Experimental analysis of the optical spectra of directionally bistable semiconductor ring lasers

The optical spectrum of monolithic Semiconductor Ring Lasers (SRLs) is measured simultaneously for both lasing directions with a grating-based OSA, in the regimes of bidirectional and unidirectional operation. In the unidirectional operation regime the SMSR is larger than 25 dB, and the directional extinction ratio (i.e., the ratio of the power emitted in the two opposite directions) is larger than 20 dB. The influence of the current injected in the active output waveguides that act as SOAs is outlined. In the unidirectional regime the linewidth of the SRL is measured by an heterodyne technique, revealing linewidth values around 2 MHz.