Low-Loss Connection of Embedded Optical Fiber Sensors Using a Self-Written Waveguide

This letter reports on a new concept for making a low-loss connection to an optical fiber sensor, which is embedded in a fiber reinforced composite material for structural health monitoring. First, a cross section of the composite is made to reveal the end-face of the embedded optical fiber. Then, an external fiber is aligned and an intermediate polymer-based self-written waveguide (SWW) is fabricated between both fibers. This SWW bridges the gap and serves as mode size converter ensuring a low-loss optical connection even if both fibers have dissimilar mode field diameters. The advantage of this approach is that no special care needs to be taken during the composite production cycle not to damage the sensor fiber in- or egress points, since it will be reconnected afterward.