Abstract: Fiber cladding surface plasmon resonance (SPR) sensors can be employed in biochemical sensing without the requirement of cladding removal, but with the limitation of lack of architectural variety. In this paper, a new type of cladding SPR sensor construction based on S-type fiber is proposed. The S-type fiber is first fabricated by electrofusion technology, and then coated with a 50 nm gold film on its cladding surface. In the S-type fiber, light is coupled from the fiber core to the cladding, and contacted with the gold film on the cladding surface to form a fiber cladding SPR sensor, thus, realizing the detection of Hg²⁺ molar concentration. The resonance valley wavelength of the SPR sensor changes from 633.03 nm to 645.09 nm as the Hg²⁺ molar concentration increasing from 5 pmol/L to 5 mmol/L. The detection sensitivity reaches 1.382 nm/lg(mmol/L). The manufacture of S-type fiber cladding SPR sensor features with simplicity and can be used for single-mode and multi-mode optical fibers to realize cladding SPR sensors which are especially useful in the field of biochemical detection.

Key words: S-type fiber, optical fiber surface plasmon resonance (SPR) sensing, cladding SPR sensing, heavy metal ion detection