An Innovative Receiver for Incoherent SAC-OCDMA Enabling SOA-Based Noise Cleaning: Experimental Validation

We propose a new low complexity receiver for spectral amplitude optical coded division multiple access (SAC OCDMA) that enables intensity noise reduction using semiconductor optical amplifiers (SOAs). Compared to the standard receiver requiring two optical filters at the receiver side, our receiver requires only one optical filter. While a 1.4-dB power penalty in incurred, network capacity is unchanged, i.e., BER floors due to intensity noise have the same level. The primary motivation for the low complexity receiver is not reduced component count, but rather modifying the receiver so that promising SOA noise mitigation techniques might be employed to increase system capacity. SOA noise cleaning suffers from a major limitation: filtering after the SOA can negate most of the signal enhancement, the so-called post SOA filtering issue. The only solution to date for the post-SOA filtering effect in SAC-OCDMA is prohibitively complex McCoy et al., J. Lightw. TechnoL, vol. 25, no. 1, pp. 394-401, Jan. 2007, i.e., requiring multiple SOAs per client. We demonstrate that our proposed receiver drastically limits the client side filtering, thus maintaining noise suppression and overcoming the post-SOA filtering effect. We compare BER at up to 10 Gb/s with and without noise cleaning. When a noise cleaning module is used, BER improvement of several orders-of-magnitude is observed when only a few users are active in the network. Examination of the noise properties, however, leads us to conclude that highly populated networks will have diminished improvement.