An optical fiber that transmits laser beams generated by a laser diode in an
optical
module is provided with a fiber grating. The fiber grating passes most of the laser
beams and reflects some of them to a photodiode provided on the back side of the
laser diode. The photodiode also receives scattered laser beams from the laser
diode. The photodiode outputs a current equivalent to the amount of received laser
beams. An APC circuit controls emission of laser beams by the laser diode based
on this current.
