Holographic multichannel RF-matched filtering and fiber-optic frequency comb generation.

摘要

Photorefractive holography has been used to perform correlation operations within a variety of optical pattern recognition systems. By demonstrating novel techniques for recording steady-state holograms of MHz-bandwidth time-varying waveforms, this thesis extends holographic pattern recognition to the RF domain for use in radar, target identification, and communications receivers. Angularly multiplexing reference waveform holograms within a single photorefractive crystal permits realization of a multichannel matched filter in an integrable two-dimensional geometry having performance capabilities equivalent to those of a bank of parallel analog filters. Such an optical system offers advantages in speed through parallel processing and in flexibility through the ability to program new reference waveform holograms.;Two RF holographic recording techniques are developed which circumvent the relatively slow response of photorefractive crystals. The first records a static replica of the RF waveform displayed on a spatial light modulator. The second repeatedly samples the actual RF waveform being recorded with synchronized picosecond optical pulses. In this manner, RF holographic recording is effectively reduced to the recording of a static image.;Optical frequency comb generators are useful for a number of applications in optical communications. A fiber-optic frequency comb generator expands a modulated lightwave into a comb of discrete, equispaced frequencies through four-wave mixing in an optical fiber. By means of a coupled-wave analysis, the sign and magnitude of the fiber dispersion are shown to control comb expansion by affecting the interference among different four-wave mixing interactions at particular comb frequencies. Positive dispersion pulls four-wave mixing interactions into phase and thus promotes comb expansion. Zero and negative dispersions suppress expansion by pulling the four-wave mixing interactions out of phase.;Dispersion mapping, with decreasing positive dispersion along the fiber, engineers fiber links for maximum comb bandwidths. A frequency comb spanning 1.1 THz is experimentally demonstrated by managing dispersion in a 35 km link of dispersion-shifted fiber.