Incident light rays (11) given from an optical fiber (10)
are converted into parallel light rays (12) by a collimator lens (2).
The parallel light rays (12) are demultiplexed in accordance with wavelengths
by a diffraction grating (3). After the demultiplexed light rays arrive
at the collimator lens (2) again, the light rays are converted into convergent
light rays (14) and converged into a photo acceptance element array. Because
the converging/image-forming positions of respective channels are arranged at irregular
pitches in accordance with wavelengths, signals of the channels can be taken out
accurately and efficiently from photo acceptance elements respectively when the
photo acceptance elements are provided in the converging/image-forming positions respectively.
