Supermode Switching in Coherently-Coupled Vertical Cavity Surface Emitting Laser Diode Arrays

Abstract

We report and analyze the supermode switching with current injection found for coherently-coupled dual-element vertical cavity surface emitting laser arrays. The output power, spectral characteristics, and far-field mode profile are measured for a range of bias current operating conditions. The couplinginduced enhanced output power from an in-phase or out-of-phase supermode is confirmed when approximately equal currents are injected into each array element. We observe that the coherent supermode switches from out-of-phase to in-phase supermode with increasing equal current injection. The switching is found to be consistent with coupled mode theory and a 1-dimensional spatial supermode model. The calculated modal gain of the out-ofphase and in-phase array supermodes are consistent with the observed switching of the coherent supermodes.

Analysis of Coherence and Coupling in Vertical Cavity Surface Emitting Laser Arrays

“…First, perpendicular to the coherent ridge (I 1 ∝ −I 2 ) but within the coherent region the phase has a smoothly varying gradient, indicating beam-steering and non-Hermitian modes [18,19]. Second, at higher currents along the coherent ridge (I 1 ∝ I 2 ) the phase tends to be relatively constant except in the region of low |κ i | and low peak ratio at approximately (I 1 , I 2 ) = (4.5, 5.2), where a discontinuity of approximately 180 • is found, as would be expected for a transition from one array supermode to the other [12].…”

“…One recently proposed method is a Fourier-method beam profile analysis [9] that can provide insight into the array coupling, lasing mode suppression ratio, and inter-cavity phase difference in a simple but resilient manner [10]. Another is optical power analysis that exploits the coherent power enhancement effect to estimate the imaginary coupling coefficient from the strength of the power enhancement effect [7] using either conventional modeling techniques [11,12] or machine learning methods [13]. In this work we use output power and beam analysis to quantify the effects of coherence for photonic crystal VCSEL arrays.…”