Defect in photonic time crystals

Photonic time crystals (PTCs) provide a completely new platform exhibiting light wave amplification owing to periodically varying electromagnetic properties. The need to control this amplification is becoming increasingly important, especially with the emergence of metasurface-based practical realization of PTCs. This paper investigates the introduction of isolated temporal defect in PTCs to establish an increased degree of control over the amplification. We find that in the presence of the defect, the transmittance and reflectance become close to unity for a specific value of momentum kd within the band gaps accompanied by a significant impact on the amount of amplification. We show the impact of the temporal defect on the exponential growth of the intensity with PTC periods. The effect primarily depends on the Floquet frequency of the PTC, which becomes real at kd giving rise to four pulses instead of two as an outcome of gap propagation. We further demonstrate that by manipulating the temporal and dielectric properties of the defect, the defect state in the momentum can be tuned to serve the design interest for specialty applications.