Search

The non-linear responses of optical materials offer useful mechanisms for optical switching, novel optical sources, and harmonic frequency conversion. However, the non-linear response of traditional materials is usually extremely weak and requires high input power for excitation. In this study, we theoretically propose a scheme for enhancing the third harmonic generation (THG) efficiency and output power of layered graphene disks array by introducing a plasmonic antibonding state with enhanced oscillation strength due to plasmonic coupling. We verify that, the THG efficiency of a double-layer stacked graphene/SiO2 disk structure under relatively low input intensity can be significantly enhanced more than one order of magnitude with appropriate design, as compared with monolayer patterned graphene nanostructure. We also demonstrate that the THG efficiency can be further improved by optimizing the geometry parameters such as spacer distance and Fermi energy. Our results offer an effective mechanism for significantly improving THG efficiency in the mid-infrared and terahertz ranges, thereby paving the way for new frequency converters and modulators in optical communication and signal processing. [ABSTRACT FROM AUTHOR]

The coupling between the high order localized resonant mode and diffraction mode in meta-molecule arrays consisting of three identical split ring resonators (SRRs) in each cell was demonstrated numerically with finite difference time domain method. By introducing both the near-field interaction and diffraction coupling mechanism, two types of interesting resonant modes are observed. One is the excitation of the second and the third-order plasmon resonance simultaneously with linear polarized light at normal incidence. The other one is a dark plasmonic state with sharper line shape produced by the third-order plasmon resonance and diffraction coupling. These resonant modes based on the ‘designed’ coupling scheme present higher quality factors than those in hybridized plasmonic state due to the electric dipole interaction, which is of great interest for application in the field of nanophotonic devices such as sensing, detector and spaser. [ABSTRACT FROM AUTHOR]

We present a computational study of the transmission resonances in a symmetry-broken square coaxial aperture with an inserted particle offset (δ) from the centre. According to the distribution characteristics of oscillating charges on the exit surface, the TE11- and TE21-like mode resonances in the hole may be regarded as dipole and quadrupole plasmon resonances, respectively. It is found that symmetry breaking, due to the particle offset, makes the quadrupole plasmon resonance, which is dark in symmetric geometry, visible. Based on the charge oscillation induced light emission mechanism, we qualitatively explain the variation of the transmission peaks of dipole and quadrupole plasmon resonances with the geometrical parameter δ, and the refractive index of the dielectric filled in the hole. Using polarization-dependent surface charge plots, we illustrate two distinct mode configurations of quadrupole plasmon resonance. Our findings will be of value in tuning the electromagnetic wave in subwavelength optics and designing chemical and biomedical sensors. [ABSTRACT FROM AUTHOR]

We propose a scheme of a sensitive biosensor based on optical bistability (OB) in a biological semiconductor quantum dot (SQD)-DNA coupled nanohybrid. By plotting bistability phase diagrams within the system’s parameter space, we show that the bistable effect can be switched on or off by only tuning the pumping intensity or the detuning of the pump field from the exciton resonance. Simultaneously, we reveal that the bistability only exists in the strong SQD-DNA coupling regime. Specifically, we derive the matching relation between the excitation conditions and the coupling strength when the bistability just appears. Moreover, we demonstrate that the OB is highly sensitive to the SQD-DNA coupling strength which is strongly correlated to the length of DNA molecules and DNA concentration. This investigation may be useful for opening a new way to build optical switches and providing a novel and convenient platform to detect DNA molecules. [ABSTRACT FROM AUTHOR]