8 September 2006 Multi-bit delay differential-phase-shift-keyed optical demodulation
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Proceedings Volume 6343, Photonics North 2006; 63433V (2006); doi: 10.1117/12.708241
Event: Photonics North 2006, 2006, Quebec City, Canada
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.
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Yannick Keith Lize, Louis Christen, Robert Gomma, Scott Nuccio, Narander Jayachandran, Alan E. Willner, Raman Kashyap, "Multi-bit delay differential-phase-shift-keyed optical demodulation", Proc. SPIE 6343, Photonics North 2006, 63433V (8 September 2006); doi: 10.1117/12.708241; https://doi.org/10.1117/12.708241
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KEYWORDS
Interferometers

Demodulation

Receivers

Tolerancing

Dispersion

Polarization

Modulation

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