An optical system including a forward and a backward Raman pump module positioned along a transmission fiber; a noise matrix computing module configured to: determine, for first gains of the optical signal, a first noise associated with the first gain of the forward Raman pump; determine, for second gains of the optical signal, a second noise associated with the second gain of the backward Raman pump module; generate a noise matrix based on i) the first noise for each first gain of the forward Raman pump module and ii) the second noise for each second gain of the backward Raman pump module; identify a span loss of the optical signal as the optical signal is transmitted along the transmission fiber; identify a combination of a particular first gain of the forward Raman pump module and a particular second gain of the backward Raman pump module.