The enhancement on optical attenuation by a tunable non-smooth mirror

Here the attenuation effect of a variable optical attenuator (VOA) with a tunable non-smooth mirror is investigated experimentally and analytically. The working principle of this VOA is based on the non-uniform deformation shape of a mirror membrane by thermally driven bimorph actuators. Before deformation, the surface roughness of Rymax and insertion loss of the mirror membrane are calibrated as 15 nm and 0.53 dB, respectively. The attenuation tests on smooth and non-smooth concave mirrors are also conducted. In simulation, the attenuation effects by various smooth spherical shapes are modeled by ray tracing method and Gaussian beam theory, and the simulation results are compared with experimental data. It is found that the attenuation behaviors between simulation and calibration results on smooth, spherical concave mirrors have good agreement. Also, by comparing the experimental results from smooth and non-smooth concave mirrors, the attenuation is found to be enhanced by the non-smooth mirror surface evidently. The maximum dynamic range of attenuation is found to be more than 40 dB at input voltage of 46 V.