Modelling of the surface plasmon resonance waveguide sensor with Bragg grating

The operation of a novel device – a waveguide surface plasmon resonance sensor with a UV-written Bragg grating – is theoretically analysed using two methods. In the simple perturbation approach, the metal/dielectric layer system supporting the resonance excitation of the surface plasma wave is considered to be a perturbation of the original dielectric waveguide with Bragg grating that is analysed using a coupled-mode theory. The second approach consists of the rigorous method of bi-directional mode expansion and propagation using the Floquet mode formalism developed recently for the analysis of waveguide grating structures. The results of both approaches are mutually compared, and the operation characteristics of this novel sensing device are briefly described.     

Symmetric surface plasmon resonance sensing structure excited by a planar waveguide

In this paper, we describe a novel waveguide surface plasmon resonance sensing structure, which consists of a symmetric structure and a planar waveguide. The core component is the symmetric structure of the metal layer, tested sample, and metal layer. The refractive index matching condition of this structure can be adjusted through the thickness of the sample. The planar waveguide is used to excite the surface plasmon wave, and then the parameters are tested and analyzed. The surface plasmon wave is excited when glycerin solutions with concentrations of 0%–70% are used to detect at thicknesses of 300 and 500 nm. The problem that the effective refractive index of the ion exchange planar waveguide is large and using this index to excite the surface plasmon wave between the metal and dielectric for detection is difficult to achieve can be countered by appropriately choosing the thickness of the dielectric in order to be able to measure different refractive indices.     

Adjustable surface plasmon resonance with Au,Ag, and Ag@Au core-shell nanoparticles

We report an experimental study on the synthesis of metal nanoparticles （NPs） with adjustable optical density based on surface plasmon resonance （SPR）. Metal NPs prepared by laser ablation in liquid method and the effect of laser parameters on the size, distribution, wavelength of SPR of Ag, Au, and mixture of Ag-Au, and Ag core/Au shell NPs are investigated. Our results show that the adjustable SPR band can be achieved in each class of NPs which is suitable for adjustable optical window applications.     

Fiber-optic surface plasmon resonance-based sensor with AZO/Au bilayered sensing layer

We describe a surface plasmon resonance-based fiber sensor based on a side-polished graded-index mul- timode fiber, in which an Al-doped zinc oxide/gold （AZO/Au） bilayer is deposited on the side-polished surface of the fiber core to improve the detection sensitivity of the device. The AZO/Au layer is used as the active sensing member of the device with a combination of a 75-nm-thick AZO layer and a 40-nm-thick Au layer. Such a device is then applied to the concentration measurement of CHaCOONa solutions, as an example showing a good response to concentration variation. The results indicate that the additional AZO layer in the active sensing member may lead to higher detection sensitivity and greater measurement stability in the measurements of solution concentration.     

Surface plasmon resonance detection using amorphous carbon/Au multilayer structure

Surface plasmon resonance (SPR) can be used to detect the change in reflective index on a metal surface. In this report, we propose detection of the SPR can easily be applied to estimate the thickness of the amorphous carbon (a-C:H) films. To detect changes in film thickness using SPR, devices with an a-C:H/Au structure were fabricated. The a-C:H films were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) and sputtering, and the obtained film densities were 1.4 and 1.6 g/cm³, respectively. By the deposition of an 11-nm thick a-C:H film on a Au layer by sputtering, the SPR angle changed from 44.90° to 47.05°. For a-C:H deposited by ECR-CVD, the SPR angle was shifted from 44.24° for Au without the a-C:H layer to 58.44° after deposition of 45 nm thick a-C:H film. In both systems of the SPR angle increased with increasing the film thickness. The rate at which the SPR angle shifted depended on the a-C:H film density. These results show that the thickness of an a-C:H film can be determined by the SPR angle shift on an a-C:H layer using a-C:H/Au device with an a-C:H film of the same density.     

Modelling of surface plasmon resonance waveguide sensor by complex mode expansion and propagation method

Light propagation in a surface plasmon resonance sensor based on a planar glass ion-exchanged waveguide covered with a thin gold layer is modelled using the eigenmode propagation and matching technique. Optical field distribution along the sensor and the dependence of the transmitted power on the refractive index of the sensed medium is calculated. Experimental results obtained with K+↔Na+ ion-exchanged waveguides are also reported. This revised version was published online in November 2006 with corrections to the Cover Date.     

Compact and efficient coupler to interface hybrid dielectric-loaded plasmonic waveguide with silicon photonic slab waveguide

A coupler is proposed to interface a hybrid dielectric-loaded plasmonic waveguide (HDLPW) with a silicon photonic slab waveguide. The HDLPW is firstly designed and optimized to attain the best tradeoff between the mode confinement and the propagation distance. The designed coupler is inspired from the taper configuration and numerically modeled through finite-difference time-domain (FDTD) simulation. The results demonstrate that a high confinement and low loss of the energy is achieved from a silicon photonic slab waveguide into the dielectric slot of area 50×200 nm² in the HDLPW. The transmission attained through the coupler with a compact size of 400 nm is found to be as high as 80% (1 dB). Further, the planar nature of taper configuration makes the coupler easy to fabricate using the state-of-the-art CMOS facilities. The proposed coupler is useful in enabling the integration between photonic and hybrid plasmonic waveguides and thus realizing on-chip hybrid integrated circuits.     

Effects of thickness & shape on localized surface plasmon resonance of sexfoil nanoparticles

Localized surface plasmon(LSPR) resonance and sensing properties of a novel nanostructure(sexfoil nanoparticle)are studied using the finite-difference time-domain method. For the sandwich sexfoil nanoparticle, the calculated extinction spectrum shows that with the thickness of the dielectric layer increasing, long-wavelength peaks blueshift, while shortwavelength peaks redshift. Strong near-field coupling of the upper and lower metal layers leads to electric and magnetic field resonances; as the thickness increases, the electric field resonance gradually increases, while the magnetic field resonance decreases. The obtained refractive index sensitivity and figure of merit are 332 nm/RIU and 3.91 RIU~(-1), respectively. In order to obtain better sensing ability, we further research the LSPR character of monolayer Ag sexfoil nanoparticle. After a series of trials to optimize the thickness and shape, the refractive index sensitivity approximates 668 nm/RIU, and the greatest figure of merit value comes to 14.8 RIU~(-1).     

Unidirectional excitation of surface plasmon polaritons in T-shaped waveguide with nanodisk resonator

The unidirectional excitation of surface plasmon polaritons (SPPs) in a novel configuration is numerically investigated by the finite-difference time-domain method. It is found that the transmission varies periodically with the increase of distance between the nanodisk resonator and horizontal nanoslit, which can be interpreted by the interference theory. The operating wavelength of this structure can be tuned by altering the refractive index of the nanodisk resonator. This subwavelength-scale structure exhibits high transmission (～58%) due to the constructive interference of the SPP modes, and thus can find important applications on the manipulation of SPP excitation in highly integrated optical circuits.     

Large dielectrophoresis force and torque induced by localized surface plasmon resonance of Au nanoparticle array

A new approach is proposed for manipulating and rotating micro- or nano-objects by using polarized laser light with low intensity. The polarized light excites resonant dipoles on a cap-shaped Au nanoparticle array, which generates a highly nonuniform radiation field that induces large dielectrophoresis force on dielectric objects. The orientation control of the objects is realized by adjusting the polarization direction of the incident light. Theoretical modeling, fabrication, and characterization results for the cap-shaped Au nanoparticle array, as well as preliminary trapping results, are reported.     

Multipole surface plasmon resonance of an aluminium surface

The surface photoelectric effect and the surface plasmon resonances appear when a p/transverse magnetic polarized laser hits a gas-solid interface. We model this effect in the long wave length (LWL) domain (λ_vac > 10 nm, ?ω < 124 eV) by combining the Ampère-Maxwell equation, written in classical approximation, with the material equation for the susceptibility. The resulting model, called the vector potential from the electron density (VPED), calculates the susceptibility as a product of the bulk susceptibility and the electron density of the actual system. The bulk susceptibility is a sum of the bound electron scalar susceptibility taken from the experiment and of the conduction electron non-local isotropic susceptibility tensor in a jellium metal (Lindhard, 1954 [1]). The electron density is the square of the wave function solution of the Schrödinger equation. The analysis of observables, the reflectance R and the photoelectron yield Y as well as the induced charge density permits to identify and characterize the multipole surface plasmon resonance of Al(111) appearing at ω_m ∼ 0.8ω_p or 11-12 eV.     

Grating-coupled surface plasmon resonance in conical mounting with polarization modulation

A grating-coupled surface plasmon resonance (GCSPR) technique based on polarization modulation in conical mounting is presented. A metallic grating is azimuthally rotated to support double-surface plasmon polariton excitation and exploit the consequent sensitivity enhancement. Corresponding to the resonance polar angle, a polarization scan of incident light is performed, and reflectivity data are collected before and after functionalization with a dodecanethiol self-assembled monolayer. The output signal exhibits a harmonic dependence on polarization, and the phase term is used as a parameter for sensing. This technique offers the possibility of designing extremely compact, fast, and cheap high-resolution plasmonic sensors based on GCSPR.     

Measuring physical parameters with surface plasmon resonance heterodyne interferometry

If the incident angle of a light beam on the boundary surface between the thin metal film of a surface plasmon resonance (SPR) apparatus and a test medium is equal to or very near the resonant angle, then the phase difference between the p- and s-polarizations of the reflected light is related to the associated physical parameter. The phase difference can be measured accurately with heterodyne interferometry. If the relationship between the phase difference and the associated physical parameter is specified, then the associated physical parameter can be estimated from the phase difference data. This method has the benefits of both common-path interferometry and heterodyne interferometry, such as simple structure, high stability, high resolution, easy operation, and rapid real-time measurement.     

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF₂ underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.     

表面等离子体共振技术的一些新应用

介绍了表面等离子体共振技术在表面等离子体共振传感器、扫描近场光学显微技术、薄膜光学和膜厚测量、全息成像技术、Q开关、精密角度测量等领域的新应用.     

Polarization modulation spectroscopy of surface plasmon resonance

The features of surface plasmon resonance in gold nanofilms deposited on the surface of a total-internal-reflection prism have been investigated theoretically, using the Fresnel equation, and experimentally, with application of the polarization modulation technique. The angular characteristics of the polarization difference of the reflection coefficients for s-and p-polarized light, Δρ = R _s ² ? R _p ² , were measured in the wave-length range λ = 0.4–2.0 μm. It is shown that the characteristics of Δρ, in contrast to the results of standard measurements by the surface plasmon resonance method, have a resonance peak. Due to this, the characteristics of the polarization difference contain nonresonant components whose magnitudes are determined by the internal reflection coefficients for the metal and insulator; these parameters depend on the film thickness. The calculated and experimental data coincide when the model assumes exponential dependence of the refractive indices and extinction coefficients on the thickness of the metal film. It is established that the characteristic parameter of the exponential is a metal film thickness of 11.0 ± 0.5 nm, at which the film optical parameters correspond to the bulk characteristics.     

A hybrid long-range surface plasmon waveguide comprising a narrow metal stripe surrounded by the low-index dielectric regions

A novel hybrid long-range surface plasmon waveguide structure comprising a narrow metal stripe, two relative low-index dielectric regions and dielectric ridges is proposed and analyzed. With the dielectric ridges and the two relative low-index dielectric regions symmetrically distributed on both sides of the narrow metal stripe, a symmetric hybrid long range mode with low electromagnetic transmission loss and subwavelength scale confinement is achieved. By optimizing the parameters, the propagation length of the proposed waveguide is increased to over two times to that of the conventional symmetric dielectric loaded surface plasmon waveguide, but the mode size only increases about 20%. For this benefit, the hybrid long-range surface plasmons waveguide is a good candidate for realizing high density photonic integration circuits.     

The surface ace plasmon resonance effect in holography

A hologram has been made using a surface plasmon resonance wave as the reference beam. The surface wave was stimulated on a 1200-line/mm aluminum reflection grating that was coated with a thin layer of high resolution photographic emulsion. Experimental results are presented.     

Evanescently coupled resonance in surface plasmon enhanced transmission

The optical transmission through subwavelength holes in metal films can be enhanced by several orders of magnitude by enabling interaction of the incident light with independent surface plasmon (SP) modes on either side of the film. Here, we show that this transmission is boosted by an additional factor of 10 when the energies of the SP modes on both sides are matched. These results, confirmed by a three-dimensional theoretical analysis, give a totally new understanding of the phenomenon of SP enhanced transmission. It is found that the holes behave like subwavelength cavities for the evanescent waves coupling the SPs on either side of the film. In this unusual device, the reflection at either end of the cavity is provided by the SP modes which act as frequency dependent mirrors.