Active transmission line: light amplificationby backward-stimulated Raman scatteringin polarization-maintaining optical fiber

The possibility of an active transmission line with a polarization-maintaining optical fiber has been investigated by means of backward-stimulated Raman gain. The fourth Stokes line of the stimulated Raman scattering is placed near 1.3, m with pumping light of 1.06-ym wavelength, in which Raman gain at 1.30 μm is produced in terms of a strong pump that is due to the third Stokes line at 1.24 μm. A laser diode (InGaAsP/InP) operating at 1.30 pm is used as signal light to meet the Raman gain. As a result, a Raman gain as high as 20 dB and a gain coefficient of 2.0 × 10-12 cm/W have been obtained. It is shown experimentally that it is important to meet exactly the polarization directions between the pump and the signal pulses to obtain a large Raman gain.