Key Signal Detection And Processing Technologies In Short-reach Optical Fiber Transmission Systems

Recently,the meaning of Internet is enriched by the emerging new services,such as virtual reality,real-time games,smart home,etc.The communication network is used not only to deliver information,but also to provide content oriented and personalized services.Then,massive high-speed data centers will be deployed,and the bandwidth requirements of various devices in the user side will explosively increase.As the base of communication network,optical fiber transmission systems are faced with new challenges.On one hand,high-speed fiber interconnect technologies are required for data center deployment.On the other hand,both mobile and fixed access systems are calling for optical fiber transmission technologies with both high capacity and low cost.Therefore,researches about high-speed short-reach transmissions are of great significance for realizing the next-generation communication networks.In the thesis,we have researched several signal detection and processing technologies in high-speed short-reach transmission systems.Firstly,we study advanced equalization algorithms for signal distortion suppression in high-speed intensity modulation direct detection(IM-DD)systems.According to the theoretical analysis,high speed transmissions are mainly limited by bandwidth limitation and nonlinear distortions.To handle these problems,we propose three advanced equalization algorithms.:(1)Partial response signaling can improve the tolerance to bandwidth limitation effect,by compressing spectrum.We propose to combine coding and MLSE for signal demodulation in partial response systems.Compared with the conventional MLSE,the proposed scheme can avoid error propagation.Experimental results of C-band DM-DD transmission indicate that,under the limitation of HD-FEC,transmission of 100 Gbps PAM-4 over 15-km can be achieved.(2)Feedback based equalization can effective compensate signal distortion caused by bandwidth limitation effect.We propose Volterra-DFE by introducing nonlinear kernels,which helps a lot to reduce nonlinear distortions.Experimental results of C-band DM-DD transmission indicate that,under the limitation of SD-FEC,transmission of 60 Gbps PAM-4 over 80 km can be achieved.(3)THP coding can be regarded as a “transmitter-side” DFE.We propose nonlinear Tomlinson Harashima precoding(THP)by using Volterra,to better mitigate the nonlinear distortions.Experimental results of C-band MZM based DD transmission indicate that,under the limitation of HD-FEC,transmission of 84-Gbps PAM-4 over 80-km and 107-Gbps PAM-4 over 40-km can be respectively achieved.Secondly,we study signal detection and processing methods for polarization division multiplexing and intensity modulation(PDM-IM)transmission systems.For polarization de-multiplexing,receiver based on polarization diverse Kramers-Kronig(KK)detection is used to recover the optical field,which reduces hardware complexity compared with coherent methods.To enhance the performance of KK detection,we propose a carrier-suppressed PDM-PAM-4 modulation to provide a stable carrier to signal power ratio(CSPR).Also,since carrier recovery is not required for demodulation,requirements of the laser linewidth are relaxed.The demonstrational experiments are designed according to downstream transmission requirements of PON system.Results indicate that,29 dB power budget can be achieved for 20-km/40-km transmissions of 100 Gbps PDM-PAM-4.Thirdly,we study high-speed optical fiber transmission technologies for digital mobile fronthual systems.And we propose to special PAM modulation and optimized sample bit mapping,to improve the fidelity of mobile signals.According to the theoretical analysis,different sample bit has different weight,thus causing different distortion on mobile signal when bit error occurs.With this regard,the basic concept of this work is providing good quality to high order sample bits in priority.On one hand,for the SNR limited transmission systems,we respectively propose uneven PAM-4 modulation and hybrid PAM-2/-4 modulation.On the other hand,for nonlinear distortion limited transmission systems(systems based on EML or DML),we propse bit interleaving.According to the experimental results,the proposed special modulation and optimize bit mapping can lead to remarkable performance improvement,compared with conventional PAM-4 modulation.Fourthly,we study high-speed optical fiber transmission technologies for analog mobile fronthaul systems.We propose to adopt parallel signal detection to enable connection between multiple points to point,which cannot be realized based on the conventional analog transmission.And the parallel signal detection doesn't introduce any signal penalty and is compatible to IM-DD systems.Furthermore,based on the parallel signal detection,we propose analog mobile fronthual structures,to support resource sharing of optical transmission layer.The proposed structures are respectively based on WSS and AWGR.Finally,we verify our proposals by experimental demonstrations,results of which can meet the performance requirements of mobile signal.