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5.3 μm-Emitting Diffraction-Limited Leaky-Wave-Coupled Quantum Cascade Laser Phase-Locked Array
摘要： A three-element phase-locked array of ~5.3 μm-emitting quantum cascade lasers fabricated by a two-step MOCVD process is demonstrated which operates in a diffraction-limited beam to 5.3 W peak pulsed power. To compensate for overetching at the array edges, the fabrication process was modified such that it resulted in array elements of equal width. The resulting array operates in a pure in-phase array mode, in agreement with simulations based on the actual device dimensions, which indicate that resonant leaky-wave coupling occurs for this device’s geometry. Measured uniform near-field intensity profiles confirm resonant coupling. Simulations indicate that chirping of the element widths would allow for modification of the near-field intensity profile to mitigate the effects of thermal lensing in continuous-wave operation.
关键词： semiconductor laser arrays,Leaky waves
更新于2025-09-12 10:27:22
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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) - Ultrafast All-Optical Switching in III-V Semiconductor Resonant Nanostructures
摘要： All-dielectric high-index resonant nanostructures offer plentiful opportunities for tailoring characteristics of scattered radiation. In fact, the low level of ohmic losses at optical frequencies and the presence of pronounced magneto-dipolar modes in scattering spectra of dielectric nanoresonators pave the way to numerous scattering effects that could be employed for many practical applications [1]. To further advance the performance of dielectric nanophotonic devices, it is crucial to make them reconfigurable, i.e. to provide a method to manipulate optical properties of the material that they are made of. The electron-hole injection, carried out by optical means, is a promising solution for this task (Fig. 1A). Direct-gap semiconductors are perfectly suitable for that purpose, because this class of materials retains advantages typical for dielectrics and, at the same time, is defined by smaller bandgap widths, compared to dielectrics. The latter feature significantly decreases a value of the pumping pulse fluence that is required to noticeably change the optical response of a resonant nanostructure. Indeed, it was numerically shown that the change of the trajectory of the probing pulse constituted 20° for an asymmetric dimer comprised of two silicon (Si) spheres of different radii for the energy fluence of the pumping pulse Φ(cid:3020)(cid:3036) = 1.6 mJ cm(cid:2879)(cid:2870) [2]. On the other hand, there is an experimental study of all-optical switching in gallium arsenide (GaAs) metasurface that indicated the change of its reflection coefficient ?(cid:1844) = 0.35 for the fluence Φ(cid:3008)(cid:3028)(cid:3002)(cid:3046) = 0.31 mJ cm(cid:2879)(cid:2870) [3]. Although there are already some numerical results on the light scattering in the asymmetric dimer, it is still urgent to carry out the corresponding experiment. For that purpose, it is important to change the geometry of the system (cylinders instead of spheres) and its material (GaAs in place of Si). The system has an asymmetric scattering profile in the regular regime owing to its asymmetric geometry. The geometry also stipulates the difference in absorption cross-sections of the cylindrical resonators. Because of this difference in absorption, the change of the material’s optical parameters is not equal for the two cylinders. Therefore, under certain conditions, after the pumping of the nanostructure, the scattering diagram becomes symmetric. Our numeric results demonstrate the symmetrization of the indicatrix for the pumping fluence Φ(cid:2869) = 0.9 mJ cm(cid:2879)(cid:2870) (the corresponding change of the probe scattering direction was calculated to be 7°) for the dimer with following geometrical parameters: radii – 85 nm and 90 nm, height – 200 nm, distance between the centers of the disks – 450 nm. The central wavelength of the pulse spectrum was (cid:2019)(cid:2869) = 820 nm. The dimer nanoantenna is an ultrafast optical switch that can be used, for instance, to distribute optical signals between two waveguides in integrated photonic circuits. The design of the switch makes its fabrication compatible with modern technological methods. The all-optical modulation can be observed not only in single asymmetric nanoantennas, but also in phased-array metasurfaces composed of supercells with resonators of the different size. In particular, we considered a metasurface that could control the intensities (i.e. transmission coefficients) in the diffraction orders that are formed after the scattering on the nanostructure. In our experiments, the most pronounced relative change of the transmission coefficient was detected in the first order: ?(cid:1846) (cid:1846) = 9.7% for the fluence of the pumping pulse Φ(cid:2870) = 0.02 mJ cm(cid:2879)(cid:2870) (Fig. 2B). The metasurfaces of that kind can also be used as all-optical switches.
关键词： ultrafast optics,resonant nanostructures,III-V semiconductor,all-optical switching
更新于2025-09-12 10:27:22
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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) - Feedback Insensitive External-Cavity Semiconductor Ring Laser Utilizing a Weak Intracavity Isolator
摘要： External optical feedback (EOF), caused by the return loss of connected circuits, is well known to have a strong impact on the performance of semiconductor lasers [1]. Feedback effects are usually prevented by placing an optical isolator at the output of the laser. A strong isolation value of approximately 60dB is typically required for tunable lasers. It has proven difficult to implement sufficiently strong optical isolators in a form suited to photonic integration [2]. For this reason we have previously proposed a ring laser with weak intracavity isolation to enable a feedback insensitive integrated tunable laser [3]. In such a laser the isolator is used only to enforce unidirectional operation of the device and the returned signal couples in the lossy counter-propagating direction. Using our rate equation analysis it was predicted that 10dB intracavity isolation completely suppresses the effects of EOF over the operating range of interest in terms of output power, linewidth and relative intensity noise. In such a cavity, the weak isolation can now be implemented with known integration schemes [2]. In this contribution we demonstrate for the first time that insensitivity can indeed be achieved using a ring laser with weak intracavity optical isolation. The laser system is schematically shown in Fig. 1 and is implemented using polarization maintaining optical fiber, a multi-quantum well semiconductor optical amplifier and an optical isolator consisting of a free space Faraday rotator and two polarizers. By changing the orientation of the polarizers the amount of isolation can be set, allowing for a direct comparison to our theory. Finally, two 3dB fiber-fused splitters are used as output couplers to make the laser cavity as symmetrical as possible when no isolation is provided.
关键词： intracavity isolation,External optical feedback,optical isolator,ring laser,semiconductor lasers
更新于2025-09-12 10:27:22
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On the Asymmetric Generation of a Superradiant Laser with a Symmetric Low-Q Cavity
摘要： On the basis of numerical solution to the Maxwell–Bloch equations within the one-dimensional two-level model of a superradiant laser with a symmetric cavity in which the photon lifetime is less than the incoherent relaxation time of the optical-dipole oscillations of active centers, the phenomenon of the spontaneous asymmetric generation of counter-propagating waves under continuous uniform pumping of the active medium is revealed. It is shown that the observed symmetry breaking of the spatial profiles of counter-propagating waves of the electromagnetic field and, the polarization and inversion of the population of active-medium levels in the case of a small inhomogeneous broadening of the spectral line of its working transition occurs due to the asymmetric half-wave nonlinear grating of inversion of the energy-level population produced by these waves.
关键词： asymmetric generation,superradiant semiconductor laser
更新于2025-09-12 10:27:22
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Distinctive characteristics of carrier-phonon interactions in optically driven semiconductor quantum dots
摘要： We review distinct features arising from the unique nature of the carrier-phonon coupling in self-assembled semiconductor quantum dots. Because of the discrete electronic energy structure, the pure dephasing coupling usually dominates the phonon effects, of which two properties are of key importance: The resonant nature of the dot-phonon coupling, its non-monotonic behavior as a function of energy, and the fact that it is of super-Ohmic type. Phonons do not only act destructively in quantum dots by introducing dephasing, they also offer new opportunities, e.g. in state preparation protocols. Apart from being an interesting model systems for studying fundamental physical aspects, quantum dot and quantum dot-microcavity systems are a hotspot for many innovative applications. We discuss recent developments related to the decisive impact of phonons on key figures of merit of photonic devices like single or entangled photon sources under aspects like indistinguishability, purity and brightness. All in all it follows that understanding and controlling the carrier-phonon interaction in semiconductor quantum dots is vital for their usage in quantum information technology.
关键词： Non-Markovian dynamics,quantum information processing,optical manipulation,Semiconductor quantum dots,carrier-phonon interaction,photonics
更新于2025-09-12 10:27:22
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Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires
摘要： Semiconductor-superconductor hybrid systems have outstanding potential for emerging high performance nanoelectronics and quantum devices. However, critical to their successful application is the fabrication of high quality and reproducible semiconductor-superconductor interfaces. Here, we realize and measure axial Al-Ge-Al nanowire heterostructures with atomically precise interfaces, enwrapped by an ultra-thin epitaxial Si layer further denoted as Al-Ge/Si-Al nanowire heterostructures. The heterostructures were synthesized by a thermally induced exchange reaction of single-crystalline Ge/Si core/shell nanowires and lithographically defined Al contact pads. Applying this heterostructure formation scheme enables self-aligned quasi one-dimensional crystalline Al leads contacting ultra-scaled Ge/Si segments with contact transparencies greater than 96%. Integration into back-gated field-effect devices and continuous scaling beyond lithographic limitations allows us to exploit the full potential of the highly transparent contacts to the 1D hole gas at the Ge-Si interface. This leads to the observation of ballistic transport as well as quantum confinement effects up to temperatures of 150 K. Low temperature measurements reveal proximity-induced superconductivity in the Ge/Si core/shell nanowires. The realization of a Josephson field-effect transistor allows us to study the sub-gap structure caused by multiple Andreev reflections. Most importantly, the absence of a quantum dot regime indicates a hard superconducting gap originating from the highly transparent contacts to the 1D hole-gas, which is potentially interesting for the study of Majorana zero modes. Moreover, underlining the importance of the proposed thermally induced Al-Ge/Si-Al heterostructure formation technique, our system could contribute to the development of key components of quantum computing such as gatemon or transmon qubits.
关键词： 1D hole gas,hard superconducting gap,transparent contacts,superconductor-semiconductor hybrids,nanowire heterostructure,germanium
更新于2025-09-12 10:27:22
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Theory of Frequency-Modulated Combs in Lasers with Spatial Hole Burning, Dispersion, and Kerr Nonlinearity
摘要： Frequency-modulated (FM) frequency combs constitute an exciting alternative to generate equidistant spectra. The full set of Maxwell-Bloch equations is reduced to a single master equation for lasers with fast gain dynamics to provide insight into the governing mechanisms behind phase locking. It reveals that the recently observed linear frequency chirp is caused by the combined effects of spatial hole burning, group velocity dispersion, and Kerr nonlinearity due to asymmetric gain. The comparison to observations in various semiconductor lasers suggests that the linear chirp is general to self-starting FM combs.
关键词： dispersion,spatial hole burning,semiconductor lasers,Kerr nonlinearity,Frequency-modulated combs
更新于2025-09-12 10:27:22
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[IEEE 2019 Joint Conference of the IEEE International Frequency Control Symposium anEuropean Frequency and Time Forum (EFTF/IFC) - Orlando, FL, USA (2019.4.14-2019.4.18)] 2019 Joint Conference of the IEEE International Frequency Control Symposium and European Frequency and Time Forum (EFTF/IFC) - Blue Microlasers for Metrology Applications
摘要： We report on the proof of the principle demonstration of spectrally pure blue semiconductor lasers with sub-MHz linewidth. The lasers are potentially suitable for application in compact optical clocks and quantum computers. The lasers are created by locking a Fabry-Perot (FP) laser chip to a mode of a crystalline whispering gallery mode (WGM) resonator characterized with quality factor exceeding a billion. Self-injection locking ensures monochromaticity of the laser.
关键词： whispering gallery mode,self-injection locked semiconductor laser,optical microresonator
更新于2025-09-12 10:27:22
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Facile one-pot synthesis of gold/tin oxide quantum dots for visible light catalytic degradation of methylene blue: Optimization of plasmonic effect
摘要： Discovery and development of novel photocatalysts with superior performance in visible light is a fundamental step toward tackling several environment and energy related issues. In this study, a simple one-pot solvothermal approach was adopted to fabricate a series of novel SnO2 quantum dot/gold (SQD/Au) nanocomposites. The structure, morphology, chemical composition, and the optical and photocatalytic performance of the as-prepared SQD/Au nanocomposites were described. The dispersion of Au nanoparticles (NPs) over SQDs can significantly improve the synergistic charge transfer mechanism, which retards the reunion of photoinduced electron-hole pairs and results in decreased emission intensity. In particular, the SQD/Au nanocomposites with 1.00 mL in 100 mM gold chloride loading achieve a methylene blue (MB) degradation of 99% under visible light illumination within 150 min. This can be ascribed to the plasmonic effect of Au NPs in the visible region and the SQDs acting as an electron tank to receive the photoinduced electrons. Furthermore, the formation of a Schottky barrier between SQDs and Au NPs improved the charge separation efficiency, and enhanced the photocatalytic activity. A possible photocatalytic mechanism for the improved degradation efficiency of MB by SQD/Au nanocomposites is also proposed.
关键词： Photocatalysis,SnO2,Metal-semiconductor,Quantum dots,Plasmonic effect
更新于2025-09-12 10:27:22
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Photocurrent deviation from linearity in an organic photodetector due to limited hole transport layer conductivity
摘要： It has been demonstrated that p-doped polymer layers are a convenient replacement as hole transport layer (HTL) for the widely used Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), yielding comparable photodetection performances at low light intensities. In this work, we aim to evaluate the response of organic photodetectors (OPDs) with increasing light intensity when p-doped PBDTTT-c is used as HTL. Photocurrent linearity measurements are performed on devices processed with both PEDOT:PSS and p-doped PBDTTT-c to better determine the role of the HTL. We show a deviation of the photocurrent from linearity for light intensities above 10?3 W/cm2 at 0 V applied bias due to distinct mechanisms depending on the HTL material. While space charge limited photocurrent (SCLP) explains the non-linearity at high light intensity for the device processed with PEDOT:PSS, bimolecular recombination is responsible for the loss in linearity when p-doped PBDTTT-c is used as HTL. The replacement of PEDOT:PSS by p-doped PBDTTT-c, which is 6 orders of magnitude less conductive, induces Langevin recombination, causing photocurrent non-linearity. Therefore, this study emphasizes the need for highly conductive transport layers when photodetection applications are targeted, and motivates further improvements in organic semiconductor doping.
关键词： Photocurrent linearity,Organic semiconductor doping,Organic photodetectors
更新于2025-09-12 10:27:22