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Highly reflective infrared modulator for the CO2 laser wavelength range Host Publication: MIOMD 2014 - Mid Infrared Optoelectronics Materials and Devices XII (October 5-9, 2014), Montpelier France Authors: W. Vandermeiren, J. Stiens, G. Shkerdin, C. De Tandt and R. Vounckx Publication Date: Oct. 2014
Abstract: A quantum well infrared modulator for the CO2 laser wavelength range is presented here. The working principle is based on intersubband transitions in a single AlGaAs/GaAs quantum well structure. CO2 laser light at normal incidence is coupled to an evanescent wave by means of a sub-wavelength diffraction grating. Modulation of the zeroth order reflective mode is achieved by applying an electric field across the quantum well. The model for deriving the complex refractive index of the quantum well region is briefly described and used for numerical diffraction efficiency simulations. It is shown that the modulation depth is to a certain degree inversely proportional to the on-state reflectivity of the modulator. Experimental results achieved on different samples with varying grating height and period are presented. This study focuses on grating parameters targeting relatively high on?state reflectivities in the range of 75ᇳ % and modulation depths in the range of 10?30 %. The experimental results are in good agreement with our model and diffraction efficiency calculations. Absolute modulation depths of the order of 15% were experimentally observed.
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