Shaping the light emission characteristics of laser systems is of great importance in various areas of science and technology. In a typical lasing arrangement, the transverse spatial profile of a laser mode tends to remain self-similar throughout the entire cavity. Going beyond this paradigm, we demonstrate here how to shape a spatially evolving mode such that it faithfully settles into a pair of bi-orthogonal states at the two opposing facets of a laser cavity. This was achieved by purposely designing a structure that allows the lasing mode to encircle a non-Hermitian exceptional point while deliberately avoiding non-adiabatic jumps. The resulting state transfer reflects the unique topology of the associated Riemann surfaces associated with this singularity. Our approach provides a route to developing versatile mode-selective active devices and sheds light on the interesting topological features of exceptional points.
Experimental data for an InP-based 40-stage quantum cascade laser structure grown on a 6-in. GaAs substrate with a metamorphic buffer are reported. The laser structure had an Al0.78In0.22As/In0.73Ga0.27As strain-balanced active region composition and an 8 μm-thick, all-InP waveguide. High reflection coated 3 mm × 30 μm devices processed from the wafer into a ridge-waveguide configuration with a lateral current injection scheme delivered over 200 mW of total peak power at 78 K with lasing observed up to 170 K. No signs of performance degradation were observed during a preliminary 200-min reliability testing. Temperature dependence for threshold current and slope efficiency in the range from 78 K to 230 K can be described with characteristic temperatures of T0 ≈ 460 K and T1 ≈ 210 K, respectively. Lasing was extended to 303 K by applying a partial high reflection coating to the front facet of the laser.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.