Plasmonic nanoantenna arrays as efficient etendue reducers for optical detection

Optical detectors require the efficient collection of incident light onto a photodetector. Refractive or reflective optics are commonly used to increase the collected power. However, in the absence of losses, such optics conserve etendue and therefore pose a limit on the field of view and the active area of the detector. A promising method to overcome this limitation is to use an intermediate layer of fluorescent material that omnidirectionally absorbs the incident light and preferentially emits toward the photodetector. We demonstrate here that plasmonic nanoantenna phased arrays are a promising platform to improve the emission efficiency of thin luminescent layers and provide an efficient method to reduce optical etendue. In particular, we show an almost constant optical absorption of the luminescent layer on top of the array with the angle of incidence and a strong beamed emission in small solid angles in the forward direction. These results pave the way for novel optical communication detectors incorporating nanofabricated plasmonic materials as optical etendue reducers.