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PT-symmetric transverse mode splitting in coupled quantum cascade lasers
摘要： Separation of transverse modes in waveguides typically achieved by manipulating mode effective indices is of current interest in integrated optics and various designs have been proposed. Recently, implementation of non-Hermitian optics under parity time (PT) symmetry has led to an alternate class of devices employing gain and loss media with far reaching results. Introduction of PT symmetry to non-Hermitian systems results in real solutions while symmetry breaking results in imaginary eigenvalues. However, applications of PT symmetry in the infrared devices is quite limited. In this work, we demonstrate a mode splitter that can separate transverse modes in coupled PT symmetric in realistic quantum cascade lasers (QC lasers). We study the effects of gain and loss for coupled PT symmetric QC laser waveguides and show that TE0 and TE1 modes can be separated with proper choice of gain and loss values.
关键词： quantum cascade lasers,parity-time symmetry,photonic devices,optical waveguide,optical systems,Mode splitter
更新于2025-09-12 10:27:22
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Properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers
摘要： The properties of self-mixing interference in terahertz distributed feedback quantum cascade lasers (THz DFB-QCLs) were studied by coupled wave theory and the multimode rate equation method. Under weak self-mixing optical feedback, the response behaviors of the DFB-QCLs are similar to those of Fabry–P(cid:2)erot lasers and can be described by the Lang–Kobayashi equations with a modi?ed feedback parameter. The amplitudes of the self-mixing power and frequency signals decrease with the increasing DFB coupling factor. Under strong feedback, new side modes arise, which broaden the laser linewidth. The number of side modes decreases with the increasing DFB coupling factor. The simulation also demonstrates that the maximum power mode of a THz DFB-QCL under strong self-mixing feedback is the minimum linewidth mode. These results support the development of self-mixing interferometers based on DFB-QCLs.
关键词： DFB-QCLs,Lang–Kobayashi equations,self-mixing interference,distributed feedback quantum cascade lasers,terahertz
更新于2025-09-12 10:27:22
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Integration of Mid-Infrared Light Sources on Silicon Based Waveguide Platforms in 3.5 — 4.7 μm Wavelength Range
摘要： Mid-infrared light sources are attracting attention for use in spectroscopic sensing, thermal imaging, and infrared countermeasures. Integration of these sources on Si-based waveguides allows for more functional and complex photonic circuits to be integrated on a single chip. This paper focuses on the key aspects of this integrated platform. The operation of silicon-on-insulator waveguides beyond 4.0 μm wavelength with increasing waveguide core thickness is discussed, and the effects of various cladding materials on waveguide propagation loss is demonstrated. Low loss waveguides and Mach-Zehnder interferometers in Ge-on-Si waveguide platform are discussed and beam combiners in the form of arrayed waveguide gratings are demonstrated in both the platforms. Interband cascade lasers are integrated on silicon-on-insulator waveguides with direct bonding to realize Fabry-Perot lasers. Power scaling of integrated lasers is validated by integrating quantum cascade lasers with silicon-on-insulator beam combiners. Results for the first integrated Fabry-Perot quantum cascade lasers on Ge-on-Si waveguides are discussed, together with the potential use of these waveguides to provide a better heat sink for integrated mid-infrared light sources.
关键词： Quantum Cascade Lasers,Silicon Photonics,Interband Cascade Lasers,Semiconductor Waveguides
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) - High-Power Mid-Infrared Quantum Cascade Semiconductor Lasers
摘要： Quantum cascade lasers (QCLs) employ intersubband transitions between conduction-band (CB) energy states in multi-quantum-well (MQW) structures, carrier tunneling between adjacent MQW stages, and coherent-light emission from multiple (30-50) stages. Unlike interband-transition semiconductor lasers, QCLs are not affected by Auger recombination in the mid-infrared wavelength range (l= 3-20 μm); thus, allowing them to readily reach lasing at room temperature (RT). However, using multiple stages leads to high voltages (3 10 V) that significantly decrease the wall-plug efficiency, hwp. Thus, although pulsed RT operation was obtained in 1996, it took until 2002 to achieve CW RT operation and until 2008 to obtain 1 W CW power.
关键词： Quantum cascade lasers,QCLs,high-power,semiconductor lasers,mid-infrared
更新于2025-09-11 14:15:04
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Efficient method for transport simulations in quantum cascade lasers
摘要： An efficient method for simulating quantum transport in quantum cascade lasers is presented. The calculations are performed within a simple approximation inspired by Büttiker probes and based on a finite model for semiconductor superlattices. The formalism of non-equilibrium Green's functions is applied to determine the selected transport parameters in a typical structure of a terahertz laser. Results were compared with those obtained for a infinite model as well as other methods described in literature.
关键词： Büttiker probes,quantum cascade lasers,non-equilibrium Green's functions,quantum transport,semiconductor superlattices
更新于2025-09-11 14:15:04
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Optimization of cavity designs of tapered AlInAs/InGaAs/InP quantum cascade lasers emitting at 4.5 μm
摘要： In this work design, fabrication and characterization of mid-infrared AlInAs/InGaAs/InP QCLs taper quantum cascade lasers are presented. In order to increase output power while keeping good beam quality, taper design of resonator was used. We have studied devices emitting at 4.5 μm with different shapes (linear, concave and convex) and angles of taper waveguide section, to optimize the output beam parameters, namely M2 and brightness. Experimental results demonstrate that convex geometry taper laser with 1.7o taper shows the best performance, the highest output power up to 5 W and the smallest horizontal beam divergence of 5.6o in the fundamental mode. This design is also characterized by the highest brightness.
关键词： quantum cascade lasers,cavity design,tapered laser
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) - N-Type Ge/SiGe Quantum Cascade Heterostructures for THz Emission
摘要： Terahertz (THz) semiconductor based quantum cascade lasers (QCLs) represent powerful and compact integrated light sources. To date they have been realized with various III-V materials where LO phonon emission becomes very effective as the temperature is increased, limiting the maximum operating temperature to 200K. To overcome this limitation, non-polar material systems are attractive because of their weaker e-phonon interaction. Theoretical studies have indicated n-type Ge/SiGe heterostructures where transport is associated to L electrons, as the most promising architecture [1]. Experimentally, sharp intersubband transitions in n-type strain compensated Ge/SiGe QWs have been observed in the 20-50 meV region [2]. Recently, non-equilibrium Green’s functions calculations proved to be efficient in optimising high temperature performance of GaAs/AlGaAs THZ QCLs [3]. In the effort of realizing a Ge/SiGe THz QCL, we present here a QCL structure designed by means of non-equilibrium Green’s functions [4], whose the bandstructure is reported in Fig.1(a). Epitaxial growth of strain-compensated Ge/SiGe heterostructure (≈1.5 μm thick) has been carried out by means of UHV-CVD yielding very good sample quality as visible from Fig.1(b). Mesa devices for transport experiments have been fabricated by dry etching and metallization. In Fig.1(c) a series of I-V curves as a function of the heatsink temperature display a thermally activated behaviour with Eact (cid:3) 10 meV. From low temperature (4 K) magnetotransport [5] in a magnetic field parallel to the current direction shows characteristics oscillations. we can deduce an energy distance between the lasing states of E23 =19.5 meV, in good agreement with the theoretical calculation. Optical experiments are ongoing and experimental results will be presented.
关键词： THz,UHV-CVD,quantum cascade lasers,Ge/SiGe heterostructures,non-equilibrium Green’s functions
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Open-Source Simulation Software for Quantum Cascade Lasers
摘要： We review the state of the art in open-source simulation and optimization tools for quantum cascade lasers (QCLs) and present the mbsolve project, which is a tool for QCL dynamics simulations.
关键词： open-source,quantum cascade lasers,dynamics simulations,mbsolve,simulation software
更新于2025-09-11 14:15:04
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On-Chip Dual-Comb Source Based on Terahertz Quantum Cascade Lasers Under Microwave Double Injection
摘要： High-power and broadband dual-comb sources in the terahertz frequency regime are much in demand for fast and high-resolution spectroscopies. The terahertz quantum cascade laser (QCL) is a powerful radiation source in the frequency range between 1 and 5 THz, which is an ideal candidate for frequency-comb and dual-comb generations in this frequency regime. In this work, we report on broadband on-chip dual-comb sources based on terahertz QCLs emitting at approximately 4.2 THz with a single plasmon waveguide configuration. Due to the fast intersubband transitions in QCLs, the dual-comb lines can be detected by employing the laser self-detection scheme. A finite-element analysis shows that a weak optical coupling between the two laser combs is sufficient for generating dual-comb lines via the nonlinear multiheterodyne frequency beatings. The noise-equivalent power of the QCL detector is also evaluated for different optical powers; furthermore, a microwave double injection is employed to stabilize the comb frequency and broaden the optical comb bandwidth. We find that even with weak radio-frequency powers, the optical comb bandwidth can be significantly broadened from 86 to 166 GHz. The double injection also allows us to investigate the carrier offset noise of QCL combs.
关键词： quantum cascade lasers,frequency combs,microwave double injection,dual-comb sources,terahertz
更新于2025-09-11 14:15:04
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Temporal stability and absolute composition issues in molecular beam epitaxy of AlGaAs/GaAs THz QCL
摘要： The operation of the terahertz quantum cascade lasers (THz QCL) is strongly dependent on the repeatable fabrication of the well and barrier layers with the certain thicknesses throughout the whole active region stack epitaxial growth. This emphasizes the importance of the strict control of the growth rates and the stability of Si and group III effusion cell fluxes during growth [1]. It was reported [2] that two THz QCLs based on nominally identical multilayer heterostructures Al0.15Ga0.85As/GaAs emit at the different frequencies of 2.59 and 2.75 THz because of unintentional small deviations in the GaAs and AlAs growth rates (4 and 1.6 % respectively). Authors [3] determined the thickness tolerance for working lasing heterostructures to be minimally above 2% while the structures with thickness deviation 4.3 and 6.5 % are not lasing. In [4] the Ga cell temperature has to be increased to maintain a GaAs constant growth rate while the Al cell temperature remains nearly constant because variation in AlAs growth rate can be neglected. By using such growth rate compensation technique the two nominally identical structures approximately 10 mkm overall thick were found to show thickness difference of ~ 1 %. Thus calibration procedures and accurate analysis techniques become crucial to provide enhanced metrology possibilities.
关键词： molecular beam epitaxy,metrology,AlGaAs/GaAs,terahertz quantum cascade lasers,growth rates
更新于2025-09-10 09:29:36