Optimization of hollow-core photonic Bragg fibers towards practical sensing implementations

Abstract

Hollow-core photonic bandgap Bragg fibers have a wide range of industrial sensing applications. Spectral scalability of the transmission window and detection accuracy are of particular importance in developing practical sensing instrumentations. In this work, we experimentally demonstrate the wavelength scalability of the fiber bandgap positions by simply controlling the fiber diameters and the bilayer thicknesses. In order to increase the spectral sensitivity and improve the detection accuracy of the sensing system, we propose to enhance the sensitivity by optimizing the Bragg fiber geometry. Both theoretical analysis and experimental demonstrations have been performed to verify the methodology. By designing and fabricating Bragg fibers with optimized bilayer thickness contrast, we have significantly enhanced the sensitivity by more than 32%. The optimized spectral sensitivity achieved experimentally in this work is 1850nm/RIU, which, to the best knowledge of the authors, is the highest value for the Bragg fiber-based refractive index sensors. Additionally, the influence of temperature on the sensor performance has been studied, and the temperature stability of our Bragg fiber sensor with aqueous solutions in the fiber core is only 45pm/°C. The presented fiber sensor can inherently integrate optical detection with microfluidics, thus allowing for online monitoring of the refractive index/concentration of many industrial fluids, trace amount of biomolecules, real-time detection of binding and affinity, study of kinetics, with enhanced accuracy.