Bistable operation and spectral tuning of an injection laser with an external dispersive resonator

An investigation was made of spectral tuning of an AlGaAs–GaAs laser with an external dispersive resonator operating in the single-frequency emission regime. It was found that the dependence of the output power on the wavelength is in the form of a hysteresis loop, i.e., that bistable lasing takes place. This behavior is due to the presence of a composite resonator which includes the resonator formed by the laser diode itself and the external dispersive resonator. The refractive index of the diode semiconductor depends on the degree of inversion. This gives rise to an optical nonlinearity of the active medium of the diode since the degree of inversion depends on the intensity of the emitted radiation. Consequently, the optical system of the laser becomes analogous to the well-known optical bistable systems containing a Fabry–Perot interferometer and characterized by an optical nonlinearity.