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      Vol. 3 ， Issue 3 ， 2014

        Original Articles

      • Suejit Pechprasarn,Bei Zhang,Darren Albutt,Jing Zhang,Michael Somekh
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.68
        Abstract：As disease diagnosis becomes more sophisticated, there is a requirement to measure small numbers of molecules attached to, for instance, an antibody. This requires a sensor capable not only of high sensitivity but also the ability to make measurements over a highly localized region. In previous publications, we have shown how a modified confocal microscope allows one to make localized surface plasmon (SP) measurements on a scale far smaller than the surface plasmon propagation distance. The present implementation presents a new ultrastable interferometer system, which greatly improves the noise performance. Hitherto, we have used the central part of the back focal plane to form a reference beam with the reradiated surface plasmons. In the current system, we block the central part and use the spatial light modulator to deflect s-polarized light into the pinhole to form an interference signal with the surface plasmons, thus creating an ultrastable interferometer formed with two beams incident at very similar angles. We demonstrate the superior noise performance of the system in hostile environments and examine further adaptations of the system to further enhance noise performance.  
        Keywords：biosensor;common path;confocal microscopy;interferometry;surface plasmon   
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        Published：2024-09-30
      • Bao-Qin Chen,Ming-Liang Ren,Rong-Juan Liu,Chao Zhang,Yan Sheng,Bo-Qin Ma,Zhi-Yuan Li
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.70
        Abstract：Ultrabroadband laser sources are highly desirable in a wide variety of modern science disciplines ranging from physics, chemistry and materials science to information communications and processing. Here we present the design and fabrication of a chirped periodically poled lithium niobate (CPPLN) nonlinear photonic crystal that supports multiple orders of quasiphase matching with finite bandwidth and allows for the simultaneous broadband generation of second and third harmonics with high conversion efficiency. Moreover, the chirp rate has a significant influence on the conversion efficiency and bandwidth. The CPPLN scheme offers a promising approach for the construction of short-wavelength laser sources and enables the generation of the three primary colors—red, green and blue—from a single crystal, which may have potential applications in large-screen laser displays.  
        Keywords：chirped periodically poled lithium niobate;quasiphase matching;second-harmonic generation;third-harmonic generation   
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        Published：2024-09-30
      • Vadym Apalkov,Mark I Stockman
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.72
        Abstract：We propose a novel nanospaser that operates in the mid-infrared region and utilizes a nanopatch of graphene as its plasmonic core and a quantum-well cascade as its gain medium. This design takes advantage of the low optical losses in graphene resulting from its high electron mobility. The proposed quantum cascade graphene spaser generates optical fields with unprecedentedly high nanolocalization, which is characteristic of graphene plasmons. This spaser will be an efficient nanosource of intense and coherent hot-spot fields in the mid-infrared spectral region with potential widespread applications in mid-infrared nanoscopy, nanospectroscopy, nanolithography, and optoelectronic information processing.  
        Keywords：graphene;quantum cascade laser;quantum well;spaser   
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        Published：2024-09-30
      • Wei-Ping Qin,Zhen-Yu Liu,Chol-Nam Sin,Chang-Feng Wu,Guan-Shi Qin,Zhe Chen,Ke-Zhi Zheng
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.74
        Abstract：Cooperative luminescence (CL) occurs in spectral regions in which single ions do not have energy levels. It was first observed more than 40 years ago, and all results reported so far are from a pair of ions. In this work, upconverted CL of three Yb3+ ions was observed in the ultraviolet (UV) region under near-infrared (NIR) excitation. The UV CL intensity showed a cubic dependence on the NIR pump power, whereas the luminescence lifetime was nearly one-third the luminescence lifetime of single Yb3+ ions. The triplet CL (TCL) has a clear spectral structure, in which most emission peaks are consistent with the self-convoluted spectra from single Yb3+ ions. Blue shifts were observed for certain peaks, indicating complex interactions among the excited Yb3+ ions. The probability of the TCL process versus the average distances among three Yb3+ ions was derived via the first- and second-order corrections to the wave functions of lanthanide ions, indicating that the formation of Yb3+ clusters containing closely spaced ions favors the occurrence of the multi-ion interaction processes. Furthermore, the cooperative sensitization of one Gd3+ ion by four excited Yb3+ ions (Yb3+-tetramer) was demonstrated experimentally, which exhibited a novel upconversion mechanism—cluster sensitization. Our results are intriguing for further exploring quantum transitions that simultaneously involve multiple ions.  
        Keywords：cooperative luminescence;cooperative sensitization;quantum transition;ytterbium cluster   
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        Published：2024-09-30
      • Aleksandr Polyakov,Mauro Melli,Giuseppe Cantarella,Adam Schwartzberg,Alexander Weber-Bargioni,P James Schuck,Stefano Cabrini
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.76
        Abstract：The expansion of nanoscale optics has generated a variety of scanning probe geometries that yield spatial resolution below 10 nm. In this work, we present a physical model for coupling far-field radiation to plasmonic modes on the surface of a scanning probe, and propose a scheme for extending the working distance of such a probe. In a subsurface application, an optical transformer at the tip of a probe can be coupled to a remote near-field antenna placed inside the sample at a distance away from the surface, expanding the effective working distance up to 100 nm.  
        Keywords：optical transformer;plasmonic tip;plasmon coupling   
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        Published：2024-09-30
      • Anders Pors,Michael G Nielsen,Thomas Bernardin,Jean-Claude Weeber,Sergey I Bozhevolnyi
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.78
        Abstract：Efficient excitation of surface plasmon polaritons (SPPs) remains one of the most challenging issues in areas of plasmonics related to information communication technologies. In particular, combining high SPP excitation efficiency and acceptance of any polarization of incident light appeared to be impossible to attain due to the polarized nature of SPPs. Here we demonstrate plasmonic couplers that represent arrays of gap SPP resonators producing upon reflection two orthogonal phase gradients in respective linear polarizations of incident radiation. These couplers are thereby capable of efficiently converting incident radiation with arbitrary polarization into SPPs that propagate in orthogonal directions dictated by the phase gradients. Fabricated couplers operate at telecom wavelengths and feature the coupling efficiency of ~25% for either of two linear polarizations of incident radiation and directivity of SPP excitation exceeding 100. We further demonstrate that an individual wavelength-sized unit cell, representing a meta-scatterer, can also be used for efficient and polarization sensitive SPP excitation in compact plasmonics circuits.  
        Keywords：gap surface plasmons;metamaterials;metasurfaces;surface plasmon polaritons   
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        Published：2024-09-30
      • Nora Tischler,Ivan Fernandez-Corbaton,Xavier Zambrana-Puyalto,Alexander Minovich,Xavier Vidal,Mathieu L Juan,Gabriel Molina-Terriza
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.64
        Abstract：An analysis of light–matter interactions based on symmetries can provide valuable insight, particularly because it reveals which quantities are conserved and which ones can be transformed within a physical system. In this context, helicity can be a useful addition to more commonly considered observables such as angular momentum. The question arises how to treat helicity, the projection of the total angular momentum onto the linear momentum direction, in practical experiments. In this paper, we put forward a simple but versatile experimental treatment of helicity. We then apply the proposed method to the scattering of light by isolated cylindrical nanoapertures in a gold film. This allows us to study the helicity transformation taking place during the interaction of focused light with the nanoapertures. In particular, we observe from the transmitted light that the scaling of the helicity transformed component with the aperture size is very different to the direct helicity component.  
        Keywords：helicity;nanoaperture;nanophotonics;optics;symmetry   
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        Published：2024-09-30
      • Martin Schumann,Tiemo Bückmann,Nico Gruhler,Martin Wegener,Wolfram Pernice
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.56
        Abstract：Integrated optical chips have already been established for application in optical communication. They also offer interesting future perspectives for integrated quantum optics on a chip. At present, however, they are mostly fabricated using essentially planar fabrication approaches like electron-beam lithography or UV optical lithography. Many further design options would arise if one had complete fabrication freedom in regard to the third dimension normal to the chip without having to give up the virtues and the know-how of existing planar fabrication technologies. As a step in this direction, we here use three-dimensional dip-in direct-laser-writing optical lithography to fabricate three-dimensional polymeric functional devices on pre-fabricated planar optical chips containing Si3N4 waveguides as well as grating couplers made by standard electron-beam lithography. The first example is a polymeric dielectric rectangular-shaped waveguide which is connected to Si3N4 waveguides and that is adiabatically twisted along its axis to achieve geometrical rotation of linear polarization on the chip. The rotator's broadband performance at around 1550 nm wavelength is verified by polarization-dependent grating couplers. Such polarization rotation on the optical chip cannot easily be achieved by other means. The second example is a whispering-gallery-mode optical resonator connected to Si3N4 waveguides on the chip via polymeric waveguides. By mechanically connecting the latter to the disk, we can control the coupling to the resonator and, at the same time, guarantee mechanical stability of the three-dimensional architecture on the chip.  
        Keywords：direct laser writing;integrated optics;nanophotonic circuits;polarization conversion   
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        Published：2024-09-30
      • Jing Yang,Fangfang Luo,Tsung Sheng Kao,Xiong Li,Ghim Wei Ho,Jinghua Teng,Xiangang Luo,Minghui Hong
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.66
        Abstract：Light collection efficiency is an important factor that affects the performance of many optical and optoelectronic devices. In these devices, the high reflectivity of interfaces can hinder efficient light collection. To minimize unwanted reflection, anti-reflection surfaces can be fabricated by micro/nanopatterning. In this paper, we investigate the fabrication of broadband anti-reflection Si surfaces by laser micro/nanoprocessing. Laser direct writing is applied to create microstructures on Si surfaces that reduce light reflection by light trapping. In addition, laser interference lithography and metal assisted chemical etching are adopted to fabricate the Si nanowire arrays. The anti-reflection performance is greatly improved by the high aspect ratio subwavelength structures, which create gradients of refractive index from the ambient air to the substrate. Furthermore, by decoration of the Si nanowires with metallic nanoparticles, surface plasmon resonance can be used to further control the broadband reflections, reducing the reflection to below 1.0% across from 300 to 1200 nm. An average reflection of 0.8% is achieved.  
        Keywords：anti-reflection;broadband;laser micro/nanoprocessing;surface plasmons   
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        Published：2024-09-30
      • Jaesang Lee,Michael Slootsky,Kyusang Lee,Yifan Zhang,Stephen R Forrest
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.62
        Abstract：We demonstrate threefold directional light concentration from an organic light-emitting diode luminaire for use in spot lighting and other applications where high intensity illumination is required. The concentrating luminaire comprises four triangular, large-area green electrophosphorescent organic light emitting diodes (PHOLEDs) deposited on plastic substrates and assembled into a pyramidal structure with an open base that serves as the light exit aperture. The PHOLED surfaces are highly reflective to direct the emission from the devices to the aperture independent of the original emission position within the pyramid. The far-field intensity profile of the concentrator has a 'batwing' distribution that meets the requirements for general lighting for uniform illumination of planar surfaces.  
        Keywords：large-area PHOLED;luminaire;phosphorescence;plastic substrates   
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        Published：2024-09-30

        Reviews

      • Yingzhou Huang,Yurui Fang,Zhenglong Zhang,Ling Zhu,Mengtao Sun
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.80
        Abstract：Due to its amazing ability to manipulate light at the nanoscale, plasmonics has become one of the most interesting topics in the field of light–matter interaction. As a promising application of plasmonics, surface-enhanced Raman scattering (SERS) has been widely used in scientific investigations and material analysis. The large enhanced Raman signals are mainly caused by the extremely enhanced electromagnetic field that results from localized surface plasmon polaritons. Recently, a novel SERS technology called remote SERS has been reported, combining both localized surface plasmon polaritons and propagating surface plasmon polaritons (PSPPs, or called plasmonic waveguide), which may be found in prominent applications in special circumstances compared to traditional local SERS. In this article, we review the mechanism of remote SERS and its development since it was first reported in 2009. Various remote metal systems based on plasmonic waveguides, such as nanoparticle–nanowire systems, single nanowire systems, crossed nanowire systems and nanowire dimer systems, are introduced, and recent novel applications, such as sensors, plasmon-driven surface-catalyzed reactions and Raman optical activity, are also presented. Furthermore, studies of remote SERS in dielectric and organic systems based on dielectric waveguides remind us that this useful technology has additional, tremendous application prospects that have not been realized in metal systems.  
        Keywords：nanowire;plasmonic waveguide;remote-excitation;surface-enhanced Raman scattering   
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      • Weng W Chow,Frank Jahnke,Christopher Gies
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.82
        Abstract：This review addresses ongoing discussions involving nanolaser experiments, particularly those related to thresholdless lasing or few-emitter devices. A quantum-optical (quantum-mechanical active medium and radiation field) theory is used to examine the emission properties of nanolasers under different experimental configurations. The active medium is treated as inhomogeneously broadened semiconductor quantum dots embedded in a quantum well, where carriers are introduced via current injection. Comparisons are made between a conventional laser and a nanolaser with a spontaneous emission factor of unity, as well as a laser with only a few quantum dots providing the gain. It is found that the combined exploration of intensity, coherence time, photon autocorrelation function and carrier spectral hole burning can provide a unique and consistent picture of nanolasers in the new regimes of laser operation during the transition from thermal to coherent emission. Furthermore, by reducing the number of quantum dots in the optical cavity, a clear indication of non-classical photon statistics is observed before the single-quantum-dot limit is reached.  
        Keywords：nanolasers;optoelectronics;photon statistics;quantum light sources;quantum optics;semiconductor quantum dots;thresholdless lasing   
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      • Xiaofeng Fan,Weitao Zheng,David J Singh
        Vol. 3, Issue 3, (2014) DOI: 10.1038/lsa.2014.60
        Abstract：Light scattering by small particles has a long and interesting history in physics. Nonetheless, it continues to surprise with new insights and applications. This includes new discoveries, such as novel plasmonic effects, as well as exciting theoretical and experimental developments such as optical trapping, anomalous light scattering, optical tweezers, nanospasers, and novel aspects and realizations of Fano resonances. These have led to important new applications, including several ones in the biomedical area and in sensing techniques at the single-molecule level. There are additionally many potential future applications in optical devices and solar energy technologies. Here we review the fundamental aspects of light scattering by small spherical particles, emphasizing the phenomenological treatments and new developments in this field.  
        Keywords：light scattering;Mie theory;nano-optics;small particles;surface plasmons   
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