Fig. 4: Optical phase-change memory device and its respective principle of operation.

a Information is stored in the phase state of the GST section on top of the nanophotonic waveguide. b Demonstration of binary memory operation between the crystalline (lower, level 0) and amorphous (upper, level 1) states of a 5 μm GST device for multiple repetitions of the same switching cycle. Figure reproduced with permission from ref. 52, © 2015 Nature Publishing Group