BLESSAN Tony Mathew : Band engineering and mode selection in a driven-dissipative photonic lattices

Résumé de thèse :

The engineering of specialty lasing systems with unconventional mode structures is one of the modern challenges in the development of integrated coherent sources. The goals are to engineer miniaturised configurations, with high efficiency, and enhanced functionalities. Some examples of successful configurations include Bound States in the Continuum [1], lasing modes with Orbital Angular Momentum [2], the use of Dirac-based band structures [3] and topological lasers [4]. In this work, we address the challenge of engineering and implementing a two-dimensional lattice of coupled photonic micropillars one-dimensional lasing line modes. Such a configuration opens the possibility of implementing densely packed independent lasing modes in a two dimensional matrix.

To engineer line lasing modes in a two-dimensional lattice, we introduce a novel lattice configuration, named the orbital Lieb SP lattice. It is based on a square Lieb lattice that combines micropillars of two different diameters to design orbital bands with a hybrid S and P mode nature. Each micropillar is composed of two dielectric Bragg mirrors confining a l cavity with an InGaAs quantum well. Figure 1(a) displays a schematic of the lattice: B sites with large diameter occupy the corners of a square lattice, while A and C sites, with small diameter, are positioned at the midpoints of the edges of the square structure. The diameter difference leads to different energy confinement resulting in SP mode interactions: px, py orbitals of B sites couple to s orbitals of C and A sites as depicted in Fig. 1(b). This coupling allows for an exotic band dispersion in which each band is dispersive along one direction and flat along the perpendicular one, as shown in Fig. 1(c). Consequently, the eigenmodes are line modes confined in one direction and propagating in the other direction. Here, we experimentally demonstrate the selective lasing into these line modes (Fig. 1(d)). By exciting the lattice with an elongated Gaussian spot along either vertical or horizontal orientations we show lasing along any desired line of the lattice. Figure 1(e) shows the case of lasing in two crossing line modes. Surprisingly, the two modes phase lock producing an exotic mode laser in the form of a cross.

Our results open interesting perspectives in the use of orbital lattices to engineer unconventional lasing configurations and raise questions about the mechanisms behind the mode-locking of orthogonal lasing modes.