An optical module for use in detecting a plurality of different wavelengths by
making use of the multiple wavelength selectivity of an etalon. The optical module
includes a semiconductor laser, a lens for converting a beam emitted from the semiconductor
laser into a substantially parallel beam, a beam splitter for splitting the converted
beam into a reflected beam and a transmitted beam, and a light-receiving element
disposed such that one of the split beams is incident thereupon through an etalon,
wherein a center of the reflected beam from the etalon occurring as the beam is
incident upon the etalon is arranged to return to a region other than a beam-emitting
portion of the semiconductor laser.
