Temperature determination in optoelectronic waveguide modulators

Optoelectronic devices are particularly sensitive to temperature changes in duced by the absorption of light and the passage of current. In order to st udy the thermal issues arising in a InGaAsP-based Mach-Zehnder (MZ) optical modulator, a nonlinear finite-element thermal model of the device was cons tructed. The model considers the variation with temperature of both the the rmal conductivity of the semiconductors composing the device and the optica l absorption. To that effect, the optical absorption was measured inside th e waveguide as a function of temperature. An experimental method using liqu id crystals to measure the surface temperature was also developed. Both wer e used to evaluate the temperature inside a variable optical attenuator pre sent on the modulator. Good agreement with the model and the experiment is found over a wide range of operating conditions. These tools are expected t o play a key role in understanding thermal issues in future photonic device s, in view of the desire to integrate multiple devices on a common substrat e and the continuous increase of the optical powers in fiber systems.