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Helical Microfiber Bragg Grating Printed by Femtosecond Laser for Refractive Index Sensing

A microfiber helical Bragg grating is demonstrated for use in refractive index measurements. The proposed sensor was fabricated using a femtosecond laser-induced multiphoton polymerization technique. The grating was cured along with the microfiber, and its reflection spectra, transmission spectra, refractive index, and temperature cross sensitivity were investigated. The refractive index sensitivities of ~229 and ~120 nm/RIU were achieved, corresponding to high order and fundamental modes, respectively. This helical microfiber Bragg grating exhibits high refractive index sensitivity and good mechanical strength and could potentially be used for optical functionality integration.