<title>Optical fiber PPM employing direct detection optically preamplified receivers</title>

Abstract

n-ary pulse position modulation (PPM) has been shown to be an effective modulation format for optical fiber communications in that it can be used to exchange excess fiber bandwidth for receiver sensitivity. The combination of this modulation technique with optical preamplification should lead to further improvements in receiver sensitivity. Here we present a theoretical analysis for such a combination and demonstrate that the incorporation of optical preamplification leads to a sensitivity improvement of 12.5 dB. The sensitivity of an equivalent PCM system was calculated to be 110 photons/bit compared to 33 photons/bit for a PPM system employing moderate operating parameters. This represents an improvement of 5 dB and furthermore demonstrates that an optically preamplified PPM system can offer receiver sensitivities beyond the fundamental limit of an optically preamplified PCM system.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.