Large-Scale Fabrication and Analysis of Polarization Behavior in VCSELs With Tailored Apertures

While maintaining a stable polarization state is crucial for many optical applications, intentional polarization instability/bistability is also important for certain photonics applications, such as Ising computers or optical neural networks, where polarization bit encoding has been proposed. Vertical-cavity surface-emitting lasers (VCSELs), with their compact footprints and low power consumption, are ideal light sources for such applications. However, while methods of achieving polarization stability are well-known, the engineering of VCSELs with controllable yet easily switchable (unstable) polarization states remains challenging. In this study, we introduce a method of tailoring oxide apertures to compensate for inherent gain anisotropy and yield the desired instability. By fabricating and analyzing the polarization behavior of hundreds of VCSELs with diverse oxide aperture shapes and sizes, we identify clear trends linking aperture designs to polarization tendencies. Firstly, theoretical analysis is applied to investigate the impact of aperture design on the polarization state of multi-mode VCSELs. Subsequently, VCSELs with bespoke aperture designs are fabricated and tested, which then show predictable polarization state and switching. Under varying current injection, VCSELs reveal diverse polarization switching behaviors. The large-scale fabrication and testing conducted in this study provide recommendations for engineers seeking specific polarization behavior, presenting a promising approach to encode information into VCSEL polarization states for computational tasks.