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Spectral linewidth reduction of quantum cascade lasers by strong optical feedback
摘要： In this work, we propose to employ strong optical feedback to narrow the spectral linewidth of quantum cascade lasers without using any phase control. Rate equation analysis demonstrates that optical feedback beyond a certain level always reduces the laser linewidth for any feedback phase. It is also found that the linewidth becomes less sensitive to the feedback phase for higher feedback strength. Simulations show that optical feedback with a feedback ratio of ?10 dB can suppress the laser linewidth by about two orders of magnitude. This is in contrast to near-infrared laser diodes, which can be easily destabilized by strong feedback.
关键词： quantum cascade lasers,spectral linewidth reduction,optical feedback
更新于2025-09-23 15:19:57
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An antipodal Vivaldi antenna for improved far-field properties and polarization manipulation of broadband terahertz quantum cascade lasers
摘要： We present an antipodal Vivaldi antenna for broadband double metal waveguide terahertz quantum cascade lasers and frequency combs. Its exponentially curved flare profile results in an adiabatic in-plane mode expansion, producing an improved far-field with a single-lobed beam of (23° × 19°) full width half maximum with an octave-spanning bandwidth. The antenna also acts as a wave retarder, rotating the polarization from vertical toward horizontal polarization by a frequency-dependent angle. The laser’s emission spectrum and current–voltage characteristics are not affected, as well as frequency comb operation. Measurements agree well with numerical simulations, and the proposed antenna covers a broad spectral range (1.5–4.5 THz).
关键词： antipodal Vivaldi antenna,broadband,polarization manipulation,far-field properties,terahertz quantum cascade lasers
更新于2025-09-23 15:19:57
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Biomedical applications of mid-infrared quantum cascade lasers – a review
摘要： Mid-infrared spectroscopy has been applied to research in biology and medicine for more than 20 years and conceivable applications have been identified. More recently, these applications have been shown to benefit from the use of quantum cascade lasers due to their specific properties, namely high spectral power density, small beam parameter product, narrow emission spectrum and, if needed, tuning capabilities. This review provides an overview of the achievements and illustrates some applications which benefit from the key characteristics of quantum cascade laser-based mid-infrared spectroscopy using examples such as breath analysis, the investigation of serum, non-invasive glucose monitoring in bulk tissue and the combination of spectroscopy and microscopy of tissue thin sections for rapid histopathology.
关键词： quantum cascade lasers,glucose monitoring,mid-infrared spectroscopy,histopathology,breath analysis,biomedical applications
更新于2025-09-19 17:15:36
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Modeling of optical signal processing based on injection-locked broadband quantum cascade lasers
摘要： An all-optical signal processing approach has been presented which relies on gain competition between interconnected wavelengths in a broadband QCL. It has been shown that optical injection-locking, as the physical mechanism which modifies the inter-coupling between widely separated wavelengths, induces spectral reshaping through suppressing or raising the output intensity at intended wavelengths. Our developed model which is based on an experimental demonstration of an ultra-broadband QCL reveals a correlation between the intensity and modulation response of the injection-locked wavelengths. Also, it has been shown that logic operations and extremely wideband wavelength conversion between the mid and far-IR spectral regions of the laser can be accomplished.
关键词： Broadband cascade lasers,mid-infrared signal processing potential,Quantum cascade lasers
更新于2025-09-19 17:13:59
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Electrically pumped topological laser with valley edge modes
摘要： Quantum cascade lasers are compact, electrically pumped light sources in the technologically important mid-infrared and terahertz region of the electromagnetic spectrum1,2. Recently, the concept of topology3 has been expanded from condensed matter physics into photonics4, giving rise to a new type of lasing5–8 using topologically protected photonic modes that can efficiently bypass corners and defects4. Previous demonstrations of topological lasers have required an external laser source for optical pumping and have operated in the conventional optical frequency regime5–8. Here we demonstrate an electrically pumped terahertz quantum cascade laser based on topologically protected valley edge states9–11. Unlike topological lasers that rely on large-scale features to impart topological protection, our compact design makes use of the valley degree of freedom in photonic crystals10,11, analogous to two-dimensional gapped valleytronic materials12. Lasing with regularly spaced emission peaks occurs in a sharp-cornered triangular cavity, even if perturbations are introduced into the underlying structure, owing to the existence of topologically protected valley edge states that circulate around the cavity without experiencing localization. We probe the properties of the topological lasing modes by adding different outcouplers to the topological cavity. The laser based on valley edge states may open routes to the practical use of topological protection in electrically driven laser sources.
关键词： terahertz,topological photonics,valley edge states,Quantum cascade lasers,electrically pumped lasers
更新于2025-09-19 17:13:59
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Quantum cascade laser lives on the edge
摘要： Electromagnetic waves with frequencies in the terahertz range (300?GHz to 10?THz) have applications in many areas, from imaging and security screening to the atmospheric and biological sciences. Semiconductor devices called quantum cascade lasers (QCLs) provide the most compact and efficient way to generate terahertz radiation. In QCLs, electrons cascade down in energy through a series of discrete quantum energy levels, emitting a photon at each step1. But, as with all compact semi conducting lasers, QCLs are notoriously sensitive to fabrication imperfections, which results in device-to-device variability of the laser output frequency. Now, on page 246, Zeng et al.2 report the realization of a terahertz QCL that is insensitive to such disorder. This achievement opens the door for terahertz lasers and optoelectronics that have unprecedented stability and fabrication reproducibility.
关键词： topological protection,terahertz radiation,topological insulators,photonics,quantum cascade lasers
更新于2025-09-19 17:13:59
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Thermal analysis and heat dissipation improvement for quantum cascade lasers through experiments, simulations, and structure function
摘要： We quantified the thermal resistance of quantum cascade lasers (QCLs) using their structure functions and increased the laser output by employing ridge structures in which thermal resistance was reduced. To improve heat properties, three different QCL devices were prepared as follows. One was a device whose ridge was covered with SiO2, another was a device whose ridge was embedded with Au, and the other was a device whose ridge was embedded with Cu. The temperature distributions were measured with a thermoviewer and were analyzed with three-dimensional simulations. From the results, improved heat dissipation by embedding the ridge was clarified. Furthermore, the structure functions obtained by static mode measurement suggested that the thermal resistance was improved from 9.3 to 6.5 K W?1 by embedding the ridge. As a result of the improvement, the QCL with the Au-embedded ridge had a 1.5-fold higher laser power than the QCL with the SiO2-covered ridge.
关键词： thermal resistance,laser output,heat dissipation,structure function,quantum cascade lasers
更新于2025-09-19 17:13:59
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High power edge-cum-surface emitting terahertz laser arrays phased locked by vacuum guided plasmon waves
摘要： Terahertz semiconductor quantum-cascade lasers (QCLs) are widely implemented with metallic cavities that support low-loss plasmonic optical modes at long wavelengths. However, resonant optical modes in such cavities suffer from poor radiative characteristics due to their subwavelength transverse dimensions. Consequently, single-mode terahertz QCLs with metallic cavities and large (>100 mW) output power have only been realized in the surface-emitting con?guration that affords a large radiating surface. Here, we demonstrate a method to enhance radiative outcoupling from such plasmonic lasers for high-power emission in the edge-emitting (end-?re or longitudinal) direction. Single-sided plasmon waves propagating in vacuum are resonantly excited in surrounding medium of metallic cavities with the QCL semiconductor medium. The vacuum guided plasmon waves with a large wavefront phase-lock multiple metallic cavities longitudinally, which leads to intense radiation in multiple directions, including that in the longitudinal direction in a narrow single-lobed beam. The multicavity array radiates predominantly in a single spectral mode. A peak-power output of 260 mW and a slope ef?ciency of 303 mW/A are measured for the end-?re beam from a 3:3 THz QCL operating at 54 K in a Stirling cooler. Single-mode operation and lithographic tuning across a bandwidth of (cid:2)150 GHz are demonstrated.
关键词： quantum-cascade lasers,surface-emitting,plasmonic,phase-locking,edge-emitting,terahertz
更新于2025-09-19 17:13:59
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Passive synthesis rules of coupled-cavity quantum cascade lasers
摘要： A new approach to passive electromagnetic modelling of coupled–cavity quantum cascade lasers is presented in this paper. One of challenges in the rigorous analysis of such eigenvalue problem is its large size as compared to wavelength and a high quality factor, which prompts for substantial computational efforts. For those reasons, it is proposed in this paper to consider such a coupled-cavity Fabry-Perot resonant structure with partially transparent mirrors as a two-port network, which can be considered as a deterministic problem. Thanks to such a novel approach, passive analysis of an electrically long laser can be split into a cascade of relatively short sections having low quality factor, thus, substantially speeding up rigorous electromagnetic analysis of the whole quantum cascade laser. The proposed method allows to determine unequivocally resonant frequencies of the structure and the corresponding spectrum of a threshold gain. Eventually, the proposed method is used to elaborate basic synthesis rules of coupled–cavity quantum cascade lasers.
关键词： Threshold gain,Quantum cascade lasers,Lasers,Coupled cavities,Resonance characterization
更新于2025-09-16 10:30:52
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One-dimensional, surface emitting, disordered Terahertz lasers
摘要： Quantum cascade lasers are, by far, the most compact, powerful, and spectrally pure sources of radiation at terahertz frequencies, and, as such, they are of crucial importance for applications in metrology, spectroscopy, imaging, and astronomy, among many others. However, for many of those applications, particularly imaging, tomography, and near-field microscopy, undesired artifacts, resulting from the use of a coherent radiation source, can be detrimental. Random lasers can offer a concrete technological solution to the above issue. They, indeed, maintain a high degree of temporal coherence, as traditional lasers, while only exhibiting low spatial coherence, which can allow for the prevention of coherent artifacts, such as speckles. In this study, we report on the development of one-dimensional THz-frequency random wire lasers, patterned on the top surface of a double-metal quantum cascade laser with fully randomly arranged apertures, not arising from the perturbation of a regular photonic structure. By performing finite element method simulations, we engineer photonic patterns supporting strongly localized random modes in the 3.05–3.5 THz range. Multimode laser emission over a tunable-by-design band of about 400 GHz and with ～2 mW of peak power has been achieved, associated with 10○ divergent optical beam patterns. The achieved performances were then compared with those of perturbed Fabry–Perot disordered lasers, showing continuous-wave operation in the 3.5–3.8 THz range with an order of magnitude larger average power output than their random counterpart, and an irregular far field emission profile.
关键词： Anderson localization,Disordered photonic systems,Quantum cascade lasers,Random lasers,Terahertz frequencies
更新于2025-09-16 10:30:52