Embodiments of the present specification provide an apparatus for detecting an angle of rotation of a rotating member. A light source emits light rays which are conditioned by a light conditioner to control a light beam geometry and emission pattern of the light rays. The conditioned rays are incident on an optical disk that emits refracted rays in form of a light spot on an optical detector. The optical disk rotates in synchronization with the rotating member. The optical detector uses position of the light spot to output an analog signal continuous and ratio-metric to the angle of rotation of the rotating member.