Modal analysis of capillary optical fibers and their possible applications in sensing

Capillary optical fibers (COFs) recently show great promise due to their simplest structure for different sensing applications. Confinement loss (CL) is one of the key parameters that changes with physical sensing measurands. This paper describes a systemic way to understand different modes in COFs, which is necessary for understanding different sensing mechanisms and to design highly sensitive COF based sensors. Here, the CL of the designed COFs are investigated both analytically and numerically. COMSOL Multiphysics was used to simulate and analyze the loss spectra over the wavelength from 500 nm to 3000 nm. The effects of changing different design parameters such as the radius of air core, relative permittivity, and width of the cladding layer are investigated thoroughly. Single-mode behavior was noticed by changing the permittivity of cladding materials. The findings of this work could be useful to understand the basic sensing mechanism of COFs and hollow core type fibers and optimize their design for realizing highly sensitive COF based sensors.