Method and system for laser linewidth detection in coherent optical communication systems

Abstract

The application provides a laser linewidth detection method and system in a coherent optical communication system, the method comprising: step S1: receiving a coherent optical signal, preprocessing the coherent optical signal, and inputting the preprocessed signal into a carrier phase recovery module; step S2: constructing a linewidth estimation model according to a signal model of a laser linewidth; step S3: collecting a phase estimation value of the carrier phase recovery module CPR with a known linewidth and SNR signal noise ratio, inputting the phase estimation value into the linewidth estimation model, and correcting the linewidth estimation value; and step S4: inputting a phase estimation value of the carrier phase recovery module CPR with an arbitrary SNR value, and estimating a to-be-measured laser linewidth. The application uses the phase estimation value of the phase recovery module and simple mathematical calculation to realize estimation of the laser linewidth. The application uses data samples to statistically estimate the deviation under different SNRs, thereby realizing accurate estimation of the laser linewidth.

Description

Technical Field

[0001] This invention relates to the field of coherent optical communication technology, and more specifically, to a laser linewidth detection method and system based on phase estimation in a coherent optical communication system. Background Technology

[0002] With the development of internet technology, the volume of internet communication data is increasing daily. To meet the demands of modern internet communication data volume, high-speed dynamic coherent optical communication network technology has received widespread attention. Among these technologies, real-time optical performance detection, used to assist in the management of dynamic optical networks, is attracting increasing attention as a core technology. Among the many system detection parameters, the estimation of the laser linewidth at the transmitting end is particularly urgent. Besides optical communication systems, single-frequency lasers are widely used in research fields such as lidar, high-resolution spectral measurement, and quantum optics. Laser linewidth is a key parameter for measuring the monochromaticity of a light source; therefore, accurate measurement of laser linewidth is crucial.

[0003] Current laser linewidth detection methods generally employ interferometers or time-delayed self-heterodyne methods, which require additional laser detection systems and cannot be widely applied in coherent optical communication systems.

[0004] Chinese patent document CN102100024A discloses a phase noise statistical characteristic monitoring device and method, and a coherent optical communication receiver. The monitoring device includes an amplitude taking unit, an unpacking unit, a delay unit, a differential unit, etc., and also includes a laser linewidth influence suppression unit, which is used to measure the size of the laser linewidth and suppress the influence of the laser linewidth in the mean square value sequence of the phase differential signal. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and system for detecting laser linewidth in a coherent optical communication system.

[0006] A laser linewidth detection method based on phase estimation in a coherent optical communication system, provided by the present invention, includes:

[0007] Step S1: Receive the coherent optical signal, preprocess the coherent optical signal, and input the preprocessed signal into the carrier phase recovery module;

[0008] Step S2: Construct a linewidth estimation model based on the signal model of the laser linewidth;

[0009] Step S3: Acquire the phase estimate value of the CPR module of the download wave with known linewidth and SNR, input it into the linewidth estimation model, and correct the linewidth estimate value;

[0010] Step S4: Input any SNR value to download the phase estimate value of the CPR phase recovery module and estimate the linewidth of the laser under test.

[0011] Preferably, the preprocessing includes: performing photoelectric conversion on the coherent optical signal through balanced photodetector, performing frequency offset compensation on the converted electrical signal, performing clock synchronization operation, eliminating signal interference using a depolarization multiplexing module to obtain an electrical signal with a single polarization state, estimating the frequency offset of the electrical signal, estimating the residual frequency offset of the signal, and then feeding it back to the frequency offset compensation module.

[0012] Preferably, step S2 includes:

[0013] Step S2.1: The mathematical module for laser linewidth is as follows: LW represents laser linewidth in Hz, fs is symbol rate in Hz, and ε(n) is carrier phase noise, which follows a normal distribution with a mean of 0 and a variance of 1.

[0014]

[0015] Step S2.2: Calculate the phase difference between the symbols before and after receiving data, estimate the linewidth value using statistical variance, and obtain the linewidth estimation model:

[0016]

[0017] Where var() represents the variance calculation function.

[0018] Preferably, step S3 includes:

[0019] Step S3.1: Acquire the phase estimate value of the CPR module of the download wave with known linewidth and SNR, input it into the linewidth estimation model, and calculate the error of the sample;

[0020] Step S3.2: Collect phase estimation values ​​under multiple line widths and SNRs to obtain the line width estimation error offset under different SNRs.

[0021] Preferably, step S4 includes:

[0022] Step S4.1: Input the estimated phase from the current phase recovery module CPR into the linewidth estimation model to obtain the linewidth estimate LW. est

[0023] Step S4.2: Using the SNR estimate of the current data, obtain the line width estimation error offset LW through interpolation. offset

[0024] Step S4.3: Subtract the two values ​​to obtain the final linewidth estimate LW. out :

[0025] LW out =LW est -LW offset .

[0026] A laser linewidth detection system based on phase estimation in a coherent optical communication system provided by the present invention includes:

[0027] Module M1: Receives coherent optical signals, preprocesses the coherent optical signals, and inputs the preprocessed signals into the carrier phase recovery module;

[0028] After balanced photoelectric detection, frequency offset compensation, clock recovery, depolarization multiplexing, frequency offset estimation, and carrier phase recovery (CPR) module;

[0029] Module M2: Construct a linewidth estimation model based on the signal model of the laser linewidth;

[0030] Module M3: Acquires the phase estimate from the CPR phase recovery module of the download wave with known linewidth and SNR, inputs it into the linewidth estimation model, and corrects the linewidth estimate;

[0031] Module M4: Input any SNR value to download the phase estimate value of the CPR phase recovery module and estimate the linewidth of the laser under test.

[0032] Preferably, the preprocessing includes: performing photoelectric conversion on the coherent optical signal through balanced photodetector, performing frequency offset compensation on the converted electrical signal, performing clock synchronization operation, eliminating signal interference using a depolarization multiplexing module to obtain an electrical signal with a single polarization state, estimating the frequency offset of the electrical signal, estimating the residual frequency offset of the signal, and then feeding it back to the frequency offset compensation module.

[0033] Preferably, the module M2 includes:

[0034] Module M2.1: The mathematical module for laser linewidth is as follows: LW represents laser linewidth in Hz, fs is symbol rate in Hz, and ε(n) is carrier phase noise, which follows a normal distribution with a mean of 0 and a variance of 1.

[0035]

[0036] Module M2.2: Calculates the phase difference between the received data symbols and estimates the linewidth value using statistical variance, thus obtaining the linewidth estimation model.

[0037]

[0038] Where var() represents the variance calculation function.

[0039] Preferably, the module M3 includes:

[0040] Module M3.1: Acquires the phase estimate value of the CPR phase recovery module for a known linewidth and SNR, inputs it into the linewidth estimation model, and calculates the linewidth estimation error of the sample.

[0041] Module M3.2: Iterates through and collects phase estimation values ​​under multiple line widths and SNR (signal-to-noise ratio) to obtain the line width estimation error offset under different SNRs.

[0042] Preferably, the module M4 includes:

[0043] Module M4.1: Inputs the estimated phase from the current phase recovery module CPR into the linewidth estimation model to obtain the linewidth estimate LW. est

[0044] Module M4.2: Using the SNR estimate from the current data, interpolation is used to obtain the linewidth estimation error offset LW. offset

[0045] Module M4.3: Subtract the two values ​​to get the final linewidth estimate LW. out :

[0046] LW out =LW est -LW offset .

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] 1. This invention uses the phase estimation value of the phase recovery module and simple mathematical calculations to estimate the laser linewidth.

[0049] 2. This invention achieves accurate estimation of laser linewidth by using data samples and statistically analyzing the linewidth estimation deviation under different signal-to-noise ratios.

[0050] 3. This invention does not modify the structure of the coherent optical communication system, does not affect data transmission, and only utilizes the phase estimation value of the phase recovery module in the receiving link to directly detect the linewidth using simple calculations. Attached Figure Description

[0051] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0052] Figure 1 This is an overall flowchart of the laser linewidth detection method in the coherent optical communication system of the present invention;

[0053] Figure 2 This is a flowchart of the line width estimation calculation in this invention. Detailed Implementation

[0054] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0055] This invention discloses a laser linewidth detection method based on phase estimation in a coherent optical communication system, referring to... Figure 1 and Figure 2 As shown, it specifically includes:

[0056] Step S1: The received optical signal passes through balanced photodetector, frequency offset compensation, clock recovery, depolarization multiplexing, frequency offset estimation, and carrier phase recovery module CPR;

[0057] Step S2: Construct a linewidth estimation model based on the signal model of the laser linewidth;

[0058] Step S3: Acquire the phase estimate value of the CPR module of the download wave with known linewidth and SNR, input it into the linewidth estimation model, and correct the linewidth estimate value;

[0059] Step S4: Input any SNR value to download the phase estimate value of the CPR phase recovery module and estimate the linewidth of the laser under test.

[0060] Step S2 includes the following process:

[0061] Step S2.1: The mathematical module for laser linewidth is as follows: LW represents laser linewidth in Hz, fs is symbol rate in Hz, and ε(n) is carrier phase noise, which follows a normal distribution with a mean of 0 and a variance of 1.

[0062]

[0063] Step S2.2: Calculate the phase difference between the symbols before and after receiving the data, and estimate the linewidth value by using statistical variance;

[0064]

[0065] Where var() represents the variance calculation function.

[0066] Step S3 includes the following process:

[0067] Step S3.1: Collect the phase estimate value of the CPR module of the download wave with a known linewidth and SNR, input it into the linewidth estimation model, and calculate the error of the sample;

[0068] Step S3.2: Collect phase estimation values ​​under multiple line widths and SNRs to obtain the line width estimation error offset under different SNRs.

[0069] Step S4 includes the following process:

[0070] Step S4.1: Input the estimated phase from the current phase recovery module CPR into the linewidth estimation model to obtain the linewidth estimate LW. est

[0071] Step S4.2: Using the SNR estimate of the current data, obtain the line width estimation error offset LW through interpolation. offset

[0072] Step S4.3: Subtract the two values ​​to obtain the final linewidth estimate LW. out :

[0073] LW out =LW est -LW offset .

[0074] Working principle: The coherent optical signal is converted into an electrical signal by the balanced photodetector module, laying the foundation for subsequent processing; preliminary electrical domain compensation compensates for the frequency offset of the electrical signal output by the balanced photodetector, correcting the signal deviation caused by frequency offset during signal transmission and ensuring signal frequency stability; clock synchronization performs a clock recovery operation to extract clock information from the signal, keeping the receiver clock synchronized with the transmitter clock, ensuring the timing accuracy of subsequent signal sampling and processing; through the depolarization multiplexing module, the information carried by different polarization states in the optical signal is separated, eliminating signal interference caused by polarization multiplexing, and obtaining an electrical signal with a single polarization state; finally, frequency offset estimation is performed again to further accurately estimate the residual frequency offset of the signal, and then fed back to the frequency offset compensation module.

[0075] The received electrical signal, processed in the previous steps, still contains random phase noise introduced by the laser linewidth, manifested as random carrier phase drift. A carrier phase recovery (CPR) module is used to track and compensate for the carrier phase, resulting in a phase-calibrated signal.

[0076] The phase value estimated by the phase recovery module is theoretically the sum of the phase value caused by the residual frequency offset and the phase value caused by the laser linewidth. Therefore, the linewidth value can be estimated by using the phase difference between the preceding and following symbols of the received data and by statistical variance.

[0077]

[0078] (1) By collecting phase estimates from the CPR module of the download waveband with multiple known linewidths and SNRs, and inputting them into the linewidth estimation model, the estimated linewidths under different SNRs are obtained.

[0079] (2) Based on the estimated value and the given value in (1), the offset value of the line width estimate under different SNR signal-to-noise ratios is obtained by using mathematical statistics.

[0080] (3) Acquire the phase estimate value of the carrier phase recovery module (CPR) in the current system, input it into the linewidth estimation model, and obtain the linewidth estimate value LW. est

[0081] (4) Collect the SNR value of the signal-to-noise ratio estimation module in the current system, interpolate the offset value in (2), and obtain the line width estimation error offset LW under the current SNR. offset

[0082] (5) Subtract the results from steps (3) and (4) to obtain the final linewidth estimate LW. out :

[0083] LW out =LW est -LW offset .

[0084] This invention also provides a coherent optical communication system with laser linewidth detection function, including a balanced photodetector module, a frequency offset estimation and compensation module, a clock recovery and synchronization module, a depolarization multiplexing module, a phase recovery module, a signal-to-noise ratio estimation module, and a linewidth estimation module. The coherent optical communication system with laser linewidth detection function can be implemented by executing the process steps of the laser linewidth detection method. That is, those skilled in the art can understand the laser linewidth detection method as a preferred embodiment of the coherent optical communication system with laser linewidth detection function.

[0085] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0086] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for detecting the linewidth of a laser in a coherent optical communication system, characterized in that, include: Step S1: Receive the coherent optical signal, preprocess the coherent optical signal, and input the preprocessed signal into the carrier phase recovery module; Step S2: Construct a linewidth estimation model based on the signal model of the laser linewidth; Step S3: Acquire the phase estimate value of the CPR module of the download wave with known linewidth and SNR, input it into the linewidth estimation model, and correct the linewidth estimate value; Step S4: Input any SNR value to download the phase estimate value of the CPR phase recovery module and estimate the linewidth of the laser under test; Step S2 includes: Step S2.1: The mathematical module for the laser linewidth is as follows. This indicates the laser linewidth, measured in Hz. Symbol rate, in Hz. The carrier phase noise follows a normal distribution with a mean of 0 and a variance of 1. Step S2.2: Calculate the phase difference between the symbols before and after receiving data, estimate the linewidth value using statistical variance, and obtain the linewidth estimation model: in This represents the variance calculation function; Step S3 includes: Step S3.1: Collect the phase estimate value of the CPR module of the download wave with a known linewidth and SNR, input it into the linewidth estimation model, and calculate the error of the sample; Step S3.2: Collect multiple line widths and SNR signals and noise ratios to obtain the line width estimation error offset under different SNRs; Step S4 includes: Step S4.1: Input the estimated phase from the current phase recovery module CPR into the linewidth estimation model to obtain the linewidth estimate. Step S4.2: Using the SNR estimate of the current data, obtain the line width estimation error offset through interpolation. Step S4.3: Subtract the two values ​​to obtain the final line width estimate. : 。 2. The laser linewidth detection method in a coherent optical communication system according to claim 1, characterized in that, The preprocessing includes: performing photoelectric conversion on the coherent optical signal through balanced photodetector, performing frequency offset compensation on the converted electrical signal, performing clock synchronization operation, eliminating signal interference using a depolarization multiplexing module to obtain an electrical signal with a single polarization state, estimating the frequency offset of the electrical signal, and then feeding it back to the frequency offset compensation module.

3. A laser linewidth detection system in a coherent optical communication system, characterized in that, include: Module M1: Receives coherent optical signals, preprocesses the coherent optical signals, and inputs the preprocessed signals into the carrier phase recovery module; After balanced photoelectric detection, frequency offset compensation, clock recovery, depolarization multiplexing, frequency offset estimation, and carrier phase recovery (CPR) module; Module M2: Construct a linewidth estimation model based on the signal model of the laser linewidth; Module M3: Acquires the phase estimate from the CPR phase recovery module of the download wave with known linewidth and SNR, inputs it into the linewidth estimation model, and corrects the linewidth estimate; Module M4: Input any SNR value to download the phase estimate value from the CPR phase recovery module and estimate the linewidth of the laser under test; The module M2 includes: Module M2.1: The mathematical module for laser linewidth is described below. This indicates the laser linewidth, measured in Hz. Symbol rate, in Hz. The carrier phase noise follows a normal distribution with a mean of 0 and a variance of 1. Module M2.2: Calculates the phase difference between the received data symbols and estimates the linewidth value using statistical variance, thus obtaining the linewidth estimation model. in This represents the variance calculation function; The module M3 includes: Module M3.1: Acquires the phase estimate value of the CPR phase recovery module for a known linewidth and SNR, inputs it into the linewidth estimation model, and calculates the sample error; Module M3.2: Iterates through and collects phase estimation values ​​under multiple linewidths and SNRs to obtain the linewidth estimation error offset under different SNRs; The module M4 includes: Module M4.1: Inputs the estimated phase from the current phase recovery module CPR into the linewidth estimation model to obtain the linewidth estimate. Module M4.2: Using the SNR estimate from the current data, interpolation is used to obtain the linewidth estimation error offset. Module M4.3: Subtract the two values ​​to get the final linewidth estimate. : 。 4. The laser linewidth detection system in a coherent optical communication system according to claim 3, characterized in that, The preprocessing includes: performing photoelectric conversion on the coherent optical signal through balanced photodetector, performing frequency offset compensation on the converted electrical signal, performing clock synchronization operation, eliminating signal interference using a depolarization multiplexing module to obtain an electrical signal with a single polarization state, and then estimating the frequency offset of the electrical signal to correct the frequency shift of the signal.

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