Optical passive components comprising: a first optical fiber for outputting pumping light; a second optical fiber for receiving the pumping light and either outputting or receiving signal light; a third optical fiber for either receiving or outputting the signal light; a wavelength selecting filter which transmits therethrough the pumping light and reflects the signal light; a mirror which reflects most of the signal light reflected by the wavelength selecting filter and transmits therethrough a portion of the signal light reflected by the wavelength selecting filter such that the wavelength selecting filter and the mirror form an optical assembly; an optical isolator which passes therethrough the signal light reflected by the mirror so as to output the signal light; and a semiconductor optical detecting device for detecting the signal light transmitted through the mirror; wherein the first, second and third optical fibers are disposed at one side of the optical assembly.