Although these devices have some differences, they also have features in common. The devices are about 50m across, and have an angular resolution of about 0.03 arc seconds. The telescopes and all components in the optical path are radiatively cooled to a temperature where their thermal emission is negligible. The devices operate at about 5AU from the Sun, where the thermal emission of our own system's zodiacal dust is negligible. The detected noise is the photon shot noise of the zodiacal dust of the external system.
Signals are very feeble and so detectors of exceptionally low noise are needed.
The signals from all planets are multiplexed by the interferometer, so that all planets of a system are observed simultaneously. The technological requirements to make these observations are harder to meet than they have been for any spacecraft to date. There are very tight tolerances for pointing, phasing and amplitude control that require new techniques to be developed. And all systems must operate where no human help can be made available. Secondly, the device has a limited angular resolution.