Hong-Son Chu

Highly sensitive graphene biosensors based on surface plasmon resonance

A surface plasmon resonance (SPR) based graphene biosensor is presented. It consists of a graphene sheet coated above a gold thin film, which has been proposed and experimentally fabricated recently [ChemPhysChem 11, 585 (2010)]. The biosensor uses attenuated total reflection (ATR) method to detect the refractive index change near the sensor surface, which is due to the adsorption of biomolecules. Our calculations show that the proposed graphene-on-gold SPR biosensor (with L graphene layers) is (1 + 0.025 L) x gamma (where gamma > 1) times more sensitive than the conventional gold thin film SPR biosensor. The improved sensitivity is due to increased adsorption of biomolecules on graphene (represented by the factor gamma) and the optical property of graphene.

Optical performance of single-mode hybrid dielectric-loaded plasmonic waveguide-based components

The single mode hybrid dielectric-loaded plasmonic waveguide is presented at the wavelength of 1.55 μm. We show that this waveguiding structure, consisting of a low-index SiO2-stripe sandwiched between a high-index Si-nanowire and a silver film, achieves both long propagation length and strong field confinement with high power intensity. Components such as 90°-circular and S-shaped bends, based on the proposed waveguide with an intensity confinement area of 50×200 nm2, can obtain a total transmission efficiency exceeding 85% for various bend radii. Finally, we demonstrate that the efficient directional couplers can be developed using two coupled waveguides. In particular, we determine the typical coupling lengths and maximum transfer power for different structural parameters of the coupler. These investigations provide the foundations for the design of chip-scale integrated plasmonic circuitry.

Active plasmonic switching at mid-infrared wavelengths with graphene ribbon arrays

An active plasmonic switch based on single- and few-layer doped graphene ribbon array operating in the mid-infrared spectrum is investigated with theoretical and numerical calculations. It is shown that significant resonance wavelength shifts and modulation depths can be achieved with a slight variation of the doping concentration of the graphene ribbon. The few-layer graphene ribbon array device outperforms the single-layer one in terms of the achievable modulation depth. Our simulations reveal that, by modulating the Fermi-energy level between 0.2 eV and 0.25 eV, a four-layer graphene ribbon array device can achieve a modulation depth and resonance wavelength shift of ∼13 dB and 0.94 μm, respectively, compared to ∼2.8 dB and 1.85 μm for a single-layer device. Additionally, simple fitting models to predict the modulation depth and the resonance wavelength shift are proposed. These prospects pave the way towards ultrafast active graphene-based plasmonic devices for infrared and THz applications.

Hybrid dielectric-loaded plasmonic waveguide and wavelength selective components for efficiently controlling light at subwavelength scale

We analyze and design a hybrid dielectric-loaded plasmonic waveguide (HDLW) featuring a long propagation length and strong field confinement, for efficient control and confinement of light in the subwavelength area of λ2/160. The HDLW is then used to build compact wavelength selective components of high optical performance, including ring resonators (RR) and add-drop filters (ADF). In particular, we demonstrate RRs having a small ring radius of 2 μm, a low transmission loss of 0.8 dB, a high extinction ratio of 21 dB, and a free spectral range of 66 nm. Moreover, an ADF with a ring radius of 2 μm features a 12 dB extinction ratio, a transmission loss of 0.9 dB, and a channel isolation level of 10 dB at the resonant wavelength. The compact footprint and superior performance of these plasmonic components make them promising building blocks for future nanoscale electronic-photonic integrated circuits for data communication and sensing applications.

Remarkable influence of the number of nanowires on plasmonic behaviors of the coupled metallic nanowire chain

We investigate the plasmonic properties in terms of plasmonic resonances, near field intensity, and charge distribution of interacting nanowires chain which consists of small and large numbers of coupled silver nanowires. We show that the dominant resonance wavelength increases monotonically as the number of nanowires increases. On the other hand, the near field intensity is not only dependent on the chain length but also on the plasmonic resonances in the same chain length. The charge distribution is also demonstrated to fully understand the dependence of plasmonic properties on the chain length.

Submicrometer radius and highly confined plasmonic ring resonator filters based on hybrid metal-oxide-semiconductor waveguide

We numerically report the submicrometer radius (0.5 μm) and high confinement (mode area ~λ(2)/1200) plasmonic ring resonators for both all-pass and add-drop filters based on the hybrid metal-oxide-semiconductor (Ag-SiO(2)-Si) waveguide platform. The best tradeoff between the propagation length and the confinement of this hybrid plasmonic waveguide platform is also discussed and compared to the dielectric-loaded plasmonic waveguide counterpart. We show that the ring resonator all-pass filter features an extinction ratio as high as 23 dB with a transmission loss of 1.5 dB, and a wide free spectral range of 168 nm with a bandwidth of 14 nm. Moreover, the demonstrated add-drop filter achieves an extinction ratio larger than 12 dB with a channel isolation between the through and drop channels of 13.5 dB at the resonant wavelength. These demonstrated plasmonic devices reveal as potential building blocks for future nanoscale electronic-photonic integrated circuits.

AIM Analysis of Electromagnetic Scattering by Arbitrarily Shaped Magnetodielectric Object

A fast solution to the electromagnetic scattering by large-scale three-dimensional magnetodielectric objects with arbitrary permittivity and permeability is presented. The scattering problem is characterized by using coupled field volume integral equation (CF-VIE). By considering the total electric and magnetic fields, i.e., the sum of incident fields and the radiated fields by equivalent electric and magnetic volume currents, the CF-VIE can be established in the volume of the scatterers. The resultant CF-VIE is discretized and solved by using the method of moments (MoM). For large-scale scattering problems, the adaptive integral method (AIM) is then applied in the MoM in order to reduce the memory requirement and accelerate the matrix-vector multiplication in the iterative solver. The conventional AIM has been modified to cope with the two sets of equivalent volume currents.

Tunable propagation of light through a coupled-bent dielectric-loaded plasmonic waveguides

We numerically show that it is easy to tune, both passively and actively, the transmission power delivered at different output ports of two coupled-bent dielectric-loaded plasmonic waveguides by varying the gap distance and refractive index of driven material between two dielectric stripes. We also investigate the near-field intensity to demonstrate that the power transmitted at different output ports can be varied to realize either equal or unequal levels, depending on the design specifications. A simple expression is proposed to predict the power transmitted to different output ports for a set of given dimensions and refractive index of the driven material.

Highly efficient on-chip direct electronic–plasmonic transducers

Photonic elements can carry information with a capacity exceeding 1,000 times that of electronic components, but, due to the optical diffraction limit, these elements are large and difficult to integrate with modern-day nanoelectronics or upcoming packages, such as three-dimensional integrated circuits or stacked high-bandwidth memories1–3. Surface plasmon polaritons can be confined to subwavelength dimensions and can carry information at high speeds (>100 THz)4–6. To combine the small dimensions of nanoelectronics with the fast operating speed of optics via plasmonics, on-chip electronic–plasmonic transducers that directly convert electrical signals into plasmonic signals (and vice versa) are required. Here, we report electronic–plasmonic transducers based on metal–insulator–metal tunnel junctions coupled to plasmonic waveguides with high-efficiency on-chip generation, manipulation and readout of plasmons. These junctions can be readily integrated into existing technologies, and we thus believe that they are promising for applications in on-chip integrated plasmonic circuits.Electronic–plasmonic transducers made from metal–insulator–metal junctions are demonstrated. The plasmon sources are coupled efficiently to plasmonic waveguides and could be used in integrated nanophotonic applications.

Integrated System-Level Electronic Design Automation (EDA) for Designing Plasmonic Nanocircuits

This paper proposes a system-level circuit simulation framework for nanoplasmonic devices, and presents an example of the simulation of a plasmonic nanocircuit. The electronic design automation environment provides an equivalent circuit model library for several plasmonic metal-insulator-metal-based devices. The accuracy of the equivalent models for the plasmonic nanocircuit library is verified by using full-wave simulations and analytical equations. These models are then used to design an ultracompact Mach-Zehnder plasmonic modulator. It is shown that the voltage required to achieve a π phase shift Vπ in the modulator can be predicted by the simulator with reasonable accuracy. The optimized design of the modulator is also presented that reduces the value of Vπ according to the required specification.