Risley prisms for broadband optical beam steering

Abstract

Risley prism beam steering uses pairs of wedge prisms that can be continuously rotated to steer light over a wide angular range. Due to the chromatic dispersion from refraction through wedge prisms, these devices typically only operate on narrowband light. Here we describe the design, development, and characterization of a broadband Risley Prism optical beam steering device capable of steering light with sub-mrad accuracy over a 40-degree field of regard. The design leverages compact rotation motors for a reduced volume profile and incorporates dual silicon and germanium prisms to achieve achromatic beam steering across an extended mid-wave infrared band from 2-5 μm. The existing device supports an optical aperture up to 110 mm, but is scalable to larger sizes depending on the application. The Risley prism was characterized in terms of its thermal response, speed, achromaticity, optical quality, and volume.