IMPROVED OPTICAL FIBER AMPLIFIER CONTROL

摘要

An optical fiber amplifier has a length of active optical fiber (11), into which pump light from a pump laser (23) is injected. The pump laser is locally controlled by a laser monitor diode (25), the pump laser and the laser monitor forming a pump laser module (24). The overall amplification of the amplifier is controlled by two control loops, a feed forward loop and a feed back loop, these two control loops also controlling the pump laser. The feed forward loop gives a fast response and receives as an input signal the output signal of an input monitoring diode (5). The feed back loop gives a slower response and sets the overall gain of the amplifier. The feed back loop uses as an input signal the signal from an output monitoring diode (19). In the feed forward loop the input power level is biased and controlled by a set values from sources (53, 59) to provide a signal corresponding to or substantially agreeing with the pump power which maintains the desired gain, the sources providing offsets of characteristic curves indicating the overall behaviour of the optical amplifier. The pump power level obtained by the conversion is then in a converter (47) converted to correspond to or agree with or to have a behaviour similar to that of the pump monitor signal locally controlling the pump laser. This gives a very fast and accurate control in spite of the non-linear behaviour of the optical fiber amplifier.