Spectral flattening by an all-fiber acousto-optic tunable filter

Abstract

An acousto-optic notch filter based on modal coupling in a two-mode optical fiber is used to flatten the spectrum of a fiber laser. The FWHM bandwidth is optimized so that only one acoustic frequency is needed. At 1090 nm the spectral variation is reduced from 4 dB to less than 0.3 dB within a bandwidth of 6 nm.