Power stabilization in an optical communication system

An optical amplifier arrangement including

• an optical amplifier (20) coupled to on an optical transmission line for receiving optical input signals and emitting amplified optical output signals,
• means (60, 80) for measuring input power to the amplifier (20),
• means (70, 90) for measuring power output from the amplifier, characterised by
• means (30, 100) for receiving data representing the proportion of ASE noise power in the amplifier input,
• means responsive to said measured input power and said received data for determining the received traffic power,
• means for calculating the amplifier gain required to obtain a desired traffic output power,
• means (100) for determining the amount of ASE power generated at the calculated amplifier gain,
• means for determining the amount of amplified propagated ASE noise power contained in an output signal and
• means (100, 21) for comparing the measured amplifier output power with the sum of the desired traffic output power, the generated ASE power and the amplified propagated ASE noise power and for adjusting the amplifier gain if these are not substantially equal.

A method of determining the amount of noise power due to amplified spontaneous emission in a signal output by an optical amplifier, including:

• measuring the input power to the amplifier,
• receiving information concerning the proportion of propagated ASE noise power in a received signal,
• determining the amount of amplified propagated ASE power contained in the amplifier output signal
• determining ASE power generated by said amplifier,
• summing said generated ASE power and said amplified propagated ASE power to obtain the amount of noise power in the amplifier output signal.

A method of stabilising the output power of an optical amplifier in an optical communications link, including:

• measuring the input power to the amplifier,
• receiving information concerning the proportion of propagated ASE noise power in a received signal,
• determining the received traffic power,
• determining amplifier gain for obtaining a desired traffic output power,
• determining ASE power generated at said gain,
• determining the amount of amplified propagated ASE noise power contained in an output signal,
• adjusting the real amplifier output power to be substantially equal to the sum of the desired traffic output power, the generated ASE power and the amplified propagated ASE noise power.