Long-range Surface Plasmon Polariton Research Articles

Grating couplers fabricated by e-beam lithography for long-range surface plasmon waveguides embedded in a fluoropolymer.

Long-range surface plasmon polariton waveguides consisting of Au stripes integrated with input and output grating couplers embedded in thick Cytop claddings are proposed and demonstrated experimentally. Under the right conditions, grating couplers enable broadside (top) coupling with good efficiency while producing a low level of background light. The scheme does not require high-quality input and output edge facets, and it simplifies optical alignments. We demonstrate coupling using a cleaved bow-tie fiber and a lensed fiber, and we determine the grating coupling efficiencies in both cases over a broad operating wavelength range. The lensed fiber produces a better overlap with the long-range surface plasmon mode of interest and thus results in a better coupling efficiency with essentially no background light as observed on an infrared camera. The measurements are compared with theoretical results obtained using a realistic model of the structures, including out-of-plane curvature in the grating profile resulting from our fabrication process. The coupling scheme along with the surface plasmon waveguides hold strong potential for biosensing applications.

A D-type fiber based symmetrical long-range surface plasmon resonance sensor with high quality factor

A D-type fiber based symmetrical long-range surface plasmon resonance (sLRSPR) sensor with high quality factor (Q-F) as high as 107.52 RIU−1 was proposed and experimentally demonstrated. The sensing structure of the proposed sensor consisted of fiber/dielectric buffer layer (DBL)/Au film/DBL/analyte, and the DBLs on both sides of the Au film in the sLRSPR sensor were identical, which greatly increased the permittivity matching degree between the analyte and the DBL near the D-type fiber, and reduced the loss of long-range surface plasmon polaritons. For LRSPR sensor, the closer the permittivities of DBL and analyte on both sides of metal film are, the easier the LRSPR is to stimulate, and thus the proposed sensor possessed higher sensitivity and higher detection accuracy. The transfer matrix method supported by the finite-difference beam propagation method and the finite element analysis was employed to optimize the sensor parameters for the first time. The refractive index sensing performance of the conventional SPR (cSPR) sensor, the conventional LRSPR (cLRSPR) sensor, and the sLRSPR sensor with optimal parameters were systematically researched by simulation and in-depth experiment. The results suggested that the sensing performance of the sLRSPR sensor was better than that of the other two sensors. This paper provided a meaningful advancement for designing an optical fiber SPR sensor with remarkable performance to measure biomass.

Novel Structures’ Configurations for Long-Range Surface Plasmon-Polaritron

In this paper, we experimentally analyze the intensity and phase dependence of the electric current in an active long-range surface plasmon polariton (LRSPP) device. It consists of a metallic waveguide embedded in a dielectric material where we have included external electric contacts. Experimental results show that the intensity beam decays almost 15 dB when we apply 150 mW, as we can obtain a phase change of 15p for the same value of electric power.

Suspended LRSPP for the development of highly integrated active plasmonic devices.

We present a novel long-range surface plasmon polariton (LRSPP) device consisting of a suspended dielectric matrix in which an electrically active, millimeter-long metallic waveguide is embedded. We show that, by opening an air gap under the lower cladding, the influence of the substrate is suppressed and the symmetry of the thermo-optical distribution around the LRSPP waveguide is preserved over extended ranges of applied electrical current with minimal optical losses. Experimental results show that, compared to a standard nonsuspended structure, our device allows either the induction of a phase change that is three times larger, for a fixed electrical power, or, equivalently, a scaling down of the device to one-tenth of its original length, for a fixed phase change.

Long-Range Surface Plasmon-Polariton Waveguide Biosensors for Human Cardiac Troponin I Detection.

Straight long-range surface plasmon-polariton (LRSPP) waveguides as biosensors for label-free detection are discussed. The sensors consist of 5-μm-wide 35-nm-thick gold stripes embedded in a low-index optical-grade fluoropolymer (CYTOPTM) with fluidic channels etched to the Au surface of the stripes. This work demonstrates the application of the LRSPP biosensors for the detection of human cardiac troponin I (cTnI) protein. cTnI is a biological marker for acute myocardial infarction (AMI), often referred to as a heart attack, which can be diagnosed by elevated levels of cTnI in patient blood. Direct and sandwich assays were developed and demonstrated over the concentration range from 1 to 1000 ng/mL, yielding detection limits of 430 pg/mL for the direct assay and 28 pg/mL for the sandwich assay (1 standard deviation), the latter being physiologically relevant to the early detection or onset of AMI. In addition, a novel approach for data analysis is proposed, where the analyte response is normalized to the response of the antibody layer.

A Novel Fiber-Based Symmetrical Long-Range Surface Plasmon Resonance Biosensor With High Quality Factor and Temperature Self-Reference

A novel wavelength modulated optical fiber-based symmetrical long-range surface plasmon resonance (sLRSPR) biosensor with high quality factor (Q-F) of 56.70 RIU−1 and temperature self-reference was proposed and demonstrated. The multilayered architecture of the sLRSPR biosensor consisted of cladding/dielectric-buffer-layer (DBL)/Au-nanofilm/DBL/analyte, and the DBLs on both sides of the Au-nanofilm were identical, which greatly increased the matching degree of the permittivities of analyte and the DBL near cladding and reduced the loss of long-range surface plasmon-polaritons. Therefore, the sLRSPR sensor displayed excellent sensing performance, and its Q-F was 3.27-folds higher than that of the conventional SPR sensor. Furthermore, the sLRSPR sensor was employed as a biosensor for the measurement of average refractive index (RI) of cell, and the temperature-sensitive optical adsorption characteristic of the DBL was utilized to provide temperature self-reference for the RI measurement. The sLRSPR biosensor realized simultaneous measurement of RI and temperature at the exactly same location, which can eliminate the measurement error introduced by temperature to RI measurement. The sLRSPR biosensor proposed in this paper possessed higher detection precision and presented greatly promising application prospects in the field of biochemistry.

Efficient directional coupling from multilayer-graphene-based long-range SPP waveguide to metal-based hybrid SPP waveguide in mid-infrared range.

Graphene-based and metal-based surface plasmon polariton (SPP) waveguides have attracted intense research interest because they can be used as basic components to propagate electromagnetic (EM) waves in future optical integrated systems. We propose a directional coupler, which can couple EM energy from a multilayer-graphene-based cylindrical long-range SPP waveguide to a metal-based cylindrical hybrid SPP waveguide in the mid-infrared range. This coupler exhibits relatively low coupling length, high coupling efficiency, low insertion loss, and high extinction ratio after adjustment of the wave vector mismatch of the two waveguides. Moreover, this coupler is tolerant to practical fabrication errors like misalignment of graphene layres, and can effectively work in the range of Fermi energy Ef > 0.6 eV when the mobility of graphene varies from 10000 to 800 cm2/Vs. Hence, the coupler offers potential applications in signal routing and information exchange between graphene-based and metal-based SPP waveguides in photonic integrated circuits.

Enhancement of Long-Range Surface Plasmon Excitation, Dynamic Range and Figure of Merit Using a Dielectric Resonant Cavity.

In this paper, we report a theoretical framework on the effect of multiple resonances inside the dielectric cavity of insulator-insulator-metal-insulator (IIMI)-based surface plasmon sensors. It has been very well established that the structure can support both long-range surface plasmon polaritons (LRSPP) and short-range surface plasmon polaritons (SRSPP). We found that the dielectric resonant cavity under certain conditions can be employed as a resonator to enhance the LRSPP properties. These conditions are: (1) the refractive index of the resonant cavity was greater than the refractive index of the sample layer and (2) when light propagated in the resonant cavity and was evanescent in the sample layer. We showed through the analytical calculation using Fresnel equations and rigorous coupled wave theory that the proposed structure with the mentioned conditions can extend the dynamic range of LRSPP excitation and enhance at least five times more plasmon intensity on the surface of the metal compared to the surface plasmon excited by the conventional Kretschmann configuration. It can enhance the dip sensitivity and the dynamic range in refractive index sensing without losing the sharpness of the LRSPP dip. We also showed that the interferometric modes in the cavity can be insensitive to the surface plasmon modes. This allowed a self-referenced surface plasmon resonance structure, in which the interferometric mode measured changes in the sensor structure and the enhanced LRSPP measured changes in the sample channel.

Highly Sensitive SPR Sensor Based on Hybrid Coupling Between Plasmon and Photonic Mode

In this letter, we propose a new configuration of surface plasmon resonance sensor based on hybrid coupling between long-range surface plasmon polariton (LRSPP) and dielectric planar waveguide mode (WGM) for ultrasensitive refractive index sensing. The multilayer Otto configuration supports both LRSPP and photonic WGM. Under phase matching condition, these two modes can be dramatically coupled with each other forming hybrid modes and consequently splitting the resonance. By optimizing the structure parameters, an intensity sensitivity as high as 3081/RIU is achieved, which corresponds to 1.2-fold enhancement comparing to the conventional LRSPP sensor. Moreover, the sensor can be modified for detecting the analyte according to different targeting refractive index ranges by simply replacing the dielectric medium.

Magnetoplasmonic crystal waveguide.

We propose a perspective type of insulator-metal-insulator magnetoplasmonic crystal waveguide, composed of a gold grating placed between two garnet layers. Using an original non-perturbing method for the deposition of the upper magneto-dielectric layer, we fabricate the samples and provide experimental results evidencing the coupling of surface plasmon-polaritons propagating on the opposite Au/garnet interfaces. In contrast to traditional Au/garnet magnetoplasmonic crystals, spectra of the magneto-optical effect measured in transmission through this waveguide demonstrate rather specific features: a high-quality resonance for the long-range surface plasmon-polariton and a broad 60 nm wide resonance for the short-range surface plasmon-polariton. Our findings open new routes towards the development of high-sensitivity robust magnetoplasmonic sensors.

Flexible Thermo-Optic Variable Attenuator based on Long-Range Surface Plasmon-Polariton Waveguides.

A flexible thermo-optic variable attenuator based on long-range surface plasmon-polariton (LRSPP) waveguide for microwave photonic application was investigated. Low-loss polymer materials and high-quality silver strip were served as cladding layers and core layer of the LRSPP waveguide, respectively. By using finite element method (FEM), the thermal distribution and the optical field distribution have been carefully optimized. The fabricated device was characterized by end-fire excitation with a 1550 nm laser. The transmission performance of high-speed data and microwave modulated optical signal was measured while using a broadband microwave photonics link. The results indicated that the propagation loss of the LRSPP waveguide was about 1.92 dB/cm. The maximum attenuation of optical signal was about 28 dB at a driving voltage of 4.17 V, and the variable attenuation of microwave signals was obviously observed by applying different driving voltage to the heater. This flexible plasmonic variable attenuator is promising for chip-scale interconnection in high-density photonic integrated circuits and data transmission and amplitude control in microwave photonic systems.

Low detection limits using sandwich and inhibition assays on long-range surface plasmon waveguide biosensors

A long-range surface plasmon polariton waveguide composed of a gold stripe embedded in CYTOP with an etched microfluidic channel has been used as a label-free real-time biosensor to demonstrate enhanced assay formats capable of very low detection limits. Specifically, sandwich and inhibition (competitive) assays were developed and demonstrated using Bovine Serum Albumin (BSA) and anti-BSA produced in rabbit as a model bio-specific pair. Carbodiimide coupling to a self-assembled COOH-terminated alkanethiol monolayer on the gold stripe was used to immobilize biomaterial to its surface. The optical output power from the biosensor was measured continuously over time and converted into surface mass density. Titration curves were extracted for both immunoassays. We demonstrate that protein concentrations in solution of 10 pg/ml can be detected with a signal-to-noise ratio of 20 using this new optical biosensor technology.

Fabrication of long range surface plasmon waveguide biosensors in a low-index fluoropolymer

The authors report the fabrication of long-range surface plasmon polariton biosensors consisting of thin narrow Au stripes embedded in a low refractive index fluoropolymer with etched fluidic channels. The fabrication process incorporates a sacrificial SiO2 channel etch stop layer to avoid waveguide damage and prevent channel over-etching, and an Al etch mask to minimize thermal cracking of the fluoropolymer during channel etching. Process details are reported along with fabrication results, and the optical and biosensing performance of the fabricated devices are demonstrated. The biosensors were tested for bulk sensitivity and bovine serum albumin (BSA) protein adsorption producing notable changes for solutions with different refractive indices (increment of 2 × 10−3) and a change in insertion loss of 0.1 dB as a monolayer of BSA forms on the device.

Long-range surface plasmon polariton detection with a graphene photodetector.

We present an integration of a single Ag nanowire (NW) with a graphene photodetector and demonstrate an efficient and compact detection of long-range surface plasmon polaritons (SPPs). Atomically thin graphene provides an ideal platform to detect the evanescent electric field of SPPs extremely bound at the interface of the Ag NW and glass substrate. Scanning photocurrent microscopy directly visualizes a polarization-dependent excitation and detects the SPPs. The SPP detection responsivity is readily controlled up to ∼17 mA/W by the drain-source voltage. We believe that the graphene SPP detector will be a promising building block for highly integrated photonic and optoelectronic circuits.

Polymer/silica hybrid integration waveguide Bragg grating based on surface plasmon polaritons.

We proposed a device composed of a Bragg grating and a long-range surface plasmon polariton waveguide. The waveguide is formed by embedding a thin Au stripe in negative UV photoresist (SU-8 2005). The corrugated grating structure is created on a silica substrate using contact lithography and inductively coupled plasma etching, which is transferred onto the SU-8 2005 film by a spin coating process, producing a periodic modulation of refractive index along the waveguide. We achieve a transmission peak with an extinction ratio of 17dB and a 3-dB bandwidth of 0.9nm at a wavelength of 1575.2nm. We achieve a reflection peak with a side-mode suppression ratio of 9.7dB, a 3-dB bandwidth of 0.9nm at a wavelength of 1575.2nm when the heating electrode isn't working. The shift of the reflection peak with heating power over the range 0-6mW is approximately 2.9nm. This thermal dependence exhibits an average slope of -0.48 nm/mW.

Modeling of enhanced spontaneous parametric down-conversion in plasmonic and dielectric structures with realistic waves

A numerical study of the enhancement of the spontaneous parametric down-conversion in plasmonic and dielectric structures is considered. The modeling is done using a nonlinear transfer-matrix method which is extended to include vacuum fluctuations and realistic waves (e.g. Gaussian beam). The results indicate that in the case of short-range surface plasmon polaritons, the main limiting factor of the enhancement is the short length of the coherent buildup. In the case of long-range surface plasmon polaritons or dielectric guided waves, the very narrow resonances are the main limiting factor instead.

Quasi-phase-matched second harmonic generation of long-range surface plasmon polaritons

In this paper, we experimentally demonstrate the second harmonic generation of long-range surface plasmon polaritons via quasi-phase matching in lithium niobate. After depositing a 9/13 nm thick Au film on periodically poled lithium niobate, TiO2 of about 2.3 μm in thickness is evaporated on the sample as a refractive-index-matching material. This dielectric (periodically poled lithium niobate)-metal(Au)-dielectric(TiO2) sandwich structure can support the transmission of long-range surface plasmon polaritons through it. By designing a moderate ferroelectric domain period of periodically poled lithium niobate, the phase mismatch between the fundamental wave and second harmonic wave of the long-range surface plasmon polaritons can be compensated and a second harmonic wave can be generated effectively. This can be used to provide integrated plasmonic devices with attractive applications in quantum and classic information processing.

Photonic Crystal-Supported Long-Range Surface Plasmon-Polaritons Propagating Along High-Quality Silver Nanofilms

Long-range surface plasmon-polaritons (LRSPP) with a propagation length equal to 180 microns at the wavelength of 633 nm have been observed at the interface of 12.5 nm-thick silver nanofilm, coated by a 20 nm-thick protective ZnS layer, with air. Their propagation has been supported by a specially prepared 40-layer 1D Photonic Crystal designed in such a manner that silver layer has been deposited directly onto thin ZnS layer, earlier shown to be a non-oxide material most suitable for the preparation of high-quality thin silver nanofilms.

Excitation of Multiple Surface Plasmon-Polaritons by a Metal Layer Inserted in an Equichiral Sculptured Thin Film

Excitation of multiple surface plasmon-polaritons(SPPs) by an equichiral sculptured thin film with a metal layer defect was studied theoretically in the Sarid configuration, using the transfer matrix method. Multiple SPP modes were distinguished from waveguide modes in optical absorption for p- polarized plane wave. The degree of localization of multiple SPP waves was investigated by calculation of the time averaged Poynting vector. The results showed that the long-range and short-range SPP waves can simultaneously be excited at both interfaces of metal core in this proposed structure which may be used in a broad range of sensing applications.

Flexible long-range surface plasmon polariton single-mode waveguide for optical interconnects

We present the design, fabrication and characterization of long-range surface plasmon polariton waveguide arrays with materials, mainly silicones, carefully selected with the aim to be used as mechanically flexible single-mode optical interconnections, the so-called “plasmonic arc” working at 1.55µm. The fabricated plasmonic arcs show a TM/TE polarization ratio of ~25 dB. By using the cut-back method, the straight propagation loss at 1.55µm is estimated to 0.5-1 dB/mm and coupling loss to ~1-2 dB/facet after dicing. In the free-standing S-curved configuration, the bending loss of single cladding plasmonic arc is 2.2-2.8 dB/90° at bending radius 2.5 mm. For double cladding plasmonic arcs, it is decreased to 0.7-1.7 dB/90° for the same radius. The coupling loss with single-mode glass PCB waveguides is estimated to be 1.7 dB/interface in the best condition.