Xiaoxu Li

Electronic post-compensation of WDM transmission impairments using coherent detection and digital signal processing.

A universal post-compensation scheme for fiber impairments in wavelength-division multiplexing (WDM) systems is proposed based on coherent detection and digital signal processing (DSP). Transmission of 10 x 10 Gbit/s binary-phase-shift-keying (BPSK) signals at a channel spacing of 20 GHz over 800 km dispersion shifted fiber (DSF) has been demonstrated numerically.

Comments on “Theoretical Analysis of Gain-Recovery Time and Chirp in QD-SOA”

For original paper see Ben-Ezra et al., ibid., vol.17, no.9, p.1803 (2005). The authors point out that in the above letter, the rate equation model (REM) for quantum-dot (QD) semiconductor optical amplifiers (SOAs) is incorrect because the rate of carrier transition from the excited state (ES) of QD to the wetting layer (WL) was given by Nwh/tau2w, proportional to the carrier density in the WL (Nw).

All-Optical Carrier Synchronization Using a Phase-Sensitive Oscillator

An all-optical carrier synchronization (carrier-phase and polarization recovery) scheme from binary phase-shift keying signals is proposed and demonstrated for the first time. The proposed scheme uses a degenerate optical parametric oscillator which has a phase-sensitive amplifier as a gain block.

WDM Transmission over 320 km EDFA-Amplified SSMF Using 30 Gb/s Return-to-Zero Optical Differential 8-Level Phase-Shift Keying (OD8PSK)

Fiber transmission of optical differential 8-level phase-shift keying (OD8PSK) signals is demonstrated for the first time. Co-polarized 8 WDM channels of 10 Giga-symbol/s or 30 Gb/s return-to-zero (RZ) OD8PSK signals with a channel spacing of 50 GHz were transmitted over 320 km of standard single mode fiber (SSMF) with an EDFA spacing of 80 km. The BER of the worst WDM channel after transmission of 320 km was 2.3x10-5.

All-optical passive clock extraction of 40 Gbit/s NRZ data using narrow-band filtering

A passive all-optical scheme for clock extraction from non return-to- zero (NRZ) data has been proposed based on narrow-band filtering. Two equally effective embodiments of the proposed scheme have been demonstrated experimentally. A carrier-to-noise ratio (CNR) of 30 dB has been achieved at 40 Gbit/s using fiber Bragg gratings (FBG).

Combined impacts of group velocity dispersion, Kerr effect and polarization mode dispersion in optical fibers

This paper is contributed to discuss the impacts of group velocity dispersion, nonlinear Kerr effect and polarization mode dispersion in optical fibers. Using split-step Fourier method, we first analytically analyze that the interaction of Kerr effect and polarization mode dispersion results in the pulse asymmetric spectra. Then we study that polarization mode dispersion and group velocity dispersion play their roles independently, and that, depending on the relative magnitudes, the two factors affect the pulse differently. Finally, we research the combined impacts of group velocity dispersion, Kerr effect and polarization mode dispersion. Detailed investigation reveals that the combined effects are different in anomalous and normal group velocity dispersion regime. We point out that increased Kerr effect can suppress the impact of polarization mode dispersion in anomalous chromatic dispersion regime, and that, for the given values of incident power and polarization mode dispersion, anomalous group velocity should be large enough for the polarization mode dispersion to be effectively suppressed by the Kerr effect.

Static Gain, Optical Modulation Response, and Nonlinear Phase Noise in Saturated Quantum-Dot Semiconductor Optical Amplifiers

A rate equation model preserving charge neutrality for quantum-dot semiconductor optical amplifiers (QD-SOAs) is established to investigate the nonlinear gain dynamics in the saturation regime. The static gain of QD-SOA is calculated assuming overall charge neutrality and compared with that without overall charge neutrality. Optical modulation response and nonlinear phase fluctuation through saturated QD-SOAs are calculated numerically based on a small-signal analysis. The gain dynamics of QD-SOAs are strongly dependent on the current injection level. The carrier reservoir in the wetting layer and continuum state is necessary for QD-SOAs to operate with high gain, high saturation power, and ultrafast gain recovery.

Joint Fiber and SOA Impairment Compensation Using Digital Backward Propagation

An electronic scheme for joint postcompensation of fiber and semiconductor optical amplifier (SOA) impairments based on coherent detection and digital backward propagation is proposed and demonstrated. A 10-GBd amplitude-phase-modulated transmission system was demonstrated experimentally using semiconductor optical amplification. The Q-factor of the received signal was improved by 5 dB with simultaneous fiber and SOA impairment compensation in the electrical domain.

Electrical Postcompensation of SOA Impairments for Fiber-Optic Transmission

An electrical postcompensation scheme for semiconductor optical amplifier (SOA) impairments has been proposed. An on-off keying transmission over 100-km standard single-mode fiber and three SOAs was demonstrated experimentally with SOA impairment compensation. An 8-dB improvement in Q-factor has been achieved.

All-Optical Carrier Phase and Polarization Recovery Using a Phase-Sensitive Oscillator

An all-optical carrier phase and polarization recovery scheme from PSK signals is proposed and demonstrated for the first time. The scheme uses a phase-sensitive optical oscillator with a phase sensitive amplifier as the gain block.