Broadband Dipole Absorption in Dispersive Photonic Time Crystals

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 renders 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.