Figure 14.

a) Microring resonator integrating WO_x/graphene/hBN into SiN waveguide. Resonator transmission spectra was tuned to critical coupling condition after UV–ozone oxidation of WSe₂, showing the reduction of insertion loss of graphene by WO_x doping. Reproduced with permission.^{[ 19 ]} Copyright 2021, Springer Nature. b) Transmittance of intrinsic graphene (97.7%) increase to 99.2% using a WO_x layer at telecommunication wavelength (1550 nm). Reproduced with permission.^{[ 19 ]} Copyright 2021, Springer Nature. c) Schematic diagram of ultralow‐loss phase tuning of monolayer WS₂ using the WS₂–HfO₂–WO_x/graphene capacitor structures. Monolayer WS₂ can be electrostatically doped by applying a bias voltage between two electrodes (TMD and WO_x/graphene) across the dielectric HfO₂, which changes the refractive index while minimizing absorption.