Sensor properties and surface characterization of silver-deposited SPR optical fibers

The response curves and sensor properties of silver-deposited optical fibers with Ag film thicknesses of 20.0 - 80.0 nm based on surface plasmon resonance (SPR) were investigated. The response of the Ag-deposited optical fiber sensor depends on the thickness of the Ag film. The Ag-deposited optical fiber sensors show higher responses than those deposited with Au. The reflection properties of Ag films with thicknesses of 30.5 - 70.2 nm due to the SPR phenomenon were also measured and considered. The surfaces of these Ag films consist of various spherical grains with diameters of 30 - 90 nm and the surface height distribution is almost random, having a value of more than 8 nm. X-ray photoelectron spectroscopy (XPS) showed the presence of very thin (0.3 nm) native oxide layers on the Ag films. The Ag-deposited optical fiber sensor exhibited no change in the sensor properties following prolonged use for 4 months. The response curves of the Ag-deposited optical fiber sensors by use of SPR theoretical equations were calculated and compared with those obtained by experimentation.