Specifying power-frequency bistability of external cavity semiconductor lasers

The analytical expression of the threshold carrier density, on which the refractive index depends, of the grating tuned external cavity semiconductor laser (ECLD) is used to study the optical bistability. Proper choice of the reference carrier density leads to an implicit analytical expression of the oscillation frequency in terms of the carrier density. As a result, an analytical expression is deduced for the frequency width of the hysteresis loop. It turns out that three parameters, i.e, the linewidth enhancement factor cu, reflectivities of the external reflector and facet adjacent to the external cavity, are of vital importance in deciding the bistability of the ECLD. In addition, an equation the above three parameters should satisfy for observing the hysteresis loop on the P-v (power-frequency) curve of the ECLD, has also been established.