A method of compensating for channel power depletion induced by Raman amplification noise in a hybrid distributed Raman amplifier-Erbium doped fibre amplifier, the method comprising: determining an equivalent noise figure (12, 30) for a virtual amplifier equivalent to the hybrid distributed Raman amplifier-Erbium doped fibre amplifier, and having an input power equal to the input power of the Erbium doped fibre amplifier when the distributed Raman amplifier is off and an output power equal to the Erbium doped fibre amplifier output power; determining a compensation power ΔP; and providing a control signal for controlling the hybrid amplifier such that an optical signal amplified by the hybrid amplifier has a total output power equal to a predetermined nominal output power of the optical signal plus the compensation power, wherein the distributed Raman amplifier has a noise figure NF Ram, the Erbium doped fibre amplifier has a noise figure NF Edfa, the distributed Raman amplifier has net Raman gain G Ram, wherein the net Raman gain is a gain of the Raman amplifier without a Raman amplification noise; and the virtual amplifier has insertion losses L R, and the equivalent noise figure NF EQ is determined using the equation: NF EQ = NF Ram + NF Edfa G Ram L R, and the noise figure of the distributed Raman amplifier is determined from a Raman gain value using a pre-determined relationship between Raman gain and noise; wherein the control signal is for controlling the hybrid amplifier such that the compensating power is added only by the Erbium doped fibre amplifier, wherein the method further comprises determining a total equivalent noise bandwidth, and the compensation power is determined from the equivalent noise figure, the total equivalent noise bandwidth, the Raman gain, the insertion losses and an input power at the Erbium doped fibre amplifier of an optical signal to be amplified, and wherein the compensation power ΔP is determined using the equation: ΔP = 10 ⋅ log 10 1 + β ⋅ NF EQ ⋅ G Ram / Lr Pin_e where β = hf 0 B N, where h is Planck's constant, f 0 is the frequency of the centre of the amplifier bandwidth, and B N is the total equivalent noise bandwidth and P in_e is the input power at the Erbium doped fibre amplifier of an optical signal to be amplified; wherein the total equivalent noise bandwidth is in the range 32 nanometres to 34 nanometres. determining an equivalent noise figure (12, 30) for a virtual amplifier equivalent to the hybrid distributed Raman amplifier-Erbium doped fibre amplifier, and having an input power equal to the input power of the Erbium doped fibre amplifier when the distributed Raman amplifier is off and an output power equal to the Erbium doped fibre amplifier output power; determining a compensation power ΔP; and providing a control signal for controlling the hybrid amplifier such that an optical signal amplified by the hybrid amplifier has a total output power equal to a predetermined nominal output power of the optical signal plus the compensation power, wherein the distributed Raman amplifier has a noise figure NF Ram, the Erbium doped fibre amplifier has a noise figure NF Edfa, the distributed Raman amplifier has net Raman gain G Ram, wherein the net Raman gain is a gain of the Raman amplifier without a Raman amplification noise; and the virtual amplifier has insertion losses L R, and the equivalent noise figure NF EQ is determined using the equation: NF EQ = NF Ram + NF Edfa G Ram L R, and the noise figure of the distributed Raman amplifier is determined from a Raman gain value using a pre-determined relationship between Raman gain and noise; wherein the control signal is for controlling the hybrid amplifier such that the compensating power is added only by the Erbium doped fibre amplifier, wherein the method further comprises determining a total equivalent noise bandwidth, and the compensation power is determined from the equivalent noise figure, the total equivalent noise bandwidth, the Raman gain, the insertion losses and an input power at the Erbium doped fibre amplifier of an optical signal to be amplified, and wherein the control signal is for controlling the hybrid amplifier such that the compensating power is added only by the Erbium doped fibre amplifier, wherein the compensation power ΔP is determined using the equation: ΔP = 10 ⋅ log 10 1 + β ⋅ NF EQ ⋅ G Ram / Lr Pin_e where β = hf 0 B N, where h is Planck's constant, f 0 is the frequency of the centre of the amplifier bandwidth, and B N is the total equivalent noise bandwidth and P in_e is the input power at the Erbium doped fibre amplifier of an optical signal to be amplified; wherein the total equivalent noise bandwidth is in the range 32 nanometres to 34 nanometres.