Continuous-wave terahertz quantum cascade lasers based on quasi-flatband BIC and 2D dual-patch arrays

Area of Science:

• Optics and Photonics
• Semiconductor Devices
• Quantum Engineering

Background:

• Terahertz quantum cascade lasers (THz-QCLs) are crucial for various applications, but their performance is often limited by thermal management and beam quality.
• Bound states in the continuum (BICs) offer a route to enhance light-matter interaction, but their practical implementation in THz-QCLs faces challenges due to fabrication imperfections and finite device sizes.

Purpose of the Study:

• To design and demonstrate a THz-QCL incorporating quasi-flatband BICs for improved performance.
• To investigate the impact of photonic band structure engineering on laser characteristics.
• To achieve higher operating temperatures, enhanced output power, and superior beam quality in THz-QCLs.

Main Methods:

• Utilized a two-dimensional dual-patch rhombic lattice to engineer photonic band structures with quasi-flatband BICs.
• Designed the lattice to achieve low group velocity near the Γ-point for enhanced BIC robustness.
• Incorporated controlled patch asymmetry for tunable radiation efficiency and a distributed array design for improved thermal dissipation.

Main Results:

• Demonstrated pulsed operation up to 123 K and continuous-wave (CW) operation up to 89 K.
• Achieved an optimized CW output power of 8.0 mW at 20 K with a Gaussian beam profile.
• Obtained a narrow far-field divergence of 7° × 9° due to the distributed array design.

Conclusions:

• The quasi-flatband BIC design significantly enhances THz-QCL performance, particularly in operating temperatures and beam quality.
• This approach offers a promising pathway for developing practical THz-QCLs for diverse applications.
• The study highlights the potential of BIC-based photonic structures for next-generation terahertz optoelectronics.