Measurement of SOA Linewidth Enhancement Factor With a Sagnac Fiber Loop

We demonstrate a novel method to measure the linewidth enhancement factor (
$alpha$
-factor) of the semiconductor optical amplifier (SOA). We derived theoretically the quantitative relationships among the
$alpha$
-factor, the cross-gain modulation, the cross-phase modulation, and the contrast ratio of an SOA-based Sagnac fiber loop. We found that the
$alpha$
-factor value can be calculated directly from the maximum power contrast ratio measurement. Our experiment results show that the obtained
$alpha$
-factor fluctuates within a small range of 5.23 to 6.83 when the bias current varies from 130 to 240 mA. Compared with existing measurement methods, our method is more attractive because of its simple configuration and better stability.