Photonic crystal fiber-based plasmonic sensors for the detection of biolayer thickness

The application of metallized photonic crystal fibers in surface plasmon resonance sensors of biolayer thickness is demonstrated. By the judicious design of photonic crystal fibers, the effective refractive index of the fundamental core mode can be tuned to enable efficient phase matching with a plasmon anywhere from the visible to near IR. Among other advantages of the presented sensors we find high sensitivity in the visible and near-IR spectral regions, as well as high coupling efficiency from an external Gaussian beam. Based on the numerical simulations, we present designs using various types of photonic crystal fibers, including holey fibers with and without defect, as well as honeycomb photonic crystal fibers. We find that in addition to the fundamental plasmonic excitation, higher order plasmonic modes can also be excited. In principle, using several plasmonic excitations at the same time can enhance sensor detection limit. Both amplitude and spectral-based methodologies for the detection of changes in the biolayer thickness are discussed. Sensor resolutions of the biolayer thickness as high as 0.039-0.044 nm are demonstrated in the whole 600-920 nm region. Finally, we perform analysis of the effect of imperfections in the metal layer geometry on the sensor sensitivity.