Plasmon‐induced hot‐electron generation provides an efficient way to convert light into electric current. The investigation of the optoelectronic response in two‐dimensional materials and metallic hybrid nanostructure attracts increasing research interest. Here, we present a tunneling effect of plasmonic hot electrons that is generated from Au nanoparticles, which can vertically tunnel through graphene monolayers. A strong photocurrent induced by the hot electrons was measured in this graphene‐based vertical photodetector with its intensity maximum reached at the plasmon resonance wavelength. The tunneling effect of plasmonic hot electrons was investigated by gradually increasing the incident laser power and bias voltage between the top and bottom electrodes. The dynamic attenuation of plasmonic hot electrons in an excited state was further investigated with multilayered graphene sheets. These results show that our vertical hybrid structure can function as an effective design for the tunneling photodetector, and enable the realization of complex nanophotonic devices that are based on graphene and other 2D materials, such as optical transistors and plasmonic hot‐electron sensors.
Periodic arrays of plasmonic nanoantennas can enhance the directionality of light emission of nearby fluorophores and, therefore, have a great potential for a broad range of applications. Unfortunately, their narrow spectral bandwidth and the anisotropy of their optical resonances limit the use of these structures in applications such as solid state lighting. In this article, we study an alternative for periodic structures: Vogel's golden spirals. These spirals are deterministic structures with an approximate circular symmetry and a Fourier transform that is much more broadband than that of periodic lattices. Combining k‐space Stokes polarimetry and theoretical calculations, we first investigate the light scattering from Vogel's arrays and the coupling between individual nanoantennas. Next, photoluminescence measurements show that the spirals can enhance the forward emission of incoherent fluorescent sources embedded in a waveguide that also encloses the spiral. The enhancement occurs over a broad spectral band, proving the potential of Vogel's golden spirals for broadband light‐emitting devices.
Dewetting of thin metal films is one of the most widespread method for functional plasmonic nanostructures fabrication. However, simple thermal‐induced dewetting does not allow to control degree of nanostructures order without additional lithographic process steps. Here we propose a novel method for lithography‐free and large‐scale fabrication of plasmonic nanostructures via controllable femtosecond laser‐induced dewetting. The method is based on femtosecond laser surface pattering of a thin film followed by a nanoscale hydrodynamical instability, which is found to be very controllable under specific irradiation conditions. We achieve control over degree of nanostructures order by changing laser irradiation parametrs and film thickness. This allowed us to exploit the method for the broad range of applications: resonant light absorbtion and scattering, sensing, and potential improving of thin‐film solar cells.
Traditional detour‐phase hologram is a powerful optical device for manipulating phase and amplitude of light, but it is usually not sensitive to the polarization of light. By introducing the light‐metasurface interaction mechanism to the traditional detour phase hologram, we design a novel plasmonic nano‐slits assisted polarization selective detour phase meta‐hologram, which has attractive advantages of polarization multiplexing ability, broadband response, and ultra‐compact size. The meta‐hologram relies on the dislocations of plasmonic slits to achieve arbitrary phase distributions, showing strong polarization selectivity to incident light due to the plasmonic response of deep‐subwavelength slits. To verify its polarization sensitive and broadband responses, we experimentally demonstrate two holographic patterns of an optical vortex and an Airy beam at p‐ and s‐polarized light with wavelengths of 532nm, 633nm and 780nm, respectively. Furthermore, we realize an application example of the meta‐hologram as a polarization multiplexed photonic device for multi‐channel optical angular momentum (OAM) generation and detection. Such meta‐holograms could find widespread applications in photonics, such as chip‐level beam shaping and high‐capacity OAM communication.
Plasmonic waveguides are promising in many applications because of their subwavelength field confinement, which can strongly enhance light‐matter interactions. Nevertheless, how to efficiently evaluate their Kerr nonlinear performance is still an open question because of the presence of relatively large linear losses. Here a simple and versatile figure of merit (FOM) is proposed for Kerr nonlinear waveguides with linear losses. To derive the FOM, a generalized full‐vectorial nonlinear Schrödinger equation governing nonlinear pulse propagation in a lossy waveguide is developed, and an approximate analytic solution of the degenerate four wave mixing conversion efficiency is derived and validated. The effectiveness of the FOM is verified with an all‐plasmonic and a hybrid‐plasmonic waveguide configuration. Rigorous results show that the optimal waveguide length for the highest conversion efficiency is ln 3 times the attenuation length. At this length, the upper limits of the conversion efficiency and the nonlinear phase shift are determined by the FOM. These results provide fundamental theory and useful guidance in exploring plasmonic waveguides for nonlinear optical applications.
Since the surface plasmon polariton (SPP) has received a great deal of attention because of its capability of guiding light within the subwavelength scale, finding methods for arbitrary SPP field generation has been a significant issue in the area of integrated optics. To achieve such a goal, it will be necessary to generate a plasmonic complex field. In this paper, we propose a novel method for generating a plasmonic complex field propagating with arbitrary curvatures by using double‐lined distributed nanoslits. As a unit cell, two facing nanoslits are used for tuning both the amplitude and the phase of excited SPPs as a function of their tilted angles. For verification of the proposed design rule, the authors experimentally demonstrate some plasmonic caustic curves and Airy plasmons.
Surface‐plasmon‐polariton waves are two‐dimensional electromagnetic surface waves that propagate at the interface between a metal and a dielectric. These waves exhibit unusual and attractive properties, such as high spatial confinement and enhancement of the optical field, and are widely used in a variety of applications, such as sensing and subwavelength optics. The ability to precisely control the spatial and spectral properties of the surface‐plasmon wave is required in order to support the growing interest in both research and applications of plasmonic waves, and to bring it to the next level. Here, we review the challenges and methods for shaping the wavefront and spectrum of plasmonic waves. In particular, we present the recent advances in plasmonic spatial and spectral shaping, which are based on the realization of plasmonic holograms for the optical nearfield.
The interaction of light with a single gold nanorod (GNR) depends strongly on the polarization and wavelength of the light. For isolated GNRs, the maximum of the polarization (wavelength)‐dependent linear and nonlinear absorption appear at the same excitation polarization (wavelength). Here, it is demonstrated that these relationships can be manipulated in a GNR assembly composed of randomly distributed and oriented GNRs by controlling the plasmonic coupling strength between GNRs. It is revealed that the strongly localized modes resulting from the plasmonic coupling of GNRs play a crucial role in determining these relationships. For a GNR tetramer, it is shown by numerical simulation that the maximum two‐photon absorption achieved at a particular polarization can be switched to the minimum absorption and vice versa by controlling the coupling strength. More importantly, it is demonstrated both numerically and experimentally that the two‐photon‐absorption peak of a GNR assembly can be made to be different from its single‐photon‐absorption peak by increasing the coupling strength. Both properties are distinct from previous experimental observations. Our findings provide a useful guideline for engineering the interaction of light with complex plasmonic systems.
Nanostructures that feature nonreciprocal light transmission are highly desirable building blocks for realizing photonic integrated circuits. Here, a simple and ultracompact photonic‐crystal structure, where a waveguide is coupled to a single nanocavity, is proposed and experimentally demonstrated, showing very efficient optical diode functionality. The key novelty of the structure is the use of cavity‐enhanced material nonlinearities in combination with spatial symmetry breaking and a Fano resonance to realize nonreciprocal propagation effects at ultralow power and with good wavelength tunability. The nonlinearity of the device relies on ultrafast carrier dynamics, rather than the thermal effects usually considered, allowing the demonstration of nonreciprocal operation at a bit‐rate of 10 Gbit s−1 with a low energy consumption of 4.5 fJ bit−1.
Efficient amplification of spoof surface plasmon polaritons (SPPs) is proposed at microwave frequencies by using a subwavelength‐scale amplifier. For this purpose, a special plasmonic waveguide composed of two ultrathin corrugated metallic strips on top and bottom surfaces of a dielectric substrate with mirror symmetry is presented, which is easy to integrate with the amplifier. It is shown that spoof SPPs are able to propagate on the plasmonic waveguide in broadband with low loss and strong subwavelength effect. By loading a low‐noise amplifier chip produced by the semiconductor technology, the first experiment is demonstrated to amplify spoof SPPs at microwave frequencies (from 6 to 20GHz) with high gain (around 20dB), which can be directly used as a SPP amplifier device. The features of strong field confinement, high efficiency, broadband operation, and significant amplification of the spoof SPPs may advance a big step towards other active SPP components and integrated circuits.
The generation of sub‐optical‐cycle, carrier–envelope phase‐stable light pulses is one of the frontiers of ultrafast optics. The two key ingredients for sub‐cycle pulse generation are bandwidths substantially exceeding one octave and accurate control of the spectral phase. These requirements are very challenging to satisfy with a single laser beam, and thus intense research activity is currently devoted to the coherent synthesis of pulses generated by separate sources. In this review we discuss the conceptual schemes and experimental tools that can be employed for the generation, amplification, control, and combination of separate light pulses. The main techniques for the spectrotemporal characterization of the synthesized fields are also described. We discuss recent implementations of coherent waveform synthesis: from the first demonstration of a single‐cycle optical pulse by the addition of two pulse trains derived from a fiber laser, to the coherent combination of the outputs from optical parametric chirped‐pulse amplifiers.
Following Mie theory, nanoparticles made of a high‐refractive‐index dielectric, such as silicon, exhibit a resonator‐like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive‐index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.
Nanoscale photonic systems involve a broad variety of light–matter interaction regimes beyond the diffraction limit and have opened the path for a variety of application opportunities in sensing, solid‐state lighting, light harvesting, and optical signal processing. The need for numerical modeling is central for the understanding, control, and design of plasmonic and photonic nanostructures. Recently, the increasing sophistication of nanophotonic systems and processes, ranging from simple plasmonic nanostructures to multiscale and complex photonic devices, has been calling for highly efficient numerical simulation tools. This article reviews the state of the art in numerical methods for nanophotonics and describes which method is the best suited for specific problems. The widespread approaches derived from classical electrodynamics such as finite differences in time domain, finite elements, surface integral, volume integral, and hybrid methods are reviewed and illustrated by application examples. Their potential for efficient simulation of nanophotonic systems, such as those involving light propagation, localization, scattering, or multiphysical systems is assessed. The numerical modeling of complex systems including nonlinearity, nonlocal and quantum effects as well as new materials such as graphene is discussed in the perspective of actual and future challenges for computational nanophotonics.
Light manipulation is paramountly important to the fabrication of high‐performance optoelectronic devices such as solar cells and photodetectors. In this study, a high‐performance near‐infrared light nanophotodetector (NIRPD) was fabricated based on a germanium nanoneedles array (GeNNs array) with strong light confining capability, and single‐layer graphene (SLG) modified with heavily doped indium tin oxide nanoparticles (ITONPs), which were capable of inducing localized surface plasmon resonance (LSPR) under NIR irradiation. An optoelectronic study shows that after modification with ITONPs the device performance including photocurrent, responsivity and detectivity was considerably improved. In addition, the ITONPs@SLG/GeNNs array NIRPD was able to monitor fast‐switching optical signals, the frequency was as high as 1 MHz, with very fast response rates. Theoretical simulations based on finite‐element method (FEM) revealed that the observed high performance was not only due to the strong light‐confining capability of the GeNNs array, but also due to the plasmonic ITONPs‐induced hot electron injection. The above results suggest that the present NIRPD will have great potential in future optoelectronic devices application.
Microresonator‐based Kerr frequency comb (microcomb) generation can potentially revolutionize a variety of applications ranging from telecommunications to optical frequency synthesis. However, phase‐locked microcombs have generally had low conversion efficiency limited to a few percent. Here we report experimental results that achieve conversion efficiency ( on‐chip comb power excluding the pump) in the fiber telecommunication band with broadband mode‐locked dark‐pulse combs. We present a general analysis on the efficiency which is applicable to any phase‐locked microcomb state. The effective coupling condition for the pump as well as the duty cycle of localized time‐domain structures play a key role in determining the conversion efficiency. Our observation of high efficiency comb states is relevant for applications such as optical communications which require high power per comb line.
We report on the theoretical investigation of plasmonic resonances in metallic Möbius nanorings. Half‐integer numbers of resonant modes are observed due to the presence of an extra phase π provided by the topology of the Möbius nanostrip. Anomalous plasmon modes located at the non‐orientable surface of the Möbius nanoring break the symmetry that exist in conventional ring cavities, thus enable far‐field excitation and emission as bright modes. The far‐field resonant wavelength as well as the feature of half‐integer mode numbers is constant to the change of charge distribution on the Möbius nanoring due to the topology of Möbius ring. Owing to the ultra‐small mode volume induced by the remaining dark feature, an extremely high sensitivity as well as a remarkable figure of merit is obtained in our numerical calculations for sensing performance. The topological metallic nanostructure provides a novel platform for the investigation of localized surface plasmon modes exhibiting unique phenomena for potential plasmonic applications.
This article presents a novel III‐V on silicon laser. This work exploits the phenomenon that a passive silicon cavity, side‐coupled to a III‐V waveguide, will provide high and narrow‐band reflectivity into the III‐V waveguide: the resonant mirror. This results in an electrically pumped laser with a threshold current of 4 mA and a side‐mode suppression ratio up to 48 dB.
Red‐light photodetectors without filters are in urgent need for narrowband applications such as full‐color imaging and multi‐output visible light communication (VLC). However, their development is hindered by the lack of small‐band‐gap and narrowband response materials. Without wavelength filters, a new type of photodetector with a simple single‐layer architecture is developed, based on a stable small‐band‐gap squarylium dye and characterized by a detectivity peak at 680 nm and full width at half maximum of 80 nm. The device, which exhibits high stability in air and humid conditions, shows a significantly low dark current of ∼2 nA·cm−2 at −2 V and high specific detectivity of 3.2 × 1012 Jones. The response current ratio of the device to red, green, and blue lights with a luminous flux amplitude ratio of 3:6:1 (standard ratio for white light) is 100:12:1.1. These properties indicate that the squarylium dye red‐light photodetectors are promising for VLC and other narrowband optoelectronic applications.
Monocrystalline titanium dioxide (TiO2) micro‐spheres support two orthogonal magnetic dipole modes at terahertz (THz) frequencies due to strong dielectric anisotropy. For the first time, we experimentally detected the splitting of the first Mie mode in spheres of radii m through near‐field time‐domain THz spectroscopy. By fitting the Fano lineshape model to the experimentally obtained spectra of the electric field detected by the sub‐wavelength aperture probe, we found that the magnetic dipole resonances in TiO2 spheres have narrow linewidths of only tens of gigahertz. Anisotropic TiO2 micro‐resonators can be used to enhance the interplay of magnetic and electric dipole resonances in the emerging THz all‐dielectric metamaterial technology.
Use of resonant light forces opens up a unique approach to high‐volume sorting of microspherical resonators with much higher uniformity of resonances compared to that in coupled‐cavity structures obtained by the best semiconductor technologies. In this work, the spectral response of the propulsion forces exerted on polystyrene microspheres near tapered microfibers is directly observed. The measurements are based on the control of the detuning between the tunable laser and internal resonances in each sphere with accuracy higher than the width of the resonances. The measured spectral shape of the propulsion forces correlates well with the whispering‐gallery mode resonances in the microspheres. The existence of a stable radial trap for the microspheres propelled along the taper is demonstrated. The giant force peaks observed for 20‐μm spheres are found to be in a good agreement with a model calculation demonstrating an efficient use of the light momentum for propelling the microspheres.
