CW operation of an injection ring laser

CW single-frequency operation of a semiconductor laser with a ring resonator has been demonstrated for the first time. An arrangement is proposed which makes it possible to minimize the coupling between the oppositely directed waves. The optical arrangement is described, including its components and its operation. Output spectra of the ring laser with and without an in-resonator Fabry-Perot etalon are presented. The residual reflection coefficient at the ends of the diode is determined by studying its superluminescence spectra. A power-current characteristic of the ring laser is plotted as the sum of the power levels of the two oppositely directed waves. The lasing threshold is about 5 mW. A clear nonlinearity is shown in the relationship between the power levels P(minus) and P(plus) of the oppositely directed travelling waves: the relative importance of P(minus) increases above 7 mW.