Fiber-Pigtailed Electrothermal MEMS Iris VOA

A high-performance variable optical attenuator, which is based on an electrothermally actuated iris with a square pupil, is demonstrated. The device is fabricated from two separate dies that are formed by deep reactive ion etching of bonded silicon-on-insulator material. The iris die is inserted into an elastic clamp on a base-plate die carrying spring-mounted fiber alignment features, allowing the iris to be held in the optical path between two expanded core fibers. A novel aperture that dynamically reduces the clearances between the shutter blades is used to achieve an extinction of 25 dB and a wavelength dependent loss of plusmn1 dB at 1550-nm wavelength. Synchronous blade motion is achieved using thermally optimized folded electrothermal actuators with undercut hot arms, which reduce the operating power to 240 mW and allow a high mechanical resonant frequency. Optical analysis is carried out using a scalar model and diffraction theory. Thermomechanical analysis is performed using a 1-D model and finite element simulation (ANSYS). Good agreement is obtained between the models and by experimentation.