Effects of etch holes on optical properties of microelectro mechanical system deformable mirror

Micro electro mechanical system (MEMS) deformable mirrors fabricated by surface technics have the advantages of small volume, high resolution and low driving voltage et al.. However a large number of etch holes on the mirror formed in a regular array structure affect the optical properties of the deformable mirror (DM). We design and manufacture MEMS DM cell based on surface technics, which can be used in the research of effects of etch holes on optical properties of DMs. From the Fraunhofer diffraction theory, diffraction patterns created by two-dimensional etch hole arrays on MEMS DMs have been investigated. Research result shows that when the dimensions of etch holes increase and adjacent spacings of etch holes decrease, the central zero-order diffracted light intensity decreases and the diffraction effect increases, leading to decreases of the effective reflection surface and reflectivity of DM surface. The etch hole structures affect measurement performance of Shark-Hartmann wavefornt sensor on wavefront aberration. Because they can reduce the energy of focal spot and reduce the accuracy of wavefornt measurement with the disturbance of wavefornt enhanced and focused spot adjacent crosstalk.