Session IC07 - Optical Devices and Applications.
ORAL session, Tuesday morning, March 23
Room 365W, GWCC
Ordinary light emitting diodes have a high refractive index and an isotropic spontaneous emission pattern. Total internal reflection severely limits the external efficiency of these devices, with the small fraction of photons that escape distributed over a widely divergent beam profile. We have addressed these issues by using the back surface of the substrate to redirect photon trajectories. Using optical excitation in a prototype device, we observe excellent beam directivity and record efficiency (\eta > 60% at 1.6 \mum). By translating the excitation position, we also observe uniform deflection of the emitted beam. We propose a light emitting diode structure where the radiation pattern is controlled by selective excitation of a grid of junctions near the focus of the reflector.