High sensitivity multimode–multimode–multimode structure fiber sensor based on modal interference

A novel double-parameter sensor based on a multimode–multimode–multimode (MMM) fiber structure has been proposed and experimentally demonstrated. The principle of operation depends on the effects of a series of interference signal superposition, which include core–core mode interference and core–cladding mode interference. Three dips in the transmitted spectrum of the MMM fiber structure can be observed due to the modal interference effects. The high temperature sensitivities are 0.0771 nm/°C, 0.152 nm/°C and 0.0582 nm/°C at the three dips of 1555.65 nm, 1560.48 nm and 1550.12 nm respectively from 20 °C to 70 °C. The refractive index sensitivities are 54.33 nm/RIU, 108.23 nm/RIU and almost 0 nm/RIU from 1.34 to 1.39 at the same three dips. The sensor reveals the advantages of easy fabrication and low cost.