Abstract: An optical amplifier for determining the attenuation of a length of optical fibre (7) to which it is adapted to be connected comprising means (5) to receive an input signal from the optical fibre (7), means (6) to output an amplified signal to the optical fibre (7), a gain medium (2) and a pump means (3) arranged to generate the amplified signal from the input signal, the amplifier (1) further comprising means (13) to measure the optical power of the signal leaving the gain medium and means (14) to measure the optical power of the signal backscattered from the optical fibre (7), wherein the pump means (3) is controlled by a control means (4), the control means (4) being adapted to modulate the pump means (3) with a determination signal, the control means (4) being adapted to change the frequency of the determination signal over a plurality of determination frequencies while keeping the amplitude of the determination signal constant, the control means (4) further being adapted to calculate the attenuation of t

Abstract: A method and apparatus for restoration of operating conditions of a WDM optical ring network comprising a plurality of amplifiers linked together in a ring after a break or fault has occurred in the network. The method comprises in response to repair of the break or other fault, increasing output power or/and pump power of an amplifier in the network such that the output power or/and pump power increases substantially in accordance with a ramp function.

Abstract: A wavelength division multiplex optical ring network comprises optical fibre (1-4) arranged in a ring configuration and a plurality of doped fibre optical amplifiers (17-20) arranged in the ring. The spectral response in the ring is configured such in use amplified spontaneous emission (ASE) noise circulates around the ring in a lasing mode to clamp the gain of each doped fibre optical amplifier. Each optical amplifier (17-20) includes respective control means (28) which in use control the optical amplifier to produce a substantially constant output power or to maintain a substantially constant pump power. In the event of loss of the lasing peak, detection means switches the doped fibre optical amplifiers to a different mode of gain control, for example, a mode to produce constant gain at the value before the loss of the lasing peak. Optionally, after a predetermined delay, the optical amplifiers may revert to constant output power or pump power mode.

Abstract: In an optical add/drop amplification device (1) arranged between fibre spans (2, 3) in an optical telecommunications system, comprising a first input amplifier (4), a channel add/drop device (7) and an output amplifier (8) connected in a series path, the input amplifier (4) is arranged to produce substantially constant output power, such that the output power of amplified spontaneous emission (ASE) noise compensates in use for loss of signal power in the event of breakage of a fibre span, to ensure survival of any channels added at the add/drop device. In accordance with the invention, an additional input amplifier (9) is provided to produce the compensating ASE noise in the event of failure of the first input amplifier.

Abstract: A traffic survival method in optical fiber telecommunication systems and in particular DWDM and having amplification sites (10) with ADD/DROP of channels and arranged between fiber spans is described and claimed. In accordance with the method the ASE noise produced in amplifiers (13) in the site is amplified in power to compensate at output the power of channels (n) lost by breakage of the site inpul span. An amplification device with ADD/DROP and a telecommunication system with it is also described and claimed.