Anomalous tuning of single mode AlGaAs diode lasers

Deviations from the normal tuning of a TJS AlGaAs diode laser have been observed. In the usual situation, the emitted wavelength of a single mode diode laser as a function of temperature is described by a "staircase" function, that is, the tuning curve consists of regions of smoothly increasing wavelength as a function of temperature separated by positive wavelength mode hops. We have observed a tuning curve for which the regions of smooth temperature tuning are separated by negative wavelength mode hops. It is suggested that this effect is due to the existence of structure in the laser's effective gain curve.