An optical sub-assembly 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. A first fluid is caused to flow through the first conduit system. A semiconductor chip includes a power transistor formation region to form a power transistor, a logic circuit formation region to form a logic circuit, and an analog circuit formation region to form an analog circuit. Optionally, the particles may be non-degradable, rigid, of different shapes, and smaller than the gaps but able to bridge them.