Apparatus comprising a quantum cascade laser having improved distributed feedback for single-mode operation

This invention pertains to quantum cascade (QC) lasers, and to apparatus and systems that comprise a QC laser. More particularly, the invention pertains to quantum cascade distributed feedback (QC-DFB) lasers. An article comprising a QC-DFB laser is disclosed. In the QC-DFB laser, an overlying grating structure achieves relatively strong coupling of the guided mode to the grating, and is thus highly effective in inducing single-mode operation even under cw operating conditions. The grating structure includes grooves etched in a plasmon-enhanced confinement layer (PECL) disposed adjacent and in contact with an upper metallic electrode. The grating structure and the PECL are designed such that in the grooves, the laser mode travelling in the waveguide can couple efficiently to the surface-plasmon at the electrode interface. This results in strong modulation of the laser mode, leading to strong modulation of, inter alia, the effective refractive index.