| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a multiport coupler, and an optical fiber amplifier, a fiber laser device and a resonator with using the same, capable of achieving high light beam quality to be output. <P>SOLUTION: A multiport coupler 3 includes: an optical fiber for signal light 15; optical fibers for excitation light 25; and a bridge fiber 50 of which one end side is reduced in diameter. The optical fiber for signal light 15 and each of the optical fibers for excitation light 25 are connected to the bridge fiber 50 from the other end side of the bridge fiber 50 which is not reduced in diameter. A refractive index of an inside clad 57 of the bridge fiber 50 is set to be lower than a refractive index of a core 56 and higher than a refractive index of an outside clad 58. If r1 represents an outer diameter of the inside clad 57 on the part which is not reduced in diameter, r2 represents the smallest diameter on the part which is reduced in diameter, NA0 represents a numerical aperture of the core 16 of the optical fiber for signal light 15, and NA1 represents a numerical aperture of the inside clad 57, the following formula is satisfied: (r1/r2)×NAO≥NA1. <P>COPYRIGHT: (C)2012,JPO&INPIT |
