Dependence of Beam Quality on Optical Intensity Asymmetry in In-Phase Coherently Coupled VCSEL Array

Abstract

Dependence of beam quality on optical intensity asymmetry among elements in in-phase coherently coupled vertical cavity surface emitting lasers array is analyzed using the finite-difference time domain solutions software. The analysis results reveal that the coupling efficiency of in-phased array decreases and the divergence increases as the level of optical intensity asymmetry increases. Furthermore, an addressable separated-contact three-element triangular in-phased array is fabricated and measured to verify the analysis. The array exhibits a relatively high of coupling efficiency of 24% and a near-diffraction-limit divergence of 3.2° (1.12 times of the diffraction limit, D.L.) when the optical intensity of each element is adjusted to be uniform. By degrading the optical intensity symmetry, the coupling efficiency decreases to 17.07% and the divergence increases to 4.03° ( $1.37\times \text {D.L}$ .). After that, a much larger $10\times 10$ array exhibiting in-phase characteristics is produced and its beam quality and optical uniformity are measured and discussed. Analysis and experiment results demonstrate that symmetric optical intensity among elements is essential for in-phased array to achieve high beam quality. Employing separate contacts in the array is proved an effective way to obtain uniform optical intensity and achieve high beam quality.