Thesis (Ph. D.)--University of Rochester. The Institute of Optics, 2019.
With the rapid development of integrated photonics, multiple material
platforms, including silicon, silica, diamond, silicon nitride, aluminum
nitride, and gallium arsenide, have been widely studied for photonic
applications on a chip scale. Particularly, integrated platforms have attracted
considerable attention in nonlinear optics, due to boosted nonlinear optical
interactions induced by the tight optical confinement.
Over the past few decades, lithium niobate (LiNbO3 or LN), with its
intriguing material properties, has been extensively studied for nonlinear
optics. Recent advances in wafer bonding and etching technology have
enabled the fabrication of high-quality LN nanophotonic devices, which
have the potential for nonlinear optics with high efficiencies and novel
functionalities. This thesis is devoted to the development of nonlinear optical
applications based on the LN integrated photonic platform. This thesis starts with a discussion of the thermo-optic property of LN,
which is essential for realizing and tuning phase matching in nonlinear
optical processes. The large thermo-optic birefringence of LN enables the
demonstration of a self-referenced temperature sensor based on a microdisk
resonator, exhibiting both a high sensitivity and a high resolution. The large
thermo-optic birefringence is further exploited to demonstrate thermally tunable second-harmonic generation in an LN nanophotonic waveguide,
which simultaneously achieves a large tuning slope and a high conversion
efficiency. In order to further increase the efficiency, semi-nonlinear
nanophotonic waveguides are proposed and demonstrated as a universal
design principle, which offers a large mode overlap by breaking the spatial
symmetry of the optical nonlinearity, resulting in extremely efficient optical
parametric generation.
Optical microresonators are widely employed to enhance nonlinear
optical interactions. This thesis continues on to present applications of
LN microresonators in nonlinear optics. First, cavity-enhanced secondharmonic
generation and difference-frequency generation are demonstrated
in an LN microring resonator with modal phase matching. Then, cyclic
phase matching, due to the material anisotropy, is utilized in an X-cut
LN microdisk to realize spontaneous parametric down-conversion with an
extremely large bandwidth. Finally, Kerr frequency comb generation is
demonstrated in an LN microring resonator with an optical quality factor
of 2.5 million.
