Femtosecond laser printed microoptics in hydrogenated amorphous silicon

Conventional optics (e.g. lenses or mirrors) manipulates the phase via optical path difference by controlling thickness or refractive index of material. Recently, a promising type of optics emerged which exploits geometric phase shift, when a lightwave is transformed by parameter other than optical path difference, e.g. polarization. Here, wavefront is modified by introducing spatially varying anisotropy and is a result of Panchatraman-Berry phase [1]. Theoretically any phase pattern can be achieved solely by means of geometric phase with efficiencies reaching 100% [2]. This allows continuous optical phase shifts and without phase resets, in stark contrast to conventional elements, wherein phase profiles are encoded as discrete optical path variations in refractive index or thickness, limiting performance. The geometric phase optics is a promising alternative for controlling and manipulating light, but it stumbles on the lack of adequate fabrication technology