Unipolar-Encoding/Bipolar-Decoding for Optical CDMA Using an Electro-optical Phase Modulator and Fiber Bragg Grating Arrays

摘要

In this paper, we propose a novel approach to implementing unipolar-bipolar phase-time encoding/decoding for optical code division multiple access (CDMA) networks. In the proposed approach, an electrooptic phase modulator and two fiber Bragg grating (FBG) arrays are employed to perform En/De coding. At the transmitter, a low-bit-rate data sequence modulates the optical phase and is then mapped to a high-bit-rate optical sequence via the encoder FBG array in a unipolar way. At the receiver, an identical FBG array that functions as a matched filter is used. Bipolar decoding is achieved by locating the optical carriers on either the positive or the negative slopes of the reflection responses of the decoder FBG array. The proposed encoding/decoding scheme is equivalent to a sequence inversion keyed direct sequence CDMA, which can provide an improved performance compared with the conventional incoherent scheme using optical orthogonal codes. In addition, compared with bipolar decoder applying balanced detection, this approach has a simpler architecture. A proof-of-principle experiment is demonstrated.