| 摘要 |
PURPOSE:To suppress a transmitted power to a light receiving board of a next stage to be less than a certain value and realize a system with a simple structure when an optical fiber amplifier is used as an optical preamplifier. CONSTITUTION:A WDM coupler 2 couples an input light signal 6 and an exciting laser beam from an exciting laser diode 3 with each other and supplies a coupled light to an erbium-doped optical fiber 1. A light signal emitted from the erbium-doped fiber 1 is divided into an output light signal 7 and a monitoring light signal by an output monitoring branching coupler 4. A control circuit 5 controls a current applied to the exciting laser diode 3 in accordance with the monitoring light signal so as to keep the light output power of the output light signal 7 constant. With this constitution, as the light output is so controlled as to be constant, a transmitted power to a light receiving board of a next stage can be suppressed to be less than a certain value and, further, the system can be constituted with small scale hardware. |
