The applications of phase-change memory in optical memory and in-memory/neuromorphic computing. (a) The integrated all-optical non-volatile memory based on PCM material Ge₂Sb₂Te₅ (GST). Here, the PCM material is placed on the top of a waveguide. The data recording is realized by the optical near-field effects. The writing and erasing operations are achieved by the laser pulse passes through the waveguide while the read operation relies on the transmission signal modulated by the optical absorption of PCM materials. (b) The illustration of in-memory arithmetic computing by optically-controlled phase change. (c) The all-optical neuromorphic computing system based on PCM material GST. The input pulses can induce the phase change (recrystallization) of PCM material, which in turn changes the output signals. Both the in-memory computing and the neuromorphic computing utilize the accumulation effect of the crystallization. Panel (a) is reproduced from Ref. [7] with permission from the Nature Publishing Group. Panel (b) is reproduced from Ref. [8] with permission from the John Wiley and Sons. Panel (c) is reproduced from Ref. [9] with permission from the Nature Publishing Group.