Aluminosilicate glass waveguide platform for connecting optical fiber sensors embedded in composite materials

Abstract

In this paper, the building blocks for a smart glass connector platform are presented. The connector is meant to connect optical fibers, which cannot be connected using conventional connector or splicing technology, e.g. optical sensing fibers embedded in composite structures for structural health monitoring purposes. We are setting up a technology platform using aluminosilicate glass substrates as interposer between 2 optical fibers that need to be connected. Using femtosecond laser technology, this interposer can be equipped with basic building blocks such as low-loss intermediate single mode waveguides, couplers and Bragg grating sensors. To this end, femtosecond laser-written waveguides are inscribed in aluminosilicate glass (Xensation (R) Cover float glass) and the laser parameters are optimized. Waveguides with estimated propagation losses of 0.65 dB/cm are obtained and are subsequently used to make couplers in glass. These couplers can be tuned in coupling ratio between 87:13 and 15:85 by varying the coupling length from 1 to 4.5 mm at a pitch of 17 mu m. In addition, fs-laser written Bragg gratings were manufactured, with the goal to add monitoring capabilities to the interposer. These were realized by modulating the fs-laser pulse train and as such a reflectivity up to 5.9% was achieved in the C-band for 23 mm long Bragg gratings. When properly designed, these can be made compatible with standard read out equipment for fiber Bragg gratings (FBGs).