The present invention provides a WDM optical system that includes a tunable filter for selecting one or more optical channels from a WDM optical signal. A portion of a WDM signal enters a first optical filter stage that exhibits a periodic transmission spectrum and possesses individually tunable filter elements. A second optical filter stage receives throughput from the first filter stage and has a periodic transmission spectrum and individually tunable filter elements. A controller electrically communicates with the optical filter to select individual optical channels from the portion of the wavelength division multiplexed optical signal received through the filter input port; each selected optical channel is output via a filter throughput port. In an exemplary embodiment, each tunable filter element is a micro-ring resonator and the micro-ring resonators in the first filter stage have a different free spectral range (FSR) than the micro-ring resonators of the second filter stage.