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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Vibration Sensor Based On Graphene-coated Excessively Tilted Fiber Grating
摘要： few-layers graphene assembled on excessively tilted fiber grating (ExTFG). tilted range of 0~0.5 m-1, bending We report the bending strain and low frequency vibration characteristics of few-layers graphene-coated excessively (ExTFG), which fiber grating enhanced the mechanical characteristics at the expense of sensitivity. The experimental results show that, in the curvature strain sensitivities of transverse electric (TE) and transverse magnetic (TM) modes based on wavelength variation are -2.78 nm/m-1 and -1.49 nm/m-1, respectively, and those based on intensity variation are -0.11 dB/m-1 and -0.24 dB/m-1, respectively. For the low frequency vibration, the maximum acceleration sensitivities of TE and TM modes at 3dB points are STE=46.64 mv/g and STM=73.84 mv/g, respectively, which also the larger than those of other wavelength positions. The proposed graphene-coated ExTFG may potential application prospects in optical fiber strain, torsion and vibration sensors.
关键词： Graphene,Vibration sensor,Bending strain,Excessively tilted fiber grating (ExTFG)
更新于2025-09-12 10:27:22
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Optical response of (InGa)(AsSb)/GaAs quantum dots embedded in a GaP matrix
摘要： The optical response of (InGa)(AsSb)/GaAs quantum dots (QDs) grown on GaP (001) substrates is studied by means of excitation and temperature-dependent photoluminescence (PL), and it is related to their complex electronic structure. Such QDs exhibit concurrently direct and indirect transitions, which allows the swapping of Γ and L quantum confined states in energy, depending on details of their stoichiometry. Based on realistic data on QD structure and composition, derived from high-resolution transmission electron microscopy (HRTEM) measurements, simulations by means of k · p theory are performed. The theoretical prediction of both momentum direct and indirect type-I optical transitions are confirmed by the experiments presented here. Additional investigations by a combination of Raman and photoreflectance spectroscopy show modifications of the hydrostatic strain in the QD layer, depending on the sequential addition of QDs and capping layer. A variation of the excitation density across four orders of magnitude reveals a 50-meV energy blueshift of the QD emission. Our findings suggest that the assignment of the type of transition, based solely by the observation of a blueshift with increased pumping, is insufficient. We propose therefore a more consistent approach based on the analysis of the character of the blueshift evolution with optical pumping, which employs a numerical model based on a semi-self-consistent configuration interaction method.
关键词： k · p theory,strain,type-I transitions,Raman spectroscopy,photoluminescence,photoreflectance spectroscopy,quantum dots,blueshift
更新于2025-09-12 10:27:22
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Strain Effects on the Band Gap and Diameter of CdSe Core and CdSe/ZnS Core/Shell Quantum Dots at Any Temperature
摘要： We present the results of an experimental study about strain effects on the core band gap and diameter of spherical bare CdSe core and CdSe/ZnS core/shell quantum dots (QDs) synthesized by using a colloidal technique at varying temperatures. Structural characterizations were made by using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques. Optical characterizations were made by using UV-Vis absorption and fluorescence emission spectroscopies. The XRD analysis suggests that the synthesized bare CdSe core and CdSe/ZnS core/shell QDs have zinc blende crystal structure. HRTEM results indicate that the CdSe core and CdSe/ZnS QDs have average particle sizes about 3.50 nm and 4.84 nm, respectively. Furthermore, compressive strain causes an increase (decrease) in the core band gap (diameter) of spherical CdSe/ZnS core/shell QDs at any temperature. An elastic strain-modified effective mass approximation (EMA) predicts that there is a parabolic decrease (increase) in the core band gap (diameter) of QDs with temperature. The diameter of spherical bare CdSe core and CdSe/ZnS core/shell QDs calculated by using the strain-modified EMA, with core band gap extracted from absorption spectra, are in excellent agreement with the HRTEM data.
关键词： diameter,quantum dots,band gap,CdSe,strain effects,CdSe/ZnS,temperature
更新于2025-09-12 10:27:22
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Precise stress control of inorganic perovskite films for carbon-based solar cells with an ultrahigh voltage of 1.622?V
摘要： All-inorganic cesium lead bromide (CsPbBr3) perovskite solar cell is one promising candidate to balance high efficiency and poor stability of organic-inorganic hybrid photovoltaics. The charge carrier transport can be maximized for high-efficiency devices through precise stress control during perovskite grain growth process to obtain high-quality full-bromine CsPbBr3 halide films. We present here the monolayer-aligned and large-grained CsPbBr3 perovskite films through precise control of crystallization temperature of PbBr2 film because the lattice volume is enlarged by 2.18 times during the phase conversion from PbBr2 to CsPbBr3, which helps to minimize residual-stress-induced grain boundaries and defect-induced charge recombination. Upon further interfacial modification by nitrogen doped carbon quantum dots, the hole transporting materials free, all-inorganic CsPbBr3 perovskite solar cell achieves a champion efficiency as high as 10.71% with an ultrahigh open-circuit voltage of 1.622 V. Moreover, the unencapsulated solar cell demonstrates remarkable long-term stability in 85% humidity in air atmosphere.
关键词： Stability,Strain engineering,Crystal growth,Cesium lead bromide,Charge recombination,Inorganic perovskite solar cell
更新于2025-09-12 10:27:22
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Theoretical correlation and effect of annealing on the photoresponse of vertically strain-coupled In <sub/>0.5</sub> Ga <sub/>0.5</sub> As/GaAs quantum dot heterostructures
摘要： Here, we propose a di?erent approach for growing strain-coupled In0.5Ga0.5As quantum dot infrared photodetectors (QDIPs) with varying dot layer periodicity. Strain calculation is done throughout the quantum dot (QD) heterostructures, which has a signi?cant e?ect on the carrier probability density functions. The localization of the electron probability density function in each heterostructure has a strong correlation with the photoresponse. The con?ned electron wavefunction in the top QD layer of the optimized device heterostructure (trilayer QDIP having dot layer periodicity of three) would be useful for hyperspectral imaging applications owing to its narrow (8.67 meV) photoresponse. Rapid thermal annealing treatment was carried out on the trilayer QDIP to investigate the enhancement in its optoelectronic properties. The dark current density reduced by two orders, and the operating temperature increased by 30 °C for the 650 °C-annealed counterpart. Also, the responsivity enhanced by two times (2.05 A/W at ?1 V) for the annealed QDIP.
关键词： In0.5Ga0.5As,rapid thermal annealing,photoresponse,strain-coupled,quantum dot infrared photodetectors
更新于2025-09-12 10:27:22
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Investigation of interactions between ultrafast laser beams and screen-printed silver nanopaste films
摘要： This study aims to investigate the interaction between ultrafast laser beams and screen-printed silver (Ag) nanopaste ?lms for strain sensors. After single pulse ablation of Ag nanopaste ?lms with a thickness of 4.58 μm, the ablation threshold was approximately 0.2 J/cm2. By increasing single pulse laser ?uences from 0.78 J/cm2 to 1.87 J/cm2, the laser-ablated line widths and depths of Ag nanopaste ?lms were ranging from 22 ± 0.1 μm and 4 ± 0.09 μm to 44.8 ± 1.4 μm and 4.2 ± 0.05 μm, respectively. The sheet resistance of laser-processed Ag nanopaste ?lms was measured by a four-point probe instrument. When the single pulse laser ?uences set from 4.7 mJ/cm2 to 1.97 J/cm2, the measured sheet resistances near the laser-ablated line edge of 0.5 mm were 59.52 ± 0.76 mΩ/sq and 115.83 ± 6.11 mΩ/sq, respectively. The optimal ultrafast laser processing parameters consisting of the areal laser ?uence of 47.4 J/cm2, the laser pulse repetition rate of 300 kHz, the scanning speed of galvanometers of 500 mm/s, and the overlapping rate of laser spots of 96.1% were used to pattern strain sensors with transversal and longitudinal electrode structures on Ag ?lm/glass substrates.
关键词： Sheet resistance,Silver (Ag) nanopaste ?lms,Single pulse ablation,Strain sensor,Ultrafast laser
更新于2025-09-12 10:27:22
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GaAs Quantum Dot in a Parabolic Microcavity Tuned to <sup>87</sup> Rb D <sub/>1</sub>
摘要： We develop a structure to efficiently extract photons emitted by a GaAs quantum dot tuned to Rubidium. For this, we employ a broadband microcavity with a curved gold backside mirror which we fabricate by a combination of photoresist reflow, dry reactive ion etching in an inductively coupled plasma and selective wet chemical etching. Precise reflow and etching control allows us to achieve a parabolic backside mirror with a short focal distance of 265 nm. The fabricated structures yield a predicted (measured) collection efficiency of 63 % (12 %), an improvement by more than one order of magnitude compared to unprocessed samples. We then integrate our quantum dot parabolic microcavities onto a piezoelectric substrate capable of inducing a large in-plane biaxial strain. With this approach, we tune the emission wavelength by 0.5 nm/kV, in a dynamic, reversible and linear way, to the Rubidium D1 line (795 nm).
关键词： two-photon resonance fluorescence,strain tuning,microcavity,single-photon source,extraction efficiency,semiconductor quantum dots
更新于2025-09-12 10:27:22
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Excitonic complexes in MOCVD-grown InGaAs/GaAs quantum dots emitting at telecom wavelengths
摘要： Hereby, we present a comprehensive experimental and theoretical study of the electronic structure and optical properties of excitonic complexes in strain-engineered InGaAs/GaAs quantum dots (QDs) grown by metalorganic chemical vapor deposition and emitting at the 1.3-μm telecommunication window. Single QD properties have been determined experimentally for a number of nanostructures by means of excitation-power-dependent and polarization-resolved microphotoluminescence and further compared with the results of confined states calculations employing the eight-band k·p theory combined with the configuration interaction method. The origin of excitonic complexes has been exemplarily confirmed based on magneto-optical and correlation spectroscopy study. Understanding the influence of structural parameters and compositions (of QDs themselves as well as in the neighboring strain-reducing layer) allows identification of which of them are crucial to control the emission wavelength to achieve the telecommunication spectral range or to affect binding energies of the fundamental excitonic complexes. The obtained results provide deeper knowledge of control and limitations of the investigated structures in terms of good spectral isolation of individual optical transitions and spatial confinement, which are crucial in view of QD applications in single-photon sources of high purity at telecom wavelengths.
关键词： strain-reducing layer,biexciton,quantum dots,single-photon sources,exciton,telecommunication wavelengths
更新于2025-09-12 10:27:22
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Influence of multiple laser impacts on thin leading edges of turbine blade
摘要： Laser shock peening is a mechanical surface improvement treatment used to enhance the fatigue life of critical components. This paper investigates the influence of multiple square laser impacts to study their special effect on the diverse mechanical behaviours of the thin leading edge surface of turbine blades. Most works existing in the literature have presented experimental investigations. The originality of our paper is to validate and numerically simulate the proposed model. Indeed, a 3D finite element method of a thin leading edge specimen, Ti–6Al–4V, of a turbine blade is numerically simulated using the ABAQUS software. The mechanical surface modifications (residual stresses, equivalent plastic strains and Johnson–Cook superficial damage) induced by the multiple square laser impact are examined in detail. The main purpose of this investigation is to determine the effects of single-sided and double-sided laser shock peening.
关键词： turbine blade,thin leading edge,Ti–6Al–4V,multiple square laser impacts,finite element method,equivalent plastic strain,Laser shock peening,Johnson–Cook superficial damage,compressive residual stress
更新于2025-09-12 10:27:22
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Application of Raman and Brillouin Scattering Phenomena in Distributed Optical Fiber Sensing
摘要： We present a review of the basic operating principles and measurement schemes of standalone and hybrid distributed optical fiber sensors based on Raman and Brillouin scattering phenomena. Such sensors have been attracting a great deal of attention due to the wide industrial applications they offer, ranging from energy to oil and gas, transportation and structural health monitoring. In distributed sensors, the optical fiber itself acts as a sensing element providing unique measurement capabilities in terms of sensing distance, spatial resolution and number of sensing points. The most common configuration exploits optical time domain reflectometry, in which optical pulses are sent along the sensing fiber and the backscattered light is detected and processed to extract physical parameters affecting its intensity, frequency, phase, polarization or spectral content. Raman and Brillouin scattering effects allow the distributed measurement of temperature and strain over tens of kilometers with meter-scale spatial resolution. The measurement is immune to electromagnetic interference, suitable for harsh environments and highly attractive whenever large industrial plants and infrastructures have to be continuously monitored to prevent critical events such as leakages in pipelines, fire in tunnels as well as structural problems in large infrastructures like bridges and rail tracks. We discuss the basic sensing mechanisms based on Raman and Brillouin scattering effects used in distributed measurements, followed by configurations commonly used in optical fiber sensors. Hybrid configurations which combine Raman and Brillouin-based sensing for simultaneous strain and temperature measurements over the same fiber using shared resources will also be addressed. We will also discuss advanced techniques based on pulse coding used to overcome the tradeoff between sensing distance and spatial resolution affecting both types of sensors, thereby allowing measurements over tens of kilometers with meter-scale spatial resolution, and address recent advances in measurement schemes employing the two scattering phenomena.
关键词： distributed fiber optic sensing,Raman scattering,non-linear phenomena in optical fibers,Brillouin scattering,strain and temperature measurements
更新于2025-09-12 10:27:22