| 摘要 |
PROBLEM TO BE SOLVED: To reduce the surge of an amplified output signal despite the sudden fluctuation or the input signal light by varying the loop gain of automatic level control in response to the level of the input signal light given to an optical fiber amplifier in regard to the automatic level control where the monitor signal of the optical output signal amplified by the optical fiber amplifier is fed back to the exciting light of the amplifier. SOLUTION: A comparator 8 compares the monitor signal sent from an output level monitor circuit 10 with the reference voltage 11, controls the current of an excited light source 5 via a current source 6 based on the result of the said comparison, and keeps the optical output of an erbium doped optical fiber amplifier at a desired level. An input fluctuation detection circuit 21 generates a detection signal to send it to a variable value element 22 in response to the level fluctuation of the input signal light that is detected by an optical input monitor circuit 2. The element 22 consists of an FET and varies its resistance value according to a detection signal to limit the gain of the comparator 8. For instance, the element 22 reduces its resistance value to lower the loop gain against a short break. |
