Integrated Optical-Frequency Mixers

Optical frequency (OF) mixers based on periodically poled lithium niobate (PPLN) waveguides are among the most efficient nonlinear optical devices available today. An attractive technology for communications applications, OF mixers have been used to demonstrate many important all-optical signal-processing functions including wavelength conversion, dispersion compensation by spectral inversion, and 160 Gbit/s optical time-division multiplexing.

Integrated-optic structures extend the functionality of OF mixers even further. This thesis develops a useful new set of components compatible with PPLN waveguides that includes couplers, small radius bends, mode sorters, and asymmetric quasi-phasematching (QPM) gratings. These components are used to demonstrate two novel solutions to a recurring problem for nonlinear optical devices: how to distinguish and spatially separate the interacting waves. Integrated OF mixers can separate the output waves from the residual input waves either through a waveguide interferometer or by multiplexing modes. This separation enables bi-directional wavelength conversion, or spectral inversion without offset.

The advanced fabrication techniques developed for integrated OF mixers also enable a new type of bulk nonlinear optical device based on fine transverse patterning of QPM gratings. Control over the spatial amplitude and phase of the nonlinear output leads to a variety of familiar effects from physical optics. These include diffraction from grating "slits," beam steering, and focusing of the nonlinear output through a QPM lens.