Analysis of DBR lasers and MOPA with saturable absorption gratings

The effect of saturable absorption in the grating regions of second-order surface-emitting DBR lasers and high-power M-MOPA, edge emitting with DBR master oscillator and flared amplifier, has been analyzed numerically. As the pumping current increases, light penetrates further into the end gratings, due to saturation, resulting in narrower far field and higher reflectivity. The latter, in turn, reduces the external differential efficiency. Thus, one obtains a nonlinear L-I curve which may also include bistability effect, especially for small pumping currents above threshold, with a large absorption coefficient and long gratings, in agreement with previously observed experimental data