

[0016] Generate the LFM chirp signal based on the obtained time-domain RF-OFDM signal, where the frequency of the LFM chirp signal is greater than the frequency of the time-domain RF-OFDM signal, and the frequency change period of the LFM signal is not less than twice the longest transmission time of light in the optical fiber.

[0017] Further, the signal transmitting unit includes a first digital signal processing unit, an arbitrary waveform generator connected to the output end of the first digital signal processing unit, an electrical amplifier connected to the output end of the arbitrary waveform generator, a modulator connected to the output end of the electrical amplifier, a laser connected to one input end of the modulator, and a third optical amplifier connected to the output end of the modulator.

[0018] Further, the modulator is a Mach-Zehnder modulator.

[0019] Further, the sensing and receiving unit includes a first optical amplifier, a first optical bandpass filter, a coherent receiver, an electrical low-pass filter, a first oscilloscope, and a second digital signal processing unit connected in sequence. The first optical amplifier is connected to an output end of the optical splitter, and the coherent receiver is connected to the output end of the signal transmitting unit.

[0020] Further, the communication receiving unit includes a second optical amplifier, a second optical bandpass filter, a photodiode, a second oscilloscope, and a third digital signal processing unit connected in sequence. The other end of the second optical amplifier is connected to the transmission optical fiber.

[0021] On the other hand, the present invention also discloses an optical fiber monitoring system, which uses the above optical fiber communication and sensing integrated system to monitor the state of the optical fiber, locate optical fiber faults, and use the optical fiber for early warning.

[0022] Based on the above technical solutions, the beneficial effects of the present invention compared with the prior art are as follows:

[0023] An optical fiber communication and sensing integrated system provided by the present invention includes a signal transmitting unit, a communication receiving unit, a sensing and receiving unit, and a transmission link unit. The signal transmitting unit is used to generate a communication and sensing integrated waveform and send it to the communication receiving unit and the sensing and receiving unit; the sensing and receiving unit is used to perform coherent demodulation on the communication and sensing integrated optical signal to extract phase information, and is also used to distinguish the vibration intensity and frequency of the transmission optical fiber by detecting and analyzing the change of the phase information; the communication receiving unit is used to convert the communication and sensing integrated optical signal into a communication and sensing integrated electrical signal to obtain the original communication information.

[0024] The present invention utilizes an LFM linear frequency modulation signal to load a time-domain RF-OFDM signal to generate a waveform for integrated communication and sensing. OFDM is a multi-carrier modulation technology. Since the original signal is insensitive to the digital modulation format of the original signal after IFFT transformation and loses the characteristics of the digital modulation format, higher-order digital modulation can be used to achieve higher transmission rates and spectral efficiencies. Moreover, due to the use of the Hermitian symmetric structure, the time-domain output signal has only a real part, minimizing the impact on the sensing signal component. Only the sensing information of the RF component is used to detect changes in the optical fiber link, further improving the accuracy of sensing. In addition, the present invention extracts the phase of the DC component in the Rayleigh scattering signal to resolve the position and change intensity frequency of the optical fiber, and uses the high-frequency component to carry communication information and the DC and low-frequency components to carry sensing information, achieving the goal of non-interfering fiber-optic communication distributed sensing for communication and sensing. The present invention solves the problems of low modulation format, low transmission rate, and insufficient spectral utilization of communication signals in existing fiber-optic integrated communication and sensing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. is a schematic structural diagram of an optical fiber integrated communication and sensing system according to an embodiment of the present invention;

[0026] Figure 2 FIG. is a schematic structural diagram of a communication receiving unit according to an embodiment of the present invention;

[0027] Figure 3 FIG. is a schematic flow diagram of a first digital signal processing unit generating a time-domain RF-OFDM signal according to an embodiment of the present invention;

[0028] Figure 4 FIG. is a schematic diagram of determining the power of RF signal A when a first digital signal processing unit generates a time-domain RF-OFDM signal according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] For ease of understanding, some technical terms related to the embodiments of the present invention are explained as follows:

[0030] OFDM (Orthogonal Frequency-Division Multiplexing) is a multi-carrier modulation technology. Because it can effectively combat frequency-selective fading and overcome inter-symbol interference, OFDM can be efficiently combined with MIMO to achieve high-speed data transmission. The wireless local area network standard IEEE802.11g details the OFDM data frame structure.

[0031] A Hermitian matrix, also translated as "Hermite matrix" or "Hermitian matrix", refers to a self-conjugate matrix. For each element in the i-th row and j-th column of the matrix, it is equal to the conjugate of the element in the j-th row and i-th column. The elements on the main diagonal of a Hermitian matrix are all real numbers, and its eigenvalues are also real numbers.

[0032] The inverse Fourier transform (IFFT) is an algorithm that converts the frequency-domain representation of a signal into the time-domain representation of the signal.

[0033] In order to make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] It is worth pointing out that the defects pointed out in the above background art existing in the prior art are the results obtained by the inventor through practice and careful research. Therefore, the process of discovering the above problems and the solutions proposed by the embodiments of the present invention below for the above problems should be the contributions made by the inventor to the present invention during the process of the present invention.

[0035] In some embodiments, as Figure 1 shown, an optical fiber communication and sensing integrated system mainly includes a signal sending unit 10, a communication receiving unit 40, a sensing receiving unit 30, and a transmission link unit 20, where:

[0036] The output end of the signal sending unit 10 is respectively connected to the circulator 22 and the sensing receiving unit 30, and is used to generate a time-domain RF-OFDM signal with a Hermitian symmetric structure for the communication information; it is also used to generate an LFM linear frequency modulation signal according to a preset rule, and generate a communication and sensing integrated waveform by using the time-domain RF-OFDM signal (radio frequency - orthogonal frequency division multiplexing signal) and the LFM linear frequency modulation signal, and then generate a communication and sensing integrated electrical signal and a communication and sensing integrated optical signal respectively for output.

[0037] Specifically, the main operations of the signal sending unit 10 include:

[0038] 1. Generate a time-domain RF-OFDM signal with a Hermitian symmetric structure. As combined with Figure 3 shown, it may include the following steps:

[0039] S110, perform digital modulation on the communication information.

[0040] Digital modulation formats that a string of communication information as a "0", "1" bit stream can adopt include multi-level amplitude shift keying (MASK), multi-level phase shift keying (MPSK), multi-level quadrature amplitude modulation (MQAM), etc.

[0041] For example, a binary bit stream such as 0000, 1000, 0100, 1100, 0010, 1010, 0110, 1110, 0001, 1001, 0101, 1101, 0011, 1011, 0111, and 1111. After 16QAM modulation, symbols -3 + 3i, -3 + 1i, -3 - 3i, -3 - 1i, -1 + 3i, -1 + i, -1 - i, -1 - 1i, 3 + 3i, 3 + 1i, 3 - 3i, 3 - 1i, 1 + 3i, 1 + 1i, 1 - 3i, and 1 - 1i are obtained.

[0042] S120, according to the requirements of the Hermitian conjugate matrix, fill the modulated communication information into the preset OFDM data frame structure to obtain the OFDM frequency-domain symbol.

[0043] In specific implementation, after the communication information bit stream is mapped into a symbol sequence such as MPSK or MQAM, it is then converted from a serial symbol sequence to a parallel symbol stream. Every N symbols after the serial-to-parallel conversion are filled into the OFDM data frame structure according to the requirements of the Hermitian conjugate matrix, that is, the negative frequency is the conjugate symmetric complex number of the positive frequency, so as to obtain the OFDM frequency-domain symbol (that is, the OFDM symbol is a composite signal of N parallel symbols).

[0044] For the convenience of understanding, taking 4 OFDM symbols with 8 subcarriers as an example, fill the above 16QAM symbols into the OFDM frame, and the OFDM frame arrangement is shown as:

[0045]

[0046] Among them, the first column is the 0-frequency component, the first 7 columns are positive frequencies, the frequency increases column by column, the 7th column is the positive highest frequency, the last 8 columns are negative frequencies, the frequency decreases column by column, the 8th column is the negative highest frequency, and there is no positive frequency with equal frequency, so this column should also be filled with 0. This data frame is symmetric about the 8th column, and the right part of the symmetry axis is the conjugate symmetric complex number of the left part. For example, the 2nd column and the 16th column are a pair, and the 3rd column and the 15th column are a pair. The 4th to 7th columns are the information to be transmitted, the 11th to 14th columns are their conjugate complex numbers, and the rest are filled with 0.

[0047] S130, add the radio frequency signal RF as a low-frequency DC signal at the zero-frequency component of the OFDM frequency-domain symbol, fill 0 bits at the preset low-frequency component, and then obtain the time-domain radio frequency - orthogonal frequency division multiplexing signal through the inverse Fourier transform (IFFT).

[0048] The OFDM frame after inserting the DC a in the frequency domain is represented as:

[0049]

[0050] Add an RF signal at the zero-frequency component to act as a low-frequency DC. To ensure the stability of the DC, part of the low-frequency component is filled with "0". After each row undergoes IFFT transformation, the corresponding time-domain RF-OFDM signal can be generated, and this signal only exists in the real numbers.

[0051] Assume X l is an OFDM frequency-domain symbol, x(t) is a time-domain signal, f k is the carrier frequency, N is the number of subcarriers, k represents the k-th carrier, k = 0, 1, 2.....N - 1, T s is the OFDM symbol period, t is the time, l is the l-th OFDM symbol, A is the time-domain RF signal after a undergoes IFFT transformation, then the time-domain RF-OFDM signal x(t) is expressed as:

[0052]

[0053] The ratio of the power of the RF signal A to the power of the OFDM signal should not be too small or too large. In specific applications, certain theoretical analysis and experiments are required to determine the power of the RF signal A to improve the stability of the system:

[0054] Define the measurement parameter RF-signal power ratio (RSR) as the ratio of the power of the RF signal P RF to the power of the OFDM signal P OFDM and is given by the following formula

[0055]

[0056] The power of the RF signal A will affect the transmission quality of the communication signal. Since the RF signal does not carry any information, from the perspective of communication, the RF power should be as small as possible. However, in sensing, the RF signal carries an LFM linear frequency modulation signal and Rayleigh scattering. If the RF signal is too small, it will greatly affect the resolution of sensing. Considering the restrictive relationship between communication and sensing, the power of the RF signal should be weighed. In practical applications, it is necessary to measure the bit error rate of the communication information and the resolution ability of the sensing signal of this fiber communication and sensing integrated system multiple times under different RSR settings (the relevant measurement methods refer to the existing technology and will not be elaborated here), and then obtain the normalized bit error rate and the normalized resolution, which are used to describe the communication and sensing performances respectively. It can be known that the smaller the normalized bit error rate, the better the transmission performance, and the smaller the normalized resolution, the better the sensing performance. Combining Figure 4 as shown, draw a curve with the normalized bit error rate as the left y-axis, the normalized resolution as the right y-axis, and the RSR as the x-axis. From the above analysis, it can be seen that the normalized bit error rate increases with the increase of RSR, and the normalized resolution decreases with the increase of RSR. When the two curves intersect, the RSR at this time can be considered as a compromise point, maintaining a relatively good sensing performance while ensuring excellent communication quality.

[0057] 2. Generate LFM signal:

[0058] LFM is a chirp signal whose frequency varies with time t and this variation is also periodic. The frequency of the LFM signal should be much greater than that of the RF - OFDM signal, which can ensure distortion - free loading of the communication signal. The frequency change period of the LFM signal should not be less than twice the longest transmission time of light in the optical fiber, which is to ensure that each received scattered signal is within the same LFM change period. LFM is expressed as:

[0059]

[0060] where f i is the initial phase, r is a constant, T is the frequency change period, which cannot be less than twice the longest transmission time of light in the optical fiber. The constant r and the initial phase f i have a constraint relationship: fi = rT, and this quadratic function should be axisymmetric about time t = 0. The longest transmission time of light in the optical fiber refers to the total length of the transmission optical fiber divided by the speed of light.

[0061] 3. Generate integrated communication and sensing signal:

[0062] Multiply the time - domain RF - OFDM signal and the LFM signal to load the LFM on the time - domain RF - OFDM signal to generate the integrated communication and sensing signal s(t), which can be expressed as

[0063]

[0064] 4. Generate an integrated communication and sensing electrical signal from the integrated communication and sensing signal, and then load it into the optical domain to generate an integrated communication and sensing optical signal.

[0065] In some embodiments, the signal sending unit 10 includes a first digital signal processing unit 11 (DSP), an arbitrary waveform generator 12 connected to the output end of the first digital signal processing unit 11, a power amplifier 13 connected to the output end of the arbitrary waveform generator 12, a modulator 15 connected to the output end of the power amplifier 13, a laser 14 connected to one input end of the modulator 15, and a first optical amplifier 16 connected to the output end of the modulator 15. The first digital signal processing unit 11 (DSP) generates the time - domain RF - OFDM signal and the LFM signal, and multiplies the time - domain RF - OFDM signal and the LFM signal to obtain the integrated communication and sensing waveform.

[0066] The integrated sensing waveform is generated by an AWG (Arbitrary Waveform Generator 12, which can generate electrical signals of any shape according to the input signal) to generate a corresponding integrated sensing electrical signal; and the laser 14 generates a beam of laser light, which together with the electrical signal drives the modulator 15 to load the electrical signal onto the optical domain, thereby generating an integrated sensing optical signal. In some embodiments, the laser 14 generates a laser with a wavelength of 1550 nm and a power of 10 dBm. In other embodiments, the modulator 15 employs a Mach-Zehnder Modulator, which can split the input light into two equal signals that respectively enter the two optical branches of the modulator 15.

[0067] OFDM is a multi-carrier modulation technique. Since the original signal is insensitive to the digital modulation format of the original signal after IFFT transformation and loses the characteristics of the digital modulation format in the time domain signal, higher-order digital modulation can be used to achieve higher transmission rates and spectral efficiencies. Moreover, due to the Hermitian symmetric structure, the time-domain output signal has only a real part, minimizing the impact on the sensing signal component. Only the sensing information of the RF component is used to detect changes in the optical fiber link, further improving the accuracy of sensing.

[0068] The transmission link unit 20 includes an optical splitter 21, a circulator 22, a transmission optical fiber 23, and a vibrator 24. The input end of the optical splitter 21 is connected to the signal sending unit 10, and the two output ends are respectively connected to the input end of the circulator 22 and the sensing receiving unit 30; the two output ends of the circulator are respectively connected to the transmission optical fiber 23 and the sensing receiving unit 30; the other end of the transmission optical fiber 23 is also connected to the communication receiving unit 40 and receives the vibration of the vibrator 24.

[0069] The so-called distributed sensing means that it can detect the vibration changes at any point in the optical fiber. In this embodiment, for the convenience of description, the end of the transmission optical fiber can be called the test optical fiber 23, and a vibrator is added here to receive the vibration. In other embodiments, an additional section of test optical fiber can be added to the transmission optical fiber to receive the vibration of the vibrator. In this case, the connection sequence of the optical fiber is transmission optical fiber - test optical fiber - transmission optical fiber.

[0070] In some embodiments, the integrated communication and sensing optical signal output by the signal transmission unit 10 passes through the optical splitter 21, which divides the signal light into two parts. One part of the light is used as the reference light for sensing signal processing, and the other part is used for transmitting communication signals. In practical applications, considering that the local oscillator signal and the received signal power in coherent reception will affect the performance, within the dynamic range of the receiver, the greater the power, the better. Therefore, the splitting ratio of the optical splitter 21 is preferably 1:1. At the end of the transmission optical fiber 23, before the communication receiving end, a vibrator 24 with a fixed frequency is used to vibrate the optical fiber. When the optical fiber is affected by external force vibration, the length, core diameter, and core refractive index of the optical fiber will all change, resulting in a change in the phase of the light wave propagating in the optical fiber. The change Δφ in its phase information can be expressed as:

[0071]

[0072] β is the propagation constant, L is the original optical fiber length, n is the original core refractive index of the optical fiber, a is the original core diameter of the optical fiber, ΔL is the change value of the optical fiber length, Δn is the change value of the core refractive index of the optical fiber, and Δa is the change value of the core diameter of the optical fiber. In some embodiments, the propagation constant β = 2*pi / lambda, where lambda is the optical wavelength.

[0073] Parameters such as the magnitude of the external disturbance and the phase change on the optical fiber are linearly related. Therefore, the relevant information of the external vibration signal can be sensed by detecting the phase change. The communication light generates Rayleigh scattering effect in the optical fiber, and the scattered light is mainly Rayleigh scattering, which is expressed as:

[0074]

[0075] Where: ω is the optical field frequency, Δω is the phase change introduced by the modulator 15, is the phase change caused by the external force, and the definitions of other parameters refer to the previous text.

[0076] The sensing and receiving unit 30 is used to extract the phase information after coherent demodulation of the received integrated communication and sensing optical signal, and is also used to distinguish the vibration intensity and frequency of the transmission optical fiber 23 by detecting and analyzing the phase change.

[0077] In some embodiments, the sensing and receiving unit 30 includes a second optical amplifier 31, a first optical band-pass filter 32, a coherent receiver 33, an electrical low-pass filter 34, a first oscilloscope 35, and a second digital signal processing unit (not shown in the figure) connected in sequence. The second optical amplifier 31 is connected to an output end of the optical splitter 21, and the coherent receiver 33 is connected to the output end of the signal transmission unit 10.

[0078] In the sensing receiving unit 30, an optical amplifier amplifies the power of the scattered signal, and an optical band-pass filter filters out the out-of-band noise. The reference optical signal and the scattered optical signal are simultaneously input into a coherent receiver to complete coherent demodulation. There is a frequency-phase difference between the LFM (Linear Frequency Modulation) signals of the reference light and the scattered light because the frequency of the scattered light changes after passing through the optical fiber, which can be expressed as:

[0079]

[0080] Where: Δt is twice the propagation time of the light reaching any point in the optical fiber, which can be determined by the sampling frequency and the number of samples of the oscilloscope. The definitions of other parameters refer to the previous text. Specifically, the distance between the transmitting end and the receiving end of the communication system is determined, so the transmission length is determined. The first oscilloscope 35 is set to be triggered by an external source for sampling, and the transmitted signal is used as the trigger source to sample the scattered signal. At this time, the starting time and the sampling frequency can be determined. According to a certain sample point of the sampling, calculate the total number of sample points between this sample point and the sampling starting point, and divide the total number of sample points by the sampling frequency to determine the propagation time of the light reaching any point in the optical fiber.

[0081] After obtaining the x 感知接收 (t) signal, a low-pass filter is used to filter out the RF signal to prevent the communication information from having an adverse impact on the sensing. The expression of the filtered low-frequency signal is:

[0082]

[0083] After calculating the time of light propagation, the distance of the optical fiber receiving vibration can be determined C is the speed of light. After removing the residual LFM signal term, we get:

[0084]

[0085] Since the optical field frequency and the phase change introduced by the modulator 15 are deterministic terms, the phase information Δφ(t) can be further extracted. By detecting and analyzing the phase change, the vibration intensity and frequency can be distinguished to achieve distributed optical fiber vibration sensing.

[0086] In the signal processing process of this embodiment, content such as in-phase and quadrature imbalance compensation algorithm (IQ compensation), frequency offset compensation algorithm, downsampling, and synchronization algorithm to achieve frame synchronization, channel equalization, removing residual LFM phase, and removing modulation phase may also be involved. Those skilled in the art can take corresponding processing according to specific situations.

[0087] The communication receiving unit 40 is used to convert the received integrated communication and sensing optical signal into an integrated communication and sensing electrical signal to obtain the original communication information.

[0088] In some embodiments, the communication receiving unit 40 may include a third optical amplifier 41, a second optical bandpass filter 42, a photodiode 43, a second oscilloscope 44, and a third digital signal processing unit (not shown in the figure) that are connected in sequence. The other end of the third optical amplifier 41 is connected to the transmission optical fiber 23.

[0089] At the communication receiving end, an optical amplifier compensates for the power loss of the optical fiber link, an optical bandpass filter filters out-of-band noise, a photodiode 43 performs direct detection, and the oscilloscope stores the detected electrical signal. The third digital signal processing unit extracts the envelope information of the stored data to obtain the RF-OFDM signal, and then uses a synchronization algorithm to achieve frame synchronization, channel equalization of the transmitted symbols, and digital demodulation to obtain the transmitted bit stream. The obtained expression of the RF-OFDM communication signal is

[0090]

[0091] where h(t) is the channel response function and n(t) is the noise. The transmitted data X can be obtained by performing the receiving-end algorithm processing on the received signal. l . The receiving-end algorithm can adopt existing related technologies, and the present invention places no restrictions thereon.

[0092] In the embodiments of the present invention, OFDM modulation is used for communication information, an RF signal is added at the 0-frequency component to act as a low-frequency direct current, and some low-frequency components are filled with 0. The entire OFDM data frame structure satisfies the Hermitian conjugate symmetry structure to ensure that the time-domain information is all real numbers. The receiving end directly detects the optical signal and then demodulates the RF-OFDM signal to complete the transmission of high-rate and high-spectral-efficiency information. The LFM linear frequency modulation signal is used as an electrical carrier to load the RF-OFDM signal. After receiving the Rayleigh scattering signal, the DC RF component is separated, the frequency and phase changes are detected, and distributed sensing is achieved through the frequency and phase changes.

[0093] Compared with the prior art, the present invention uses LFM to load a time-domain RF-OFDM signal to generate a communication and sensing integrated waveform. OFDM is a multi-carrier modulation technology. Since the original signal is insensitive to the digital modulation format of the original signal after IFFT transformation and loses the characteristics of the digital modulation format, high-order digital modulation can be used to achieve higher transmission rates and spectral efficiencies. Moreover, due to the Hermitian symmetric structure, the time-domain output signal has only a real part, minimizing the impact on the sensing signal component. Only the sensing information of the RF component is used to detect the change of the optical fiber link, further improving the accuracy of sensing. In addition, the present invention extracts the phase of the DC component in the Rayleigh scattering signal to resolve the change position and change intensity frequency of the optical fiber, and uses the high-frequency component to carry communication information and the DC and low-frequency components to carry sensing information, achieving the goal of non-interfering fiber communication distributed sensing between communication and sensing. The present invention solves the problems of low modulation format, low transmission rate, and insufficient spectral utilization rate of communication signals in the existing optical fiber communication and sensing integrated technology.

[0094] The optical fiber communication and sensing integrated system of the present invention also has the advantages of high reliability and distributed measurement. The transmission optical fiber can achieve long-distance continuous measurement and control, accurately measure information such as strain, damage, vibration, and temperature of any point of the transmission optical fiber, and thus form a monitoring area with a large range, improving the detection level of the environment. Based on the above advantages, the integration of optical fiber communication and sensing can effectively improve the efficiency and quality of information transmission and processing, with stable performance. At the same time, it can also reduce costs and energy consumption, which is one of the important directions for the development of future information technology. The integration of optical fiber communication and sensing can be applied to many fields, such as intelligent manufacturing, smart city, intelligent transportation, healthcare, etc., and has broad application prospects.

[0095] In addition, based on a similar inventive concept, an embodiment of the present invention further provides an optical fiber monitoring system, including the optical fiber communication and sensing integrated system described in any one of the above.

[0096] Optionally, in some embodiments, the optical fiber communication and sensing integrated system disclosed in the present invention can be applied to an optical fiber monitoring system. Using the above optical fiber communication and sensing integrated system, the vibration change of any point in the optical fiber can be detected to realize the monitoring of the optical fiber state, locate optical fiber faults, and use the optical fiber for early warning. For example, in the field of earthquake monitoring, the earthquake situation can be judged by monitoring the vibration or temperature change of the optical fiber. Another example is that the system can be applied to the field of undersea or underground optical fiber monitoring. If an optical cable is wiretapped or damaged, optical fiber sensing can locate the specific position of the wiretapping or damage. For example, when the optical fiber is broken by heavy snow in winter or damaged at a construction site, the optical fiber communication and sensing integrated system can locate the fault point in the first time.

[0097] In the foregoing detailed description, various features are combined in a single embodiment to simplify the present invention. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are expressly recited in each claim. On the contrary, as reflected in the appended claims, the present invention lies in a state less than all of the features of the single disclosed embodiment. Accordingly, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the present invention.

[0098] The above description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but those of ordinary skill in the art should recognize that the various embodiments can be further combined and arranged. Accordingly, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Further, with respect to the term "comprising" as used in the specification or claims, this term is inclusive in a manner similar to the term "including" as interpreted when used as a transitional word in a claim. Additionally, any use of the term "or" in the claims or specification is to be meant "non-exclusive or".

Claims

1. An integrated optical fiber communication and sensing system, characterized in that It includes a signal transmission unit, a communication reception unit, a sensing reception unit, and a transmission link unit, where: The transmission link unit includes a transmission optical fiber and a vibrator. One end of the transmission optical fiber is respectively used to connect to the signal transmission unit and the sensing reception unit. The other end of the transmission optical fiber is also connected to the communication reception unit and receives the vibration of the vibrator; The signal transmission unit is used to generate a time-domain RF-OFDM signal with a Hermitian symmetric structure from the original communication information; it is also used to generate an LFM linear frequency modulation signal according to a preset rule, generate a communication and sensing integrated waveform using the time-domain RF-OFDM signal and the LFM linear frequency modulation signal, generate a communication and sensing integrated electrical signal based on the communication and sensing integrated waveform, and then convert the communication and sensing integrated electrical signal into a communication and sensing integrated optical signal and output it; The sensing reception unit is used to extract phase information after coherent demodulation of the received communication and sensing integrated optical signal, and is also used to distinguish the vibration intensity and frequency of the transmission optical fiber by detecting and analyzing the change of the phase information; The communication reception unit is used to convert the received communication and sensing integrated optical signal into a communication and sensing integrated electrical signal, and then obtain the original communication information based on the communication and sensing integrated electrical signal.

2. The integrated optical fiber communication and sensing system according to claim 1, characterized in that The transmission link unit further includes an optical splitter and a circulator. The input end of the optical splitter is connected to the signal transmission unit, and the two output ends of the optical splitter are respectively connected to the input end of the circulator and the sensing reception unit; the two output ends of the circulator are respectively connected to the transmission optical fiber and the sensing reception unit.

3. The fiber optic communication and sensing integrated system according to claim 1, wherein The signal transmission unit generates a time-domain RF-OFDM signal with a Hermitian symmetric structure from the communication information, including: Performing digital modulation on the communication information; Filling the modulated communication information into a preset OFDM data frame structure according to the Hermitian conjugate matrix structure to obtain an OFDM frequency-domain symbol; Adding a radio frequency signal RF as a low-frequency DC signal at the zero-frequency component of the OFDM frequency-domain symbol, filling 0 bits at the preset low-frequency components, and then performing an inverse Fourier transform to obtain a time-domain RF-OFDM signal.

4. The fiber optic communication and sensing integrated system according to claim 1, characterized in that, The signal transmission unit is used to generate an LFM linear frequency modulation signal according to a preset rule, including: Generating the LFM linear frequency modulation signal according to the obtained time-domain RF-OFDM signal, where the frequency of the LFM linear frequency modulation signal is greater than the frequency of the time-domain RF-OFDM signal, and the frequency change period of the LFM signal is not less than twice the longest transmission time of light in the transmission optical fiber.

5. The integrated optical fiber communication and sensing system according to claim 1, characterized in that, The signal transmission unit includes a first digital signal processing unit, an arbitrary waveform generator connected to the output end of the first digital signal processing unit, an electrical amplifier connected to the output end of the arbitrary waveform generator, a modulator connected to the output end of the electrical amplifier, a laser connected to one input end of the modulator, and a third optical amplifier connected to the output end of the modulator.

6. The integrated optical fiber communication and sensing system according to claim 5, wherein, The first digital signal processing unit is configured to generate a time-domain RF-OFDM signal and a LFM chirp signal, and multiply the time-domain RF-OFDM signal and the LFM chirp signal to obtain a integrated communication and sensing waveform.

7. The fiber optic communication and sensing integrated system according to claim 2, wherein The sensing receiving unit includes a first optical amplifier, a first optical bandpass filter, a coherent receiver, an electrical low-pass filter, a first oscilloscope, and a second digital signal processing unit connected in sequence. The first optical amplifier is connected to an output end of the optical splitter, and the coherent receiver is connected to an output end of the signal transmitting unit.

8. The integrated optical fiber communication and sensing system according to claim 1, wherein The communication receiving unit includes a second optical amplifier, a second optical bandpass filter, a photodiode, a second oscilloscope, and a third digital signal processing unit connected in sequence. The other end of the second optical amplifier is connected to the transmission optical fiber.

9. The integrated optical fiber communication and sensing system according to claim 2, wherein The splitting ratio of the optical splitter is 1:

1.

10. An optical fiber monitoring system, characterized in that, It includes the fiber optic integrated communication and sensing system according to any one of claims 1 to 9.

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