Controllable all-optical modulation speed in hybrid silicon-germanium devices utilizing the electromagnetically induced transparency effect

Incorporating auxiliary all-optical modulation speeds as optional response modes into a single metamaterial is a promising research route towards advanced terahertz (THz) applications ranging from spectroscopy and sensing to communications. Particularly, a plethora of dynamically tunable optical functionalities are determined by the resonant light-matter interactions. Here, an electromagnetically induced transparency (EIT) resonator stacked with two traditional semiconductor films, namely silicon (Si) and germanium (Ge), is experimentally demonstrated. A giant switching feature of the EIT window with a peak at 0.65 THz occurs when the Si or Ge film is excited by ultrafast optical pulses, allowing for an optically tunable group delay of the THz wave packet. The recovery time for the slow and fast on-off-on switching cycles is 1.7 ns and 11 ps, respectively, which are mapped as the pump delay time of Si and Ge. Two optional response modes are integrated on the same device, where the modulation speed varies by three orders of magnitude, endowing the modulator more compact. This work provides new prospects for the design and construction of novel chip-scale THz devices based on EIT and their applications in areas of sophisticated optical buffering and active filtering.