Normal incidence infrared modulator based on single quantum well intersubband transitions

An infrared modulator of which the working principle is based on evanescent wave generation
and intersubband transitions in a single AlGaAs/GaAs quantum well is presented here. 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 re?ective mode is achieved by applying an
electric ?eld across the quantum well. The model for deriving the complex refractive index of
the quantum well region is presented and used for numerical diffraction ef?ciency simulations
as a function of the groove height and period. Two specimens with different groove heights
were fabricated. Experiments are conducted at a wavelength of 10.6µm. At this wavelength a
relatively strong absolute modulation depth of about 20% could be observed. The experimental
results are in good agreement with our model and diffraction efficiency calculations.

Publication year:2014

Keywords:IR modulator, quantum well, evanescent waves, Q-switching