Terahertz quantum cascade laser coupled with high efficiency to the low loss optical modes of cylindrical hollow-core waveguides

We demonstrate that azimuthally polarized micro-ring THz quantum-cascade lasers can be coupled to hollow metallic waveguides with efficiencies >= 96% and perfectly matched with the TE01 waveguide mode, giving attenuation losses < 3dB/m. The use of Ag coated-flexible pipe waveguides allows propagation of either vertically polarized or azimuthally polarized QCL beams with propagation losses as low as 2.1-4.4 dB/m and bending losses lower than 1.2 dB.