Subwavelength Nanowire Research Articles

An optimized self-adaptive thermal radiation turn-down coating with vanadium dioxide nanowire array

Insulator-to-metal temperature phase transition Vanadium Dioxide (VO2) can enable radiative property switching in the mid- to far-infrared wavelengths. With computational optimization of grating arrangement and layer thickness parameters, we identify a monolithic high-performance turn-down thermal emittance coating of no more than 2 μm thick, consisting of a VO2 sub-wavelength nanowire grating array on an index-matched Fabry-Perot dielectric thin film on an additional absorbing VO2 sublayer. The working principles of this optimized VO2 structure are its gradient refractive index allowing high through-coating transmittance in the cold state, and its near-unity emissivity from semi-metal-insulator-metal plasmonic coupling in the hot state. This anisotropic patterned structure also considers performance over polarized incident light. A survey of other Fabry-Perot cavity materials with refractive index matching points to higher turn-down performances given an optimal VO2 nanowire volume filling ratio. With 24-hour solar and environmental analysis in comparison to other VO2 metasurfaces and multilayers, this coating enables responsive passive radiative cooling at high temperatures exceeding transition. This nano/micro-patterned coating could potentially impact self-cooling of the solar cells, batteries, and electrical devices where risk presents at high temperatures.

Anomalously Strong Second‐Harmonic Generation in GaAs Nanowires via Crystal‐Structure Engineering

AbstractGaAs‐based semiconductors are highly attractive for diverse nonlinear photonic applications, owing to their non‐centrosymmetric crystal structure and huge nonlinear optical coefficients. Nanostructured semiconductors, for example, nanowires (NWs), offer rich possibilities to tailor nonlinear optical properties and further enhance photonic device performance. In this study, it is demonstrated highly efficient second‐harmonic generation in subwavelength wurtzite (WZ) GaAs NWs, reaching 2.5 × 10−5 W−1, which is about seven times higher than their zincblende counterpart. This enhancement is shown to be predominantly caused by an axial built‐in electric field induced by spontaneous polarization in the WZ lattice via electric field‐induced second‐order nonlinear susceptibility and can be controlled optically and potentially electrically. The findings, therefore, provide an effective strategy for enhancing and manipulating the nonlinear optical response in subwavelength NWs by utilizing lattice engineering.

Pushing the limit of high-Q mode of a single dielectric nanocavity

High index dielectric nanostructure supports different types of resonant modes. However, it is very challenging to achieve high-Q factor in a single subwavelength dielectric nanoresonator due to non-hermtian property of the open system. Here, we present a universal approach of finding out a series of high-Q resonant modes in a single nonspherical dielectric nanocavity by exploring quasi-bound state in the continuum. Unlike conventional method relying on heavy computation (ie, frequency scanning by FDTD), our approach is built upon leaky mode engineering, through which many high-Q modes can be easily achieved by constructing avoid-crossing (or crossing) of the eigenvalue for pair leaky modes. The Q-factor can be up to 2.3*10^4 for square subwavelength nanowire (NW) (n=4), which is 64 times larger than the highest Q-factor (Q=360) reported so far in single subwavelength nanodisk. Such high-Q modes can be attributed to suppressed radiation in the corresponding eigenchannels and simultaneously quenched electric(magnetic) at momentum space. As a proof of concept, we experimentally demonstrate the emergence of the high-Q resonant modes (Q=380) in the scattering spectrum of a single silicon subwavelength nanowire.

Improvement of laser absorption and control of particle acceleration by subwavelength nanowire target

The effects of the subwavelength nanowire target on the enhanced laser absorption, heating of electrons, and acceleration and control of energetic ions are investigated by using two-dimensional particle-in-cell simulations. Compared with the flat target, the conversion efficiency and acceleration of target normal sheath acceleration can be improved remarkably. In the condition considered in this paper, the conversion efficiency from the laser to electrons can be increased by about four times (14.74% to 65.78%), and the cutoff energy of electrons can be raised by 1.5 times. Furthermore, the cutoff energies of both protons and carbon ions are increased by almost two times. The dependence of this effect for different nanowire widths is discussed by numerical simulations. It is found that the efficiency from the laser to electrons reaches the highest value when the nanowire width is d=0.2 μm. The optimum width for C6+ ions is d=0.3 μm, while d=0.8 μm is better for proton acceleration. Thus, the laser absorption, electron heating, and ion acceleration could be controlled by selecting the width of subwavelength nanowires.

Nanowire photonics toward wide wavelength range and subwavelength confinement [Invited

Semiconductor nanowires have attracted much attention for photonic applications, especially for lasers, because of their availability in a wide variety of materials and compositions, exceptionally small size, and rich functionality. So far, most nanowire laser studies have been done in rather short wavelength (λ) ranges of less than 1 µm. In addition, the diameter (d) of most nanowire lasers has been relatively large (d > λ/n, n is the refractive index) because of the requirement for sufficient optical confinement. Recently, however, we are seeing new trends in nanowire research towards much longer wavelengths and much thinner nanowires for photonic applications. This article reviews the latest research activities in these directions, which shows that it is possible to fabricate excellent nanowire lasers operating at telecom wavelengths or even in the mid-infrared region and extremely thin subwavelength nanowires can be applied to make nanophotonic devices in a wide range of wavelengths. We believe that these research trends will have an impact on applications for functional energy-saving devices in future photonic integrated circuits.

Low-Threshold Lasing up to 360 K in All-Dielectric Subwavelength-Nanowire Nanocavities

The ultrasmall dimensions of subwavelength nanowires have made them ideal candidates for compact and energy-efficient photonic applications and have, in particular, led to the realization of a large range of plasmonic nanolasers. Ohmic losses and short propagation lengths in metal-based plasmonic platforms, however, limit their performance. In this work, we bypass such limitations by relying instead on an all-dielectric platform: subwavelength ZnO nanowire-induced cavities integrated in SiN photonic crystal waveguides. Because of the low optical losses of this fully dielectric nanocavity, we demonstrate low-threshold lasing at high-temperatures using subwavelength nanowires as the gain material. Investigated devices consistently outperform their plasmonic counterparts in terms of lasing threshold (Pth = 3.5 MW·cm–2) and all existing subwavelength-nanowire lasers in terms of operation temperature (T = 360 K). Such a performance demonstrates the high potential of this all-dielectric platform for integrated photonic applications with low energy costs.

Photonics of Sub-Wavelength Nanowire Superlattices

Semiconductor nanowires (NWs) have widely been studied as an ideal platform for developing electronic, photovoltaic, photonic devices and biological probes in the nanoscale. The ability to synthesize high-quality NWs of various materials with a precise control in shape, doping and crystal structure is the key to the growth of NW-based technologies. In the past decade, there has been growing interest in controllably creating NW heterojunctions and periodically-modulated superlattices (SLs) because it is expected to bring new functionalities that are not present in uniform NWs. In particular, the interaction of NW SLs with light has been one of the central interests because the diameter and modulation length scale are on the same order as the wavelength of light in the optical regime. Also, degenerately-doped semiconductor NWs exhibit localized surface plasmon resonances (LSPRs), which comprises unexpected long-range interactions when the plasmon resonators are regularly placed in NW SLs. In this review, I will summarize the recent progress in photonics research of NW SLs. The topics discussed include preparation and types of NW SLs, light-trapping and light-emission properties, and plasmonic optical- and thermal-transport properties.

Highly Efficient Colored Perovskite Solar Cells Integrated with Ultrathin Subwavelength Plasmonic Nanoresonators

Highly efficient colored perovskite solar cells that exploit localized surface plasmon resonances in ultrathin subwavelength plasmonic nanoresonators are demonstrated. Localized resonances in ultrathin metal nano-strip optical resonators consisting of an array of metallic subwavelength nanowires on a transparent substrate, fabricated by using low-cost nanoimprint lithography over a large area, lead to a sharp peak in a reflection spectrum for distinctive color generation with angle-insensitive property up to 60°, and simultaneously transmit the complementary spectrum of visible light that can be efficiently harvested by the perovskite solar cells for electric power generation. The plasmonic color filter-integrated perovskite solar cells provide 10.12%, 8.17% and 7.72% of power conversion efficiencies with capabilities of creating vivid reflective red, green and blue colors. The scheme described in this work could be applied to a variety of applications such as power-generating decorations, tandem cells, power-saving wearable devices and energy-efficient reflective display technologies.

Continuous-wave operation and 10-Gb/s direct modulation of InAsP/InP sub-wavelength nanowire laser on silicon photonic crystal

We demonstrated sub-wavelength (∼111 nm diameter) single nanowire (NW) continuous wave (CW) lasers on silicon photonic crystal in the telecom-band with direct modulation at 10 Gb/s by optical pumping at cryogenic temperatures. To estimate the small signal response and pseudo-random bit sequence (PRBS) modulation of our CW lasers, we employed a new signal detection technique that employs a superconducting single photon detector and a time-correlated single photon counting module. The results showed that our NW laser was unambiguously modulated at above 10 Gb/s and an open eye pattern was obtained. This is the first demonstration of a telecom-band CW NW laser with high-speed PRBS modulation.

Subwavelength Nanowire Lasers on a Silicon Photonic Crystal Operating at Telecom Wavelengths

Here we report the successful demonstration of lasing oscillation in a subwavelength semiconductor nanowire (100 nm in diameter) at telecom wavelengths. Although a subwavelength nanowire is too thin to configure an efficient optical cavity by itself, we have combined the nanowire with a Si photonic crystal to form a nanowire-induced hybrid nanocavity. This unique configuration enables us to realize an efficient nanowire-based nanolaser on a Si platform. Our systematic study, which included L–L characteristics, emission wavelength, emission line width, emission lifetime, and photon correlation, has unambiguously revealed the lasing operation of the nanowire at 4 K. In addition, we have succeeded in changing the laser oscillation wavelength by moving the nanowire through a trench in the photonic crystal, which reveals the unique feature of this hybrid nanocavity. This is the first demonstration of telecom band subwavelength nanowire lasers, which may also be important for Si photonics applications.

Nanowire-nanoantenna coupled system fabricated by nanomanipulation.

Here we demonstrate the combination of a semiconductor nanowire and a plasmonic bowtie nanoantenna. A subwavelength InP nanowire was placed precisely in the middle of the nanogap of a gold bowtie nanoantenna with a nanomanipulator installed in a focused ion beam system. We observed a significantly large enhancement (by a factor of 110) of the photoluminescence intensity from this coupled system when the excitation wavelength was at the plasmonic resonance with its polarization parallel to the nanoantenna. Moreover, simulation results revealed that this large enhancement was caused by an interesting interplay between the plasmonic resonance of the nanoantenna and the breakdown of the field suppression effect in the subwavelength nanowire. Our results show that the combination of a nanowire and a nanoantenna gives us a new degree of freedom to design light-matter interactions on a nanoscale.

Near-infrared quarter-waveplate with near-unity polarization conversion efficiency based on silicon nanowire array.

Metasurfaces made of subwavelength resonators can modify the wave front of light within the thickness much less than free space wavelength, showing great promises in integrated optics. In this paper, we theoretically show that electric and magnetic resonances supported simultaneously by a subwavelength nanowire with high refractive-index can be utilized to design metasurfaces with near-unity transmittance. Taking silicon nanowire for instance, we design numerically a near-infrared quarter-waveplate with high transmittance using a subwavelength nanowire array. The operation bandwidth of the waveplate is 0.14 μm around the center wavelength of 1.71 μm. The waveplate can convert a 45° linearly polarized incident light to circularly polarized light with conversion efficiency ranging from 94% to 98% over the operation band. The performance of quarter waveplate can in principle be tuned and improved through optimizing the parameters of nanowire arrays. Its compatibility to microelectronic technologies opens up a distinct possibility to integrate nanophotonics into the current silicon-based electronic devices.

Waveguiding properties of a silicon nanowire embedded photonic crystal fiber

We design a photonic silicon nanowire embedded microstructured optical fiber which is a special class of waveguide whose core diameter is of subwavelength or nanometer size with the air holes in the cladding. We study the optical waveguiding properties, namely, waveguide dispersions, fractional power and effective nonlinearity by varying the core diameter. The results reveal that the air-clad silicon subwavelength nanowire exhibits several interesting properties such as tight-confinement, a large normal dispersion (82,385ps2/km) for 300nm core diameter and a large anomalous dispersion (−6817.3ps2/km) for 500nm core diameter at 1.95μm wavelength. The structure offers two zero dispersions, one at 1.26μm wavelength for a core diameter of 300nm and another at 1.83μm wavelength for 400nm core diameter. Besides, it provides a large nonlinearity (5672.7W−1m−1) at 0.450μm wavelength for 300nm core diameter. These enhanced optical properties might be suitable for various nonlinear applications.

金纳米线与亚波长狭缝结合实现局域场增强研究

In order to strengthen the electric field between two gold nanowires,a kind of structure was designed by putting them into periodical subwavelength slits.This structure combined the effect of amplifying electric field from the near-field coupled effect and the quasi-Fabry-Perot resonance.Theoretical study indicated that the electric field between gold nanowires showed periodical variation when depth of slits changes,and the peak of electric field appeared when Quasi-Fabry-Perot resonance happened,and nanowires were able to modulate the depth of resonance.The electric field turned out a sharp peak when the period was approaching to the wavelength of incident light,and it decreased rapidly as the interval of wires increased.According to the result calculated by finite element method,enhancing effect is considerable when the interval varies from 1nm to 2nm.It gets a 200electric field enhancement which means a 109 Raman enhanced factor in hot spot between the two gold nanowires in subwavelength slits by reasonably adjusting the period and depth of the slits,which is three orders of magnitude than two lonely wires.

Magneto-optical Kerr effect in resonant subwavelength nanowire gratings

Periodic arrays of nanorods can present a resonant response at specific geometric conditions. We use a multiple scattering approach to analyze the optical response of subwavelength nanowire gratings made of arbitrary anisotropic materials. When the rods are made of magneto-optical dielectrics we show that there is a complex interplay between the geometric resonances of the grating and the magneto-optical Kerr effects (MOKE) response. As we will show, for a given polarization of the incident light, a resonant magneto-optical response can be obtained by tuning the incidence angle and grating parameters to operate near the resonance condition for the opposite polarization. Our results could be important to understand and optimize MOKE structures and devices based on resonant subwavelength gratings and could open new perspectives in sensing applications.

Local plasmon excitations in one-dimensional array of metal nanowires for sensor applications

Optical properties of a one-dimensional periodic array of subwavelength metal nanowires in the regime of local plasmon excitation are investigated experimentally and theoretically. Both gas and liquid sensing by one-dimensional gold nanowires on a glass substrate produced by holographic lithography are demonstrated experimentally. The obtained spectral sensitivity of a local plasmon sensor to the refractive index of the environment is found comparable to that of a surface plasmon polariton sensor based on the grating coupler effect. The influence of nanowire shape on spectral sensitivity is studied theoretically in a differential formalism framework using a curvilinear coordinate transformation for triangular, trapezoidal, and rectangular cross sections of the nanowires. For nanowires with trapezoidal cross section, theoretical calculations for the spectral sensitivity to variation of the refractive index of the environment agree well with experimental data.