Emission wavelength multistability in semiconductor ring lasers

During the last decade, it was experimentally demonstrated that the emission wavelength of bidirectional semiconductor ring lasers (SRLs) can be selected by optical injection [1] or by wavelength-selective feedback [2] at wavelengths corresponding to the modes of the ring cavity. In the case of optical injection, upon its removal, the emission wavelength remains stable at the chosen value. It was found that this multistability can coexist with the directional bistability shown by these devices [3]; therefore it can be of interest for all-optical signal processing applications at higher-logical level.