Discrete mode tuning in terahertz quantum cascade lasers

Area of Science:

• Optics and Photonics
• Quantum Electronics
• Terahertz Technology

Background:

• Quantum cascade lasers (QCLs) are crucial for terahertz (THz) applications.
• Achieving precise frequency control in THz QCLs remains a challenge.
• Existing Fabry-Pérot (FP) cavities often support multi-mode operation.

Purpose of the Study:

• To enhance single-mode selectivity and enable discrete electronic tuning in THz QCLs.
• To investigate dual-mode lasing with electrically controlled frequency separation.
• To explore a phase-sensitive mode selection mechanism.

Main Methods:

• A holographically designed, aperiodic distributed feedback grating was used as a multi-resonance filter.
• The filter was embedded within a Fabry-Pérot (FP) THz quantum cascade laser (QCL) cavity.
• Balancing feedback strengths of filter resonances and FP cavity for mode control.

Main Results:

• Achieved purely electronic discrete tuning over 160 GHz with 30 GHz resolution for multi-moded QCLs (~2.9 THz).
• Demonstrated dual-mode lasing with electrically controlled frequency separation from 190 to 267 GHz for QCLs with dual gain peaks (~2.65 and 2.9 THz).
• Experimentally confirmed a phase-sensitive mode selection mechanism via divergent fine-tuning of lasing modes.

Conclusions:

• The multi-resonance filter effectively enhances single-mode selectivity and enables precise electronic tuning in THz QCLs.
• This approach facilitates controlled dual-mode lasing with tunable frequency separation.
• The demonstrated phase-sensitive mechanism offers advanced control over THz laser output.