RF-modulation measurement of linewidth enhancement factor and nonlinear gain of vertical-cavity surface-emitting lasers

Using RF-modulation technique of pump current, the linewidth enhancement factor /spl alpha/ and the nonlinear gain of a vertical-cavity surface-emitting laser (VCSEL) were obtained from the measured normalized phase-modulation index versus modulation frequency, is found as 2.7/spl plusmn/0.5 and the measured nonlinear gain of the VCSEL device is found to behave differently from that of edge-emitting lasers with an increase in pump level.