Van der Waals Photonic Switches

• Van der Waals photonic switches are advanced devices that use layered 2D materials to modulate light via near‐field interactions and engineered electronic bands.
• They exploit quantum tunneling, excitonic nonlinearities, and topological interface states to achieve ultrafast, low-loss, and wavelength-selective switching.
• These platforms enable integration into next-generation optoelectronics and quantum photonics with compact architectures and precise control mechanisms.

Van der Waals photonic switches leverage the unique light–matter interactions, electronic band engineering, and nano-optical control enabled by layered atomically thin materials held together by van der Waals (vdW) forces. Integrating such materials into photonic architectures facilitates highly tunable, efficient, and compact switching mechanisms spanning quantum tunneling, strong coupling, excitonic nonlinearities, atomic void channel guiding, chiro-optical bandgap control, and topological interface states. These platforms enable dynamic, low-loss, wavelength- and polarization-selective modulation suited to next-generation optoelectronics, quantum photonics, and integrated circuit technologies.

1. Fundamental Principles and Physical Mechanisms

Van der Waals photonic switches operate by modulating the optical response via controlled near-field interactions and material resonances intrinsic to 2D atomic crystals and their heterostructures. Core physical mechanisms include:

• Dynamical van der Waals atom–surface interaction: For an atom moving parallel to a surface, the nonretarded vdW interaction energy $U(z,V)$ (with separation $z$, velocity $V$) is nonlinearly dependent on both parameters as

$$U(z,V) = - \frac{\hbar}{2\pi} \int_0^\infty d\xi \int_0^\infty dk\, k\, e^{-2kz}\, \text{Im}\{ \Delta(i\xi) \alpha(i\xi + kV) \},$$

where $\alpha(\omega)$ is atomic polarizability and $\Delta(\omega)$ depends on the surface’s permittivity. Velocity-dependent modulation allows ultrafast switching of local optical properties through atomic or nanoparticle kinetic control (Dedkov et al., 2011).

• Quantum tunneling heterostructures: Devices such as Au/hBN/graphene stacks employ inelastic electron tunneling to generate photons and SPPs; the photonic local density of states (LDOS) and electronic tunneling channels are independently controlled. Coupling to resonant nanocube antennas enhances photon emission rates by several orders of magnitude, achieving efficient, bias-controllable switching via modulation of tunneling current and/or LDOS (Parzefall et al., 2018).
• Interlayer band engineering: vdW interfaces with type-II band alignments—both conduction and valence band edges at the $\Gamma$-point—enable robust, radiative interlayer transitions insensitive to lattice mismatch and layer misalignment. The switching action relies on the control of the population and radiative recombination of spatially indirect excitons, with spectral tunability via electric field, excitation power, or material choice (Ubrig et al., 2019).
• Resonant and strong coupling nanophotonics: Bulk and monolayer TMDCs (e.g., WS$_2$, MoS$_2$, WSe$_2$) offer high refractive indices ($n \approx 4$), low losses, and strong excitonic resonances, enabling deep mode confinement, Purcell enhancement, and efficient electro-optic modulation. All–vdW photonics platforms demonstrate integration of waveguides, nanocavities, and modulators with superior switching metrics compared to conventional 3D semiconductors (Ling et al., 2020), including lower switching energy per bit, smaller footprints, and stronger light–matter interaction.

2. Device Architectures and Integration Strategies

Wide-ranging vdW-based switch architectures have been reported:

• Waveguides and channel switches: Layered TMDC waveguides and atomic-void channel structures exhibit deeply subwavelength mode confinement ($>$70% power in $d<\lambda/100$ channel) with low plasmonic losses. Excitonic or phonon-polaritonic resonances of TMDCs and hBN further enhance nonlinear response, allowing rapid control of light propagation via index modulation, gating, or optical pumping (Ling et al., 2022).
• Dielectric nanoantenna integration: vdW layers can be stacked or transferred onto dielectric nanoantennas to harness Mie resonances and create strong exciton–photon coupling regimes. The dielectric function is modeled as

$$\varepsilon(\omega) = \varepsilon_\infty + \sum_j \frac{S_j}{\omega_j^2-\omega^2-i\gamma_j\omega},$$

leading to wavelength-selective, room-temperature switching through exciton–polariton states or nonlinear optical processes (Zotev et al., 2022).

• Metasurfaces and intrinsic cavity formation: vdW heterostructure metasurfaces comprising monolayer WS$_2$ encapsulated in hBN and patterned as asymmetric nanorods exploit quasi-bound states in the continuum (qBICs) to form ultrathin, high-$Q$ optical cavities. Analytical models use a coupled harmonic oscillator Hamiltonian:

$$H = \begin{pmatrix} E_{\text{qBIC}} - i\gamma & g \ g & E_X - i\gamma_X \end{pmatrix},$$

with Rabi splitting $\Omega_R \simeq 2g$ observed at excitation fluences $<1$ nJ/cm$^2$ (Sortino et al., 23 Jul 2024).

• Hybrid photonic microsphere systems: Micrometer-scale spheres coupled to TMDC monolayers (via whispering gallery modes) induce %%%%20$n \approx 4$21%%%% enhancement of electroluminescence and photoluminescence, with Purcell factors $F_P \propto Q/V$ tunable by sphere size and substrate thickness (Lee et al., 2021).
• Topological photonic gratings: Stacked WS$_2$ gratings with different filling factors produce 1D topological Jackiw-Rebbi (JR) interface states between inverted photonic bands. Coupling monolayer WSe$_2$ excitonic emission into these JR states achieves highly directional switching (up to 22$\times$ enhancement) and spatial confinement validated by s-SNOM and angle-resolved reflectance contrast (Randerson et al., 4 Jun 2025).

3. Functional Performance, Tunability, and Modal Control

vdW photonic switches offer distinct performance advantages:

Platform/Mechanism	Key Metric	Switch Modality
TMDC cavity switches	Purcell factor $F_P$ %%%%27$\alpha(\omega)$28%%%% Si	Emission/loss/phase
Atomic-void channels	$>$70% power in $<\lambda$/100 gap	Index/band switching
Quantum tunneling stack	%%%%31$n \approx 4$32%%%% PL enhancement, low power	Bias/LDOS gating
Metasurfaces (qBIC)	Saturated $2g$ at $<$1 nJ/cm$^2$	Ultrafast, nonlinear
JR gratings	10 meV linewidth, 8$^\circ$ band	Directional control
THz BSCCO arrays	50 ps switch time, 2-mode modulator	Phase/amplitude

Performance is determined by modal confinement, nonlinear response, and material anisotropy. For instance, the giant anisotropy of WS$_2$ (in-plane $n\sim4.2$, out-of-plane $n\sim2.5$) suppresses higher-order modes—allowing single-mode operation over extended parameter ranges and crosstalk distances up to 4.7 mm (Vyshnevyy et al., 2023). Nonlinear near-field spectroscopy of hBN/WS$_2$/hBN waveguides reveals exciton-polariton Rabi splittings of $\sim$50 meV, with ultrafast pump-induced transitions from strong to weak coupling—enabling all-optical switch modulation (Kondratyev et al., 15 Oct 2025).

4. Operational Principles and Modulation Schemes

Three primary approaches to photonic switching in vdW platforms are employed:

• Electrical bias or gating: In quantum tunneling and excitonic metasurface devices, the applied gate voltage modulates carrier densities, altering recombination rates, radiative lifetimes, and complex refractive index profiles. For example, beam steering by a MoSe$_2$ metasurface relies on local tuning of phase via the modulated exciton decay rates, achieving reflected beam angles of $\pm30^\circ$ at three distinct wavelengths (Li et al., 2022).
• Optical pumping/modulation: Femtosecond laser excitation in van der Waals waveguides or THz superconducting metamaterials transiently modifies the interaction strength, switching between strong and weak coupling regimes and modulating THz transmission amplitude/phase on 50 ps timescales (Delfanazari, 2023, Kondratyev et al., 15 Oct 2025).
• Mechanical displacement/atomic velocity: In dynamical vdW atom–surface switches, atomic or nanoparticle velocity directly modulates the interaction energy $U(z,V)$, with sharp, nonlinear switching sensitivity to both velocity and separation. Effective modulation requires control at the atomic scale—$\sim$0.3-1 nm gaps and $10^6$-$10^7$ m/s velocities (Dedkov et al., 2011).

5. Limitations, Challenges, and Engineering Considerations

Practical realization of vdW photonic switches presents distinct challenges:

• Extreme sensitivity to nanoscale variations: Many vdW switch mechanisms require atomically precise control of layer thickness, gap size, and alignment to preserve strong coupling, directional switching, or nonlinear response. For atomic-void channels and dynamical interactions, sub-nm tolerances are crucial.
• Material quality, integration, and losses: High crystalline quality is needed to minimize defect-induced nonradiative recombination and propagation losses. Weak interlayer bonding facilitates integration but also demands careful encapsulation (e.g., hBN protection for 2D interfaces) to maintain interface quality (Ubrig et al., 2019).
• Thermal and fluctuation sensitivity: Nonlinear and velocity-dependent mechanisms are particularly susceptible to thermal noise or slight mechanical disturbances, which can induce unwanted switching or reduce reliability.
• Operational regimes and scalability: Some systems (e.g., THz superconducting switches) require cryogenic operation, while others (e.g., quantum tunneling and TMDC circuits) are compatible with room temperature. Scaling up device integration calls for robust fabrication techniques (CVD growth, roll-to-roll transfer, robotic stacking) and process control against contamination, strain, and anisotropy variations (Meng et al., 2023).

6. Emerging Directions and Future Prospects

Van der Waals photonic switches continue to evolve across several promising fronts:

• Combination of metasurface engineering and vdW stacking: Recent advances producing ultrathin qBIC optical cavities (effective $Q>100$) merge metasurface design with atomic layer assembly, achieving strong coupling and nonlinear switch action with fluences $<$1 nJ/cm$^2$ (Sortino et al., 23 Jul 2024).
• Topological and chiral switches: vdW-based JR interface states and helical super-crystals enable robust, defect-resistant, and polarization-selective switching, opening avenues for directional emission control and chiral optics in integrated circuits (Randerson et al., 4 Jun 2025, Voronin et al., 2023).
• Integrated quantum and THz photonics: THz BSCCO vdW metamaterials combine amplitude and phase modulation at picosecond speeds, offering multifunctional operation for 6G communications and quantum light sources, albeit with ongoing challenges in cooling and fluence control (Delfanazari, 2023).
• All-optical and nonvolatile switching: Nonlinear near-field and exciton–polariton dynamics promise ultrafast, electrically or optically reconfigurable switches, enabling compact modulators for on-chip applications (Kondratyev et al., 15 Oct 2025).

Continued innovation in material synthesis, device patterning, and atomic-level control is likely to drive the deployment of van der Waals photonic switches into commercial and quantum photonic platforms. Their flexibility, tunability, and near-field sensitivity distinguish them as a cornerstone technology for future integrated nano-optics.