提出一种全光纤带通声光可调谐滤波器结构, 通过在包层腐蚀的单模光纤中引入模式转换器, 来阻断纤芯中原本传输的基模, 并同时将包层模耦合至纤芯中。结果表明, 增加声横波频率, 带通滤波器谐振峰出现“蓝移”现象, 并且, 滤波器谐振峰随着包层半径的增大而减小, 声横波功率的增加可以一定程度增大谐振波峰。在包层半径rcl=32.5 μm, 声横波功率Pa=20 mW, 频率fa=1.5 MHz处获得3 dB带宽为2.13 nm的带通滤波; 调节声横波频率fa从1.2 MHz至1.5 MHz, 可实现85.18 nm波长范围的调谐, 该波长可调谐带通滤波器可以用在增益带宽较大的光纤激光器中。

An all-fiber band-pass acousto-optic tunable filter is proposed. By introducing a mode converter into a cladding-etched single-mode fiber, the fundamental mode transmitted in the core originally is blocked and the cladding mode is coupled in the fiber core at the same time. The results indicate that the band-pass filter has a blue shift when acoustic frequency increases, and the resonant peak of the filter decreases with the increase of cladding radius, moreover, the increase of the acoustic power can also increase the resonance peak of the filter to some extent. Meanwhile, a band pass resonance peak with 3 dB bandwidth of 2.13 nm is obtained when the cladding radius is kept at 32.5 μm, and the acoustic power and frequency are fixed at 20 mW and 1.5 MHz respectively. The tunable wavelength of 85.18 nm can be achieved when the acoustic frequency is adjusted from 1.2 MHz to 1.5 MHz. The device has the potential to be applied into the fiber lasers with large gain bandwidth.