Variable optical attenuator with tunable nonsmooth curved mirror

The attenuate effect of a variable optical attenuator (VOA) with a tunable nonsmooth curved mirror is fabricated and investigated experimentally and analytically. The working principle of this VOA is based on tuning the reflective mirror membrane into the nonsmooth curved mirror to enhance the optical attenuation, compared with that of the smooth curved mirror. The attenuation depending on the radius of curvature in a smooth concave mirror is simulated. Also, the attenuation tests on smooth and nonsmooth concave mirrors are conducted experimentally. The mirror membrane of the proposed VOA can provide not only the curved shape, but also a nonsmooth shape at the same time in the mirror membrane. By comparing the experimental results between the smooth and nonsmooth curved mirrors, the attenuation is shown to be enhanced at least 60% by the nonsmooth effect when the radius of curvature is smaller than 50 mm. The mirror membrane combining gold and low-stress nitride using back-side etching is sufficiently flat to provide an insertion loss of 0.53dB, and more than 40dB attenuation after deformation.