Narrow Results

To meet the demand of delivering ever-increasing Internet traffic, optical network must response by increasing its transmission capacity. Since transmission capacity of an individual fiber is still well exceed the capacity of transmitters (TXs) and receivers (RXs), wavelength-division multiplexing (WDM), in which many TXs and RXs at the transmitting ends of a fiber are used to send and receive many signals, becomes the necessary technology for increasing the transmission capacity of each link of an optical network. This trend, however, demands for increasing density not only the TXs and RXs, but all other components at the sending and receiving ends of communications links. As the number of wavelengths in WDM configuration getting greater, the number of all these components that must be placed on one board has to increase too; hence, the density of packaging comes to micro- and even nano-scale. The TXs and RXs are produced in arrays on a chip quite similar to production of VLSI electronic circuits. At that scale, traditional optical operations used today in an optical-communications technology, such as launching light into optical fiber from TXs and directing light from optical fiber into RXs, multiplexing and demultiplexing individual channels (wavelengths), and electro-optical (E/O) and opto-electrical (O/E) conversions become problems primarily because of the diffraction limit. The problems associated with the diffraction limit are particularly acute for optical interconnects. One of the possible solutions to all these—and some other—problems could be the use of plasmonics. In the last years, the optical-communications industry shows a great interest in developing this topic, as the growing number of publications and practical results can attest.

This paper consists of two parts. The first part reviews the current trends in application of plasmonics in optical communications and the second part discusses the theoretical foundation of the proposed WDM demultiplexer and offers the scheme of possible implementation of the device.

Sensing applications of THz technology include applications for space exploration, detection of concealed objects, explosive identification, and THz cancer detection. This paper will review these and other emerging applications and existing and potential THz sources and detectors, including photonic and electronic THz devices, such as plasmonic field effect transistors capable of detecting and emitting THz radiation. Plasma wave electronics devices demonstrated THz detection using GaAs-based and GaN-based HEMTs, Si MOS, SOI, and FINFETs and FET arrays. This technology has potential to become a dominant THz electronics technology.

Terahertz (THz) sensing technology enables 6G communication, detection of biological and chemical hazardous agents, cancer detection, monitoring of industrial processes and products, and detection of mines and explosives. THz sensors support security in buildings, airports, and other public spaces. They found important applications in radioastronomy and space research and, more recently, in Artificial Intelligence-driven THz sensing of MMICs and VLSI. Exploding demand for data transfers will require using the 300 GHz band after 2028 or even before and will make the deployment of THz sensing electronics inevitable. This paper discusses the new physics of THz sensing and THz sensing devices. It also reviews the THz sensing market, and key THz sensor companies.

Plasmonic resonance of metallic nanoparticles results from coherent motion of its conduction electrons, driven by incident light. For the nanoparticles less than 10 nm in diameter, localized surface plasmonic resonances become sensitive to the quantum nature of the conduction electrons. Unfortunately, quantum mechanical simulations based on time-dependent Kohn–Sham density functional theory are computationally too expensive to tackle metal particles larger than 2 nm. Herein, we introduce the recently developed time-dependent orbital-free density functional theory (TD-OFDFT) approach which enables large-scale quantum mechanical simulations of plasmonic responses of metallic nanostructures. Using TD-OFDFT, we have performed quantum mechanical simulations to understand size-dependent plasmonic response of Na nanoparticles and plasmonic responses in Na nanoparticle dimers and trimers. An outlook of future development of the TD-OFDFT method is also presented.

Quantum plasmonics opens the option to integrate complex quantum optical circuitry onto chip scale devices. In the past, often external light sources were used and nonclassical light was coupled in and out of plasmonic structures, such as hole arrays or waveguide structures. Another option to launch single plasmonic excitations is the coupling of single emitters in the direct proximity of, e.g., a silver or gold nanostructure. Here, we present our attempts to integrate the research of single emitters with wet-chemically grown silver nanowires. The emitters of choice are single organic dye molecules under cryogenic conditions, which are known to act as high-brightness and extremely narrow-band single photon sources. Another advantage is their high optical nonlinearity, such that they might mediate photon–photon interactions on the nanoscale. We report on the coupling of a single molecule fluorescence emission through the wire over the length of several wavelengths. The transmission of coherently emitted photons is proven by an extinction type experiment. As for influencing the spectral properties of a single emitter, we are able to show a remote change of the line-width of a single terrylene molecule, which is in close proximity to the nanowire.

Spatial nonlocality in the photonic response of metallic nanoparticles is actually known to produce near-field quenching and significant plasmon frequency shifts relative to local descriptions. As the control over size and morphology of fabricated nanostructures is truly reaching the nanometer scale, understanding and accounting for nonlocal phenomena is becoming increasingly important. Recent advances clearly point out the need to go beyond the local theory. We here present a general formalism for incorporating spatial dispersion effects through the hydrodynamic model and generalizations for arbitrary surface morphologies. Our method relies on the boundary element method, which we supplement with a nonlocal interaction potential. We provide numerical examples in excellent agreement with the literature for individual and paired gold nanospheres, and critically examine the accuracy of our approach. The present method involves marginal extra computational cost relative to local descriptions and facilitates the simulation of spatial dispersion effects in the photonic response of complex nanoplasmonic structures.

The near-field distribution of surface plasmon polariton (SPP) on metallic photonic crystal slabs has been studied. Preliminary numerical simulations indicate that the interference of SPP on the exit side of metallic photonic crystal slabs can redistribute the illumination light into nano-scale spatial distribution, which beats the Rayleigh diffraction limit. The electric field distribution of SPP with a resolution of 50 nm was measured by recording the high intensity range into photoresist with a wavelength of 436 nm. Because of the small wavelength of the plasmon wave, a much higher spatial resolution can be obtained, which can provide a new nano-fabrication or nano-storage method by using optical light with a long wavelength.

The transmission properties of rectangular one-dimensional unperforated metallic periodic structures for frequencies close to the surface plasmon band are investigated experimentally and theoretically. The results reveal that it is possible to obtain unexpectedly large transmissions through thick unperforated metallic structures. The mechanisms of enhanced transmissions are attributed to resonant excitations of three kinds of plasmon radiations: coupled surface plasmon polaritons, horizontal localized groove plasmon mode, and vertical localized groove plasmons mode. Once the surface plasmon polaritons and the vertical groove plasmon modes are excited simultaneously, the transmission approaches to maximum at the coincident condition.

The spatial distribution of the interference of surface plasmon polariton (SPP) on metallic nanostructures has been studied. The results show that the transmission of electromagnetic radiation is remarkably enhanced for frequencies close to the surface plasmon band and the interference of SPP can redistribute the illumination light into subwavelength-scale spatial distribution with high intensity, which beats the Rayleigh diffraction limit. For an appropriate thickness, the transmission of an unperforated structure can be larger than that of holes or slits systems with the same periodicity and thickness when the coupled surface plasmon wave mode is excited. With the help of the interference of the horizontal plasmon excited by Bragg resonance due to the periodicity in the horizontal direction, the vertical plasmons, excited in z direction via Fabry–Perot cavity resonance in different grooves, are correlated, so the transmission is increased via the tunneling process. The properties of transparency for light but impenetrability for gas and liquid will be of importance for device applications. The information on near-field distribution from perforated metallic structures is important for understanding the underlying physics, as well as for optimizing photonic crystals for possible applications.

A mode separation approach in the nanoring resonator by a cascaded slot cavity is proposed and numerically investigated using the finite-difference time-domain (FDTD) method. With the cascaded slot cavity, the specified modes in the nanoring can be separated to realize a wide free spectral range (FSR) or single channel filtering, which provides a free degree to the plasmonic filters design. Simulation results also demonstrate that the full-width at half-maximum (FWHM) of the single channel filter obtained from the cascaded slot cavity can be effectively reduced to meet various requirements.

In this paper, a wide-angle polarization-sensitive dual-band absorber at infrared wavelengths with a multilayer grating is reported. The simulation results show that the absorber has two absorption peaks at wavelengths λ = 1.365 μm and λ = 3.035 μm with the absorption magnitudes more than 0.97 and 0.99 for TM polarization (electric field perpendicular to the strips), respectively. And this absorber reflects almost all TE polarization (electric field parallel to the strips) light. The dual-band absorption peaks can be tuned by varying the width of the strips, and the absorption magnitudes are more than 0.9 for the dual-band absorption peaks for angles up to 70°.

We report a multiband absorber with dielectric–dielectric–metal structure in the infrared regime. The simulation results show that that near-perfect absorption is originated from the guide mode resonance and surface plasmonic polaritons (SPPs) excitation. Furthermore, the absorption peaks of this multiband absorber can be tuned by changing the incidence angle or scaling the microstructure dimensions. The results of this study have possible future potential applications in thermal emitter and sensor.

In this paper we review a new electro-optic devices design strategy using long range surface plasmon (LRSP) excitation along subwavelength metal grating. It is shown that LRSP can be excited on extremely thin subwavelength metal grating embedded in symmetric dielectric ambient. Due to coupling and propagation of LRSP between the metal grating nanowires, a super-narrow reflection dip can be obtained. Compared with conventional LRSP along metal thin film, much narrower resonance is achieved through decreased damping from the existence of large dielectric gaps between the grating nanowires. This interesting phenomenon can be used to design electro-optics devices with improved performance. Examples of electro-optic modulator design with lower insertion loss and low operating voltage and spectral notch filter design with very narrow spectral width will be shown. Its application in refractive index sensing is also discussed.

Modal characteristics of plasmonic nanostrip waveguides (PNWGs) have been analyzed for their use in the design of functional plasmonic devices. Also, the beat lengths of the plasmonic nanostrip directional coupler and the multimode interference (MMI) coupler, have been analyzed. We found a peculiar phenomenon in the direction coupler, which makes the coupling length zero and does not allow the optical coupling between two parallel PNWGs. We also found that there exists a minimal beat length in the gap between the two metal films in the MMI coupler. From these results a nano-ring resonator switch and a MMI wavelength splitter were designed.

Using hydrodynamic theory of electron gas motion in metals, we obtain hyperpolarizability of the metal hemisphere in the framework of the quasistatic approach. For a silver hemisphere placed on a glass substrate and covered with TiO₂ shell, we demonstrate analytically that conduction electrons in the vicinity of the hemisphere sharp edge dominate the nonlinear optical response of the nanoparticle. The developed theory is verified by numerical simulation in COMSOL. Numerical analysis reveals that rounding of the sharp edge affects the linear polarizability and first hyperpolarizability of the hemisphere differently. We also discuss dependence of the hyperpolarizability on the dielectric shell thickness and show that both lacking of the inversion symmetry and presence of the glass–air-TiO₂ interface essentially contribute to the polarizability of the hemisphere at the frequency of the second harmonic.

Here, we propose a novel plasmonic structure, called asymmetric plasmonic nanocavity grating (APNCG), which is shown to dramatically enhance nonlinear optical process of second harmonic generation (SHG). The proposed structure consists of two different metals on both sides of lithium niobate and a thin layer of graphene. By using two different metals the nonlinear susceptibility of the waveguide would be increased noticeably causing to increase SHG. On the other hand, it consists of two identical gratings on one side. By two identical gratings, the pump beam is coupled to two opposing SPP waves, which interfere with each other and result in SPP standing wave in the region between the two gratings. The distance between two gratings will be optimized to reach the highest SHG. It will be shown that by optimizing the geometry of proposed structure and using different metals, field enhancement in APNCG waveguides can result in large enhancement of SHG.

Nonlinear plasmonic metasurfaces have recently attracted considerable interest, due to their potential for enabling nanoscale nonlinear optics. Here, we review the current progress in this topic while paying special attention to existing challenges. In order to limit our scope, we concentrate on nonlinear metasurfaces utilizing inter-particle and lattice effects and focus on metasurfaces operating close to visible and near-infrared frequencies. We will also critically discuss the short and longer term prospects of nonlinear metasurfaces to start rivaling traditional nonlinear materials in applications.

We propose a scheme of terahertz (THz) indirect detection via plasmonic-antenna enhanced sum frequency generation process, where the THz wave is converted to optical wave that is detected by photodetector. The gold antenna built in the structure can improve the conversion efficiency by enhancing both the optical wave and THz wave. The numerical simulations show that the field enhancement is influenced by the geometry of the antenna, so the conversion efficiency can be improved highly by optimizing the antenna. Compared with commercial detectors, our detection system has a much lower noise equivalent power (NEP) of 15.4pW/$\sqrt{\mathrm{\text{Hz}}}$ at 5THz.

We report on the plasmonic properties of silver-coated dielectric nanocylinders arranged according to an unconventional geometrical representation called Pascal's triangle. We performed numerical simulations to calculate the extinction spectrum and identify the collective optical modes in the geometry. For resonant excitation at 410 nm, we found pronounced field localization (50 nm) at the center of the Pascal triangle. Further, we studied the near-field intensity as a function of experimentally-relevant variables such as excitation wavelength, angle of incidence and dielectric constant of the core material. Our analysis revealed pronounced difference between near-field intensities for resonant and non-resonant excitation wavelength at various angle of incident radiation; and an increment in near-field intensity at excitation wavelengths greater than 600 nm, with increase in dielectric constant of core material. Our study has relevance in development of substrates with tunable electromagnetic hot-spots for on-chip plasmonics.

In the last few years, plasmonics has attracted much attention and has been included in the principal domains of nanophotonics that can manage optical fields at the nanodimension level. Its exquisite characteristic is to increase the electromagnetic fields at the nanometer scale particularly in the solar cell. In the plasmonic discipline, noble metals used as nanoparticles in which the density of the electron gas which oscillates at surface plasmon frequency at that time also enhances absorption via scattering. So the usage of plasmonics in solar cells offers better possibility of improving the performance through absorption, because the optical spectrum loss is principal as a part of the overall loss for the solar photovoltaic cell. So we investigated the impact of the nanoparticle size for the enhancement of extinction in terms of absorption and scattering by using surface plasmon resonance, and additionally studied the finite-difference time domain (FDTD)-based proposed model and found various plasmonic fields components and characterized optical enhancement in the plasmonic thin film solar cell.