Optical demultiplexer and optical multiplexer for wavelength division multiplex communication

An optical demultiplexer for wavelength division multiplex communication, said optical demultiplexer comprising:

• a light irradiating unit operable to irradiate a spherical wave containing a plurality of light waves with different wavelengths;
• a plurality of light receiving units operable to respectively receive the plurality of light waves contained in the spherical wave;
• a converting lens operable to convert the irradiated spherical wave into a parallel wave;
• a plurality of WDM filters operable to respectively and differently reflect in sequence only one of the light waves from among the plurality of light waves contained in the parallel wave, and to transmit therethrough each of the light waves of the plurality of light waves contained in the parallel wave having a different wavelength than the reflected one of the light waves;
• a plurality of guide lenses operable to converge each of the light waves respectively reflected by said plurality of WDM filters into each of said light receiving units, respectively;
• and
• at least one reflecting unit operable to reflect each of the light waves respectively reflected by said plurality of WDM filters to direct each of the reflected light waves to respectively return to a corresponding one of said plurality of WDM filters in which the reflected light wave was first reflected at least one more time so as to cause each of the light waves having a different wavelength than the light wave reflected by the corresponding one of said plurality of WDM filters remaining together with the light wave reflected by the corresponding one of said plurality of WDM filters to be again transmitted through the corresponding one of said plurality of WDM filters,
• wherein each of the plurality of guide lens is placed at a position so as to be operable to respectively guide one of the plurality of light waves after having been respectively reflected by said plurality of said WDM filters the at least one more time into a corresponding one of said plurality of light receiving units.