Abstract: A blockless optical multiplexing device and a method of making a blockless optical multiplexing device. The blockless optical multiplexing device comprises at least one unit, where that at least one unit is hermetically sealed in a housing. The unit further comprises a substrate that is placed into a base portion of the housing, a plurality of optical filters that are precisely secured onto the substrate, with one half of the optical filters being separated by an air gap from a second half of the optical filters, an input collimator that is mounted onto the substrate, and a plurality of output collimators that are mounted onto the substrate, with a respective one of the output collimators being aligned and associated with a respective one of the optical filters. In a preferred embodiment, the number of optical channels in the optical multiplexing device is equal to the number of the plurality of optical filters secured onto the substrate.