Abstract: A wavelength slicing apparatus and method includes two filters having passbands offset from each other and from a signal channel. The offset passbands enhance transmission where they overlap and reduce transmission where they do not overlap such that transmission of optical signals in a neighboring channel is suppressed. A third filter having a passband centered on the signal channel frequency may be included to enhance optical signal isolation. Wavelength slicing techniques may be used for channel isolation or passband flattening. Wavelength slicing can be incorporated into wavelength division multiplexing (WDM) optical switching to improve optical isolation between channels during routing, multiplexing and demultiplexing operations.