Broadband Dipole Absorption in Dispersive Photonic Time Crystals

TL;DR

This paper demonstrates that dispersive and absorptive photonic time crystals can enable broadband dipole absorption through temporal modulation, overcoming limitations of narrowband amplification and exceptional point-related instabilities.

Contribution

It reveals that considering dispersion and absorption allows broadband dipole absorption in photonic time crystals, a novel effect not limited to narrow resonance conditions.

Findings

Broadband dipole absorption occurs in dispersive, absorptive PTCs.

Temporal modulation converts emission into absorption across a wide frequency range.

The effect is robust in both stable and unstable regimes.

Abstract

Photonic media modulated periodically in time, termed photonic time crystals (PTCs), have attracted considerable attention for their ability to open momentum bandgaps hosting amplifying modes. These momentum gaps, however, generally appear only at the system's parametric resonance condition which constrain many features derived from amplification to a narrow frequency band. Moreover, they are accompanied by exceptional points (EPs) and may drive the system into an instability, which render their analysis more intricate. Here, we show that a careful consideration of dispersion and absorption can overcome these issues. By investigating the dissipated power of a point-dipole embedded in a dispersive and absorptive PTC, we unveil that temporal modulation enables the conversion of dipole emission into dipole absorption within a broadband frequency window free of EPs. We demonstrate that this effect is general, emerging in both the stable and unstable regimes, and occurs from weak modulation strength to low modulations frequencies that could be achieved for various material platforms.