Collimation of diverged beam using a cylindrical lens in a silicon-based end-fire optical phased array

Abstract

The authors demonstrate the collimation of a vertically diverged beam emitted from a silicon-based end-fire optical phased array (OPA) using an aspheric cylindrical lens. A micro-cylindrical lens with a numerical aperture of 0.8 was placed near the focal length in front of an 1 x 16 end-fire OPA with a half-wavelength (775 nm) radiator array pitch for a 1550 nm wavelength. The lens provided a great collimation effect, reducing the vertical divergence angle from 95.6 degrees to 6.7 degrees during horizontal beam steering over +/- 30 degrees. The horizontal divergence angle showed some expansion, from 7.6 degrees to 10 degrees, due to the angle-dependant curvature of the lens and the distance to the lens surface.