Xiaojun Xue

Self-Assembly of Large-Scale and Ultrathin Silver Nanoplate Films with Tunable Plasmon Resonance Properties

We describe a rapid, simple, room-temperature technique for the production of large-scale metallic thin films with tunable plasmonic properties assembled from size-selected silver nanoplates (SNPs). We outline the properties of a series of ultrathin monolayer metallic films (8-20 nm) self-assembled on glass substrates in which the localized surface plasmon resonance can be tuned over a range from 500 to 800 nm. It is found that the resonance peaks of the films are strongly dependent on the size of the nanoplates and the refractive index of the surrounding dielectric. It is also shown that the bandwidth and the resonance peak of the plasmon resonance spectrum of the metallic films can be engineered by simply controlling aggregation of the SNP. A three-dimensional finite element method was used to investigate the plasmon resonance properties for individual SNPs in different dielectrics and plasmon coupling in SNP aggregates. A 5-17 times enhancement of scattering from these SNP films has been observed experimentally. Our experimental results, together with numerical simulations, indicate that this self-assembly method shows great promise in the production of nanoscale metallic films with enormous electric-field enhancements at visible and near-infrared wavelengths. These may be utilized in biochemical sensing, solar photovoltaic, and optical processing applications.

Numerical analysis of deep sub-wavelength integrated plasmonic devices based on Semiconductor-Insulator-Metal strip waveguides

We report the first study of nanoscale integrated photonic devices constructed with semiconductor-insulator-metal strip (SIMS) waveguides for use at telecom wavelengths. These waveguides support hybrid plasmonic modes transmitting through a 5-nm thick insulating region with a normalized intensity of 200-300 μm(-2). Their fundamental mode, unique transmission and dispersion properties are consistent with photonic devices for guiding and routing of signals in communication applications. It has been demonstrated using Finite Element Methods (FEM) that the high performance SIMS waveguide can be used to fabricate deep sub-wavelength integrated plasmonic devices such as directional couplers with the ultra short coupling lengths, sharply bent waveguides, and ring resonators having a functional size of ≈1 µm and with low insertion losses and nearly zero radiation losses.

Subwavelength plasmonic waveguides based on ZnO nanowires and nanotubes: A theoretical study of thermo-optical properties

We show theoretically that plasmonic waveguide structures in ZnO nanowires and nanotubes working at optical frequencies can achieve photonic waveguiding in a subdiffraction limit. The output intensity distribution, propagation length, and thermo-optical properties with different waveguide configurations are investigated. Our results show that these waveguides have the potential to develop either high performance thermally controlled nanoscale plasmonic devices or thermally insensitive waveguides by optimizing waveguide configurations.

Integrated optical gyroscope using active Long-range surface plasmon-polariton waveguide resonator

Optical gyroscopes with high sensitivity are important rotation sensors for inertial navigation systems. Here, we present the concept of integrated resonant optical gyroscope constructed by active long-range surface plasmon-polariton (LRSPP) waveguide resonator. In this gyroscope, LRSPP waveguide doped gain medium is pumped to compensate the propagation loss, which has lower pump noise than that of conventional optical waveguide. Peculiar properties of single-polarization of LRSPP waveguide have been found to significantly reduce the polarization error. The metal layer of LRSPP waveguide is electro-optical multiplexed for suppression of reciprocal noises. It shows a limited sensitivity of ~10−4 deg/h, and a maximum zero drift which is 4 orders of magnitude lower than that constructed by conventional single-mode waveguide.

Tunable Optical Ring Resonator Integrated With Asymmetric Mach–Zehnder Interferometer

We demonstrate theoretically a tunable optical ring resonator incorporating an asymmetric Mach-Zehnder interferometer (MZI) and two phase shifters. The optimal resonance state of the ring resonator with different geometries can be achieved by tuning the two embedded phase shifters. Distinct intensity and phase responses and transmission spectra characteristics are newly observed by setting different structural parameters such as the asymmetrical path lengths of the waveguides and the coupling ratio of the directional couplers in the MZI. The performance characteristics related to the radius of the ring cavity and the propagation losses in the waveguides are also discussed. At optimal resonance, it is shown that sharp intensity response and tunable narrow-bandwidth spectra can be achieved especially for resonators with a highly asymmetrical configuration. Such device has a potential in sensing, switching and filtering applications.

Plasmonic Properties of Welded Metal Nanoparticles

Metal nanostructures show great applications in chemical sensing, biomedical detection, optical-thermal therapy, and optical communications because of their electromagnetic field enhancement properties at the visible and the near-field infrared wavelengths. Such strong optical field enhancement induced by the localized surface plasmon resonance is dependent on the configurations and the sizes of the metal nanoparticles. We presented a numerical investigation of the plasmonic properties of the individually welded silver nanoparticles fabricated by nanojoining technique. It shows that the field enhancement factor in welded silver nanostructures is much larger than in separated silver nanoparticles. The size dependent localized surface plasmon resonance spectra and the polarization sensitivity property of such configurations are also discussed.

Resonant frequency shift characteristic of integrated optical ring resonators with tunable couplers

Ring resonators integrated with tunable couplers are useful devices in integrated optics systems. The resonant frequency shift characteristic of tunable resonators is theoretically analyzed. It is shown that the resonant frequency shift range is dependent on the configurations and tuning methods of couplers. It provides an analytical explanation of the frequency shift effect by the phase transmission method and the coupled-mode theory (CMT) of asymmetric waveguides. Optimized designs of different kinds of tunable couplers are discussed in order to improve the resonant frequency stability. Moreover, the intensity–phase relationship induced by the resonant frequency shift effect is also discussed, and a more efficient configuration of optical sensors using phase modulation is proposed.

Simulation of an optical accelerometer based on integrated optical ring resonator

Tight, integrated accelerometers are current interests in Micro-Opto-electro-Mechanical-Systems (MOEMS). An optical accelerometer based on a novel integrated optical resonator is proposed. The transmission spectra and the relation between the structure parameters and the device sensitivity are simulated. This ring resonator structure shows great potential to develop high sensitive accelerometers.

Tunable microring resonator based on dielectric-loaded surface plasmon-polariton waveguides

A ultrasmall thermal tunable ring resonator based on plasmon-polariton waveguide is theoretically analyzed. The thermooptic coefficient and the temperature-dependent amplitude attenuation coefficient of the effective mode index of the plasmonic waveguide are calculated by finite element method (FEM), and the transmission characteristics of the ring resonator with different structural parameters are investigated. Such device shows high efficient tunability and may be utilized to develop novel tunable plasmonic devices.

A novel thermal controlled optical attenuator

A novel thermal controlled optical attenuator based on symmetric dielectric-loaded surface plasmon polariton (SDLSPP) waveguide is proposed and theoretically analyzed in this work. The mode effective indices, propagation lengths, the temperature dependent characteristic are analyzed using a fininte-element method (FEM). Such device can be controlled by low driving power and shows excellent tunability. The optical attenuator provides a potential for novel temperature-tunable surface plasmon polariton (SPP) devices.