Thermal resistance of etched-pillar vertical-cavity surface-emitting laser diodes

ABSTRACT We discuss our measurements on thermal impedance and thermal crosstalk of etched-pillar vertical-cavity lasers and laser arrays. The average thermal conductivity of AlAs-GaAs Bragg reflectorsis estimated to be 0.28W/(crnK) and 0.35W/(cmK) for the transverse and lateral direction, respectively.Lasers with a Au-plated heat spreading layer exhibit a 5O°i' lower thermal impedance compared tostandard etched-pillar devices resulting in a significant increase of maximum output power. For anunmounted laser of 64im diameter we obtain an improvement in output power from 20mW to 42mW.The experimental results are compared with a simple analytical model showing the importance of heatsinking for maximizing the output power ofvertical-cavity lasers.Keywords: laser, vertical-cavity, VCSEL, thermal resistance, Bragg reflectors, thermal crosstalk, heat sinking, modeling. 1. INTRODUCTION Vertical-cavity surface-emitting lasers (VCSELs) are attractive light sources for various optoelectronic applications. The potentially low production cost, simple packaging, and easy fibercoupling make VCSELs a light source of choice in short distance data links [1], [2] which offer a greatmarket potential. The 2D scaling capability is also interesting in high power applications like laser diodepumped solid state lasers. Moreover the possibility to design vertical-cavity lasers with an arbitrary shapeof the output aperture enables an easy vertical pumping scheme of Er+ doped silica optical waveguides.These devices with a pump light wavelength of 980nm can be used for all-optical switching at 1 .55 p.m.A low thermal impedance also provides a lower internal operating temperature of the laser at any outputpower level. As most degradation mechanisms [3] exhibit a thermal activation energy we expect a lower