Measurement of linewidth enhancement factor of SOA using fiber Sagnac Ring

Semiconductor optical amplifiers (SOA) are optical amplifying devices and key parts in optical switches and optical buffers. They are largely used in communication system. Linewidth enhancement factor is an important parameter for SOA. A method is proposed to measure the linewidth enhancement factor with Sagnac interferometer. Cross phase modulation (XPM) and cross gain modulation (XGM) coexist in SOA. The quantitative relation of linewidth enhancement factor to XGM and the interference extinction ratio is given. The experimental results indicate that the value of linewidth enhancement factor changes from 5. 13 to 6. 24 when the electric current varies from 130 mA to 240 mA. Supported by the National Natural Science Foundation of China (Grant No. 60272010) and National 863 project (NO. 2002AA122510)