Research On Wavelength Channel Identification And Other Key Techniques In Optical Network Monitoring

Optical network is evolving rapidly in the direction of larger capacity,higher spectral efficiency,more dynamic and flexible.Flexibel Dense Wavelength Division Multiplexing(F-DWDM)network has become one of the mainstream technology of optical networks due to their flexibility,efficiency and variable dynamic connections.However,optical network architectures have become more complex and huge,and connections have become more dynamic and flexible.Therefore,the corresponding monitoring scheme is urgently needed to guarantee the stabilization and high efficiency of the optical network.In particular,there are huge number of optical wavelength cross-connections in F-DWDM.Correct wavelength connection is a necessary for the normal operation of the optical network.Therefore,the wavelength connection status is the primary monitoring target in the optical network monitoring.The monitoring scheme based on Optical Label has a natural ability to monitor the connection status of the optical wavelength channel through the "path-following identification",but it is susceptible to the Stimulated Raman Scattering(SRS)effect under the condition of long-distance and multi-channel transmission,resulting in reduced monitoring accuracy.On the other hand,the intermediate nodes of optical networks are more cost-sensitive,and there is an urgent need for low-cost and high-accuracy wavelength channel performance and parameter monitoring/identification to provide real-time information for the network management system,which enable the optical network to have independent comprehensive perception capabilities.In addition,the monitoring scheme of the optical fiber lines between the intermediate nodes of the entire network,including the monitoring of fiber break point location,fiber attenuation,and connector status,can detect and even avoid optical fiber failures in real time,and reduce the economic loss which caused by failures of optical fiber lines.The optical fiber line monitoring of F-DWDM network is developing toward the "embedded" direction that does not occupy additional wavelengths and does not require an independent light source,but there are still problems such as poor monitoring performance due to limited transmit power.Therefore,this article focuses on the above-mentioned main problems of F-DWDM optical network monitoring,carries out research on key technologies for FDWDM networks monitoring.The main research work and innovations are as follows.1.In the wavelength channel monitoring scheme based on the Optical Label,the SRS effect causes crosstalk between optical labels of each wavelength channel after multi-span transmission,which severely limits the accuracy and reliability of optical signal-to-noise ratio(OSNR)monitoring based on Optical Label.A multi-channel OSNR reliable monitoring scheme based on digital signal processing(DSP)iteratively suppressing SRS-induced optical label crosstalk is proposed.Firstly,the scheme uses DSP to iteratively mitigate the SRS effect,avoiding the expensive optical components used in the traditional SRS mitigation scheme based on optical filter grouping.Next,the shceme calculates amplifier spontaneousemission noise before and after each erbium-doped fiber amplifier based on the optical power of each channel monitored by the optical label,and then calculates the OSNR of each channel.The simulation results have demonstrated that under the condition of 80 channels of 10× 100km optical fiber transmission,the average error and maximum error with DSP processing are reduced to 0.27 dB and 0.49 dB respectively.It should be noted that the average error of the proposed DSP scheme(0.27 dB)is reduced by 1.31 dB and 0.1 dB compared to the 2grouping scheme(1.58 dB)and 4-grouping scheme(0.37 dB)with optical filter.In the worst condition,the OSNR monitoring error is within 0.3dB.2.The wavelength channel monitoring scheme based on the Optical Label can determine the wavelength added node through the " pathfollowing identification ",but due to SRS crosstalk,the channel label can still be detected on other channels when the service signal is dropped(residual label),which cause co-channel interference with the label of the newly added service signal.The interference will degrade the accuracy of monitoring.A highly reliable F-DWDM optical network wavelength channel identification scheme based on Asynchronous Code Division Multiple Access(A-CDMA)to suppress residual optical label is proposed.The A-CDMA method is used to identify node Identifications(ID)and residual labels.The schme only uses the 10MHz orders of magnitude lowbandwidth Photoelectric Detector(PD)combined with DSP Processing to determine the wavelength connection status by monitoring the channel power and node ID of all wavelength channels at the same time.The simulation results show that in the conditon of service signal added and dropped with severe crosstalk in the C-band 80 wavelength channels,the average error and maximum error with DSP-based SRS suppression are reduced to 0.40dB and 0.99dB respectively,and can realize 100%node ID monitoring.The wavelength connection status can be accurately judged.3.In response to the demand for low-cost and dispersion-tolerant modulation format identification(MFI)of wavelength channels in FDWDM optical networks that only need to monitor optical wavelength channel parameters,a MFI scheme based on low-bandwidth direct detection and Convolutional Neural Network(CNN)in intermediate node is proposed.The proposed MFI scheme uses CNN to train and identify Asynchronous Amplitude Histograms(AAH)generated by directly detecting a small part of the optical signal from the intermediate node with low bandwidth PD.And the maximum correlation coefficient of different modulation formats is used as an index for judging the degree of differentiation of each modulation format AAH,so as to select the dispersion tolerance receiver bandwidth.The simulation and offline experimental results show that,under the condition that the chromatic dispersion is 0?16000 ps/nm,the input optical power is OdBm and 5dBm,and the OSNR range is from tolerance to above 15dB,the proposed scheme can achieve three kinds of quadrature amplitude modulation:QPSK,16QAM,and 64QAM format with 100%accuracy identification.4.The embedded optical time-domain reflectometer(OTDR)in the F-DWDM network is "embedded" in the optical supervising channel(OSC).The performance of the embedded OTDR is not only restricted by the limited transmission optical power and measurement signal time,but also the waveform distortion of the detected sequence(M sequence)caused by hardware implementation,which reduces the dynamic range.In this paper,an M sequence waveform distortion compensation method suitable for embedding correlated OTDR is designed.The designed method first detects the M sequence sent by the transmitter without backscattering as the basis for detecting distortion before detecting the backscattered signal,and performs distortion compensation based on the detected distortion.After the correct OTDR curve is obtained,the event recognition threshold is updated according to the chip width to realize automatic event recognition.The simulation results show that the dynamic range of the backward Rayleigh scattering after distortion compensation under the condition that the order of M-sequence chips is 9(length of M-sequence chips is 511)and the chip width is 6400ns reaches 19.5dB,which is close to the dynamic range of the undistorted M-sequence through the backward Rayleigh scattering system with 21dB.The dynamic range after distortion compensation is about 18dB in the offline experiment.