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A Hybrid THz Imaging System With a 100-Pixel CMOS Imager and a 3.25–3.50 THz Quantum Cascade Laser Frequency Comb
摘要： The terahertz frequency range beyond 3 THz has exciting potential to have a transformative impact in a wide range of applications, including chemical and biomedical sensing, spectroscopy, imaging, and short-distance wireless communication. While there have been significant advancements in silicon-based THz imagers in the frequency ranges below 1 THz, technological development beyond 3 THz has been impeded by the lack of solid-state sources in this frequency range. In addition, the design space beyond 3 THz opens up fundamentally new challenges across electronics and the electromagnetic interface. In this spectral range, the wavelength is small enough (λox ≈ 50 μm at 3 THz) that a vertical via from the top antenna layer to the detector is a distributed element (transmission line or radiator). In this letter, we follow a careful circuits-electromagnetics co-design approach toward a hybrid imaging system with a 100-pixel CMOS imager that interfaces with a THz quantum cascade laser frequency comb that spans 3.25–3.5 THz with mode spacing of 17 GHz. The array chip, while designed for an optimal operation across 2.7–2.9 THz, demonstrates an average noise equivalent power (NEP) (across pixels) of 1260 pW/√Hz between 3.25–3.5 THz and a projected NEP of 284 pW/√Hz across the design range of 2.7–2.9 THz. To the best of our knowledge, we demonstrate for the first time full THz imaging in a hybrid quantum cascade laser (QCL)–CMOS fashion. This approach allows future works to leverage both QCL and CMOS technologies to demonstrate new technological advances for systems in the 1–10 THz range.
关键词： hybrid imaging,quantum cascade laser,silicon,THz imaging,CMOS,terahertz,imaging,detector
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Retrieving the Phase Relation of a Quantum Cascade Laser Frequency Comb and Reconstructing its Emission Profile
摘要： In the direction of miniaturizing and expanding optical frequency comb (FC) operation in the infrared (IR), the most relevant results have recently been achieved with quantum cascade lasers (QCLs) [1–4]. By using broadband Fabry-P′erot QCLs [5] designed to have a low group velocity dispersion, FC generation was demonstrated in fully free-running operation (QCL-combs) [6,7]. Various techniques to characterize the emission of mid- and far-infrared QCL-combs have been recently developed [6, 8–12]. Here we demonstrate the possibility of monitoring the Fourier phases of the modes of a FC (sample FC). The proposed approach bases on dual-comb multi-heterodyne detection using a metrological FC as reference (LO-FC) and a subsequent Fourier transform analysis (see ?g. 1a), allowing a simultaneous retrieval of the modes phases (?g. 1b). The required stability is obtained by post-detection RF common frequency noise suppression. This approach is the most direct method for FCs characterization, being suitable for IR FCs. A mid-IR and a THz QCL-comb (sample FCs) have been characterized. As LO-FCs two difference-frequency-generated FCs have been used. The measurements consisted in series of seven consecutive acquisitions. A strong correlation among the modes and a remarkable phase stability over 10s of minutes have been evidenced (see ?g. 1c). For the THz QCL-comb all the emitted modes can be acquired, therefore it is possible to reconstruct the emission pro?le and the instantaneous frequency (?g. 1d and e), con?rming a substantial deviation with respect to typical FC pulsed operation. The observed standard deviations on the obtained phases are in the order of 8 ? 10° at tens-of-minutes timescale. Concerning the phase relation, the scattering of THz QCL-comb phases (Fourier phases) encompasses a range of 300°, a value which cannot be associated to short-pulses operation. The quadratic term found in the phase relation (?g. 1b) can be attributed to chirping in QCL-comb emission. The reconstructed emission pro?les are roughly the same from measurement to measurement over the 30 minutes. Noticeably, the QCL-comb emission deviates from a pulsed emission, even though its amplitude is deeply modulated during the round trip. The obtained instantaneous frequency con?rms that the THz QCL-comb operates in a hybrid amplitude-/frequency-modulated regime. The gained knowledge of the phase relation provides the basis for future implementation of programmable pulse shaping. The remarkable phase stability attained for the QCL-combs modes conclusively proves the high coherence characterizing their emission, demonstrating that these sources are potentially suitable for metrological applications.
关键词： Fourier phases,frequency comb,quantum cascade laser,dual-comb multi-heterodyne detection,metrological applications
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Miramar Beach, FL, USA (2019.8.19-2019.8.21)] 2019 IEEE Research and Applications of Photonics in Defense Conference (RAPID) - Laser Level Selection in Terahertz Quantum Cascade Lasers
摘要： The active region of a terahertz quantum cascade laser with two optical transitions is studied. The population of upper laser states, which correspond to 3.4 and 3.8 THz, are investigated at different operating temperatures and in a strong magnetic field.
关键词： quantum cascade laser,terahertz,intersubband transitions
更新于2025-09-11 14:15:04
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n-type Ge/SiGe Multi Quantum-Wells for a THz Quantum Cascade Laser
摘要： Exploiting intersubband transitions in Ge/SiGe quantum cascade devices provides a way to integrate terahertz light emitters into silicon-based technology. With the view to realizing a Ge/SiGe Quantum Cascade Laser, we present the optical and structural properties of n-type strain-symmetrized Ge/SiGe asymmetric coupled quantum wells grown on Si(001) substrates by means of ultrahigh vacuum chemical vapor deposition. We demonstrate high material quality of strain-symmetrized structures and heterointerfaces as well as control over inter-well coupling and electron tunneling. Motivated by the promising results obtained on ACQWs, which are the basic building block of a cascade structure, we investigate, both experimentally and theoretically, a Ge/SiGe THz QCL design, optimized through a non-equilibrium Green’s function formalism.
关键词： Ge/SiGe,THz,intersubband transitions,strain-symmetrized,Quantum Cascade Laser
更新于2025-09-11 14:15:04
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EXPRESS: External Cavity Quantum Cascade Laser-Based Mid-Infrared Dispersion Spectroscopy for Qualitative and Quantitative Analysis of Liquid-Phase Samples
摘要： Acquisition of classical absorption spectra of liquids in the mid-IR range with quantum cascade lasers (QCLs) is often limited in sensitivity by noise from the laser source. Alternatively, measurement of molecular dispersion (i.e., refractive index) spectra poses an experimental approach that is immune to intensity fluctuations and further offers a direct relationship between the recorded signal and the sample concentration. In this work, we present an external cavity quantum cascade laser (EC-QCL) based Mach–Zehnder interferometer setup to determine dispersion spectra of liquid samples. We present two approaches for acquisition of refractive index spectra and compare the qualitative experimental results. Furthermore, the performance for quantitative analysis is evaluated. Finally, multivariate analysis of a spectrally complex mixture comprising three different sugars is performed. The obtained figures of merit by partial least squares (PLS) regression modelling compare well with standard absorption spectroscopy, demonstrating the potential of the introduced dispersion spectroscopic method for quantitative chemical analysis.
关键词： liquid phase,Mid-infrared spectroscopy,QCL,quantum cascade laser,dispersion spectroscopy,mid-IR spectroscopy
更新于2025-09-11 14:15:04
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The operation of THz quantum cascade laser in the region of negative differential resistance
摘要： We investigate the light-current-voltage characteristics and emission spectra of 2.3 THz quantum cascade laser operating in the negative differential resistance (NDR) region. It was shown that the formation of electric ?eld domains (EFDs) leads to a large number of discontinuities on the current-voltage and the total optical power on current characteristics. Measurements of emission spectra at different current (before the NDR region and in the NDR region) shows that the formation of EFDs results in decrease of the output intensity, but does not in?uence on lasing frequencies. The performed calculations qualitatively explain the experimental results.
关键词： THz region,Resonant-phonon design,Quantum-cascade laser,Negative differential resistivity
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Quantum Cascade Laser using Oxidation Confinement Layers
摘要： We investigate the oxidation confinement method applied in the active layer of the ridge waveguide Quantum Cascade Laser (QCL). Threshold current of the ridge oxidized QCL is lower than the conventional one, suggesting that the current is constricted by the oxidized layers.
关键词： oxidation confinement,Quantum Cascade Laser
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Photonics Conference (IPC) - San Antonio, TX, USA (2019.9.29-2019.10.3)] 2019 IEEE Photonics Conference (IPC) - Frequency Noise Reduction of Quantum Cascade Lasers using Optical Feedback
摘要： We theoretically demonstrate that strong optical feedback can reduce the frequency noise of quantum cascade lasers by two orders of magnitude, which is almost independent on the feedback phase. In addition, the spectral linewidth of the laser with optical feedback is analytically derived.
关键词： frequency noise,quantum cascade laser,optical feedback,spectral linewidth
更新于2025-09-11 14:15:04
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Optical saturation effects in intracavity Faraday modulation spectroscopy (INFAMOS)
摘要： We report on the observation of saturation effects in Intracavity Faraday Modulation Spectroscopy (INFAMOS). A quantum cascade laser operating at ～5.3 μm is used to probe the 2Π3/2 and 2Π1/2 R(3.5) transitions in the fundamental band of nitric oxide. With average intracavity intensities up to 450 W cm?2, the saturation of these molecular transitions is observed up to a total pressure of ～240 Torr. The experimental data are interpreted by incorporating saturation into a model for the INFAMOS line shape in the homogeneously broadened limit.
关键词： Intracavity Faraday Modulation Spectroscopy,quantum cascade laser,INFAMOS,saturation effects,nitric oxide
更新于2025-09-10 09:29:36
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Piezoelectric effect-based detector for spectroscopic application
摘要： A stando? laser spectroscopy sensor based on a broadband tunable external cavity quantum cascade laser (ECQCL) and a piezoelectric e?ect-based detector was developed for simultaneous detection of multiple chemicals. Instead of using a standard infrared detector, a custom quartz crystal tuning fork (QCTF) with a high resonant frequency ( ～75 kHz) was adopted as a light detector for laser signal collection. To explore the capabilities of this technique, the impact of the position of incident light beam excitation with respect to the QCTF on the signal amplitude, resonant frequency and Q-factor was observed in detail. In addition, the in?uence of incident light intensity and pressure on the intrinsic property of the QCTF was also systematically investigated. Finally, the ECQCL sensor was successfully demonstrated for the stando? detection of plumes for three volatile organic compounds (VOCs) (i.e., alcohol, acetone and ether) at a distance of 40 m, which proves the applicability of the technique for the detection of leak plumes in security ?elds.
关键词： Spectroscopic applications,Quantum cascade laser,Remote sensing and sensors,Piezoelectric detector
更新于2025-09-09 09:28:46