Refractive index sensing performance of a Bragg grating built up on the tip of an optical fiber by reactive sputtering


Bragg gratings have been fabricated by means of sputtering on the end facet of standard multimode optical fibers towards development of refractometers. Tin oxide was selected as the coating material, and argon and oxygen were used as sputtering gases. Changes on the refractive index of the material were achieved by varying the oxygen percentage in the sputtering gas flow. A reflected peak centered at 586 nm with a full width at half maximum of 70 nm has been obtained, which provides a good structure for the development of wavelength modulated optical fiber sensors. The sensitivity of this structure to the refractive index of the surrounding medium has been studied, obtaining a linear sensitivity of 173 nm/RIU, for refractive index varying from 1.333 to 1.442.

Experimental Set-Up and Fabrication

For the corresponding experiments, multimode standard communications fibers (62.5/125-μm core and cladding diameters, respectively), a 2xl (50:50) splitter and an optical spectrometer (HR4000 from OceanOptics Inc.) have been used. The light source was a halogen white light source (ANDO AQ- 4303B) and it launches light into one arm of the splitter. The output arm of the splitter is connected, by means of an optical feedthrough, to a MMF pigtail placed inside the vacuum chamber of a Pulsed DC Sputtering System (Nadetech Inc.). Tin oxide was deposited onto the cleaved end facet of that MMF pigtail, which is centered with respect to the cathode and placed parallel to the target surface of the sputtering system. Then, the reflected light travels back through the splitter and it is collected by the spectrometer in a reflection set-up.


Keywords: Optical fiber sensors; Bragg gratings; Optical fibers; Optical device fabrication; Optical refraction; Optical variables control; Diffraction gratings; Bragg reflectors; Wavelength filtering devices; Transparent conductive coatings