This paper overviews the current status of bistable semiconductor lasers and their applications to photonic switching as well as the recent results of our research on polarization bistable VCSELs. Many kinds of bistable semiconductor lasers such as VCSELs and ring-lasers with low power consumption have been developed so far. In our experiments with 980-nm polarization-bistable VCSELs, we successfully demonstrated the following results. All-optical fl ip-fl op operation was achieved at a record low bias current of 0.85 mA using an oxidation confi nement structure. 1-bit data signals were arbitrarily sampled and memorized from 20 Gb/s PRBS RZ and 40 Gb/s NRZ signals.