Research On Infrared Optical Modulator Based On Non-Volatile Phase Change Materials

Electro-optical modulators,as the basic units for optical information modulation,play an important role in various microscale integrated nanophotonic chips of different functionalities.They can dynamically change the optical properties of tunable materials by applying external electric fields,such as controlling incident light amplitude,phase,and polarization etc.The electrical modulation abilities of various modulators are dependent on the intrinsic electro-optical properties of tunable materials.In recent years,phase-change materials(PCMs)have attracted much research attention due to their virtues including electro-optical tunability,nonvolatility,and reversibility and integration compatibility.The material phase of PCMs can reversely convert between amorphous and crystalline states if stimulated by heating,laser pulse,and electric-current pulse,exhibiting remarkable variations of their electrical and optical performance.However,the most popular pathways inducing the phase conversion in previous works are by heating and laser illumination,which limits the PCM application into integrated circuits.Phase changes driven by electrical pulses are still challenging because the proper arrangement of electrodes for light modulators should consider both electric conduction and light coupling,which brings in many constraints on the aspects of device design and fabrications.In this work,we propose a PCM optical modulator with a pair of electrodes placed in the same metal layer.The phase change material Ge Sb₂Te₃ is deposited into the slot of electrodes,which is also capped with h-BN as the protection layer.The phase conversion of Ge Sb₂Te₃ can modulate the phonon polaritons sustained in the h-BN layer.We demonstrate two-order repeatable changes of Ge Sb₂Te₃ resistivity when reversely driven by the pulsed voltage.The near-field optical imaging shows that the wavelengths of phonon-polaritons in the h-BN slab shorten if Ge Sb₂Te₃ changes from amorphous to crystalline state.However,these GST modulators are easy to break down,resulting in device failure.Therefore,with reference to phase change memories,we modify the metal/Ge₂Sb₂Te₅(GST)/metal stacked configurations for optical modulators,where the top(bottom)electrodes are replaced by N(M)branches of metal gratings.By applying bias voltages between the top and bottom electrodes,the intermediate GST can form phase-changing sites at the intersection areas of electrodes.We design a metasurface for infrared spatial light modulation working at the frequency band from 3?m to 10?m,which exhibits mode conversion between electric dipole resonances and magnetic dipole resonances,achieving dual-band perfect absorption and a modulation depth of?80%after GST phase change.This electrode configuration provides a feasible way to design electro-optical modulators.Since the ideal electrode materials should be conductive and transparent for GST optical modulators.We also proposed two-dimensional Dirac semimetal Pt Se₂ as novel electrode material,which has low absorption in infrared and high conductivity(?2.58×10⁵ S/m).We demonstrate the optical modulation performance of Pt Se₂/GST/Au stacked layers.This multilayer device can also be treated as a Fabry-Perot cavity,where the resonances can be tuned by the intermediate GST layer.By the heating method,we experimentally achieve a modulation depth of 86%and resonant-frequency shift of???877.9 cm^-1.These electrode configurations are promising to be applied into integrated optical modulators and our results provide an important reference for designing GST optical devices.