Compact in-fiber mode adapter based on double-cladding fiber for multimode fiber access networks

A simple method for coupling light from a laser diode (LD) to multimode fiber (MMF) by using a compact in-fiber mode adapter, which is constructed with double-cladding fiber is presented, for the first time. Strong cladding-mode resonance across the thin-thickness inner cladding is used to excite the cladding modes. Principle of proposed mode adapter is theoretically investigated and its performances are experimentally verified by measurement results. By comparing the direct connection between LD and MMF, the coupling efficient of transmission power is improved by using our proposed adapter.