Optical bistability in semiconductor lasers under intermodal light injection

Optical bistability in semiconductor lasers under intermodal light injection is predicted using small-signal analysis. The optical bistability is a special case of sidemode injection locking and originates from the strong gain nonlinearity introduced by external light injection. The theory can be applied to the optical bistability under both intramodal and intermodal light injection. And the difference of the optical bistabilities between intermodal and intramodal light injection is discussed. Expression for the bistable loop width is presented. Optical frequency-bistability and power-bistability in semiconductor lasers can be realized by intermodal light injection, which imply that a small (a few GHz) change of the injected light frequency or a small (several μW) change of the injected light power will induce a large (up to THz) change of the laser emitting frequency. Besides, hybrid optical bistability can be achieved by varying the bias current (only a few mA) of the laser. Dynamic properties, such as turn-on and turn-off delay and carrier overshoot during switching are discussed and some consideration of the practical aspects of the optical switching is presented