| Efficient nonlinear optical devices are designed and demonstrated in "photonic molecule''-like coupled-cavity resonator systems on a semiconductor chip. A coupled-cavity resonator may be designed to support distributed supermodes, and to allow independent control of the resonant frequency and linewidth of each supermode. Such control allows reduction of dispersion without compromising effective nonlinearity in the resonator, as well as the design of anisotropic output coupling or radiation that allows optimized nonlinear functions. Therefore this resonator manifests itself as a favorable platform for building nonlinear devices including optical parametric wavelength converters and oscillators based on four-wave mixing that call for different couplings to the signal, pump and idler modes. A physical model based on coupled-mode theory describes all relevant linear and nonlinear processes in triply-resonant microcavities, and a generalization of the usual nonlinear figure of merit is proposed to evaluate the effects of distributed supermodes on nonlinear conversion efficiency in such devices. Experimental work is presented that demonstrates coupled cavity devices for wavelength conversion in crystalline silicon, where two-photon absorption sets conversion efficiency limitations. In addition, an investigation of deposition conditions of hydrogenated amorphous silicon is described where amorphous silicon allows for a higher nonlinear figure of merit than crystalline silicon, promising increased performance in such devices. More generally, mode interference and coupling in coupled-cavity resonators, as a unique degree of freedom in integrated optics, is explored through designs of linear devices including efficient optical filters, wavelength converters, and modulators. |
