Symmetrical and asymmetrical waveguiding in very narrow conducting stripe lasers

Two-dimensional waveguiding is analyzed in very narrow conducting stripe lasers. Relatively simple closed form analytic expressions are derived for modes with both symmetrical and asymmetrical lateral distributions of gain and real refractive index. We show that the calculated far-field radiation patterns agree with those measured only if substantial real refractive index antiguiding is introduced. At higher pumping levels the dual far-field peaks observed for symmetrical lasers operating in the lowest order (TE00) mode are reproduced analytically by reducing the optical absorption in the modal wings. Highly asymmetrical far-field radiation patterns previously observed are also demonstrated to result from asymmetrical gain and refractive index variations. We conclude that measured very narrow stripe laser far-field radiation patterns can only occur if the real refractive index is significantly depressed in the region of maximum gain; that is, substantial antiguidance must be present.