[Experiments of micro-distance measurement for GMLM with spectrum analysis method].

Projection display devices are undergoing a period of multi-development, and with the maturation of MEMS technology, which leads to MEMS-based light modulators for display applications, have become one of the research focuses. The structure of MEMS-based grating moving light modulator (GMLM) is composed of the reflection plate, address electrode and four cantilevers, and movable grating plate, which is supported by four crab-cantilevers placed around, and is actuated like a piston by electrostatic force. The piston-type motion of grating can be used to modulate the phase of incident light. The micro-distance between the upper surface of movable grating and underlying reflector is a key parameter and is important to GMLM performance. Traditional measurement method such as step-machine would destroy the device; while a high accuracy and non-contact measurement machine called KYKO White Light Interferometer is expensive. In the present paper, the GMLM optical principle using scalar diffraction theory was in details analyzed. A novel non-contact wavelength scanning spectrum analysis method was put forward to measure the distance between the upper surface of movable grating and underlying reflector. The U-4100 spectrophotometer was adopted to gain spectrum information; while the spectrum analysis method using peak wavelength position was introduced to calculate the micro distance. The measurement result is consistent to theoretical result. The micro-distance is 1.131 3 microm using such non-contact wavelength scanning spectrum analysis method, while it is 1.240 0 microm with WYKO White Light Interferometer. The relative error was lower than 1%, compared with the results measured by WYKO White Light Interferometer, and the method has good repetition ability and is cheap with RMB50 Yuan each time. Furthermore, measuring pull-in voltage, resonance frequency and micro distance in MEMS-based diffraction and interference devices was proposed completely based on such non-contact wavelength scanning spectrum analysis method.