OPTICAL MICRO ENCODER WITH SUBMICRON RESOLUTION USING A VCSEL

An improved optical micro encoder using a vertical-cavity surface-emit ting laser (VCSEL) is presented in this paper. A twin-beam VCSEL is us ed in order to obtain two quasi-sinusoidal signals in phase quadrature . Directional sensing and signal interpolation have become possible. A lso, microlenses are monolithically integrated onto the VCSEL in order to improve resolution. The encoder chip size is approximately 1.5 x 2 .0 x 0.6 mm(3). Displacement measurement is performed using a scale wi th a pitch of 20 mu m, and resolution of 0.1 mu m is achieved as a res ult of signal interpolation. Additionally, the encoder is installed in to a low-height linear stage and characterized, demonstrating a possib le application. A prototype of the packaged encoder is also presented. (C) 1998 Elsevier Science S.A. All rights reserved.