Reflective cavity couplers based on resonant waveguide gratings.

We report on a novel concept for reflective diffractive cavity couplers based on resonant waveguide gratings instead of multilayer coatings. The diffracting or rather beam splitting properties are induced to the subwavelength structures by a periodic parameter modulation of the ridges. Since such a perturbation of the highly reflective system also enhances transmission stacks of two and three reflectors are considered to retrieve transmittivities as low as possible. Our calculations show that transmissions of less than 10(-4) are possible for different configurations based on silicon and silica. The results of first technological tests for the realization of stacked T-shape structures are presented. With a total effective layer thickness not exceeding 1.1 μm the discussed approaches are expected to remarkably reduce the urgent problem of coating thermal noise of conventional components for high-precision metrology.