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Optical or infrared antennas are devices that receive optical radiation and transform it into a current within the resonant structure. This high-frequency current is transduced by a given mechanism to a change in voltage or current that is read by external electronics. From this point of view, optical antennas are light detectors.
Over time, several transduction mechanisms have been proposed and realized. One of the first used is the rectification of the currents flowing through the antenna by means of tunnel and Schottky junctions properly placed at the appropriate location, typically where the current density reaches the largest value. These elements are considered generically as diodes. Another simpler transduction mechanism is based on the heating of a bolometric material due to Joule dissipation. In this case, the mechanism is dissipative and needs electronic biasing to sense variations in resistivity of the bolometric element. It happens that most of the metals used in the fabrication of optical antennas have a similar value of the parameter responsible for the change in resistance with temperature, the temperature coefficient of resistance (TCR). Some designs use this effect to make the whole resonant element act as a bolometric transducer, which can be termed a distributed bolometer. Using the change in temperature caused by thermal dissipation of currents, thermoelectric transducers based on the Seebeck effect have also been proposed and tested. In this section we present the basic principles of these transduction mechanisms.
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