We present novel filter elements with an asymmetric angle dependent transmission based on high-contrast gratings.
Asymmetric means a different efficiency for positive and negative incidence angles. Our approach provides the realization of asymmetric direction selective filters by using blaze-like grating structures combined with subwavelength
high contrast gratings respectively grating periods in the resonance domain. We also discuss the influence of the effective medium theory on the transmission function depending on the angle of the incident light. For realization of those high contrast gratings Silicon is chosen as material with high refractive index and adequate compatibility with semiconductor fabrication.
Experiments in the field of high-precision optical metrology are crucially limited by thermal noise of the optical components such as mirrors or beam splitters. Amorphous coatings stacks are found to be a main source for these thermal fluctuations. In this contribution we present approaches to realize coating free optical components based on resonant high contrast gratings (HCGs) made of crystalline silicon. It is shown that beside classical cavity mirrors the concept of HCGs can also be used for reflective cavity couplers. We compare the advantages and challenges of these HCG reflectors with distributed Bragg reflectors made of crystalline coatings for applications in optical metrology.
We report on novel concepts for reflective diffractive elements based on high-contrast gratings. To demonstrate
the possibilities for such devices reflective cavity couplers with three output ports are investigated. A diffracting
period is superposed to a highly reflective subwavelength grating in order to realize diffractive elements. This
superposition can be realized with a periodic depth, fill factor or period modulation of the reflector. Further, to
limit the total transmission of the device it is necessary to enhance its angular tolerance. We discuss different
approaches in order to realize this increased reflectivity in broad range of the angular spectrum. The contribution
focuses on the material combination silicon-silica, but the presented concepts also hold for other material
combinations with large index contrast and even for monolithic silicon structures.
We introduce concepts for direction selective transmission filters based on dielectric high-contrast gratings. The
devices act as angular bandpass filters at an incidence angle of 45° with a total transmission of 68% and a full
width at half maximum of 20°. Since the filters are based on a material combination of silicon and silicon dioxide
they provide an excellent compatibility to well established fabrication processes in semiconductor industry. The
results of measurements on fabricated samples are presented and the performance of the components is compared
to that of metallic gratings. It is found that the latter can basically provide similar filter properties, however the
feasible transmission efficiency is significantly lower than for the dielectric gratings. The presented configurations
are applicable in the field of sensors and detectors.