Small-scale refractive index sensing based on coreless microfiber operating near the turning around point

A coreless-microfiber sensor operating near the turning around point is proposed and experimentally demonstrated for small-scale refractive index (RI) sensing. Numerical simulations verify the existence of turning around point in the coreless-microfiber as the group effective RI difference between the HE11 and the HE12 modes equals zero. Experimental results show the RI sensitivity of the coreless-microfiber sensor could reach 4037.5nm/RIU around 1.333, which is consistent with the theoretical analysis results. Moreover, with the high sensing sensitivity and flexible design, the coreless-microfiber sensor operating near the turning around point has great significance application on molecular trace detection, especially in the fields of photochemical analysis and bioengineering.