Optical micro encoder using surface-emitting laser

A novel optical micro encoder using a surface-emitting laser (SEL) is presented. By using the small divergence beam from the SEL, a very simple configuration without any other optical component has become possible. A quasi-sinusoidal signal is obtained when a scale with a minimum pitch of 20 μm (i.e., 10 μm line and space) is used. In order to obtain submicron resolution, it is preferable to reduce an optical spot size on the scale. Microlenses, which can eventually be integrated onto the SEL surface, have been studied for the laser beam convergence. The diffraction patterns made by the SEL, with and without an integrated microlens, have been calculated, and the effect of using the microlens is confirmed. Microlenses have been fabricated on a glass substrate, and their profiles have been characterized. Also, microlenses are irradiated by a collimated beam from a conventional edge-emitting laser, and optical spots made by the microlenses have been observed. Although the microlens has not been integrated onto the SEL, the possibility of obtaining higher resolution using the microlens is clearly demonstrated