Patent ID: 8670673

Claim:
Method of operating an optical transmission system, wherein at least one optical data signal is transmitted over an optical transmission link, which particularly comprises at least one optical fiber, comprising steps: modulating said data signal with a test signal (s) having a predetermined modulation frequency f mod to obtain a modulated data signal receiving a reflected portion of said modulated data signal; and determining a fiber quality measure depending on said received reflected portion of said modulated signal; wherein, for said step of determining said fiber quality measure, a frequency component of said received reflected portion of said modulated signal is determined which corresponds to said predetermined modulation frequency, and wherein the frequency component is a scattering term H(f mod ) derived from said predetermined modulation frequency; a plurality of scattering terms H(f mod ) are determined for many (M) modulation frequencies f mod (m),m=1, . . .,M, wherein each scattering term H(f mod ) characterizes an amplitude and phase of said reflected portion at a specific modulation frequency f mod ; each scattering term H(f mod ) associated with a specific modulation frequency f mod is multiplied with a phase term denoting a phase shift which depends on said modulation frequency f mod and a specific position x 0 on said optical transmission link, whereby for each modulation frequency f mod a phase-shifted scattering term Hp(f mod ) is obtained; a sum of all M many phase-shifted scattering terms Hp(f mod ) is determined; and the value for said quality measure at said specific position is determined depending on said sum.