Magnetically-induced circular-polarization-dependent loss of magneto-optic fiber Bragg gratings with linear birefringence

► The magnetically-induced circular-polarization-dependent loss (MCDL) is introduced. ► The equivalent theoretical model of linearly birefringent MFBGs is proposed. ► Peak MCDLs are proportional to magnetic field and insensitive to the birefringence. ► The MCDL spectrum is measured in an Er-MFBG and the peak MCDL can be up to 1 dB.