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

Abstract

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%)

Fabrication and characterization of improved Ag/PS hollow-glass waveguides for THz transmission

“…Particular candidates of interest include cyclic olefin polymers (COP), polymethylpentene (TPX), and polystyrene (PS) as these polymers can be deposited from solution and exhibit relatively low loss at THz frequencies [13]. In this study, PS was selected as the polymer of choice due to its low absorbance at THz frequencies, simultaneous low loss in the visible and near-IR (NIR) regions, and relative ease of deposition from solution [5][6][7][8]13]. To optimize design parameters, the optical response of Ag/PS coated HGWs at THz frequencies was calculated.…”

“…Recently, improved metalcoated hollow waveguides (HWs) incorporating dielectric thin films for enhanced reflection have shown promise for use as low-loss THz waveguides. One such practical metal/dielectric coated waveguide design is the hollow glass waveguide (HGW), which has been widely used for applications involving low-loss broadband transmission at infrared (IR) wavelengths [5][6][7][8][9][10]. The basic structure of HGWs is shown in Fig.…”

THz waveguide adapters for efficient radiation out-coupling from double metal THz QCLs

“…Recently, hollow core waveguides, with a sequence of different metallic or dielectric inner coatings, with transmission losses as low as 1.5 dB/m [22][23][24], have been coupled with linearly and azimuthally polarized THz QCLs or stitched on the QCL facet [25]. Alternatively, direct coupling of a single-plasmon THz QCL to a polymeric optical fiber made of cyclic-olefin copolymer (COC) has been reported [26], enabling narrowing of the output beam shape.…”