Resonant bio- and chemical sensors using low-refractive-index-contrast liquid-core Bragg fibers

We review design principles and experimental realization of the resonant sensors that use low-refractive-index-contrast Bragg fibers filled with liquid analytes. Such fibers have been recently demonstrated using polymer/polymer, glass/air and polymer/air material combinations. Low-refractive-index-contrast Bragg fibers have narrow bandgaps whose spectral position is highly sensitive to the value of the real part of the analyte refractive index filling the fiber core. We demonstrate theoretically and experimentally that when Bragg fiber is operated in the radiation loss dominated regime it can be used as a highly sensitive sensor of changes in the real part of the analyte refractive index. The experimental sensitivity of the proposed sensor is ∼1400 nm/RIU, which is comparable to those of the waveguide-based plasmonic sensors. Finally, we experimentally explore the possibility of using low-refractive-index-contrast Bragg fibers to detect changes in thicknesses of thin layers deposited directly on the inner surface of the fiber core. A moderate sensitivity of ∼0.9 nm/μm is reported due to the poor overlap between core guided modes and the coated layer.