Slot-mode-coupled optomechanical crystals

We present a design methodology and analysis of a cavity optomechanical system in which a localized GHz frequency mechanical mode of a nanobeam resonator is evanescently coupled to a high quality factor (Q>10^6) optical mode of a separate nanobeam optical cavity. Using separate nanobeams provides flexibility, enabling the independent design and optimization of the optics and mechanics of the system. In addition, the small gap (approx. 25 nm) between the two resonators gives rise to a slot mode effect that enables a large zero-point optomechanical coupling strength to be achieved, with g/2pi > 300 kHz in a Si3N4 system at 980 nm and g/2pi approx. 900 kHz in a Si system at 1550 nm. The fact that large coupling strengths to GHz mechanical oscillators can be achieved in SiN is important, as this material has a broad optical transparency window, which allows operation throughout the visible and near-infrared. As an application of this platform, we consider wide-band optical frequency conversion between 1300 nm and 980 nm, using two optical nanobeam cavities coupled on either side to the breathing mode of a mechanical nanobeam resonator

Applications of microstructured fibers : supercontinua and novel components

Microstructured fibers are a special class of pure-silica optical fibers. They consist of a silica core, surrounded by a periodic array of air-holes running along the entire length of the fiber. These air-holes permit guidance of light through total-internal reflection. Diameter and spacing of the air-holes determines the optical properties of the fiber, therefore allowing for tailoring of the fiber according to the intended application. This thesis contains novel results on supercontinuum generation in microstructured fibers. Several critical advances have been made in tailoring of the fiber properties in order to further reduce power requirements hindering miniaturization of supercontinuum sources. In particular, the influence of a second zero-dispersion wavelength of the fiber and the input polarization of highly-birefringent fibers have been studied. Furthermore, a novel two-pump scheme allows for efficient generation of broadband blue-light. The generated supercontinua are applied to characterization of absorption and transmission spectra of novel optical components. The high spectral power density of supercontinuum allows for observation of several new excited-state absorption lines of Erbium-doped fibers and characterization of optical components with strong variations in the transmission spectrum. The second part of the thesis deals with applications developed for microstructured fibers. A tapered microstructured fiber is designed for coupling between standard fibers and photonic-crystal waveguides. An elliptical-core microstructured fiber is proposed as an efficient adapter between standard fibers and highly asymmetric waveguides. In addition, a microstructured fiber based optically bistable fiber cavity is applied to all-optical switching. In particular, an optical flip-flop is numerically studied.reviewe