Yonghua Lu

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmons enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.

Surface plasmon resonance hydrogen sensor based on metallic grating with high sensitivity

High sensitivity is obtained at larger resonant incident angle if negative diffraction order of metallic grating is used to excite the surface plasmon. A highly sensitive grating-based surface plasmon resonance (SPR) sensor is designed for the hydrogen detection. A thin palladium (Pd) film deposited on the grating surface is used as transducer. The influences of grating period and the thickness of Pd on the performance of sensor are investigated using rigorous coupled-wave analysis (RCWA) method. The sensitivity as well as the width of the SPR curves and reflective amplitude is considered simultaneously for designing the grating-based SPR hydrogen sensor, and a set of optimized structural parameters is presented. The performance of grating-based SPR sensor is also compared with that of conventional prism-based SPR sensor.

PLASMONIC EIT-LIKE SWITCHING IN BRIGHT-DARK-BRIGHT PLASMON RESONATORS

In this paper we report the study of the electromagnetically induced transparency (EIT)-like transmission in the bright-dark-bright plasmon resonators. It is demonstrated that the interferences between the dark plasmons excited by two bright plasmon resonators can be controlled by the incident light polarization. The constructive interference strengthens the coupling between the bright and dark resonators, leading to a more prominent EIT-like transparency window of the metamaterial. In contrary, destructive interference suppresses the coupling between the bright and dark resonators, destroying the interference pathway that forms the EIT-like transmission. Based on this observation, the plasmonic EIT switching can be realized by changing the polarization of incident light. This phenomenon may find applications in optical switching and plasmon-based information processing.

Optical bistability enhanced by highly localized bulk plasmon polariton modes in subwavelength metal-nonlinear dielectric multilayer structure

Optical bistability of subwavelength metal-nonlinear dielectric multilayer structure is numerically studied in this letter. It is found that very low intensity thresholds for optical bistability can be achieved due to the excitation of highly localized bulk plasmon polariton modes with TM polarized illumination. A bistability threshold of 6.9 MW/cm2 is obtained for BPP0 mode, which is much lower than the recently reported results based on the large local field enhancement at the band edge of metal-dielectric photonic band gap structure [A. Husakou and J. Herrmann, Phys. Rev. Lett. 99, 127402 (2007)].

Optical bistability effect in plasmonic racetrack resonator with high extinction ratio

In this paper, optical bistability effect in an ultracompact plasmonic racetrack resonator with nonlinear optical Kerr medium is investigated both analytically and numerically. The properties of optical bistability and pump threshold are studied at 1.55 µm with various detuning parameters by an analytical model. The transmission switch from the upper branch to the lower branch with a pulse is also demonstrated by a finite-difference time-domain method. An extinction ratio of 97.8% and a switching time of 0.38 ps can be achieved with proper detuning parameter. Such a plasmonic resonator design provides a promising realization for highly effective optical modulators and switch.

Plasmonic Coupling Effect in Ag Nanocap–Nanohole Pairs for Surface-Enhanced Raman Scattering

A plasmonic coupling structure composed of Ag nanocap–nanohole pairs was fabricated through a novel and facile method. Both surface-enhanced Raman scattering (SERS) measurements and numerical simulations show that the cap-hole system produces much larger electric field enhancement and SERS signal than the isolated structures, which is due to the plasmonic coupling effect between the gap of the cap and the hole. Additionally, the plasmonic enhancement is sensitive to the gap size, which can be controlled by the Ag layer thickness during the evaporation process. A maximum enhancement factor of 1.1×108 can be obtained with optimized gap size.

Multimode interference splitter based on dielectric-loaded surface plasmon polariton waveguides.

We numerically demonstrated 1 x N multimode interference (MMI) splitters based on dielectric-loaded surface plasmon polariton waveguides (DLSPPW). The dependences of real part of effective index, propagation length and lateral mode profiles of the waveguides on the geometrical parameters are analyzed in detail. The transmission efficiency of the MMI splitter is as much as 60%, with their splitting length being in the range of several micrometers. The performance of the device is found in agreement with results predicted by theoretical MMI self-imaging theory. Such MMI splitter is important for implementation of high density photonic integration and lab-on-a-chip applications.

Plasmonic lasing of nanocavity embedding in metallic nanoantenna array.

Plasmonic nanolasers have ultrahigh lasing thresholds, especially those devices for which all three dimensions are truly subwavelength. Because of a momentum mismatch between the propagating light and localized optical field of the subwavelength nanocavity, poor optical pumping efficiency is another important reason for the ultrahigh threshold but is normally always ignored. On the basis of a cavity-embedded nanoantenna array design, we demonstrate a room-temperature low-threshold plasmonic nanolaser that is robust, reproducible, and easy-to-fabricate using chemical-template lithography. The mode volume of the device is ∼0.22(λ/2n)(3) (here, λ is resonant wavelength and n is the refractive index), and the experimental lasing threshold produced is ∼2.70MW/mm(2). The lasing polarization and the function of nanoantenna array are investigated in detail. Our work provides a new strategy to achieve room-temperature low-threshold plasmonic nanolasers of interest in applications to biological sensoring and information technology.

Plasmonic racetrack resonator with high extinction ratio under critical coupling condition

In this paper, an ultracompact plasmonic racetrack resonator based on single mode metal-insulator-metal plasmonic gap waveguide with high coupling efficiency is investigated both analytically and numerically. The coupling properties of a plasmonic waveguide to a racetrack resonator at 1.55 μm wavelength are studied with various coupling lengths. An extinction ratio of −34.5 dB and a free-spectral range of 303 nm at the critical coupling point can be achieved. Such a plasmonic resonator design provides a promising realization for highly effective modulators and wide band filters.

Nonlinear optical and optical-limiting properties of Azobenzene liquid crystal polymer☆

The nonlinear absorption coefficient β of Azo (Azobenzene) liquid crystal polymer (LCP) was measured by using open aperture Z-scan technique with 10 ns, 532 nm laser pulses. The value of β is 9.02 cm/GW. The optical limiting (OL) response of Azo LCP in tetrahydrofuran (THF) was measured also by use of the Q-switched (10 ns) second-harmonic generation Nd:YAG pulse. We attribute the nonlinear absorption and OL property of Azo LCP to TPA effect at 532 nm.