Design of efficient all-optical code-division multiplexing systems supporting multiple-bit-rate and equal-bit-rate transmissions

We present the design of efficient all-optical code-division multiplexing ( AOCDM) systems that can transmit multiple-bit-rate (MBR) data signals over a common optical fiber. This is achieved when the proposed strict optical o rthogonal code (OOC) of autocorrelation and cross-correlation constraints o f 1 are used but without performance degradation compared with the use of c onventional OOC. We describe the design of various strict OOC's by employin g the useful concept of slot distances, and methods of code construction ar e also presented. Moreover, we give the principle of MBR data transmissions in an AOCDM system. It is shown that AOCDM systems using the proposed OOC can effectively transmit multiuser MBR and equal-bit-rate (EBR) data with n o increase of system complexity. In principle, optimal strict OOC's need th e same or a slightly larger system bandwidth compared with optimal conventi onal OOC's for EBR operation, whereas the former can require a smaller syst em bandwidth and have a better system performance than the latter for MBR t ransmissions. A new, to our knowledge, family of strict OOC's is also intro duced, whose code words can have nonconstant weights to support multiuser c ommunications with different transmission quality. Furthermore, we design l ow-cost AOCDM transmitters that are based on an efficient gain-switching sc heme that does not require an electro-optic intensity modulator to ON-OFF m odulate an optical clock pulse stream at each transmitter. The basic operat ion principle is also experimentally demonstrated. (C) 2000 Optical Society of America. OCIS codes: 060.2330, 060.4230, 060.4250, 060.4510, 060.2360, 140.3520.