Effect of dip in refractive index profile on fiber Raman gain amplifier performance

We have studied and reported the effect of practically possible linear dips in the inner core of a coaxial fiber Raman gain amplifier having step index inner and outer cores in the structure on the amplifier performance. In this work, we have used single pump wavelength of 1.465 µm. A variation of dip depth beyond 0.25% of maximum refractive index and that of dip width beyond 25% of the inner core radius deteriorate the gain performance of characteristics of this amplifier significantly along with an appreciable shift of phase matching wavelength. Within these limits, the amplifier resembles closely the behavior of an ideal one. These prescribed limits of dip depth and dip width are also valid limits above which there will be valid ground in their effect to modulate Raman gain performance and dispersion. The present study should find wide attention of system designers.