Compact multiple channel multiplexer/demultiplexer devices

Multiple channel multiplexing/demultiplexing devices include an optically transparent optical block seated atop an optically transparent beam-directing member. The optical block includes a plurality of wavelength selective elements, a plurality of reflectors, and at least one imaging optical element. The beam-directing member includes a beam folding mirror and focusing lenses. When the devices are used as demultiplexers, a multi-channel beam is directed into the optical block and relayed in a zigzag pattern onto the wavelength selective elements, which separate selected wavelengths from the beam. The separated wavelengths propagate through the beam-directing member and are focused onto optical receptors.