An optical comb filter has polarizers placed before and after two or more birefringent elements, each having a fixed retarder and an aligned tunable liquid crystal. The birefringent elements are equal in birefringence and thickness and are tuned in unison. Wavelength-dependent polarization state changes are contributed by retardation in unequal proportions on the fast and slow axes of the successive birefringent elements. The filter is tolerant of rotational alignment errors. A two element filter uses angles of 22.5 and 67.5.degree.; a three element version has 12.5, 45 and 77.5.degree.; and a four element filter has 7.5, 29.5, 60.5 and 82.5.degree.; all these angles being .+-.5.degree..