Multiple access interference cancellation in optical code division multiple access

Optical code division multiple access (OCDMA) can achieve good spectral efficiency, a high degree of security, and soft degradation in many network applications. In the first part of our work, we show that robust performance in the presence of key impairments is achieved by careful selection of encoding sequences according to correlation properties and spread-time pulse shapes. A new, coherent receiver retrieves transmitted information coherently without phase locking or fast nonlinear detectors, while minimizing multiple access interference and canceling beat noise. A key design improvement prevents link outage caused by random states of polarization without requiring polarization management. In the second part of our work, a novel coherent OCDMA scheme is proposed that uses spectral line pairing to generate signals suitable for heterodyne decoding. Both signal and local reference are transmitted via a single optical fiber and a simple balanced receiver performs sourceless heterodyne detection, canceling speckle noise and multiple access interference (MAI). Effects of fiber dispersion on system performance are studied as well. Both second and third order dispersion management is achieved by using a spectral phase encoder to adjust phase shifts of spectral components at the optical network unit (ONU). In the third part of our work, we present the first experimental demonstration of a practical, fully coherent, optical OCDMA scheme that can fully suppress multiple access interference (MAI) and speckle noise without phase locking or thresholding and gating. The scheme is sourced from an optical comb generator and uses spectral phase encoding (SPE) and a heterodyne receiver with balanced detection.