Sensor Properties and Surface Characterization of Silver-deposited SPR Optical Fibers

A Gold-Deposited Surface Plasmon Resonance-based Optical Fiber Sensor System Using Various Light-Emitting Diodes

“…The deposited Au film has a geometric thickness distribution in which the maximum value (45 nm) represents the thickness of the deposited metal. [49][50][51][52] The uncertainty of the Au thickness was less than 0.2 nm. The sensor element and Teflon tubes for sample inlets and outlets were fixed in a glass tube (12 cm long and 0.3 cm in diameter) with resin to form a sensor cell.…”

“…The preparation of the sensor elements of the metal-deposited optical fibers has previously been reported. [49][50][51][52] A part (10 cm long) of the clad and the jacket of a step-index multi-mode optical fiber (Showa Electric Wire & Cable NJ-PF200/300) was removed by immersing the optical fiber in concentrated sulfuric acid. A Au film was deposited on half of the core (200 μm in diameter) of the optical fiber by evaporation of Au (Ishifuku Metal Industry, >99.99%) at a rate of 1.0 nm/s in a high vacuum (< 6 × 10 -4 Pa) at room temperature.…”

“…We have also considered the meridional rays and assumed a single reflection without a range of incident angles in the metal-deposited multi-mode optical fibers with Au, Ag, Cu, and Al for simplicity. 47,[49][50][51][52] We calculated the response curves of the sensors with these metal films having a geometric thickness distribution. 47,[49][50][51][52] The theoretical response curves of the Au-deposited optical fiber sensor by using the three light wavelengths (563, 660, and 940 nm) without a wavelength distribution were calculated from the following Eqs.…”

“…This is based on the simple assumption that the reflectivity in the angle range (θ ± Δθ) of SPR becomes zero if a single reflection is employed without a range of angles, which is in spite of an angle distribution in the SPR spectrum in a multiple reflection, and the range of incident angles in the multi-mode optical fiber. 47,[49][50][51][52] The intensity distribution of the LED used in the theoretical calculations may be narrower than the actual distribution. The theoretical response curves have slight asymmetrical shapes caused by the responses of the thinner parts of the films at higher refractivities.…”

“…50 The sensor properties of Al-deposited and Ag-deposited SPR optical fibers were studied thoroughly along with the surface characterization of these metal films by atomic force microscopy and X-ray photoelectron spectroscopy. 51,52 These sensors promise the development of a new analytical technique for use in SPR sensing applications.…”