Xiangang Luo

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (207)461.83 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A new method is proposed to focus azimuthally polarized beam into an ultra-small or ultra-big dark spot under high numerical aperture lens system. Manipulated by proper designed binary 0-π phase plate, an ultra small dark spot regardless of side-lobe intensity is generated with main-lobe peak to peak distance shrunk to 0.24λ, which is 46% of the case without phase plate. For potential applications, shrinking the dark spot and suppressing the side-lobe intensity are analyzed, and several cases of squeezed dark spots with different levels of side-lobe intensities are presented. Additionally, using a two-zone phase plate to enlarge the dark spot is investigated in this paper, and an enlarged dark spot is readily acquired with the main-lobe peak to peak distance in a range of 100%–200%. The advantages of this method are its large scale manipulation of the dark spot size and its high performance in suppressing side-lobe intensity, which is of great worth in enhancing the performance of many systems such as optical tweezers and stimulated emission depletion (STED) microscope.
    Optics Communications 08/2015; 349. DOI:10.1016/j.optcom.2015.03.024 · 1.54 Impact Factor
  • Min Wang, Cheng Huang, Mingbo Pu, Xiangang Luo
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    ABSTRACT: A method of utilizing frequency selective surface (FSS) to reduce side lobe level (SLL) is proposed. The FSS composed of annular slot arrays loaded with resistors is divided into several regions along the electric field direction. Each region has difference transmission amplitude (TA) but the same transmission phase (TP). Through the appropriate distribution design for each region, the output wave with tapered TA and uniform TP is obtained when the FSS is illuminated by a plane wave. Thus the FSS could be utilized to reduce the antenna SLL. An H-plane sectorial horn array is adopted as an exciting source to validate its SLL reduction performance. Simulation results show that the proposed FSS superstrate makes the SLL of the horn array in the E-plane desirably suppressed from −12.4 to −25.9 dB at 10.3GHz with the gain reduced from 18.3 to 16.7 dBi. The measured results agree well with the simulated ones. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1971–1975, 2015
    Microwave and Optical Technology Letters 08/2015; 57(8). DOI:10.1002/mop.29240 · 0.62 Impact Factor
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    ABSTRACT: A tunable plasmonic perfect absorber with a tuning range of ∼650 nm is realized by introducing a 20 nm thick phase-change material Ge2Sb2Te5 layer into the metal–dielectric–metal configuration. The absorption at the plasmonic resonance is kept above 0.96 across the whole tuning range. In this work we study this extraordinary optical response numerically and reveal the geometric conditions which support this phenomenon. This work shows a promising route to achieve tunable plasmonic devices for multi-band optical modulation, communication, and thermal imaging.
    Photonics Research 06/2015; 3(3). DOI:10.1364/PRJ.3.000054
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    ABSTRACT: Lens is usually immersed into oil or other mediums to increase the numerical aperture of the focusing lens and significantly improve the focusing efficiency. V-shaped plasmonic lens has attracted many research attentions because of its advantages like ability of reduced spherical aberration, ultrathin thickness, simple design, and high adjustability. However, it is hard to apply in practice since the focusing ability of such lens is low and errors can be great. Based on the incident light which wavelength is 1.5 μm, a V-shaped plasmonic planar lens with a thickness of 30 nm is designed, and it is immersed into the medium at a refractive index of 1 to 2.5. By matching conditions of transverse wave vector and Rayleigh limit formula, when the refractive index of mediums increases, the focusing efficiency becomes stronger, the spatial resolution is higher, and the focusing spot is changed. Through this easy-to-handle method, the significant focusing effect can be obtained, and this method promotes the applications of planar focusing lens in optical focusing, optical storage, laser-writing, and miniature optical integrated devices.
    Plasmonics 06/2015; 10(3). DOI:10.1007/s11468-014-9838-5 · 2.74 Impact Factor
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    ABSTRACT: Data capacity is rapidly reaching its limit in modern optical communications. Optical vortex has been explored to enhance the data capacity for its extra degree of freedom of angular momentum. In traditional means, optical vortices are generated using space light modulators or spiral phase plates, which would sharply decrease the integration of optical communication systems. Here we experimentally demonstrate a planar chiral antenna array to produce optical vortex from a circularly polarized light. Furthermore, the antenna array has the ability to focus the incident light into point, which greatly increases the power intensity of the generated optical vortex. This chiral antenna array may have potential application in highly integrated optical communication systems.
    Scientific Reports 05/2015; 5:10365. DOI:10.1038/srep10365 · 5.58 Impact Factor
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    ABSTRACT: The geometries of objects are deterministic in electromagnetic phenomena in all aspects of our world, ranging from imaging with spherical eyes to stealth aircraft with bizarre shapes. Nevertheless, shaping the physical geometry is often undesired owing to other physical constraints such as aero- and hydro-dynamics in the stealth technology. Here we demonstrate that it is possible to change the traditional law of reflection as well as the electromagnetic characters without altering the physical shape, by utilizing the achromatic phase shift stemming from spin-orbit interaction in ultrathin space-variant and spectrally engineered metasurfaces. The proposal is validated by full-wave simulations and experimental characterization in optical wavelengths ranging from 600 nm to 2800 nm and microwave frequencies in 8-16 GHz, with echo reflectance less than 10% in the whole range. The virtual shaping as well as the revised law of reflection may serve as a versatile tool in many realms, including broadband and conformal camouflage and Kinoform holography, to name just a few.
    Scientific Reports 05/2015; 5:9822. DOI:10.1038/srep09822 · 5.58 Impact Factor
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    ABSTRACT: Flat optics, which could planarize and miniaturize the traditional optical elements, possesses the features of extremely low profile and high integration for advanced manipulation of light. Here we proposed and experimentally demonstrated a planar metalens to realize an ultra-long focal length of ~240λ with a large depth of focus (DOF) of ~12λ, under the illumination of azimuthally polarized beam with vortical phase at 633 nm. Equally important is that such a flat lens could stably keep a lateral subwavelength width of 0.42λ to 0.49λ along the needle-like focal region. It exhibits one-order improvement in the focal length compared to the traditional focal lengths of 20~30λ of flat lens, under the criterion of having subwavelength focusing spot. The ultra-long focal length ensures sufficient space for subsequent characterization behind the lens in practical industry setups, while subwavelength cross section and large DOF enable high resolution in transverse imaging and nanolithography and high tolerance in axial positioning in the meantime. Such planar metalens with those simultaneous advantages is prepared by laser pattern generator rather than focused ion beam, which makes the mass production possible.
    Scientific Reports 05/2015; 5:09977. DOI:10.1038/srep09977 · 5.58 Impact Factor
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    ABSTRACT: In this paper, we demonstrate the design of a low-scattering metamaterial shell with strong backward scattering reduction and a wide bandwidth at microwave frequencies. Low echo is achieved through cylindrical wave expanding theory, and such shell only contains one metamaterial layer with simultaneous low permittivity and permeability. Cut-wire structure is selected to realize the low electromagnetic (EM) parameters and low loss on the resonance brim region. The full-model simulations show good agreement with theoretical calculations, and illustrate that near −20dB reduction is achieved and the −10 dB bandwidth can reach up to 0.6 GHz. Compared with the cloak based on transformation electromagnetics, the design possesses advantage of simpler requirement of EM parameters and is much easier to be implemented when only backward scattering field is cared.
    Optics Express 04/2015; 23(8). DOI:10.1364/OE.23.010396 · 3.53 Impact Factor
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    ABSTRACT: Hyperbolic metamaterial composed of SiO2/Al films are explored to squeeze out bulk plasmon polaritons (BPPs) to produce large area and uniform deep subwavelength interference patterns. As examples, two and four BPPs interference lithography with half pitch 45 nm (≈λ/8) are demonstrated in experiments. Much deeper resolution up to 22.5 nm (≈λ/16) and variety of BPPs interference patterns are feasible. The period of grating structures for transferring photons to BPPs is much larger than that of BPPs interference patterns, facilitating the structures fabrication by simple and low cost methods like large area laser interference lithography. It is believed that the method provides a cost-effective, parallel, and large area nanofabrication way.
    04/2015; DOI:10.1002/adom.201400596
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    ABSTRACT: An equivalent circuit model of ‘U’-shaped split-ring resonators (SRR), the basic structure of SRR has been proposed and studied. The proposed model, other than traditional equivalent circuit model, has taken both the influence of geometrical parameters and dielectric substrate into account and investigated them in detail. Furthermore, the calculation formula of extra mutual inductance induced by periodic cells has been derived. The performance of the ‘U’-shaped SRR analyzed by the equivalent circuit model shows a good agreement with experimental measurements and numerical simulation in terahertz region. This work presents a novel method to predict the resonance frequency of complicated SPP accurately and paves an avenue for the future terahertz devices applications.
    Journal of Modern Optics 03/2015; 62(11):1-7. DOI:10.1080/09500340.2015.1015633 · 1.17 Impact Factor
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    ABSTRACT: Poor aspect profiles of plasmonic lithography patterns are suffering from evanescent waves' scattering loss in metal films and decaying exposure in photoresist. To address this issue, we experimentally report plasmonic cavity lens to enhance aspect profile and resolution of plasmonic lithography. The profile depth of half-pitch (hp) 32 nm resist patterns is experimentally improved up to 23 nm, exceeding in the reported sub-10 nm photoresist depth. The resist patterns are then transferred to bottom resist patterns with 80 nm depth using hard-mask technology and etching steps. The resolution of plasmonic cavity lens up to hp 22 nm is experimentally demonstrated. The enhancement of the aspect profile and resolution is mainly attributed to evanescent waves amplifying from the bottom silver layer and scattering loss reduction with smooth silver films in plasmonic cavity lens. Further, theoretical near-field exposure model is utilized to evaluate aspect profile with plasmonic cavity lens and well illustrates the experimental results.
    Applied Physics Letters 03/2015; 106(9):093110. DOI:10.1063/1.4914000 · 3.52 Impact Factor
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    ABSTRACT: A novel hybrid planar lens is proposed to engineer the far-field focusing patterns. It consists of an array of slits which are filled with phase-change material Ge2Sb2Te5 (GST). By varying the crystallization level of GST from 0% to 90%, the Fabry-Pérot resonance supported inside each slit can be spectrally shifted across the working wavelength at 1.55 µm, which results in a transmitted electromagnetic phase modulation as large as 0.56π. Based on this geometrically fixed platform, different phase fronts can be constructed spatially on the lens plane by assigning the designed GST crystallization levels to the corresponding slits, achieving various far-field focusing patterns. The present work offers a promising route to realize tunable nanophotonic components, which can be used in optical circuits and imaging applications.
    Scientific Reports 03/2015; 5:8660. DOI:10.1038/srep08660 · 5.58 Impact Factor
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    ABSTRACT: Optical antennas are key elements in quantum optics emitting and sensing, and behave wide range applications in optical domain. However, integration of optical antenna radiating orbital angular momentum is still a challenge in nano-scale. We theoretically demonstrate a sub-wavelength phased optical antenna array, which manipulates the distribution of the orbital angular momentum in the near field. Orbital angular momentum with topological charge of 4 can be obtained by controlling the phase distribution of the fundamental mode orbital angular momentum in each antenna element. Our results indicate this phased array may be utilized in high integrated optical communication systems.
    Optics Express 02/2015; 23(4). DOI:10.1364/OE.23.004873 · 3.53 Impact Factor
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    ABSTRACT: Dispersion engineering of metamaterials is critical yet not fully released in applications where broadband and multispectral responses are desirable. Here we propose a strategy to circumvent the bandwidth limitation of metamaterials by implementing two-dimensional dispersion engineering in the meta-atoms. Lorentzian resonances are exploited as building blocks in both dimensions of the dedicatedly designed meta-atoms to construct the expected dispersion. We validated this strategy by designing and fabricating an anisotropic metamirror, which can accomplish achromatic polarization transformation in 4-octave bandwidth (two times of previous broadband converters). This work not only paves the way for broadband metamaterials design but also inspire potential applications of dispersion management in nano-photonics.
    Scientific Reports 02/2015; 5:8434. DOI:10.1038/srep08434 · 5.58 Impact Factor
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    ABSTRACT: In this paper, we report the formation of extremely sharp (Quality factor Q~ + ∞) FR in a single layer of dielectric nanorods with perturbed periodicity. The interference between the broadband Fabry-Perot (F-P) resonance and defect induced dark mode results in refractive index sensitivity (S) of 1312.75 nm/RIU and figure of merit (FOM) of 500, offering an excellent platform for biological sensing and detection.
    Optics Express 02/2015; 23(3). DOI:10.1364/OE.23.002895 · 3.53 Impact Factor
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    ABSTRACT: Data capacity of optical communication is achieving its limit owing to the non-linear effect of optical fiber. As an effective alternative, light carrying orbital angular momentum can greatly increase the capacity for its unprecedented degree of freedom. We demonstrate the propagation of orbital angular momentum with topological charge of 1 and 2 in plasmonic circular waveguide with sub-wavelength diameter with little propagation loss of 2.73 dB/μm, which has never been observed in optical fibers with sub-wavelength diameter. We also confirm that lights carrying orbital angular momentum can be maintained in sharp bended sub-wavelength waveguide. This plasmonic waveguide may serve as a key component in on-chip systems involving OAM.
    Optics Express 02/2015; 23(3). DOI:10.1364/OE.23.002857 · 3.53 Impact Factor
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    ABSTRACT: We numerically demonstrated the sub-diffraction-limited magnified Talbot imaging in a metamaterial composed of cylindrical stacked metal/dielectric multilayer. It was found that the magnified Talbot imaging could occur without the requirement of the metal/dielectric permittivity matching condition as satisfied in the hyperlens. Specifically, in this work, a practical realization of the magnified Talbot imaging was performed by Ag/Al2O3 multilayer stack at the wavelength of 337 nm. Unlike the traditional Talbot effect, the Talbot length in this case is not a constant but a variable and the variable Talbot length can be predicted roughly by ray optics approach. The contrast of the magnified Talbot imaging is decided by both the imaginary part and the real part in permittivity of the metamaterial. In order to obtain a deep sub-wavelength magnified Talbot image at the outer surface of the cylindrical metamaterial, the outer cylindrical radius should be optimized and the imaginary part in the permittivity should be small enough.
    Applied Physics A 01/2015; 118(4). DOI:10.1007/s00339-014-8939-5 · 1.69 Impact Factor
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    ABSTRACT: In this letter, a two-layer metasurface is proposed to achieve radar cross-section (RCS) reduction of a stacked patch antenna at a broadband. The lower layer metasurface is composed of four square patches loaded with four resistors, which is utilized to reduce RCS in the operation band (2.75–3.4 GHz) of the patch antenna. The periodic square loops with four resistors mounted on each side are adopted to construct the upper layer metasurface for absorbing the incoming wave out of band. We first investigate the effectiveness of the proposed metasurface on the RCS reduction of the single stacked patch and then apply this strategy to the $1 times 4$ stacked patch array. The proposed low RCS stacked patch array antenna is fabricated and measured. The experimental results show that the designed metasurface makes the antenna RCS dramatically reduced in a broadband covering the operation band and out-of-band from 5.5–16 GHz. Moreover, the introduction of metasurface is demonstrated to have little influence on the antenna performance.
    IEEE Antennas and Wireless Propagation Letters 01/2015; 14:1-1. DOI:10.1109/LAWP.2015.2407375 · 1.95 Impact Factor
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    ABSTRACT: In this letter, we propose a dual linearly polarized unit cell with 1-bit phase resolution for transmitarray application in X-band. It consists of two-layer metallic patterns connected by a metallized via-hole. One layer of the metallic pattern is a rectangular patch with two p-i-n diodes loaded in O-slot along electric field polarization direction, which is utilized as a receiver-antenna to achieve 1-bit phase tuning. The other metallic pattern is a dual linearly polarized transmitter-antenna that adopts a square ring patch with two p-i-n diodes distributed at the cross-polarization directions. The simulation results show that the designed antenna can achieve 1-bit phase tuning and linearly polarization reconfiguration at 10.5 GHz with insertion loss of about 1.1 dB. The characteristic of the designed transmitarray element is then experimentally validated by an ad-hoc waveguide simulator. The measured results agree with the simulated ones.
    IEEE Antennas and Wireless Propagation Letters 01/2015; 14:167-170. DOI:10.1109/LAWP.2014.2358267 · 1.95 Impact Factor
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    ABSTRACT: We theoretically utilize bowtie aperture combined with metal-insulator-metal (MIM) scheme to obtain sub-32-nm (λ/12) high-aspect plasmonic spots. The improvement of the depth profile is attributed to the asymmetry electromagnetic mode excitation in MIM structure and the decaying compensation of the reflective Ag layer. A theoretical near-field exposure model has been used to evaluate the exposure depth in the photoresist. It is demonstrated that the exposure depth of the sub-32-nm plasmonic spot is more than 20 nm, which is about four times of the bowtie aperture without MIM scheme. The influences of the air gap tolerance and the ridge gap size of bowtie aperture are also discussed.
    Plasmonics 01/2015; DOI:10.1007/s11468-015-9966-6 · 2.74 Impact Factor

Publication Stats

2k Citations
461.83 Total Impact Points

Institutions

  • 2000–2015
    • Chinese Academy of Sciences
      • Institute of Optics And Electronics
      Peping, Beijing, China
  • 2013
    • Chongqing University
      • Key Laboratory of Optoelectronic Technology and System of the Education Ministry of China
      Ch’ung-ch’ing-shih, Chongqing Shi, China
  • 2011–2012
    • Southwest Jiaotong University
      • School of Information Science and Technology
      Hua-yang, Sichuan, China