Optical multiplexing/demultiplexing module

An optical multiplexing/demultiplexing module for inputting a first linearly polarized beam after exiting a first optical waveguide, and the first beam is collimated by a first lens. A second linearly polarized beam exits a second optical waveguide and is collimated by a second lens. Both beams enter an entrance surface of a uniaxial birefringent crystal. The second beam enters the crystal along an optical path which is changed by a prism. This reduces the distance between the respective points of entrance of the beams. The beams which have entered the crystal are multiplexed at an exit surface of the crystal. A resultant multiplexed beam is converged by a third lens to enter and exit a third optical waveguide.