Polarization-Selective Non-Volatile Switching in Hybrid Phase-Change Nanowires

Polarization, one of the fundamental properties of electromagnetic waves, provides extra physical dimensions for multiplexing optical information and has been essential for applications in optical communication, storage, and encryption. However, such multiplexing properties have been mostly passive thus far, and have not been employed as a tunable factor in optical systems.<br/><br/>Reconfigurable photonics on the other hand, has been rapidly growing. The use of phase change material is established as a functional block for non-volatile photonic and mixed-mode memories with prospective applications in neuromorphic and in-memory computing paradigms. These devices incorporate phase change materials as the reconfigurable elements and have been shown to achieve nanosecond switching performance with large optical modulation over a broad bandwidth. Reconfiguration in phase-change photonic devices is commonly achieved by controlling the intensity or pulse shape of an incident light wave while resonant structures are broadly employed to achieve wavelength-selective operation and enhanced modulation depths. The equivalent functionality in polarization-space is however absent. This significantly limits the addressability of distinct elements in cascaded systems without harnessing full advantages of photonic bandwidths.<br/><br/>Here, we demonstrate for the first time polarization-selective switching in hybrid phase-change nanowires,¹ wherein the optical absorption in the nanowires is modulated by polarization of incoming light. In doing so, the transient temperature profile is controlled to induce reversible switching of the hybridized phase-change element. Our hybrid nanowire consists of a two-layered system of Si/Ge₂Sb₂Te₅ (GST) where dielectric resonance of Si leads the GST to be switched in a polarization-selective manner. Such switching operation is finely modulated by changing the polarization directions, and therefore provides an important degree of freedom for control over the multilevel device states. Using this concept, we demonstrate the polarization-decoupled but electrically-interfaced multi-nanowire system to achieve polarization-selective demultiplexing at highly-confined spatial scales. We further show the use of this system to carry out matrix-vector multiplications with using polarization as a tunable variable. This leads to a huge enhancement of computing density, exceeding that of conventional electronic chips by several orders of magnitude. Our work provides the first such pathway for exploiting polarization to actively modulate device-states with applications ranging from optical encryption/storage to computing.<br/><br/><b>References</b><br/>[1] J. S. Lee, N. Farmakidis, C. D. Wright, H. Bhaskaran, ”Polarization-selective reconfigurability in hybridized-active-dielectric nanowires”, <i>Sci. Adv.</i> (2022) doi: 10.1126/sciadv.abn9459