Nonlinear distortion due to stimulated Brillouin scattering and its suppression in SCM video-transmission systems

Erbium-doped-fiber amplifiers (EDFA’s) will increase the distribution capacity of subcarrier-multiplexed (SCM) analog video systems. Long-distance SCM systems must pass 1.5-µm-wavelength signals over conventional 1.3-pm fibers because a lot of 1.3-µm fiber has already been installed and EDFA’s operate most efficiently at 1.5 µm. Unfortunately, this will lead to increased nonlinear distortion in direct modulation due to the high dispersion of the 1.3-µm fiber. One way of solving this problem is to use an external modulator with an optical source of narrow spectral bandwidth. However, this method is susceptible to stimulated Brillouin scattering (SBS). SBS rejects some of the fiber input power and degrades CNR in SCM systems.1