Diode-pumped Vertical-cavity Surface-emitting Semiconductor Lasers for Free Space Communication

Abstract

Vertical-cavity surface-emitting semiconductor lasers (VCSELs) are potentially useful for fast optical interconnection between wafers, free-space communication and formation of coherent 2-D laser arrays. The use of resonant-periodic-gain (RPG) media, in which a series of gain regions (single quantum wells or closely-spaced groups of quantum wells) with half-wave optical periodicity is aligned with the antinodes of the optical standing-wave in the laser cavity, provides enhanced gain along the cavity axis and at the designed lasing wavelength. The result is a considerable reduction of parasitic transverse amplified spontaneous emission, and considerably improved laser thresholds and spectral behavior [1]. However, the structure is not amenable to longitudinal injection pumping, and hence alternative means of efficient pumping must be found to realize its practical advantages. For optical interconnects, transverse current injection is probably best. For high-power operation and long-distance free-space communication, however, the high electrical-to-optical power conversion efficiency (~20%) and good beam quality achievable using diode laser pumping [2] are advantageous. Here we describe the use of CW and quasi-CW 740-nm diode lasers and laser arrays to pump GaAs/GaAlAs and InGaAs/GaAlAs VCSELs. Power outputs of up to 90 mW were obtained by quasi-CW pumping of the latter devices, with pump spot diameters from 6-20 μm. Since these results were limited by the available pump power at 740 nm, improved structures optimized for 780-nm pumping will be described.