Light-Intensity-Feedback-Waveform Generator Based on MEMS Variable Optical Attenuator

Increasing demands on the dynamical behavior of microelectromechanical systems (MEMS) devices are reaching a point where mechanical design by itself cannot provide further improvements. Alternative approaches based on control theory, such as the open-loop or the closed-loop driving strategies, must be used instead to provide further enhancements in device performance. In this paper, the design of a light-intensity control system for an optical waveform generator is presented. The optical waveform generator is based on the light-modulation ability of MEMS variable optical attenuators (VOA). The VOA is of shutter-insertion type driven by an electrostatic comb drive. The control system consists of an inner position-control loop and an outer light-intensity-control loop. The inner control loop improves the dynamic response of the position of the MEMS electrostatic comb actuator by using position feedback, whereas the outer feedback loop handles both light-intensity regulation and tracking. An experimental setup and a practical system characterization are given. Based on this, the feedback control system is implemented on an actual MEMS VOA. The results verify that the control system proposed in this paper does significantly improve both the accuracy and the dynamical behavior of the existing device.