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The surface plasmon resonance (SPR)-based sensor has been widely used for biodetection. One of the attractive roles is the gold nanostructure with Fano resonance. Its sharp resonant profile takes advantage of the high figure of merit (FoM) in high-sensitivity detection. However, it is still difficult to detect small molecules at low concentrations due to the extremely low refractive index changes on the metallic surface. We propose using the coupling of image dipoles of gold nanoparticles (AuNPs) and Fano resonance of periodic capped gold nanoslits (CGNs) for sensitive small-molecule detections. The coupling mechanism was verified by three-dimensional finite-difference time-domain calculations and experiments. AuNPs on CGN form image dimer assemblies and induce image dipole with resonance wavelengths ranging from 730 to 550 nm. The surface plasmon polaritons (SPPs) interact with the image dipole of the AuNP on the CGNs and then scatter out through the periodic gold caps. The experimental results show that the peak intensity of grating resonance is decreased by the effect of image dipole and exhibits the maximum intensity change when the Fano resonance matches the resonance of image dipole. The 50 nm AuNPs can be detected with a surface density of less than one particle/μm

An imaging spectroscopic system that enables spatially-resolved detection of single-particle scattering with polarization-controlled waveguide excitation scheme is presented. The detected microscopic images of inhomogeneous nanostructures are recorded in a time sequence into a data cube based on a Michelson interferometer. The interferograms on selected pixels are Fourier-transformed into multiple spectra. The waveguide excitation scheme is presented for both transmission and reflection measurements while the dark-field excitation scheme is presented in transmission measurements for comparison. Gold nanoparticles, nanorods, and particles on film are utilized in the detection of polarization-dependent spectra. Measurement results are verified with the finite-difference time-domain (FDTD) simulations. The polarization-controlled coupling conditions in nanorods and particle-on-film systems are discussed with simulated field distributions around the nanostructures.

Adding a plain photodiode to a commercial green laser pointer, we obtain a high resolution self-mixing interferometer, capable of detecting minute vibrations down to ≈4.4-nm (rms) resolution, or measuring displacements with half-wavelength (λ/2=266 nm) increments.

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.

Single gold nanorod of length 45.5 nm is detected under a home-built hyperspectral imaging system based on a polarization-controlled waveguide excitation scheme compared with the dark-field excitation and the simulation. The detected spectral intensities at the resonance wavelengths reveal the polarization-induced dipole characteristics along the rod geometries.

We show that, by adding a photodiode and a plain glass beam splitter to a commercial green laser pointer, we can obtain a very sensitive self-mixing interferometer capable of detecting minute vibrations down to submicrometer amplitude, typically ≈ 13 n m resolution, or make displacement measurements with half-wavelength ( λ / 2 = 266 n m ) count increments.

Compact lithium niobate polarization-independent electrooptic modulators using integration of polarization splitters and mode converters are presented. Experimental results show polarization-dependent loss as low as 0.04 dB can be achieved for devices fabricated on Z -cut substrates with an applied voltage of 26 V. The electrode lengths required for electrooptic modulation are 10 and 6 mm for TE and TM modes, respectively, and the total device length is only 1.6 cm. Moreover, only one diffusion step is required that greatly simplifies the fabrication process.

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.

Continuous-wave (CW) room-temperature (RT) laser operation with low energy consumption is an ultimate goal for electrically driven lasers. A monolithically integrated perovskite laser in a chip-level fiber scheme is ideal. However, because of the well-recognized air and thermal instabilities of perovskites, laser action in a perovskite has mostly been limited to either pulsed or cryogenic-temperature operations. Most CW laser operations at RT have had poor durability. Here, crystal fibers that have robust and high-heat-load nature are shown to be the key to enabling the first demonstration of ultralow-threshold CW RT laser action in a compact, monolithic, and inexpensive crystal fiber/nanoperovskite hybrid architecture that is directly pumped with a 405 nm diode laser. Purcell-enhanced light-matter coupling between the atomically smooth fiber microcavity and the perovskite nanocrystallites gain medium enables a high Q (≈1500) and a high β (0.31). This 762 nm laser outperforms previously reported structures with a record-low threshold of 132 nW and an optical-to-optical slope conversion efficiency of 2.93%, and it delivers a stable output for CW and RT operation. These results represent a significant advancement toward monolithic all-optical integration.

Plasmonic resonances in metallic nanostructures are promising for the structure-dependent color-rendering effect. In this study, bismuth is selected as an alternative plasmonic material due to its large tunable range from near-ultraviolet to near-infrared. Various sizes of core-shell bismuth nanoparticles are fabricated on a large-area silicon substrate using a one-step thermal evaporation deposition process. Particle diameters, cross-sections, and arrangement are characterized at 12 featured sections, which reveal spectral shifts and full visible colors in a hue order with a color gamut that is close to sRGB. Color palettes on the chromaticity coordinates rendered from both measured and simulation reflection spectra are in very good accordance with the microscopic image colors of all sections.

The refractive index profile of a non-bending small-core single-mode fiber was first reconstructed from the measured guided mode intensity profile and its spatial derivatives. By combining a rotating diffuser with a coherent laser source, the resulting partially coherent light source overcomes the speckles on the guided mode image of a straight fiber, and the corresponding refractive index profile was successfully reconstructed. Furthermore, guided mode images of a bent fiber with a fiber coil at midway were also measured under different coherency light excitations for comparison. The slight asymmetry of the reconstructed index profile of a bent fiber measured under coherent light excitation was greatly improved when measured under partially coherent light excitation. The generated additional leaky modes propagating partly in both core and cladding induced by the effects of the fundamental core mode deformation at the intermediate fiber bending structure and the mode transition at the bent-to-straight fiber section were averaged out with a low coherence transformed light source.

Mercuric ion, inorganic metal ion, found in three oxidation state in nature, including elemental mercury (Hg0), mercurous ion (Hg+), and mercuric ion (Hg2+). These three forms possess hazardous environmental contaminant and are extremely toxic metal materials to damage mammalian organs.[1] This work demonstrates a label-free technique for Hg2+ ions detection using capped gold nanowire arrays based sensors[2] combined with the electrochemical surface plasmon resonance method. The three-electrode electrochemical analysis (Fig. 1) and optical transmission measurement were employed to characterize the potential-current responses and the resonant peak signals were for the investigation of metal ion electrodeposition (Fig. 2). The nanostructured EC-SPR sensors were used to characterize the eletrochemical behaviors of K3Fe(CN)6/K2Fe(CN)6 redox couple and evaluate the wavelength sensitivity (480.3 nm RIU-1) with a FOM of 40.0 RIU-1 and the intensity sensitivity (1819.9 %) in the glycerol-water solutions. Fig. shows the detection limit of 1 pM Hg2+ can be obtained by the chronoamperomet- ric-spectrum analysis. The developed capped gold nanowire arrays based sensors present Hg2+ ion selectivity over the wavelength shifts of the interfering ions including Ca2+, Co2+, Ni2+, Na+, Cu2+, Pb2+, and Mn2+ ions. The developed capped gold nanoslit arrays based sensors present Hg2+ ion selectivity over the wavelength shifts of the interfering ions including Ca2+, Co2+, Ni2+, Na+, Cu2+, Pb2+, and Mn2+ ions. The proposed flexible capped gold nanowire arrays based sensor is applicable to be an EC-SPR label-free platform and enabled a rapid, sensitive and selective sensing method for aqueous Hg2+ detection. The application of biomolecule analysis can be further evaluation in the future. applicable to be an EC-SPR label-free platform and enabled a rapid, sensitive and selective sensing method for aqueous Hg2+ detection. The application of biomolecule analysis can be further evaluation in the future. Fig.1.Schematic representation of electrochemical surface plasmon resonance configuration set-up for mercury ions detection. Fig. 2 Redox current curves during the first cyclic voltammetry scan and the simultaneously measured surface plasmon resonance intensity. Fig. 3. The wavelength shifts and the intensity changes of gold nanowire arrays against Hg2+concentrations between 100|rM and 100nM. The inset shows the reduction reaction currents of amperometric responses at various Hg2+ concentrations.

The fundamental mode of a small-core step-index few-mode fiber, originally designed for single-mode operation at 1310/1550 nm, was selectively excited at visible wavelengths from a single-mode fiber by adiabatically tapering the fusion splice. A two-dimensional refractive index profile of the few-mode fiber was reconstructed directly from measured guided mode intensity distribution and its spatial partial derivatives with a modified end-fire coupling method using a differential inverse calculation algorithm, which applies only for single-mode guiding.

In this study, we demonstrate a compact imaging spectroscopic system for high-throughput detection of biomolecular interactions on plasmonic chips, based on a curved grating as the key element of light diffraction and light focusing. Both the curved grating and the plasmonic chips are fabricated on flexible plastic substrates using a gas-assisted thermal-embossing method. A fiber-coupled broadband light source and a camera are included in the system. Spectral resolution within 1 nm is achieved in sensing environmental index solutions and protein bindings. The detected sensitivities of the plasmonic chip are comparable with a commercial spectrometer. An extra one-dimensional scanning stage enables high-throughput detection of protein binding on a designed plasmonic chip consisting of several nanoslit arrays with different periods. The detected resonance wavelengths match well with the grating equation under an air environment. Wavelength shifts between 1 and 9 nm are detected for antigens of various concentrations binding with antibodies. A simple, mass-productive and cost-effective method has been demonstrated on the imaging spectroscopic system for real-time, label-free, highly sensitive and high-throughput screening of biomolecular interactions.

Polarization splitters with zinc–nickel and gallium indiffusion optical waveguides fabricated on Z-cut lithium niobate substrates are presented. The device fabrication process needs only one diffusion step and, therefore, is greatly simplified. Experimental results show that, at 1.55- $\mu \text{m}$ wavelength, the extinction ratios for the TE and TM modes are 27.8 and 24.5 dB, respectively.

Broad green generation from 500 to 565nm was observed on chirped χ(2) nonlinear photonic crystals made of periodically-poled lithium tantalate (PPLT) with single pass up-conversion efficiency ∼10%. This was ascribed to simultaneous multi-wavelength SHG and SFG due to nonlinear interaction of (signal, idler) waves in the adiabatically chirped PPLT.

Parallel excitation of optical parametric oscillations was observed on PPLT dispersed with tri-QPM structures in the transverse direction to a nano-second pump beam. It led to simultaneous IR generation from 1000 to 1150nm with slope efficiency > 30%. When a nonlinearly-chirped PPLT was subject to such IR pump, it exhibits simultaneous broad green generation from 500 to 560nm with single pass efficiency ∼10%. This was due to broad spectral coverage of QPM-SHG and SFG in the chirp structures.

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.

Long-range surface plasmon polariton waveguides composed with thin gold stripes embedded in SU-8 polymer cladding with various stripe widths were fabricated. Material properties of the polymer cladding layer, gold thin film, and the device structures were discussed. Optical properties based on modal propagation were characterized at visible to near-infrared wavelengths. The measured propagation losses of waveguide widths from 3 to 9 μm at 633, 785, and 1550 nm are 7.5-18.8, 6.8-12.5, and 1.9-3.9 dB/mm, respectively. Guiding mode properties such as overlap integrals between the simulated and the measured fields and the polarization extinction ratios of the waveguides with different stripe widths were investigated at the telecommunication wavelength. Good accordance between the measurement and simulation results was presented.

Buried-type benzocyclobutene (BCB) optical waveguides fabricated by UV pulsed-laser illumination are proposed and comprehensively characterized in this paper. The fabrication process is greatly simplified as compared to conventional dry-etched ridge-type BCB waveguides. The measured propagation loss at 1548 nm is as low as 0.6 dB/cm due to the buried waveguide structure. And the produced refractive index change is dependent upon the number of laser shots such that single-mode waveguides with different mode sizes can be tailored for efficient coupling. Furthermore, rigorous analyses of surface damage threshold, rms roughness, and chemical characteristics under different illumination conditions are presented to illustrate the design considerations and the chemical mechanism of the UV-induced BCB waveguides

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.

Two-step field-assisted ion-exchanged waveguides have been fabricated on a glass substrate. The concentration profiles of the exchanged ions were measured with electron microprobe. The waveguides were characterized under scanning electron microscope and optical microscope for the investigation of burying structures. Guiding mode patterns were characterized with near-field measurement, where symmetric profiles were observed for the burying-type waveguide. The refractive index profiles were also measured with a modified end-fire coupling method. The relation between ion concentration profiles and index profiles were compared for the waveguides with different fabrication process.

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.

High-throughput detection of a large-area chip-based gold nanoslit biosensing array was detected using an imaging system based on white light Fourier transform spectrometry, with the detection sensitivity 0.02 in index change and 60nM of anti-BSA.

A taper technique is presented which utilizes micrometer-scale SU8 waveguides to couple light into nanometre-scale silicon waveguides with high conversion efficiency. The conversion efficiency between the fibre and the silicon waveguide is investigated for different taper lengths and silicon waveguide taper tip widths. Maximum coupling efficiency is ascertained to be about 60% per coupler. The 3dB bandwidth of the presented structure is determined to be well above 100nm.

Benzocyclobutene directional couplers and 1times2 multimode interference (MMI) power splitters fabricated by ultraviolet (UV) pulsed-laser illumination are presented. With an accurate control of the fabrication process, the measured coupling lengths of the directional couplers are in good agreement with those simulated by the beam propagation method. In particular, accurate power splitting ratios of the directional couplers can be achieved by controlling the number of laser shots to obtain the required index changes. Moreover, MMI power splitters with accurate interference lengths and low imbalances can be successfully fabricated. All those reveal that UV pulsed-laser illumination is an accurate and controllable technique for the device fabrication.

Optical waveguides of zinc and nickel co-diffused on lithium niobate substrates were measured with secondary-ion-mass spectrometry for metal ion concentrations and differential optical-fields for refractive index profiles. Correlation between compositional and optical properties was studied.

Ridge structures are fabricated on gamma-ray irradiated lithium niobate substrates to modify the modal field distributions of titanium-diffused waveguides. Experimental results show the measured modal field distributions are very close to that of a fiber.

Field distributions of 1-to-N multimode interference optical power splitters with two cascaded multimode interference regions are calculated. An improved objective function is presented for the optimization of the proposed devices.

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.

Various MMI power splitters fabricated by laser illumination on benzocyclobutene are compared. With suitable beam expansion ratios, experimental results show the devices can be fabricated with high accuracy, short time, and good controllability.

Two-dimensional index profile of an optical fiber was reconstructed with the measured differential optical fields by perturbing the optical path in the end-fire coupling measurement. Good results were obtained compared with the known index profile.

Buried-type benzocyclobutene optical devices fabricated by UV-illumination are presented. The refractive index can be accurately controlled between 0.001 and 0.0038 by the proposed method. Experimental results show directional couplers and 1times2 multimode interference power splitters can be fabricated with high accuracy and good controllability.

Single-mode non-ridge benzocyclobutene optical waveguides fabricated by excimer laser illumination are presented. The induced index change is about 0.003 after 50 shot s of laser pulse exposure. The propagation loss at 1548 nm is about 0.6 dB/cm.

Increased detection sensitivity was achieved by adjusting the incident angle on periodic gold nanostructures that induced a resonant coupling between surface and substrate surface plasmon modes. For 500 nm-period gold nanoslits, a small incident angle, 7°, resulted in 2.64 times narrower linewidth and a 1.8 times increase in the figure of merit as compared to normal incidence. Furthermore, the intensity sensitivity was increased 4.5 times due to the change in the resonant coupling and redshift of the surface plasmon mode.

The evanescent tails of a guiding mode as well as its first and second derivatives were measured by a modified end-fire coupling method. The effective index of the waveguide can be obtained by simultaneously fitting these three fields using single parameter. Combined with an inverse calculation algorithm, the fields with fitted evanescent tails showed great improvement in the refractive index profiling of the optical waveguide, especially at the substrate region. Single-mode optical fibers and planar waveguides of proton-exchanged (PE) and titanium-indiffusion (Ti:LiNbO3) on lithium niobate substrates with different refractive index profiles were measured for the demonstration.

We present a modified end-fire coupling method to reconstruct two-dimensional index profiles of optical waveguides. The reconstruction is based on the measured differential optical fields and an inverse algorithm for the Helmholtz equation. The differential fields are obtained from spatially perturbed images recorded by a CCD camera. A closed-loop piezoelectric stage given a sinusoidal wave and an oil-immersion objective lens for high-resolution images are used in the measurement. A single-mode fiber and a Ti:LiNbO(3) waveguide with known index profile at 632.8 nm are measured for demonstration. The measured index profiles agree quite well with core regions of known index profiles.

The authors present two-dimensional reconstruction of the refractive index profile of an optical waveguide by using differential near-field optical microscopy. Using an inverse algorithm, the refractive index distribution is obtained directly from the measured optical near-field and its derivatives without any assumption of the index profile. The proposed method also takes advantage of subwavelength resolution and low noises in the waveguide region. Two-dimensional index profile reconstruction of a single mode fiber is measured for the demonstration. The measured optical field distribution and refractive index profile agree quite well with the calculated mode and the known index profile.