A blue superluminescent LED (SLED) with power above 100mW was fabricated. These SLED shows promise for focus-free pico-projection due to reduced interference and improved image quality. We compared different straight and curved waveguide designs with and without tilted facets. Internal and mirror losses were determined by the Hakki-Paoli method.

We present a blue InGaN research and development superluminescent light-emitting diode (SLED) that is suitable for picoprojection. The SLED reaches an output power of >100 mW with a peak wavelength of 443 nm and a spectral bandwidth of >2.6 nm as well as a single-mode far-field driven in cw mode at 25 °C. In order to figure out an optimized waveguide design, which enables such a high output power at lowest operation current, we compare the performance of diodes with curved and tilted shaped ridges in detail, using the lasing threshold current as a criterion for lasing or superluminescence, respectively.

The origin of perturbations in the Gaussian-shaped lateral far-field of blue InGaN laser diodes is explored. Near-field measurements reveal that small stray light intensity peaks beside the ridge waveguide exist. In order to prove quantitatively the impact of this stray light on the far field, an exemplary beam propagation method simulation is performed. Moreover, laser cuts as a chip technological process to block stray light from the out-couple facet are presented. These laser cuts result in a significant improvement of the lateral far-field.

An InGaN superluminescent light-emitting diode (SLED) with emission as long as 500 nm is presented. Up to now, an SLED with such a long wavelength was hindered, because the gain of indium-rich layers was not sufficient for operating in superluminescence mode. We used an epitaxial structure with high material gain as well as a special chip design of curved waveguide to solve this problem. The SLED reached an output power of >4 mW with a spectral bandwidth of 4.4 nm driven in pulsed mode.

There is a big need on R&D concerning visible lasers for projection applications. The pico-size mobile projection on the one hand awaits the direct green lasers with sufficiently long lifetimes at optical powers above 50mW. In this paper we demonstrate R&D-samples emitting at 519nm with lifetimes up to 10.000 hours. The business projection on the other hand requires high power operation and already uses blue lasers and phosphor conversion, but there is a strong demand for higher power levels. We investigate the power limits of R&D laser structures. In continuous wave operation, the power is limited by thermal roll-over. With an excellent power conversion efficiency of up to 29% the thermal roll-over is as high as 2.5W for a single emitter in TO56 can. We do not observe significant leakage at high currents. Driven in short pulse operation to prevent the laser from self heating, linear laser characteristics of optical power versus electrical current are observed up to almost 8W of optical power.