| 摘要 |
PROBLEM TO BE SOLVED: To make loads not to be imposed on a control circuit and circuits of next stages when there is an excessive light input by allowing an optical attenuation means to output an output light having a fixed level while increasing an attenuation amount when a driving current is decreased and reducing the attenuation amount when the driving current is incerased. SOLUTION: The light outputted via an optical attenuator(OATT) 10 is branched by an optical coupler 20 and a photodiode(PD) 30 inputs an output light from the coupler 20 and converts it into a current and a monitoring circuit 40 converts this current into a voltage to output it as the power of a light output. A driving current control circuit 50 controls the value of the driving current of a circuit driving the heater of the OATT 10 so that the power of the light output becomes a fixed value. Hereupon, the OATT 10 outputs the output light by attenuating an optical signal which is inputted and the attenuation factor of the OATT 10 has a characteristic in which the attenuation amount becomes the maximum when the driving current which is to be outputted by the circuit 50 is '0' or near '0' and the attenuation becomes smaller as the driving current is increased. |
