Mr. Cheng-Hsuan Lin Profile

Cheng-Hsuan Lin

at National Chiao Tung Univ

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Proceedings Article | 24 April 2003 Paper

Enhancement of optical attenuation by a tunable nonsmooth mirror

Cheng-Hsuan Lin, Wensyang Hsu

Proceedings Volume 5116, (2003) https://doi.org/10.1117/12.498969

KEYWORDS: Mirrors, Signal attenuation, Calibration, Spherical lenses, Actuators, Optical fibers, Free space, Optical components, Collimators, Power meters

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Here the attenuation effect of a variable optical attenuator (VOA) with a tunable non-smooth mirror is investigated experimentally and analytically. The working principle of this VOA is based on the non-uniform deformation shape of a mirror membrane by thermally driven bimorph actuators. Before deformation, the surface roughness of Rymax and insertion loss of the mirror membrane are calibrated as 15 nm and 0.53 dB, respectively. The attenuation tests on smooth and non-smooth concave mirrors are also conducted. In simulation, the attenuation effects by various smooth spherical shapes are modeled by ray tracing method and Gaussian beam theory, and the simulation results are compared with experimental data. It is found that the attenuation behaviors between simulation and calibration results on smooth, spherical concave mirrors have good agreement. Also, by comparing the experimental results from smooth and non-smooth concave mirrors, the attenuation is found to be enhanced by the non-smooth mirror surface evidently. The maximum dynamic range of attenuation is found to be more than 40 dB at input voltage of 46 V.

Proceedings Article | 21 November 2001 Paper

Microfabrication of hemispherical polysilicon shells standing on hemispherical cavities

Cheng-Hsuan Lin, Yi-Chung Lo, Wensyang Hsu

Proceedings Volume 4592, (2001) https://doi.org/10.1117/12.449010

KEYWORDS: Wet etching, Silicon, Etching, Polysomnography, Ultrasonics, Photomasks, Coating, Microfabrication, Printing, Surface micromachining

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In the current paper, the fabrication process of a novel proposed hemispherical polysilicon shell standing on a hemispherical silicon cavity is demonstrated. This micro-fabrication process combines both bulk and surface micromachining, which include the isotropic wet etching, a novel mask design, the thick photo resist coating and exposure, and high-aspect-ratio curved sacrificial technique. In isotropic wet etching of a hemispherical cavity, the optimal concentration of etchant is experimentally determined along with adequate ultrasonic vibration during wet etching to produce the circle-like of hemispherical cavity. The conventional alignment mark, which will be destroyed during the rather long isotropic wet etching process, is replaced by a novel mask design with the second alignment mark. Also, for a deep hemispherical cavity larger than 100úgm, the traditional photo resist can not be coated on the corner surface well. The thick photo resist, AZ4620, is found to be able to overcome this problem and be successfully exposed all through its bottom surface. Furthermore, the deposited sacrificial layer materials (PSG) on this cavity will usually result in thinner layer near the corner. In addition, the curved gap of PSG layer has the feature with high-aspect-ratio. These make the PSG etching difficult. Therefore, two steps etching process with two different hydrofluoric concentrations are used to release the PSG with 2micrometers thickness and 150micrometers arc length.

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