A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the measured rectified current, the current noise floor in the PCAs, and the incoming THz power for the same conditions. Since the THz power measurements are performed with a pyroelectric detector calibrated by the National Metrology Institute of Germany (PTB), the experimentally obtained values are directly traceable to the International System of Units (SI) for the described conditions. The agreement between the presented model and the experimental results is excellent using only one fitting parameter. A very low NEP of 1.8 fW/Hz at 188.8 GHz is obtained at room temperature.

Telecom-wavelength compatible photoconductors benefit strongly from the large amount and affordability of telecom lasers and components but there are demanding requirements on material development. We demonstrate continuous-wave (CW) photomixing with a setup that only uses ErAs:In(Al)GaAs devices with a peak dynamic range (DNR) of 78 dB and a bandwidth of ∼3.65 THz at an integration time of 300 ms and only 26 mW laser power on each device. The ErAs:InGaAs receiver further features a factor of two lower noise equivalent power (NEP) than a state-of-the-art photoconductor, despite an antenna mismatch.

The resolution along the propagation direction of far field imagers can be much smaller than the wavelength by exploiting coherent interference phenomena. We demonstrate a height profile precision as low as 31 nm using wavelengths between 0.375 mm and 0.5 mm (corresponding to 0.6 THz–0.8 THz) by evaluating the Fabry-Pérot oscillations within surface-structured samples. We prove the extreme precision by visualizing structures with a height of only 49 nm, corresponding to 1:7500 to 1:10000 vacuum wavelengths, a height difference usually only accessible to near field measurement techniques at this wavelength range. At the same time, the approach can determine thicknesses in the centimeter range, surpassing the dynamic range of any near field measurement system by orders of magnitude. The measurement technique combined with a Hilbert-transform approach yields the (optical) thickness extracted from the relative phase without any extraordinary wavelength stabilization.

We present an architecture for millimeter-wave spectrum analyzers with Hz resolution and precision based on heterodyne down-conversion using ErAs:InGaAs photoconductive mixers driven by a tunable ultra-narrow linewidth continuous-wave (CW) photonic local oscillator. Unlike previous optoelectronic or electronic architectures, there is no requirement for an external electronic spectrum analyzer or any frequency extenders, keeping the system less complex and less expensive. We demonstrate the architecture for a frequency range that surpasses the E-band range by 10 GHz, i.e. from 50 to 90 GHz, but it is easily extendable to frequencies beyond 300 GHz or to frequencies as low as 25 GHz. A minimum power of 300 fW at 72 GHz was detected when using a resolution bandwidth of 1 Hz.