Quasi PT-Symmetric Edge-Emitting Lasers Outperform PT-Symmetric Ones

In recent years, engineering the spatial distribution of optical gain and loss has emerged as a new paradigm for tailoring light transport, trapping, and its interaction with matter. In this regard, it was shown that the notion of PT-symmetry can be employed to build new on-chip laser devices that operate in single longitudinal/transverse mode. Until recently, however, obtaining realistic power output and beam qualities from these systems was impossible. A recent study on quasi-PT-symmetric (q-PTS) lasers has changed this landscape by demonstrating up to 0.5 W output power with a high-quality Gaussian beam profile. In that work, PTS was implemented only for the higher-order mode in what can be considered a two-mode supersymmetric laser. Encouraged by these results and to present a clear roadmap for building practical chip-scale lasers with high performance, here we present a detailed comparison between the performance of PTS and q-PTS lasers in terms of power, mode filtering, and beam quality. Our experimental results, which are also supported by theoretical analysis, indicate that both q-PTS and PTS lasers scale similarly in terms of output power levels as a function of the pump current. However, when it comes to mode filtering and beam quality, our results clearly indicate that quasi-PTS lasers outperform PTS counterpart devices by a large margin. This can be explained by noting that while PTS geometry provides modal filtering for the higher order modes in the lasing cavity, it introduces side lobe contribution from the passive cavity which degrades the far-field emission pattern.