Edge detection in phase-change optical data storage

We introduce a new readout scheme, called edge detection scheme, for phase-change systems. A single split detector is used to detect the intensity of the reflected beam in the far field, and the readout signal, which relies on diffraction from mark boundaries, is the difference signal of the split-detector. We derive the magnitude of the readout signal for edge detection, clarify the effect of phase on the read signal, and compare noise levels at the output of readout systems using edge detection and sum detection.