Huijian Zhang

Spectrally Efficient Quadrature Duobinary Coherent Systems With Symbol-Rate Digital Signal Processing

An enhanced digital coherent receiver including a novel blind equalization approach and maximum-likelihood sequence detection (MLSD) is proposed for dual-polarization quadrature duobinary (DP-QDB) systems. In virtue of the compact spectrum of DP-QDB signals approaching Nyquist limit, the equalization is implemented at symbol rate, which relaxes the demand on the sampling speed of analog-to-digital converters (ADCs). The proposed symbol-rate receiver is verified by 43 Gb/s experiments in the presence of chromatic dispersion and polarization-mode dispersion. This paper also investigates the tolerances to narrowband optical filtering, ADC sampling phase, duobinary-generating filter bandwidth, laser linewidth, and carrier frequency offset. Detailed modulation format comparisons are made among DP-QDB, DP-quadrature-phase-shift keying (QPSK), DP-8 quadrature amplitude modulation (QAM), and DP-16QAM. It is shown that DP-QDB with MLSD well trades off major requirements on advanced modulation formats.

Polarization demultiplexing based on independent component analysis in optical coherent receivers

A novel independent component analysis based algorithm is proposed for polarization demultiplexing. It solves the converge-to-same-source problem of constant modulus algorithm while possesses similar polarization tracking capability.

Interplay between local oscillator phase noise and electrical chromatic dispersion compensation in digital coherent transmission system

We demonstrate that the interplay between local oscillator phase noise and electrical chromatic dispersion compensation induces timing jitter as well as intensity noise. The interplay is investigated in 3000 km-long transmission (accumulated dispersion of 47,000 ps/nm) without optical dispersion compensation.

Adaptive blind equalization for coherent optical BPSK system

The widely used CMA equalization fails in coherent optical BPSK systems. A novel adaptive blind equalization method is proposed and experimentally verified in terms of frequency offset, laser linewidth, CD/PMD and polarization scrambling tolerance.

Non-linearity Tolerance of Direct Detection and Coherent Receivers for 43 Gb/s RZ-DQPSK Signals with Co-propagating 11.1 Gb/s NRZ Signals over NZ-DSF

We experimentally investigate the nonlinear impairments on 43 Gb/s RZ-DQPSK signals with direct detection and coherent receivers in a hybrid 10 G/40 G DWDM transmission over NZ-DSF with 50 GHz channel spacing.

Enhanced digital coherent receiver for high spectral-efficiency dual-polarization quadrature duobinary systems

To enable linear impairment compensation and increase OSNR tolerance, a digital coherent receiver incorporating symbol-rate blind equalization and maximum-likelihood sequence detection is proposed and experimentally verified at 43Gbit/s for dual-polarization quadrature duobinary systems.

Controlled adaptive equalization for dual-polarization coherent receivers with simple clock recovery

We present a novel controlled adaptive equalization scheme for dual-polarization coherent receivers and demonstrate data asynchronous operation that ultimately allows for simple clock recovery implementation.