Planar optics with wavelength-scale high contrast gratings

In recent years, the emergence of a new type of sub-wavelength dielectric
grating with a high refractive index contrast, typically referred to as high contrast grating, and its simple fabrication procedure have given rise to numerous applications in integrated photonics and optoelectronics. The on-going demand for miniaturised planar devices in the near-infrared spectral range and the compatibility with standard processing techniques motivated us to explore the intriguing resonance effects in high contrast gratings for the application as broadband mirrors, reflective lenses, and as part of static and tuneable Fabry-Pérot cavities.
We chose amorphous silicon as the high refractive index material. The characteristics of grating mirrors were analysed numerically and measured experimentally, confirming their suitability for use as focussing reflectors and cavity mirrors in a Fabry-Pérot interferometer. As a result, a new type of reflective diffractive lens incorporating multiple phase jumps was designed, fabricated, and experimentally tested, and showed improved performance in terms of numerical aperture compared to other devices in the literature. Furthermore, initial experiments by integrating arrays of such lenses with a microfluidic platform showed an application potential in the area of large-scale optical trapping. In an attempt to develop functional wavelength-selective filters utilising high contrast gratings and microelectromechanical systems, we investigated static cavities based on metals and gratings, which included simulation, development of the fabrication process, and optical characterisation. Following these proof-of-principle studies and the computational analysis of the mechanical behaviour of flexible membrane designs, the challenge in making tuneable devices was to fabricate a fully working tuneable filter and its characterisation.
Overall, this thesis contributes to the field of integrated and planar silicon photonics by addressing the design and the performance aspects of high contrast grating lenses with high numerical aperture as well as addressing key challenges in the fabrication of tuneable filters.