PURPOSE: To average the effects due to dependency on polarized light and to prevent the occurrence of errors due to the polarized-light dependency of an optical switch by periodically changing the amplitude of a pulse current which is made to flow through a semiconductor laser (LD), and changing the polarizing state.
CONSTITUTION: An injection-current controlling circuit 1 applies a pulse signal into an LD 2 in accordance with a timing signal 10A from a timing control circuit 10. Pulse light for measurement is generated. Every time the amplitude of the pulse signal applied to the LD 2 is added, the polarizing state is slightly changed. Thus, the light emitting wavelength of the LD 2 is changed. Since the LD 2 emits the approximately linearly polarized light, the light output of the LD 2 is inputted into a polarization maintaining optical fiber 4 through a lens 3. At this time, the angle between the polarizing plane of the light output from the LD 2 and the X axis (or Y axis) of the polarization maintaining optical fiber 4 is set at 45°. Thus, the state of the polarization can be controlled without using a mechanical movable mechanism.
FUJISAWA HIDEAKI
MIYAZONO TATSUICHI
