A birefringent active fiber laser sensor includes one or more fiber lasers 12, 14, 16, each having a pair of Bragg gratings 18, 20, embedded in a fiber 10 and excited by a common pump light 30. At least one of the lasers 12, 14, 16 has a laser cavity wit a predetermined birefrigence and a lasing light at a first lasing frequency along a first polarization axis, and at a second fusing frequency along a second polarization axis. A difference frequency between the first and the second lasing frequencies is related to the magnitude of the birefringence, and the birefringence varies in response to a perturbation. Output light 104 from each of the lasers 12,14,16 is fed to a defraction grating 106 which splits the beam 104 into different wavelength groups, each group having the two lasing frequencies and polarizations of a given laser. Each wavelength group is fed to a corresponding analyzer 122-126 which combines the first and second frequencies and polarizations for each laser to form a lower difference or "beat" frequency, thereby allowing lower frequency detection devices 138-142 to be used.