Raman gain and optical loss in GaP-AlGaP waveguides

The stimulated Raman gain coefficient and the optical loss in GaP/AlGaP semiconductor Raman amplifiers are measured for both double path and single path structures. For the double path structure, the highest gain per waveguide length is 3.27 dB/cm for a waveguide with a cross-sectional area of 4 mu m(2), under continuous wave pumping. A long waveguide with a length of 10 mm is demonstrated to have the highest gain of 2.57 dB. For a single path structure, the gains of backward scattering and forward scattering are separately measured and it is found that the gain of backward scattering is dominant. From these results, the backward gain coefficient is estimated to be 12.3 x 10(-8) W cm(-1). This value is about five times that of CS2 and LiNbO3, which is known to have the highest Raman scattering gain. However, the optical losses of the waveguides are estimated from the finesse measurement. The lowest one way loss corresponds to an effective absorption coefficient of alpha(eff) = 0.28 cm(-1). (C) 2000 American Institute of Physics. [S0021-8979(00)04307-3].