An optical sub-assembly (OSA) apparatus for use in an optical transmission
system comprises a housing, a plurality of TO-can packaged optical
devices, and a plurality of wavelength selective filters. Each of the
plurality of TO-can packaged optical devices is sensitive to optical
signal of one of a plurality of wavelengths. Each of the plurality of
wavelength selective filters is capable of directing an optical signal of
the one of the plurality of wavelengths in a pre-determined direction.
The OSA apparatus can be used as one of an optical signal receiving
apparatus and an optical signal transmitting apparatus.