Disclosed herein is a functional tunable multichannel filter which is capable of adjusting channel spacing and/or a wavelength location using polarization controllers (λ/2, (λ/4). The functional tunable multichannel filter includes one or more polarization maintaining fibers, a first polarization controller (λ/2), a second polarization controller (λ/4) and a 3 dB coupler. Additionally, the functional tunable multichannel filter is configured to tune a wavelength and adjust channel spacing by adjusting polarization of an optical signal passing through each of the polarization maintaining fibers using the first and second polarization controllers.