Fig. 1. (a) Schematic of a few-layer MoS2-based phase shifter. The part of the blue dotted square represents the coupling region between the bus waveguide and micro-ring resonator, corresponding to a coupling gap of ∼550  nm. The part of the red dotted square shows the inverse taper waveguide with 350  nm×780  nm cross section and ∼89.4° perpendicularity of the sidewall for a high coupling efficiency. The part of the green dotted square is the active modulation region. The detail illustration is shown in (b), which is the MoS2–SiN integrated structure cladded with ionic liquid (DEME+–TFSI−) to form a capacitor configuration. The bias voltage is used to induce the accumulation of charged carriers at the interface of MoS2 and then change its optical properties.

Fig. 2. (a) Broadband linear absorption spectrum of few-layer MoS2 film. The inset image is the thickness of film measured by an AFM. (b) Raman spectrum of transferred few-layer MoS2, corresponding to the typical Raman vibrational modes.

Fig. 3. (a) Normalized transmission response of the phase shifter as a function of applied bias voltage (cations doping on the interface of MoS2 film). (b) Offset of resonance wavelength, corresponding to a tuning efficiency of 29.42 pm/V. (c) Simulation results of different coupling states for a micro-ring resonator.

Fig. 4. (a) Normalized transmission response of a phase shifter as a function of applied bias voltage (anion doping on the surface of MoS2 film). (b) The offset of resonance wavelength at different voltages, which shows a lower tuning efficiency than that of cation doping.

Fig. 5. (a) Normalized transmission response of a phase shifter at high bias voltages. (b) The offset of resonance wavelength loses its linearity at −2.7  V and tends to a similar saturation state when the voltage is further increased.

Fig. 6. The effective index of the composite MoS2−SiN waveguide is exacted from the tuned resonance and plotted as a voltage dependent function. The inset images are the energy-band diagram of few-layer MoS2 under different types of charged doping, where EC−N and EV−N are the conduction band edge and valence band edge of n-type MoS2 and EF is the Fermi energy level.