Engineering the spectral bandwidth of quantum cascade laser frequency combs

Abstract

Quantum cascade lasers (QCLs) facilitate compact optical frequency comb sources that operate in the mid-infrared and terahertz spectral regions, where many molecules have their fundamental absorption lines. Enhancing the optical bandwidth of these chip-sized lasers is of paramount importance to address their application in broadband high-precision spectroscopy. In this work, we provide a numerical and experimental investigation of the comb spectral width and show how it can be optimized to obtain its maximum value defined by the laser gain bandwidth. The interplay of nonoptimal values of the resonant Kerr nonlinearity and the cavity dispersion can lead to significant narrowing of the comb spectrum and reveals the best approach for dispersion compensation. The implementation of high mirror losses is shown to be favourable and results in proliferation of the comb sidemodes. Ultimately, injection locking of QCLs by modulating the laser bias around the roundtrip frequency provides a stable external knob to control the FM comb state and recover the maximum spectral width of the unlocked laser state.

References in corpus (6)

• Theory of frequency modulated combs in lasers with spatial hole burning, dispersion and Kerr
• Coherent injection locking of quantum cascade laser frequency combs
• In-phase and anti-phase synchronization in a laser frequency comb
• Dual-comb spectroscopy for high-temperature reaction kinetics
• Mode-locked ultrashort pulses from an 8 $\mu$m wavelength semiconductor laser
• Mid-infrared quantum cascade laser frequency combs with a microstrip-like line waveguide geometry

Cited by in corpus (7)

• Ultrashort pulse generation from a graphene-coupled passively mode-locked terahertz laser
• Planarized THz quantum cascade lasers for broadband coherent photonics
• Analytical theory of frequency-modulated combs: generalized mean-field theory, complex cavities, and harmonic states
• Engineering THz-frequency light generation, detection and manipulation through graphene
• Broadband surface-emitting THz laser frequency combs with inverse-designed integrated reflectors
• Battery-operated mid-infrared diode laser frequency combs
• Quantum Cascade Lasers as Broadband Sources via Strong RF Modulation