Frequency-Modulated Combs via Field-Enhancing Tapered Waveguides
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Date
2023-12
Publication Type
Journal Article
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Abstract
Frequency-modulated (FM) combs feature flat intensity spectra with a linear frequency chirp, useful for metrology and sensing applications. Generating FM combs in semiconductor lasers generally requires a fast saturable gain, usually limited by the intrinsic gain medium properties. Here, it is shown how a spatial modulation of the laser gain medium can enhance the gain saturation dynamics and nonlinearities to generate self-starting FM combs. This is demonstrated with tapered planarized terahertz (THz) quantum cascade lasers (QCLs). While simple ridge THz QCLs typically generate combs presenting a mixture of amplitude and frequency modulation, the on-chip field enhancement resulting from extreme spatial confinement leads to an ultrafast saturable gain regime, generating a pure FM comb with a flatter intensity spectrum and a clear linear frequency chirp. The observed linear frequency chirp is reproduced using a spatially inhomogeneous mean-field theory model, which confirms the crucial role of field enhancement. In addition, the modified spatial temperature distribution within the waveguide results in an improved high-temperature comb operation, up to a heat sink temperature of 115 K, with comb bandwidths of 600 GHz at 90 K. The spatial inhomogeneity leads as well to very intense radio frequency (RF) beatnotes up to -30 dBm and facilitates dynamic switching between various harmonic states in the same device.
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published
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Journal / series
Volume
17 (12)
Pages / Article No.
2300472
Publisher
Wiley-VCH
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Date collected
Date created
Subject
field enhancement; frequency combs; frequency modulation; quantum cascade lasers; terahertz
Organisational unit
03759 - Faist, Jérôme / Faist, Jérôme
02205 - FIRST-Lab / FIRST Center for Micro- and Nanoscience
Notes
Funding
724344 - On Chip Terahertz Frequency Combs (EC)
212735 - Integrated, fast on-chip combs and detectors for coherent THz photonics (SNF)
212735 - Integrated, fast on-chip combs and detectors for coherent THz photonics (SNF)