Method and apparatus for generating a pulse width modulated signal and optical attenuator controlled by a pulse width modulated signal

摘要

An optical attenuator (200) for receiving input radiation (P i ) and attenuating the input radiation (P i ) to provide corresponding output radiation (P o ) comprises: attenuating means (210) for receiving the input radiation (P) and attenuating the input radiation (P i ) to provide the output radiation (P o ) in response to a drive signal. The attenuating means are operable to provide an attenuation dependent upon its temperature. The attenuating means include temperature modifying means (30) for modifying its temperature in response to the drive signal and controlling means (10) for receiving a signal (PR) indicative of attenuation required and for generating the corresponding drive signal. The drive signal is derived from a PWM signal in which each PWM signal cycle corresponds to a frame, a plurality of such successive frames forming a multiframe and the controlling means are operable to modify the duty ratio of one or more frames within each multiframe for providing enhanced resolution attenuation provided by the attenuator.