Fabrication of Bragg Gratings on the End Facet of Standard Optical Fibers by Sputtering the Same Material

A sputtering process has been applied to deposit quarter-wavelength stacks on the end facet of cleaved optical fibers by using only one sputtering target. Standard multimode optical fibers were used as substrates to fabricate broadband filters, and the experimentally measured spectral responses of these devices are shown. Periodical changes in the refractive index of the coating have been achieved by changing the vacuum chamber pressure. A reflected peak with a full-width at half-maximum of 20 nm centered at 440 nm has been obtained, which provides a good structure for the development of optical fiber sensors working with the wavelength detection technique. This optical structure can be used for several purposes: as tunable wavelength filters or optical fiber sensors or to improve the performance of fluorescence sensors. A theoretical analysis of these structures corroborates the experimental results and allows some rules to be obtained.