Optical properties of surface micromachined mirrors with etch holes

We have investigated the optical properties of surface-micromachined polycr ystalline silicon reflectors within the visible spectral range at five diff erent wavelengths. The measurement results of the reflectivity of various m icroreflectors at four different incident angles (20 degrees, 30 degrees, 4 5 degrees, and 60 degrees) are presented. Optical properties of microreflec tors realized using the multiuser MEMS process (MUMPS) have been investigat ed, Our studies have found that etch holes, widely used in the surface micr omachining process to reduce the time for releasing structures by sacrifici al undercutting, have a great influence on the optical properties of microm achined mirrors. Diffraction patterns created by two-dimensional etch-hole arrays on micromachined mirrors have been investigated, The diffraction by etch holes obeys the Fraunhofer diffraction theory when a collimated light source (e.g., a laser beam) is incident, We have shown that when the dimens ion of etch holes increases, an increasing portion of the incident power wi ll be diffracted and transmitted due to etch holes, leading to decreasing r eflectivity of surface micromachined mirrors. [408].