Xinwei Du

Hilbert superposition and modified signal-to-signal beating interference cancellation for single side-band optical NPAM-4 direct-detection system

We propose a Hilbert superposition and modified signal-to-signal beating interference (SSBI) cancellation scheme in an optical single side-band (SSB) modulation and direct-detection system. The optical SSB signal is generated by a relatively low-cost dual-drive Mach-Zehnder modulator (DDMZM). The two driving signals are a pair of Hilbert signals with Nyquist pulse-shaped four-level pulse amplitude modulation (NPAM-4). In addition to the transmitted baseband signal, both its Hilbert transform and the SSBI can also be detected by direct-detection, which introduce the interference to the transmitted signal. We use the first-stage Hilbert superposition cancellation (HSC) to cancel the unwanted Hilbert transform signal and a modified single-stage linearization filter which contains the second-stage HSC to deduct the SSBI in the receiver. We experimentally demonstrate that 40 Gb/s optical SSB NPAM-4 signal transmission over 80 km standard single mode fiber (SSMF).

Efficient joint timing and frequency synchronization algorithm for coherent optical OFDM systems

A joint timing and frequency synchronization algorithm is proposed for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. The timing and frequency synchronization is realized by using only one training symbol which is composed of conjugated symmetric sequence. The timing estimation of the proposed algorithm has the advantage of being robust to poor optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD), and the frequency estimation range of fractional subcarrier spacing can be achieved. The feasibility and effectiveness of the proposed joint synchronization algorithm is verified in both simulations and a 47.3 Gbit/s 16-ary quadrature amplitude modulation (16-QAM) CO-OFDM system.

A novel timing offset estimation method for coherent optical ofdm systems

We propose a novel timing offset estimation method for CO-OFDM systems, which has smaller MSE and better tolerance to laser phase noise and chromatic dispersion.

Accurate laser linewidth estimation for coherent optical systems using DA-ML carrier phase estimator

We propose an accurate laser linewidth estimation technique based on the decision-aided maximum likelihood carrier phase estimator (DA-ML). Its performance is verified in M-ary quadrature amplitude modulation (MQAM) within a wide range of the laser linewidths and SNR values.

Block decision-aided laser phase noise estimation for coherent optical OFDM systems

In this paper, we propose a block decision-aided (BL-DA) laser phase noise (LPN) estimation algorithm for coherent optical OFDM (CO-OFDM) systems. The OFDM symbols are divided into several blocks and the LPN estimation and compensation procedure is performed based on the decisions between these blocks. The proposed BL-DA algorithm can be applied for higher LPN estimation while at the same time ensuring a better estimation performance. Simulations are carried out in a 70.6 Gbit/s 16-QAM CO-OFDM system to verify the feasibility and efficiency of the BL-DA algorithm.

Chromatic dispersion monitoring by extended Kalman filter for coherent optical OFDM systems

This paper proposes to monitor the total accumulated chromatic dispersion (CD) by using extended Kalman filter (EKF) for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems. Accurate estimation performance can be achieved by only one OFDM training symbol. Simulations results show that the proposed EKF method can quickly converge to the exact dispersion value within 40 subcarriers. Besides, the influence of inter-carrier interference (ICI) induced by the carrier frequency offset (CFO) and laser phase noise (LPN) on the CD monitoring performance is also investigated. Even with the appearance of 3 GHz CFO and 200 kHz combined laser linewidth (CLW) and without compensation, the mean square error (MSE) and bit error rate (BER) of the proposed method vary little, which illustrate its good tolerance to the ICI.

Performance of two-dimensional ML detector with laser phase noise and frequency offset

Simplified Maximum Likelihood (ML) detection and annular-sector (AS) detection for two dimensional constellations is shown to significantly outperform the conventional minimum Euclidean distance (MED) detector in presence of laser phase noise and frequency offset.