Research Index / Ultrafast Technology / Electro-Thermal Probe
A method has been developed to simultaneously measure for the first time electric and thermal fields with a single probe. The Pockels effect is employed within a gallium arsenide probe to measure electric fields, using the previously described optical-fiber-based electro-optic field-mapping system. Now, in addition, the effect of photon absorption that arises due to the presence of bandtail states in the semiconductor has been used to determine the temperature at the end of the probe. The measured optical power is found to be inversely related to temperature, in agreement with theory, and experimental results have demonstrated a temperature sensitivity of 0.31 µW/ºC at 25ºC. This has led to an accuracy of ±0.5ºC between 20ºC and 60ºC. The examination of a monolithic microwave integrated circuit in a quasi-optical power-combining array and the calibration of electric field data that was corrupted by temperature-dependent effects inherent to the electro-optic probe have been used to demonstrate the capability of this combined electro-thermal measurement technique. The probe could also be useful for making localized temperature measurements in confined spaces where the flexible optical fiber could easily be inserted, or it could be used to help determine if an electrical measurement was different than expected due to elevated temperature near a location where power was being dissipated. Further investigations of the probe have also been performed in order to quantify its electrical invasiveness by examining the change in the characteristic impedance and capacitance per unit length of a planar transmission line. Measured and simulated data show that the effect is equivalent to a lumped shunt capacitance on the order of a few femtofarads. This is significant in that it indicates there is only a small local impact on the circuit or component that is being probed.
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