Determination of the gain and saturation characteristics of a semiconductor laser amplifier using a ringlaser configuration

Determination of the gain of a semiconductor laser amplifier using a tunable laser source or a set of fixed wavelength lasers is a rather time consuming exercise. The reason is that the position of the gain peak and the positions of the local maxima and minima belonging to the residual Fabry-Perot ripple are not known in advance and moreover shift with increasing drive current. Therefore determination of the peak gain at various currents levels, which is desirable to select promising devices worthy of further study or to provide feedback in a fabrication process, involves measuring the gain at various different wavelengths to ensure that the measured value corresponds to a (local) maximum. We present an alternative method of gain determination using the laser amplifier in a ringlaser configuration (fig. 1). This method is very fast and does not require a tunable signal source.