Programmable wavelength line switches and routers based on a complementary wavelength switch (CWS) building block are described for switching optical signals of different wavelengths between signal lines, with each carrying multiple wavelengths. The CWS building block is based on a complementary bandpass filter structure. The reconfigurable wavelength routers described allow any of a plurality of wavelengths on any line to be switched to any output line by programming the filters accordingly. The various implementations described are useful for wavelength division multiplexing (WDM), dense WDM, and ultra dense WDM optical communications systems, as well as for on-chip interconnects and optical signal processing.