Protecting optical sensors and detectors against excessive input signals is not only important for dealing with unintentional overloads, but also central for protecting sensors against intentional high-intensity sources such as flares or laser beams directed as countermeasures against the sensor system. In prior work, a microelectromechanical system (MEMS)-based, all optically driven deformable mirror was designed and fabricated. In this work, an optical limiter using this optically addressed, deformable mirror is proposed and designed.
Several operating mechanisms of this device have been described before and include: DC bias, DC bias accompanied by AC light modulation, and a combination of AC and DC biases. In the DC bias operating mechanism, the device de flects in a binary fashion. In the AC light modulation with the DC bias mode, it is possible to control the impedance only in a non-steady-state situation. This suggests that this operating mechanism is suitable for moving targets or similar situations where only response to transient events is desired. In very-high-frequency AC light modulation, it is possible to control the impedance between the membrane and substrate under both transient and steady-state conditions, while a combination of AC and DC provides further control of the heterojunction capacitance between the transparent ZnO electrode and substrate. For the last three operating mechanisms it was found, both experimentally and theoretically, that the membrane deflection saturates as a function of the back illumination intensity. Both the saturable deflection of the membrane and the parabolic form of this deformation are used to create a MEMS optical limiter, focused in particular on using the very-high-frequency AC bias operating mode.
This work was done by Jed Khoury and Charles L. Woods of the Air Force Research Laboratory; Bahareh Haji-saeed and John Kierstead of Solid State Scientific Corp; and William D. Goodhue of the University of Massachusetts. AFRL-0128
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