The Research On Physical Layer Transmission Technology In 50G-PON

With the rapid development of bandwidth hungry applications such as 4K/8K videos,virtual reality(VR)/augmented reality(AR)applications,5G mobile networks,cloud computing et.al,users have an urgent need for the bandwidth of optical access networks.Next-generation PON technology hopes to increase the bit rate of a single wavelength to 50 Gb/s.If 10 G optical components are still used to transmit 50 Gb/s signals,complex digital signal processing(DSP)algorithms are needed due to the severe bandwidth limitations.These algorithms are more difficult to implement in hardware and the cost is greatly risen.With the gradual maturity of 25 G optical transceiver technologies,this paper uses 25 G optical components to transmit 50 Gb/s signals,which is designed to provide a more practical and easier implementation reference for single lane 50 Gb/s transmission.This paper experimentally demonstrated a transmission of 50 Gb/s NRZ signal over 25 km standard single mode fiber(SSMF)using 25 G EML and APD.The NRZ is converted to a partially responsive duo-binary signal due to channel bandwidth limitations.When the maximum likelihood sequence estimation(MLSE)algorithm is used for equalization,an adaptive channel estimation process is introduced.Compared with the previous fixed channel coefficient algorithm,the performance of the received signal's BER is improved,and the tolerance of MLSE to the chromatic dispersion is improved,too.The receiver sensitivity reaches-24.7 dBm.When using forward feedback equalization(FFE)and decision feedback equalization(DFE)algorithms,the effects of tap numbers of FFE and DFE on system performance are studied under back-to-back and 25 km SSMF transmission.Ultimately,when using the best FFE-5+DFE-1 equalization scheme,the receiver sensitivity can reach-22.5 dBm,which is only 2.2 dB worse than the MLSE case.This paper experimentally demonstrated a transmission of 50 Gb/s PAM4 signal over 25 km SSMF using 25 G EML and PIN.When the MLSE algorithm is used for equalization,the BER performance of the MLSE is improved by the method of secondary channel estimation,and the receiver sensitivity reaches-12 dBm.The transmission performance of the PAM4 signal and its two composite signals MSB and LSB are compared,and the BER curves of these three groups of signals are given under back-to-back and 25 km SSMF transmission.In addition,the 25 G optical transceiver modules suitable for multi-level signal transmission are studied.The EAM modulator reverse bias of EML is optimized by conducting a series of experiments,and the influence curve of EAM reverse bias on the optical receiver's bit error rate(BER)performance is given.