Flexible, Low-loss Waveguide Designs for Efficient Coupling to Quantum Cascade Lasers in the Far-infrared

We coupled linearly polarized and azimuthally polarized Terahertz quantum cascade lasers (QCLs) to the low-loss optical modes of hollow core waveguides having a sequence of different metallic or dielectric inner coatings. The latter waveguides have been specifically designed to force the propagation of a dominant optical mode once the thickness (d) of the inner dielectric coating is properly chosen. Our results demonstrate that both the TE01 and the TE11 modes can be easily converted to a hybrid one when d > 6 mu m allowing the propagation of THz QCL beams with transmission losses as low as 1.5 dB/m, bending losses < 1.1 dB and reasonably high coupling efficiencies (87%)

Coupling external cavity mid-IR quantum cascade lasers with low loss hollow metallic/dielectric waveguides

We report on the optical coupling between hollow core waveguides and external cavity mid-IR quantum cascade lasers (QCLs). Waveguides with 1000 mu m bore size and lengths ranging from 2 to 14 cm, with metallic (Ag)/dielectric (AgI or polystyrene) circular cross-section internal coatings, have been employed. Our results show that the QCL mode is perfectly matched to the hybrid HE11 waveguide mode, demonstrating that the internal dielectric coating thickness is effective to suppress the higher losses TE-like modes. Optical losses down to 0.44 dB/m at 5.27 mu m were measured in Ag/polystyrene-coated waveguide with an almost unitary coupling efficiency

Integrating THz quantum cascade lasers with flexible dielectric-lined hollow metallic waveguides:Moving beyond free space optics

We demonstrate a THz optical delivery system capable of supplying a low divergence HE11 Gaussian beam at a distance of >500mm from the facet of a THz quantum cascade laser. This is achieved by optimising the optical coupling to an external hollow flexible polystyrene-lined Ag waveguide, by utilising a monolithically integrated cylindrical metal waveguide in the laser mounting block. This is shown to achieve >80% coupling efficiency between the two waveguides, whilst maintaining the spectral integrity of the laser. A comparison with other excitation geometries, such as bare laser excitation, as well as a laser with a facet coupled silicon lens, is also analysed

Research data supporting "Efficient coupling of double-metal terahertz quantum cascade lasers to flexible dielectric-lined hollow metallic waveguides"

Supporting data for paper "Efficient coupling of double-metal terahertz quantum cascade lasers to flexible dielectric-lined hollow metallic waveguides", available at: http://dx.doi.org/10.1364/OE.23.026276. Data were taken between May 2014 and June 2015.This work was supported by the EPSRC [EP/J017671/1]