All-silicon active bound states in the continuum terahertz metamaterials

Bound states in the continuum (BIC) are a non-radiative state embedded in a continuous spectrum of radiating waves. BICs have emerged as a promising platform for opto-electronic phenomena that are dependent on high quality factors. However, the quality factor of metallic metamaterial-based BICs is limited due to ohmic loss, even at terahertz frequencies. As an alternative, we investigate active all-silicon BIC terahertz metamaterials. Quasi-BIC states can be realized either through structurally symmetry breaking or by changing the incident angle of the terahertz waves, as verified with coupled mode theory (CMT). Samples fabricated using micromachining techniques were characterized using terahertz time domain spectroscopy revealing good agreement with simulations. Moreover, we investigated optical tuning of the quasi-BIC response using low-fluence (<25μJ/cm2) excitation with 1.5 eV pulses. The dynamic response is consistent with full-wave electromagnetic simulations and indicate that all-silicon metamaterials are a viable active BIC platform with potential applications including terahertz sensing and terahertz nonlinear lightwave phenomena.