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Hillbrand J, Bertrand M, Wittwer V, Opačak N, Kapsalidis F, Gianella M, Emmenegger L, Schwarz B, Südmeyer T, Beck M, Faist J. Synchronization of frequency combs by optical injection. Opt Express 2022; 30:36087-36095. [PMID: 36258545 DOI: 10.1364/oe.456775] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 08/24/2022] [Indexed: 06/16/2023]
Abstract
Optical frequency combs based on semiconductor lasers are a promising technology for monolithic integration of dual-comb spectrometers. However, the stabilization of offset frequency fceo remains a challenging feat due the lack of octave-spanning spectra. In a dual-comb configuration, the uncorrelated jitter of the offset frequencies leads to a non-periodic signal resulting in broadened beatnotes with a limited signal-to-noise ratio (SNR). Hence, expensive data acquisition schemes and complex signal processing are currently required. Here, we show that the offset frequencies of two frequency combs can be synchronized by optical injection locking, which allows full phase-stabilization when combined with electrical injection locking of both repetition frequencies frep. A single comb line isolated via an optical Vernier filter serves as Master oscillator for injection locking. The resulting dual-comb signal is periodic and stable over thousands of periods. This enables coherent averaging using analog electronics, which increases the SNR and reduces the data size by one and three orders of magnitude, respectively. The presented method will enable fully phase-stabilized dual-comb spectrometers by leveraging on integrated optical filters and provides access for comparing and stabilizing fceo to narrow-linewidth optical references.
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Opačak N, Cin SD, Hillbrand J, Schwarz B. Frequency Comb Generation by Bloch Gain Induced Giant Kerr Nonlinearity. Phys Rev Lett 2021; 127:093902. [PMID: 34506198 DOI: 10.1103/physrevlett.127.093902] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 07/08/2021] [Indexed: 06/13/2023]
Abstract
Optical nonlinearities are known to coherently couple amplitude and phase of light, which can result in the formation of periodic waveforms. Such waveforms are referred to as optical frequency combs. Here we show that Bloch gain-a nonclassical phenomenon that was first predicted in the 1930s-can play an essential role in comb formation. We develop a self-consistent theoretical model that considers all aspects of comb dynamics: band structure, electron transport, and cavity dynamics. In quantum cascade lasers, Bloch gain gives rise to a giant Kerr nonlinearity, which enables frequency modulated combs and serves as the physical origin of the linewidth enhancement factor. Bloch gain also triggers the formation of solitonlike structures in ring resonators, paving the way toward electrically driven Kerr combs.
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Affiliation(s)
- Nikola Opačak
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Sandro Dal Cin
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Johannes Hillbrand
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Benedikt Schwarz
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
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Beiser M, Opačak N, Hillbrand J, Strasser G, Schwarz B. Engineering the spectral bandwidth of quantum cascade laser frequency combs. Opt Lett 2021; 46:3416-3419. [PMID: 34264227 DOI: 10.1364/ol.424164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Accepted: 05/11/2021] [Indexed: 06/13/2023]
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 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 favorable and results in proliferation of the comb sidemodes. Ultimately, injection locking of QCLs by modulating the laser bias around the round trip frequency provides a stable external knob to control the frequency-modulated comb state and recover the maximum spectral width of the unlocked laser state.
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Krüger LM, Hillbrand J, Heidrich J, Beiser M, Weih R, Koeth J, Phillips CR, Schwarz B, Strasser G, Keller U. High-speed interband cascade infrared photodetectors: photo-response saturation by a femtosecond oscillator. Opt Express 2021; 29:14087-14100. [PMID: 33985134 DOI: 10.1364/oe.423498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Accepted: 04/13/2021] [Indexed: 06/12/2023]
Abstract
Interband cascade infrared photodetectors (ICIPs) combine interband optical transitions with fast intraband transport to achieve high-frequency and broad-wavelength operation at room temperature. Here we study the bias-dependent electronic impulse response of ICIPs with a mid-infrared synchronously pumped optical parametric oscillator (OPO). Since the OPO produces ultrashort 104-fs pulses, it is possible to probe the impulse response of the ICIP. From this impulse response, we identify two characteristic decay times, indicating the contribution of electron as well as hole carriers. A reverse bias voltage applied to the ICIP reduces both time scales and leads to an increased electrical cut-off frequency. The OPO emits up to 500 mW average power, of which up to 10 mW is directed to the ICIP in order to test its saturation characteristics under short-pulse illumination. The peak of the impulse response profile as well as the average photocurrent experience a gradual saturation behavior, and we determine the corresponding saturation powers by measuring the photo-response as a function of average power directed to the ICIP. We demonstrate that an increasing reverse bias increases the saturation power as well as the responsivity of the ICIP.
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Hillbrand J, Matthieu Krüger L, Dal Cin S, Knötig H, Heidrich J, Maxwell Andrews A, Strasser G, Keller U, Schwarz B. High-speed quantum cascade detector characterized with a mid-infrared femtosecond oscillator. Opt Express 2021; 29:5774-5781. [PMID: 33726109 DOI: 10.1364/oe.417976] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/18/2020] [Accepted: 01/20/2021] [Indexed: 06/12/2023]
Abstract
Quantum cascade detectors (QCD) are photovoltaic mid-infrared detectors based on intersubband transitions. Owing to the sub-picosecond carrier transport between subbands and the absence of a bias voltage, QCDs are ideally suited for high-speed and room temperature operation. Here, we demonstrate the design, fabrication, and characterization of 4.3 µm wavelength QCDs optimized for large electrical bandwidth. The detector signal is extracted via a tapered coplanar waveguide (CPW), which was impedance-matched to 50 Ω. Using femtosecond pulses generated by a mid-infrared optical parametric oscillator (OPO), we show that the impulse response of the fully packaged QCDs has a full-width at half-maximum of only 13.4 ps corresponding to a 3-dB bandwidth of more than 20 GHz. Considerable detection capability beyond the 3-dB bandwidth is reported up to at least 50 GHz, which allows us to measure more than 600 harmonics of the OPO repetition frequency reaching 38 dB signal-to-noise ratio without the need of electronic amplification.
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Hillbrand J, Opačak N, Piccardo M, Schneider H, Strasser G, Capasso F, Schwarz B. Mode-locked short pulses from an 8 μm wavelength semiconductor laser. Nat Commun 2020; 11:5788. [PMID: 33188222 PMCID: PMC7666187 DOI: 10.1038/s41467-020-19592-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 10/11/2020] [Indexed: 11/13/2022] Open
Abstract
Quantum cascade lasers (QCL) have revolutionized the generation of mid-infrared light. Yet, the ultrafast carrier transport in mid-infrared QCLs has so far constituted a seemingly insurmountable obstacle for the formation of ultrashort light pulses. Here, we demonstrate that careful quantum design of the gain medium and control over the intermode beat synchronization enable transform-limited picosecond pulses from QCL frequency combs. Both an interferometric radio-frequency technique and second-order autocorrelation shed light on the pulse dynamics and confirm that mode-locked operation is achieved from threshold to rollover current. Furthermore, we show that both anti-phase and in-phase synchronized states exist in QCLs. Being electrically pumped and compact, mode-locked QCLs pave the way towards monolithically integrated non-linear photonics in the molecular fingerprint region beyond 6 μm wavelength. Producing pulses in the mid-IR often requires bulky sources and has been inaccessible with compact and versatile quantum cascade lasers (QCLs). Here, the authors demonstrate actively mode-locked, mid-IR QCL operation at room temperature.
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Affiliation(s)
- Johannes Hillbrand
- Institute of Solid State Electronics, TU Wien, Guß, Vienna, Austria. .,Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
| | - Nikola Opačak
- Institute of Solid State Electronics, TU Wien, Guß, Vienna, Austria
| | - Marco Piccardo
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.,CNST - Fondazione Istituto Italiano di Tecnologia, Via Pascoli 70/3, 20133, Milano, Italy
| | - Harald Schneider
- Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
| | | | - Federico Capasso
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
| | - Benedikt Schwarz
- Institute of Solid State Electronics, TU Wien, Guß, Vienna, Austria. .,Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
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Hillbrand J, Auth D, Piccardo M, Opačak N, Gornik E, Strasser G, Capasso F, Breuer S, Schwarz B. In-Phase and Anti-Phase Synchronization in a Laser Frequency Comb. Phys Rev Lett 2020; 124:023901. [PMID: 32004013 DOI: 10.1103/physrevlett.124.023901] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Indexed: 06/10/2023]
Abstract
Coupled clocks are a classic example of a synchronization system leading to periodic collective oscillations. Already in 1665, Christiaan Huygens described this phenomenon as a kind of "sympathy" among oscillators. In this work, we describe the formation of two types of laser frequency combs as a system of oscillators coupled through the beating of the lasing modes. We experimentally show two completely different types of synchronization in a quantum dot laser-in-phase and splay-phase states. Both states can be generated in the same device, just by varying the damping losses of the system. This modifies the coupling among the oscillators. The temporal laser output is characterized using both linear and quadratic autocorrelation techniques. Our results show that both pulses and frequency-modulated states can be generated on demand within the same device. These findings allow us to connect laser frequency combs produced by amplitude-modulated and frequency-modulated lasers and link these to pattern formation in coupled systems such as Josephson-junction arrays.
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Affiliation(s)
- Johannes Hillbrand
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Dominik Auth
- Institute of Applied Physics, Technische Universität Darmstadt, Schlossgartenstrasse 7, 64289 Darmstadt, Germany
| | - Marco Piccardo
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Nikola Opačak
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Erich Gornik
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Gottfried Strasser
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
| | - Federico Capasso
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Stefan Breuer
- Institute of Applied Physics, Technische Universität Darmstadt, Schlossgartenstrasse 7, 64289 Darmstadt, Germany
| | - Benedikt Schwarz
- Institute of Solid State Electronics, TU Wien, Gusshausstrasse 25-25a, 1040 Vienna, Austria
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
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Hillbrand J, Jouy P, Beck M, Faist J. Tunable dispersion compensation of quantum cascade laser frequency combs. Opt Lett 2018; 43:1746-1749. [PMID: 29652355 DOI: 10.1364/ol.43.001746] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2018] [Accepted: 03/06/2018] [Indexed: 06/08/2023]
Abstract
Compensating for group velocity dispersion is an important challenge to achieve stable midinfrared quantum cascade laser (QCL) frequency combs with large spectral coverage. We present a tunable dispersion compensation scheme consisting of a planar mirror placed behind the back facet of the QCL. Dispersion can be either enhanced or decreased depending on the position of the mirror. We demonstrate that the fraction of the comb regime in the dynamic range of the laser increases considerably when the dispersion induced by the Gires-Tournois interferometer compensates the intrinsic dispersion of the laser. Furthermore, it is possible to tune to the offset frequency of the comb with the Gires-Tournois interferometer while the repetition frequency is almost unaffected.
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