Image Number 6 for United States Patent #7184621.
A four-channel multi-wavelength transmitter optical sub assembly (TOSA) with an integrated multiplexer is described that includes four lasers, four collimating lenses, a multiplexer, an isolator, a focusing lens, and an optical fiber. The integrated multiplexer comprises three filters in two stages, with each filter combining a transmission and a reflection beam into one beam. Four collimated beams are combined into one beam and then focused onto the fiber by the focusing lens. The optical paths of all channels are short and possibly the same length. The invention allows using either transistor outline (TO) can packaged lasers or lasers in chip on submount. In some embodiments, four coupling lenses that focus the light onto fiber directly can be used instead of the collimating and focusing lenses, providing a more compact assembly. One or more filters can be beam-splitters to relax coating and assembling tolerances, thus reducing the cost.