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Opt Lett. 2013 ;38(17):3336-9.
Kroker S, Käsebier T, Kley EB, Tünnermann A.
Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-University, Jena, Germany. stefanie.kroker@uni jena.de
Abstract
We report on stacked high-contrast grating reflectors with virtually angular independent reflectance for transverse-magnetic polarized light. The investigated structure consists of two-layer pairs of amorphous silicon and silicondioxide that are designed for a wavelengths of 1550 nm. The large angular tolerance results from coupling of the two involved silicon gratings and is achieved if the modal fields in thereflectors are matched. With this approach, a reflectance of more than 96% in the entire angular spectrum is feasible. Experimentally we demonstrate a reflectance of more than 98% for incidence angles up to 60° and more than 90% up to 80°.
Additional information:
Grating structures made of high index materials with periods slightly below the wavelength of light have attracted recent interest in several fields of application. For example, they can be used as mirrors in optoelectronic devices, as beam steering devices to shape in a well-defined manner as well as for reflective components with low thermal noise in high precision metrology. Here, particularly silicon is a material of great interest which provides beside very good optical properties an excellent structurability. Virtually for all application the broadband character of the optical function of these gratings plays a major role. This feature enables for example the realization of highly-efficient angular independent reflectors. The coupling of two or more broadband mirrors even gives more degrees of freedom in order to tailor their interaction with light and thus the optical response of the elements. In this contribution we demonstrate a nearly angular independent reflector based on two coupled silicon grating structures for a wavelength of 1550 nm.
