Improved designs of optical multiplexing/demultiplexing module are disclosed for use in multiplexing a composite optical signal into respective individual channels or wavelengths or demultiplexing individual channels or wavelengths into a composite optical signal. According to one embodiment, the optical multiplexing/demultiplexing module comprises an array of collimators, an array of optical filters and an array of mirrors. The collimators are boned to a common substrate after being aligned with a respect optical filter. Different from the prior art devices, the aligned positions of the collimators are secured or held up by preformed wedges. A bonding agent is then applied only to respective contacts between the collimators and the wedges. The wedges are further bonded to a common substrate to secure the collimators.