HIGH-SENSITIVITY AND TEMPERATURE-INSENSITIVE REFRACTOMETER BASED ON TNHF STRUCTURE FOR LOW-RANGE REFRACTIVE INDEX MEASUREMENT

Refractive index (RI) measurements find extensive use in biochemical sensing field. However, currently available RI sensors exhibit excessive temperature crosstalk and have low sensitivity in the low RI range. To solve this, a high-sensitivity and temperature-insensitive refractometer based on a tapered no-core-hollow-core fiber (TNHF) structure is proposed for low-range RI measurement. The TNHF comprises two Mach-Zehnder interferometers that are introduced within the tapered nocore fiber and hollow-core fiber, thereby establishing a composite interference. The results of an experimental evaluation demonstrate that maximum sensitivities of 482.74 nm/RIU within an RI range of 1.335 ∼ 1.3462 can be achieved, which is greater than that achieved using a traditional modal interferometer structure. Significantly, the refractometer exhibits ultra-low temperature sensitivities of 0.062 dB/◦C and 6.5 pm/◦C, which can alleviate the temperature crosstalk. The refractometer can be realistically applied in many fields requiring high precision RI measurement due to its advantages of low cost, ease of manufacture, high sensitivity, and temperature insensitivity.