All-Optical Wavelength-Shift-Free NRZ-DPSK to RZ-DPSK Format Conversion with Pulsewidth Tunability by an SOA-Based Switch

Gazi Mohammad SHARIF  Quang NGUYEN-THE  Motoharu MATSUURA  Naoto KISHI  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E97-C   No.7   pp.755-761
Publication Date: 2014/07/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E97.C.755
Type of Manuscript: Special Section PAPER (Special Section on Opto-electronics and Communications for Future Optical Network)
Category: 
Keyword: 
Differential phase shift keying (DPSK),  format conversion,  wavelength-shift-free,  pulsewidth tunable operation,  cross-phase modulation (XPM),  cross-gain modulation (XGM),  

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Summary: 
We demonstrate an all-optical non-return-to-zero differential phase shift keying (NRZ-DPSK) to return-to-zero differential phase shift keying (RZ-DPSK) format conversion with wavelength-shift-free and pulsewidth tunable operations by using a semiconductor optical amplifier (SOA)-based switch. An NRZ-DPSK signal is injected into the SOA-based switch with an RZ clock, and is converted to RZ-DPSK signal owing to the nonlinear effects inside the SOA. In this scheme, the wavelength of the converted RZ-DPSK signal is maintained as the original wavelength of the input NRZ-DPSK signal during the format conversion. Moreover, the pulsewidth of the converted signal is tunable in a wider operating range from 30 to 60 ps. The format conversion with pulsewidth tunability is based on cross-phase modulation (XPM) and cross-gain modulation (XGM) effects in the SOA. The clear eye diagrams, optical spectra and the bit-error-rate (BER) characteristics show high conversion performance with the wide pulsewidth tuning range. For all cases of the converted RZ-DPSK signal with different pulsewidths, the receiver sensitivities at a BER of 10-9 for the converted RZ-DPSK signal were 0.7 to 1.5 dB higher than the receiver sensitivity of the input NRZ-DPSK signal.