All -optical network access and demultiplexing using nonlinear optical loop mirrors with novel fibers

High-speed network access through all-optical time-division-multiplexed add/drop multiplexers can help to increase single channel speeds and network flexibility. This dissertation discusses a data packet add/drop multiplexer comprised of all-optical fiber devices, and in particular, the nonlinear optical loop mirror as a demultiplexer. Using short 100 Gb/s words, both the add and drop functions controlled by an all-optical header processor are demonstrated by looping the add/drop multiplexer on itself to form a simple sequential network. The reading of the payload bits is performed by an all-optical demultiplexer.;The nonlinear optical loop mirror (NOLM) is an attractive candidate for all-optical demultiplexing of high-rate data streams because the nonlinearity of optical fiber responds much faster than the speed of electronics. Two-wavelength (2lambda) NOLMs have an inherent sensitivity to the input polarization because the nonlinear phase shift coefficients for the parallel and orthogonal polarizations of the fiber are different. This becomes an obstacle to its applications in a real-world system where the signal polarization varies with environmental conditions. Polarization insensitivity, achievable through the use of specialty fibers, removes a fundamental limitation to the implementation of 2lambda NOLMs in all-optical networks.;Two different methods of creating circularly-polarized fiber for a polarization insensitive NOLM are implemented. In the first method, the polarization sensitivity is reduced from 5 dB to as low as 0.5 dB by twisting dispersion-shifted fiber at 8 turns/m. By demultiplexing from short 100 Gb/s words, an improved Q-parameter is demonstrated for the twisted-fiber demultiplexer using a synchronized laser with a phase-locked-loop synchronization scheme as the local control pulse source. In the second method, a polarization-insensitive (90% transmission) NOLM using high-nonlinearity, circularly-polarized, spun fiber is demonstrated. The residual polarization dependence leads to approximately 1.5 dB power penalty difference in the bit-error-rate measurements for the input signals with polarizations corresponding to the maximum- and minimum-outputs. The fiber is spun at 16 turns/m during the drawing process, and thus, is intrinsically circularly polarized rather than externally biased as with twisted fiber.;Experimentally obtained data is confirmed through simulations and and several design trade-offs are determined, including the sources of power penalty. Simulations of the spun fiber NOLM show the expected polarization sensitivity is comparable to the experimentally obtained values and confirm that the spun fiber is close to a perfectly circularly-polarized fiber. The polarization sensitivity versus wavelength separation is also simulated, with the dispersive walk-off effect taken into account. Again, the results are comparable to experimental results. And lastly, calculations show that the power penalty is due to a combination of NOLM induced amplitude fluctuations and control pulse cross-talk.