VARIABLE LIGHT ATTENUATOR

摘要

A variable light attenuator consisting of a Mach-Zehnder interferometer in which high precision feedback control can be carried out with high response by controlling loop gain to compensate for the nonlinear characteristics of attenuation amount. The variable light attenuator (122), for measuring the intensity of output signal light from the attenuator and performing feedback control on attenuation amount so that a desired intensity is attained, comprises means (211, 212) for delivering an output level measurements depending on the intensity of output signal light, means (220, 221, 213) for controlling attenuation amount of the variable light attenuator (122) depending on the difference between the output level measurement and a desired output level target value, and means (220, 214, 216) performing feedback control to compensate for the nonlinear characteristics of loop gain varying depending on the attenuation amount of the Mach-Zehnder interferometer.