High-speed Fiber-optics Communication System Based On Self-coherent Detection

The adoption of coherent detection, together with advanced modulation formats andmultiplexing techniques, is ideal to achieve high receiver sensitivity, excellent spectralefficiency (SE), and long transmission distance for fiber-optic transmission. However,current optical coherent detection has several disadvantages, e.g., the high cost of coherentreceiver. It is well-known that the costly system setups have become the bottleneck of thefurther development of coherent optical communication system.After the theoretical elaboration on coherent optical communication system, theinvestigations is carried out for self-homodyne detection system based on mode divisionmultiplexing (MDM) technique, and self-heterodyne detection system based on sub-carriermultiplexing technique. Both the research directions can reduce the system cost largely.The main content of the thesis includes: Firstly, the thesis elaborates on the basicconstruction and principle of coherent detection system. The generations of high-ordermodulation formats and the DSP algorithms are discussed in detail. After that, MDM systembased on self-homodyne coherent detection is investigated theoretically and demonstratedthrough simulation. An analytical investigation on the ASE-limited self-homodyne coherentsystem based on FMF is presented. The accuracy of our model is verified in the context of112Gbps PM-QPSK transmission system. DC offset elimination is shown necessary toreduce distortion of QPSK constellation. Meanwhile, a closed-form analytical BER formulais verified with deviation less than0.2dB at BER=10-3, while the predicted optimum powerratio between data signal and PT signal agrees well with the simulation result. In addition,the adaptive equalization using modified constant modulus algorithm (MCMA) is showneffectively for the proposed system. Lastly, the subcarrier multiplexing (SCM) basedself-heterodyne (SH) coherent detection for PM-16QAM format is proposed anddemonstrated. A digital signal processing (DSP) scheme is proposed to eliminate imagefrequency interference (IFI) arising in such detection. And an analytical BER formula isverified by numerical simulations with deviation less than0.3dB at BER=1e-3. Afterverifying the analytical model accuracy, the key parameters of the proposed SH coherentdetection can be optimized further, including the filter bandwidth, subcarrier frequencyspacing, and modulation index (MI) ratio between the data and PT signal.