Surface Plasmon Resonance Sensor Based on a Tapered Multimode Fiber With a Long Inner Air-Cavity

In this letter, a surface plasmon resonance sensor based on a tapered multimode fiber with a long inner air-cavity is proposed and demonstrated for refractive index measurement. The inner air-cavity in multimode fiber is formed by etching the fiber end, followed by fusion splicing it with another section of unetched multimode fiber before being tapered. The tapered fiber surface is coated with a Cr + Ag metal layer of similar to 50 nm by means of magnetron sputtering. The experimental results obtained show that the sensor has good refractive index sensitivity of similar to 3137.68 nm/RIU in the refractive index range of 1.335-1.37. The device is compact and has good robustness and operation durability.