Modelling and measurement of the absolute level of power radiated by antenna integrated THz UTC photodiodes

Abstract

We determine the output impedance of uni-travelling carrier (UTC) photodiodes at frequencies up to 400 GHz by performing, for the first time, 3D full-wave modelling of detailed UTC photodiode structures. In addition, we demonstrate the importance of the UTC impedance evaluation, by using it in the prediction of the absolute power radiated by an antenna integrated UTC, over a broad frequency range and confirming the predictions by experimental measurements up to 185 GHz. This is done by means of 3D full-wave modelling and is only possible since the source (UTC) to antenna impedance match is properly taken into account. We also show that, when the UTC-to-antenna coupling efficiency is modelled using the classical junction-capacitance/series-resistance concept, calculated and measured levels of absolute radiated power are in substantial disagreement, and the maximum radiated power is overestimated by a factor of almost 7 dB. The ability to calculate the absolute emitted power correctly enables the radiated power to be maximised through optimisation of the UTC-to-antenna impedance match.

Accurate modelling and measurement of the impedance match between UTC photodiodes and THz antennas

“…We also performed 3D full-wave modelling of detailed UTC photodiode structures, as shown in Fig. 2, to achieve accurate knowledge of the UTC output impedance up to 400 GHz [6]. The model is very detailed, e.g.…”

High-Speed Photodetectors for Microwave Photonics

“…In order to achieve high radiation power, the transition between the PD and the antenna needs to be carefully designed. It has been shown that impedance matching has a significant effect on the radiation power of integrated photonic emitters [24] and that maximum RF power can be extracted from the PD by conjugate impedance matching. In [25], a matching network was used to achieve conjugate matching between the MUTC PD and the Vivaldi antenna.…”

“…[27,[29][30][31][32][33], either a Teflon or Si lens was used to improve the directional gain of the antenna. Planar antenna structures include Yagi [34,35], bow-tie [18,24], and slot [29,35], however, impedance matching between PD and antenna was not reported for these structures. In contrast, the integrated photonic emitters reported in refs.…”

High performance waveguide uni-travelling carrier photodiode grown by solid source molecular beam epitaxy

“…The total power emitted by an antenna depends on the impedance match with the driving source and the radiation efficiency. The absolute level of power emitted by an antenna over the frequency range can be calculated and predicted if the UTC impedance is known and the coupling efficiency between UTC and antenna taken into account [27] [28]. We presented a comprehensive study of UTC-PD output impedance and frequency photoresponse in [27].…”