A cascaded system of two acousto-optical cells is proposed and experimentally demonstrated for optical notch rejection filtering in the spectral range from 1400 nm to 1600 nm. Two similar paratellurite acousto-optical devices for unpolarized light are used in a free-space gap of a fiber line. Compensation for birefringence in anisotropic paratellurite devices provides a diffraction regime that is insensitive to polarization of light. High extinction ratios up to 40 dB are measured.