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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) - A broadband polarization-rotating antipodal Vivaldi antenna for improved far-field properties of terahertz quantum cascade lasers
摘要： Double metal waveguide based terahertz quantum cascade lasers (QCLs) have excellent properties in terms of compactness, large bandwidth and low waveguide dispersion. However, as they confine the optical mode to subwavelength dimensions, their far-field is highly divergent. Our antipodal Vivaldi antenna is designed to produce a single-lobed far-field pattern with a beam width of less than 20°, spanning over two octaves in frequency (1.5-4.5 THz). Far-field measurements agree well with numerical simulations.
关键词： Vivaldi antenna,quantum cascade lasers,far-field,terahertz,broadband
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) - Narrower Far Field and Higher Efficiency in 1 kW Diode-Laser Bars using Improved Lateral Structuring
摘要： High power, efficient diode-laser bars with narrow far field angles are sought for many applications, for example in the 9xx nm-range for the pumping of Yb:YAG disc and slab lasers. In previous work, broad-area (BA) diode-laser bars with 4 mm resonator length operated with high conversion efficiency η = 62% at operating power Pop = 1 kW in quasi-continuous wave testing (200 μs, 10 Hz), by using low optical loss and low-resistivity vertical structures and high fill-factors (~70%). Lateral far field (95% power) was θ95% > 10°. However, higher η and narrower θ95% are needed for industrial application, and we seek improvements by altering the lateral bar structure for a fixed vertical design (from [1], wavelength λ = 930 nm, loss αi ≈ 0.4 cm-1). First, narrower θ95% at Pop = 1 kW was sought. In previous studies on 90 μm-wide single emitters, deep implantation through the active region was shown to reduce gain at the emitter edges, suppressing higher-order lateral modes, for smaller θ95%, at the price of reduced η and Pop. A similar implantation approach is assessed here in high fill-factor bars, and the drop in η is mitigated by reducing the implantation depth. Second, higher η at Pop = 1 kW was sought, by increasing the fill-factor, for lower electrical resistance.
关键词： lateral structuring,efficiency,narrow far field,high power,diode-laser bars
更新于2025-09-12 10:27:22
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Extremely high-brightness tapered photonic crystal diode laser with narrow-emitting aperture
摘要： High-brightness tapered photonic crystal diode lasers in the 980 nm range are investigated. The tapered lasers with a 20 μm wide light-emitting aperture achieved 2.55 W at 3.2 A. The beam quality factor M2 in the vertical and lateral directions are 1.16 and 1.48 at 2.5 A. Maximum brightness ?2 · sr at the second moment level is achieved. The devices also shows a narrow far-field of 17.1° × 6.5° in the vertical and lateral directions and a high efficiency of 53%. The proportion of the first-order mode in the lasing emission is also investigated based on the measured beam quality factor.
关键词： high-brightness,beam quality factor,far-field,tapered photonic crystal diode laser,narrow-emitting aperture
更新于2025-09-11 14:15:04
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A Truncated Singular Value Decomposition Enhanced Nested Complex Source Beam Method
摘要： This work presents a novel matrix compression algorithm to improve the computational efficiency of the nested complex source beam (NCSB) method. The algorithm is based on the application of the truncated singular value decomposition (TSVD) to the multilevel aggregation, translation, and disaggregation operations in NCSB. In our implementation, the aggregation/disaggregation matrices are solved by the truncated far-field matching, which is based on the directional far-field radiation property of the complex source beams (CSBs). Furthermore, the translation matrices are obtained according to the beam width of CSBs. Due to the high directivity of the radiation patterns of CSBs, all the far-field related interaction matrices are low-ranked. Therefore, TSVD can be employed and a new set of equivalent sources can be constructed by a linear combination of the original CSBs. It is proved that the radiation power of the new sources is proportional to the square of the corresponding singular values. This provides a theoretical guideline to drop the insignificant singular vectors in the calculation. In doing so, the efficiency of the original NCSB method can be much improved while a reasonably good accuracy is maintained. Several numerical tests are conducted to validate the proposed method.
关键词： matrix compression algorithm,far-field radiation property,nested complex source beam,truncated singular value decomposition,computational efficiency
更新于2025-09-11 14:15:04
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Passive localization and classification of mixed near-field and far-field sources based on high-order differencing algorithm
摘要： A novel method called high-order differencing algorithm (HODA) is presented for localization of mixed sources. Five special cumulant matrices are constructed. The first one only contains the angle information. By modifying its rank and using an ESPRIT-like approach, the initial DOA set (IDOAS) is formed. The four others, pairwise, contain common far-field information. By two differencing operations, the far-field information is eliminated, and the difference cumulant matrices (DCMs) are obtained. After the rank modification is executed, the DCMs are reconstructed. By applying an ESPRIT-like approach to them, electrical angles are extracted. The extracted data is compared with IDOAS to obtain valid information of near-field sources (NFSs). A mechanism called kurtosis testing algorithm (KTA) is presented for identifying far-field sources (FFSs). KTA is able to identify even those FFSs that are located at the same angle with NFSs. To control the error of statistical differencing, an appropriate number of snapshots is considered. Analyses show that HODA prevents aperture loss; it does not require pairing, knowing the number of NFSs or FFSs, and heavy searches. The results confirm its good performance in terms of classification, the correct estimation of sources with different fields and the same DOAs, estimation accuracy and computational complexity.
关键词： Multiple mixed near-field and far-field sources,Proper number of snapshots,High-order differencing
更新于2025-09-10 09:29:36
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Aggregation States of Organic Dye Molecules in Organic – Inorganic Hybrid Films Studied by Near-Field and Far-Field Fluorescence Spectroscopy
摘要： Near-field fluorescence spectroscopy in conjunction with far-field fluorescence and Raman spectroscopy has been applied to investigate the aggregation states of cyanine dye of 2-[5-(1,3-Dihydro-3,3-dimethyl-1-octadecyl-2H-indol-2-ylidene)-1,3-pentadienyl]-3,3-dimethyl-1-octadecyl-3H-indolium perchlorate (NK3175) molecules in the depth direction, from the nanometer-scale top surface to the bulk, in the hybrid films consisted of NK3175 and a clay compound (SWN). The far-field Raman spectra reveal that these hybrid films contained both NK3175 molecules which did not take part in the adsorption and those adsorbed on SWN. The near-field photoluminescence (PL) spectra in the outermost surface within ca. 30 nm exhibit a significant blue shift for the hybrid films as compared to their respective PL spectra in the bulk, implying that the top surface of these hybrid films becomes more polar and/or rigid in terms of the microenvironment around NK3175 molecules compared to the bulk of them, in contrast to the case for the other hybrid film which was prepared by the alternative method. These results provide new information on the aggregation states of organic dye molecules not only in the bulk but in the nanometer-scale top surface of organic-inorganic hybrid systems.
关键词： far-field fluorescence,Raman spectroscopy,organic-inorganic hybrid films,aggregation states,Near-field fluorescence spectroscopy,cyanine dye
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Planar Directivity of a Dipole Array
摘要： We develop a technique for fast evaluation of superdirective performance of coupled meta-atoms. Traditionally, the directivity of a small antenna is obtained from measurements of the far-field radiated power over a spherical surface. We propose an alternative method of finding the directivity from a faster polar scan over a circular path, by introducing the “planar directivity” (D2D) for dipole arrays. We derive analytical expressions for maximum achievable values of directivity and D2D, establish the correlation between them, and identify the range of parameters (inter-element distance, coupling constant, quality factor) for which the conversion of D2D to D for superdirective dimers is possible.
关键词： dipole arrays,planar directivity,far-field measurements,metamaterials,superdirectivity
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Rapid characterization of metasurface unit cells using Scanning Differential Heterodyne Microscopy
摘要： The performance of metasurfaces is reduced due to factors like fabrication uncertainties and near-field coupling, which can be solved by direct characterization of individual elements. Recent techniques use near-field scanning to observe direct properties of elements, which use AFM tips that are not stable for large areas. In this study, we demonstrate Scanning Differential Heterodyne Microscopy (SDHM) technique as a tool for phase and amplitude characterization of unit cells in reflective phase-gradient metasurfaces with the aim to predict the far-field performance. The use of heterodyne 2-probe beam scanning to monitor surface modulations, provides fundamental advantage of rapid and robust phase-amplitude optical data acquisition essential for large scale metasurface investigations and applications.
关键词： phase and amplitude characterization,Scanning Differential Heterodyne Microscopy,SDHM,far-field performance,metasurfaces
更新于2025-09-10 09:29:36
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Camera selection in far-field video surveillance networks
摘要： Since camera networks for surveillance are becoming extremely dense, finding the most informative and desirable views from different cameras are of increasing importance. In this paper, we propose a camera selection method to achieve the goal of providing the clearest visibility possible and selecting the cameras which exactly capture targets for the far-field surveillance. We design a benefit function that takes into account image visibility and the degree of target matching between different cameras. Here, visibility is defined using the entropy of intensity histogram distribution, and the target correspondence is based on activity features rather than photometric features. The proposed solution is tested in both artificial and real environments. A performance evaluation shows that our target correspondence method well suits far-field surveillance, and our proposed selection method is more effective at identifying the cameras that exactly capture the surveillance target than existing methods.
关键词： target correspondence,camera selection,far-field surveillance,activity feature
更新于2025-09-09 09:28:46
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UHF Reader Antenna for Near and Far-Field RFID Operation
摘要： In order to detect the RFID tags kept inside an enclosure, the reader antenna can couple energy into another antenna kept in the near-field region. To detect the tags placed in the far-field, the reader antenna should have a good gain. Usually, these two requirements compete with each other due to the effect of coupling on the frequency of operation of the antenna system. In this work modification to a loop antenna is proposed such that it can operate in both near and far-field. Loop antenna with high impedance surface (HIS) reflector results in a low-profile antenna pair where both the antennas can interchangeably operate in near-field and far-field, with their operating frequency band independent of the spacing between the antennas. The performance of the proposed antennas is compared with that of several other antennas by measuring the read range of RFID tags. It is found that the proposed antennas perform better in comparison with the other antennas when detecting the tags placed inside an enclosure. When operating as a far-field antenna, their performance is very close to that of a conventional RFID reader antenna which is optimized only for far-field operation.
关键词： near-field coupling,far-field near-field antenna,RFID,UHF,high impedance surface,loop antennas
更新于2025-09-04 15:30:14