Realization of surface plasmon resonance sensor in standard optical fibers

A new Surface Plasmon Resonance (SPR) sensor design is proposed and fabricated based on an optical fiber with a photo-written Tilted Fiber Bragg Grating (TFBG) and a thin gold deposited layer. The TFBG allows the transfer of light from the core mode into a multitude of cladding modes, each wavelength corresponding to a different incidence angle. The most pronounced SPR effect was obtained for a gold thickness of 20 nm, however every tested thickness showed SPR at a certain level. To characterize the uniformity of gold films, the coated fiber were imaged using Atomic Force Microscopy (AFM) and showed a high level of graininess, as expected from such thin layers. Scanning Electron Microscope (SEM) images were used to characterize the quality of the gold coating before and after experiments. Despite the high non-uniformity and graininess of gold coating, the angular spread of SPR is as narrow as expected from theory. The sensitivity obtained reaches 454 nm per refractive index unit.