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Dynamic Laser Absorptance Measured in a Geometrically Characterized Stainless-Steel Powder Layer
摘要： The relationship between real powder distributions and optical coupling is a critical building block for developing a deeper physical understanding of laser-additive manufacturing and for creating more reliable and accurate models for predictable manufacturing. Laser-light absorption by a metal powder is distinctly different from that of a solid material, as it is impacted by additional parameters, such as particle size, shape distribution, and packing. Here, we use x-ray computed tomography to experimentally determine these parameters in a thinly spread austenitic stainless-steel powder on a metal substrate, and we combine these results with optical absorptance measurements during a 1 ms stationary laser-light exposure to simulate the additive-manufacturing process. Within the thinly spread powder layer, the particle volume fraction changes continuously from near zero at the powder surface to a peak value of 0.72 at a depth of 235 μm, with the most rapid increase taking place in the first 100 μm. The relationship between this particle volume fraction gradient and optical absorptance is investigated using an analytical model, which shows that depth-averaged absorptance measurements can measure the predicted average value, but will fail to capture local effects that result from a changing powder density. The time-averaged absorptance remains at levels between 0.67 and 0.80 across a two orders of magnitude range in laser power, which is significantly higher than that observed in solid stainless-steel experiments. The dynamic behavior of the absorptance, however, reveals physical phenomena, including oxidation, melting, and vapor cavity (keyhole) formation, as well as quantifying the effect of these on the absorbed energy.
关键词： keyhole formation,laser-additive manufacturing,stainless-steel powder,x-ray computed tomography,optical coupling,optical absorptance,particle volume fraction
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Singapore, Singapore (2018.4.22-2018.4.26)] 2018 IEEE 13th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS) - Optical Coupling of 3D Silicon Micromirrors
摘要： Free space optical coupling is considered the important feature which affects on the performance of the optical systems. Where coupling elements such as lenses and mirrors are aided in overcome the divergence of the Gaussian beams and to achieve phase matching. Here we concentrate on the studying of the free space coupling of 3D (spherical) mirror based on the propagation of a Gaussian beam. The design and fabrication of 3D mirror in the Optical microelectromechanical systems (MEMS) are studied. The coupling efficiency is a very important factor in the design of any MEMS circuit. High coupling efficiency is obtained by assembling optical parts which increase the integration effort. In this work, we report a high coupling efficiency, monolithically integrated 3D silicon micromirror that is capable of influencing on the Gaussian beams which propagate in the plane of the silicon substrate. A micromachining method is presented for fabricating the 3D micromirror.
关键词： micromachining,3D silicon micromirrors,optical coupling,MEMS,Gaussian beams
更新于2025-09-23 15:19:57
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[IEEE 2019 21st International Conference on Transparent Optical Networks (ICTON) - Angers, France (2019.7.9-2019.7.13)] 2019 21st International Conference on Transparent Optical Networks (ICTON) - Spin Plasmonics and Surface Enhanced Raman Spectroscopy in Label Free Biomolecular Sensing
摘要： We report the results of a study of an optical sensor based on a channel-drop technique with two cascaded cavities in photonic-crystal slabs. Quality factors and intensities of the resonant modes of the sensor were analyzed with three-dimensional simulations. With the introduction of a re?ector in the bus-channel and by control of the coupling between the two cavities and the drop-channel, the drop ef?ciency can be remarkably increased. In addition to the simulation, the two cavity sensor is fabricated and tested for optical response to water and oil in?ltration. Both direct visual imaging and quantitative analysis were applied in experiment. A difference of refractive index Δn = 0.12 between water and oil samples results in a wavelength shift of 18.3 nm, which greatly matches the simulation result of 20 nm and indicates a sensitivity of 153 nm RIU?1. Both resonant peaks for water and oil in?ltration have good selectivity in their transmission spectrum. The contrast between the broadband output of the bus-channel and the highly wavelength-selective outputs of the drop-channel opens opportunities for the two cascaded-cavity system as a fundamental building block for a multiplex drop-channel array for all-optical sensing, which can be widely used for bio/chemical detection and environmental monitoring.
关键词： photonic integrated circuits,multiplexing,optical sensors,photonic crystals,optical coupling,Cavity resonators,optical waveguide,optical devices
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 14th Malaysia International Conference on Communication (MICC) - Selangor, Malaysia (2019.12.2-2019.12.4)] 2019 IEEE 14th Malaysia International Conference on Communication (MICC) - Analyzing the Effects of LED Lamp Arrangements on Performance of an Indoor Visible Light Communication System
摘要： We report the results of a study of an optical sensor based on a channel-drop technique with two cascaded cavities in photonic-crystal slabs. Quality factors and intensities of the resonant modes of the sensor were analyzed with three-dimensional simulations. With the introduction of a re?ector in the bus-channel and by control of the coupling between the two cavities and the drop-channel, the drop ef?ciency can be remarkably increased. In addition to the simulation, the two cavity sensor is fabricated and tested for optical response to water and oil in?ltration. Both direct visual imaging and quantitative analysis were applied in experiment. A difference of refractive index Δn = 0.12 between water and oil samples results in a wavelength shift of 18.3 nm, which greatly matches the simulation result of 20 nm and indicates a sensitivity of 153 nm RIU?1. Both resonant peaks for water and oil in?ltration have good selectivity in their transmission spectrum. The contrast between the broadband output of the bus-channel and the highly wavelength-selective outputs of the drop-channel opens opportunities for the two cascaded-cavity system as a fundamental building block for a multiplex drop-channel array for all-optical sensing, which can be widely used for bio/chemical detection and environmental monitoring.
关键词： optical waveguide,optical coupling,optical sensors,multiplexing,optical devices,photonic integrated circuits,photonic crystals,Cavity resonators
更新于2025-09-19 17:13:59
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High-performance upconversion luminescent waveguide using a rare-earth doped microtube with beveled ends
摘要： Upconversion luminescence-based waveguides can achieve optical signal transmission and visible light emission with near-infrared light excitation and their quality is highly dependent on the coupling efficiency between the light and waveguide. Here, a new luminescent waveguide formed by a rare-earth doped microtube with beveled ends was designed to increase the optical coupling efficiency for vertical waveguide-excitation. The beveled end enabled the near-infrared light to effectively couple into the waveguide and produce a visible transmission pattern and directional emission, which was not possible using conventional luminescent waveguides without beveled ends. It was found that the beveled end can not only improve the input and the output signal efficiency, but also control the coupling efficiency and transmission pattern. In particular, a coupling efficiency of B68% could be obtained with the optimized beveled waveguide with a rotation angle of 301. The high optical coupling efficiency and multi-channel luminescent waveguide enabled by the microtube with beveled ends allowed for a deeper understanding of vertical waveguide excitation, and it extends the potential applications of luminescent waveguides for bioimaging and optical communication.
关键词： rare-earth doped microtube,beveled ends,upconversion luminescence,waveguide,optical coupling efficiency
更新于2025-09-16 10:30:52
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Fabrication and optical characterization of photonic crystal nanocavities with electrodes for gate-defined quantum dots
摘要： Among various solid-state systems, gate-defined quantum dots (QD) with high scalability and controllability for single electron spin qubits are promising candidates to realize quantum spin-photon interface. The efficiency of the spin-photon interface is expected to be significantly enhanced by optical coupling of gate-defined QDs with photonic crystal (PhC) nanocavities. As the first step towards this optical coupling, we designed and experimentally demonstrated a PhC nanocavity with electrodes. The electrodes, which can form a single QD, were introduced on the top surfaces of two-dimensional PhC nanocavities with a position accuracy of a few tens of nanometers. Despite the electrodes, a resonant mode was confirmed for the PhC nanocavities through micro-photoluminescence spectroscopy. This work marks a crucial step towards optical coupling between gate-defined QDs and PhC nanocavities.
关键词： optical coupling,quantum spin-photon interface,quantum dots,photonic crystal nanocavities
更新于2025-09-16 10:30:52
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Modulated photonic-crystal surface-emitting laser with elliptical lattice points for two-dimensional coupling enhancement
摘要： Modulated photonic-crystal surface-emitting lasers (M-PCSELs) are new semiconductor lasers that can emit a laser beam in arbitrary directions. Therefore, they can be regarded as a next-generation light source for light detection and ranging. In this manuscript, we numerically investigate the characteristics of M-PCSELs, including one- and two-dimensional optical coupling constants and radiation constants, by using three-dimensional coupled wave theory. We also carry out lattice point designs and show that the two-dimensional optical coupling can be enhanced by more than four times over our previous M-PCSEL devices by employing elliptical lattice points. Moreover, we find that two-dimensional optical coupling can be maintained even when large lattice point position modulations are introduced for large radiation constants. These results indicate that more stable two-dimensional oscillation and a higher slope efficiency are expected in M-PCSELs with elliptical lattice points.
关键词： elliptical lattice points,M-PCSELs,radiation constants,Modulated photonic-crystal surface-emitting lasers,two-dimensional optical coupling
更新于2025-09-12 10:27:22
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Development of an Optical Coupling with Ground-Side Absorption for Antenna-Coupled Kinetic Inductance Detectors
摘要： Antenna-coupled kinetic inductance detectors (KIDs) have recently shown great promise as microwave detection systems with a large number of channels. However, this technique, still has di?culties in eliminating the radiation loss of the resonator signals. To solve this problem, we propose a design in which the absorption area connected to an antenna is located on the ground-side of a coplanar waveguide. Thereby, radiation loss due to leakage from the resonator to the antenna can be considerably reduced. This simple design also enables the use of a contact aligner for fabrication. We have developed KIDs with this design, named as the ground-side absorption (GSA)-KIDs and demonstrated that they have higher quality factors than those of the existing KIDs, while maintaining a good total sensitivity.
关键词： superconducting detector,kinetic inductance detectors,optical coupling
更新于2025-09-11 14:15:04
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[IEEE NAECON 2018 - IEEE National Aerospace and Electronics Conference - Dayton, OH, USA (2018.7.23-2018.7.26)] NAECON 2018 - IEEE National Aerospace and Electronics Conference - The Art of the Impossible: Sorting Dielectric Microspheres by using Light
摘要： Use of resonant light forces opens up a unique approach to high-volume sorting of microspherical resonators with 1/Q accuracy, where Q is the resonance quality factor. Based on a two-dimensional model, it is shown that the sorting can be realized by allowing spherical particles to traverse a focused beam. Under resonance with the whispering gallery modes (WGM), the particles acquire significant velocity along the laser beam which should allow sorting dielectric microspheres with almost identical positions of their WGM resonances. This is an enabling technology for developing super-low-loss coupled-cavity structures and devices.
关键词： optical coupling,optical force,microsphere,whispering gallery mode,photonic molecule
更新于2025-09-09 09:28:46
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RADIATION FIELD AND OPTICAL COUPLING EVALUATION USING A NEW MATHEMATICAL MODEL
摘要： The mathematical model elaborated in this paper is based on the concept of intrinsic modes in order to analyze and synthesize optical wave propagation along a non-uniform optical structure which is used in integrated optics communication as tapered optical coupler. The new mathematical model is simply developed by introducing modi?cations to the intrinsic integral, and its numerical evaluation illustrates the electromagnetic ?eld distribution inside a taper thin ?lm and also outside the waveguide constituted by the substrate and the cladding of lower refractive index. The proposed method permits e?ciently tracking the behaviour of the optical waves both inside and outside the optical waveguide, and quantifying the radiation and optical coupling occurring from the taper thin ?lm of higher refractive index to adjacent mediums until a total energy transfer; this happens at thicknesses lower than waveguide cuto? thickness of each mode. The new model can be applied to all types of tapered optical coupler, made from di?erent optical materials and having di?erent wedge angles.
关键词： intrinsic modes,tapered optical coupler,mathematical model,optical wave propagation,electromagnetic ?eld distribution,radiation and optical coupling
更新于2025-09-04 15:30:14