Progress and properties of high-power coherent vertical-cavity surface-emitting laser arrays

ABSTRACT We discuss the potential of using coherently-coupled vertical cavity surface emitting laser arrays ashigh-intensity light sources. In particular, the design and performance of a novel two-dimensional phase-coupled grid Contact vertical cavity Surface Emitting Laser Array (C-SELA) is reported. We discuss theoptical properties of the C-SELA; in addition to the usual out-of-phase array mode, we demonstrate in-phase SELA coupling. We introduce a simple physical model to describe our experimental results. Over 1.2Watt optical power emission is obtained at room temperature from an electrically-excited lOxlO C-SELA.This laser array exhibited a low threshold current density of only 600Amps/cm2 and over 60% single-endeddifferential quantum efficiency. I . INTRODUCTION High power semiconductor lasers have a number of important commercial, medical, and military appli-cations.1'2 To date, little research has been conducted into the potential of using Vertical Cavity SurfaceEmitting Lasers (VCSELs) as a high intensity light source. The advantages of using VCSELs for highpower include ease of manufacture and testing of 2D arrays and thus low cost production, good optical pro-perties, and a buried active region beneath a distributed mirror, low surface power density due to increasedemission area and hence, the potential for low catastophic optical damage. We have studied variousapproaches to achieving large coherent output power from VCSELs.3 These include using a broad-areaemission window, a closely-spaced individually-pixellated VCSEL array, and a novel approach using a gridcontact to force coherence across the array by modulating the gain and reflectivity. We demonstrated highcoherent optical output power exceeding 0.53 W in a single coherent supermode from an 8x8 phase-coupledpatterned grid Contact vertical cavity Surface Emitting Laser Array (C-SELA).3 The C-SELA exhibits asmooth L-I and a low-voltage (1 .6V threshold voltage) electrical characteristic overcoming some of themajor problems associated with VCSELs. Another similarly-sized 8x8 SELA was studied in which all ele-ments were individually pixellated. In contrast to the C-SELA, it was found that the pixelated SELA,although exhibiting an extremely large external quantUm efficiency rj