Bofang Zheng

Brillouin Controlled Phase Matching in Optical Parametric Processing of Coherent Signals

We demonstrate the recovery of phase-matched condition in fiber-based four-wave mixing (FWM) using gain-transparent stimulated Brillouin scattering (SBS). The phase term introduced by SBS offers additional FWM conversion efficiency (CE). Our approach is implemented in a coherent communication system using a 10-Gbaud/s QPSK signal in the proof of concept experiment. A CE enhancement of ~11 dB has been achieved. As a result of optical signal-to-noise ratio enhancement, the Q factor is improved by 5.4 dB. Compared with directly detected signals, coherent signals are highly susceptible to phase noise. Therefore, we further evaluate possible phase noise degradation caused by SBS on the FWM pump, emphasizing on the frequency range of interest in our coherent system. The results are compared with those obtained from the conventional FWM configuration, confirming that the impact of SBS on the phase noise is insignificant.

Mitigation of Kerr-induced nonliear distortion by superimposing the sidebands of a multiband-CAP signal

We show that the upper and lower sidebands of a multiband carrier-less amplitude phase (CAP) signal fulfil the condition of phase-conjugated twin waves. Through simulation and experiments, the reduction of intrachannel and interchannel nonlinear distortions are demonstrated. The optimum launched power for 200 km transmission is improved by 2 dB in a two-channel wavelength division multiplexing (WDM) system.

Raman-Assisted Phase-Sensitive Amplification Enabled Optical Add-Drop Filter

We present a novel reconfigurable optical add-drop filter based on phase-sensitive amplifiers (PSAs). By manipulating the relative phase among an optical pump, signals, and idlers, spectral selectivity can be achieved along with low noise amplification. The use of backward Raman amplification enhances the phase-sensitive operation of the parametric process, enabling higher stopband isolation and lower intra-band crosstalk. A Raman-assisted phase-sensitive amplifier (RA-PSA) is characterized in detail, showing a 7.8-dB combined gain extinction ratio enhancement and 10.85-dB gain improvement. For the first time, we demonstrate an RA-PSA enabled optical add-drop filter with less than 0.4-dB penalty using three-channel QPSK signals. The novel scheme provides a simple way to enhance the extinction ratio of the PSA enabled add-drop filter, which can be an essential subsystem in optical links based on phase-sensitive amplification.

Self-Oscillating Optical Frequency Comb Based on a Raman-Pumped Brillouin Optoelectronic Oscillator

We demonstrate the generation of a self-oscillating optical frequency comb using a Raman-pumped Brillouin optoelectronic oscillator. In this scheme, stimulated Brillouin scattering is utilized as a frequency selective component. Due to the narrow gain bandwidth of stimulated Brillouin scattering, which is ~30 MHz in a single mode fiber with about 11 GHz frequency shift, microwave signal with very low phase noise can be generated. Thus, the optical comb driven by this optoelectronic oscillator is highly coherent. In our experiment, a 7-line optical comb with 2.7 dB variation of 10.89 GHz spacing is obtained with a phase noise of -93 dBc/Hz at 10 kHz offset.

Enhancing performance of fiber-based FWM in coherent communication system by SBS-induced nonlinear phase

We demonstrate the use of SBS to re-establish phase-matched condition for four-wave mixing in a coherent communication system. A 6.6 dB Q-factor improvement along with 11.5 dB OSNR enhancement is obtained in the output idler.

Mitigation of Nonlinear Impairment by Coherently Superimposing CAP Sideband Signals

We propose to utilize the Hermitian symmetry of carrier-less amplitude phase (CAP) signals to mitigate distortion caused by fiber nonlinearity. The upper and lower frequency sidebands of CAP signals constitute phase-conjugated twin waves. Hence, coherent superposition of the two sidebands at the receiver can improve signal-to-noise ratio and compensate nonlinear impairment. We experimentally demonstrate that this scheme can improve the Q factor by ~1.6 dB after 80-km transmission. When the fiber length is extended to 240 km, the Q factor still exceeds the 7% hard decision forward error correction threshold by ~0.4 dB, showing potential application of the scheme for access and metro networks.

Binary Pattern Controlled Optical Pulse-Rate Multiplication Based on Fractional Temporal Self-Imaging Effect

We demonstrate electrically adjustable multiplication of 9.72 GHz pedestal-free picosecond pulses using fractional temporal self-imaging effect. Various multiplication factors of 2, 4 and 8 are achieved and up to ∼80 GHz pulse train is generated.