Coherent ultrashort light pulse code-division multiple access communication systems

Abstract

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.

Demonstration of a four-channel WDM/OCDMA system using 255-chip 320-Gchip/s quarternary phase coding gratings

“…The wavelength spacing of 4 nm used in this experiment was chosen to ensure that the system suffered no significant WDM crosstalk. It is worth noting that although the current experimental system has a relatively low spectral efficiency, the use of such long code sequences should support a far larger number of users per wavelength channel than demonstrated herein, (theoretically of the order of several tens of users when used in conjunction with nonlinear thresholding techniques [5]). It has also been shown that the use of nonlinear optical filtering techniques permits denser wavelength spacings in WDM/OCDMA systems, indeed spectral efficiencies as high as 1.6 Bit/s/Hz have recently been experimentally demonstrated [6].…”

Polymeric Optical Code-Division Multiple-Access (CDMA) Encoder and Decoder Modules

“…The received data streams are split through a 1 × M splitter and finally decoded by the predefined code sequences. Optical CDMA as an alternative to other optical multiplexing schemes such as wave-length division multiplexing (WDM) and TDM, not only inherits the advantages of microwave CDMA such as efficient bandwidth usage, robust and secure communication over open channels, but also has many additional attractive features including higher granularity and scalability within optical networks, optical transparency to data format and rate, improved cross-talk performance and more flexible asynchronous access [3][4][5][6][7][8]. In addition, optical CDMA scheme avoids the optical-to-electrical and electrical-to-optical conversion processes and eliminates the bandwidth constrains set by conventional electronics technologies (<10 GHz).…”

Code Generator for Optical ZCZ Sequence with Zero-Correlation Zone 2^z

“…The optical direct sequence spread spectrum (DS-SS) system can be expected to enable high-speed communication using a wide band [1][2][3]. Multiple access interference (MAI) cancellation methods with the optical orthogonal code (OOC) or modified prime sequence code (MPSC) have been proposed in the optical code division multiple access (CDMA) system [4,5].…”