We developed and demonstrated a novel method for sub-diffraction limit optical microscopy based Fluorescence Resonance Energy Transfer (FRET). The method relies on separating a FRET pair between a probe and the sample (see publications). The close range and strong distance dependence of the FRET efficiency guarantees that the resolution is limited not by the wavelength but by the Forster radius for energy transfer which is of the order of a few nanometers. We are currently developing alternatives that do not require scanning the probe across the sample as described in our previous works.