Ultra-Broadband Confinement in Deep Sub-Wavelength Air Hole of a Suspended Core Fiber

We demonstrate low loss (0.4043 dB/Km at 1.55 μm) deep sub-wavelength broadband evanescent field confinement in low index material from near IR to mid IR wavelengths with the aid of an specialty optical fiber whilst achieving at least 1.5 dB improvement of figure of merit over the previous design. Plane strain analysis has been conducted to foresee fiber material dependent fabrication challenges associated with such nanoscale feature due to thermal stress. Size dependence of air hole is explained rigorously by modifying the existent slot waveguide model. We report significant improvement of field intensity, interaction length, bandwidth and surface sensitivity over the conventional free standing nanowire structure. The effect of metal layer thickness on surface plasmon resonance sensitivity is explored as well. A method to obtain strong evanescent field in such structure for medical sensing is also demonstrated. The proposed technique to enhance sub-wavelength confinement is expected to be of potential engineering merits for optical nanosensors, atomic scale waveguide for single molecule inspection and ultra-low mode volume cavity.