Showing papers on "Total internal reflection published in 2010"

Membrane-type acoustic metamaterial with negative dynamic mass

Abstract: We present the experimental realization and theoretical explanation of a membrane-type acoustic metamaterial of very simple structure,capable of breaking the mass density law of sound attenuation in the 100—1000Hz regime by a significant margin(~200 times).Due to the membrane's weak elastic moduli,low frequency oscillation patterns can be found even in a small elastic film with fixed boundaries defined by a rigid grid.The vibrational eigenfrequencies can be tuned by placing a small mass at the center of the membrane sample.Near-total reflection is achieved at a frequency in between two eigenmodes where the in-plane average of the normal displacement is zero.By using finite element simulations,a negative dynamic mass is explicitly demonstrated at frequencies around the total reflection frequency.Excellent agreement between theory and experiment is obtained.We also show that the present mechanism can explain the phenomenon of total microwave transmission through subwavelength slits in metallic fractals,at frequencies intermediate between two local resonances.

Room temperature plasmon laser by total internal reflection

Abstract: Plasmon lasers create and sustain intense and coherent optical fields below light's diffraction limit with the unique ability to drastically enhance light-matter interactions bringing fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. However, these important applications require room temperature operation, which remains a major hurdle. Here, we report a room temperature semiconductor plasmon laser with both strong cavity feedback and optical confinement to 1/20th of the wavelength. The strong feedback arises from total internal reflection of surface plasmons, while the confinement enhances the spontaneous emission rate by up to 20 times.

Acoustic metamaterial panels for sound attenuation in the 50–1000 Hz regime

Abstract: We show experimentally that thin membrane-type acoustic metamaterials can serve as a total reflection nodal surface at certain frequencies. The small decay length of the evanescent waves at these frequencies implies that several membrane panels can be stacked to achieve broad-frequency effectiveness. We report the realization of acoustic metamaterial panels with thickness ≤15 mm and weight ≤3 kg/m2 demonstrating 19.5 dB of internal sound transmission loss (STL) at around 200 Hz, and stacked panels with thickness ≤60 mm and weight ≤15 kg/m2 demonstrating an average STL of >40 dB over a broad range from 50 to 1000 Hz.

Refractive index engineering with subwavelength gratings for efficient microphotonic couplers and planar waveguide multiplexers

Abstract: We use subwavelength gratings (SWGs) to engineer the refractive index in microphotonic waveguides, including practical components such as input couplers and multiplexer circuits. This technique allows for direct control of the mode confinement by changing the refractive index of a waveguide core over a range as broad as 1.6–3.5 by lithographic patterning. We demonstrate two experimental examples of refractive index engineering, namely, a microphotonic fiber-chip coupler with a coupling loss as small as −0.9dB and minimal wavelength dependence and a planar waveguide multiplexer with SWG nanostructure, which acts as a slab waveguide for light diffracted by the grating, while at the same time acting as a lateral cladding for the strip waveguide. This yields an operation bandwidth of 170nm for a device size of only ~160μm×100μm.

Total transmission and total reflection by zero index metamaterials with defects

Abstract: We theoretically investigate microwave transmission through a zero-index metamaterial loaded with dielectric defects. The metamaterial is impedance matched to free space, with the permittivity and permeability tending towards zero over a given frequency range. By simply varying the radii and permittivities of the defects, total transmission or reflection of the impinging electromagnetic wave can be achieved. The proposed defect structure can offer advances in shielding or cloaking technologies without restricting the object's viewpoint. Active control of the observed exotic transmission and reflection signatures can occur by incorporating tunable refractive index materials such as liquid crystals and ${\mathrm{BaSrTiO}}_{3}$.

Light collection and illumination systems employing planar waveguide

Abstract: An apparatus for distributing light from a waveguide through a collimating array, or collecting light over a given area into a waveguide. Light received within a waveguide is propagated transmissively and retained by total internal reflection, except in response to impinging upon deflector elements which sufficiently redirect the light to escape the waveguide into a collimator array that aligns and distributes the light. In a light collector, a collection array collects and collimates the received light and directs it at the surface of a waveguide, within which deflectors properly positioned in relation to each collector of the collector array, deflect the angle of the light so that it propagates through the waveguide in response to total internal reflection. The apparatus can be fabricated into an efficient and compact form.

Switchable metamaterial reflector/absorber for different polarized electromagnetic waves

Abstract: We demonstrate a controllable electromagnetic wave reflector/absorber for different polarizations with metamaterial involving electromagnetic resonant structures coupled with diodes. Through biasing at different voltages to turn ON and OFF the diodes, we are able to switch the structure between nearly total reflection and total absorption of a particularly polarized incident wave. By arranging orthogonally orientated resonant cells, the metamaterial can react to different polarized waves by selectively biasing the corresponding diodes. Both numerical simulations and microwave measurements have verified the performance.

Switchable metamaterial reflector/absorber for different polarized electromagnetic waves

Abstract: We demonstrate a controllable electromagnetic wave reflector/absorber for different polarizations with metamaterial involving electromagnetic resonant structures coupled with diodes. Through biasing at different voltages to turn ON and OFF the diodes, we are able to switch the structure between nearly total reflection and total absorption of a particularly polarized incident wave. By arranging orthogonally orientated resonant cells, the metamaterial can react to different polarized waves by selectively biasing the corresponding diodes. Both numerical simulations and microwave measurements have verified the performance.

High performance Fresnel-based photovoltaic concentrator

Abstract: In order to achieve competitive system costs in mass-production, it is essential that CPV concentrators incorporate sufficient manufacturing tolerances. This paper presents an advanced concentrator optic comprising a Fresnel lens and a refractive secondary element, both with broken rotational symmetry, an optic producing both the desired light concentration with high tolerance (high acceptance angle) as well as an excellent light homogenization by Kohler integration. This concentrator compares well with conventional Fresnel-based CPV concentrators.

Efficient collimation of light with optical wedge

Abstract: Embodiments of optical collimators are disclosed. For example, one disclosed embodiment comprises an optical waveguide having a first end, a second end opposing the first end, a viewing surface extending at least partially between the first end and the second end, and a back surface opposing the viewing surface. The viewing surface comprises a first critical angle of internal reflection, and the back surface is configured to be reflective at the first critical angle of internal reflection. Further, a collimating end reflector comprising a faceted lens structure having a plurality of facets is disposed at the second end of the optical waveguide.

Plasmon Hybridization in Individual Gold Nanocrystal Dimers: Direct Observation of Bright and Dark Modes

Abstract: We apply a nanomanipulation technique to assemble pairs of monodispersed octahedral gold nanocrystals (side length, 150 nm) along their major axes with a varying tip-to-tip separation (25−125 nm). These pairs are immobilized onto indium tin oxide coated silica substrates and studied as plasmonic dimers by polarization-selective total internal reflection (TIR) microscopy and spectroscopy. We confirm that the plasmon coupling modes with the scattering polarization along the incident light direction result from the transverse-magnetic-polarized incident light, which induces two near-field-coupled dipole moments oriented normal to the air−substrate interface. In such cases, both in-phase (antibonding) and antiphase (bonding) plasmon coupling modes can be directly observed with the incident light wave vector perpendicular and parallel to the dimer axis, respectively. The observation of antiphase plasmon coupling modes (“dark” plasmons) is made possible by the unique polarization nature of the TIR-generated eva...

Roughness induced backscattering in optical silicon waveguides.

Abstract: We report on the direct observation of backscattering induced by sidewall roughness in high-index-contrast optical waveguides based on total internal reflection. Our results demonstrate that backscattering is one of the most severe limiting factors in state-of-the art silicon on insulator nanowires employed in densely integrated photonics. We also derive the general relationship between backscattering and geometrical and optical parameters of the waveguide. Further, the role of roughness in polarization rotation and coupling with higher-order modes is pointed out.

Klein Tunneling in Deformed Honeycomb Lattices

Abstract: We study the scattering of waves off a potential step in deformed honeycomb lattices. For deformations below a critical value, perfect Klein tunneling is obtained; i.e., a potential step transmits waves at normal incidence with nonresonant unit-transmission probability. Beyond the critical deformation a gap forms in the spectrum, and a potential step perpendicular to the deformation direction reflects all normally incident waves, exhibiting a dramatic transition form unit transmission to total reflection. These phenomena are generic to honeycomb lattices and apply to electromagnetic waves in photonic lattices, quasiparticles in graphene, and cold atoms in optical lattices.

Total reflection and transmission by epsilon-near-zero metamaterials with defects

Abstract: In this work, we investigate wave transmission through an epsilon-near-zero metamaterial waveguide embedded with defects. We show that by adjusting the geometric sizes and material properties of the defects, total reflection and even transmission can be obtained, despite the impedance mismatch of epsilon-near-zero material with free space. Our work can greatly simplify the design of zero-index material waveguide applications by removing the dependence on permeability.

Experimental determination of the sensitivity of Bloch surface waves based sensors.

Abstract: Detection of glucose in water solution for several different concentrations has been performed with the purpose to determine the sensitivity of Near Infrared Bloch Surface Waves (λ = 1.55μm) upon refractive index variations of the outer medium. TE-polarized electromagnetic surface waves are excited by a prism on a silicon nitride multilayer, according to the Kretschmann configuration. The real-time reflectance changes induced by discrete variations in glucose concentration has been revealed and analyzed. Without using any particular averaging strategy during the measurements, we pushed the device detection limit down to a glucose concentration of 2.5mg/dL, corresponding to a minimum detectable refractive index variation of the water solution as low as 3.8·10−6.

Planar optical system for wide field-of-view polychromatic imaging

Abstract: A planar optical system for wide field-of-view polychromatic imaging includes a planar waveguide including two plane parallel faces, an entry coupler including a first diffraction grating, and an exit coupler including a second diffraction grating. The diffraction gratings are low line density diffraction gratings that have a pitch greater than the wavelength of use such that the grating is adapted to couple an entry beam having a mean angle of incidence i0 ranging between 30 to 60 degrees into the waveguide by positive first order (+1) diffraction, the coupled beam defining an internal angle of incidence greater than the angle of total internal reflection and less than γ=80 degrees, and the second grating is adapted to receive the coupled beam and to diffract it out of the waveguide by negative first order (−1) diffraction at a mean exit angle i1 ranging between 30 to 60 degrees.

Photonic crystal enhanced fluorescence using a quartz substrate to reduce limits of detection.

Abstract: A Photonic Crystal (PC) surface fabricated upon a quartz substrate using nanoimprint lithography has been demonstrated to enhance light emission from fluorescent molecules in close proximity to the PC surface. Quartz was selected for its low autofluorescence characteristics compared to polymer-based PCs, improving the detection sensitivity and signal-to-noise ratio (SNR) of PC Enhanced Fluorescence (PCEF). Nanoimprint lithography enables economical fabrication of the subwavelength PCEF surface structure over entire 1x3 in2 quartz slides. The demonstrated PCEF surface supports a transverse magnetic (TM) resonant mode at a wavelength of λ = 632.8 nm and an incident angle of θ = 11°, which amplifies the electric field magnitude experienced by surface-bound fluorophores. Meanwhile, another TM mode at a wavelength of λ = 690 nm and incident angle of θ = 0° efficiently directs the fluorescent emission toward the detection optics. An enhancement factor as high as 7500 × was achieved for the detection of LD-700 dye spin-coated upon the PC, compared to detecting the same material on an unpatterned glass surface. The detection of spotted Alexa-647 labeled polypeptide on the PC exhibits a 330 × SNR improvement. Using dose-response characterization of deposited fluorophore-tagged protein spots, the PCEF surface demonstrated a 140 × lower limit of detection compared to a conventional glass substrate.

Mode localization and the Q-factor of a cylindrical microresonator

Abstract: As opposed to the modes in an optical spherical/spheroidal microresonator, the whispering gallery modes in a long cylindrical microresonator are delocalized. Consequently, a circulating light beam that is evanescently coupled into the cylinder and experiences total internal reflection eventually radiates out along the cylinder axis. However, the self-interference of such a beam can produce a resonant mode that is strongly localized along the axial direction. Specifically, the mode characteristic width is (αβ)−1/2, where α and β are the attenuation and propagation constants of the cylinder material. The Q-factor of this mode can be almost as large as the Q-factor of modes in a spheroidal microresonator with the same α divided by 2.542.

Quantitative dispersion microscopy

Abstract: Refractive index dispersion is an intrinsic optical property and a useful source of contrast in biological imaging studies. In this report, we present the first dispersion phase imaging of living eukaryotic cells. We have developed quantitative dispersion microscopy based on the principle of quantitative phase microscopy. The dual-wavelength quantitative phase microscope makes phase measurements at 310 nm and 400 nm wavelengths to quantify dispersion (refractive index increment ratio) of live cells. The measured dispersion of living HeLa cells is found to be around 1.088, which agrees well with that measured directly for protein solutions using total internal reflection. This technique, together with the dry mass and morphology measurements provided by quantitative phase microscopy, could prove to be a useful tool for distinguishing different types of biomaterials and studying spatial inhomogeneities of biological samples.

Optical forces near a nanoantenna

Abstract: The Maxwell stress tensor method is used to calculate the optical forces acting upon a glass nanosphere in the proximity of optically excited gold nanoantenna structures The dependence of optical forces over a full range of excitation angles is explored: the total internal reflection excitation does not bring any particular advantage to trapping efficiency when compared to the normal incidence excitation Our calculations show multiple trapping sites with similar trapping properties for the normal and the total internal reflection cases, respectively; furthermore, the convective heating probably dominates over any optical forces in such systems

Bloch surface waves in ultrathin waveguides: near-field investigation of mode polarization and propagation

Abstract: In this work, we use a multi-heterodyne scanning near-field optical microscope to investigate the polarization and propagation of Bloch surface waves in an ultrathin (∼λ∕10) ridge waveguide. First, we show that the structure sustains three surface modes, and demonstrate selective excitation of each. Then, by numerically processing the experimental data, we retrieve the transverse and longitudinal components of each of the modes, in good agreement with the calculated fields. Finally, we provide an experimental estimation of the effective indices and the dispersion relations of the modes.

A 2-D Artificial Dielectric With ${0 \leq n for the Terahertz Region

Abstract: We demonstrate a 2-D artificial dielectric medium suitable for the terahertz region by exploiting the characteristic frequency dependence in the phase velocity of the lowest order transverse-electric (TE1) mode of the parallel-plate waveguide (PPWG). This artificial medium exhibits a plasma-like behavior having a frequency-dependent refractive index that varies between zero and unity. Using this medium, we demonstrate the optical phenomena of total internal reflection and Brewster's effect, and also demonstrate a convergent PPWG-lens.

Guided-mode resonant wave plates.

Abstract: We introduce half-wave and quarter-wave retarders based on the dispersion properties of guided-mode resonance elements. We design the wave plates using numerical electromagnetic models joined with the particle swarm optimization method. The wave plates operate in reflection. We provide computed results for reflectance and phase in the telecommunication spectral region near 1.55 microm wavelength. A surface-relief grating etched in glass and overcoated with silicon yields a half-wave plate with nearly equal amplitudes of the TE and TM polarization components and pi phase difference across a bandwidth exceeding 50 nm. Wider operational bandwidths are obtainable with more complex designs involving glass substrates and mixed silicon/hafnium dioxide resonant gratings. The results indicate a potential new approach to fashion optical retarders.

Light-emitting device

Abstract: The invention relates to a light-emitting device, comprising a plurality of light sources, an optical plate, a plurality of concave structures and at least one light-emitting structure, wherein the optical plate is arranged above the light sources and provided with an upper surface and a lower surface The concave structures extend towards the inside of the optical plate from the upper surface of the optical plate, each concave structure is correspondingly arranged above one light source, and the lateral surface of each concave structure has at least two inclined angles The light-emitting structures are arranged on at least one of the upper surface and the lower surface of the optical plate, wherein light generated by the light sources positioned below each concave structure generates total reflection on the side surface of the concave structure and continuously carries out at least one total reflection in the optical plate and emits light out of the optical plate until coming across the light emergent structure

Freeform surface design for a light-emitting diode-based collimating lens

Abstract: A freeform collimating lens is designed to project light rays emitted from an LED light source to a far target plane Generally, the projection distance is assumed to be more than 100 m, and the light beam to have negligible divergence The lens consists of a total internal reflection (TIR) side surface, a spherical surface in the rear, a vertical plane surface in the outer part of the front, and a freeform refractive surface in the central part of the front Light rays emitted from the LED source with large spread angles hit the TIR surface and are redirected parallel to the light axis, and those having small spread angles will be collimated by the freeform refractive surface, which is designed with a simple approximation method, and then travel parallel to the light axis Computer simulation results show that an optical efficiency of 815% is achieved under a view angle of ±5 deg and for a 1 mm×1 mm LED source

Nanometer axial resolution by three-dimensional supercritical angle fluorescence microscopy.

Abstract: We report a noninvasive fluorescence microscopy method and demonstrate nanometer resolution along the optical axis. The technique is based on the influence of the microscope slide on the angular intensity distribution of fluorescence. Axial positions are determined by measuring the proportion of light emitted below the critical angle of total internal reflection, which behaves in a classical way, and light emitted above the critical angle, which is exponentially dependent on the distance of the fluorophore from the microscope slide.

Light mixing optics and systems

Abstract: In one aspect, a light-mixing optic is disclosed for use with one or more light sources such as light emitting diodes. In one embodiment, an exemplary optic can include an optical body disposed about an optical axis and having an input and an output surface and a peripheral surface extending between the two. The input surface can form a central cavity for receiving light from the light sources, if not the light sources themselves. Further, the input surface can be shaped to refract substantially all of the light received from the one or more light sources away from the optical axis to the peripheral surface of the optic, where that light (e.g., substantially all of it) can be redirected (e.g., via total internal reflection or specular reflection) to the output surface. An array of micro-lenses or other surface features can be formed on the output surface. Further embodiments, as well as exemplary design methods, are also disclosed.

Goos-H\"{a}nchen-like shifts for Dirac fermions in monolayer graphene barrier

Abstract: We investigate the Goos-H\"{a}nchen-like shifts for Dirac fermions in transmission through a monolayer graphene barrier. The lateral shifts, as the functions of the barrier's width and the incidence angle, can be negative and positive in Klein tunneling and classical motion, respectively. Due to their relations to the transmission gap, the lateral shifts can be enhanced by the transmission resonances when the incidence angle is less than the critical angle for total reflection, while their magnitudes become only the order of Fermi wavelength when the incidence angle is larger than the critical angle. These tunable beam shifts can also be modulated by the height of potential barrier and the induced gap, which gives rise to the applications in graphene-based devices.