摘要：
Rapid identification of plant disease is essential for food security. Deep learning, the latest breakthrough in computer vision, is promising for plant disease severity classification, as the method avoids the labor-intensive feature engineering and threshold-based segmentation. Using a public dataset of 54,306 images of diseased and healthy plant leaves collected under controlled conditions, a deep convolutional neural network and unsupervised methods are used to identify 14 crop species and 26 diseases. The trained model achieves an accuracy of 89.83% on a held-out test set, demonstrating the feasibility of this approach.
摘要：
One of the current challenges in second-harmonic generation (SHG) is to increase the efficiency of the second-harmonic conversion process while maintaining or even decreasing the fundamental-harmonic pump powers in a compact device. Here, we put forward an on-chip scheme to realize high-efficiency optical SHG in active-passive-coupled microring resonators with the aid of the intrinsic second-order nonlinearity. By careful analysis and extensive simulations, it is found that the introduction of an active microring resonator makes the strong SHG process feature an ultralow-power pump threshold, which is about four orders of magnitude lower than that in a single-microring resonator SHG system reported previously by X. Guo et al. [Optica 3, 1126 (2016)]. The observed SHG is enhanced by a factor of over 200 compared to the single-microring-resonator SHG system. The SHG conversion efficiency of over 72% can be reached with optical pump power as low as a few microwatts for our proposed device. This investigation may open a new route towards development of easily fabricated radiation sources of coherent high-energy (shorter-wavelength) photons with an ultralow-power laser-triggered SHG process.
摘要：
We present a perturbation technique to study the linear and nonlinear output characteristics of coherent photon transport in a parity-time ( PT)-symmetric double-microcavity system where one passive cavity contains a single quantum emitter. It is found that (i) for the linear transmission of a low-power input probe field, the output spectra of the proposed PT-symmetric system exhibit a single transparent resonance dip and two symmetric, strongly amplifying sidebands, i.e., an inverted dipole-induced transparency; and (ii) for the nonlinear transmission of the input probe field, giant optical third-order nonlinearities with high linear transmission rate and vanishing nonlinear absorption can be achieved efficiently when the system parameters are tuned properly so that a PT-symmetry phase transition occurs. The obtained results can be useful for quantum information processing, quantum nondemolition measurements of photons, and optical signal processing.
摘要：
A lot of experimental and theoretical studies of a system in cavity quantum electrodynamics (cavity QED), which consists of two spatially separated quantum emitters strongly coupled to a single optical cavity mode, have recently attracted much interest in the quantum optics community for various quantum information applications. Here, we propose a method for high-order harmonic generation in a photonic crystal microcavity coupled to single semiconductor quantum dots (QDs). The system is coherently driven by a bichromatic laser consisting of the control and signal fields at low input power (a few nanowatts) and the cavity output power via the cavity loss channel is monitored. Via numerical simulations, we thoroughly explore the difference of the generated high-order harmonic spectra between two QDs, one QD, and zero QDs in microcavity. The results clearly indicate that harmonic generation can be significantly enhanced via collective coherent coupling in the case of two spatially separated QDs coupled to the same photonic crystal microcavity mode. In addition, we present a study of the carrier-envelope phase (CEP) effect on high-order harmonic spectra, which may provide the insight of CEP effect in a new regime. Beyond this, our obtained results also apply to other classes of single-mode cavity-QED setup incorporating two-level atoms or comparable solid-state emitters.
摘要：
Based on a single atom coupled to a fiber-coupled, chip-based microresonator [B. Dayan et al., Science 319, 1062 (2008)], we put forward a scheme to generate optical frequency combs at driving laser powers as low as a few nanowatts. Using state-of-the-art experimental parameters, we investigate in detail the influences of different atomic positions and taper-resonator coupling regimes on optical-frequency-comb generation. In addition to numerical simulations demonstrating this effect, a physical explanation of the underlying mechanism is presented. We find that the combination of the atom and the resonator can induce a large third-order nonlinearity which is significantly stronger than Kerr nonlinearity in Kerr frequency combs. Such enhanced nonlinearity can be used to generate optical frequency combs if driven with two continuous-wave control and probe lasers and significantly reduce the threshold of nonlinear optical processes. The comb spacing can be well tuned by changing the frequency beating between the driving control and probe lasers. The proposed method is versatile and can be adopted to different types of resonators, such as microdisks, microspheres, microtoroids or microrings.
摘要：
<jats:p>The influence of barium doping on the oxygen-ion diffusion and phase transition in the La<jats:sub>2</jats:sub>Mo<jats:sub>2</jats:sub><jats:sub>-</jats:sub><jats:sub>y</jats:sub>W<jats:sub>y</jats:sub>O<jats:sub>9</jats:sub><jats:sub>-</jats:sub><jats:sub>δ</jats:sub> (y=0, 1.0) oxide-ion conductors has been systematically investigated via dielectric techniques. In the Ba-doped La<jats:sub>2</jats:sub>Mo<jats:sub>2</jats:sub>O<jats:sub>9</jats:sub> samples there are only two dielectric relaxation peaks P<jats:sub>d1</jats:sub> and P<jats:sub>d2</jats:sub>, which are associated with the short-distance diffusion of oxygen vacancies. But in the Ba-doped La<jats:sub>2</jats:sub>MoWO<jats:sub>9</jats:sub> members, three peaks are detected, including peak P<jats:sub>d1</jats:sub>, P<jats:sub>d2</jats:sub>, and peak P<jats:sub>h</jats:sub>. The last is associated with the phase transition process from the static disordered state to the dynamic disordered state of oxygen ion/vacancy distribution.</jats:p>
作者机构：
[Li, Jie] School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan, China;[Xu, Dong Lai] School of Science and Engineering, Teesside University, Middlesbrough, TS1 3BA, United Kingdom
会议名称：
4th International Conference on Materials Science and Information Technology, MSIT 2014
摘要：
Electromagnetic wave absorbers can be widely used in Electromagnetic Compatibility (EMC). We proposed a novel multilayer structure of metal alloy-ferrite-plastic composites. A new structure with Frequency Selected Surface (FSS), which has filter characteristic, embedded in the composites was fabricated to improve the absorption performance. In bandwidth of 8.04GHz, the reflectivity was smaller than-8dB and the thickness was only 2.6mm. The reflectivity was measured using a standard NRL Arch technique in a frequency range of 3-18 GHz. The experimental results indicate that it is possible to make a desirable thin, broadband EMW absorber by the incorporation of an FSS into the magnetic absorbing materials.
作者机构：
[Li, Jie] School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan, China;[Xu, Dong Lai] School of Science and Engineering, Teesside University, Middlesbrough, TS1 3BA, United Kingdom
通讯机构：
[Li, J.] S;School of Electrical and Electronic Engineering, Wuhan Polytechnic University, Wuhan, China
会议名称：
4th International Conference on Advanced Engineering Materials and Technology, AEMT 2014
关键词：
Diamond nitrogen-vacancy centers;Optical ring cavity;Optical bistability;Elliptically polarized light
摘要：
We explore laser-polarization-dependent and magnetically controlled optical bistability (OB) in an optical ring cavity filled with diamond nitrogen-vacancy (NV) defect centers under optical excitation. The shape of the OB curve can be significantly modified in a new operating regime from the previously studied OB case, namely, by adjusting the intensity of the external magnetic field and the polarization of the control beam. The influences of the intensity of the control beam, the frequency detuning, and the cooperation parameter on the OB behavior are also discussed in detail. These results are useful in real experiments for realizing an all-optical bistate switching or coding element in a solid-state platform. (C) 2013 Elsevier B.V. All rights reserved.
关键词：
Photonic crystals (PCs);Spontaneous emission;Microwave field
摘要：
The spontaneous emission properties of a microwave-field-driven four-level atom embedded in anisotropic double-band photonic crystals (PCs) are investigated. We discuss the influences of the band-edge positions, Rabi frequency and detuning of the microwave field on the emission spectrum. It is found that several interesting features such as spectral-line enhancement, spectral-line suppression, spectral-line overlap, and multi-peak structures can be observed in the spectra. The proposed scheme can be achieved by use of a microwave-coupled field into hyperfine levels in rubidium atom confined in a photonic crystal. These theoretical investigations may provide more degrees of freedom to manipulate the atomic spontaneous emission. (C) 2012 Elsevier B.V. All rights reserved.
