A method for optical transmission and monitoring in PON

Abstract

A method for optical transmission and monitoring of Point-of-Oriented (PON) belongs to the field of optical fiber communication. The method involves: constructing an optical fiber communication system; receiving an optical signal and converting it into an electrical signal; calculating the second and fourth moments of the electrical signal; measuring the actual OSNR of the optical signal from step one using a spectral analyzer; calculating a signal kurtosis reference value using the second and fourth moments and the actual OSNR; fitting the signal kurtosis using baud rate, transmit power, and transmission distance to obtain a signal kurtosis expression; substituting the signal kurtosis expression into a statistical moment method to calculate an OSNR estimate; and realizing PON optical transmission based on the OSNR estimate. This invention achieves lower OSNR estimation errors than existing methods in optical fiber communication systems with various baud rates. Furthermore, by directly fitting the signal kurtosis using baud rate, transmit power, and transmission distance, this invention avoids the selection and calculation of signal correlation functions, achieving lower computational complexity than existing nonlinearly corrected statistical moment methods.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication and relates to a method for optical transmission and monitoring of PON. Background Technology

[0002] Passive Optical Networks (PONs), as a highly efficient fiber optic access technology, play a vital role in modern communication and technological development. PONs distribute optical signals from a central office to multiple user terminals via passive optical splitters, reducing system complexity while improving network reliability and stability. This enables high-speed, efficient, and low-cost broadband access services, and is widely used in home broadband, enterprise access, and other scenarios. With the ever-increasing demand for high-speed data transmission and the rapid development of emerging technologies such as cloud computing and the Internet of Things (IoT), PONs have become a key technology driving the upgrading of communication infrastructure and supporting the development of smart cities and the IoT. However, due to its passive nature, signals are inevitably affected by link loss, fiber dispersion, and nonlinear effects during transmission, impacting the reliability of the communication system. In PON systems, the Optical Signal-to-Noise Ratio (OSNR) is a crucial parameter for evaluating the transmission performance of optical links. OSNR reflects the degree of noise interference to the optical signal in the link; monitoring its changes allows for the timely detection of potential problems in the link. Real-time OSNR monitoring is essential for ensuring system performance and reliable operation, providing critical support for network maintenance, performance optimization, and resource allocation.

[0003] Researchers have proposed various methods for monitoring OSNR in optical communication systems, including Statistical Moments-Based (SMB) methods, Error Vector Magnitude (EVM) methods, Asynchronous Amplitude Histogram (AAH) methods, differential pilot methods, spectral analysis methods, and deep learning-based OSNR monitoring methods. The EVM method estimates OSNR by measuring the magnitude of the error vector between the received signal and the ideal constellation points. This method requires processing the constellation diagram after carrier phase recovery, and the estimation accuracy depends on digital signal processing algorithms. The performance of the AAH method is easily affected by the sampling aperture time. The pilot length of the differential pilot method significantly affects the OSNR estimation accuracy, and the introduction of pilot signals reduces spectral efficiency to some extent. Statistical moment-based methods can effectively capture the high-order complex features of signals and distinguish between signals and noise, attracting widespread attention from scholars both domestically and internationally. However, traditional statistical moment methods have some drawbacks; they only perform well in low-nonlinear scenarios. In recent years, with the continuous increase in transmission distance, greater transmit power is needed to overcome signal loss and dispersion during transmission to achieve the same transmission performance. However, higher transmit power also exacerbates the nonlinear effects of the system. On the one hand, nonlinear noise and amplifier spontaneous emission (ASE) noise are mixed together, and traditional statistical moment methods cannot effectively separate the two, resulting in a significant deviation between the OSNR estimate and the actual value under high signal-to-noise ratio conditions. On the other hand, traditional statistical moment methods estimate OSNR based on the assumption that noise follows a Gaussian distribution. However, nonlinear effects can cause the statistical characteristics of noise to deviate from a Gaussian distribution, leading to a mismatch between traditional statistical moment methods and the actual channel environment. Therefore, traditional statistical moment methods cannot accurately monitor OSNR.

[0004] In recent years, researchers have nonlinearly modified traditional statistical moment methods (SMMs) using correlation functions and correction factors. The performance of modified SMM algorithms is highly dependent on the accuracy of the correlation function and correction factor; different communication systems require different correlation functions and correction factors for different transmit powers, transmission distances, and signal baud rates. However, existing nonlinear modified SMM methods only use transmit power and transmission distance as fitting parameters for the correlation function and correction factor, without including baud rate. In recent years, with the continuous increase in the transmission rate of Passive Optical Networks (PONs), the calculation error of nonlinear modified SMM methods has become increasingly significant with the increase in baud rate. Therefore, there is an urgent need for a new optical transmission and monitoring method for PONs. Summary of the Invention

[0005] To address the issues of large errors in traditional OSNR monitoring methods due to the increasing nonlinearity caused by the continuous improvement of transmission rates in modern PONs, and the high complexity of existing nonlinear correction OSNR monitoring methods which are only applicable to PONs with specific baud rates, this invention aims to provide a PON optical transmission and monitoring method. This method calculates the second and fourth moments of the signal and the signal kurtosis reference value using a constellation diagram obtained through a constant modulus algorithm. Then, it directly fits the signal kurtosis expression using baud rate, transmit power, and transmission distance, reducing OSNR estimation errors caused by signal non-Gaussianity and inappropriate selection of correlation functions in nonlinear scenarios. It also solves the problem that existing nonlinear correction OSNR monitoring methods are only applicable to PONs with specific baud rates and have high complexity. The fitted signal kurtosis expression is then substituted into the traditional statistical moment method to obtain the OSNR estimate. This invention achieves lower OSNR estimation errors than existing methods in various fiber optic communication systems with different baud rates. Furthermore, by directly fitting the signal kurtosis using baud rate, transmit power, and transmission distance, this invention avoids the selection and calculation of signal correlation functions, achieving lower computational complexity than existing nonlinear correction statistical moment methods.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention discloses a method for optical transmission and monitoring of a PON, comprising the following steps:

[0008] Step 1: Set up an optical fiber communication system, receive optical signals, convert them into electrical signals, and then calculate the second and fourth moments of the electrical signals;

[0009] An optical fiber communication system comprises a transmitter, an optical fiber transmission link, and a receiver. The transmitter mainly includes a bit sequence generation module, a digital-to-analog converter, and an optoelectronic signal modulator. The optical fiber transmission link includes optical fiber, an optical power amplifier, and an adjustable optical attenuator. The receiver mainly includes an optical power amplifier, an adjustable optical attenuator, a spectrum analyzer, a receiver, and a digital signal processing module. At the transmitter, the bit sequence generation module generates a series of binary pseudo-random bit sequences, which are mapped to digital symbols. The digital symbols are then converted into analog electrical signals by the digital-to-analog converter. Subsequently, the optoelectronic signal modulator modulates the analog electrical signals onto an optical carrier, converting the electrical signals into optical signals. The optical signals then travel through the optical fiber... After transmission through a certain span of optical fiber in the transmission link, the optical signal is pre-amplified using an optical power amplifier, and the signal power is adjusted using an adjustable optical attenuator. At the receiving end, after transmission through the optical fiber link, the optical signal is post-amplified by an optical power amplifier; the signal power is adjusted using an adjustable optical attenuator, and then the signal light is split into two paths. One path is connected to a spectrum analyzer for signal spectrum analysis, and the other path is processed digitally by a receiver. The digital signal processing module is used to implement IQ imbalance compensation and orthogonal normalization, dispersion compensation, clock recovery, channel dynamic equalization, and polarization demultiplexing. The constant modulus algorithm is used to implement channel dynamic equalization and polarization demultiplexing. The constellation diagram obtained by the constant modulus algorithm is used to calculate the second moment μ2 and the fourth moment μ4 of the received signal, as follows.

[0010] μ2=E{|y n | 2} (1)

[0011] μ4=E{|y n | 4} (2)

[0012] Among them, y n To receive signals.

[0013] Step 2: Measure the true OSNR of the optical signal from Step 1 using a spectral analyzer;

[0014] The true OSNR can be measured using an integration method with a spectral analyzer. The specific implementation method is as follows:

[0015] Step 5.1: Signal Power Measurement: Turn on the test channel OTU, use a spectrum analyzer to perform an integral measurement across the entire signal spectrum, and record the total signal power, denoted as P. Signal ;

[0016] Step 5.2: Background noise power measurement: Turn off the test channel OUT to stop signal transmission, and measure the background noise power within the channel, denoted as P. Noise ;

[0017] Step 5.3: Noise Measurement within the Equivalent Noise Bandwidth: With the OTU off, select the equivalent noise bandwidth of the spectrometer and measure the noise power within a 0.1nm bandwidth range, denoted as P. Noise0.1nm ;

[0018] Step 5.4: OSNR is calculated using the following formula:

[0019]

[0020] Step 3: Calculate the signal kurtosis reference value using the second and fourth moments obtained in Step 1 and the actual OSNR measured in Step 2;

[0021] Obtain the signal kurtosis reference value k a_reference The method is as follows:

[0022]

[0023] OSNR acc Br is the actual OSNR measured in step two, and Br is the equivalent noise bandwidth.

[0024] Step 4: Fit the signal kurtosis using baud rate, transmit power, and transmission distance to obtain the signal kurtosis expression;

[0025] The transmission distance D, the transmit power LP, and the signal kurtosis reference value k are used to construct the signal. a_reference The constructed three-dimensional scatter plot is fitted to the three-dimensional scatter points in LP-k. a_reference and Dk a_reference The projection expression on a plane,

[0026] h = k a_reference (LP,D0,Rs) (5)

[0027] g = k a_reference (LP0,D,Rs) (6)

[0028] Where h and g are LP-k a_reference and Dk a_reference The projection expression on the plane, where D0 and LP0 represent a predetermined transmission distance and transmit power, and Rs is the baud rate;

[0029] Treating the baud rate as a constant, taking the partial derivatives of equations (5) and (6) with respect to LP and D respectively, we get...

[0030]

[0031] Where f LP f is the partial derivative of h with respect to LP. D Let g be the partial derivative of D;

[0032] For fLP Regarding the indefinite integral of LP, we obtain the surface k. a (LP,D,Rs) expression:

[0033] k a (LP,D,Rs)=∫f LP dLP+C(D) (9)

[0034] Where C(D) is an expression for D introduced by the indefinite integral;

[0035] For surface k a Find the partial derivative of (LP,D,Rs) with respect to D.

[0036]

[0037] Combine equation (10) with f D By comparing the expressions for C(D), the surface k can be determined. a The form of (LP,D,Rs) is as follows:

[0038]

[0039] Where a, b, c, d, f, k, l are the coefficients of each term; f correction For the correction term, the expression is:

[0040] f correction =m·sin(LP)+n·sin(D)+p·Rs·LP 4 ·D+u·Rs·LP 3 ·D+v·Rs 2 ·LP 3 ·D (12)

[0041] Where m, n, p, u, v are the coefficients of each term;

[0042] By solving for the values ​​of each coefficient using computer fitting tools, the surface k can be obtained. a (LP,D,Rs), i.e., the signal kurtosis expression:

[0043]

[0044] Step 5: Substitute the signal kurtosis expression obtained in Step 4 into the statistical moment method to calculate the OSNR estimate, and realize PON optical transmission based on the OSNR estimate.

[0045] Based on the second and fourth moments obtained in step one and the k obtained in step four... a (LP,D,Rs) yields the signal-to-noise ratio (SNR):

[0046]

[0047] The OSNR is then calculated using SNR and baud rate, and the result is the OSNR estimate.

[0048]

[0049] Beneficial effects:

[0050] 1. The present invention discloses a PON optical transmission and monitoring method, which reduces the OSNR estimation error caused by the non-Gaussianity of the signal and the inappropriate selection of the correlation function in nonlinear scenarios by directly using baud rate, transmit power and transmission distance to fit the signal kurtosis expression.

[0051] 2. The optical transmission and monitoring method for PON disclosed in this invention incorporates baud rate into the signal kurtosis fitting process, which can overcome the shortcomings of existing nonlinear correction OSNR monitoring methods that are only applicable to PONs with specific baud rates.

[0052] 3. Compared with traditional algorithms, the optical transmission and monitoring method for PON disclosed in this invention has a lower average OSNR estimation error in PON networks with multiple baud rates. In particular, the disclosed monitoring method exhibits excellent monitoring performance in both low and high OSNR regions.

[0053] 4. The optical transmission and monitoring method for PON disclosed in this invention estimates OSNR by directly fitting the signal kurtosis, avoiding the multiplication operations introduced by the nonlinear noise estimation through the correlation function in traditional methods, greatly reducing the complexity of optical transmission and monitoring methods, and realizing fast real-time OSNR monitoring in PON. Attached Figure Description

[0054] Figure 1 This is a flowchart of a PON optical transmission and monitoring method disclosed in this invention;

[0055] Figure 2 This refers to the DP-QPSK coherent optical fiber communication system described in this embodiment of the invention.

[0056] Figure 3 This is a fitting effect diagram of the optical transmission and monitoring method of PON disclosed in this invention at different baud rates.

[0057] Figures a, b, c, and d correspond to 25 Gbaud, 30 Gbaud, 40 Gbaud, and 50 Gbaud, respectively.

[0058] Figure 4 The present invention discloses an optical transmission and monitoring method for PON, and shows the OSNR monitoring error curves in DP-QPSK systems at different baud rates.

[0059] Figures a, b, c, and d correspond to 25 Gbaud, 30 Gbaud, 40 Gbaud, and 50 Gbaud, respectively. Detailed Implementation

[0060] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0061] Example 1:

[0062] In Fiber to the Home (FTTH) broadband, operators typically use a PON (Plasma Optical Network) architecture to transmit optical signals from the central office to multiple home users. The network signal is provided by the operator's Optical Line Terminal (OLT) and transmitted through the PON network to the Optical Network Unit (ONU) equipment. OSNR (Optical System Frequency Reduction) is a crucial indicator of signal quality, especially for long-distance transmission or densely distributed user networks, requiring continuous monitoring to ensure stable network performance. If users report broadband network anomalies, the operator needs to use OSNR monitoring to determine if there is a problem with the link.

[0063] like Figure 1 As shown in the figure, the optical transmission and monitoring method of PON disclosed in this embodiment has the following specific implementation steps:

[0064] Step 1: Set up an optical fiber communication system, receive optical signals, and calculate the second and fourth moments;

[0065] A typical PON (Personal Optical Network) consists of a central office, fiber optic transmission links, and a user side. The central office primarily configures the OLT (Optical Line Terminal), generates multiple data streams for internet, IPTV (Internet Protocol TV), and voice calls, and transmits signals using QPSK or other modulation methods. It mainly includes a bit sequence generation module, a digital-to-analog converter, and an optoelectronic signal modulator. The fiber optic transmission link transmits the optical signals generated by the OLT through the PON network to the user end, where they are distributed to multiple home users via a passive optical splitter. This includes the PON fiber optic link and the passive optical splitter. The user side consists of ONU (Optical Network Unit) devices, responsible for receiving downlink signals, performing optoelectronic conversion, and outputting broadband signals. These mainly include a receiver, a digital signal processing module, a spectral analysis module, and an OSNR (Optical State Recognition) monitoring module. The DP-QPSK coherent fiber optic communication system described above... Figure 2As shown: At the central office, the bit sequence generation module generates a series of binary pseudo-random bit sequences. The generated bit sequences are mapped to QPSK digital symbols. A digital-to-analog converter converts these digital symbols into analog electrical signals. Subsequently, a photoelectric signal modulator modulates the analog electrical signals onto an optical carrier, converting the electrical signals into optical signals. The optical signals are transmitted from the central office through a certain span of optical fiber to the user end, where they are distributed to multiple home users via a passive optical splitter. At the user side, the optical signals are split into two paths. One path is connected to a spectrum analyzer for signal spectrum analysis, and the other path undergoes digital signal processing after passing through a receiver. The digital signal processing module includes the following steps: IQ imbalance compensation and orthogonal normalization, dispersion compensation, clock recovery, channel dynamic equalization, and polarization demultiplexing. The channel dynamic equalization and polarization demultiplexing steps use a constant modulus algorithm. The received signal processed by the constant modulus algorithm is acquired and used to calculate the second moment μ2 and the fourth moment μ4. The calculation method is as follows:

[0066] μ2=E{|y n | 2} (1)

[0067] μ4=E{|y n | 4} (2)

[0068] Among them, y n To receive signals.

[0069] Step 2: Measure the true OSNR of the optical signal from Step 1 using a spectral analyzer;

[0070] The true OSNR can be measured using an integration method with a spectral analyzer. The specific operation method is as follows:

[0071] Step 5.1: Signal Power Measurement: Turn on the test channel OTU, use a spectrum analyzer to perform an integral measurement across the entire signal spectrum, and record the total signal power, denoted as P. Signal ;

[0072] Step 5.2: Background noise power measurement: Turn off the test channel OUT to stop signal transmission, and measure the background noise power within the channel, denoted as P. Noise ;

[0073] Step 5.3: Noise Measurement within the Equivalent Noise Bandwidth: With the OTU off, select the equivalent noise bandwidth of the spectrometer and measure the noise power within a 0.1nm bandwidth range, denoted as P. Noise0.1nm ;

[0074] Step 5.4: OSNR is calculated using the following formula:

[0075]

[0076] Using a spectral analyzer, the actual OSNR was measured under conditions of 25-50 Gbaud baud rate, -10 to 4 dBm transmit power, and 400 to 1200 km transmission distance, respectively, and used as a reference value to calculate the OSNR estimation error.

[0077] Step 3: Calculate the signal kurtosis reference value using the second and fourth moments obtained in Step 1 and the actual OSNR measured in Step 2;

[0078] Obtain the signal kurtosis reference value k a_reference The method is as follows:

[0079]

[0080] OSNR acc The actual OSNR is measured in step two, and Br is the equivalent noise bandwidth, set to 12.5 GHz.

[0081] Step 4: Fit the signal kurtosis using baud rate, transmit power, and transmission distance to obtain the signal kurtosis expression;

[0082] The transmission distance D, the transmit power LP, and the signal kurtosis reference value k are used to construct the signal. a_reference The constructed three-dimensional scatter plot is fitted to the three-dimensional scatter points in LP-k. a_reference and Dk a_reference The projection expression on a plane,

[0083] h = k a_reference (LP,D0,Rs) (5)

[0084] g = k a_reference (LP0,D,Rs) (6)

[0085] Where h and g are LP-k a_reference and Dk a_reference The projection expression on the plane, where D0 and LP0 represent the transmission distance and transmit power for a specific transmission power, and Rs is the baud rate;

[0086] Treating the baud rate as a constant, taking the partial derivatives of equations (5) and (6) with respect to LP and D respectively, we get...

[0087]

[0088] Where f LP f is the partial derivative of h with respect to LP. D Let g be the partial derivative of D;

[0089] For f LP Regarding the indefinite integral of LP, we obtain the surface k. a (LP,D,Rs) expression:

[0090] k a (LP,D,Rs)=∫f LP dLP+C(D) (9)

[0091] Where C(D) is an expression for D introduced by the indefinite integral;

[0092] For surface k a Find the partial derivative of (LP,D,Rs) with respect to D.

[0093]

[0094] Combine equation (10) with f D By comparing the expressions for C(D), the surface k can be determined. a The form of (LP,D,Rs) is as follows:

[0095]

[0096] Where a, b, c, d, f, k, l are the coefficients of each term; f correction For the correction term, the expression is:

[0097] f correction =m·sin(LP)+n·sin(D)+p·Rs·LP 4 ·D+u·Rs·LP 3 ·D+v·Rs 2 ·LP 3 ·D (12)

[0098] Where m, n, p, u, v are the coefficients of each term;

[0099] The values ​​of each coefficient are obtained by solving the curve k using a computer fitting tool. a (LP,D,Rs), i.e., the signal kurtosis expression:

[0100]

[0101] The fitting effect of the signal kurtosis reference value of PON at different baud rates is shown in the figure. Figure 3 As shown in the figure, Figures a, b, c, and d correspond to 25Gbaud, 30Gbaud, 40Gbaud, and 50Gbaud PON systems, respectively. It can be seen that the established model shows a good fit in all four baud rate scenarios.

[0102] Step 5: Substitute the obtained signal kurtosis expression into the traditional statistical moment method to calculate the OSNR estimate;

[0103] Based on the second and fourth moments obtained in step one and the k obtained in step four...a (LP,D,Rs) yields the signal-to-noise ratio (SNR):

[0104]

[0105] The OSNR is then calculated using SNR and baud rate, and the result is the OSNR estimate.

[0106]

[0107] By comparing the optical transmission and monitoring method for PON disclosed in this invention with traditional statistical moment methods, error vector magnitude methods, and nonlinearly corrected statistical moment methods, the OSNR monitoring error curves of 25Gbaud, 30Gbaud, 40Gbaud, and 50Gbaud DP-QPSK modulated PON networks are shown below. Figure 4 As shown in Figures a, b, c, and d, the optical transmission and monitoring method for PON disclosed in this invention achieves good estimation accuracy under four test baud rate conditions. The average estimation errors for 25, 30, 40, and 50 Gbaud systems are 0.64 dB, 0.41 dB, 0.51 dB, and 0.72 dB, respectively. Compared with traditional algorithms, the average estimation error of the proposed method is improved by 3.8 dB, 3.04 dB, 2.52 dB, and 2.29 dB, respectively. Particularly in the lower and higher OSNR regions, the optical transmission and monitoring method for PON disclosed in this invention exhibits superior estimation performance, with a maximum error reduction of over 6 dB.

[0108] This invention discloses a PON optical transmission and monitoring method, which estimates OSNR by directly fitting signal kurtosis, avoiding the multiplication operations introduced by traditional methods that use correlation functions for nonlinear noise estimation. After fitting the signal kurtosis expression through 28 multiplication operations, this method requires only 4 multiplication operations for each data sample, significantly reducing the algorithm's complexity. This disclosed PON optical transmission and monitoring method can accurately monitor the OSNR of high-speed PON networks in real time.

[0109] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for optical transmission and monitoring in a PON, characterized in that: Includes the following steps, Step 1: Set up an optical fiber communication system, receive optical signals, convert them into electrical signals, and then calculate the second and fourth moments of the electrical signals; Step 2: Measure the true OSNR of the optical signal from Step 1 using a spectral analyzer; Step 3: Calculate the signal kurtosis reference value using the second and fourth moments obtained in Step 1 and the actual OSNR measured in Step 2; Step 4: Fit the signal kurtosis using baud rate, transmit power, and transmission distance to obtain the signal kurtosis expression; The specific implementation method for step four is as follows: The transmission distance D, the transmit power LP, and the signal kurtosis reference value k are used to construct the signal. a_reference The constructed three-dimensional scatter plot is fitted to the three-dimensional scatter points in LP-k. a_reference and Dk a_reference The expression for projection on a plane, h=k a_reference (LP,D0,Rs) (1) g=k a_reference (LP0,D,Rs) (2) Where h and g are LP-k a_reference and Dk a_reference The projection expression on the plane, where D0 and LP0 represent a predetermined transmission distance and transmit power, and Rs is the baud rate; Treating the baud rate as a constant, taking the partial derivatives of equations (1) and (2) with respect to LP and D respectively, we get... Where f LP f is the partial derivative of h with respect to LP. D Let g be the partial derivative of D; For f LP Regarding the indefinite integral of LP, we obtain the surface k. a (LP,D,Rs) expression: k a (LP,D,Rs)=∫f LP dLP+C(D) (5) Where C(D) is an expression for D introduced by the indefinite integral; For surface k a Find the partial derivative of (LP,D,Rs) with respect to D. Combine equation (6) with f D By comparing the expressions for C(D), the surface k can be determined. a The form of (LP,D,Rs) is as follows: Where a, b, c, d, f, k, l are the coefficients of each term; f correction For the correction term, the expression is: f correction =m·sin(LP)+n·sin(D)+p·Rs·LP 4 ·D+u·Rs·LP 3 ·D+v·Rs 2 ·LP 3 ·D(8) Where m, n, p, u, v are the coefficients of each term; The values ​​of each coefficient are obtained by solving the curve k using a computer fitting tool. a (LP,D,Rs), i.e., the signal kurtosis expression: Step 5: Substitute the signal kurtosis expression obtained in Step 4 into the statistical moment method to calculate the OSNR estimate, and realize PON optical transmission based on the OSNR estimate.

2. The optical transmission and monitoring method for PON as described in claim 1, characterized in that: The optical fiber communication system described in step one includes a transmitter, an optical fiber transmission link, and a receiver. The transmitter mainly includes a bit sequence generation module, a digital-to-analog converter, and an optoelectronic signal modulator. The optical fiber transmission link includes an optical fiber, an optical power amplifier, and an adjustable optical attenuator. The receiver mainly includes an optical power amplifier, an adjustable optical attenuator, a spectrum analyzer, a receiver, and a digital signal processing module. At the transmitter, the bit sequence generation module generates a series of binary pseudo-random bit sequences, which are mapped to digital symbols. The digital symbols are converted into analog electrical signals by the digital-to-analog converter. Subsequently, the analog electrical signals are modulated onto the optical carrier by the optoelectronic signal modulator, converting the electrical signals into optical signals. After the optical signal is transmitted through a certain span of optical fiber in the optical fiber transmission chain, the optical power amplifier is used to pre-amplify the optical signal, and an adjustable optical attenuator is used to adjust the signal optical power. At the receiving end, after the optical signal is transmitted through the optical fiber link, it is post-amplified by the optical power amplifier. An adjustable optical attenuator is used to adjust the signal optical power, and then the signal light is split into two paths. One path is connected to a spectrum analyzer for signal spectrum analysis, and the other path is processed into digital signals after passing through a receiver. The digital signal processing module is used to implement IQ imbalance compensation and orthogonal normalization, dispersion compensation, clock recovery, channel dynamic equalization and polarization demultiplexing. Among them, the constant modulus algorithm is used to implement channel dynamic equalization and polarization demultiplexing.

3. The optical transmission and monitoring method for PON as described in claim 1, characterized in that: The constant modulus algorithm uses the constellation diagram obtained from equations (10) and (11) to calculate the second moment μ2 and the fourth moment μ4 of the received signal: μ2=E{|y n | 2 } (10) μ4=E{|y n | 4 } (11) Among them, y n To receive signals.

4. The optical transmission and monitoring method for a PON as described in claim 1, characterized in that: In step two, the OSNR is measured using an integration method with a spectrometer. The specific implementation method is as follows: Step 5.1: Signal Power Measurement: Turn on the test channel OTU, use a spectrum analyzer to perform an integral measurement across the entire signal spectrum, and record the total signal power, denoted as P. Signal ; Step 5.2: Background noise power measurement: Turn off the test channel OUT to stop signal transmission, and measure the background noise power within the channel, denoted as P. Noise ; Step 5.3: Noise Measurement within the Equivalent Noise Bandwidth: With the OTU off, select the equivalent noise bandwidth of the spectrometer and measure the noise power within a 0.1nm bandwidth range, denoted as P. Noise0.1nm ; Step 5.4: OSNR is calculated using the following formula:

5. The optical transmission and monitoring method for a PON as described in claim 1, characterized in that: Step 3 obtains the signal kurtosis reference value k a_reference The method is as follows: OSNR acc Br is the actual OSNR measured in step two, and Br is the equivalent noise bandwidth.

6. The optical transmission and monitoring method for a PON as described in claim 1, characterized in that: The specific implementation method for step five is as follows; Based on the second and fourth moments obtained in step one and the k obtained in step four... a (LP,D,Rs) yields the signal-to-noise ratio (SNR): The OSNR is then calculated using the SNR and baud rate; the result is the estimated OSNR value.

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