Fast optical wavelength bistability under the mode-hopping phenomenon in semiconductor lasers

In this work, we have demonstrated experimentally the electro-optical switch, logic and memory operations at the speed of as fast as nanosecond region, utilizing the mode-hopping phenomenon of a laser diode. We have also confirmed the hysteresis (wavelength bistability) region being still effective under even such a high speed. The sample laser diode used in the experiments was a O.8m GaAlAs-type and 1.3m InGaAsP-type one. The measured speed of switching was within nanosecond region, which was limited by the driving capabilities and the light detection response, not by the phenomenon itself. In order to confirm the reproducibility of the hopped wavelength in the experiments, the fluctuations in the ambient temperature of the laser diode are precisely controlled to be within 1.0 mK through a thermoelectric cooler attached to the heat sink of the laser diode by which both cooling and heating are possible. As an example of the fast logic operation, we have achieved the actual N X N channel optical wavelength-division-multiplexing system using a O.8m GaAlAstypevvisible injection laser diode and also a 1.3m InGaAsP-type long-wavelength laser diode of which the wavelength is rather suitable for fiber optic routing systems. Moreover we carried out the simulation to explain the behavior of the wavelength bistability seen in these laser diode samples and also estimated how fast these switches or memories can operate, based on some well-known analyses for the mode-hopping phenomenon. In addition, the gain-suppression mechanism in semiconductor lasers was included in this analysis. As a consequence, the result of estimation suggests that the speed of wavelength-switching may become about an order of magnitude longer than the carrier lifetime of the device. Therefore, we can conclude that the dominating physics of the wavelength bistability based on the mode-hopping phenomenon is a very fast thermal processes caused by modulating the injection current.