Reversible Switching of Optical Phase Change Materials Using Graphene Microheaters

Abstract

Reconfigurable photonic systems featuring minimal power consumption are crucial for integrated optical devices in real-world technology. Current active devices available in foundries, however, use volatile methods to modulate light, requiring a constant supply of power and significant form factors. Essential aspects to overcoming these issues are the development of nonvolatile optical reconfiguration techniques which are compatible with on-chip integration with different photonic platforms and do not disrupt their optical performances. In this paper, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that employs undopedgraphene microheaters to thermally and reversibly switch the optical phase-change material Ge2Sb2Se4Te1 (GSST). An in-situ Raman spectroscopy method is utilized to demonstrate, in realtime, reversible switching between four different levels of crystallinity. Moreover, a 3D computational model is developed to precisely interpret the switching characteristics, and to quantify the impact of current saturation on power dissipation, thermal diffusion, and switching speed. This model is used to inform the design of nonvolatile active photonic devices; namely, broadband Si3N4 integrated photonic circuits with small form-factor modulators and reconfigurable metasurfaces displaying 2π phase coverage through neural-network-designed GSST meta-atoms. This framework will enable scalable, low-loss nonvolatile applications across a diverse range of photonics platforms.

Electrically Reconfigurable Nonvolatile Metasurface Using Optical Phase Change Materials

“…Based on the optimized heater design, Fig. 2c maps the average heater temperature for different pulse duration and voltage combinations, and the results (550 -630 K for crystallization and 1020 K for amorphization) are in excellent agreement with our prior data 42,50 .…”

“…As an example of phase and wave front control, we further realized active switching of a Huygens' surface beam deflector using the platform. Moreover, the electrical switching design and the geometric optimization approach for large-aperture metasurfaces demonstrated herein are also transferrable to other emerging heater materials such as silicon 56,57 and graphene 50 to enable a diverse array of reconfigurable metasurface devices.…”

Reconfigurable all-dielectric metalens with diffraction-limited performance

“…We have recently demonstrated highly consistent electrothermal switching of GSST over 1,000 phase transition cycles using on-chip metal micro-heaters 44 . Additionally, reversible switching of GSST and other phase change materials using transparent graphene and doped Si heaters have also been validated [57][58][59] . In this regard, the use of GSST rather than the classical GST alloy uniquely benefits from not only GSST's low optical attenuation but also its improved amorphous phase stability.…”

Tunable nanophotonics enabled by chalcogenide phase-change materials

“…In a pioneering work, Rios et al demonstrated a hybrid framework incorporating a graphene heater to electrothermally switch a large area of GSST [231]. Minimal optical loss, high intrinsic in-plane thermal conductivity, low heat capacity, and scalability make graphene a potential candidate for efficient conversion of PCMs in reconfigurable PICs.…”