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It is desirable that a surface plasmon resonance (SPR) sensor is highly sensitive to binding interactions within the sensing region, generate evanescent fields with long penetration depths, and utilize a metal film that is very stable even in extreme environmental conditions. In this study, we present the first example of a wavelength-modulated waveguide SPR sensor with a bimetallic silver-gold film for surface plasmon excitation. The underlying silver yields better evanescent field enhancement of the sensing surface, while the overlying gold ensures that the stability of the metallic film is not compromised. It is shown experimentally that in terms of dλ/dn, the bimetallic film waveguide SPR configuration has a sensitivity of 1232 nm/RIU, greater than two times improvement from the 594 nm/RIU achievable with single gold film waveguide SPR sensor. The higher sensitivity, compact nature, and better evanescent field enhancement of this configuration provides the potential to biosensing applications. [ABSTRACT FROM AUTHOR]

We demonstrate an enhancement of fluorescence emission due to bimetallic silver–gold film-induced surface plasmon wave extension. Rhodamine B (RhB) dyes were excited by the evanescent wave field produced from surface plasmon polaritons excited on metal-deposited sections along an embedded strip waveguide. Various silver–gold combinations were used to quantify for the evanescent field enhancement. The underlying silver yields better evanescent field enhancement, while the overlying gold ensures that the stability of the sensing surface is not compromised. In comparison to the conventional single gold film surface plasmon resonance (SPR) configuration, the two-layered metallic structure is capable of enhancing the surface plasmon polariton (SPP) evanescent field considerably, as verified experimentally by the ca. 4.0 times improvement in the RhB fluorescence emission. The compact waveguide structure and improved electric field probing depth can potentially be exploited for on-chip SPR – fluorescence excitation of less concentrated fluorophore-labelled biological and chemical analytes, with a capability of massively parallel processing for high throughput screening. [ABSTRACT FROM AUTHOR]

The use of coherent optical signal processing in long-distance optical communication systems has dramatically increased data capacity enabling encoding of multiple-bit information in the phase of a light beam. Direct detection of phase information of a high-speed modulated light remains challenging and requires an external, local oscillator for referencing, which is expensive for short-reach optical communications, for example, in data centers. The availability of less-complex integrated photonics devices for coherent signal detection will alleviate this bottleneck. On the other hand, phase information of coherent, orthogonally polarized light beams can be extracted from their polarization states, and it is, therefore, possible to achieve phase measurements via fast polarization detection. Here, an on-chip nanodisk device is demonstrated for high-speed coherent optical signal detection enabled by spin–orbit coupling in Si-photonics circuitry. In a coherent communication experiment with up to 32 GBaud rate, the high-speed phase-shift keying and quadrature amplitude modulation signals detected by a Si nanodisk based polarization measurements at multiple wavelengths in the C-band are recovered with a bit error rate below the forward error correction threshold. The proposed on-chip nanodisk device shows promise in high-speed coherent optical communication applications where phase detection is required at low cost and small footprint. [ABSTRACT FROM AUTHOR]

Spin-momentum locking, a manifestation of topological properties that governs the behavior of surface states, was studied intensively in condensed-matter physics and optics, resulting in the discovery of topological insulators and related effects and their photonic counterparts. In addition to spin, optical waves may have complex structure of vector fields associated with orbital angular momentum or nonuniform intensity variations. Here, we derive a set of spin-momentum equations which describes the relationship between the spin and orbital properties of arbitrary complex electromagnetic guided modes. The predicted photonic spin dynamics is experimentally verified with four kinds of nondiffracting surface structured waves. In contrast to the one-dimensional uniform spin of a guided plane wave, a two-dimensional chiral spin swirl is observed for structured guided modes. The proposed framework opens up opportunities for designing the spin structure and topological properties of electromagnetic waves with practical importance in spin optics, topological photonics, metrology and quantum technologies and may be used to extend the spin-dynamics concepts to fluid, acoustic, and gravitational waves. [ABSTRACT FROM AUTHOR]

By using a metal-insulator-metal waveguide with temporally oscillating core width, the single frequency of incident surface plasmon polaritons (SPPs) could be converted to many discrete frequencies with equivalent intervals. The conversion efficiency is affected by the waveguide structure and also the amplitude and frequency of the oscillation. Finite-difference time-domain simulations revealed that the SPP frequency shift behavior is analogous to the spatial light diffraction in optical waveguide arrays. The discrete frequencies of SPPs can further be controlled by varying the initial phase of the waveguide core width oscillation. The results are explained analytically using the coupled mode theory. [ABSTRACT FROM AUTHOR]

Carrying orbital angular momentum per photon, the optical vortex has elicited widespread interest. Here, we demonstrate that dual coaxial longitudinal polarization vortices can appear upon a nonparaxial propagation of a tightly focused Pancharatnam-Berry tailored Laguerre-Gaussian beam. Most importantly, it is capable of accessing arbitrary independent topological charges for both vortices, as well as predesigned tunable spacing distances between them. [ABSTRACT FROM AUTHOR]

The data rate in a single-mode fiber is approaching the capacity limit given by the Shannon theory. Mode division multiplexing, such as few modes, orbital angular momentum, and cylindrical vector beam (CVB) multiplexing, has shown great potential to further increase data capacity in both free-space and fiber communication. We propose and demonstrate high-order CVB multiplexing communication in an air-core photonics crystal fiber (PCF). The simulation results show that the 19-cell air-core PCF supports transmission of CVB modes from ±1 to ±4 orders. In the experiment, ±1- to ±4-orders CVBs are transmitted in 8.25-m-long air-core PCF with the mode purities higher than 76.5%. We demonstrate four coaxial CVB channel communication by multiplexing the ±2- and ±3-orders CVB modes. Each CVB channel carries 10-Gbit/s on-off keying signals and the measured bit error rates satisfy the forward error correction threshold. CVB communications based on air-core PCF can be used in short-distance optical communication with high capacity and low optical latency. [ABSTRACT FROM AUTHOR]

The article cities a research study on generating a tailored two-dimensional (2D) coherent surface plasmon polariton (SPP) field distribution. It is said that the ability to tailor a SPP field can help in a broad range of nanophotonic applications. The inherent constraints in a 2D coherent field distribution were revealed in the study.

We explore a radially polarized vortex beam with broken axial symmetry under tight focusing conditions. The beam's three mutually orthogonal polarization components (radial, azimuthal, and longitudinal) are all rotated by an angle of π/2 with respect to the input field in the focal plane. We validate this effect experimentally. Finally, we prove that this effect can be used to transport nanoparticles. [ABSTRACT FROM AUTHOR]

The gap mode enhancement of metal nanoparticles is introduced into wide-field Raman microscopic imaging, where it produces a more efficient Raman scattering map compared with the scanning mechanism based on a single nanoparticle. Patterned surface plasmon illumination technique is employed to extend spatial resolution of the wide-field Raman imaging to 133 nm achieved by a modified total internal reflection microscope. The images by different Raman shifts are extracted by using narrow band pass dielectric filters. The technique can serve as a robust tool for wide-field surface enhanced Raman imaging. [ABSTRACT FROM AUTHOR]

Photoacoustic Doppler (PAD) power spectra showing an evident Doppler shift represent the major characteristics of the continuous wave-excited or burst wave-excited versions of PAD flow measurements. In this paper, the flow angle dependences of the PAD power spectra are investigated using an experiment setup that was established based on intensity-modulated continuous wave laser excitation. The setup has an overall configuration that is similar to a previously reported configuration, but is more sophisticated in that it accurately aligns the laser illumination with the ultrasound detection process, and in that it picks up the correct sample position. In the analysis of the power spectra data, we find that the background power spectra can be extracted by combining the output signals from the two channels of the lock-in amplifier, which is very useful for identification of the PAD power spectra. The power spectra are presented and analyzed in opposite flow directions, at different flow speeds, and at different flow angles. The power spectra at a 90° flow angle show the unique properties of symmetrical shapes due to PAD broadening. For the other flow angles, the smoothed power spectra clearly show a flow angle cosine relationship. [ABSTRACT FROM AUTHOR]

Under the usual approximation of treating a biological particle as a spheroidal droplet, we consider the analysis of its size and shape with the high frequency photoacoustics and develop a numerical method which can simulate its characteristic photoacoustic waves. This numerical method is based on the calculation of spheroidal wave functions, and when comparing to the finite element model (FEM) calculation, can reveal more physical information and can provide results independently at each spatial points. As the demonstration, red blood cells (RBCs) and MCF7 cell nuclei are studied, and their photoacoustic responses including field distribution, spectral amplitude, and pulse forming are calculated. We expect that integrating this numerical method with the high frequency photoacoustic measurement will form a new modality being extra to the light scattering method, for fast assessing the morphology of a biological particle. [ABSTRACT FROM AUTHOR]

Monitoring the cells' apoptosis progression could provide a valuable insight into the temporal events that initiate cell death as well as the potential for rescue of apoptotic cells. In this paper, we engineered a novel and robust method for monitoring apoptosis of tumor cells based on dynamic laser tweezers, using A549 and HeLa cell line as typical samples. The entire experiment can be completed in a few hours with small amount of fluid sample, presenting great advantages of celerity, microscaled measurement, and label-free explorations without perturbing experimental conditions in combination with other probes. Validity and stability of this method are verified experimentally in terms of physical parameters of the system. The proposed technique has great potential in improving cancer treatment by monitoring the objective efficacy of tumor cell killing. [ABSTRACT FROM AUTHOR]

Mapping near-field profiles and dynamics of surface plasmon polaritons is crucial for understanding their fundamental optical properties and designing miniaturized photonic devices. This requires a spatial resolution on the sub-wavelength scale because the effective polariton wavelength is shorter than free-space excitation wavelengths. Here by combining total internal reflection excitation with surface-enhanced Raman scattering imaging, we mapped at the sub-wavelength scale the spatial distribution of the dominant perpendicular component of surface plasmon fields in a metal nanoparticle-film system through spectrally selective and polarization-resolved excitation of the vertical gap mode. The lateral field-extension at the junction, which is determined by the gap-mode volume, is small enough to distinguish a spot size ∼0.355λ0 generated by a focused radially polarized beam with high reproducibility. The same excitation and imaging schemes are also used to trace near-field nano-focusing and interferences of surface plasmon polaritons created by a variety of plasmon lenses. [ABSTRACT FROM AUTHOR]

Here we investigate theoretically and numerically the coupling between surface plasmon polaritons (SPPs) in monolayer graphene sheet arrays that have a period much smaller than the wavelength. We show that when the collective SPP is excited with an out-of-phase illumination, the beam tends to propagate toward the opposite direction of the Bloch momentum, reflecting a negative coupling between the constituent SPPs. In contrast, for in-phase illumination, the incident beam is split into two collective SPPs that are highly collimated and display low propagation loss. Moreover, the coupling between the individual SPPs results in a reduction of the modal wavelength of the SPP in comparison with that of a single graphene sheet. [ABSTRACT FROM AUTHOR]

Symmetry and topology govern many electronic, magnetic, and photonic phenomena in condensed matter physics and optics, resulting in counterintuitive skyrmion, meron, and other phenomena important for modern technologies. Here we demonstrate photonic spin lattices as a new topological construct governed by the spin-orbit coupling in an optical field. The symmetry of the electromagnetic field in the presence of the spin-orbit interaction may result in only two types of photonic spin lattices: either hexagonal spin-skyrmion or square spin-meron lattices. We show that these spin structures correspond to the lowest energy of the electromagnetic field configuration, therefore, energetically stable. We further show that in the absence of spin-orbit coupling these spin topologies are degenerated in dynamic field skyrmions, unifying the description of electromagnetic field topologies. The results provide a new understanding of electromagnetic field topology and its transformations as well as new opportunities for applications in quantum technologies, spin optics, and topological photonics. [ABSTRACT FROM AUTHOR]

A nanotechnology technique for biophotonics applications is proposed and simulated. The comparison of transmittance spectra of the two-dimensional photonics lattices with different dielectric constant of the circular rods or holes, which show slab structures of two-dimensional photonic lattices composed of a triangular or square array of circular rods or holes, are obviously feasible to be applied for biosensing in lab-on-chip applications. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1171–1175, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22372 [ABSTRACT FROM AUTHOR]

We developed a microfluidic biochip to perform laser guidance on two cell types, chick embryonic forebrain neurons and spinal cord neurons. Observation of neurons under a high-magnification microscope, which we obtained from these two cell types, showed no difference in morphology. However, when flowing in the microfluidic channel and simultaneously being laser guided, the two cell types gained quite different guidance speeds under the same experimental conditions. The results demonstrate that different cell types with the same morphology (e.g., size, shape, etc.) can be effectively distinguished from each other by measuring the difference in guidance speeds (the maximum flow speed minus the initial flow speed). This technique is expected to provide a new approach to high-throughput, label-free cell sorting with high sensitivity. [ABSTRACT FROM AUTHOR]

Mapping the near-field distribution of vector-field components, including those of the electric and magnetic fields, is crucial for understanding the intricate physical processes in the near field. However, imaging the near field of magnetic fields is challenging. We propose a flexible technique for mapping the longitudinal magnetic field using a nano-antenna probe. Unlike traditional techniques for mapping the near field of the magnetic field with a symmetry breaking probe, the magnetic resonances of silicon nanoparticles are analyzed and the directionally scattered light is extracted to reconstruct the longitudinal magnetic field distribution. An artificial mapping system is set up to verify whether the longitudinal magnetic component can be mapped. Using this technique, the conversion of spin angular momentum to orbital angular momentum is also demonstrated. The potential application of this technique is the full vector-field mapping of the electromagnetic fields and the near-field visualization of physical processes. [ABSTRACT FROM AUTHOR]

Optical vortex beams have many potential applications in the particle trapping, quantum encoding, optical orbital angular momentum (OAM) communications and interconnects. However, the on-chip compact OAM detection is still a big challenge. Based on a holographic configuration and a spin-dependent structure design, we propose and demonstrate an on-chip spin-controlled OAM-mode directional coupler, which can couple the OAM signal to different directions due to its topological charge. While the directional coupling function can be switched on/off by altering the spin of incident beam. Both simulation and experimental measurements verify the validity of the proposed approach. This work would benefit the on-chip OAM devices for optical communications and high dimensional quantum coding/decoding in the future. [ABSTRACT FROM AUTHOR]

A metal-dielectric waveguide (MDW) structure working in an aqueous environment was investigated. The energy of the MDW mode is primarily confined near the interface between two dielectric layers, therefore significantly lowering the mode loss comparing with a conventional surface plasmon polariton (SPP), whose energy is concentrated to a metal-dielectric interface. The transfer matrix method was used to analyze the mode characteristics of the MDW structure, showing good agreement with the results obtained by directly solving Maxwell’s equations. Further experiments revealed that the propagation length of evanescent wave accompanying with the MDW mode is approximately one-order of magnitude larger than the SPP mode. This MDW structure in an aqueous environment is expected to be able to overcome the limitations associated with the traditional SPP modes, and to have significant potential for bio-sensing and imaging applications. [ABSTRACT FROM AUTHOR]

Metallic nanoparticle–film gaps are widely used as high-efficiency surface-enhanced Raman scattering (SERS) substrates owing to the plasmonic hybridization of the propagating surface plasmon polaritons on the films and the localized surface plasmons on the nanoparticles. Here, based on both theoretical and experimental studies, we reveal the enhancement mechanism of gap-mode SERS in a single nanoparticle–film gap by comparing the SERS intensity under different incident polarizations. The results demonstrate that the SERS signal can be significantly enhanced under illumination with radial polarization and can be significantly suppressed under azimuthal polarization (as compared with under traditional linear polarization). This is attributed to the distinct longitudinal electric field distributions of the excited surface plasmon polaritons. The results of our work will be of great interest for single-particle SERS research and quantitative molecular detection. [ABSTRACT FROM AUTHOR]