  Long-wave infrared (LWIR, 8-14 um) photonics is a rapidly growing research
field within the mid-IR with applications in molecular spectroscopy and optical
free-space communication. LWIR-applications are often addressed using rather
bulky tabletop-sized free-space optical systems, preventing advanced photonic
applications such as rapid-time-scale experiments. Here, device miniaturization
into photonic integrated circuits (PICs) with maintained optical capabilities
is key to revolutionize mid-IR photonics. Sub-wavelength mode confinement in
plasmonic structures enabled such miniaturization approaches in the
visible-to-near-IR spectral range. However, adopting plasmonics for the LWIR
needs suitable low-loss and -dispersion materials with compatible integration
strategies to existing mid-IR technology. In this work we further unlock the
field of LWIR/mid-IR PICs, by combining photolithographic patterning of organic
polymers with dielectric-loaded surface plasmon polariton (DLSPP) waveguides.
In particular, polyethylene shows favorable optical properties, including low
refractive index and broad transparency between ~2-200 um. We investigate the
whole value chain, including design, fabrication, and characterization of
polyethylene-based DLSPP waveguides and demonstrate their first-time plasmonic
operation and mode guiding capabilities along s-bend structures. Low bending
losses of ~1.3 dB and straight-section propagation lengths of ~1 mm, pave the
way for unprecedented, complex on-chip mid-IR photonic devices. Moreover,
DLSPPs allow full control of the mode parameters (propagation length and
guiding capabilities) for precisely addressing advanced sensing and
telecommunication applications with chip-scale devices.
