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Proceedings Paper

Multi-bit delay differential-phase-shift-keyed optical demodulation
Author(s): Yannick Keith Lize; Louis Christen; Robert Gomma; Scott Nuccio; Narander Jayachandran; Alan E. Willner; Raman Kashyap
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Paper Abstract

Differential-phase-shift-keyed optical modulation (DPSK) has generated a lot of attention in fiber optic transmission over the past few years mainly because of its 3dB optical signal-to-noise ratio (OSNR) improvement over standard intensity modulated transmission [1] offering high receiver sensitivity, high tolerance to major nonlinear effects in high-speed transmissions [2], and high tolerance to coherent crosstalk [3]. To demodulate DPSK, a delay-line interferometer is usually employed to provide a one-bit delay such that a bit interferes on the following bit to provide constructive or destructive interference depending on the phase difference [4]. However, with the use of logical pre-coding a multi-bit delay can be used instead of a single-bit delay. It was recently reported that a two- or four-bit delay might be advantageous in allowing polarization interleaving between bits to lessen the detrimental effects of fiber nonlinearities in fiber optic transmission [5-7]. Multi-bit delay was also proposed as a method to correct errors from amplified spontaneous emission (ASE) noise-limited transmission [8-9]. We present here simulation and experimental results on the penalty of using multi-bit delay demodulation for DPSK detection. We present Q-factor degradation as a function of delay and find that the Q penalty scales with 0.5 x delay for integer delays. We also present results of the detrimental effect of spectral filtering from the reduced free-spectral-range (FSR) in a multi-bit delay interferometer. We also find that it exhibits reduced dispersion tolerance. If not taken into account, these important limitations and more stringent tolerance on the frequency offset may reduce the effectiveness of multi-bit delay methods and prohibit practical implementation.

Paper Details

Date Published: 8 September 2006
PDF: 8 pages
Proc. SPIE 6343, Photonics North 2006, 63433V (8 September 2006); doi: 10.1117/12.708241
Show Author Affiliations
Yannick Keith Lize, Univ. of Southern California (United States)
Ecole Polytechnique de Montreal (Canada)
Louis Christen, Univ. of Southern California (United States)
Robert Gomma, Ecole Polytechnique de Montreal (Canada)
Scott Nuccio, Univ. of Southern California (United States)
Narander Jayachandran, Univ. of Southern California (United States)
Alan E. Willner, Univ. of Southern California (United States)
Ecole Polytechnique de Montreal (Canada)
Raman Kashyap, Ecole Polytechnique de Montreal (Canada)

Published in SPIE Proceedings Vol. 6343:
Photonics North 2006
Pierre Mathieu, Editor(s)

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