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16 August 2004 A MEMS-based all-dielectric tunable optical filter with increased tuning range
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A detailed study of the tuning characteristic of a novel MEMS-based tunable optical filter is presented together with supporting characterization results. The device is based on a Fabry-Perot interferometer employing a solid-state silicon resonator and silicon-based distributed Bragg reflectors (DBR). It is fabricated as a free-standing membrane, which is suspended through micro-machined arms. Tuning is achieved by thermal modulation of the resonator’s optical thickness. The tuning behavior of thin film interference filters differs significantly from filters based on an etalon structure. An analytical approach is presented to include effects caused by the Bragg reflectors. Based on this model different material systems are investigated in order to improve the achievable tuning range. A maximum reflectance of 99.8 % and a stop band width of 783 nm are achieved. A minimum spectral width of 1.19 nm and an insertion loss of 1.7 dB have been measured in transmission measurements for filter membranes, consisting out of a λ/2 layer of amorphous silicon and Bragg reflectors each with 12 λ/4 layer-pairs of silicon nitride and silicon dioxide. Using external heating the filter shows a tuning efficiency of 51.7 pm K-1, as predicted through the proposed effective resonator length model.
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Dennis Hohlfeld and Hans Zappe "A MEMS-based all-dielectric tunable optical filter with increased tuning range", Proc. SPIE 5455, MEMS, MOEMS, and Micromachining, (16 August 2004);

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