Parametric Interactions of Short Optical Pulses in Quasi-Phase-Matched Nonlinear Devices


Broad applicability of ultrashort pulses has been demonstrated across many fields in science and technology. The short pulse duration enables the fastest known measurement techniques for chemical reactions and biological processes, as well as the delivery of communications data at ever increasing bit rates. Ultrashort pulses possess large bandwidths, useful in optical frequency metrology and optical coherence tomography. The high peak power available in ultrashort pulses enables athermal machining of metals and dielectrics, and has opened new doors to the study of physics in the presence of the largest-amplitude electric fields ever generated in a laboratory.

While the properties of short duration, broad bandwidth, and high peak power, make ultrashort pulses attractive for many applications, they pose unique challenges in the context of frequency conversion and amplification. This thesis addresses how quasi-phase-matching (QPM) technology is well suited to address these challenges through the engineering of devices by patterning nonlinear materials. QPM devices are shown to enable tunable control of the phase response of second-harmonic generation (SHG), engineering of broad-bandwidth SHG using spectral angular dispersion, and tailoring of spatial solitons that exist through nonlinear phase shifts present in cascaded frequency conversion.

In this dissertation, we show the tunable control of dispersion through lateral and longitudinal patterning of nonlinear materials in the 60-fold compression of pulses during SHG. We discuss both the conditioning of ultrashort pulses and the engineering of nonlinear devices for broadband frequency conversion with high conversion efficiency and low peak intensity using spectral angular dispersion in second-harmonic generation; including the optimization of conversion efficiency enabled by QPM technology. We show the tailoring of multicolor spatial solitons through the use of chirped-period QPM gratings for enhanced conversion to signal and idler in an optical parmetric amplifier. Additionally, we discuss the fundamental limitations to spatial soliton generation and propagation caused by the amplification of parametric noise, which is shown experimentally to affect both the spatial confinement and frequency content of multicolor solitons. Experiments are conducted using periodically-poled lithium niobate (PPLN), but all are generally applicable to any QPM material system.


July, 2005