| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of parts in the transmission path of a main signal and a transmission loss in an optical fiber amplifier, by making an isolator at the light exit side of the (X)th step function as an isolator at the light entry side of the (X+1)th step of light direct amplifiers which are connected to each other in series. SOLUTION: An optical fiber amplifier (EDFA) 11 as a preamplifier is provided with a photocoupler 14 having a wave selection function, an isolator 15, an optical fiber (EDF) 16 and a photocoupler 17 in this order. Light exciting sources 18, 19 are connected to the photocouplers 14, 17 and an isolator is not arranged at the light exit side. An EDFA 12 as a postamplifier is the same as the EDFA 11 and has an isolator 21 at the light entry side. The light entry side isolator 21 functions also as the light exit side isolator of the EDFA 11 to prevent an oscillation caused by that the reflected light goes and returns in the EDF 16 and a passing loss caused by the presence of the isolator at the light exit side of the EDFA 11. |
