Technique for measurement of the Raman gain coefficient in optical fibers

We demonstrate a simple, novel technique for measurement of the Raman gain spectrum in optical fibers. We measure the stimulated Raman scattered power generated by a square pulse as a function of its pulse width. Because of fiber dispersion, increasing the pulse width increases the interaction length of the pump and Stokes pulses and leads to a higher Stokes power. The dependence of growth rate of Stokes power on pulse width gives the Raman gain coefficient. Our technique does not require calibration against a standard or absolute measurement of the Stokes signal. We show that gain values obtained with this technique agree well with direct pump-probe measurements.