Topological insulator vertically-emitting laser array

We present the first experimental demonstration of a topological insulator VCSEL array. Our laser consists of 30 emitters, emitting in a single frequency, displaying interference proving that the emitters act as a single laser.

Topological insulators are systems exhibiting edge conductance that presents immunity against disorder and defects. Initially, this concept was related to electrons in condensed matter, but recently, this plentiful phenomenon was demonstrated in many wave systems such as photonics, cold atoms, acoustics and more. Several years after establishing that topological properties can endow the transport of light with immunity against scattering from imperfections, it was suggested to utilize topological platforms to force injection locking of many semiconductor laser emitters. It was proposed [1],[2] that proper design of a multi-laser array can lead to an edge mode that must flow from one laser to another, force injection locking despite some inevitable variations in the resonators, and eventually make all the elements lase together as a single coherent high power source. This idea was subsequently demonstrated [3],[4] in an array of asymmetrically coupled ring resonators [5], based on standard semiconductor laser technology [13]. Since then, topological insulator lasers were demonstrated in a variety of configurations, e.g., topological quantum cascade laser with valley edge modes [6], topological bulk laser based on band-inversion-induced reflection [7], and a topological insulator laser with next-nearest-neighbor coupling [8]. It is now clear that the topological insulator laser is currently the most promising application of topological photonics, with many new ideas emerging, for example, utilizing topology in synthetic dimensions to force an array of semiconductor lasers to emit mode-locked pulses [9].