The Recovery Technology Research Of Faster-than-nyquist Signal Based On 7.5GHz-bandwidth Optical Modulator

At present,the main body of DWDM's core optical network is 7.5GHz.With the rapid growth of cable bandwidth demand,the speed of the core optical network will be even higher in the future which can be up to 25G or even more.In order to improve the bandwidth utilization based on the existing bandwidth and modulation,the Faster-than-Nyquist bandwidth recovery technology has attracted more and more attention.As the research background,the 7.5GHz optical transmission link is established through the research of parameters and ideal device model of7.5GHz commercial devices in the optical fiber link.To have research on such Faster-than-Nyquist bandwidth signal,specific excitation is given to observe the system response to make a quantitative analysis of distortion of the signal.On this basis,to reduce the algorithm complexity of signal recovery technology,a signal recovery scheme based on frequency domain filtering and simplified maximum likelihood estimation is proposed in this paper.The signal is filtered by the 4 order Bessel analog filter.And the least mean square algorithm is used to estimate the channel.By adding the prior information,weakening the Viterbi condition and replacing the core operation,the maximum likelihood estimation is simplified.The experiment shows that the algorithm can modulate the data signal of 41Gbit/s by the current 7.5GHz electro-optical intensity modulator under the PRBS 15 test vector with bit error rate of 10^-5,which means the modulation efficiency can be up to 5.47 bit/s/Hz.The SNR can be as low as3.2 decibels in the condition that bit error rate is 10^-4 and the length is 50km.The algorithm complexity can be reduced from exponential to constant.The conclusion means that the algorithm is effective to recover the signal in the existing system.