Optical mode control of surface-plasmon quantum cascade lasers

Surface-plasmon waveguides based on metallic strips can provide a two dimensional optical confinement. This concept has been successfully applied to quantum cascade lasers, processed as ridge waveguides, to demonstrate that the lateral extension of the optical mode can be influenced solely by the width of the device top contact. For devices operating at a wavelength of lambda approximate to 7.5 mu m, the room-temperature threshold current density was reduced from 6.3 kA/cm(2) to 4.4 kA/cm(2) with respect to larger devices with full top metallization.