Optical interferometry is not a remote sensing concept. It is an optics and high-level astronomy concept. Telescopes are limited in resolution relative to the maximum distance between points on their primary mirror (the diameter, conventionally). Interferometer telescope arrays combine the beams of two to six telescope mirrors that are located hundreds of meters away in order to achieve higher resolution than it's possible to construct a telescope mirror for.
In theory it's possible to construct a satellite optical interferometer for earth observation rather than astronomical use, but these things are incredibly hard to build, requiring the mirrors to be precisely located in positions on the order of tens of atoms. I'm aware that the GEOINT community can put to shame anything that NASA's developed, and it would be very useful, but a large interferometer surviving a rocket launch is a tall order, and not really necessary when one has spyplanes.
Interferograms created from Synthetic Aperture Radar are a common source of highly detailed local Digital Elevation Models (DEMs). Unless you're dealing directly with satellite data, you shouldn't have to mess with these concepts, though - you'd just be dealing directly with a DEM.
What are you trying to do?