All -optical waveform recognition and its applications in ultrashort pulse optical CDMA systems
The progress of high-speed optical communication systems will soon require signal processing capabilities beyond the limit of the electronic devices within the system. An inevitable solution to this problem is the development of all-optical signal processing technologies. ^ This thesis presents the detailed studies of two nonlinear optical signal processing devices for a proposed ultrashort pulse optical code-division multi-access (CDMA) system. In such a system, recognizing different short optical waveforms is required to de-multiplex different channels and is also a research challenge to be solved. We first studied a two-photon absorption waveguide nonlinear photodetector and demonstrated the pulseshape dependence of the photocurrents using various sub-picosecond optical pulses. This scheme has the advantages in terms of compactness and easiness to use. We later developed an optical spectral correlation scheme based on second harmonic generation in long nonlinear crystals. By using periodically-poled lithium niobate and waveguide structures, we realized ∼30 dB contrast ratio and sub-pJ operating power which are significant improvements over other prior schemes studied. We also first proposed a modified coding scheme for the CDMA system that would be compatible with the novel detection schemes we studied. ^
Major Professor: Andrew M. Weiner, Purdue University.
Engineering, Electronics and Electrical|Physics, Optics