Fiber characterization and polarization-insensitive NOLM for high-speed communication systems.
Andersen, John Kai
1999
Abstract
In the first part of the thesis we introduce a new method to characterize picosecond optical pulses that employs nonlinear propagation through optical fibers as a diagnostic tool. This technique takes advantage of the well-known nonlinear response of optical fibers and well-developed models for nonlinear pulse propagation to extract information about pulse characteristics such as chirp and background content. The major advantage of this method is it uses only standard diagnostic tools such as autocorrelation and optical power measurements. We demonstrate this novel method by experimentally determining pulse properties of two 2 ps pulse sources with peak powers of ≈ 12.5 W, using fiber lengths of 204 m and 404 m of Corning SMF-28 fiber. The method's fidelity is confirmed by comparing it with a direct method utilizing a sub-ps optical sampling system and finding the difference to be less than 15%. For additional confirmation we compare the predicted propagation behavior based on the measured pulse parameters to the experimental propagation behavior over longer lengths of fiber (25 km). We also experimentally demonstrate a new method to determine the optical nonlinearity of single mode optical fiber. The technique uses the nonlinear aspects of soliton pulse propagation to extract information about the fiber characteristics. Fiber nonlinearity can degrade the performance of communication systems by, for example, causing crosstalk and signal distortions. Measuring the fiber nonlinearity would greatly aid system designers in building and upgrading communication systems. The method is utilized to determine values for n<sub>2</sub>/ Aeff , where n<sub>2</sub> is the nonlinearity of the glass and Aeff is effective area of the core, on various lengths of Corning SMF-28 fiber and Corning SMF-DS fiber. The nonlinear optical loop mirror (NOLM) is an attractive candidate for all-optical demultiplexing of 40+ Gb/s data streams. However, in a typical NOLM there is a 5 dB sensitivity to the signal polarization state. This represents a significant obstacle to its use in a real system where the signal polarization varies with environmental conditions. The use of twisted fiber in the NOLM equalizes the nonlinear coefficients and reduces the polarization sensitivity of the switch to less than 0.5 dB. Also, acting as a demultiplexer the NOLM must be able to handle variations in arrival time between the incoming signal and the local clock. This acceptance window must be tailored in accordance with the system requirements for signal jitter tolerance. A method to calculate the expected performance of an arbitrary timing window is developed and applied to experimentally measured timing windows.Subjects
Characterization Diagnostics Fiber High-speed Communication Nolm Nonlinear Optical Loop Mirror Polarization-insensitive Pulse Propagation Systems
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