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This work presents a sensitive handheld refractometer using a tapered fiber tip, a multimode fiber, and a tiny mirror. The taper fiber tip was made using a modified wet etching method. The angular intensity distribution of the transmission light from the tapered fiber is sensitive to the refractive index of the surrounding solution. The low angular wave was reflected and collected by a multimode fiber. By setting a small collection angle and 10-mm distance between the fibers and the mirror, the maximum intensity sensitivity reaches up to 7.8 × 105%/RIU (refractive index unit). The sensor resolution of the sensor probe can achieve 8.7 × 10−5 RIU under 0.25% laser intensity stability. The simple handheld refractometer can be used to determine the properties of various liquids. For the glucose solution measurement under handheld condition, 0 to 50 °Bx can be distinguished by monitoring the intensity change. Considering the hand vibration and environmental disturbance, the sensor resolution was 1.22 °Bx.

A tapered fiber sensor was developed to detect the presence of condensed water and frost. The rough surface of the tapered fiber efficiently scattered the light propagating through the tapered fiber. The scattering loss is selective to the medium surrounding the tapered region of the fiber. Compared to the transmission intensity in the air, liquid water on the tapered fiber causes a 40% increase in transmission, whereas the presence of frost decreases the light transmission by 15%. Frost induces roughness on the surface of the tapered fiber and as a result increases light scattering and transmission losses. In contrast, liquid water uniformly covers the tapered fiber surface and reduces the light scattering. Furthermore, the amount of frozen water on the tapered surface is related to the duration of the transmission intensity peak during the defrosting process. The proposed detection scheme based on a rough tapered fiber can be utilized in real-time remote monitoring systems of the frost formation in large refrigeration systems.

A compact imaging smartphone spectrometer utilizing a lightweight aspheric concave blazed-grating is presented for multichannel spectral detection. The lightweight concave diffraction grating is fabricated on a plastic substrate using a two-step thermal-embossing method in a cost-effective and mass-productive way, which enables a large-area, smooth and aspheric concave surface while preserving a blazed-grating structure. The blazed-grating serves as a key single element for aberration-free light focusing and highly-efficient light diffraction. It thus eliminates extra moving optics in the spectrometer and improves the optical characteristics and system integration, which are proven by both simulation and experiments. Spectral linewidth of 1 nm is achieved by combining the concave grating with a smartphone camera. This compact imaging smartphone spectrometer is only about the size of a match-box. Spectra can be obtained directly from the detected images using a developed application (APP) interface. High-throughput plasmonic resonance sensing using microfluidic silver nanoslit arrays under various glycerin environments is demonstrated, and the detected resonance wavelength response is comparable with that detected by a commercial compact spectrometer.

A simple design for shifting the resonance wavelength of silver nanoslits using an electrowetting-on-dielectric (EWOD) cell is proposed. The EWOD cell comprises a polycarbonate (PC) substrate with Teflon-coated silver nanoslits and a glass substrate with Teflon-coated electrodes. A glycerol droplet is placed between the two substrates, and out of the path of a probe beam at zero electric field. Application of an electric field smaller than 0.3 V/µm on the electrodes moves the glycerol droplet into the path of the probe beam, shifting the resonance wavelength of the silver nanoslits by 135 nm. A change (0.33) in the refractive index of the effective medium that is adjacent to the silver nanoslits causes a large shift in the resonance wavelength. The spectral shift of the silver nanoslits is repeatable by the electric field. This simple design is a great achievement for high-performance electro-optical devices with large wavelength shift ranges such as optical switches, variable optical attenuators, and sensor applications.

A chip-based ultrasensitive surface plasmon resonance (SPR) sensor in a checkerboard nanostructure on plastic substrates is presented for digital detection. The sensing elements on the checkerboard are composed of silver-capped nanoslit arrays, which were fabricated using the thermal-embossing nanoimprint method, to meet the demand for low-cost and rapid fabrication. Sharp Fano resonances in the optimized nanoslit arrays provide high-intensity sensitivities (20,000% per refractive index unit), with an element size of 12.5µm. The polarization-dependent transmission in the checkerboard pattern produces optical isolation between sensing elements and results in a crosstalk lower than 1%. Protein-antibody experiments demonstrated that the digital detection limit was up to 1pg/mL, which is approximately 1000 times lower than that of conventional analog detection. For a 140µm×140µm checkerboard pattern, the dynamic range was approximately 100 times higher than that of conventional surface plasmon resonance measurements. This new digital detection method is very useful for detecting ultralow concentrations of analytes with a nonuniform distribution on the sensor surface.

We presented a surface plasmon resonance (SPR) sensor with an angular sensitivity up to 440 deg/RIU by using (±1,∓1) mode on a hexagonal gold nanohole array. The large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method with 180-nm-hole diameter and 600-nm period. A flat dispersion curve deviated from Bragg condition for (±1,∓1) mode occurred when incident angle was larger than 20°. The finite-difference time-domain calculations verified that plasmonic mode changed from surface plasmon mode to cavity mode in nanoholes. Such mode transition resulted in the large change of dispersion curve. The angular sensitivity of the (±1,∓1) mode near the transition band was 6.2 times higher than surface plasmon mode under Bragg condition and 4.5 times higher than prism-based SPR sensors at 850 nm wavelength. Biosensing experiments for antigen-antibody interactions verified the surface binding sensitivity was higher than prism-based SPR machine.

Periodic aluminum-capped nanoslit arrays were produced on a polycarbonate plastic substrate by rapid hot embossing nanoimprint lithography and thermal evaporation, and they were used as a transparent window for blue-emitting polymer light-emitting diodes (PLEDs). The external quantum efficiency of blue-emitting PLEDs was enhanced by the surface plasmon polaritons of the periodic aluminum-capped nanoslit arrays. A maximum current efficiency of 4.84 cd/A was achieved for the proposed PLED, which was over 2.2 times that of the reference PLED (2.18 cd/A). These results demonstrate that periodic nanostructure can assist in the simple and low-cost fabrication of high-performance polymer optoelectronic devices.

An axicon fiber tip combined with a camera device is developed to sensitively detect refractive indexes in solutions. The transparent axicon tips were made by etching optical fibers through a wet end-etching method at room temperature. When the axicon fiber tip was immersed in various refractive index media, the angular spectrum of the emitted light from the axicon fiber tip was changed. Using a low numerical aperture lens to collect the directly transmitted light, a high intensity sensitivity was achieved when the tip cone angle was about 35 to 40 degrees. We combined the axicon fiber tip with a laser diode and a smartphone into a portable refractometer. The front camera of the smartphone was used to collect the light emitted from the axicon fiber tip. By analyzing the selected area of the captured images, the refractive index can be distinguished for various solutions. The refractive index sensitivity was up to 56,000%/RIU, and the detection limit was 1.79 &times, 10&minus, 5 RIU. By measuring the refractive index change via the axicon fiber tip, the concentration of different mediums can be sensitively detected. The detection limits of the measurement for sucrose solutions, saline solutions, and diluted wine were 8.86 &times, 3 &deg, Bx, 0.12&permil, and 0.35%, respectively.

We propose a spectral contrast method to map the transmission images of surface plasmon resonance (SPR) in metallic nanostructures. Comparing the intensities between two neighboring wavelength bands near the SPR wavelength, the signal-to-noise ratio for biosensing applications obtained using the proposed method is found to be ten times higher than that obtained by conventional intensity analysis and 1.6 times better than that obtained by peak-wavelength fitting. The dynamic range and linearity of the refractive index are comparable to the peak-wavelength shift measurement. Based on the detection method, a spectral modulation system for the optical microscope is developed, combined with a gold-capped nanowire array, to measure the biointeractions in microfluidic devices. The experimental results show that the proposed method obtained multiple detections with a detection limit of 1.04 × 10−5 refractive index units. Two types of analysis methods for SPR images are used to study the protein-antibody interactions. The region-of-interest analysis supports multiplexing detections in a compact microfluidic sensor. The effective pixel analysis eliminates low-response pixels and enhances the signal-to-noise ratios for sensitive label-free detection.

We propose a position-sensitive measurement method for tracking resonant signals of surface plasmon resonance (SPR) in periodic metallic nanostructures. Compared with conventional measurement methods, such as wavelength interrogation, intensity interrogation and spectral integration, this approach provides superior noise reduction and simple calculation process. Experimental results show that the limit of detection reaches to 5.88 × 10−6 RIU by using a portable spectrometer with a spectral resolution of 0.4 nm. The relationship between shot noise and signal noise was theoretically compared. The superior noise reduction of the resonant position tracking method is useful for the smartphone-based SPR measurement. The protein-antibody interactions using the smartphone and gold nanoslit arrays as the SPR sensor are demonstrated. It verifies that a smartphone can be used for sensitive measurement of binding-kinetics of the proteins.

We performed experimental measurements and theoretical simulation based on an efficient half-space Green’s function method to investigate the diffraction patterns of light scattered from the biological structure on 1D reflection grating made of metal and polymer. The 1D grating provides higher-order reflected light, which can boost the image signal for off-specular reflection. This can facilitate the micro-ellipsometry imaging experiment when an incident angle of light is at a large angle, while the detection camera is placed at the upright position. The micro-ellipsometry images for s- and p-polarized reflectance and their phase difference (Rs, Rp, and Δ) was taken by a modified Optrel MULTISKOP system with rotating compensator configuration for various angles of incidence and wavelengths ranging from 450nm to 750nm. By using an 80X objective lens, the pixel size for our image is around 164nm. We can further increase the magnification and the numerical aperture by using a substrate collocated with a homemade acrylic resin lens, and the pixel size can be reduced to 50 nm. Based on the above, we study the optical properties of metallic/dielectric nanostructures and nearby biological systems including bacteria, and cancer cells via an imaging micro-ellipsometer combined with detailed theoretical modeling. By using specular and off-specular micro-ellipsometry imaging, we can achieve sufficient sensitivity to collect signals from a small area (around 10μm X 10μm and obtain a 3D image mapping of the morphology and dielectric properties of the biological system of interest.

We present a convenient and low-cost method to fabricate large-area polycarbonate AR nanostructures to improve the luminous intensity and image clarity of a commercial 2.0-inch OLED display panel in bright condition. The polycarbonate AR nanostructures were nanoimprinted by the graded-density nanoporous silicon template with nanoparticle-catalyzed etching. After attaching on the display panel to reduce the light reflection on the substrate, the brightness enhancement and decrease of ambient light reflection were observed. Due to the enhancement of contrast ratio, the quality index of the Lena image test was improved from 0.85 to 0.92 under strong ambient illumination.

The internal and external efficiency of polymer light emitting devices were found can be simultaneously improved by insertion a high refractive index material, titanium oxide (TiOx), to the emission layer and a prism sheet attached to the substrate. The TiOx layer increased the internal efficiency due to a better electron injection and hole confinement. However, it led a wider angular emission profile with more photons trapped in the substrate. By using the prism sheet, those trapped light was efficiently coupled to the air. The extraction efficiency enhancement was increased from 33.1% to 54.4% and the overall current efficiency was improved up to 86%.

We present an antireflection structure consisted of irregular nanopillars to reduce the substrate surface reflection of OLED/OPV hybrid device, which both the luminous efficiency and energy conversion efficiency had great improvement. The nanopillars were made on flexible polycarbonate substrates by using nanoimprint method with anodized aluminum oxide template. The average reflectivity of the patterned polycarbonate substrate in visible wavelength was reduced to 3.3% in the optimized case. With the antireflection structure, the luminous intensity for OLED was improved 49.8% as compared to the device with flat substrates. The power conversion efficiency for OPV was improved from 0.48% to 0.55%, which had 14.6% enhancement at normal incidence.

Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, high-throughput and low-cost fabrication techniques are the main issues which should be addressed. In this study, chip-based nanostructures for intensity-sensitive detection were fabricated and tested using a thermal-annealing-assisted template-stripping method. Large-area uniform nanoslit arrays with a 500 nm period and various slit widths, from 30 to 165 nm, were made on plastic films. A transverse magnetic-polarized wave in these gold nanostructures generated sharp and asymmetric Fano resonances in transmission spectra. The full width at half-maximum bandwidth decreased with the decrease of the slit width. The narrowest bandwidth was smaller than 10 nm. Compared to nanoslit arrays on glass substrates using electron-beam lithography, the proposed chip has a higher intensity sensitivity up to 10367%/RIU (refractive index unit) and reaches a figure of merit up to 55. The higher intensity sensitivity for the template-stripped nanostructure is attributed to a smoother gold surface and larger grain sizes on the plastic film, which reduces the surface plasmon propagation loss.

Nanosphere lithography is used to pattern metallic thin films to form hexagonal nanohole arrays with both high conductivity and good transparency. We fabricated a silver thin film with a transparency of up to 85% and a sheet resistance lower than 35 Ω/□, which is comparable to the commercial ITO electrode. The nanohole array not only increased the transparency but also helped extracting the guided light trapped in organic layers. Compared to the reference device with ITO anodes, Alq 3 -based organic light-emitting devices with the silver nanohole arrays reduced the turn-on voltage by 0.82 V and improved the current efficiency by up to 68.8% due to extraction enhancement.

We present an antireflection structure consisted of tapered nanopillars to simultaneously increase light extraction efficiency and image contrast of flexible organic light-emitting devices. The nanopillars were made by imprinting the anodized aluminum oxide on polycarbonate substrates. The thermal viscosity effect formed the nanopillars with tapered shapes. Such tapered nanopillars show excellent antireflection properties for a wide range of incident angles and wavelengths. The transmittance was greatly improved from 52.8% to 89.1% at 60° incident angle for 150-nm-height nanopillars. With this antireflection structure, the device efficiency was improved 69% as compared to devices with flat substrates. Due to wide-angle antireflection, the ANSI image contrast ratio was also significantly improved.

A near-field coupling method for studying propagation properties of surface plasmon polariton (SPP) in subwavelength dielectric-loaded SPP waveguides (DLSPPWs) is presented. In this method, a tapered fiber probe is employed to generate a nanometer optical spot. When this spot is near the entrance of the DLSPPW with its polarization parallel to the waveguide, a strong guiding wave is observed by a leakage radiation microscope. For DLSPPWs with a dielectric height of about 600 nm, we observed SPP waves with zigzag propagation patterns at 650 nm wavelength. Such zigzag propagation results in a great reduction of propagation loss. In addition, the zigzag wave has a strong optical confinement. The bending loss for an L-bend DLSPPW is only about 0.4 dB.

Gold nanoslit arrays have multiple resonances due to localized plasmons, Bloch wave surface plasmon polaritons, and Wood’s anomaly. Different structures result in different resonances and affect the detection sensitivity of the nanoslits. We systematically compared different structure parameters such as period, slit widths, and gold film thickness by using a spectral integration method. The experimental results show the detection sensitivity had an optimal value for a 500-nm period and 130-nm-thick nanoslits. Moreover, the sensitivity increases with the decrease of the slit widths. It was improved about three times when the size was reduced from 230 to 56 nm. The optimized structure can achieve a detection limit of 5 × 10−6 refractive index unit when the stability is 0.2%. Combining multispectral images and the spectral integration method, we demonstrate real-time and multiple detections of antigen–antibody interactions.

A simple surface plasmon resonance (SPR) ellipsometry equipped with a dove prism and micro-fluidic flow cell is adopted to investigate and study basic properties of biomolecular interaction. Using a dove prism greatly simplifies the optical alignment and the use of micro-fluidic cell helps reduce significantly the volume of the biological sample required in the experiment. By recording the ellipsometry data in terms of relative changes in the ellipsometric parameters, Psi and Delta as sensor signals we can understand the biomolecular interaction. Spectroscopic measurements were performed to check the bulk sensitivity, which further helps determine the corresponding wavelength for maximum sensitivity. Furthermore, dynamic measurements at a fixed wavelength were also done and allow the observation of real-time response to the changes in surface properties on a metallic film. Such a simple technique gives an index resolution around 1.64x10(-6) which is better than the conventional SPR method based on the resonance angular detection. This technique yields sensitivity sufficient enough to detect changes in the effective thickness of biomolecular layer. Biological processes such as adsorption of protein to metal and protein-protein interaction can be understood from the optical response of the sample surface. Such technique is a promising candidate in developing profitable and user-friendly biosensors. Furthermore, this kind of characterization technique is non-destructive, label free, and sensitive with a sub-nanometer resolution in thickness.

The wavelength sensitivities of three kinds of nanostructures (nanoslits, nanoholes, and concentric circles) with various aperture sizes were compared in water environment. These nanostructures were made on a 110-nm-thick gold film with a period of 600 nm. Surface plasmon resonances in these nanostructures produce transmission dips near the phase-matching conditions while peaks at longer wavelengths. The wavelength sensitivities measured at dips are close to theoretical predictions and about 1.5 times larger than those measured at peaks. Such sensitivity difference is attributed to various surface plasmon distributions, as illustrated by the finite-difference time-domain calculations. In addition, the sensitivity decreases with the increase of aperture size. The nanoslit array and concentric circles have better sensitivities than the nanohole array due to the no cut-off transmission.

Ellipsometric measurements coupled with efficient theoretical modeling are used to determine the size and distribution density of Au nanoparticles on a multilayer film. The rigorous coupled-wave analysis (RCWA) and finiteelement Green's function method were used to model the polarization-dependent reflectivity, and the model calculations are in reasonable agreement with the measurements. This demonstrates that the spectroscopic ellipsometry could be a useful optical tool for nondestructive nanometrology. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This study develops a coupled waveguide-surface plasmon resonance (CWSPR) biosensor with a subwavelength grating structure for the real-time analysis of biomolecular interactions. In the proposed optical metrology system, normally incident white light is coupled into the waveguide layer through the subwavelength grating structure thereby enhancing the wave vector which excites the surface plasmons on the metal sensing surface. The proposed CWSPR biosensor not only retains the same sensing sensitivity as that of a conventional surface plasmon resonance device, but also yields a sharper dip in the reflectivity spectrum and therefore provides an improved measurement precision. Moreover, the metrology setup overcomes the limitations of the conventional Kretschmann attenuated total reflection approach and is less sensitive to slight variations in the angle of the incident light. The experimental results confirm that the current CWSPR biosensor provides a straightforward yet powerful technique for real-time biomolecular interaction analysis.

We present an accurate method to determine the effective refractive index and thickness of biomolecular layer by using Fano resonance modes in dual-period gold nanogrid arrays. The effective refractive index changes along the x and y directions are simultaneously measured and obtained by using a modified dispersion relation. The thickness of the surface layer is calculated by a three-layer waveguide equation without any fitting parameters. The accuracy of the proposed method is verified by comparing the results with the known coated dielectric layer and self-assembly layers. The applications of this method and nanogrid chips for determining the thickness and surface concentration of antigen/antibody interactions are demonstrated.

A portable grating-based spectrometer for plasmonic biosensing is presented. Spectral resolution on the order of nm is achieved within wavelength range 628–640nm. The spectrometer shows good sensitivity response by testing the biosensor with glycerin solutions.

Nanocavities inscribed in a gold thin film is optimized and arranged to form a metasurface. We demonstrate both numerically and experimentally that surface plasmon vortex carrying orbital angular momentum can be generated under linearly-polarized optical excitation.

This work presents a photomask lithography for mass manufacture of 100 nm photonic bandgap structures with designed defects. The photomask is composed of 300 nm thick dielectric rod arrays in order to generate edge diffracted beams. As the rod sizes are smaller than one wavelength, diffracted beams from the edges merge together and form subwavelength beaming arrays at rod regions. Theoretical calculations and optical near-field measurements verify the existence of subwavelength focused beams. Furthermore, the focused beams are not affected by the neighbouring defects in the near-field region. Using the transparent photomask, a simple laser exposure system and reactive dry etching method, we demonstrate the fabrication of subwavelength photonic bandgap structures with designed channel defects in a silicon substrate.

We report a simple method to efficiently improve the detection limit of surface plasmon resonance in periodic metallic nanostructures by using small angle illumination and spectral integration analysis. The large-area gold nanoslit arrays were fabricated by thermal-annealing template-stripping method with a slit width of 60 nm and period of 500 nm. The small angle illumination induced a resonant coupling between surface plasmon mode and substrate mode. It increased ~2.24 times intensity sensitivity at 5.5° incident angle. The small-angle illumination also resulted in multiple resonant peaks. The spectral integration method integrated all changes near the resonant peaks and increased the signal to noise ratio about 5 times as compared to single-wavelength intensity analysis. Combining both small angle and spectral integration, the detection limit was increased to one order of magnitude. The improvement of the detection limit for antigen-antibody interactions was demonstrated.

The beaming effect and interference patterns on the exit surface of multiple nano metallic slits with micrometer pitch were observed by scanning near-field optical microscopy. The near-field light intensity for multiple slits had a longer propagation tail and a smaller diverging angle as compared to that in a single slit. From finite-difference time-domain calculations, we verify that these fringe patterns come from the interference effect of longitudinal electric field, which is propagating along the surface. The beaming light in the slit openings is also attributed to the addition of longitudinal fields.

This paper presents a novel wet etching method for LiNbO/sub 3/ using electric-field-assisted proton exchange. By applying voltage with appropriate polarity on designed electrodes placed on both sides of substrate, the induced electric-field distribution can effectively suppress or enhance proton diffusion in the lateral and depth directions. Thus, the proton-exchanged range in LiNbO/sub 3/ can be expertly manipulated. Because the proton-exchanged region can be removed by using a mixture of HF/HNO/sub 3/ acids, the proposed wet-etching method can effectively control the shape of the etched region in the LiNbO/sub 3/ substrate. Under appropriate electrode and proton-exchange parameters, a vertical sidewall with smooth surface is successfully produced, which makes fabricating reflection mirrors and T-junctions in LiNbO/sub 3/ possible. By utilizing the proposed wet-etching method, optical integrated circuits with higher integration density can be fabricated in LiNbO/sub 3/.

We present a new setup of polarization modulated near-field optical microscopy for actually measuring the mesoscale crystallization of thin films. In comparison to previous transmission mode polarization near-field optical microscopy, our new collection mode microscopy provides no axial polarization, free of fiber birefringence and flexibility for tuning wavelength. The Jones matrix calculation verifies that the crystallization of the sample can be obtained by simply subtracting the polarization vector from anisotropy of the tip. The crystallization domains for thermal annealed naphthaphenylene benzidine thin films are observed by the system, stripe domains with averaged ∼15% dichroic ratios are first measured.

The internal and external efficiency were found can be simultaneously improved by insertion a high refractive index material, titanium oxide (TiOx), to the emission layer and a prism sheet attached to the substrate. The TiOx layer resulted in a better electron-hole balance and thus increased the internal efficiency. However, it also led a wider angular FWHM of emission profile with more photons trapped in the substrate. By using the prism sheet, those trapped light was efficiently coupled to the air. The extraction efficiency enhancement at normal direction was increased from 33.1% to 54.4% without any device electricity degeneration. The overall current efficiency was improved 86% when 20-nm-thick TiOx film was used.

We present a low-cost method to fabricate large-area polycarbonate AR nanostructures to improve the luminous intensity and image clarity of a commercial 2.0-inch display panel in bright condition. The polycarbonate AR nanostructures were nanoimprinted by the graded-density nanoporous silicon template with nanoparticle-catalyzed etching. The average reflectivity of the AR film in visible wavelength region was reduced from 10.2% to 4.8% in the optimized case. After attaching on the display panel to reduce the light reflection on the substrate, the brightness enhancement and decrease of ambient light reflection were observed. Due to the enhancement of contrast ratio, the quality index of the Lena image test was improved from 0.85 to 0.92 under strong ambient illumination.

Nanostructure-based sensors are capable of sensitive and label-free detection for biomedical applications. However, plasmonic sensors capable of highly sensitive detection with high-throughput and low-cost fabrication techniques are desirable. We utilized the thermal-embossing template-stripping method to fabricate large-area two-layered gold nanoslits on polymer films with low cost and ultrahigh SPR sensitivities. We found that a transverse magnetic-polarized wave in the nanoslits generated extremely sharp and asymmetric Fano resonances in transmission spectra. The full width at half-maximum bandwidth (FWHM) was only 3.88 nm (0.0063 eV) and the wavelength sensitivity was 644 nm/RIU (1.018 eV/RIU) for 650-nm-period nanoslits. In addition, the extremely sharp resonance leads to an ultrahigh intensity sensitivity up to 48117 %/RIU. Compared to previous single-layer SPR sensors, the proposed structure has a much narrower bandwidth as seen in Fig. 1(a) and Fig. 1(b). The figure of merit (FOM) of Fano mode reaches up to 166 (FOME=162). We attribute such high sensitivity to enhanced resonant effects by the second gold layer. It caps the gap plasmon in nanoslits, resulting an enhanced cavity mode. In addition, the outside surface plasmon wave between nanoslits is better confined, resulting an enhanced SPR mode. The strength of Fano coupling between both modes can be tuned by the thickness of gold film and slit width as seen in Fig. 1(c). The optimal Fano coupling is achieved when the gold layer thickness is close to the height of nanoslits. A protein-protein interaction experiment based on the interactions between bovine serum albumin (BSA) and anti-BSA were measured using two-layer gold nanoslits with a 600 nm period. Fig. 1(d) shows the normalized intensity change of as a function of the interaction time for protein-protein interactions. The measured intensity signal is at a wavelength of 810 nm. It is stable with time when the PBS buffer is injected into the microfluidic device. The BSA coated on the gold surface resulted in an intensity change of 13%. For the Anti-BSA, the 375 μg/mL concentration caused an intensity change up to 237%. Using the intensity measurement, the signal-to-noise ratio for Anti-BSA molecules is up to 1185 when the intensity stability is 0.2%.

Surface plasmon resonance (SPR) sensing is a real-time and label-free detection technique which has the potential to benefit numerous important fields, including medical diagnostics, environmental monitoring, and food safety. However, such a sensing technique is not suited for molecular identification. On the other hand, the surface-enhanced Raman scattering (SERS) spectroscopy is a highly specific technique to identify molecules [1]. In this study, we proposed the fabrication of multifunctional plasmonic biochips and established an optical platform to integrate plasmonic sensing and surface-enhanced Raman scattering techniques. Periodic metallic nanostructures with rough metal surfaces were made on a plastic substrate using nanoimprinting and oblique angle deposition technique [2]. The gold nanoslits with a period of 750 nm were made on a polymer film using a silicon template. A thin gold film was then deposited on the plastic film using the oblique angle deposition technique. The transmission spectra of the biochips with different deposition angles were measured. Transverse- magnetic polarized wave in the gold nanostructure with a deposition angle of 75° generated a sharp and asymmetric Fano resonance in transmission spectrum. It was due to the interference of broad-band cavity resonance in the grooves and narrowband surface plasmon resonance on the periodic gratings. We also measured the SERS spectra of para- mercaptobenzoic (pMBA) acid molecules on different plasmonic biochips. It was found that the SERS signal for the periodic nanostructure was 10 times the background SERS signal. The SERS signal increased by 5 times when the deposition angle was increased from 0° to 75°. In addition, the optical systems for measuring transmission and SERS spectra were integrated. The 785-nm laser light was normally incident on the plasmonic biochip. The reflected light and transmitted light were collected and measured by a charge-coupled device array spectrometer and Raman spectrometer, respectively. The quantification and qualification analysis of the sample can be accomplished at the same time by measuring the changes in transmitted intensity and SERS spectra. Therefore, the combination of plasmonic sensing and SERS spectroscopy provides a promising way for multifunctional chemical analysis to increase the reliability of biological detection and can benefit sensing applications.

The true anisotropic images taken with the polarization modulation near-field optical microscope are often influenced by the linear dichroism of the tapered fibre probe. In this paper, we develop a new method to separate the anisotropic image form probe's dichroism. Our calculations show that the near-field optical image is simply a vector sum of the sample's dichroism and the probe's dichroism, when the probe's anisotropy is small. With this result, we demonstrate the true anisotropic images of poly(phenylene vinylene) (PPV) thin films. The PPV films show non-uniform mesoscale dichroic domains with average domain size, approximately 0.3 mm, and the coefficient for linear dichroism is 1.25 x 10(4) cm(-1).

A novel self-aligned fabrication process for LiNbO/sub 3/:Ni ridge waveguides has been proposed. By using the self-aligned trilayered structure composed of Ni-Ti-Si, the fabrication process is significantly simplified, and takes advantage of suppression of the unwanted planar waveguides and high-coupling efficiency to a single-mode fiber as compared to the conventional processes. Detailed investigations into the characteristics of the ridge waveguides have also proved to be informative under different fabrication parameters. Moreover, the novel self-aligned fabrication process was applied to fabricate a ridge waveguide Mach-Zehnder modulator. The measured half-wave voltage and extinction ratio mere 20.5 V and 12 dB (@1.3 /spl mu/m), and were 4.2 V and 8 dB (@0.6328 #gm).

A method to directly measure the bending angle of a vibrating tapered optical fiber probe is demonstrated. This modified optical beam deflection method allows the vibrational amplitude and angle to be measured independently. The results show that there is a bending in the tip shaft. The merits of using this vibrational angle for distance regulation in near-field scanning optical microscopy are discussed.

A near field optical microscope with a scanning area up to 1 mm×1 mm was demonstrated. The scanning element is the tapered fiber probe and a cylindrical lens is used to focus the feedback laser. Instead of the vibrational amplitude, the vibrational angle signal is used to regulate the distance between the probe and sample. The microscope was employed to map out the evanescent wave on a channel waveguide.

We present here the results of theoretical as well as experimental studies of shear force interactions in near-field scanning optical microscopy. A continuum mechanical model that considers the realistic tapered fiber shape was used to calculate the shear force during the interactions. The frequency spectra at different probe/sample separations show that the shear force is a combination of elastic and frictional force. The relative strengths of these two forces depend on the tilt angle between the probe and the sample surface.

The shear forces between a tapered fiber probe and a glass slice sample were determined without any fitting parameter. The calculations were based on a continuous mechanical model which includes the realistic tapered fiber shape. The input parameters for the model, the vibration amplitude and phase changes during the tip and sample interactions, were measured directly by a modified beam diffraction method.

The motion of tapered fiber probes was studied both theoretically and experimentally. A continuum-mechanical model, including both the intrinsic and the external loss, is proposed to account for the vibration dynamics of the probe. The intrinsic loss was found to be the dominant damping factor experimentally. Analytical solutions based on a realistic probe geometry were obtained for the model in the presence of intrinsic loss. The results are compared with the measured overall motions of the tapered probe. The calculations agree well with the experimental results.

A precisely controlled metallic nanomesh was fabricated by using nanosphere lithography to pattern the silver thin film to form hexagonal nanohole arrays with excellent uniformity, high conductivity and good transparency. An Alq(3) based OLED, with the silver nanomesh electrode of high ðll factor of 70.2% demonstrated a considerable luminous efðciency of 4.8 cd/A, which is 60.9% higher than the referenced device with ITO anode. The periodical nanohole array not only increased the transparency but also helped extracting surface plasmonic wave in organic layers. By attaching the microlens array to further extract the trapped light in substrate, the extraction efficiency enhancement of device with nanomesh anode was 73.8% higher than 50.2% of the referenced device with ITO anode. And the overall current efficiency of device with nanomesh anode was 87.7% higher than traditional ITO based device.

We report that the angular and periodic dependence of the surface-plasmon-polaritons in gold nanodisks can be suppressed by nanorod substrates, which decreases the dipolar coupling and enhance their localization.

An optofluidic platform for real-time monitoring of live cell secretory activities is constructed via Fano resonance in a gold nanoslit array. Large-area and highly sensitive gold nanoslits with a period of 500 nm are fabricated on polycarbonate films using the thermal-annealed template-stripping method. The coupling between gap plasmon resonance in the slits and surface plasmon polariton Bloch waves forms a sharp Fano resonance with intensity sensitivity greater than 11 000% per refractive index unit. The nanoslit array is integrated with a cell-trapping microfluidic device to monitor dynamic secretion of matrix metalloproteinase 9 (MMP-9) from human acute monocytic leukemia cells in situ. Upon continuous lipopolysaccharide (LPS) stimulation, MMP-9 secretion is detected within 2 h due to ultrahigh surface sensitivity and close proximity of the sensor to the target cells. In addition to the advantage of detecting early cell responses, the sensor also allows interrogation of cell secretion dynamics. Furthermore, the average secretion per cell measured using our system well matches previous reports while it requires orders of magnitude less cells. The optofluidic platform may find applications in fundamental studies of cell functions and diagnostics based on secretion signals.

A novel large-angle low-loss direction-coupler type power divider with designed ratio between output waveguides is proposed. The radiation loss is greatly reduced by using a micro-prism at the bend corner to compensate the phase mismatch due to bending. A normalized transmitted power of the power divider with a bend angle of 10/spl deg/ simulated by the semivectorial beam propagation method is about 93%, which is much larger than those were reported for single-mode waveguides. Application of more micro-prisms is also shown. The calculated loss of a symmetric large-angle 3-dB directional coupler with eight micro-prisms is less than 0.953 dB. >

Angular dependent surface plasmon resonances of gold nanoslits with different grating periods were compared between their transmission and reflection spectra. Surface plasmon Bloch wave dominated the reflection mode and gap plasmon dominated the transmission measurement.

The authors demonstrated an efficient color conversion layer (CCL) by using nanosphere arrays in down-converted white organic light-emitting diodes (WOLEDs). The introduced periodical nanospheres not only helped extract the confined light in devices, but also increased the effective light path to achieve high-efficiency color conversion. By applying a CCL with red phosphor on a 400-nm-period nanosphere array, we achieved 137% color conversion ratio for blue OLEDs, which was 2.68 times higher than conventional flat CCL. The resulting luminous efficiency of WOLEDs with patterned CCLs (20.97 cd/A, 1000 cd/m2) was two times higher than the efficiency of the flat device (10.26 cd/A, 1000 cd/m2).