Wavelength-selective switches (WSSs) having embedded multiplexer or demultiplexer functionality include a stack of planar waveguide circuits (PLCs) in which all but one of the PLCs have identical features consisting of a single waveguide connected to a free space region, further connected to a waveguide array that terminates at the PLC edge facet, which are placed at the front focal plane of a lens, generating a spectrally resolved optical signal at the back focal plane of the lens. Due to the use of a single lens, the spectrally resolved optical signal of all the PLCs are superimposed, differing only by propagation direction. A tilting micro-mirror array at the back focal plane reflects the spectral components, implementing a wavelength-selective switch. The reflected light can couple to any of the remaining PLCs, for multiplexing, or to the different PLC in the stack, which implements the multiplexer/demultiplexer.