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Proceedings Paper

Improving bit error rate through multipath differential demodulation
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Paper Abstract

Differential phase shift keyed transmission (DPSK) is currently under serious consideration as a deployable datamodulation format for high-capacity optical communication systems due mainly to its 3 dB OSNR advantage over intensity modulation. However DPSK OSNR requirements are still 3 dB higher than its coherent counter part, PSK. Some strategies have been proposed to reduce this penalty through multichip soft detection but the improvement is limited to 0.3dB at BER 10-3. Better performance is expected from other soft-detection schemes using feedback control but the implementation is not straight forward. We present here an optical multipath error correction technique for differentially encoded modulation formats such as differential-phase-shift-keying (DPSK) and differential polarization shift keying (DPolSK) for fiber-based and free-space communication. This multipath error correction method combines optical and electronic logic gates. The scheme can easily be implemented using commercially available interferometers and high speed logic gates and does not require any data overhead therefore does not affect the effective bandwidth of the transmitted data. It is not merely compatible but also complementary to error correction codes commonly used in optical transmission systems such as forward-error-correction (FEC). The technique consists of separating the demodulation at the receiver in multiple paths. Each path consists of a Mach-Zehnder interferometer with an integer bit delay and a different delay is used in each path. Some basic logical operations follow and the three paths are compared using a simple majority vote algorithm. Receiver sensitivity is improved by 0.35 dB in simulations and 1.5 dB experimentally at BER of 10-3.

Paper Details

Date Published: 13 February 2007
PDF: 7 pages
Proc. SPIE 6457, Free-Space Laser Communication Technologies XIX and Atmospheric Propagation of Electromagnetic Waves, 64570F (13 February 2007); doi: 10.1117/12.701671
Show Author Affiliations
Yannick Keith Lize, ITF Labs. (Canada)
Univ. of Southern California (United States)
École Polytechnique de Montréal (Canada)
Louis Christen, Univ. of Southern California (United States)
Scott Nuccio, Univ. of Southern California (United States)
Alan E. Willner, Univ. of Southern California (United States)
Raman Kashyap, École Polytechnique de Montréal (Canada)

Published in SPIE Proceedings Vol. 6457:
Free-Space Laser Communication Technologies XIX and Atmospheric Propagation of Electromagnetic Waves
Steve Mecherle; Olga Korotkova, Editor(s)

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