| 摘要 |
PROBLEM TO BE SOLVED: To obtain light beams of uniform light intensity by correcting variation in light intensity of both light beams, generated by switching a light beam to two optical paths, due to secular change and temperature variation. SOLUTION: A modulation magnetic field is applied to a Faraday rotator 8 to rotate the polarization direction of linear polarized light incident on the Faraday rotator 8 and emit the linear polarized light, and the light emitted from the Faraday rotator 8 is switched between a first light beam 15a and a second light beam 15b according to the polarization direction. The modulation magnetic field applied to the Faraday rotator 8 is brought under feedback control based upon the light intensities of the first light beam 15a and second light beam 15b to equalize maximum light intensities of the first light beam 15 and second light beam 15b to each other, thereby surely emitting the two light beams having the same light intensity without reference to the assembly state of an optical path switching device 3, secular change, and temperature variation while suppressing a decrease in light use efficiency. COPYRIGHT: (C)2009,JPO&INPIT
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