Performance Enhancing Technologies Towards Diverse Signal Distortions In High-speed Optical Fiber Communication Systems

The physical layer signal distortions directly restrict the further update of the highspeed optical fiber communication networks.To improve the transmission performance,this dissertation studies the key techniques for transmission performance improvements in the presence of the chirp effects of the directly modulated lasers(DML),the polarization interference in SSMF,the joint nonlinear distortion from chromatic dispersion and square-law detection,according to their specificity,in the directmodulation coherent-detection system(DM/CD),the polarization division multiplexing(PDM)coherent optical system,and the intensity-modulation direct-detection(IM/DD)system,respectively.For the DM/CD systems,the utilizations of the chirp effects in the DML are studied.Theoretically,the MIMO diversity models of the DM/CD systems are constructed by changing “chirp hinders transmission” to “chirp facilitates transmission”.At the receiver,the intensity and the adiabatic chirp are used to demodulate the signals in the intensity and frequency dimensions simultaneously.Alternatively,when the DML operates at the injection locking mode,the intensity and phase can be demodulated simultaneously by using the intensity and the transient chirp.For angle modulation dimensions,the residual terms are compensated by introducing the Volterra nonlinear equalization with the first three orders,where the transmission performance is better than linear equalization.By comparing the transmission performances among the DML-based intensity,frequency and phase modulations,we find the frequency and phase modulations are more suitable for the transmissions at low received optical power and long transmission distances.Moreover,C-band 23 Gb/s and 46 Gb/s PAM-4 signals over 2800 km and beyond 1000 km SSMF transmissions are experimentally demonstrated without any temperature controllers,any frequency offset compensators,or any help from intensity dimension signals.The achieved rate-distance product per polarization is close to the recent transmission record worldwide.For the high-speed PDM-CO systems,studies focus on solving the DSP-enhanced performance degradation and the polarization interference.Firstly,the MAP detection and its simplified version are proposed to approach the optimum decision performance for probabilistically-shaped constellations,where up to 0.5-d B OSNR gain is observed in CO-OFDM systems.It is also found the simplified MAP detector is robust against the residual constellation rotation and the normalization error.Secondly,an error-shaped constant modulus algorithm(ES-CMA)is proposed to solve the equalization problem of the conventional CMA for probabilistically shaped constellations.The demultiplexing and equalization effectiveness of ES-CMA is verified for all the source entropies.Thirdly,a modified Kalman filter(MKF)is proposed using a modified measurement equation to improve the tracking performance of the conventional Kalman filter(CKF).The reason of “the slight modification results in a significant tracking extreme improvement” is theoretically analyzed for the first time,i.e.,the improvement of the noise tolerance at the decision-directed stage.Simulations show 3-d B OSNR gain for the MKF compared with the CKF.The RSOP tracking extreme is extended from 22 MHz to 37 MHz.Besides,MKF has better initialization flexibility on the covariance matrices.For the IM/DD systems,the IM/DD multi-plane field-reconstruction model is established based on the Gerchberg-Saxton(G-S)iterative algorithm to mitigate the signal-signal beating interference(SSBI)induced by the joint distortion of the fiber dispersion and the square-law detection.To improve the global optimum feature of the conventional G-S algorithm,we propose the data-aided iterative algorithm(DIA),the decision-directed data-aided iterative algorithm(DD-DIA)and the multi-constraint iterative algorithm(MCIA)by introducing pilot symbols,decision-generated pseudopilot symbols and the reuse of the channel coding redundancy,correspondingly,to establish the symbol's continuous amplitude plane,the discrete amplitude plane and the time-dependent bit plane.The MCIA can support beyond 100-Gb/s 400-km fiber transmission in the simulations of ideal dispersive channel,which indicates that the MCIA-enabled high capacity IM/DD transmission system would be AWGN-dominated,rather than SSBI dominated.To improve the sensitivity of the DIA,the DD-DIA,and the MCIA to the bandwidth limitation,the hybrid MCIA is proposed for the first time by combining the MCIA and the equalization techniques,which achieves the transparency of the under-fitted ISI residuals to the iterations.Furthermore,a two-stage adaptive dispersion parameter estimator is proposed using the first stage for initialization and the second stage for parameter tracking.The hybrid MCIA enjoys ?17.9 times fiber length estimation error tolerance after embedding the adaptive estimator into the iterations.Finally,an experimental demonstration is conducted using the hybrid MCIA where a Cband 112-Gb/s optical double sideband PAM-4 signal is transmitted over 100-km standard single mode fiber.The transmission capacity,i.e.,11.2 Tb/s·km,breaks the transmission record to the best of our knowledge for the structure-modification-free IM/DD transmissions.The proposed algorithm only introduces the iteration and linear equalizers for field reconstruction.With the help of the proposed algorithms,the SSBI cancellation only requires the frequency-domain linear EDC operation.By utilizing or compensating the signal distortions and DSP-induced performance degradation,the system transmission capacities and algorithm robustness are improved significantly.