Extinction ratio of stripe-geometry DH AlGaAs lasers with "soft" turn-on

The effect of high spontaneous emission on the extinction ratio of modulated laser-diode signals is discussed. A calculation based on the spectra taken from oxide-defined narrow-stripe lasers at "on" and "off" levels shows that high spontaneous emission at the "on" level can degrade the apparent extinction ratio of the source, due to material dispersion in optical fibers, and affect transmission bandwidth and useful device lifetime.