The impact of chromatic dispersion on the complex electric field of an optical phase-coded duobinary signal is investigated through numerical simulation. The evolution of the optical field is most clearly represented by the optical constellation diagram at varying transmission distances. Dispersion causes distortion and rotation of the optical constellation, leading to eye closure of the received signal. When direct detection is employed rapid eye closure starts after approximately 213km. In this letter, the use of coherent detection is suggested to extend this transmission distance. A decision directed phase locked loop is suggested to establish the feasibility of use of coherent detection for this modulation format. Employing coherent detection increases this dispersion limit by 70km.
We present two novel modulation formats, namely, optical differential 8-level phase-shift keying (OD8PSK) and differential polarization-phase-shift keying (DPolPSK) for high-spectral efficiency optical transmission. Both formats are constant-amplitude, tolerant to fiber nonlinearities, especially cross-phase modulation (XPM). Both formats use direct detection without the use of either active polarization control or phase locking at the receiver. DPolPSK also addresses practical use of polarization.
All-optical regeneration of differential phase-shift keyed signals based on phase-sensitive amplification in a nonlinear fiber Sagnac interferometer is described. Nearly ideal phase regeneration can be achieved in the undepleted pump regime, with output differential phase noise limited only by fast fluctuations of the pump phase relative to the DPSK signal. Operating in the depleted pump regime offers the possibility of simultaneously regenerating both phase and amplitude information of DPSK signals while providing low noise, phase-sensitive gain.
A scheme for wavelength and polarization insensitive all-optical clock extraction and enhancement of nonreturn-to-zero (NRZ) data is proposed and demonstrated. At 10 Gbit/s, more than 7-dB clock enhancement and 19-dB clock-to-data suppression ratio (CDSR) enhancement have been realized using a semiconductor optical amplifier (SOA) and a reflective fiber Bragg grating (FBG) over a 30-nm input wavelength range.
The two-section gain-coupled DFB laser can be designed to exhibit self pulsing. The self-pulsing dynamics have been exploited to demonstrate a variety of application in high-speed optical communication systems, including wavelength and polarization-independent all-optical clock recovery up to 100 Gb/s and conversion from the NRZ or RZ format to CSRZ format.
A semiconductor laser based microwave/millimeter wave fiber-optic link is proposed and demonstrated. The microwave/millimeter-wave frequency response is realized using optical injection locking. This narrow-band high-frequency link can operate in the frequency-modulated (FM), phase-modulated (PM) and QAM formats.
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