EFFECT OF THE Y-JUNCTION OUTPUT COUPLER ON THE LASING THRESHOLD OF SEMICONDUCTOR RING LASERS

We report the first measurements of the effect of a Y-junction output coupler on the continuous-wave (cw) lasing threshold of rib-waveguide semiconductor ring lasers. We show that the Y-junction induced loss in this type of ring diode laser depends on the ring radius (r), and inc reases the lasing threshold current density substantially for devices with r < 200 mum. For our devices with radii of 50-100 mum, the Y-junc tion loss term is shown to be the dominant factor affecting the cw las ing threshold. We also report the first measurements of the dependence of the cw lasing threshold on the width (w) of the Y-junction output coupler, and show that the threshold current density increases linearl y for 0 less-than-or-equal-to w less-than-or-equal-to 9 mum.