A Controllable Plasmonic Resonance in a SiC-Loaded Single-Polarization Single-Mode Photonic Crystal Fiber Enables Its Application as a Compact LWIR Environmental Sensor.

Near-perfect resonant absorption is attained in a single-polarization single-mode photonic crystal fiber (SPSM PCF) within the long-wave infrared (LWIR) range from 10 to 11 μm. The basic PCF design is a triangular lattice-based cladding of circular air holes and a core region augmented with rectangular slots. A particular set of air holes surrounding the core is partially filled with SiC, which exhibits epsilon near-zero (ENZ) and epsilon negative (ENG) properties within the wavelength range of interest. By tuning the configuration to have the fields of the unwanted fundamental and all higher order modes significantly overlap with the very lossy ENG rings, while the wanted fundamental propagating mode is concentrated in the core, the SPSM outcome is realized. Moreover, a strong plasmonic resonance is attained by adjusting the radii of the resulting cylindrical core-shell structures. The cause of the resonance is carefully investigated and confirmed. The resonance wavelength is shown to finely shift, depending on the relative permittivity of any material introduced into the PCF's air holes, e.g., by flowing a liquid or gas in them. The potential of this plasmonic-based PCF structure as a very sensitive, short length LWIR spectrometer is demonstrated with an environmental monitoring application.