Disclosed herein is an integrated optical sub-assembly for a diplexer, which can adopt a low-price small aperture isolator by disposing an isolator closer to a ferrule, such that the isolator may be distanced from a laser diode, and so the total cost can be reduced and the construction can be simplified; and an integrated optical sub-assembly for a triplexer, which has simplified construction for reducing the manufacturing costs, and whose exterior dimension can be reduced and the manufacturing can be easier by adopting a ball lens for narrowing the beam width.