Highly Efficient Dielectric Optical Incoupler for Quantum Well Infrared Photodetectors

In this letter, we propose a highly efficient alldielectric optical incoupler for a quantum well infrared photodetector (QWIP) operating in the very long wavelength infrared regime from 14 to 16 μm. The microstructure is comprised of a thin top-contact/QWs/bottom-contact semiconductor layer sandwiched by a germanium layer drilled with periodic holes and a flat low-refractive index substrate. By exploiting the waveguide mode, the dielectric optical incoupler can convert infrared radiation efficiently into the QWs layer with strong infrared absorption for QWs at the specific wavelength of 14.9 μm, of which the absorption increases 7.5-fold compared with an isotropic active region without any designed framework. More importantly, a large electrical field component (Ez) normal to the plane of QWs can be obtained with a large value of coupling efficiency (η) of |Ez|2 reaching up to 1.4. A slight dispersion (over 40°) and weak polarization dependence of the guided mode supported by the dielectric incoupler might be beneficial to highperformance infrared photodetectors.