Electrically driven lasing of a topological defect in a vertical cavity laser array

We present electrically driven lasing from a topological defect in a vertical cavity laser array, realizing a Su-Schrieffer-Heeger Hamiltonian. We investigate the threshold behavior and demonstrate a roadmap towards efficient topological laser devices.

Topological insulators are a fascinating and relatively new class of materials that are conducting at the surface while they are insulating in the bulk. After a first demonstration in high-mobility electron transport [1], [2], the concept has been extended to a range of physical systems including cold atoms and photonics. Today, topological photonics is a fast growing field of physics, which covers a wide range from fundamental physics to applied photonic engineering and potential industrial applications. After implementations of non-trivial topologies in linear band structures [3], [4], [5], [6], the field has moved towards non-Hermitian physics where Parity-Time (PT) symmetric photonic systems play a crucial role [7], [8]. In this context, topological lasers have been envisaged [9] and realized [10] in arrays of coupled ring resonators. While even the electrical pumping has been technologically possible here, this system suffers from the fact that the outcoupling of light is fundamentally limiting the device performance. Therefore, people have looked for ways to transfer the powerful concept of topological lasers to industry-friendly vertical cavity surface emitting lasers. Using the crystalline topological insulator model [11], it has been shown that injection locking is possible here to obtain coherent laser emission from a large array of vertical laser resonators [12]. This work focusses on the electrical operation of such coupled resonator networks to demonstrate the potential for a new generation of laser devices. In order to simplify the structure, we have implemented a topological domain boundary defect in a one-dimensional Su-Schrieffer-Heeger (SSH) chain of vertical resonators [13], [14]. The sample consist of p-i-n doped GaAs/AlAs-based distributed Bragg reflectors surrounding a cavity region hosting InGaAs quantum wells. The resonator lattice is made of coupled single resonators with a diameter of 3.5 µm, which are fabricated using electron beam lithography and subsequent plasma etching.