Moems-based Micro-optical Adaptive Micromirror

Traditional adaptive optics real-time adjusts distortion caused by atmospheric disturbances through the deformation of large-sized mirror to acquire sharp image. However, the disadvantage of large mirror area and hard to control increased the size, the weight and the power consumption of system, which can't satisfy the need of miniaturization in modern aviation. Micro-optical adaptive system is the combination of micro-optics and traditional optics which real-time adjusts wave-front and aberration as well as realizes imaging clearly in complex environment. The development of Micro-Opto-Electro-Mechanical Systems (MOEMS) has made fabricating micron-sized deformable arrays possible. Those system advantages of miniaturization, low power consumption, modest cost and fitting mass production can be realized by applying micro-arrays in atmospheric optics.A novel adjustable focal length optical adaptive micro-mirror based on MOEMS is presented. Based on bi-metal effect, deformable micro-mirrors utilize heat stress to change the mirror curvature so focal length changes. Compared with traditional deformable micro-mirror, micro-mirror fabricated by our method has the advantage of low driving voltage and large driving force. Besides, it is easy to be fabricated. Micro-machining processes such as oxygenation, photolithography, chemical etching and sputtering are experimented. A 4×4 bi-metal adjustable focal length micro-mirror arrays have been completed. Each unit has an area of 3x3mm with the thickness of silicon 60μm and aluminum film 150nm. Deformable mirror area covers 79% of the total mirror area. Dynamic performance of adjustable focal length micro-mirror is tested using laser wave-front interferometer. Experiment results demonstrate that the micro-mirror can produce uni-directional continuous deformation with the maximum deformation of 15.8μm and nonlinearity lag of 27%. It can work at 0-2.5V with an adjustable focal length ranging from ∞ to 0.036m.