Hybrid Plasmonic Cavity Research Articles

Giant electric field enhancement for plasmonic imaging via graphene based nanoslit optical superlens

We present theoretical investigations on designing a simple double nano-slit superlens for dramatically improving imaging quality for advanced plasmonic photolithography through introducing graphene as a plasmonic integrator. It is proposed that more than 235 times enhancement of localized electric field can be assured as the graphene layer is embedded in the designed superlens. It is observed that by introducing graphene for superlensing, dominant enhancement of electric field amplitudes of interference imaging profiles can be observed at a properly designed photoresist with optimal thickness. We further show by systematically examining design parameters for the graphene-based superlens, clarifying the overall geometric and material parameter influences on the plasmonic imaging pattern characteristics. The results are attributed to the unique role of graphene participating in strong hybrid plasmonic cavity coupling modes for supporting localized electric fields of the nanoslit superlensing. This study shows proper designing of graphene-based optical superlens can potentially realize high-quality, low-cost and simple-realized nano-imaging for advanced plasmonic photolithography applications.

Hybrid photonic–plasmonic crystal nanocavity sensors

We have investigated a hybrid photonic–plasmonic crystal nanocavity consisting of a silicon grating nanowire adjacent to a metal surface with a gain gap between them. The hybrid plasmonic cavity modes are highly confined in the gap due to the strong coupling of the photonic crystal cavity modes and the surface plasmonic gap modes. Using finite-element method (FEM), guided modes of the hybrid plasmonic waveguide (WG) were numerically determined at a wavelength of 1550 nm. The modal characteristics such as WG confinement factors and modal losses of the fundamental hybrid plasmonic modes were obtained as a function of groove depth at various gap heights. Furthermore, the band structure of the hybrid crystal modes corresponding to a wide band gap of 17.8 THz is revealed. To enclose the optical energy effectively, a single defect was introduced into the hybrid crystal. At a deep subwavelength defect length as small as 270 nm, the resonant mode exhibits a high quality factor of 567 and an ultrasmall mode volume of 1.9 × 10− 3 (λ/neff)3 at the resonance wavelength of 1550 nm. Compared to conventional photonic crystal nanowire cavities in the absence of a metal surface, the factor Q/Vm is significantly enhanced by about 15 times. The designed hybrid photonic–plasmonic cavity sensors exhibit distinguished characteristics such as sensitivity of 443 nm/RIU and figure of merit of 129. The proposed nanocavities open new possibilities for various applications with strong light–matter interaction, such as biosensors and nanolasers.

Plasmonic Resonators: Hybrid Plasmonic Cavity Modes in Arrays of Gold Nanotubes (Advanced Optical Materials 4/2017)

Plasmonic Resonators: Hybrid Plasmonic Cavity Modes in Arrays of Gold Nanotubes (Advanced Optical Materials 4/2017)

Hybrid Plasmonic Cavity Modes in Arrays of Gold Nanotubes

Plasmonic structures are known to confine light at the nanometer scale, and they exhibit enhanced electromagnetic fields localized in small mode volumes. Here, plasmonic resonators based on a metamaterial consisting of periodic arrays of gold nanotubes embedded into anodic aluminum oxide are studied and strong confinement of local fields with low losses is demonstrated. Higher‐order resonance modes of surface plasmons localized in gold nanotubes when the nanotube length exceeds some critical values are observed. The numerical simulations suggest that, the electric fields associated with some higher‐order longitudinal modes for the long nanotubes and some lower‐order longitudinal modes for the short nanotubes or the nanotubes with thin walls, are mainly localized at the interfaces between aluminum oxide and gold in the form of the standing‐wave longitudinal plasmonic modes, partially localized in the pores and at two ends of the nanotubes owing to the strong coupling of the Fabry–Pérot resonances with extraordinary optical transmission effect in the periodical structures through the inner nanochannels of the nanotubes, so that the nanotubes play a role of efficient cavity resonators. The existence of hybrid plasmonic resonant cavity modes with asymmetrical distributions of the electric field resulting from the near‐field coupling of both transversal and longitudinal modes in the gold nanotube metamaterials is revealed.

Ultrahigh Purcell factor in low-threshold nanolaser based on asymmetric hybrid plasmonic cavity.

A low-threshold nanolaser with all three dimensions at the subwavelength scale is proposed and investigated. The nanolaser is constructed based on an asymmetric hybrid plasmonic F-P cavity with Ag-coated end facets. Lasing characteristics are calculated using finite element method at the wavelength of 1550 nm. The results show that owing to the low modal loss, large modal confinement factor of the asymmetric plasmonic cavity structure, in conjunction with the high reflectivity of the Ag reflectors, a minimum threshold gain of 240 cm−1 is predicted. Furthermore, the Purcell factor as large as 2518 is obtained with optimized structure parameters to enhance rates of spontaneous and stimulated emission.

Hybrid plasmonic biosensor for simultaneous measurement of both thickness and refractive index

A novel hybrid plasmonic biosensor using a sub-wavelength reflection metal grating is proposed and analyzed. The simulation results show that the hybrid plasmonic-cavity (HPCM) are wavelength dependent on both the refractive index (RI) and thickness of the surrounding analyte layer, with a sensitivity of 448nm/RIU (refractive index unit) and 75nm/μm, respectively. However wavelength related to the cavity resonant mode (CRM) is only sensitive to the environmental refractive index changes. In principle it is possible to determine both RI and thickness of the coating layer simultaneously.

Optical design of organic solar cell with hybrid plasmonic system

We propose a novel optical design of organic solar cell with a hybrid plasmonic system, which comprises a plasmonic cavity coupled with a dielectric core-metal shell nanosphere. From a rigorous solution of Maxwell's equations, called volume integral equation method, optical absorption of the active polymer material has a four-fold increase. The significant enhancement mainly attributes to the coupling of symmetric surface wave modes supported by the cavity resonator. The dispersion relation of the plasmonic cavity is characterized by solving an 1D eigenvalue problem of the air/metal/polymer/metal/air structure with finite thicknesses of metal layers. We demonstrate that the optical enhancement strongly depends on the decay length of surface plasmon waves penetrated into the active material. Furthermore, the coherent interplay between the cavity and the dielectric core-metal shell nanosphere is undoubtedly confirmed by our theoretical model. The work offers detailed physical explanations to the hybrid plasmonic cavity device structure for enhancing the optical absorption of organic photovoltaics.