1. Introduction
Raman fiber laser and its applications as a pump source for distributed Raman amplifiers are currently experiencing renewed interest as a result of recent prospects of 40Gb/s WDM system implementations [1]. The introduction of resonant and cascaded. all-fiber geometries that utilize fused WDM couplers[2] or Bragg gratings[3] has enhanced conversion efficiencies and allows extended wavelength coverage in CW operation. To obtain a tunable wavelength 'operation of the Raman laser, WDM couplers which have comparatively broad bandwidth are preferred.