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Proceedings Paper

Ultra-high contrast shutter with a tunable optical cavity
Author(s): Mohsen Jafari; L. Jay Guo; Mina Rais-Zadeh
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Paper Abstract

This paper introduces an ultra-high-contrast reflective electro-optical shutter that achieves a record-breaking amplitude modulation index of 53 dB by employing Germanium Telluride (GeTe) in a Fabry-Pérot (FP) cavity. GeTe is a chalcogenide glass which possesses very dissimilar refractive index values when switched between its two stable amorphous and crystalline phases. In this work, an ultra-thin GeTe film is sandwiched between two optical mirrors to enhance light modulation due to GeTe refractive index change. Moreover, a buried NiCr Joule-heater was used to provide a localized heat/heat-sink required for GeTe phase transition. On top of this heater, an ultra-thin GeTe film is integrated at the position of FP cavity’s maximum filed strength. GeTe being at this position tunes FP’s reflection spectrum most effectively when transitioned between its two phases. FP’s stop-band (dip) frequencies are very sensitive to the GeTe refractive index. This property is used to achieve ultra-high light amplitude modulation at these frequencies. However, FP bandpass high reflectivity helps maintaining a low forward loss of less than 3 dB, when GeTe is amorphized. The field enhancement was produced by multiple reflections between two mirrors and used to tune the stopband edges in the spectrum in an effort to achieve ultra-high contrast modulation. Moreover, due to efficient multiple light reflection from the top mirror back to the cavity, modulation index was improved by 7× compared to total light absorption in a single GeTe film on a gold substrate. Finally, having multiple tunable stopbands was found to be useful in applications requiring a multi-frequency shutter. GeTe crystallization happens with application of 5 V rectangular pulses with 2 μsec pulsewidth.

Paper Details

Date Published:
Proc. SPIE TFE17, International Workshop on Thin-Films for Electronics, Electro-Optics, Energy and Sensors, ; doi: 10.1117/12.2279569
Show Author Affiliations
Mohsen Jafari, Univ. of Michigan (United States)
L. Jay Guo, Univ. of Michigan (United States)
Mina Rais-Zadeh, Univ. of Michigan (United States)
NASA Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. TFE17:
International Workshop on Thin-Films for Electronics, Electro-Optics, Energy and Sensors
Guru Subramanyam, Editor(s)

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