Optical micro encoder using a twin-beam VCSEL with integrated microlenses

An improved optical micro encoder using a vertical-cavity surface-emitting laser (VCSEL) is presented in this paper. A twin-beam VCSEL is used to obtain two quasi-sinusoidal signals in phase quadrature, thereby both. detection of the displacement direction and signal interpolation have become possible. Also, microlenses monolithically integrated onto the VCSEL improve resolution. The encoder size is approximately 1.5x2.0x0.6 mm(3). Displacement measurement was performed using a scale with a pitch of 20 mu m, and resolution of 0.1 mu m has been achieved with signal interpolation.