Parity-time (PT) symmetry is an intriguing phenomenon in quantum mechanics, whereby a non-Hermitian Hamiltonian that obeys PT symmetry can exhibit completely real eigenvalues. In recent years, the extension of PT symmetry into the field of photonics has led to a plethora of new class of photonics devices that operate based on PT-symmetric exceptional points (EPs), such as PT-symmetric lasers, EP-enhanced sensors, and coherent perfect absorbing (CPA) anti-lasers.

Among these novel devices, PT-symmetric lasers are especially attractive from the perspective of practical applications, as the optical coupling in the system can be engineered to achieve enhanced side mode suppression without compromising the lasing threshold and the fabrication complexity. However, single-mode lasing in PT-symmetric micro-cavity lasers has so far only been demonstrated in systems fabricated by conventional top-down approaches. Meanwhile, bottom-up growth of III-V laser cavities has recently emerged as a promising alternative to the conventional top-down fabrication method, as it can potentially realise micro-cavity lasers with superior sidewall qualities, which is crucial to laser performance especially at the submicron dimensions. 

In this project, we aim to explore PT-symmetric lasing in III-V semiconductor micro-cavity lasers that are epitaxially grown on their substrates, free from any etching-induced damage. In particular, we aim to demonstrate performance improvements by exploiting some of the unique features of bottom-up grown laser cavities, such as coupling strength tuning by engineering the cavity sidewall facets, and enhanced lasing efficiencies due to the superior sidewall facet quality.