Side-coupled optical fiber devices for sensing applications

We demonstrate experimentally the light coupling between two types of optical fiber devices, including the long period fiber gratings (LPFGs) and fiber tapers. Optical power transfer is achieved through evanescent field coupling between the cladding modes. The output spectra from the LPFG couplers exhibit band-pass/band-rejection pattern, which could be used as add/drop filters. The output spectra from the fiber taper couplers show an interference pattern similar to a Mach-Zehnder interferometer. By fixing the fiber devices in a capillary glass tube, we demonstrated a miniaturized coupler for displacement sensing.