Mode Converter Based on Tapered Insertion of Special Fiber

We propose to use a short fiber insertion of a special fiber between standard fibers as a mode converter, which is controlled by tapering the insertion. The special fiber has a small core or no core and excites cladding modes at the splice with the standard fiber. We have simulated and measured transmission of modes through such a fiber section. Tapering allows one to precisely control the length of special fiber insertion and adds flexibility in obtaining spectra desirable for sensing applications.