Showing papers on "Total internal reflection published in 2012"

Complete optical absorption in periodically patterned graphene.

Abstract: We demonstrate that 100% light absorption can take place in a single patterned sheet of doped graphene. General analysis shows that a planar array of small particles with losses exhibits full absorption under critical-coupling conditions provided the cross section of each individual particle is comparable to the area of the lattice unit cell. Specifically, arrays of doped graphene nanodisks display full absorption when supported on a substrate under total internal reflection and also when lying on a dielectric layer coating a metal. Our results are relevant for infrared light detectors and sources, which can be made tunable via electrostatic doping of graphene.

Room temperature sub-diffraction-limited plasmon laser by total internal reflection

Abstract: Plasmon lasers can operate at dimensions well below the diffraction limit. Their small size promises uses in nanophotonic circuits and for other size-critical applications. The demonstration of a sub-diffraction-limited plasmon laser with low losses, which enables its room-temperature operation, takes a significant step towards realizing the potential of these lasers.

High-Q optical sensors for chemical and biological analysis.

Abstract: Optical sensors represent a vitally important class of analytical tools that have been used to provide chemical information ranging from analyte concentration and binding kinetics to microscopic imaging and molecular structure. Optical sensors utilize a variety of signal transduction pathways based on photonic attributes that include absorbance, transmission, fluorescence intensity, refractive index, polarization, and reflectivity. Within the broad classification of optical sensors, refractive index (RI) sensors, which include devices such as surface plasmon resonance instruments, interferometers, diffraction gratings, optical fibers, photonic crystals, and resonant microcavities, have emerged as promising technologies over the past two decades. These optical sensors based on the change in RI associated with analyte binding involve an impressive array of instrumentation that allows for label-free1 molecular sensing without the added complexity of fluorescent or enzymatic tags. By removing the requirement for labels, RI-based sensing allows for real-time and direct detection of molecular interactions at a dielectric interface. Though many manifestations of RI-based sensors have been proposed and demonstrated, high-quality factor (high-Q) optical sensors based on multi-pass photonic microstructures have recently emerged as an extremely promising, and perhaps the most sensitive, class of label-free sensors. Major advantages of many high-Q sensors include multiple-pass interactions between the propagating electromagnetic radiation and the respective analyte binding event, as well as the intrinsic chip-integration and wafer-scale fabrication that accompany many semiconductor-based sensing modalities. High-Q optical sensors involve microstructures that confine light due to differences in RI between a micropatterned material and its surrounding. This confinement supports multi-pass light interactions based on either multiple reflections or many circumnavigations. In both cases, this results in an increased effective optical path length that improves the sensitivity of the device. The Q factor of a given device is a measure of the resonant photon lifetime within a microstructure (higher Q factor = longer lifetime), and therefore Q is directly correlated to the number of times a photon is recirculated and allowed to interact with the analyte.2 Light is confined by either total internal reflection at a core/cladding interface (microcavities) or by the spatially periodic modulation of materials with different RI properties (photonic crystals), and resultant high-Q sensors interact with their local environments via an evanescent optical field that extends from the sensor surface and decays exponentially with distance.3, 4 A more detailed treatment of microcavity technology involving whispering gallery mode (WGM) sensing will be presented in the following section. High-Q optical sensors, whether based on guided-mode optics or photonic crystal (PC) structures, support resonances at very specific wavelengths, and these resonances are responsive to changes in the effective RI at the device surface. For most microcavity sensors, the wavelengths of light transmitted between an adjacent waveguide or optical fiber and the cavity is attenuated at narrow resonant wavelengths that are a function of the RI at the microcavity surface; for most PC sensors, light is back-reflected only at precise resonance wavelengths. As the Q factor of a device increases, the photon lifetime increases, and the resonance wavelength peak becomes narrower. For both microcavity and PC sensors, the relative shift in resonance wavelengths is directly proportional to the effective RI sampled by the confined optical mode, which samples the dielectric interface via the evanescent wave extending from the sensor surface. Since most analytes, such as organic (bio)molecules in water or gases in air, have a greater dielectric permittivity (and thus higher RI) than the surrounding medium, their binding or association with the sensor surface leads to an increase in effective RI sampled by the optical mode.4 Though factors such as biological and spectroscopic noise often set the practical limit of detection for any sensor system, the narrow resonance wavelengths associated with high-Q cavities provide an opportunity to resolve tiny spectral shifts that accompany a very small number of analyte binding interactions. The impressive sensitivity of microcavity and PC devices to minute changes in the effective RI at the sensor surface is the basis for most of the recent applications of high-Q optical sensors. The development of high-Q photonic devices has been tremendously enabled by recent advances in micro- and nanofabrication methods, and the application of these devices for chemical and biomolecular analysis has only come to fruition within the past decade. This review focuses on the most exciting research in this area over the period of 2009–2011, although enabling findings and developments that precede this range are also covered. Recent reviews have summarized advances that may include some treatment of high-Q sensors, but these reviews have been broadly focused on advances in label-free sensors in general,5–8 on applications of silicon photonics that include sensing among many others,9 or on a general treatment of optical devices for sensing that includes the devices of interest.10–13 Other excellent reviews are more narrowly focused and cover different aspects of high-Q technology, focusing specifically on ring resonator technology,14, 15 microsphere resonators,16 photonic crystals,4, 17 microfluidic integration with optical sensors,18, 19 and high-Q mechanical sensors.20 This review considers recent advances in high-Q and ultra-high-Q optical sensors for addressing fundamental challenges in measurement science, giving special attention to those techniques that demonstrate useful chemical or biomolecular measurement capabilities within relevant real-world matrices. Although not rigorously fitting within some strict definitions of high-Q devices, photonic crystal sensors are covered as they represent an exciting complementary technology that, in many ways, is more advanced at present than many high-Q microcavity sensor configurations. As this review is intended to target the broad community of practicing analytical chemists, particular focus is given to signal transduction mechanisms, surface chemistry, assay methodologies, and interesting new measurement applications, leaving detailed explanations of device optics and engineering to other, more topical reviews21, 22 and the collection of articles from the optics community cited herein. Specifically, this review will briefly discuss the theoretical basis of high-Q optical sensing, including the multitude of sensor geometries within the category of multi-pass optical sensors. Recent advances in high-Q sensor surface chemistry, capture agent immobilization, assay design, and amplification techniques are covered, as well as interesting demonstrations of these technologies in impact areas such as quantitative detection, affinity profiling, multiplexed sensing, nanoparticle analysis, light manipulation, lasers, thermal sensing, and integrated detection techniques. Finally, we provide our own critical analysis of the field in general, offering thoughts on areas in which improvements are most needed to inform the future outlook and reach the goals of high-Q optical sensing.

Design of Novel Compound Fresnel Lens for High-Performance Photovoltaic Concentrator

Abstract: We present a new design of compound Fresnel-R concentrator which is composed of two lenses: a primary lens (Fresnel lens) that works by total internal reflection at outer sawteeth but refraction at inner sawteeth, and a ringed secondary lens that works by refraction. In contrast to previous Fresnel lens concentrators, this design increases the acceptance angle, improves the irradiance uniformity on the solar cell, and reduces the aspect ratio significantly. Meanwhile several sawteeth of the primary Fresnel lens can correspond to a same ring of secondary lens, which will efficiently lower the complexity of designing and manufacturing. Moreover, in order to reduce the influence of manufacturing tolerances and to increase the optical efficiency further, the central part of the bottom of the secondary lens which directly adhered to the solar cell is designed as a cone-shaped prism to collect the sunlight that does not reach the solar cell. Finally, we provide simulations and analyses of the design method an optical efficiency more than 80% and an aspect ratio smaller than 0.5 can be achieved.

An Introduction to Integrated Optics

Abstract: 1 General Background Review.- 1. Maxwell's Equations.- 2. Definitions of Various Types of Medium.- 3. Wave Equation.- 4. Description of Other Material Parameters.- 5. Boundary Conditions.- 6. Fresnel Equations.- 7. Special Examples.- 8. Separation of Longitudinal and Transverse Coordinates.- 9. Definition of Various Types of Modes.- 2 Film-Waveguides and Zig Zag Waves.- I. An Introduction of Film-Waveguides-Zig Zag Waves.- (i) Dual Concept of Ray and Wave Optics.- (ii) The A and B Waves.- (iii) Electric and Magnetic Field.- (iv) Waveguide Modes and the Total Reflection Phenomenon.- (v) Field Distribution of a Waveguide Mode.- (vi) Effective Thickness of the Waveguide and Power Flow.- (vii) Different Waveguide Modes.- II Prism-Film Couplers and Zig Zag Waves.- III Materials for Film-Waveguides and Their Losses.- 3 One-Dimensional Confinement.- 1. Guided Modes of a Slab Waveguide.- 2. Graphical Solution of the Governing Transcendental Equations.- 3. Dispersion in Thin Films.- 4 Rectangular Dielectric Waveguides.- I Introduction.- II Marcatili's Analysis.- III Circular Harmonic Analysis.- A. Analysis.- B. Computed Results.- 1. Mode Configurations.- 2. Propagation Curves.- IV Comparison of Methods.- 5 Loss Mechanisms in Dielectric Waveguides.- I Introduction.- II Radiation Loss.- III Bend Loss.- A. Velocity Approach.- B. Model Analysis.- 6 Thin-Film Waveguide Fabrication and Testing Considerations.- I Introduction.- II Dimensional Considerations.- III Circuit Fabrication.- A. Etched Waveguide Fabrication.- 1. Masking and Etching.- 2. Summary of Process.- 3. Results.- B. Ion Bombardment Fabrication.- IV Measurement Techniques.- A. Determination of Refractive Index and Thickness.- 1. Stylus Measurements.- 2. Interferometer.- 3. Abbe Refractometer.- 4. Abeles Method.- 5. Prism Coupler Method.- B. Attenuation Measurements.- V Conclusion.- 7 Electron and Ion Beam Microfabrication of Integrated Optics Elements.- Electron Beam Micropattern Definition and Fabrication.- Ion Beam Sputtering for Micropattern Processing.- Scanning Electron Microscopy.- Results of Beam Microfabrication.- Conclusions and Summary.- 8 Introduction to Optical Waveguide Fibers.- I Propagation.- 1.1 Ray Theory.- 1.2 Rays in Step Refractive Index Waveguides.- 1.3 Ray Theory for Gradient Refractive Index Waveguides.- 1.4 Mode Theory.- 1.5 Mode Theory of Step Refractive Index.- 1.6 Mode Theory of Gradient Refractive Index Fibers.- II Information Capacity.- 2.1 Pulse Broadening in Single Mode Fibers.- 2.2 Pulse Broadening in Multimode Fibers.- III Attenuation.- 9 Fiber Optics Applications.- 1. Systems Applications.- 2. Near Term Fiber Optic Data Links.- 3. Input Coupling Losses.- 10 Coupled Mode Formalism for Guided Wave Interactions.- 1. Coupled Mode Formalism.- 2. Coupling Equation.- 3. Nonlinear Interactions.- 4. Photoelastic Coupling.- 5. Coupling by a Surface Corrugation.- 6. Eigen Modes of a Perturbed Waveguide.- 11 Optical Directional Couplers.- 1. Introduction.- 2. Coupled Mode Formalism.- 3. Dual Channel Directional Coupler - Theory and Experiment.- 4. Derivation of the Coupling Coefficient.- 5. Coupling Between Planar Guides.- 6. Coupling Between Channel Guides.- 7. Multichannel Directional Coupler - Coupling Coefficient Measurement.- 8. The Coupling Coefficient Sign.- 9. Ridged Channel Waveguides and Directional Couplers.- 10. Directional Coupler - Switch Modulator.- 11. Light Multiplexing by Directional Coupling.- 12. Appendix I.- 12 Periodic Couplers.- I Introduction.- II Direct Analysis of Beam Coupling.- II.1 Spectral Representation of Electromagnetic Waves.- II.2 The Prism Coupler.- II.3 Fields in the Periodic Medium.- II.4 Fields in the Coupler.- III Reciprocal Analysis of Periodic Couplers.- III.1 The Equation for Coupling Efficiency.- III.2 Aperture Fields.- IV Design Considerations.- 13 Modulation.- 1. Introduction.- 2. Modulation Analysis.- 3. Modulator Characteristics.- 4. Characteristics of Other Modulation Techniques.- 5. Circuit Aspects of Modulators.- 6. An Example.- 14 Acousto-Optical Interactions in Guided Wave Structures.- I Introduction.- II Reviews of Acousto-Optic Interactions.- 2.1 Photoelastic Effect.- 2.2 Acousto-Optic Interaction Mechanisms.- III Acousto-Optic Interaction in Guided Wave Structure - Analysis.- 3.1 Acoustic Surface Waves and Optical Guided Waves.- 3.2 Collinear Interaction of Optical Guided Waves and Acoustic Surface Waves.- 3.3 Bragg Diffraction of Optical Guided Waves by Acoustic Surface Waves.- IV Acousto-Optic Interactions in Guided Wave Structures - Experimental Results and Discussions.- 4.1 Collinear Interaction.- 4.2 Bragg Deflection of Optical Guided Waves by Acoustic Surface Waves.- 4.3 Anisotropic Light Diffraction by Acoustic Surface Waves.- V Device Parameters for Acousto-Optic Devices.- 5.1 Efficiency.- 5.2 Bandwidths and Number of Resolvable Spots.- 5.3 Speed.- 5.4 Figures of Merit.- VI Device Applications and Conclusions.- 15 Laser Source Considerations in Integrated Optics.- I Introduction.- II Resonant Feedback Structures.- A. Dispersion Relations for Periodic Structures.- B. Lasers Using Periodic Structures as the Distributed Resonant Feedback Structure (DFB Lasers).- C. Lasers Using Periodic Structures as the Resonant Reflectors in the Fabry-Perot Type of Cavities.- D. Order-of-Magnitude Estimates.- III The Active Medium.- A. Dye Lasers.- B. Semiconductor Lasers.- C. Doped Insulating Solids.- D. Gaseous Lasers.- Appendix - Derivation of Eqs. (5) and (13).

Reflection distributions of textured monocrystalline silicon: implications for silicon solar cells

Abstract: A common misconception is that alkaline textured silicon solar cell surfaces are characterised by features that are pyramidal and bounded by {111} planes. In preference to the typical approach of observing scanning electron microscope images, we analyse reflection distributions from various pyramidal textures and find that {111} faceted pyramids are a poor approximation to the features on such surfaces. We conclude that features are hillocks, with an octagonal base. Furthermore, the characteristic base angle of the texture depends on the etchant and is closer to 50–52° than the commonly accepted value of 54.74°. Analyses of antireflection, light trapping, photogeneration and surface recombination properties of textured surfaces should take this feature morphology into account. The base angle has a strong influence on the hemispherical reflectance of the textured surface, with higher angles resulting in reduced reflectance. The influence of this reflection enhancement upon device performance is smallest when an optimised antireflection coating is applied; compared with an array of {111} faceted pyramids, a hillock morphology with 50° base angle results in a 0.2% reduction in photogenerated current in a typical cell. Additionally, as base angle is reduced, an encapsulant of increasingly higher refractive index is required to drive internal reflection at the air–glass interface of light initially reflected from the cell surface. The development of texturing processes resulting in higher base angles is encouraged. Copyright © 2012 John Wiley & Sons, Ltd.

Excitation of surface electromagnetic waves in a graphene-based Bragg grating

Abstract: Here, we report the fabrication of a graphene-based Bragg grating (one-dimensional photonic crystal) and experimentally demonstrate the excitation of surface electromagnetic waves in the periodic structure using prism coupling technique. Surface electromagnetic waves are non-radiative electromagnetic modes that appear on the surface of semi-infinite 1D photonic crystal. In order to fabricate the graphene-based Bragg grating, alternating layers of high (graphene) and low (PMMA) refractive index materials have been used. The reflectivity plot shows a deepest, narrow dip after total internal reflection angle corresponds to the surface electromagnetic mode propagating at the Bragg grating/air boundary. The proposed graphene based Bragg grating can find a variety of potential surface electromagnetic wave applications such as sensors, fluorescence emission enhancement, modulators, etc.

Mode conversion behavior of SH guided wave in a tapered plate

Abstract: The present study explores mode conversion of shear horizontal (SH) guided wave when it impinges on smooth defects in plates. The fundamental (SH 0 ) and the first higher (SH 1 ) modes were selectively generated by an electromagnetic acoustic transducer in aluminum plates and the propagating modes at various points were detected by a pinducer. The defects had a flat bottom region and tapered edges. Remaining thickness at the bottom defected region was smaller than the so-called cut-off thickness of SH 1 mode. Both modes exhibited unique mode conversion behaviors in tapered edge, which were interpreted with the dispersion relation. Total reflection of SH 1 mode was also observed at a specific condition. Numerical simulation revealed that the continuous wavenumber change in the tapered region and the consequent zero value at cut-off thickness cause this total reflection.

Coexistence of positive and negative refractive index sensitivity in the liquid-core photonic crystal fiber based plasmonic sensor

Abstract: We present and numerically characterize a liquid-core photonic crystal fiber based plasmonic sensor. The coupling properties and sensing performance are investigated by the finite element method. It is found that not only the plasmonic mode dispersion relation but also the fundamental mode dispersion relation is rather sensitive to the analyte refractive index (RI). The positive and negative RI sensitivity coexist in the proposed design. It features a positive RI sensitivity when the increment of the SPP mode effective index is larger than that of the fundamental mode, but the sensor shows a negative RI sensitivity once the increment of the fundamental mode gets larger. A maximum negative RI sensitivity of -5500nm/RIU (Refractive Index Unit) is achieved in the sensing range of 1.50-1.53. The effects of the structural parameters on the plasmonic excitations are also studied, with a view of tuning and optimizing the resonant spectrum.

Topological Aberration of Optical Vortex Beams: Determining Dielectric Interfaces by Optical Singularity Shifts

Abstract: We predict the splitting of a high-order optical vortex into a constellation of unit vortices, upon total internal reflection of the carrier beam, and analyze the splitting. The reflected vortex constellation generalizes, in a local sense, the familiar longitudinal Goos-Hanchen and transverse Imbert-Fedorov shifts of the centroid of a reflected optical beam. The centroid shift is related to the center of the constellation, whose geometry otherwise depends on higher-order terms in an expansion of the reflection matrix. We derive an approximation of the amplitude around the constellation as a complex analytic polynomial, whose roots are the vortices. Increasing the order of the initial vortex gives an Appell sequence of complex polynomials, which we explain by an analogy with the theory of optical aberration.

Design, manufacturing, and performance analysis of mid-infrared achromatic half-wave plates with diamond subwavelength gratings

Abstract: In this paper, we present a solution for creating robust monolithic achromatic half-wave plates (HWPs) for the infrared, based on the form birefringence of subwavelength gratings (SWGs) made out of diamond. We use the rigorous coupled wave analysis to design the gratings. Our analysis shows that diamond, besides its outstanding physical and mechanical properties, is a suitable substrate to manufacture mid-infrared HWPs, thanks to its high refractive index, which allows etching SWGs with lower aspect ratio. Based on our optimized design, we manufactured a diamond HWP for the 11-13.2 μm region, with an estimated mean retardance ~3.143±0.061 rad (180.08±3.51°). In addition, an antireflective grating was etched on the backside of the wave plate, allowing a total transmittance between 89% and 95% over the band.

Optical characterisation of 3-D static solar concentrator

Abstract: The focus of this research is to develop a solar concentrator which is compact, static and, at the same time, able to collect maximum solar energy. A novel geometry of a 3-D static concentrator has been designed and coined the Square Elliptical Hyperboloid (SEH) to be integrated in glazing windows or facades for photovoltaic application. The 4× SEH is optically optimised for different incident angles of the incoming light rays. The optimised SEH is obtained by investigating its different non-dimensional parameters such as major axis over minor axis of the elliptical entry and the height over side of the exit aperture. Evaluating the best combination of the optical efficiency and the acceptance angle, results confirm that the 4× SEH built from dielectric material, working with total internal reflection, is found to have a constant optical efficiency of 40% for an acceptance angle equal to 120° (−60°, +60°). This enables capture of the sun rays all day long from both direct beam light and diffuse light making it highly suitable for use in northern European countries. A higher optical efficiency of 70% is obtained for different dimensions of the SEH; however, the acceptance angle is only 50°. The optimised SEH concentrator has been manufactured and tested; the experimental results show an agreement with the simulation results thus validating the optical model.

Sensitive Real-Time Monitoring of Refractive Indexes Using a Novel Graphene-Based Optical Sensor

Abstract: Based on the polarization-sensitive absorption of graphene under conditions of total internal reflection, a novel optical sensor combining graphene and a microfluidic structure was constructed to achieve the sensitive real-time monitoring of refractive indexes. The atomic thickness and strong broadband absorption of graphene cause it to exhibit very different reflectivity for transverse electric and transverse magnetic modes in the context of a total internal reflection structure, which is sensitive to the media in contact with the graphene. A graphene refractive index sensor can quickly and sensitively monitor changes in the local refractive index with a fast response time and broad dynamic range. These results indicate that graphene, used in a simple and efficient total internal reflection structure and combined with microfluidic techniques, is an ideal material for fabricating refractive index sensors and biosensor devices, which are in high demand.

Photonic jets from resonantly excited transparent dielectric microspheres

Abstract: We report on the theoretical investigations of the near-field diffraction patterns from micrometer-sized spherical dielectric particles illuminated by a light wave upon the excitation of morphology-dependent resonances in the internal field. The specific spatial area, which constitutes the so-called photonic jet (PJ), is studied. The longitudinal and transverse dimensions of the PJ are calculated along with its peak intensity as a function of the distance from a particle. The numerical calculations show that at a resonance depending on its quality factor, the PJ can “stick” to the particle; its intensity can increase to a several orders of magnitude, and its width can decrease but mostly near the microsphere surface. The average length of the PJ remains nearly unchanged.

Design Rule of Nanostructures in Light‐Emitting Diodes for Complete Elimination of Total Internal Reflection

Abstract: Cone-shaped nanostructures with controllable side-wall angle are success- fully fabricated with a SiO(2) nanosphere lithography (NSL) etching mask. Vertical LEDs with cone-shaped nanostructures with a 24.1° side-wall angle provide 6% more light output power compared to those using hexagonal pyramids formed by photochemical etching. This achievement is attributed to effective elimination of total internal reflection by angle-controlled nanostructures.

Nearly three orders of magnitude enhancement of Goos-Hanchen shift by exciting Bloch surface wave.

Abstract: Goos-Hanchen effect is experimentally studied when the Bloch surface wave is excited in the forbidden band of a one-dimensional photonic band-gap structure. By tuning the refractive index of the cladding covering the truncated photonic crystal structure, either a guided or a surface mode can be excited. In the latter case, strong enhancement of the Goos-Hanchen shift induced by the Bloch-surface-wave results in sub-millimeter shifts of the reflected beam position. Such giant Goos-Hanchen shift, ~750 times of the wavelength, could enable many intriguing applications that had been less than feasible to implement before.

On the Role of Fresnel Factors in Sum-Frequency Generation Spectroscopy of Metal–Water and Metal-Oxide–Water Interfaces

Abstract: We performed sum-frequency generation (SFG) spectroscopic measurements on water in contact with supported thin metal and metal-oxide films. We employed an internal reflection configuration and varied the angles of incidence of the visible and infrared beams and measured the SFG signals using different polarization combinations. While SFG is a surface-specific vibrational spectroscopy, the shape of the SFG spectra can be fully accounted for by the bulk response of the materials through the frequency-dependent enhancement of the local incident infrared fields at the interface, i.e., Fresnel effects. We find that the dispersion of the refractive index of the bulk water phase leads to a strong enhancement of the electric field at the interface at specific infrared frequencies. These local, frequency-dependent fields act on the frequency-independent, nonresonant SFG response of the electrons at the surfaces of the metal or metal-oxide films. As a result, the measured SFG spectra closely follow this infrared fr...

A 3D glass optrode array for optical neural stimulation

Abstract: This paper presents optical characterization of a first-generation SiO2 optrode array as a set of penetrating waveguides for both optogenetic and infrared (IR) neural stimulation. Fused silica and quartz discs of 3-mm thickness and 50-mm diameter were micromachined to yield 10 × 10 arrays of up to 2-mm long optrodes at a 400-μm pitch; array size, length and spacing may be varied along with the width and tip angle. Light delivery and loss mechanisms through these glass optrodes were characterized. Light in-coupling techniques include using optical fibers and collimated beams. Losses involve Fresnel reflection, coupling, scattering and total internal reflection in the tips. Transmission efficiency was constant in the visible and near-IR range, with the highest value measured as 71% using a 50-μm multi-mode in-coupling fiber butt-coupled to the backplane of the device. Transmittance and output beam profiles of optrodes with different geometries was investigated. Length and tip angle do not affect the amount of output power, but optrode width and tip angle influence the beam size and divergence independently. Finally, array insertion in tissue was performed to demonstrate its robustness for optical access in deep tissue.

Fluorescence excitation and imaging of single molecules near dielectric-coated and bare surfaces: a theoretical study.

Abstract: Summary Microscopic fluorescent samples of interest to cell and molecular biology are commonly embedded in an aqueous medium near a solid surface that is coated with a thin film such as a lipid multilayer, collagen, acrylamide, or a cell wall Both excitation and emission of fluorescent single molecules near film-coated surfaces are strongly affected by the proximity of the coated surface, the film thickness, its refractive index and the fluorophore’s orientation For total internal reflection excitation, multiple reflections in the film

Efficient polarized directional backlight

Abstract: By introducing a stack of alternating high and low index dichroic material layers on the exit surface of a waveguide for a wedge type directional backlight, natural reflectivity differences between polarized components can be increased, effectively reflecting the vast proportion of S-polarized light rays, while at the same time transmitting the P-polarized light rays, of light impacting the exit surface of the waveguide at an angle sufficient to exit the waveguide. This recovers polarization in wedge type backlight systems, increasing illumination exiting the waveguide. Also, on the back reflecting surface of the waveguide, a birefringent material can be added to efficiently transform S-polarized reflected light from the dichroic stack, into returning P-polarized light. Because returning rays that are now P-polarized by the birefringent material have already achieved the critical angle for exiting the waveguide, the rays transformed to P-polarization can now also exit the waveguide, increasing waveguide illumination.

Characterization of a 3D optrode array for infrared neural stimulation.

Abstract: This paper characterizes the Utah Slant Optrode Array (USOA) as a means to deliver infrared light deep into tissue. An undoped crystalline silicon (100) substrate was used to fabricate 10 × 10 arrays of optrodes with rows of varying lengths from 0.5 mm to 1.5 mm on a 400-μm pitch. Light delivery from optical fibers and loss mechanisms through these Si optrodes were characterized, with the primary loss mechanisms being Fresnel reflection, coupling, radiation losses from the tapered shank and total internal reflection in the tips. Transmission at the optrode tips with different optical fiber core diameters and light in-coupling interfaces was investigated. At λ = 1.55μm, the highest optrode transmittance of 34.7%, relative to the optical fiber output power, was obtained with a 50-μm multi-mode fiber butt-coupled to the optrode through an intervening medium of index n = 1.66. Maximum power is directed into the optrodes when using fibers with core diameters of 200 μm or less. In addition, the output power varied with the optrode length/taper such that longer and less tapered optrodes exhibited higher light transmission efficiency. Output beam profiles and potential impacts on physiological tests were also examined. Future work is expected to improve USOA efficiency to greater than 64%.

Light source device and display

Abstract: A light source device includes: a light guide plate having a first internal reflection plane and a second internal reflection plane which face each other; one or more light sources each applying illumination light through a side surface of the light guide plate into an interior thereof; and an optical device disposed to face the light guide plate, and modulating, for each of partial regions thereof, a state of light rays exiting therefrom. One or both of the first and the second internal reflection planes each have scattering regions each allowing the illumination light from the light sources to be scattered and exit from the first internal reflection plane of the light guide plate, and one or both of the first and second internal reflection planes each have total-reflection regions allowing the illumination light from the light sources to be reflected in a manner of total-internal-reflection.

Light-coupling optical systems and methods employing light-diffusing optical fiber

Abstract: Light-coupling systems and methods that employ light-diffusing optical fiber are disclosed. The systems include a light source and a light-diffusing optical fiber optically coupled thereto. The light-diffusing optical fiber has a core, a cladding and a length. At least a portion of the core comprises randomly arranged voids configured to provide substantially spatially continuous light emission from the core and out of the cladding along at least a portion of the length. A portion of the light-diffusing optical is embedded in an index-matching layer disposed adjacent a lower surface of a transparent sheet. Light emitted by the light-diffusing optical fiber is trapped within the transparent sheet and index-matching layer by total internal reflection and is scattered out of the upper surface of the transparent sheet by at least one scattering feature thereon.

Control of dispersion in photonic crystal waveguides using group symmetry theory.

Abstract: We demonstrate dispersion tailoring by coupling the even and the odd modes in a line-defect photonic crystal waveguide. Coupling is determined ab-initio using group theory analysis, rather than by trial-error optimisation of the design parameters. A family of dispersion curves is generated by controlling a single geometrical parameter. This concept is demonstrated experimentally with very good agreement with theory.

Reflection of Plane Waves in a Semiconducting Medium under Photothermal Theory

Abstract: In this paper photothermal theory was used to study the reflection of waves at the surface of a semi-infinite semiconconducting medium. Using the harmonic wave method, the reflection coefficient ratios were obtained analytically under coupled thermoelastic theory and plasma theory for an incident CI wave, which is one coupled thermoelastic plasma wave and an incident rotational wave. The variations of the amplitude of reflection coefficient ratios with the angle of incidence are shown graphically for silicon. Effects of the thermal frequency, the thermoelastic coupling parameter, and the thermoelectric coupling parameter were given by numerical results. Also, the energy ratios for reflected waves were computed to check the numerical results.

Plasmon Waveguide Resonance Raman Spectroscopy

Abstract: Raman spectra were collected from a 1.25 M aqueous pyridine solution, 100-nm polystyrene film or a trimethyl(phenyl)silane monolayer at a plasmon waveguide interface under total internal reflection (TIR). The plasmon waveguide resonance (PWR) interface consisted of a sapphire prism/49 to 50 nm Au/548 to 630 nm SiO2 and a monolayer, thin film or aqueous analyte. The Raman peak area as a function of incident angle was measured using a 785-nm excitation wavelength, and was compared to the Raman peak area obtained at a sapphire or sapphire/50 nm Au interface. In contrast to measurements at a bare sapphire prism, increased surface sensitivity and signal were obtained from the PWR interface. In contrast to measurements at a bare Au film where only p-polarized incident light generates an enhanced interfacial electric field, plasmon waveguide interfaces enable excitation with orthogonal polarizations using s- or p-polarized incident light. The Raman scatter from a monolayer was recorded at the PWR interface with ...

Long-distance directed transfer of microwaves in tubular sliding-mode plasma waveguides produced by KrF laser in atmospheric air

Abstract: A new regime of the sliding-mode propagation of microwave radiation in plasma waveguides in atmospheric air is studied both experimentally and theoretically. The mechanisms of air photoionization and relaxation under propagation of 25-ns pulses of KrF laser are investigated. It is shown that a tubular plasma waveguide of large radius (much larger than wavelength of the microwave signal) can be produced in the photoionization of air molecules by 248-nm radiation of KrF-laser. We experimentally demonstrate the laser-enhanced transfer of 38-GHz microwave signal to a distance of at least 60 m. The mechanism of the transfer is determined by total internal reflection of the signal on the optically less dense wall of the plasma waveguide. Analytical and numerical simulations performed for various waveguide radii and microwave radiation wavelengths show that the propagation length increases with decrease in the wavelength reaching a few kilometers for submillimeter waves. Medium-size KrF laser facility with about...

Efficient broadband energy transfer via momentum matching at hybrid junctions of guided-waves

Abstract: Momentum matching at hybrid junctions is examined for efficient broadband energy transfer between internal reflection guided waves and evanescence-based plasmonic-gap guided waves. We demonstrate a nanoscale orthogonal junction coupler between 50 nm air-filled plasmonic slot waveguides (PSWs) and 450 nm silicon rib waveguides. Non-resonant junction coupling efficiency of 50 ± 2 % between 1450 nm and 1650 nm is achieved experimentally and PSW propagation loss is directly measured to be only 2.5 dB/μm. This taperless hybrid junction reduces PSW-based device footprint and enhances device tolerance to temperature and fabrication process variations, serving as a potential platform for hybrid silicon-plasmonic interconnects.

Directional excitation of surface plasmon polaritons via nanoslits under varied incidence observed using leakage radiation microscopy

Abstract: Surface Plasmon Polaritons (SPPs) are excited at the interface between a thin gold film and air via the illumination of nanoslits etched into the film. The coupling efficiency to the two propagation directions away from the slits is determined by leakage radiation microscopy, when the angle of incidence of the pump beam is changed from 0° to 20°. We find that preferential coupling of SPPs into one direction can be achieved for non-normal incidence in the case of single slits and slit pairs. The proportion of SPP excited into one direction can be in excess of 90%. We further provide a simple model of the process, and directly compare the performances of the two approaches.