Surface-plasmon quantum cascade microlasers with highly deformed resonators

We report the demonstration of surface-plasmon microcylinder quantum cascade lasers with circular and deformed resonators. An improved self-alignment fabrication technique was developed that allows the use of wet etching, necessary to achieve smooth and clean surfaces, in combination with the deposition of the surface-plasmon-carrying metal layer up to the very edge of the resonator, where the optical mode is mostly located. The diameter of the microcylinders ranges from 75 to 180 μm while their deformation coefficient ε ranges from ε=0 to ε=0.32. Circular microcylinder lasers show a reduction of ∼50% of the threshold current density with respect to devices with standard ridge-waveguide resonators. On the other hand, highly deformed microcylinder lasers exhibit a complex mode structure, suggesting the onset of chaotic behavior.