Abstract

High-brightness single laser diodes based on the widespread taper design have demonstrated output powers of a few Watts with a single transverse mode operation [1]. The use of arrays of such lasers result in a further increase of the laser power, but with the drawback of a loss in the spatial brightness. To overcome this limitation numerous external-cavity configurations have been proposed which induce a coherence between the individual emitters of the array and result in a brightness improvement [2]. In this work we describe two external cavities intended to improve the spatial brightness of a bar of N = 6 index-guided tapered laser diodes emitting around 975 nm. The lateral structure of the emitters consists of a short ridge single-mode section, a 2.3 mm-long narrow-angle tapered ridge and a common amplified free-space 0.2 mm-long section. The array pitch is p = 30 μm, and the near-field 1/e² full-width (1/e²-FW) of each emitter is 30 μm too, so the filling factor of this array is 100% on the front facet and the emission section is w = 180 μm wide. No adjacent coupling between emitters is evidenced in the free running laser emission of the array alone, and its 1/e²-FW divergence is ~80 mrad in the slow axis. Our external cavity designs aim at controlling the slow-axis beam divergence of the whole array by inducing an angular-filtered feedback into the lasers [3,4]. The configuration forces the array to operate in the out-of-phase mode, which has two main lobes in its far-field profile at ± λ/2p = ± 16 mrad. We take benefit of the angular selectivity of volume Bragg gratings to favour an asymmetrical feedback on one of these peaks. The far-field of the extended-cavity array is thus expected to exhibit one diffraction-limited peak in the symmetric direction (Figure 1).

© 2009 IEEE