Research And Application Of Key Technologies For Short-and Medium-reach Optical Transmission With Direct Detection

With the rapid development of communication technology,new applications such as4K/8K high-definition video,unmanned driving,telemedicine,and 5G are approaching our daily lives.However,to allow everyone to enjoy the conveniences brought by the Internet,the optical communication networks,especially the short-and medium-reach optical transmission network(<80km),are facing serious challenges such as insufficient capacity,high latency,and unstable access.Passive optical networks(PON),mobile fronthaul(MFH),and datacenter interconnects(DCI)are the well-known short-and medium-reach optical transmission networks.These short-and medium-reach optical transmission networks have the features of large coverage,dense distribution,and flexible structures that can satisfy the diversified application scenarios.Therefore,the capacity growth rate of short-and medium-reach optical transmission networks is much higher than that of long-haul optical transmission networks.However,the coherent communication technology in long-haul transmission scenarios for high-capacity transmission cannot be directly moved into the short-and medium-reach optical transmission networks because the short-and medium-reach scenarios are sensitive to system costs,power consumption,and footprints.On the contrary,direct detection technology with low-cost and small-footprint is very suitable for short-and medium-reach scenarios.Therefore,it is imperative to develop the short-and medium-reach optical transmission networks based on direct detection,and it is significant to study the related key technologies for improving transmission efficiency and capacity.On the one hand,the transmission efficiency of MFH is important for the applications of 5G and even B5 G mobile networks.On the other hand,PON will merge with the mobile networks to carry some mobile services.Additionally,the DCI is bearing a large amount of data traffics.In this thesis,the transmission efficiency and wireless access in MFH,the covered subscriber numbers and data rate in PON,and the high-speed transmission in DCI,will be discussed.Some equalization algorithms,wireless access technologies and high-capacity system architectures were proposed.Experiments and simulations were implemented to verify these proposed schemes.The main contents and results are as follows:(1)A multi-channel multiplexing scheme using the carrierless amplitude and phase modulation(CAP)filters was proposed and applied in MFH,considering the orthogonal characteristics of the digital filters in multi-dimensional CAP technology.A multi-user asynchronous access A-Ro F system based on Multi-band CAP technology was proposed and experimentally demonstrated.The experimental results show that the Ro F system based on Multi-band CAP has 1d B receiver sensitivity gain than OFDMA when introducing other wireless interferences,and it also supports stable and seamless asynchronous access for many users.Furthermore,A carrier aggregation(CA)scheme based on multi-dimensional orthogonal CAP digital filters was proposed and experimentally demonstrated.The experimental results show that the proposed CA scheme is bandwidth-efficient and synchronization-insensitive.After 36 20 MHz LTE signals are aggregated using the proposed method,the occupied bandwidth is within 1.348 GHz.The results show that the proposed schemes help realize a high-efficiency mobile fronthaul.(2)A bidirectional high-capacity PON architecture that can cover lots of subscribers was proposed based on multi-core fiber and Kramers-Kronig(KK)direct detection,and a Rayleigh backscattering(RB)noise avoidance scheme was designed for the system.The proposed system was outstanding in the aspects of spectral efficiency,receiver sensitivity,cost,and RB noise mitigation.Via simulation and experiment,the results show that the receiver sensitivity of the proposed system is about 3d B lower than that of the coherent receiver,the linewidth tolerance is higher than that of heterodyne detection,it can support lasers with 2MHz linewidth,and it is very convenient for dispersion compensation at the receiver.In an experiment with symmetrical 60 Gbps SSB-Nyquist-16 QAM signals transmission over 50 km multi-core fiber,receiver OSNR gain about 4.7d B and 4.5d B for downlink and uplink,respectively,can be obtained,thanks to the designed RB noise avoidance scheme.(3)A low-complexity FFE+PF+IC joint equalization scheme for short-and medium-reach IMDD transmission systems was proposed.The IC algorithm is a specially designed interference cancellation algorithm,and its complexity is only about 3% of the MLSE algorithm.In the experiment,100Gb/s ODSB PAM4 and 100Gb/s OSSB PAM4 signals were transmitted over 10 km and 80 km SSMF,respectively,with bit error rate(BER)below the SD-FEC threshold,thanks to the proposed FFE+PF+IC joint equalization scheme.A novel TDD-Volterra equalizer was proposed and verified in an IMDD experiment.The experimental results show that the proposed TDD-Volterra equalizer can effectively mitigate the level-dependent equalization effects appeared in the traditional Volterra equalizer.With the help of TDD-Volterra,the BER of 180Gb/s PAM8 signal after 2km SSMF transmission in the experiment can reach the HD-FEC threshold.Compared with the traditional Volterra equalizer,the complexity of the TDD-Volterra equalizer can be reduced by more than 50%.Moreover,A Volterra-DFE equalizer that can effectively suppress the high-frequency enhanced noise was proposed and vierified in a DML-based IMDD experimental system.The results show that with the help of Volterra-DFE equalizer,4×64Gbit/s PAM4 signals and 4×96Gbit/s PAM8 signals can be transmitted over 30 km SSMF and 15 km SSMF,respectively.A maximum power gain of 3.3d B was obtained for4×96Gbit/s PAM8 signal transmission.Compared with the traditional Volterra equalizer,the proposed Volterra-DFE equalizer can reach a target BER value with lower complexity,and the computational complexity is reduced by 38% in our experiment.