an interleaver comprises a serial array of optical elements to which a multichannel , continuous spectrum , composite signal is input and two multichannel , non - continuous spectrum , composite signals are output . two embodiments are disclosed . one such embodiment provides output composite signals which are spectrally symmetric in that each such non - continuous spectrum contains the same number of channels albeit of alternating center wavelengths . the other such embodiment provides output composite signals which are spectrally asymmetric in that each such non - continuous spectrum contains either a different number of channels or an equal number of channels of narrower or wider passband . each of the preferred embodiments comprises an array of optical elements which split the input composite signal into components of different polarization states , selectively add phase shifts to some of these components and recombine them a number of times . the inventive arrays operate on the incident composite signal light beam to produce interference effects which attenuate the unwanted wavelength components in each composite output signal and reinforce the desired wavelength components .