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In this research, we propose a deep learning model employing gated recurrent units (GRUs) for the transmission spectrum prediction, and computational inverse designing of all-optical plasmonic devices (AOPDs), which may a crucial role in the precise fabrication process of photonic integrated circuits (PICs). This shift from a conventional simulation-based design to a GRU-based model offers a significant advantage in terms of accuracy and precision. The technique facilitates the intricate design process by simulating the propagation of Surface Plasmon Polaritons (SPPs) within the plasmonic structures of AOPDs. The forward modeling approach presented here demonstrates a substantial improvement in computational efficiency over the finite-difference time-domain method, adeptly forecasting transmission spectra characterized through the analysis of various geometrical parameters. The inverse modeling process infers the necessary design parameters to produce specific transmission spectra, markedly expediting the design process and eclipsing the time-intensive nature of traditional optimization methods. With a prediction loss (MSE) of 0.168 and 0.9217, this research substantiates the efficacy of GRUs in streamlining the forward and inverse design processes of AOPDs for integration into PICs. [ABSTRACT FROM AUTHOR]

The transient analysis of electromagnetic problems is important in the designing of plasmonic devices. It is useful for clarifying physical phenomena with extremely short timescales, because transient response affects the device performance. A time-domain computational technique is proposed for the transient analysis of electromagnetic problems with nanostructures. Our method is based on boundary integral equations in the complex frequency domain and fast inverse Laplace transforms. The advantage of our method is that the objects can be modeled by surface structure, dispersive media can be easily considered, computational error analysis is simple, and the electromagnetic field at the desired observation time can be obtained. [ABSTRACT FROM AUTHOR]

Metal nanostructures exhibit specific optical characteristics owing to their localized surface plasmon resonance (LSPR) and have been studied for applications in various optical devices. The LSPR property strongly depends on the size and shape of metal nanostructures; thus, plasmonic devices must be designed and fabricated according to their uses. Nanoimprint lithography (NIL) is an effective process for repeatedly fabricating metal nanostructures with controlled sizes and shapes and require optical properties. NIL is a powerful method for mass-producible, low-cost, and large-area fabrication. However, the process lacks flexibility in adjusting the size and shape according to the desirable optical characteristics because the size and shape of metal nanostructures are determined by a single corresponding mold. Here, we conducted a re-shaping process through the air-plasma etching of a polymer’s secondary mold (two-dimensional nanopillar array made of cyclo-olefin polymer (COP)) to modulate the sizes and shapes of nanopillars; then, we controlled the spectral characteristics of the imprinted plasmonic devices. The relationship between the structural change of the mold, which was based on etching time, and the optical characteristics of the corresponding plasmonic device was evaluated through experiments and simulations. According to evaluation results, the diameter of the nanopillar was controlled from 248 to 139 nm due to the etching time and formation of a pit structure. Consequently, the spectral properties changed, and responsivity to the surrounding dielectric environment was improved. Therefore, plasmonic devices based on the re-shaped COP mold exhibited a high responsivity to a refractive index of 906 nm/RIU at a wavelength of 625 nm.

Plasmonic structures possess rich physics related to the sensitivity of plasmon resonance to the change in the environmental dielectric constant, the enhanced light scattering and optical extinction, and the local field enhancement enabled strong light-matter interactions, which have been applied in refractive-index sensors, optical feedback in various micro- or nano-cavity lasers, surface enhanced Raman scattering spectroscopy, and high-sensitivity molecular detection. However, ultrafast optical response is another important aspect of plasmons, which can be utilized to achieve switching of optical signals in different spectral bands. These optical switching designs are very important for applications in optical logic circuits and optical communication system. In this review, we summarize a series of reports on ultrafast plasmonic optical switches, where we focus our discussions on the structural and device designs, instead of on their physics. By categorizing the designs of optical switches into different groups by their featured performances, we intend to propose the development trend and the commonly interested mechanisms of such ultrafast optical switches. We hope this review will supply helpful concepts and technical approaches for further development and new applications of ultrafast optical switching devices.

Plasmon thin film transistor has great potential to be applied in present-day technologies including modern medical diagnostics. Here, we report the fabrication of plasmon thin film transistor, realized by depositing a nanocomposite material on a pre-fabricated transistor substrate. Plasma polymerized aniline rubrene hybrid semiconductor and gold nanoparticles are synthesized in a combined plasma process to form the nanocomposite material. Absorption spectra indicate that the polymer shows broad absorption in the UV–Visible region and inclusion of Gold nanoparticles (Au NPs) results in strongly enhanced absorption in the visible region of the electromagnetic spectrum due to plasmon resonance. The prepared thin film transistor device shows substantial increment of drain current when irradiated by a light source 520 nm, leading to significantly high responsivity and detectivity. The plasmon thin film transistor with enhanced photoresponse in the visible region can be a promising device for application in future technologies such as in the field of imaging, plasmonic integrated circuits, Human Machine Interfaces. It can also be used for varied medical applications e.g. biosensors and biomedical devices for personalized use. [ABSTRACT FROM AUTHOR]

We propose an active plasmonic device based on graphene. By using a diffractive grating on silicon, highly confined plasmonic waves in monolayer graphene are efficiently excited. The high electric field of the surface plasmons near the graphene layer makes them ideal for use in biosensors, where a very small change in refractive index should be detected. A small change in the refractive index of surroundings medium, induces a large change in resonant wavelength. The spectral shift per refractive index unit (∆λ0/RIU) of the sensor is considerable and exceeding 2000 nm/RIU with a narrow line width spectral of the plasmon resonances. The figure of merit for this sensor is approximately equal to 14.2 and electrical tuning can be achieved by adjusting the Fermi level in graphene. Therefore, this grating plasmonic structure is highly sensitive and can be used in high resolution biosensing applications. [ABSTRACT FROM AUTHOR]

Realizing multiple beam shaping functionalities in a single plasmonic device is crucial for photonic integration. Both plasmonic Bessel-like beams and bottle beams have potential applications in nanophotonics, particularly in plasmonic based circuits, near field optical trapping, and micro manipulation. Thus, it is very interesting to find new approaches for simultaneous generation of surface plasmon polariton Bessel-like beams and bottle beams in a single photonic device. Two types of polarization-dependent devices, which consist of arrays of spatially distributed sub-wavelength rectangular slits, are designed. The array of slits are specially arranged to construct an X-shaped or an IXI-shaped array, namely X-shaped device and IXI-shaped devices, respectively. Under illumination of circularly polarized light, plasmonic zero-order and first-order Bessel-like beams can be simultaneously generated on both sides of X-shaped devices. Plasmonic Bessel-like beam and bottle beam can be simultaneously generated on both sides of IXI-shaped devices. By changing the handedness of circularly polarized light, for both X-shaped and IXI-shaped devices, the positions of the generated plasmonic beams on either side of device can be dynamically interchanged.

This paper reports a general stepwise route assembling interface-mediated RAFT polymerization of 2-methoxyethoxy ethyl methacrylate and conversion of dodecyl trithiocarbonate end groups to thiol groups for gold nanoparticle assemblies. We intended by this way a new plasmonic device made of gold nanoparticles (Au NPs) and temperature responsive [poly((2-methoxyethoxy)ethyl) methacrylate] [poly(MEO 2 -MA)] brush on a silicon substrate. This polymeric layer replies to temperature changing by conformational variation and is therefore able to change the distance between the Au NPs on the brush layer with 5,5-dithiobis(2-dinitrobenzoic acid) (DTNB). We show that an increment of the external temperature reversibly stimulates a significant increase of the DTNB SERS signal. [ABSTRACT FROM AUTHOR]

We proposed a novel method to design a broadband plasmonic unequal-power splitter with a rectangular ring resonator directly connected to the input and output waveguides. By properly assigning the locations of the input and output waveguides, the splitting ratio is controlled by manipulating the output waveguide widths while the reflectance is eliminated by adjusting the input waveguide width without varying any other design parameters. To obtain the design parameters of the input and output waveguide widths, analytical expressions of the splitting ratio and the reflectance are established by using the equivalent circuit based on the transmission line model. Design examples of unequal-power splitters with splitting ratio of 0.5 are numerically demonstrated. The analysis based on equivalent circuit is well confirmed by the finite difference time domain simulation. The simulated results show that the unequal-power splitters have a flat and wide band over the wavelength range from 1500 nm to 1600 nm by using a compact rectangular ring resonator with the dimensions of 550 nm × 275 nm. [ABSTRACT FROM AUTHOR]

Abstract: Recent progress of nano-technology with near-field scanning optical microscope (NSOM) is surveyed in this article. We focus mainly on NSOM, nano-scale spectroscopy with NSOM, probe technology of NSOM, and study of nano-structured metallic surface with NSOM. First, we follow developments of aperture NSOM and apertureless NSOM, and then address progress of NSOM-combined spectroscopy which is so sufficiently advanced with apertureless NSOM technology to provide chemical information on length scales of a few nanometers. Recent achievement of nano-scale Raman and IR spectroscopy will be introduced. Finally, research on nano-optic elements using surface plasmon polariton with NSOM is introduced as an example of NSOM applications to nano-structured metallic surfaces. [Copyright &y& Elsevier]

Metal nanostructures exhibit specific optical characteristics owing to their localized surface plasmon resonance (LSPR) and have been studied for applications in various optical devices. The LSPR property strongly depends on the size and shape of metal nanostructures; thus, plasmonic devices must be designed and fabricated according to their uses. Nanoimprint lithography (NIL) is an effective process for repeatedly fabricating metal nanostructures with controlled sizes and shapes and require optical properties. NIL is a powerful method for mass-producible, low-cost, and large-area fabrication. However, the process lacks flexibility in adjusting the size and shape according to the desirable optical characteristics because the size and shape of metal nanostructures are determined by a single corresponding mold. Here, we conducted a re-shaping process through the air-plasma etching of a polymer's secondary mold (two-dimensional nanopillar array made of cyclo-olefin polymer (COP)) to modulate the sizes and shapes of nanopillars; then, we controlled the spectral characteristics of the imprinted plasmonic devices. The relationship between the structural change of the mold, which was based on etching time, and the optical characteristics of the corresponding plasmonic device was evaluated through experiments and simulations. According to evaluation results, the diameter of the nanopillar was controlled from 248 to 139 nm due to the etching time and formation of a pit structure. Consequently, the spectral properties changed, and responsivity to the surrounding dielectric environment was improved. Therefore, plasmonic devices based on the re-shaped COP mold exhibited a high responsivity to a refractive index of 906 nm/RIU at a wavelength of 625 nm. [ABSTRACT FROM AUTHOR]

Here we propose a straightforward method to functionalize gold nanostructures by using an appropriate peptide sequence already selected toward gold surfaces and derivatized with another sequence for the capture of a molecular target. Large scale 3D-plasmonic devices with different nanostructures were fabricated by means of direct nanoimprint technique. The present work is aimed to address different innovative aspects related to the fabrication of large-area 3D plasmonic arrays, their direct and easy functionalization with capture elements, and their spectroscopic verifications through enhanced Raman and enhanced fluorescence techniques. [ABSTRACT FROM AUTHOR]

Surface plasmon polaritons are electromagnetic waves coupled to collective electron oscillations propagating along metal-dielectric interfaces, exhibiting a bosonic character. Recent experiments involving surface plasmons guided by wires or stripes allowed the reproduction of quantum optics effects, such as antibunching with a single surface plasmon state, coalescence with a two-plasmon state, conservation of squeezing, or entanglement through plasmonic channels. We report the first direct demonstration of the wave-particle duality for a single surface plasmon freely propagating along a planar metal-air interface. We develop a platform that enables two complementary experiments, one revealing the particle behavior of the single-plasmon state through antibunching, and the other one where the interferences prove its wave nature. This result opens up new ways to exploit quantum conversion effects between different bosonic species as shown here with photons and polaritons.

Advanced optical materials or interfaces are gaining attention for diagnostic applications. However, the achievement of large device interface as well as facile surface functionalization largely impairs their wide use. The present work is aimed to address different innovative aspects related to the fabrication of large-area 3D plasmonic arrays, their direct and easy functionalization with capture elements, and their spectroscopic verifications through enhanced Raman and enhanced fluorescence techniques. In detail, we have investigated the effect of a Au-based nanoCone array, fabricated by means of direct nanoimprint technique over large area (mm(2)), on protein capturing and on the enhancement in optical signal. A selective functionalization of gold surfaces was proposed by using a peptide (AuPi3) previously selected by phage display. In this regard, two different sequences, labeled with fluorescein and biotin, were chemisorbed on metallic surfaces. The presence of Au nanoCones array consents an enhancement in electric field on the apex of cone, enabling the detection of molecules. We have witnessed around 12-fold increase in fluorescence intensity and SERS enhancement factor around 1.75 × 10(5) with respect to the flat gold surface. Furthermore, a sharp decrease in fluorescence lifetime over nanoCones confirms the increase in radiative emission (i.e., an increase in photonics density at the apex of cones).