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Thermal modeling and temperature measurements in optoelectronic waveguide devices

Optoelectronic devices are particularly sensitive to temperature changes induced by light absorption and current flow. In order to study the thermal issues arising in the Mach-Zehnder optical modulator manufactured by Nortel, a non-linear finite-element thermal model of the device was constructed, which computes the internal temperature as a function of the applied voltage and optical power in the waveguide. An experimental technique was also developed, in which liquid crystals are used to measure the temperature on the device surface. The model predictions and the experimental results were found to agree well over wide ranges of optical power and voltage. The model and the technique have produced evidence of a thermal cross-talk between an integrated laser and the modulator: the peak internal temperature inside the modulator is higher in integrated devices than in the stand-alone configuration for identical voltage and optical power. Because of the desire to integrate multiple devices on a common substrate and the continuous increase of the optical powers in optical fiber systems, thermal issues will only become more important in future systems.