High gain parametric processes in quasi-phase-matching proton-exchange lithium niobate waveguides

Developments in nonlinear optical materials and solid-state lasers led to rapid progress in nonlinear optics in recent years. Among the many fields of nonlinear optics, chi(2) parametric processes are among the major tools for generating coherent radiation indispensable in optical communication, spectroscopy and medical applications.

Involving short pulses with high peak power, high gain parametric processes, including optical parametric amplification (OPA) and optical parametric generation (OPG), have been widely used for near- and mid-infrared light sources. Most such research so far has been demonstrated in bulk crystals. On the other hand, waveguides can enhance the beam intensity along the whole device and significantly increase the gain in parametric processes, and have been widely applied in processes such as second-harmonic generation. However a thorough study of the use of waveguides in high-gain parametric processes is absent. This dissertation addresses the challenges in such applications and demonstrates how waveguide structures and quasi-phase-matching (QPM) gratings can be tailored to improve the performance of high gain parametric processes.

We demonstrate high parametric gain for OPA in reverse-proton-exchange lithium niobate waveguides with periodically-poled QPM gratings. Picojoule OPG threshold with picosecond pump pulses near 780 nm is illustrated, which is over two orders of magnitude lower than that in bulk crystal under similar conditions. Furthermore we demonstrate control over the temporal properties of the output products from OPG with picosecond pump pulses near 780 nm. By synthesizing either the QPM gratings or the waveguide structures we demonstrate one order of magnitude smaller time-bandwidth products at designed wavelengths and obtain near transform-limited output from OPG. We also illustrate mode demultiplexing for OPA using asymmetric Y-junctions, in which the signal and idler in different waveguide modes are separated with a contrast of 27.5 dB. The high gain parametric processes in waveguides may therefore find practical application with the engineerable QPM gratings and waveguide structures.