| 摘要 |
PROBLEM TO BE SOLVED: To maintain constant output even if there is any transient change in input light by exercising such a feedforward control that the values of the output of an input signal light detecting means are added to driving signals for a semiconductor laser for excitation through a feedforward compensator. SOLUTION: Such a feedforward compensation that the values of the output from an input light monitor 15 are added to driving signals for a semiconductor laser 14 for excitation at an adder 10 through a feedforward compensator F(s)17 and response speed is thereby improved. Further, the feedforward compensator F(s)17 has the property of reducing output with an increase of input signal light 1. Since there is inverse relation between the level of input signal light 1 and the driving current of the semiconductor laser 14 for excitation in the ALC and further there is nonlinear relationship wherein saturation occurs when the level of input signal light 1 is increased, feedforward compensation is performed in advance in accordance with the property. |
