Planarized THz quantum cascade lasers for broadband coherent photonics

Senica, Urban; Forrer, Andres; Olariu, Tudor; Micheletti, Paolo; Cibella, Sara; Torrioli, G.; Beck, Mattias; Faist, Jérôme; Scalari, Giacomo

doi:10.1038/s41377-022-01058-2

Cited by 30 publications

(31 citation statements)

References 54 publications

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“…6D) shows the presence of pulses of ~12 ps in width over a weak background, thus indicating an amplitude modulated comb. This is in clear contrast to what observed in standard Fabry-Perot terahertz QCLs that behave as frequency-modulated combs with a quasi-constant output, while showing pulsed operation only under strong injection (≳ 30 dBm) (26,31). The phase difference between adjacent modes, reported on top of the spectra, is not perfectly flat.…”

Section: Resultscontrasting

confidence: 69%

Terahertz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers

et al. 2023

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Quantum cascade lasers (QCLs) constitute an intriguing opportunity for the generation of on-chip optical dissipative Kerr solitons (DKSs). Originally demonstrated in passive microresonators, DKSs were recently observed in mid-infrared ring QCL paving the way for their achievement even at longer wavelengths. To this end, we realized defect-free terahertz ring QCLs featuring anomalous dispersion leveraging on a technological platform based on waveguide planarization. A concentric coupled waveguide approach is implemented for dispersion compensation, while a passive broadband bullseye antenna improves the device power extraction and far field. Comb spectra featuring sech 2 envelopes are presented for free-running operation. The presence of solitons is further supported by observing the highly hysteretic behavior, measuring the phase difference between the modes, and reconstructing the intensity time profile highlighting the presence of self-starting 12-picosecond-long pulses. These observations are in very good agreement with our numeric simulations based on a Complex Ginzburg-Landau Equation (CGLE).

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Section: Resultscontrasting

confidence: 69%

Terahertz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers

et al. 2023

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“…We then performed Shifted Wave Interference Fourier Transform (SWIFT) spectroscopy measurements [2,30] to assess the comb coherence and reconstruct the time domain profile using a fast hot electron bolometer (HEB) detector [31,32] (a more detailed explanation of the working principle and setup used is in ref. [14]). A relatively weak RF signal (-10 dBm at the output of the RF source) was injected at the roundtrip frequency f rep to stabilize the comb repetition rate and to give the QCL and the spectrum analyzer a common time-base allowing the IQ demodulation.…”

Section: Linear Chirp and Flatter Spectrummentioning

confidence: 99%

“…Recent important milestones in THz QCL development include advances in high-temperature narrowband operation, [6][7][8] comb formation in ring cavities, [9] spontaneous pulses from solitons, [10] heterogeneous integration on silicon substrates, [11] operation as fast detectors, [12,13] and the development of a planarized waveguide platform with improved dispersion, radio frequency (RF) and thermal properties. [14] For use in spectroscopy, combs with flat intensity spectra are often desired, as this relaxes the conditions on the required signal-to-noise ratio (or integration time) for measuring all the spectral components. From this perspective, mid-infrared (mid-IR) QCLs are considered more suitable than THz QCLs due to their fast saturable gain, which is the main cause of self-starting frequency-modulated (FM) combs.…”

Section: Introductionmentioning

confidence: 99%

Frequency‐Modulated Combs via Field‐Enhancing Tapered Waveguides

Senica,

Dikopoltsev,

Forrer

et al. 2023

Laser & Photonics Reviews

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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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“…[ 14 ] Since QCLs typically have cavity lengths in the mm range, the repetition rate of the optical waveform, and hence the spacing between two adjacent frequency comb lines, is on the order of 10 GHz, which is well‐suited for the implementation of hybrid optical and microwave functionalities. [ 15 ] The key lies in combining the QCL active region with a metal‐metal waveguide structure, formed by contact layers on the top and bottom of the active region. [ 16 ] In this way, simultaneously an optical waveguide and a microwave transmission line is obtained, which can be designed to support co‐propagation of the optical field and microwave–electronic signal.…”

Section: Introductionmentioning

confidence: 99%

“…[ 27 ] This paradigm of hybrid device design has recently culminated in an approach for independently tailoring the terahertz and microwave properties based on a planarized waveguide geometry. [ 15 ]…”

Section: Introductionmentioning

confidence: 99%

Theory of Hybrid Microwave–Photonic Quantum Devices

Jirauschek

2023

Laser & Photonics Reviews

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The Maxwell–Lindblad transmission line (MLT) equations are introduced as a model for hybrid photonic and microwave‐electronic quantum devices. The hybrid concept has long enabled high‐bandwidth photodetectors and modulators by using waveguide structures supporting microwave–optical co‐propagation. Extending this technique to quantum‐engineered lasers provides a route for greatly improved short‐pulse and frequency comb operation, as impressively demonstrated for quantum cascade lasers. Even more, the self‐organized formation of coupled microwave and optical oscillation patterns has recently enabled photonics‐based ultralow‐noise microwave generation. The MLT model provides a suitable theoretical description for hybrid quantum devices by combining optical and microwave propagation equations with a Lindblad‐type approach for the quantum active region dynamics. A stable numerical scheme is presented, enabling realistic device simulations in excellent agreement with experimental data. Based on numerical results and analytical considerations, it is demonstrated that the functionality of the investigated hybrid quantum devices does not only rely on local coupling effects, but rather benefits from microwave‐optical co‐propagation, settling an ongoing debate. The MLT equations provide the basis for systematic device development and extension of the concept to other quantum‐engineered hybrid devices based on, for example, quantum dot or interband cascade structures, as well as for simplified analytical models providing additional intuitive insight.

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Planarized THz quantum cascade lasers for broadband coherent photonics

Cited by 30 publications

References 54 publications

Terahertz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers

Terahertz optical solitons from dispersion-compensated antenna-coupled planarized ring quantum cascade lasers

Frequency‐Modulated Combs via Field‐Enhancing Tapered Waveguides

Theory of Hybrid Microwave–Photonic Quantum Devices

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