Controlling the Directionality of Spontaneous Emission by Evanescent Wave Coupling

Various applications such as projectors, micro-displays for wearable and portable electronics, and biosensors re-quire spontaneous light sources with a well-defined spatial directionality. Despite extensive research devoted to con-trolling the radiation process of spontaneous emissions, there is still a lack of reliable method for achieving high directionality stable enough for practical applications against variations in device operating conditions. In this paper, we report a novel approach toward controlling the directionality of spontaneous emissions by employing the evanescent wave coupling effect in a small ridge or truncated cone structure.