830nm graded index double barrier separate confinement heterostructure laser diodes with small vertical divergence and temperature insensitive characteristics

Abstract

Semiconductor laser diodes (LDs) are preferred as pump sources for many solid state laser systems. However, these applications require mainly high output power and narrow beam divergence of LDs to achieve high conversion and coupling efficiencies. Widening the transverse mode to reduce power density at the facet is one direct approaching to increase the catastrophic optical damage (COD). A reduced optical confinement factor can be naturally obtained in lasers with wide waveguides, providing narrow far field emission [1]. Various optimizing methods of laser heterostructures focus on the beam divergence reduction and then contribute to high COD level. Unfortunately, a decrease of the confinement factor is inevitably connected with a deterioration of the laser performance, such as threshold current, slop efficiency, and maximum output power. Several designs have been proposed to mitigate these side effects, such as utilization of a large optical cavity (LOC) into separate-confinement heterostructure (SCH) layers [2], inserting additional layers to control waveguide properties of conventional SCHs [3], or using the vertically integrated passive array [4]. A main disadvantage of LOC design is, however, the deterioration of the laser diode performance as waveguide layers are modified excessively thick to reach very high power operation. Compared with the LOC structure into SCH LDs, the LDs with the double barrier separate-confinement heterostructure (DBSCH) structure possess superior characteristics in both COD levels and beam divergence with only moderate deterioration of LD performance in slope efficiency and characteristic temperature [5]. For DBSCH LDs, pair of wide-gap barrier layers which possess low refractive index are inserted into the interfaces between the waveguide and cladding layers, which will widen the transverse mode by modifying the epitaxial layers of double barriers (DBs).