Layered coaxial transmitter optical subassemblies (TOSAs) with a support bridge therebetween may be used in an optical transmitter or transceiver for transmitting optical signals at multiple channel wavelengths. The coaxial TOSAs may include cuboid type TO laser packages having substantially flat outer surfaces that may be mounted on substantially flat outer surfaces on a transmitter or transceiver housing or on the support bridge. The support bridge supports and isolates one layer of the TOSAs mounted over another layer of the TOSAs such that the TOSAs may be stacked to fit within a small space without sacrificing optical coupling efficiency.