Fourier beam analysis of photonic crystal coupled triangular VCSEL array

Abstract

We show that a photonic crystal triangular VCSEL array can lase in three possible coherent supermodes with three distinctive far-field beam profiles. To determine a dominant supermode at a given level of current injection, we define the peak ratio as the ratio between any sidelobe peak to the central peak of the Fourier transform of the far-field. The peak ratio and the number of sidelobes we show provides a numerical method to determine the dominant supermode in a coherent triangular VCSEL array. Coherent operation is found with approximately equal current injection into each element producing a single spectral resonance and structured far-field profile. We compare experimentally extracted peak ratios for an array nominally emitting at 850nm to those calculated from a complex waveguide modal simulation. This Fourier method based far-field analysis may be useful to determine a useful beam profile for target applications.