Narrowband thermal emitters based on photonic crystals

Abstract

Thermal emitters generally exhibit a broad spectrum and are widely used for various light sources from far-infrared to the visible range. However, in many applications involving non-dispersive infrared sensing and thermo-photovoltaics, only a specific spectral component that is much narrower than the original broad spectrum of thermal emitters is utilized, which reduces efficiency. Therefore, it is important to develop a single-mode narrow-bandwidth thermal emitter that achieves high emissivity at a target wavelength while suppressing it as much as possible at other wavelengths. To achieve such an ideal spectrum, we demonstrated mid-infrared thermal emitters by combining multiple quantum wells (MQWs) and two-dimensional photonic crystal (PC) slabs [1]. In our emitters, intersubband transitions of MQWs allow a strong interaction between light and matter around a target wavelength, and a γ — point resonant effect of PCs further narrow down the thermal emission peak at a target wavelength and enable vertical emission. Ultrafast modulation (∼MHz) of thermal emission without changing the temperature of emitters has been also realized by changing the electron density of MQWs using applied electric field [2]. Near-infrared narrowband thermal emitters have been also recently demonstrated by using arrays of intrinsic Si nanorods [3].