Tunable stopband filter by using differential strains in all-fiber acoustooptical filter

This letter presents a tunable stopband filter by using an all-fiber acoustooptical tunable filter (AF-AOTF) subject to differential strains. With the proposed filter, narrow and wide tunable stopbands of 0.4-nm 12-dB bandwidth and 4-nm 12-dB bandwidth, respectively, are demonstrated by experiments. Compared to the conventional approach of simply cascading two stages of AF-AOTFs to produce the same stopband, the proposed filter has improved the tunability of stopband.