| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 97 === This study aims at developing a novel pitch and blaze angle tunable grating device via Micro-Electro Mechanical Systems (MEMS) technologies. Grating is a powerful optical component for dispersing incident ray into specific angular direction corresponding to individual optical wavelength. After the first tunable grating device GLVTM was reported, tunable grating devices initiated a new region of optics since device design is variable, enabling easy construction of a flexible optical system. Pitch tunable gratings and blaze angle tunable gratings have been developed individually, but grating with these two tuning functions simultaneously has never been presented so far. In our group, we have been developing such gratings to bring more applications.
According to the grating equation, the constructively interfered wavelength is in proportion to the grating pitch for the same diffraction angle. Thus we can tune the grating pitch and then detect all spectral lines sequentially by a photodetector. Besides, blaze angle tuning could adjust the intensity of the spectrum and enhance the grating performance.
In our device, the pitch tuning function is carried out by bulk-micromachined thermal actuators, and the blaze angle tuning function is realized by electrostatic actuators. In order to enlarge the pitch tuning range, a novel thermal actuator is designed for our grating device. The experimental results show that the maximum output displacement of this actuator is over 316�慆 within 5.48W.
The non-uniform stiffness results from non-uniform pre-strain on the slats, which comes from the quality control of our fabrication facility available. Thus the blaze angle of our grating device presently could only work with on-off two modes. Although the blaze angle is tuned by electrostatic force via non-linear pull-in phenomenon, it is theoretically possible to tune the blaze angle stably before the pull-in happens if the quality of the fabrication facility is good to achieve good structure pre-strain uniformity.
Although this tunable grating device does not function well due to some fabrication limits of available facilities, experimental results verify that this is a workable tunable grating design with feasible fabrication process. If better fabrication facilities are available, the full features of the high-performance grating device could be realized soon and bring more applications.
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