Given K simultaneously active users, an Optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always C Gt K at any given time for any truly asynchronous OCDMA system that employs quasi-orthogonal codes, there is always a set of unused codes. We here propose to exploit these unused codes to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log2(M)-tuple of bits so that each user effectively uses a multi-dimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system and find in closed form an upper bound on the average probability of error. Moreover, we report for the first time that, under lightly loaded, non interference-limited conditions, the multi-dimensional OCDMA scheme here proposed allows us to obtain both higher spectral efficiency and lower bit- error probability (BEP) than a conventional OCDMA system, which employs one code only per user. The analysis here presented allow us to formulate a useful system design criterion that yields truly asynchronous OCDMA systems with very high spectral efficiency.

We propose a novel optical networking concept enabling the routing of groups of spectrally phase encoded (SPE) optical code division multiple access (OCDMA) signals. This code grouping is based on particular properties of the Hadamard sequences, i.e. the existence of a multiplicative basis based on Walsh sequences. We describe here how this code grouping concept permits groups of SPE codes to be passively "labeled" and routed as groups on the basis of those labels and provide simulation results demonstrating the process. The ability to deal with groups of codes has important implications for routing and for the overall signal obscurity provided by OCDMA.

Given K users simultaneously active, an optical CDMA (OCDMA) receiver needs to discriminate among K codes. Since the number of available codes C is always CGtK at any given time for an asynchronous OCDMA system employing quasi-orthogonal codes, there is always a set of unused codes and these codes can be exploited to increase the spectral efficiency of the system. This can be accomplished by exclusively assigning to each user a set of M codes which represent a log2(M)-tuple of bits so that each user effectively uses a multidimensional modulation (multiple information bits per code are conveyed). In this paper, we analyze the performance of such a system, and find that an upper bound on the probability of error can be expressed in terms of the performances of the conventional case where one code only per user is employed. Moreover, we also find that, under certain conditions, the multidimensional modulation here proposed allows us to obtain higher spectral efficiency, higher power efficiency, and lower bit-error rate (BER) than conventional OCDMA, which employs one code per user

We propose and experimentally validate a novel method for transmitting several OCDMA channels in the unused bandwidth of a single WDM channel, thus allowing the OCDMA and SONET signals to share the same WDM channel. The theoretical justification of this new modulation scheme is based on a powerful property of spectrally phase-encoded OCDMA signals which is reported and proved for the first time: the operation of spectral phase encoding allows us to convey broadband signals over a disjoint (non-contiguous) frequency support. Remarkably, this property' does not impair signal orthogonality' so that it can be exploited both in synchronous and asynchronous OCDMA.

We present initial results on a WDM compatible spectrally phase encoded optical CDMA (OCDMA) system that uses 16 phase-locked laser lines within an 80-GHz tunable window and an ultrahigh frequency resolution encoder/decoder. The described system differs from conventional OCDMA systems by independently phase encoding individual spectral line of a mode locked laser (MLL). We report here novel properties of phase codes and we also demonstrate compatibility of the proposed OCDMA system with conventional WDM networking by simultaneous transmission of two 2.5 Gb/s OCDMA users in one DWDM window along with six DWDM channels in other DWDM windows through a transparent reconfigurable network having 25 km node spacing.