SEMICONDUCTOR LASERS

Science, 363, 623–626 (2019)

Supersymmetry (SUSY) emerged within particle physics as a means to relate two fundamentally different classes of elementary particles: bosons (integer spin, Bose-Einstein statistics) and fermions (half integer spin, Fermi-Dirac statistics). Extensions to the Standard Model have also been proposed based on SUSY theory in order to resolve long-standing issues in quantum field theory, including the nature of vacuum energy, origin of mass scales and dark matter. Even though the experimental validation of SUSY is still an ongoing issue, supersymmetric/isospectral techniques have already found applications in low-energy physics, nonrelativistic quantum mechanics, and nonlinear dynamics, to name a few. On the other hand, waveguide laser arrays have been a subject of intense investigations for the purpose of building high-power phase-locked lasers, which are immune to the detrimental effects of nonlinearities or filamentation. Nevertheless, such systems suffer from multimode operation, which in turn leads to a chaotic emission.

Recently, a group led by Dr Mercedeh Khajavikhan in University of Central Florida proposed and demonstrated a scheme for filtering the undesired transverse supermodes of laser arrays by using the SUSY concept. In their proof of the concept experiment, the primary array is comprised of five identical coupled ridge-waveguide cavities. By applying appropriate SUSY transformations, a superpartner index profile can be synthesized with propagation eigenvalues that match the higher order modes of the main array (besides the fundamental in-phase mode). The arrangement was realized on an InP wafer with InGaAsP quantum wells as the gain material. Uniform pumping was applied to the main arrays, while loss was introduced in the superpartner array by blocking the pump beam using a knife edge. Under these pumping conditions, the system emits a diffraction-limited, narrow, and low-divergent beam, as opposed to conventional multi-transverse modes emission. The respective spectrum measurements indicate phase-locking in the fundamental in-phase mode. Their results may pave the way for the design of high-radiance single mode laser arrays, and provide a fertile ground in order to study the interplay between non-hermiticity, nonlinearity, and supersymmetry.

Chuanbo Li (School of Science, Minzu University of China, Beijing, China); Ming Li (Institute of Semiconductors, CAS, Beijing, China)

doi: 10.1088/1674-4926/40/4/040201