Multi‐Level Electro‐Thermal Switching of Optical Phase‐Change Materials Using Graphene

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 overcome 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. Herein, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that uses undoped‐graphene microheaters to thermally and reversibly switch the optical phase‐change material Ge2Sb2Se4Te1 (GSST). An in situ Raman spectroscopy method is utilized to demonstrate, in real‐time, 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.

Non‐Volatile Reconfigurable Integrated Photonics Enabled by Broadband Low‐Loss Phase Change Material

“…Since the cyclability of blanket film SbS has been recently reported using laser pulses, [34,53] we believe the low cyclability of our device is more of a heater design issue rather than SbS's material issue. Transparent conductors whose conductivity is thermally stable such as graphene [54] and FTO [55] could provide a better solution for operation with large number of cycles.…”

On-Chip Integrated Photonic Devices Based on Phase Change Materials

“…Rather, to switch, either electrical means or optical means are used which achieve the temperature required for switching between crystalline and amorphous phases. Although some electro-thermal methods have also been improved recently through the use of devices such as graphene heaters [79], considered as a fundamental mechanism, there is a lag in switching speed [80]. Among these three means of switching, optical switching produces the fastest switching, followed by electrical switching, while thermal switching remains the slowest [19,36].…”

“…However, most importantly as per the current thrust of society toward energy conservation, the electronic method of switching is also wasteful in terms of energy, leading to higher cost per switch. Recently, some graphene-based models have been suggested (schematically shown in Figure 6b) due to their success in limiting the energy waste in electrically controlled PCM-based photonic devices [79,92].…”

Tunable Metasurfaces: The Path to Fully Active Nanophotonics

“…For example, the integration of graphene with PCMs as discussed in Section 2.1 has been demonstrated using GSST. [ 165 ] The interesting characteristics of graphene and 2D materials, in general, could play a big part in tunable metasurfaces in the visible regime, as the methods of fabricating and manipulating them at the nanoscale improve.…”