Characterization and nonlinear cleanup of noise in optical communication systems

Abstract

In the first half of my thesis, I will present experimentally measured photon statistics of RZ/NRZ signals in an optically pre-amplified direct-detection receiver, and show that the results are in good agreement with quantum photodetection theory. Specifically, the ZEROs are described by a degenerate Bose-Einstein distribution, while the ONEs are described by a non-central-negative-binomial distribution. We will compare the exact quantum mechanical approach with the semiclassical Gaussian approximation in terms of evaluating the bit-error rate and the optimal decision threshold. I will then describe a nonlinear pulse filter that transmits incident pulses while rejecting cw background as well as ASE noise. The filter is realized by constructing a nonlinear optical Sagnac loop that is imbalanced by asymmetric dispersion. In the first demonstration at 30 Mb/s, a relative extinction of 22 dB (with respect to the pulse) is measured for the cw background. We also demonstrate cleanup of in-band ASE noise at 10 Gb/s. Other researchers have adopted my techniques and buHt similar pulse filters to clean up compressed pulses so as to build a pedestal-free, 5-ps 16-wavelength WDM source at 10 Gb/s and a 210-fs single-channel TDM source at 640 Gb/s.