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We analyze a new technique for encoding and decoding of coherent ultrashort light pulses. In particular, we discuss the temporal and statistical behavior of pseudonoise bursts generated by spectral phase coding of ultrashort optical pulses. Our analysis is motivated by recent experiments that demonstrate high resolution spectral phase coding of picosecond and femtosecond pulses and suggest the possibility of ultrahigh speed code-division multiple access (CDMA) communications using this technique. We trace the evolution of coherent ultrashort pulses into low intensity pseudonoise bursts as a function of the degree of phase coding. For random coding we find that the encoded pulse obeys Gaussian statistics and that the intensity probability distribution function is a negative exponential. These results are utilized to analyze the performance of a proposed CDMA optical communications system based upon encoding and decoding of ultrashort light pulses. We derive the bit error rate (BER) as a function of data rate, number of users, and receiver threshold; and we discuss the performance characteristics for a variety of system parameters. We find that performance improves dramatically with increasing code length. Lltrashort light pulse CDMA could provide tens to hundreds of users with asynchronously multiplexed, random access to a common optical channel.

Optical signal propagation through underwater channels is affected by three main degrading phenomena, namely absorption, scattering, and fading. In this paper, we experimentally study the statistical distribution of intensity fluctuations in underwater wireless optical channels with random temperature and salinity variations as well as the presence of air bubbles. In particular, we define different scenarios to produce random fluctuations on the water refractive index across the propagation path, and then examine the accuracy of various statistical distributions in terms of their goodness of fit to the experimental data. We also obtain the channel coherence time to address the average period of fading temporal variations. The scenarios under consideration cover a wide range of scintillation index from weak to strong turbulence. Moreover, the effects of beamcollimator at the transmitter side and aperture averaging lens at the receiver side are experimentally investigated. We show that the use of a transmitter beam-collimator and/or a receiver aperture averaging lens suits single-lobe distributions such that the generalized Gamma and exponentiated Weibull distributions can excellently match the histograms of the acquired data. Our experimental results further reveal that the channel coherence time is on the order of 10 −3 seconds and larger which implies to the slow fading turbulent channels.