Transmissive diffraction grating(s), reflector(s), and multiple optical sources/receivers are arranged such that each one of multiple optical signals at corresponding different wavelengths co-propagating along a multiplexed beam path would: (i) be transmissively, dispersively diffracted at a multiplexed transmission region of a grating; (ii) propagate between the multiplexed transmission region and multiple demultiplexed transmission regions of a grating undergoing reflection(s) from the reflector(s); (iii) be transmissively, dispersively diffracted at the demultiplexed transmission regions; and (iv) propagate between the demultiplexed transmission regions and the sources/receivers along multiple demultiplexed beam paths.