Tunable add/drop filter for CWDM system using cladding mode coupling assisted by long-period fiber gratings

We propose a tunable fiber add/drop filter suitable for coarse wavelength division multiplexing (CWDM) systems. The light coupling between two fibers was performed through the cladding modes assisted by two identical long-period fiber gratings (LPGs). Experimentally, 75% net coupling efficiency was achieved and the side lobes were suppressed by -24 dB.