Work

High Q‐contrast terahertz quantum cascade laser via bandgap‐confined bound state in the continuum

Year: 2025

Type: article

Abstract: Photonic bound states in the continuum (BICs) are optical modes that remain highly localized despite co‐existing with radiating waves in the continuum, attracting considerable attention for both fundamental studies and technological innovations. Conventional single‐mode BIC lasers predominantly focus on maximizing the Q‐factor of a specific mode, often overlooking the critical role of Q‐contrast – the difference in Q‐factors between the highest‐Q BIC mode and competing modes – which is crucial for achieving stable single‐mode lasing. In this study, we present a compact, high Q‐contrast BIC laser, enabled by strategically optimizing the alignment of the TM 1 band of the core domain with the shell domain to confine the high Q‐factor mode within the core. Using a quantum cascade laser chip operating in the terahertz (THz) regime, this design achieves a Q‐contrast ratio of approximately 2.3, resulting in stable single mode lasing across the dynamic region with a side‐mode suppression ratio of ∼20 dB. These findings underscore the pivotal role of Q‐contrast in photonic lasers, with promising implications for applications in THz lasers, sensors, harmonic signal generators and modulators.

Source: Nanophotonics

DOI: 10.1515/nanoph-2024-0757