We demonstrate a simple, novel technique for measurement of the Raman
gain spectrum in optical fibers. We measure the stimulated Raman scatt
ered power generated by a square pulse as a function of its pulse widt
h. Because of fiber dispersion, increasing the pulse width increases t
he interaction length of the pump and Stokes pulses and leads to a hig
her Stokes power. The dependence of growth rate of Stokes power on pul
se width gives the Raman ganin coefficient. Our technique does not req
uire calibration against a standard or absolute measurements of the St
okes signal. We show that gain values obtained with this technique agr
ee well with direct pump-probe measurements. (C) 1996 Optical Society
of America.