E. P. Li

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.

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.

A modular implementation of dispersive materials for time-domain simulations with application to gold nanospheres at optical frequencies

The development of photonic nano-structures can strongly benefit from full-field electromagnetic (EM) simulations. To this end, geometrical flexibility and accurate material modelling are crucial requirements set on the simulation method. This paper introduces a modular implementation of dispersive materials for time-domain EM simulations with focus on the Finite-Volume Time-Domain (FVTD) method. The proposed treatment can handle electric and magnetic dispersive materials exhibiting multi-pole Debye, Lorentz and Drude models, which can be mixed and combined without restrictions. The presented technique is verified in several illustrative examples, where the backscattering from dispersive spheres is calculated. The amount of flexibility and freedom gained from the proposed implementation will be demonstrated in the challenging simulation of the plasmonic resonance behavior of two gold nanospheres coupled in close proximity, where the dispersive characteristic of gold is approximated by realistic values in the optical frequency range.

Accurate high-speed eye diagram simulation of silicon-based modulators

Optical modulation is one of the key determinants to the operating speed of a network. In this work, we report an accurate methodology to study high-speed eye diagram from electrical and optical simulation data of individual modulators. The methodology constitutes electrical parameters such as capacitance, conductance and transitioning times to model time response and effective complex refractive index from optical simulations of phase shifter arms and in turn model the phase change and resultant loss induced by each arm. This methodology is suitable for interferometer-based optical devices and has been applied to silicon-based depletion mode modulators at 10-, 40-Gbps.

Enhancing the light transmission of plasmonic metamaterials through polygonal aperture arrays

While plasmonic metamaterials find numerous applications in the field of nanophotonic devices, a device may work as a normal or plasmonic device, depending on whether it operates at the resonance mode. In this paper, the extraordinary light transmission through coaxial polygonal aperture arrays, including circle, hexagon, square, and triangle geometries, is studied using FDTD simulation. Circular, hexagonal and squared aperture arrays have similar high transmission rate, while triangular aperture array has considerably lower transmission rate. It is found that the transmission peaks reflect the resonance modes propagating along the direction of neighboring apertures. We hence rearrange the apertures from square lattice to triangle lattice to obtain a uniform resonance mode along the neighboring apertures. This leads to enhanced light transmission. The study gains understanding of new properties of the metamaterials based on plasmonic resonance.

Enhancement of light energy extraction from elliptical microcavity using external magnetic field for switching applications

In this letter, the extraction efficiency of light energy from an elliptically shaped microcavity laser is enhanced with external magnetic field. The magnetic field causes electrons to accumulate on the minor arc edge of the elliptical microcavity due to Lorentz force. As a result, the field amplitude at the minor arc edge is higher, and this improves light energy tunneling mechanism from the edge. The extraction efficiency from the microcavity increases by more than 30% after the application of magnetic field. Alternating the direction of the magnetic field allows the elliptical microcavity to function as a switching device.

Electrically controlled silicon-based photonic crystal chromatic dispersion compensator with ultralow power consumption

We show full 3-Dimensional (3D) electrical and optical simulation of a tunable silicon-based Photonic Crystal (PhC) Chromatic Dispersion Compensator (CDC) with high power efficiency and ultra-low power consumption (114nW), operating at a speed of 40.5MHz. The device exploits a structure where the optical field maximum is not in a PhC waveguide, but rather in a hybrid Si3N4/Si/SiO2 structure that will allow greater ease of fiber coupling due to larger mode size and reduced loss. The CDC is broadband, and produces constant 2 nd order chromatic dispersion over an optical communication band such as C-band.

Focused ion beam assisted interface detection for fabricating functional plasmonic nanostructures

Plasmonic nanoscale devices/structures have gained more attention from researchers due to their promising functions and/or applications. One important technical focus on this rapidly growing optical device technology is how to precisely control and fabricate nanostructures for different functions or applications (i.e., patterning end points should locate at/near the interface while fabricating these plasmonic nanostructures), which needs a systematic methodology for nanoscale machining, patterning, and fabrication when using the versatile nanoprecision tool focused ion beam (FIB), that is, the FIB-assisted interface detection for fabricating functional plasmonic nanostructures. Accordingly, in this work, the FIB-assisted interface detection was proposed and then successfully carried out using the sample-absorbed current as the detection signal, and the real-time patterning depth control for plasmonic structure fabrication was achieved via controlling machining time. Besides, quantitative models for the sample-absorbed currents and the ion beam current were also established. In addition, some nanostructures for localized surface plasmon resonance biosensing applications were developed based on the proposed interface detection methodology for FIB nanofabrication of functional plasmonic nanostructures. It was shown that the achieved methodology can be conveniently used for real-time control and precise fabrication of different functional plasmonic nanostructures with different geometries and dimensions.

Focused Ion Beam Nano-Precision Machining for Analyzing Photonic Structures in Butterfly

Nano-precision machining using focused ion beam (FIB) is widely applied in many fields. So far, FIB-based nanofabrication for specific nanoscale applications has become an interesting topic to realize more diversities for nano-construction. Through FIB machining, we can easily achieve the required nano- and micro-scale patterning, device fabrication, and preparation of experimental samples. Nowadays, there is an increasing trend to learn from nature to design novel multi-functional materials and devices. Thus, more interestingly, another advantage of FIB is that it can be conveniently used to analyze the natural photonic structures, e.g., those in the butterfly which exhibits amazing optical phenomena due to sub-wavelength structural color. Accordingly, in the present study, structural analyses for butterfly wings were carried out using FIB. It is found that the photonic structures for the backside and frontside of the butterfly wing studied differ considerably. The difference accounts for the different colors on the dorsal and ventral sides of butterfly wings.

Two- and three-dimensional studies of a silicon-based chromatic dispersion compensator

In this work, we demonstrate two- and three-dimensional (3D) simulations of an active silicon-based photonic crystal chromatic dispersion compensator utilizing the free carrier dispersion effect. The device has a low power consumption of 114nW and its intrinsic device modulation speed is predicted to function at 40.5MHz. Due to the device architecture, simulation must be carried out in 3D so as to fully encapsulate the effects of the photonic crystal contributions in the active silicon. The novel device allows waveguiding and electrical transport to be individually tailored to a large extent.