Scalability techniques in electronically processed CDMA for low cost and flexible optical access networks

Recently, the coding and decoding of code-division multiple-access (CDMA) signals using electronic transversal filters at a chip rate of 18 Gchips/s for use in passive optical access networks (PONs) was demonstrated. The system used 7-chip transversal filters giving a potential for 7 users, where each user had a data rate of 1.25 Gb/s. In this paper, we show two techniques to scale up the electronically processed CDMA (ECDMA) system, namely by increasing the number of chips in the code and doubling the capacity using I and Q modulation of two in-quadrature channels. For increasing the number of chips, we demonstrate an electronically processed Walsh Code with 16 chips at 18 Gchip/s. An auto-cross correlation ratio of 18.1 dB is achieved between two orthogonal codes after transmission over 10 km of SMF. In addition, I-Q modulation of two electronic CDMA channels using the same electronic transversal filters is demonstrated. Here, two in-quadrature channels with chip rates of 18 Gchip/s show the potential of current technology for future 40 Gb/s throughput ECDMA PONs.