Generation, filtering, and application of subcarriers in optical communication systems

I investigate several novel aspects of subcarriers in optical communication systems, including generation, filtering, and applications such as synchronization, contention resolution, and tunable dispersion compensation.; Low-biased modulation is attractive but inefficient. I develop an optically-efficient RF modulator that uses a novel arrangement of two low-biased Mach-Zehnder modulators within a ring laser. By recirculating the unused output of the first modulator, I improve optical efficiency by over seven dB.; Laser sources for optical heterodyning must have high spectral purity and be tunable. Using a delayed self-heterodyne interferometer and narrow-linewidth fiber laser, I study the evolution of the interferometer output with increasing fiber delay. I demonstrate the importance of a long fiber delay and a Voigt fit to the output to determine the true fundamental linewidth. I also demonstrate a stable narrow-linewidth single-mode erbium-doped fiber ring laser with a 40-nm tuning range of 1522–1562 nm. I achieve wide tunability using a highly-stretchable FBG, representing a 3.5-fold increase in tuning range over prior art using FBGs.; Subcarrier filtering in the optical domain avoids electronic processing bottlenecks and costly optical-to-electrical-to-optical conversions. I present a novel all-fiber narrowband notch or bandpass filter based on pump-induced saturable gain or absorber gratings in a loop mirror. The loop-mirror filter has potential bandwidths from the sub-MHz to beyond the GHz regimes, and is optically tunable.; Fast and efficient routing, multiplexing, and contention resolution requires incoming bit streams to be synchronized before entering a network switching node. I demonstrate bit synchronization of two NRZ input signals to within 1/8 of a bit time using a subcarrier for determining the time delay between two baseband channels.; Contention resolution without optical buffering or deflection routing can reduce network traffic delays. I demonstrate an optical contention resolution technique that combines two identical-wavelength contending 2.5 Gb/s channels into the same output-port wavelength channel.; Dispersion can cause serious power fading in subcarrier-multiplexed transmission. I use a tunable nonlinearly-chirped FBG in a phase diversity configuration to achieve distance-independent microwave and millimeter-wave power fading compensation for DSB subcarrier-multiplexed systems.