We propose a new type of dynamically tunable birefringence comb filter based on a semiconductor optical amplifier Sagnac loop interferometer. By optically modulating the birefringence of the amplifier, we demonstrate a tuning of the output wavelengths. The shift of wavelength increases monotonically with the power of the control light until saturation occurs. The tuning relation is independent of the comb spacing governed by the length and birefringence of the polarization maintaining fiber inside the loop. A tuning range up to 59% of the comb spacing has been achieved at 18.5 dBm input power.