Global transmission diagrams for evanescent waves in a nonlinear hyperbolic metamaterial

A theoretical model of a nonlinear hyperbolic metamaterial is presented in the form of a stack of subwavelength layers of linear plasmonic and nonlinear dielectric materials. A broad picture of the properties of evanescent waves （high-k modes） in this stack is investigated by plotting global transmission diagrams. The presence of nonlinearity strongly modifies these diagrams. The emergence and modification of nonlinear evanescent waves is observed. Some signatures of nonlinear phenomenon such as formation of orbits and trajectories around fixed points are also seen in our work.

Far-field super-resolution imaging by nonlinearly excited evanescent waves

Abbe’s resolution limit,one of the best-known physical limitations,poses a great challenge for any wave system in imaging,wave transport,and dynamics.Originally formulated in linear optics,the Abbe limit can be broken using nonlinear optical interactions.We extend the Abbe theory into a nonlinear regime and experimentally demonstrate a far-field,label-free,and scan-free super-resolution imaging technique based on nonlinear four-wave mixing to retrieve near-field scattered evanescent waves,achieving a sub-wavelength resolution ofλ∕5.6.This method paves the way for numerous new applications in biomedical imaging,semiconductor metrology,and photolithography.

Generation of sub-half-wavelength micro-optical traps by dichroic evanescent standing waves

The bi-dimensional optical lattices formed by several sets of laser evanescent standing waves propagating at the surface of a dielectric prism are investigated. The characteristics of the optical traps including their depths and the sizes are analysed. It is shown that the micro-optical lattice with a sub-half-wavelength size can be achieved by the interference of the selected evanescent waves. The scheme together with the recently developed atomic chip may be used for atomic quantum manipulation.

Disintegration of Linear Edge Waves

It is demonstrated that offshore wavenumbers of edge waves change from imaginary wavenumbers in deep water to real wavenumbers in shallow water. This finding indicates that edge waves in the offshore direction exist as evanescent waves in deep water and as propagating waves in shallow water. Since evanescent waves can stably exist in a limited region while propagating waves cannot, energy should be released from nearshore regions. In the present study, the instability region is predicted based on both the full water wave solution and the shallow-water wave approximation.

Linearly polarised three-colour lasing emission from an evanescent wave pumped and gain coupled fibre laser

A novel Whispering-Gallery-Mode （WGM） fibre laser, emitting linearly polarised three-colour light, is demonstrated by pumping and gain coupling with evanescent waves. The pump light is longitudinally coupled into a bare optical fibre immersed in a dye solution of lower refractive index. The dye molecules around the bare fibre are excited by the evanescent waves of pump light when they propagate along the fibre in a total internal reflection. When the pump beam within the fibre is a meridian beam, the WGM lasing emission from the fibre laser is a linearly polarised transverse electric wave, while it is a mixed wave of the linearly polarised transverse electric and magnetic waves if the pump beam is a skew beam within the fibre. Because the excited molecules are located within the evanescent field of WGM, a good spatial overlap between the dye gain and the evanescent field leads to a high pumping efficiency and a longer gain distance along the fibre. Once the bare fibre is inserted into three glass capillaries filled with Rhodamine 6G, 610 and 640 dye solutions, respectively, WGM laser oscillations at the wavelengths of 567-575, 605-614 and 656-666 nm occur simultaneously, and a linearly polarised three-colour lasing emission is achieved in a single optical fibre.

Near-field characteristics of highly non-paraxial subwavelength optical fields with hybrid states of polarization

The vectorial structure of an optical field with hybrid states of polarization （SOP） in the near-field is studied by using the angular spectrum method of an electromagnetic beam. Physical images of the longitudinal components of evanescent waves are illustrated and compared with those of the transverse components from the vectorial structure. Our results indicate that the relative weight integrated over the transverse plane of the evanescent wave depends strongly on the number of the polarization topological charges. The shapes of the intensity profiles of the longitudinal components are different from those of the transverse components, and it can be manipulated by changing the initial SoP of the field cross-section. The longitudinal component of evanescent wave dominates the near-field region. In addition, it also leads to three-dimensional shape variations of the optical field and the optical spin angular momentum flux density distributions.

The transmission enhancement of a THz pulse through an Ag/Ag_2 O layer detected by terahertz time-domain spectroscopy

This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS （time-domain spectroscopy）. As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500μm-GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening.

Surface-enhanced Raman scattering sensor based on fused biconical taper zone of optical fiber

In this paper, a novel surface-enhanced Raman scattering （SERS） sensor combined with fused biconical taper fiber （FBTF） and film coated with silver sols is proposed. This structure is designed to significantly increase the SERS active surface when the length of the taper is increased and the radius is reduced, since the penetration depth is inversely proportional to the taper radius and proportional to the taper length according to the fiber-optic evanescent-wave theory. Based on the SERS sensing principle, the feasibility of FBTF sensor is analyzed in this paper. As a result, the Raman spectrum of R6G is obtained from the fused biconical taper zone surface coating with the silver sols in our experiments. The detected concentration is up to 10-7mol/L.

Detection of Fuel Adulteration Using Wave Optical with Machine Learning Algorithms

Fuel is a very important factor and has considerable influence on the air quality in the environment,which is the heart of the world.The increase of vehi-cles in lived-in areas results in greater emission of carbon particles in the envir-onment.Adulterated fuel causes more contaminated particles to mix with breathing air and becomes the main source of dangerous pollution.Adulteration is the mixing of foreign substances in fuel,which damages vehicles and causes more health problems in living beings such as humans,birds,aquatic life,and even water resources by emitting high levels of hydrocarbons,nitrogen oxides,and carbon monoxide.Most frequent blending liquids are lubricants and kerosene in the petrol,and its adulteration is a considerable problem that adds to environ-mental pollution.This study focuses on detecting the adulteration in petrol using sensors and machine learning algorithms.A modified evanescent wave opticalfiber sensor with discrete wavelet transform is proposed for classification of adult-erated data from the samples.Furthermore,support vector machine classifier is used for accurate categorization.The sensor isfirst tested with fuel and numerical data is classified based on machine learning algorithms.Finally,the result is eval-uated with less error and high accuracy of 99.9%,which is higher than all existing techniques.

In vivo spatial-spectral photoacoustic microscopy enabled by optical evanescent wave sensing

In addition to offering morphological visualizations via capture of the spatial distributions of optical absorption,photoacoustic imaging technology can reveal abundant physical information about biological particles,including their orientation,density,and viscoelasticity,through analysis of the pressure transients in the spectral domain.However,the low-amplitude wideband photoacoustic signals of intrinsic microscopic optically-absorbing objects under the action of confined photoacoustic excitation power continue to hinder simultaneous photoacoustic structural imaging and spectroscopic analysis of the nonfluorescent chromophores in living biological tissues because of the inadequate responses to photoacoustic impulses observed in most photoacoustic imaging setups that include piezoelectric transducers.Building upon a recently-developed optical evanescent wave sensor that can respond to ultrasound with high sensitivity over a broad frequency range,we propose in vivo spatial-spectral photoacoustic microscopy for recovery of structural imaging in three dimensions and characterization of anatomical features in the acoustic frequency domain.Label-free photoacoustic images of a living zebrafish are acquired in which spectroscopically-resolved differentiation of the microarchitecture is accessed,along with isometric micrometer-scale volumetric visualizations.The proposed imaging technology could potentially provide more comprehensive evaluations of the physiopathological status of living small animals.

A Micro Structure POF Relative Humidity Sensor Modified With Agarose Based on Surface Plasmon Resonance and Evanescent Wave Loss

A novel high sensitivity relative humidity(RH)sensor was proposed by using micro structure plastic optical fiber(POF)based on the surface plasmon resonance(SPR)effect and the evanescent wave(EW)loss.The micro structure was fabricated on the POF and coated with a gold layer and agarose,adopting the sputtering and dip-coating technique.These construction effects on the attenuation of power caused by the SPR effect and the EW loss were used to perform RH detections.The agarose9s different refractive indexes(RIs)caused fluctuations in the transmission power when the humidity increased.The demonstrated experimental results showed that the proposed sensor achieved a linear response from 20%RH to 80%RH with a high sensitivity of 0.595μW/%.The proposed sensor had the advantages of fast response and recovery.Furthermore,the temperature dependence and the repeatability test of the sensor were also performed.

Optimization of evanescent wave imaging for the visualization of protein adsorption layers

We have optimized the settings of evanescent wave imaging for the visualization of a protein adsorption layer.The enhancement of the evanescent wave at the interface brought by the incident angle,the polarized state of light beam as well as a gold layer is considered.In order to improve the image contrast of a protein monolayer in experiments,we have optimized three factors- the incident angle,the polarization of light beam,and the thickness of an introduced thin gold layer with a theoretical simulation.

Organic semiconductors-coated polyacrylonitrile(PAN) electrospun nanofibrous mats for highly sensitive chemosensors via evanescent-wave guiding effect

We report the first use of organic semiconductors （OSCs）-coated PAN nanofibrous mats as highly responsive fluorescence quenching-based chemosensors for 2,4,6-trinitrotoluene （TNT） and H2O2 detection in vapor phase. Conjugated polymers, poly（triphenylaminealt-biphenylene vinylene） （TPA- PBPV）, and small organic molecules, l-horonic-ester pyrene and 1,6-bisboron-ester pyrene, were coated onto the nanofibers fabricated by electrospinning. By introducing the nanofibers structure, a 9-fold fluorescence intensity enhancement and a 14-fold sensitivity enhancement were achieved, which could be attributed to its high area-to-volume ratio, excellent gas permeability, and more importantly, the evanescent-wave effect occurred once the diameters of the fibers were small enough. Since the organic semiconductors coated onto the nanofibrous mats could be replaced by other functional materials, the nanofibers-enhanced detection strategies could be extended to more general domains including chemical and environmental detection.

Evanescent Wave Absorption Sensor Based Tapered Plastic Optical Fiber Coated with Monolayer Graphene for Ethanol Molecules Detection

An evanescent wave absorption （EWA） sensor based tapered plastic optical fiber （TPOF） coated with monolayer graphene film for ethanol molecules detection is demonstrated in this study. The continuous and monolayer graphene films were grown on a Cu foil by using chemical vapor deposition （CVD） technology. Polymethyl methacrylate （PMMA） was used as the carrier to support the transfer of graphene from Cu foil to the skinless tapered optical fiber core. The accuracy of the TPOF sensor with graphene （G-TPOF sensor） is much higher than that without gra- phene （TPOF sensor）, which can be attributed to the molecules enriched on the surface of graphene. The absorbance （A） and the concentrations of ethanol solution show an excellent proportional relationship in a range of 0--100%. The dynamic response of the G-TPOF sensor has shown strong reversibility, repeatability and stability at room temperature. The response time and recovery time of the G-TPOF sensor for different concentrations are all less than 30 s. Beyond that, we selected the Chinese liquor as the analyte, and the results are consistent with the concen- tration-list obtained in the experiment.

Flexible Evanescent Wave Interference Lithography System for Sub-half-Wavelength Complex Relief Structures Fabrication

Surface microstructures impart various useful properties to objects,for example,improving optical characteristics,wettability,and sliding properties.It is well known that biomimicking relief structures are effective in making such properties arise and have been studied to be applied to various devices.Furthermore,they are expected to be utilized not only for improving a particular property but also for adding more complex functions on a device's urface by fabricating different multi-functional structures on a single surface in the future.However,to begin with,artificially fabricating such biomimicking special functional relief is difficult.One typical feature of biomimicking surfaces is the dual-scale structure,the smaller one of which is less than 200 nm.Moreover,in the case of realizing the more complex devices,it is necessary to fabricate various forms as changing process conditions dynamically.In this study,we proposed and developed a flexible evanescent wave interference lithography system as a novel fabrication method,which allows us to realize the fabrication of sub-half-wavelength complex relief structures.Firstly,we theoretically analyzed the fundamental behavior of the fabricated structure and found that the proposed concept has the potential to realize one of the target complex structures.Secondly,we developed the proposed system with high process flexibility,in which the number of beams,the azimuth angles,and the polarization can be simply manipulated.Finally,we validated the concept of the designed system by some experiments,where we fabricated dual-scale structures with 840-nm and 190-nm fringe patterns simultaneously.

Highest Achievable Detection Range for SPR Based Sensors Using Gallium Phosphide （GAP） as a Substrate： a Theoretical Study

In the present study, we have theoretically modelled a surface plasmon resonance （SPR） based sensing chip utilizing a prism made up of gallium phosphidee. It has been found in the study that a large range of refractive index starting from the gaseous medium to highly concentrated liquids can be sensed by using a single chip in the visible region of the spectrum. The variation of the sensitivity as well as detection accuracy with sensing region refractive index has been analyzed in detail. The large value of the sensitivity along with the large dynamic range is the advantageous feature of the present sensing probe.

From microscopy to nanoscopy via visible light

The resolution of conventional optical equipment is always restricted by the diffraction limit,and improving on this was previously considered improbable.Optical super-resolution imaging,which has recently experienced rapid growth and attracted increasing global interest,will result in applications in many domains,benefiting fields such as biology,medicine and material research.This review discusses the contributions of different researchers who identified the diffractive barrier and attempted to realize optical super-resolution.This is followed by a personal viewpoint of the development of optical nanoscopy in recent decades and the road towards the next generation of optical nanoscopy.

ERROR ESTIMATION FOR NUMERICAL METHODS USING THE ULTRA WEAK VARIATIONAL FORMULATION IN MODEL OF NEAR FIELD SCATTERING PROBLEM

In this paper, we investigate the use of ultra weak variational formulation to solve a wave scattering problem in near field optics. In order to capture the sub-scale features of waves, we utilize evanescent wave functions together with plane wave functions to approximate the local properties of the field. We analyze the global convergence and give an error estimation of the method. Numerical examples are also presented to demonstrate the effectiveness of the strategy.

High-responsivity 40 Gbit/s InGaAs/InP PIN photodetectors integrated on silicon-on-insulator waveguide circuits

This paper presents a high-responsivity and high-speed InGaAs/InP PIN photodetector integrated onto the silicon waveguide substrate utilizing the divinyltetramethyldisiloxane-benzocyclobutene （DVS-BCB） adhesive bonding method. A grating coupler is adopted to couple light from the fiber to the silicon waveguide. Light in the silicon photonic waveguide is evanescently coupled into the photodetector. The integrated photodetector structure is first simulated using the FDTD （finite difference time domain） solutions software and the simulation results show a detection efficiency of 95%. According to the simulation result, the integrated photodetector is fabricated. The measured responsivity of the fabricated integrated photodetector with a detection length of 30μm is 0.89 A/W excluding the coupling loss between the fiber and the grating coupler and the silicon propagation loss at the wave-length of 1550 nm with a reverse bias voltage of 3 V. Measured 3-dB bandwidth is 27 GHz using the Lightwave Component Analyzer （LCA）. The eye diagram signal test results indicate that the photodetector can operate at a high speed of 40 Gbit/s. The integrated photodetector is of great significance in the silicon-based optoelectronic integrated chip which can be applied to the optical communication and the super node data transmission chip of the high-performance computer.

Chip-compatible wide-field 3D nanoscopy through tunable spatial frequency shift effect

Spatial frequency shift(SFS) microscopy with evanescent wave illumination shows intriguing advantages, including large field of view(FOV), high speed, and good modularity. However, a missing band in the spatial frequency domain hampers the SFS superresolution microscopy from achieving resolution better than 3 folds of the Abbe diffraction limit. Here, we propose a novel tunable large-SFS microscopy, making the resolution improvement of a linear system no longer restricted by the detection numerical aperture(NA). The complete wide-range detection in the spatial frequency domain is realized by tuning the illumination spatial frequency actively and broadly through an angle modulation between the azimuthal propagating directions of two evanescent waves. The vertical spatial frequency is tuned via a sectional saturation effect, and the reconstructed depth information can be added to the lateral superresolution mask for 3D imaging. A lateral resolution of λ/9, and a vertical localization precision of ~λ/200(detection objective NA = 0.9) are realized with a gallium phosphide(GaP) waveguide. Its unlimited resolution enhancing capability is demonstrated by introducing a designed metamaterial chip with an unusual large refractive index. Besides the great resolution enhancement, this method shows better anti-noise capability than classical structured illumination microscopy without SFS tunability. This method is chip-compatible and can potentially provide a massproducible illumination chip module achieving the fast, large-FOV, and deep-subwavelength 3D nanoscopy.