Bistable injection lasers

A simple model is given which explains the main features of an injection laser with inhomogeneous current injection. A set of three rate equations is used, one for the density of the carriers in the gain section, one for those in absorbing section and one for the density of photons in the lasing mode. Experimental results of this device placed in an external optical cavity are also reported. Depending on the biasing condition the device will be bistable or pulsating. In the bistable mode the laser can be switched on and off by varying the amount of optical feedback and it can be used as an optical stylus to read an optical disk. In the pulsating mode ultrashort pulses through passive mode locking can be generated at a repetition rate corresponding to the round trip in the external optical cavity.