Fano Structures Research Articles

Integration of Fano resonances with inverse-designed power splitter

Computer-aided intelligent algorithms are beneficial to realize miniaturized devices with ultra-low energy consumption. In this paper, a single-channel Fano structure is designed and the maximum peak-to-valley contrast 0.973 is achieved. A power splitter with the size of 1 μm × 3 μm is proposed by using inverse design method based on topology optimization, whose average transmittance for each port is about 0.489 within the wavelength range of 1450–1650 nm. Finally, the double-channel outputs with the same and different Fano resonances are achieved by integrating with the optimized Fano structures. Our study is conducive to realize efficient and multi-functional photonic integrated circuits.

Some examples of log Fano structures on blow-ups along subvarieties in products of two projective spaces

We give a series of examples of log Fano manifolds in any dimension greater than or equal to three by using successive blow-ups along subvarieties in products of two projective spaces. More precisely, we first blow-up a product of two projective spaces along a smooth hypersurface contained in a fiber of one of the two projections and then along the strict transform of a fiber (intersecting the center of the first blow-up) of the other projection. By computing the nef cone and giving an explicit boundary divisor, we show that the resulting variety is always a log Fano manifold. Moreover, the effective cone and the extremal contractions are described. Note that this variety depends on three integral parameters: the dimensions of the two projective spaces and the degree of the hypersurface, which is the center of the first blow-up. Hence, we obtain a series of examples of log Fano manifolds. We also determine which ones are weak Fano.

CROW-based Fano structures for all optical switching devices.

In this paper, an improved optical Fano switch based on coupled resonator optical waveguides (CROWs) is presented. The new topological design is employed to achieve steeper and highly asymmetric Fano resonances (FRs). Physically, in the proposed structures, due to the increase in the effective refractive index at the center of the CROW, a confined mode arises in the continuum background according to the variational theorem and leads to FR. The results show that in CROW-based Fano switches, the Fano spectrum is improved by tuning the number of nanocavities. The ratio between the slope ratio and linewidth shows an improvement of 55.25% from single to CROW5. As an important application of FR, an ultra-compact device with a CROW-based Fano structure is demonstrated. The results of the numerical finite difference time domain simulation agree well with the theoretical coupled mode theory.

Plasmonic Fano Resonance in Homotactic Aluminum Nanorod Trimer: the Key Role of Coupling Gap

Recently, the Fano effect of aluminum nanostructures has attracted a lot of attentions in several detector and sensor applications, but the role of coupling gap in it remains unintuitive. In this paper, a homotactic aluminum rod trimer (HART) is designed to form the plasmonic Fano resonances and visualize the important role of coupling gap size. The plasmon hybridization model and far field images were used to qualitatively describe the formation mechanism of Fano resonance. The simulation results intuitively show that the Fano dip of HART with a smaller coupling gap size has a higher red-shift speed when increasing the refractive index of surrounding environment or the length of HART with a fixed axial ratio (LS/LL = 0.6). Our study provides the insights to the key role of coupling gap in the performance of Fano structures.

Signal reshaping and noise suppression using photonic crystal Fano structures.

We experimentally demonstrate the use of photonic crystal Fano resonances for reshaping optical data signals. We show that the combination of an asymmetric Fano resonance and carrier-induced nonlinear effects in a nanocavity can be used to realize a nonlinear power transfer function, which is a key functionality for optical signal regeneration, particularly for suppression of amplitude fluctuations of data signals. The experimental results are explained using simulations based on coupled-mode theory and also compared to the case of using conventional Lorentzian-shaped resonances. Using indium phosphide photonic crystal membrane structures, we demonstrate reshaping of 2 Gbit/s and 10 Gbit/s return-to-zero on-off keying (RZ-OOK) data signals at telecom wavelengths around 1550 nm. Eye diagrams of the reshaped signals show that amplitude noise fluctuations can be significantly suppressed. The reshaped signals are quantitatively analyzed using bit-error ratio (BER) measurements, which show up to 2 dB receiver sensitivity improvement at a BER of 10-9 compared to a degraded input noisy signal. Due to efficient light-matter interaction in the high-quality factor and small mode-volume photonic crystal nanocavity, low energy consumption, down to 104 fJ/bit and 41 fJ/bit for 2 Gbit/s and 10 Gbit/s, respectively, has been achieved. Device perspectives and limitations are discussed.

Pulse carving using nanocavity-enhanced nonlinear effects in photonic crystal Fano structures.

We experimentally demonstrate the use of a photonic crystal Fano resonance for carving-out short pulses from long-duration input pulses. This is achieved by exploiting an asymmetric Fano resonance combined with carrier-induced nonlinear effects in a photonic crystal membrane structure. The use of a nanocavity concentrates the input field to a very small volume leading to an efficient nonlinear resonance shift that carves a short pulse out of the input pulse. Here, we demonstrate shortening of ∼500 ps and ∼100 ps long pulses to ∼30 ps and ∼20 ps pulses, respectively. Furthermore, we demonstrate error-free low duty cycle return-to-zero signal generation at 2Gbit/s with energy consumption down to ∼1 pJ/bit and power penalty of ∼2 dB. The device physics and limitations are analyzed using nonlinear coupled-mode theory.

Log Fano structures and Cox rings of blow-ups of products of projective spaces

The aim of this paper is twofold. First, we determine which blow-ups of products of projective spaces at general points are varieties of Fano type, and give boundary divisors making these spaces log Fano pairs. Second, we describe generators of the Cox rings of some cases.

Plasmonic split ring resonator with energy enhancement for the application of bio-sensing and energy harvesting based on the second harmonic generation and multi Fano resonance

Abstract Plasmonic characteristic has been implemented for optical enhancement and the Fano resonance is noticed based on the interaction of the dark and bright mode at nano particle and for more enhancement, the second harmonic generation and multi Fano have been suggested. In this paper, we have designed a nano-antenna based on plasmonic, Fano, multi Fano and SHG modes and for this aim we have developed a single ring nano-particle with one and two split ring resonator elements for arousing multi Fano (SHG mode). Exactly, by arousing the Fano and multi Fano modes, the Extinction Cross Section is reduced in comparison with Plasmonic mode based on concentrating energy in the near field. We have shown that the angles of polarization have no effect on the extinction cross-section in multi Fano structure and it is independent of the polarization angle. We have revealed that how the multi Fano would be useful for light trapping and energy harvesting. We have obtained the wider bandwidth for the electric field in comparison with plasmonic and Fano structures which makes our proposed structure useful in energy harvesting applications such as solar cell at higher frequency ranges and an active area for wider bandwidth is achievable. For spectroscopy and optimal imaging, the figure of merit (FOM) is considered as a quality meter for the optical particles. The (FOM) of the external biological materials are compared for all three prototyped plasmonic, Fano and multi Fano structures.

Explicit log Fano structures on blow-ups of projective spaces

In this paper, we determine which blow-ups X of P n at general points are log Fano, that is, when there exists an effective Q-divisor Δ such that − ( K X + Δ ) is ample and the pair ( X , Δ ) is klt. For these blow-ups, we produce explicit boundary divisors Δ making X log Fano.

Ultrafast Nonlinear Plasmonic Spectroscopy: From Dipole Nanoantennas to Complex Hybrid Plasmonic Structures

The key property of metal nanostructures is their unique ability to channel far-field radiation to subwavelength dimensions. The resulting strongly confined and enhanced electromagnetic fields boost nonlinear optical effects at the nanoscale. In this Review article we highlight and summarize the recent most important investigations and advances in the field of “nonlinear plasmonic spectroscopy”, and we present results of second- and third-harmonic spectroscopy experiments of plasmonic nanoantenna arrays that consist of different unit cell elements, ranging from dipole nanoantennas to complex hybrid plasmonic structures. The experiments on dipole nanoantennas show that nonlinear optical processes can be enhanced by plasmonic resonances either at the fundamental laser wavelength or at the spectral position of the harmonic signal. Furthermore, we investigate the quadrupolar third-harmonic response of dolmen-type plasmonic Fano structures and find that the third-harmonic polarization field of the quadrupolar ...

Fano resonances in THz metamaterials composed of continuous metallic wires and split ring resonators.

We demonstrate theoretically and experimentally that Fano resonances can be obtained in terahertz metamaterials that are composed of periodic continuous metallic wires dressed with periodic split ring resonators. An asymmetric Fano lineshape has been found in a narrow frequency range of the transmission curve. By using a transmission line combined with lumped element model, we are able to not only fit the transmission spectra of Fano resonance which is attributed to the coupling and interference between the transmission continuum of continuous metallic wires and the bright resonant mode of split ring resonators, but also reveal the capacitance change of the split ring resonators induced frequency shift of the Fano resonance. Therefore, the proposed theoretical model shows more capabilities than conventional coupled oscillator model in the design of Fano structures. The effective parameters of group refractive index of the Fano structure are retrieved, and a large group index more than 800 is obtained at the Fano resonance, which could be used for slow light devices.

Third Harmonic Mechanism in Complex Plasmonic Fano Structures.

We perform third harmonic spectroscopy of dolmen-type nanostructures, which exhibit plasmonic Fano resonances in the near-infrared. Strong third harmonic emission is predominantly radiated close to the low energy peak of the Fano resonance. Furthermore, we find that the third harmonic polarization of the subradiant mode interferes destructively and diminishes the nonlinear signal in the far-field. By comparing the experimental third harmonic spectra with finite element simulations and an anharmonic oscillator model, we find strong indications that the source of the third harmonic is the optical nonlinearity of the bare gold enhanced by the resonant plasmonic polarization.

Coupled Fano resonators

We theoretically investigate coupled Fano structures which combine the characteristics of both directly coupled Fabry-Perot cavities (DCFPC) and a side-coupled integrated spaced sequence of resonators (SCISSOR). Asymmetric and symmetric Fano resonances in a single and doubly-coupled Fano unit are analytically derived based on Fabry-Perot approach. It is found that doubly-coupled Fano units show a special asymmetric EIT-like lineshape. This structure shows an index changing sensitivity of 10(-6), about two orders higher than that of the single Fano resonator, which is promising for index sensor application. A unique frequency detuning method of EIT like lineshape is also found in the doubly-coupled Fano units. The multiple coupled Fano unit structure demonstrates potentials for applications of tunable optical filter and slow light, whereas for the latter it shows much higher group delay than that of SCISSORS and DCFPC with the same parameters.

Andreev reflection and the Kondo effect in side-coupled double quantum dots

We study the transport due to the Andreev reflection through side-coupled double quantum dots, using the numerical renormalization group (NRG). We find that superconducting interference via the side dot is suppressed as increasing the Coulomb interaction, and the conductance in the Kondo regime is enhanced. This behavior stands in stark contrast to the normal conductance, in which a wide valley is seen in the Kondo regime. It is further elucidated that two separate Fano structures appear in the gate-voltage dependence of the Andreev transport, where a single plateau appears in the normal transport.

Andreev transport through side-coupled double quantum dots

We study the transport through side-coupled double quantum dots, connected to normal and superconducting (SC) leads with a $T$-shape configuration. We find, using the numerical renormalization group, that the Coulomb interaction suppresses SC interference in the side dot, and enhances the conductance substantially in the Kondo regime. This behavior stands in total contrast to a wide Kondo valley seen in the normal transport. The SC proximity penetrating into the interfacial dot pushes the Kondo clouds, which screens the local moment in the side dot, toward the normal lead to make the singlet bond long. The conductance shows a peak of unitary limit as the cloud expands. Furthermore, two separate Fano structures appear in the gate-voltage dependence of the Andreev transport, where a single reduced plateau appears in the normal transport.

Transport spectroscopy in a time-modulated open quantum dot

We have investigated the time-modulated coherent quantum transport phenomena in a ballistic open quantum dot. The conductance $G$ and the electron dwell time in the dots are calculated by a time-dependent mode-matching method. Under high-frequency modulation, the traversing electrons are found to exhibit three types of resonant scatterings. They are intersideband scatterings: into quasibound states in the dots, into true bound states in the dots, and into quasibound states just beneath the subband threshold in the leads. Dip structures or fano structures in $G$ are their signatures. Our results show structures due to 2$\hbar\omega$ intersideband processes. At the above scattering resonances, we have estimated, according to our dwell time calculation, the number of round-trip scatterings that the traversing electrons undertake between the two dot openings.

Discrete 4d photoabsorption spectrum of Ba^2+

The role of true collective effects in the 4d photoabsorption spectrum of Ba2+ is shown to be minor. The most significant departures from independent particle behavior are in fact due to correlations involving the 5p, not the 4d, shell; their importance is magnified by the delicate balance of opposing single-particle forces. Reevaluation of the ionization limit reveals the presence of Beutler–Fano structures in the experimental data, the first that have been observed for excitations underneath closed shells.