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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.
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