A tunable optical filter filters is provided that has a pair of tunable Bragg grating units optically coupled to respective ports of a 4-port circulator for filtering a selected wavelength band or channel of light from a DWDM input light. Each grating unit includes an array of Bragg gratings written or embedded within a respective tunable optical element to provide a tunable optical filter that functions over a wide spectral range greater than the tunable range of each grating element. The reflection wavelengths of the array of gratings of each respective grating element is spaced at a predetermined spacing, such that when a pair of complementary gratings of the grating elements are aligned, the other complementary gratings are misaligned. Both of the optical elements may be tuned to selectively align each complementary grating over each corresponding spectral range.