Patent ID: 6697187
Filing Date: 2004-02-24
Classification: H01S

Abstract:
A method for determining a power setting for each of a plurality of Raman pumps of a Raman amplifier used to enhance signal propagation in a given fiber medium, the method comprising steps of:solving a non-linear system of fiber propagation equations having a general form comprising: &dd;Psi&dd;z=-Î±si&it;Psi+&Sum;p=1Np&it;Cp,si&it;Pp&it;Psi+&Sum;j=1i-1&it;Csi,sj&it;Psj&it;Psi-&Sum;j=i+1Ns&it;Csi,sj&af;(Î»sjÎ»s&it;â€ƒ&it;i)&it;Psj&it;Psi(1)where z=fiber length, Psi=signal power for signal i, &agr;si=attenuation co-efficient of the fiber at wavelength of signal i, Cp,si=Raman coupling co-efficient between pump p and signal i, Pp=Raman pump power for laser p, Csi,sj=Raman coupling co-efficient between signal i and signal j, Psj=signal power for signal j, &lgr;si=wavelength of signal i, &lgr;sj=wavelength of signal j, Np=number of pump lasers and Ns=number of signal channels; and &dd;Ppi&dd;z=Î±pi&it;Ppi+&Sum;s=1Ns&it;Cpi,s&af;(Î»sÎ»p&it;â€ƒ&it;i)&it;Ps&it;Ppi-&Sum;j=1i-1&it;Cpi,pj&it;Ppj&it;Ppi+&Sum;j=i+1Np&it;Cpi,pj&af;(Î»pjÎ»p&it;â€ƒ&it;i)&it;Ppj&it;Ppi(2)where z=fiber length, Ppi=Raman pump power for laser i, &agr;pi=attenuation co-efficient of the fiber at wavelength of Raman pump i, Cpi,s=Raman coupling co-efficient between pump i and signal s, Cpi,pj=Raman coupling co-efficient between pump i and pump j, Ps=signal power for signal s, &lgr;s=wavelength of signal s, &lgr;pi=wavelength of pump i, &lgr;pj=wavelength of pump j, Ns=number of signal channels and Np=number of pump lasers; to pre-compute table values for a look-up table, the table values representing, for each of a plurality of average Raman gain values, a corresponding normalized power value for each Raman pump required to provide substantially uniform gain across a plurality of signal wavelengths; determining a linear relationship between a total Raman pump power and an average Raman gain in the given fiber medium; determining a required total Raman pump power to achieve a desired average Raman gain using the linear relationship; looking up a normalized power value in the look-up table corresponding to the desired average Raman gain for each Raman pump; and multiplying the normalized power value for each Raman pump by the required total Raman pump power to determine the power setting for the respective Raman pump.