Mode-locked pulses from mid-infrared Quantum Cascade Lasers

Wang, Christine Y.; Kuznetsova, Lyuba; Gkortsas, V. M.; Diehl, Laurent; Kärtner, Franz X.; Belkin, Mikhail; Belyanin, Alexey; Li, X.; Ham, Donhee; Schneider, Harald; Grant, P. D.; Song, Chunying; Haffouz, S.; Wasilewski, Z. R.; Liu, H. C.; Capasso, Federico

doi:10.1364/oe.17.012929

Cited by 176 publications

(143 citation statements)

References 30 publications

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“…Fundamental mode-locking of QCLs has led to intense discussion in the literature [32][33][34] . Mode-locked operation of QCLs is difficult to achieve but have been demonstrated at cryogenic temperatures in the mid-infrared in a design where the upper-state lifetime was significantly increased using a highly diagonal laser transition 32 and in the terahertz where that lifetime is naturally much longer 35 .…”

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confidence: 99%

Dual-comb spectroscopy based on quantum-cascade-laser frequency combs

et al. 2014

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Dual-comb spectroscopy performed in the mid-infrared-where molecules have their strongest rotovibrational absorption lines-offers the promise of high spectral resolution broadband spectroscopy with very short acquisition times (ms) and no moving parts. Recently, we demonstrated frequency comb operation of a quantum-cascade-laser. We now use that device in a compact, dual-comb spectrometer. The noise properties of the heterodyne beat are close to the shot noise limit. Broadband (15 cm À 1 ) high-resolution (80 MHz) absorption spectroscopy of both a GaAs etalon and water vapour is demonstrated, showing the potential of quantum-cascade-laser frequency combs as the basis for a compact, all solid-state, broadband chemical sensor.

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confidence: 99%

Dual-comb spectroscopy based on quantum-cascade-laser frequency combs

et al. 2014

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“…As a result, some way of locking the modes together must be employed. Yet all the numerous attempts [14][15][16] to mode-lock QCL had limited success, and the practical achievements did not match numerous theoretical predictions. This problem can be traced to the fact that the in the QCL the relaxation time between the upper and lower laser levels (often referred to a "gain recovery time"), τ 21 is measured in picoseconds, and is thus much shorter than the cavity round trip time τ rt that is typically about 50-100ps in a few mm long cavity.…”

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confidence: 99%

Coherent frequency combs produced by self frequency modulation in quantum cascade lasers

Khurgin

Dikmelik

Hugi

et al. 2014

Applied Physics Letters

133

106

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One salient characteristic of Quantum Cascade Laser (QCL) is its very short τ ~ 1ps gain recovery time that so far thwarted the attempts to achieve self-mode locking of the device into a train of single pulses. We show theoretically that four wave mixing, combined with the short gain recovery time causes QCL to operate in the self-frequencymodulated regime characterized by a constant power in time domain and stable coherent comb in the frequency domain. Coherent frequency comb may enable many potential applications of QCL's in sensing and measurement.Quantum cascade lasers (QCL's) 1 are versatile sources of coherent radiation in the mid and far infrared regions of the spectrum, in which many chemical compounds have characteristic strong fundamental absorption lines. The atomic-like joint density of state character of intersubband transitions, combined with quantum engineering 2-4 , allows the development of QCLs with heterogenous active regions 5 covering a very large spectral range. Recently, by combining such broadband active regions with an external cavity 6 , continuous tuning over large spectral ranges have been achieved in the 8-10 and 3-5μm wavelength range 7 . However, these sources, tunable over hundreds of wavenumbers, require a cavity with moving components, naturally limiting their tuning speed as well as their compactness.In the last decade, a new approach to broadband spectroscopy has been proposed and implemented by the use optical frequency combs 8,9 . In a dual comb spectrometer 10-12 , two optical combs with slightly different mode spacing are beaten onto a fast detector. Since each pair of modes (one from each combs) can be made to beat at a slightly different frequency, a Fourier transform of the signal on the detector enables a direct reading of the optical spectrum. So far, such technique has been demonstrated using combs based on mode-locked lasers, in which the periodic time optical output, consisting of pulses spaced by the round-trip period of the cavity, ensures the periodicity of the comb optical spectrum.To reduce the power consumption and size, it would be very attractive to generalize this technique for semiconductor lasers. Furthermore, for many applications, it would be especially interesting to do so in the mid-infrared region of the spectrum, where many molecules have their strong fundamental absorption lines and where the generation of combs is more challenging 13 . However, in the conventional free-running multi-mode laser the modes are not evenly spaced due to material dispersion and the broadening of the individual modes prevent the generation of well-separated beat notes in the RF domain. As a result, some way of locking the modes together must be employed. Yet all the numerous attempts 14-16 to mode-lock QCL had limited success,

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“…Based on this principle, active mode-locking has been achieved in the mid-infrared with active regions based on photon-assisted tunnelling transitions (as shown in Fig. 3c) [37] where very long intersubband lifetimes in the 2 This, neglects the case of harmonic mode-locking, where two or more pulses are circulating in the cavity. Usually this form of modelocking is not preferred because of the additional jitter between pulses.…”

Section: Mode-locking Of Qclsmentioning

confidence: 99%

Quantum Cascade Laser Frequency Combs

Faist

Villares²,

Scalari³

et al. 2016

Nanophotonics

198

137

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It was recently demonstrated that broadband quantum cascade lasers can operate as frequency combs. As such, they operate under direct electrical pumping at both mid-infrared and THz frequencies, making them very attractive for dual-comb spectroscopy. Performance levels are continuously improving, with average powers over 100 mW and frequency coverage of 100 cm −1 in the midinfrared region. In the THz range, 10 mW of average power and 600 GHz of frequency coverage are reported. As a result of the very short upper state lifetime of the gain medium, the mode proliferation in these sources arises from four-wave mixing rather than saturable absorption. As a result, their optical output is characterized by the tendency of small intensity modulation of the output power, and the relative phases of the modes to be similar to the ones of a frequency modulated laser. Recent results include the proof of comb operation down to a metrological level, the observation of a Schawlow-Townes broadened linewidth, as well as the first dual-comb spectroscopy measurements. The capability of the structure to integrate monothically nonlinear optical elements as well as to operate as a detector shows great promise for future chip integration of dual-comb systems.

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Mode-locked pulses from mid-infrared Quantum Cascade Lasers

Cited by 176 publications

References 30 publications

Dual-comb spectroscopy based on quantum-cascade-laser frequency combs

Dual-comb spectroscopy based on quantum-cascade-laser frequency combs

Coherent frequency combs produced by self frequency modulation in quantum cascade lasers

Quantum Cascade Laser Frequency Combs

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