A branched wavelength division multiplexed optical system comprising: a first trunk terminal (A) configured to provide a trunk input signal on a trunk path , said trunk input signal occupying a plurality of express channels and a plurality of drop channels; a branch terminal (B) configured to provide a branch input signal on a branch path , said branch input signal occupying a plurality of add channels; an optical add-drop multiplexer, OADM, coupled to said trunk path and said branch path for receiving said trunk input signal and said branch input signal and providing a trunk output signal on said trunk path and a branch output signal on said branch path , said trunk output signal comprising said express channels and said add channels, said branch output signal comprising said drop channels; and a second trunk terminal (C) coupled to said OADM and configured to receive said trunk output signal, at least one of said first trunk terminal (A) and said branch terminal (B) being configured to adjust an output power of said trunk input signal or said branch input signal, respectively, to recover from a fault on said trunk path or said branch path , characterised in that said adjustment is to minimize a merit function based on optical signal-to-noise ratio and non-linear phase shift, wherein said at least one of said first trunk terminal (A) and said branch terminal (B) is configured to adjust first and second power ratios in said trunk input signal or said branch input signal, respectively, to minimize said merit function, wherein said first power ratio is expressed as: r 1 = ∑ P sig P launch = ∑ P sig ∑ P sig + ∑ P IB + ∑ P OB and wherein said second power ratio is expressed as: r 2 = ∑ P IB ∑ P IB + ∑ P OB where P sig , P IB , P OB and P launch are utilized channel power, in-band loading signal power, out-of-band loading signal power, and total launched power, respectively, of the trunk input signal or said branch input signal. a first trunk terminal (A) configured to provide a trunk input signal on a trunk path , said trunk input signal occupying a plurality of express channels and a plurality of drop channels; a branch terminal (B) configured to provide a branch input signal on a branch path , said branch input signal occupying a plurality of add channels; an optical add-drop multiplexer, OADM, coupled to said trunk path and said branch path for receiving said trunk input signal and said branch input signal and providing a trunk output signal on said trunk path and a branch output signal on said branch path , said trunk output signal comprising said express channels and said add channels, said branch output signal comprising said drop channels; and a second trunk terminal (C) coupled to said OADM and configured to receive said trunk output signal, at least one of said first trunk terminal (A) and said branch terminal (B) being configured to adjust an output power of said trunk input signal or said branch input signal, respectively, to recover from a fault on said trunk path or said branch path , characterised in that said adjustment is to minimize a merit function based on optical signal-to-noise ratio and non-linear phase shift, wherein said at least one of said first trunk terminal (A) and said branch terminal (B) is configured to adjust first and second power ratios in said trunk input signal or said branch input signal, respectively, to minimize said merit function, wherein said first power ratio is expressed as: r 1 = ∑ P sig P launch = ∑ P sig ∑ P sig + ∑ P IB + ∑ P OB and wherein said second power ratio is expressed as: r 2 = ∑ P IB ∑ P IB + ∑ P OB where P sig , P IB , P OB and P launch are utilized channel power, in-band loading signal power, out-of-band loading signal power, and total launched power, respectively, of the trunk input signal or said branch input signal. <EOS>