Jian Hong Ke

Linewidth-Tolerant and Low-Complexity Two-Stage Carrier Phase Estimation for Dual-Polarization 16-QAM Coherent Optical Fiber Communications

Two novel linewidth-tolerant, low-complexity feedforward carrier phase estimation algorithms are described for dual-polarization 16-ary quadrature-amplitude-modulation with coherent detection. For both algorithms, the carrier phase is estimated in two stages. The first stage employs either a simplified quadrature-phase-shift-keying (QPSK) partitioning algorithm or the blind phase search (BPS) algorithm. The second stage employs a novel QPSK constellation transformation algorithm. The performance and linewidth tolerance of both algorithms are evaluated using experimental and simulation data, and the hardware complexity is assessed. For both proposed two-stage algorithms, the linewidth symbol duration product is 1.3 × 10-4 for a 1 dB penalty in optical signal-to-noise ratio at a bit error ratio of 10-3. This performance is comparable to a single-stage BPS algorithm with a large number of test phases, but with a reduction of the hardware complexity by factors of about 2.5-11.

Linewidth-Tolerant and Low-Complexity Two-Stage Carrier Phase Estimation Based on Modified QPSK Partitioning for Dual-Polarization 16-QAM Systems

Three novel linewidth-tolerant, low-complexity, two-stage feed-forward carrier phase estimation algorithms are introduced for dual-polarization 16-ary quadrature amplitude modulation (DP 16-QAM) with coherent detection. The first stage employs either the quadrature phase-shift keying (QPSK) partitioning algorithm, simplified QPSK partitioning algorithm, or blind phase search (BPS) algorithm. The second stage employs a novel modified QPSK partitioning algorithm. Based on experimental data, all three algorithms achieve comparable performance for DP 16-QAM back to back and transmission systems. The linewidth tolerance for the three algorithms is numerically studied. A linewidth symbol duration product of 1.3×10-4 is demonstrated for a 1 dB optical signal-to-noise-ratio penalty at a bit error ratio 10-3 of for all the proposed algorithms, which is comparable to the single-stage BPS algorithm with a large number of test phases. Reductions in the hardware complexity by factors of about 1.7-5.3 are achieved in comparison to the single-stage BPS algorithm.

400 Gbit/s single-carrier and 1 Tbit/s three-carrier superchannel signals using dual polarization 16-QAM with look-up table correction and optical pulse shaping.

A 448 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal and a 1.206 Tbit/s three-carrier DP 16-QAM signal are demonstrated using look-up table (LUT) correction and optical pulse shaping. The LUT correction is used to mitigate the effects of transmitter-based pattern-dependent distortion due to the high symbol rates. A programmable optical filter is employed to narrow the modulated signal spectrum and thereby enhance the spectral efficiency and reduce the requirements on the receiver bandwidth and analog-to-digital converter sampling rate. By combining these techniques, the back-to-back required optical signal-to-noise ratios are 26.6 dB and 27.2 dB for BER = 10(-3), and transmission over 1200 and 1500 km of standard single-mode fiber with EDFA amplification was achieved for the 448 Gbit/s signal (12% forward error correction (FEC) overhead) and 1.206 Tbit/s signal (20% FEC overhead), respectively.

Assessment of Intrachannel Nonlinear Compensation for 112 Gb/s Dual-Polarization 16QAM Systems

For 112 Gb/s dual-polarization 16-ary quadrature amplitude modulation systems, the performance and complexity of the low-pass filter (LPF)-assisted digital back-propagation (DBP) algorithm for mitigating intrachannel fiber nonlinearity are investigated. Comparison is made with both linear equalization and the standard DBP algorithm for single-channel transmission (simulation and experiment) and for wavelength division multiplexed (WDM) transmission with channel spacings of 50 and 35 GHz (simulation). With optimized values for the algorithm parameters, the simulation results show that, compared to linear equalization, the 0.2 steps/span LPF-assisted DBP algorithm can increase the transmission distance by 84%, 40%, and 17% for a single-channel, 50 GHz channel-spaced WDM, and 35 GHz channel-spaced WDM transmission, respectively. These improvements in the transmission distance are 54%, 75%, and 77% of those achieved with the 4 steps/span standard DBP algorithm but at considerably lower complexity. Single-channel experimental results show that the 0.25 steps/span LPF-assisted DBP algorithm can increase the transmission distance by 43%, which is 68% of the improvement achieved with the 4 steps/span standard DBP algorithm. Compared to the standard DBP algorithm, the LPF-assisted DBP algorithm can allow a reduction in the number of steps/span, but with an increased computational complexity for each step. The two DBP algorithms are compared in terms of the number of real multiplications per bit, thus allowing the algorithm with lower complexity to be determined at a given level of performance.

Carrier Phase Estimation for DP-16QAM Using QPSK Partitioning and Quasi-Multiplier-Free Algorithms

A low complexity and linewidth tolerant two-stage carrier phase estimation (CPE) by using QPSK partitioning and quasi-multiplier free algorithm is proposed for DP-16QAM signal. The performance, linewidth tolerance of the algorithm are numerically and experimentally demonstrated.

Implication of Parameter Values on Low-Pass Filter Assisted Digital Back Propagation for DP 16-QAM

The low-pass filter (LPF) assisted digital back propagation (DBP) algorithm is investigated for 112 Gb/s dual-polarization 16-ary quadrature-amplitude-modulation transmission up to 2400 km. The performance implications of the parameter values for the LPF-DBP algorithm are considered in detail through determining the dependence of the bit error ratio (BER) on the number of nonlinear compensation (NLC) steps per span for optimum parameter values and the sensitivity of the BER to nonoptimum parameter values. The sensitivity to nonoptimum values is investigated as well for different transmission lengths and launch powers. It is shown that the optimum parameter values depend on the NLC step size, but that for a given step size representative values can be used for a range of transmission lengths and channel launch powers.

Generation and transmission of DPSK signals using a directly modulated passive feedback laser

The generation of differential-phase-shift keying (DPSK) signals is demonstrated using a directly modulated passive feedback laser at 10.709-Gb/s, 14-Gb/s and 16-Gb/s. The quality of the DPSK signals is assessed using both noncoherent detection for a bit rate of 10.709-Gb/s and coherent detection with digital signal processing involving a look-up table pattern-dependent distortion compensator. Transmission over a passive link consisting of 100 km of single mode fiber at a bit rate of 10.709-Gb/s is achieved with a received optical power of -45 dBm at a bit-error-ratio of 3.8 × 10(-3) and a 49 dB loss margin.

Low-Pass Filter Assisted Digital Back Propagation Algorithm for 112 Gb/s DP 16-QAM

Insight about the low-pass filter assisted digital back-propagation algorithm is provided by considering the impact of the nonlinear compensation on the correction/generation of symbol errors and the effect of the step size on the effective nonlinear compensation.

Performance of PM QPSK and PM 16-QAM coherent optical fiber communication systems

The performance of polarization multiplexed, quadrature phase shift keying (PM QPSK) and polarization multiplexed 16-ary quadrature amplitude modulation (PM 16-QAM) is considered with an emphasis on the signal processing algorithms that compensate transmission impairments and implement key receiver functions.