Optical switching apparatus is provided for selectively switching first wavelength components of wavelength division multiplexed optical signals from an input port to an output port and one or more corresponding add wavelength components of wavelength division multiplexed add optical signals from an add port to the output port. A Sagnac provides the selective switching. The Sagnac interferometer includes a plurality of phase modulators coupled into the Sagnac loop. Each phase modulator operates on wavelength components and add wavelength components at a predetermined one wavelength of a plurality of predetermined wavelengths to determine whether an output wavelength component is coupled from the input port or the add port to the output port.
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