| 摘要 |
PURPOSE:To obtain an optimum backup system of an excitation light source to provide for emergency. CONSTITUTION:An optical directional coupler 8a, 8b for coupling and separating which couples and separates excited light are connected to front and rear ends of a rare-earth element-added optical fiber 1 which propagates signal light, semiconductor laser units 3a, 3b for excitation in which excited light is made to enter and it is propagated to the rare-earth element-added optical fiber 1 are respectively connected to each ends of the two optical directional coupler 8a, 8b, while a driving circuit 4 which drives either of the semiconductor laser units 3a, 3b for excitation via a changeover switch 7 is provided, a light receiving circuits 5a, 5b for monitoring are connected to the other ends of the light directional coupler 8a, 8b, outputs of light receiving circuits 5a, 5b for monitoring are inputted to comparator circuits 6a, 6b, the outputs are compared with the reference voltage 11, and the changeover switch 7 is controlled so that either of the semiconductor laser units 3a, 3b for excitation are driven by outputs of the comparator circuits 6a, 6b. |
