Optical code division multiplex system with multiphase mapping

Recently, optical code division multiplex (CDM) systems have been attracting great interest. Conventionally, on-off keying (OOK), pulse position modulation (PPM), and the multibit sequence in a sequence period (MS) have been applied to optical CDM systems. However, power efficiency is low in OOK, and a bandwidth efficient scheme is required in PPM and MS to achieve a high bit rate, making the design of optical devices difficult. In this paper, we propose an optical CDM system with multipulse mapping to achieve higher transmission rates than those of the conventional systems. In multipulse mapping, the user data are encoded into a combination of the pulse positions and the shifts of signature sequences. We theoretically analyze the bit error rate (BER) performance of the proposed system with multipulse mapping and show that the proposed system achieves better BER performance than the system with MS and the combined system with M-ary PPM and MS. We also show that the proposed system with multipulse mapping achieves higher bit rate than the other systems, when the required laser power for BER≤10 ^-9 is constant.