arXiv subjects

Sihao Zhang

Publications and source records attributed to Sihao Zhang.

3 recordsLinked to original sources

arXiv2026

Temporal Weyl Physics and Topological Control of Direction-Selected Radiation in Anisotropic Photonic Time Crystals

Anisotropic photonic time crystals, enabled by periodic temporal modulation of a uniform anisotropic medium, exhibit asymmetric momentum-bandgap structures and offer unique control over light-matter interactions. Here, we introduce and construct temporal Weyl points in APTCs within a synthetic three-dimensional space defined by two phase parameters and the quasi-frequency. The temporal response reveals robust Fermi arcs linking TWPs of opposite topological charge. Unlike spatial counterparts, these Fermi arcs emerge only after the first temporal supercell comprising multiple periods of APTCs, reflecting causality. We further show that TWPs generate a directional near-zero radiation trajectory in momentum space with tunable radiation from stationary charges embedded in APTCs, while the associated Fermi arcs robustly suppress radiation at selected directions and frequencies. Our findings establish temporal Weyl physics in photonic time crystals and uncover new opportunities for topological control of light-matter interactions through the time dimension.

physics.optics↗

arXiv2024

Longitudinal optical phonons in photonic time crystals containing a stationary charge

Lorentzian-type media support optical phonons that oscillate with longitudinal polarization parallel to the wave direction, at a wave vector-independent frequency at which the permittivity becomes zero. Here, we study the interactions between the longitudinal optical phonons and Lorentzian medium-based dispersive photonic time crystals (PTCs). We demonstrate that a stationary charge embedded in the PTCs can excite these longitudinal modes through the conversion of the static polarization field induced by the charge. Furthermore, the PTCs can develop a momentum bandgap across the entire wave vector space to amplify the longitudinal modes. Remarkably, this infinite momentum bandgap can be established with minimal temporal modulation of the refractive index when creating the PTCs. Our approach expands the range of waves that can be manipulated in PTCs and shows potential for observing momentum bandgap phenomenon in realistic optical experiments, where the modulation depth of the refractive index is severely constrained.

physics.optics↗

arXiv2024

Non-uniform wave momentum bandgap in biaxial anisotropic photonic time crystals

Photonic time crystals (PTCs) host momentum bandgaps enabling intriguing non-resonant light amplification in propagating waves, but opening substantial bandgaps demands refractive index changes too extreme for conventional nonlinear optics. Here, we introduce momentum bandgaps for non-uniform waves, including evanescent and ghost types, by extending PTCs to biaxial anisotropic photonic time crystals that periodically alternate between uniform biaxial anisotropy and isotropic media over time. We show that ghost waves, unlike evanescent waves, sustain only momentum bandgaps, opening wide bandgaps at even the smallest modulation depths. Moreover, we demonstrate momentum bandgap effects on non-uniform waves that can be amplified, or through decaying modes, selectively attenuated. We find that ghost wave momentum bandgaps uniquely boost refracted over reflected waves under one-way incidence, in stark contrast to balanced amplification seen in both propagating and evanescent waves. Our approach expands time-varying metamaterials by integrating wave characteristics, bridging the gap between conventional nonlinear optics and PTC momentum bandgaps, and shedding new light on extreme manipulation of surface polaritons.

physics.optics↗