| 摘要 |
PURPOSE:To allow the excitation by a large-output LD light source having a large focusing spot diameter by using a rod-shaped preform as a medium for optical amplification including a rare earth element to expand the effective sectional area for excitation. CONSTITUTION:Both ends of the Er-added optical fiber preform rod 10 which consists of a core part 11 added with the rare earth element and a clad part 12 and has the outside diameter of 40 to 50 times the diameter of an ordinary optical fiber are stretched to form tapered parts 13, 13' and single mode fiber parts 9, 9'. The length of the tapered parts 13, 13' is taken sufficiently longer than the outside diameter of the rod, by which the light signal is propagated at a low loss with substantially no mode conversion received therein. The excitation is executed from the outer periphery or tapered parts 13, 13' of the large-diameter rod-shaped preform 10 in such a manner and, therefore, the focusing light spot of the excited laser is not always required to be <=several mum. The restriction of the condensing spot shape of the LD which is the light source for excitation is relieved in this way and the excitation from the side face of the optical amplifier medium is enabled. In addition, the simultaneous use of plural pieces of the light source for excitation is possible and, therefore, the high optical amplification degree is obtd. |
