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Proceedings Paper

External laser intensity modulation based on a MEMS micro-mirror for photo-acoustic gas sensing
Author(s): Li Li; George Stewart; Graham Thursby; Norhana Arsad; Deepak Uttamchandani; Brian Culshaw; Yiding Wang
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Paper Abstract

An external laser intensity modulation system based on a micro-electromechanical systems (MEMS) mirror is presented in this paper, for application to gas sensing. The micro mirror is driven by the electrothermal actuator. The rotation direction is decided by the relative position between the driving actuator and the axis of micro-mirror. In contrast to the traditional technique of current modulation of tunable diode lasers where wavelength modulation (WM) is combined with intensity modulation (IM), the IM can be separated from WM and wavelength tuning through the external modulation furnished by the mirror reflection. The MEMS mirror with 10μm thick structure material layer and 100nm thick gold coating is formed as a circular mirror with 2mm diameter. The mirror is attached to an electrothermal actuator and is fabricated on a chip that is wire-bonded and placed on a PCB holder. There are four electrothermal actuators orthogonal to each other that are connected to the circular mirror. Double-loop serpentine springs are used to attach the four actuators to the micro mirror. Each three-beam actuator is attached to a spring at one end that connects the actuator to the mirror and fixed to the substrate at the other end. The actuators are of two different types regarding length: 1.8 mm from hereon called the long actuator and 1.35 mm called the short actuator. Characterizing the frequency response and measuring the modulation performance of the MEMS mirror is presented in this work. Intensity modulation depth from very low values to about 100 percent can be achieved through adjusting the MEMS mirror's reflection position and driving voltage. The intensity-modulated laser source is used for photoacoustic gas sensing in order to recover the target gas absorption line profile based on tunable diode laser spectroscopy. The target gas is 1 percent acetylene balanced by nitrogen and the target absorption line is P17 of acetylene at 1535.39nm. Good agreement between experimental results and theoretical simulations is obtained.

Paper Details

Date Published: 22 October 2010
PDF: 8 pages
Proc. SPIE 7657, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems, 76570M (22 October 2010); doi: 10.1117/12.864033
Show Author Affiliations
Li Li, Univ. of Strathclyde (United Kingdom)
Jilin Univ. (China)
George Stewart, Univ. of Strathclyde (United Kingdom)
Graham Thursby, Univ. of Strathclyde (United Kingdom)
Norhana Arsad, Univ. of Strathclyde (United Kingdom)
Univ. of National Malaysia (Malaysia)
Deepak Uttamchandani, Univ. of Strathclyde (United Kingdom)
Brian Culshaw, Univ. of Strathclyde (United Kingdom)
Yiding Wang, Jilin Univ. (China)

Published in SPIE Proceedings Vol. 7657:
5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Design, Manufacturing, and Testing of Micro- and Nano-Optical Devices and Systems
Tianchun Ye; Sen Han; Masaomi Kameyama; Song Hu, Editor(s)

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