Highly efficient Raman amplification in a polarization-preserving optical fiber

Abstract

In a forward pump configuration, a Raman gain coefficient of 4.8×10⁻¹¹ cm/W and a gain as high as 40 dB/W have been successfully attained with a combination of 1.34‐μm pump and 1.42‐μm signal pulses. A 20‐dB gain at a wavelength of 1.52 μm was also obtained at a 3.7‐W input. The test fiber is a 1‐km‐long polarization‐preserving and absorption‐reducing type polarization‐preserving fiber which has a GeO₂ highly doped core with a small core diameter of 4.5 μm. It is also shown that the 3‐dB gain bandwidth is around 130–135 cm⁻¹ and that optical power ratio of the amplified signal to the spontaneous emission is about 24 dB for the 1.42‐μm 1st Stokes line.