Abstract: An arrangement for providing real-time, in-service OTDR measurements in an optical communication system utilizing distributed Raman amplification. One or more of the laser diodes used to provide the pump light necessary to create optical gain is modified to also generate short duration pulses that ride above or below the conventional pump light. These short duration pulses (which co-exist with the pump light within the optical fiber) are used in performing OTDR measurements, with a conventional processing system used to evaluate reflected pulses and create the actual OTDR measurements.

Abstract: An arrangement for providing real-time, in-service OTDR measurements in an optical communication system utilizing distributed Raman amplification. One or more of the laser diodes used to provide the pump light necessary to create optical gain is modified to also generate short duration pulses that ride above or below the conventional pump light. These short duration pulses (which co-exist with the pump light within the optical fiber) are used in performing OTDR measurements, with a conventional processing system used to evaluate reflected pulses and create the actual OTDR measurements.

Abstract: An optical amplifier for amplifying the channel signals of a WDM signal comprises an amplifier arrangement for amplifying a band of the channels. The amplifier arrangement comprises an amplifier (6) and a filter (8). The filter comprises a controllable optical filter having an attenuation characteristic which comprises a region of positive gradient and a region of negative gradient with respect to input frequency. The magnitude and alignment along the frequency axis of the attenuation characteristic is variable, such that the filter can be tuned to provide gain flattening for the amplified band of channels. The filter can be tuned to the requirements of a particular sub-band, whilst identical filters can be used for each sub-band. This invention enables identical filters to be used, and gives good pump power efficiency, as the attenuation of each filter can be controlled to the desired level, thereby avoiding the need for large increases in pump power.