Complementary bipolar spectral polarization coding over fiber-grating-based differential photodetectors

Abstract

This study proposes a spectral polarization coding scheme for the implementation of complementary bipolar optical correlation in a noncoherent optical code-division multiple-access network. The coder- decoders are implemented over differential photodetectors based on fi- ber Bragg gratings and polarization beamsplitters. Traditionally, comple- mentary unipolar spectral amplitude coding SAC schemes are used to transmit the specific codeword on data bit 1 and its complementary codeword on data bit 0. In the proposed scheme, the spectral amplitude is incorporated with polarization coding as the specific signature address code. A Walsh-Hadamard code is employed as the signature address to allocate to each specified wavelength to an individual vertical or horizon- tal state of polarization. The results indicate that multiple-access interfer- ence can theoretically be eliminated by correlation subtraction at the differential photodetectors. Neglecting the effects of shot noise and ther- mal noise, and considering only phase-induced intensity noise with a degree-of-polarization setting of P=0 for the ideal case, the bit error rate BER versus the number of simultaneous active users is improved by 43% in the proposed scheme over the complementary unipolar SAC scheme for a 10 9 error probability. Setting P=1 for the worst case, the BER performance of the proposed scheme matches that of the comple- mentary unipolar SAC scheme. © 2006 Society of Photo-Optical Instrumentation