Rate-Flexible Optical CDMA Networks Based on Coherent Modulation Formats

Coherent techniques in optical access networks might become a major paradigm shift since the introduction of fiber-optic communications due to recent advances in coherent optical technology. In this paper, we propose, design, and assess the performance of coherent access networks based on optical code-division multiple-access (OCDMA) considering three distinct coherent modulation formats, namely, binary phase-shift keying, quadrature phase-shift keying, and 16-quadrature amplitude modulation. We design a flexible network architecture based on these coherent modulation formats to provide either single rate transmissions or multiple data rate transmissions. In this way, the network supports rate-flexible services with all user classes transmitting at the same rate or classes of users transmitting at different data rates. We derive new closed-form bit error rate expressions to assess the performance of the rate-flexible coherent OCDMA network. Results shown that rate-flexible data traffic from different user classes can coexist almost transparently in terms of network performance. The rate-flexible OCDMA network might be a prospective alternative for implementing coherent access networks with modulation formats as a service according to different traffic demand requirements while supporting high capacity, security, and numbers of users.