Showing papers on "Total internal reflection published in 2019"

Colouration by total internal reflection and interference at microscale concave interfaces.

Abstract: Many physical phenomena create colour: spectrally selective light absorption by pigments and dyes1,2, material-specific optical dispersion3 and light interference4–11 in micrometre-scale and nanometre-scale periodic structures12–17. In addition, scattering, diffraction and interference mechanisms are inherent to spherical droplets18, which contribute to atmospheric phenomena such as glories, coronas and rainbows19. Here we describe a previously unrecognized mechanism for creating iridescent structural colour with large angular spectral separation. Light travelling along different trajectories of total internal reflection at a concave optical interface can interfere to generate brilliant patterns of colour. The effect is generated at interfaces with dimensions that are orders of magnitude larger than the wavelength of visible light and is readily observed in systems as simple as water drops condensed on a transparent substrate. We also exploit this phenomenon in complex systems, including multiphase droplets, three-dimensional patterned polymer surfaces and solid microparticles, to create patterns of iridescent colour that are consistent with theoretical predictions. Such controllable structural colouration is straightforward to generate at microscale interfaces, so we expect that the design principles and predictive theory outlined here will be of interest both for fundamental exploration in optics and for application in functional colloidal inks and paints, displays and sensors. A mechanism for creating patterns of iridescent structural colour by total internal reflection of light beams along a concave optical interface leading to interference is described, for complex microscopic systems and for systems as simple as condensed water drops.

Optical properties of photoresists for femtosecond 3D printing: refractive index, extinction, luminescence-dose dependence, aging, heat treatment and comparison between 1-photon and 2-photon exposure

Abstract: Femtosecond 3D printing has emerged as an important technology for manufacturing nano- and microscopic optical devices and elements. Detailed knowledge of the dispersion in the visible and near-infrared spectral range is crucial for the design of these optical elements. Here we provide refractive index measurements for different UV-doses, aging times, heat treatment and 2-photon exposed structures for the photoresists IP-S, IP-Dip, IP-L, OrmoComp, IP-Visio, and PO4. We use a modified and automized Pulfrich refractometer setup, utilizing critical angles of total internal reflection with an accuracy of 5·10−4 in the visible and near-infrared spectral range. We compare Cauchy and Sellmeier fits to the dispersion curves. We also give Abbe numbers and Schott Catalog numbers of the almost entirely polymerized resists. Additionally, we provide quantitative extinction and luminescence measurements for all photoresists.

Guiding of visible photons at the ångström thickness limit.

Abstract: Optical waveguides are vital components of data communication system technologies, but their scaling down to the nanoscale has remained challenging despite advances in nano-optics and nanomaterials. Recently, we theoretically predicted that the ultimate limit of visible photon guiding can be achieved in monolayer-thick transition metal dichalcogenides. Here, we present an experimental demonstration of light guiding in an atomically thick tungsten disulfide membrane patterned as a photonic crystal structure. In this scheme, two-dimensional tungsten disulfide excitonic photoluminescence couples into quasi-guided photonic crystal modes known as resonant-type Wood’s anomalies. These modes propagate via total internal reflection with only a small portion of the light diffracted to the far field. Such light guiding at the ultimate limit provides more possibilities to miniaturize optoelectronic devices and to test fundamental physical concepts. A monolayer WS2 membrane patterned as a photonic crystal sustains guided optical modes that propagate via total internal reflection.

Broadband out-of-plane coupling at visible wavelengths

Abstract: Photonic integrated circuits require efficient interfaces to fiber optic components for applications in optical communication, computing, and sensing. Current optical interconnects rely on edge or grating couplers with limitations in terms of alignment tolerances, efficiency, and bandwidth, respectively. Here, we present a scalable coupling concept that allows fiber-to-chip coupling to the fundamental transverse electric and transverse magnetic modes based on three-dimensional nanostructures exploiting total internal reflection. We demonstrate close to octave-spanning highly efficient coupling to nanophotonic waveguides in the visible wavelength range. Our coupling scheme can be adjusted for other wavelength regimes and fiber mode-field diameters.

Probing Charged Aqueous Interfaces Near Critical Angles: Effect of Varying Coherence Length

Abstract: Angle-resolved vibrational sum frequency generation experiments have been used to study the silica–water interface as a function of ionic strength. Well below the critical angle, the sum frequency intensity increases up to 10–4 M NaCl and then drops. However, near the critical angle, a plateau may be observed up to 10–4 M. We first demonstrate that this is a result of the interaction of a long Debye length at low ionic strength with a long coherence length near the critical angles. In order to account for the behavior at the lowest concentrations where surface potentials are typically large, it is necessary to consider an electrostatic potential that extends into the bulk aqueous phase beyond the Debye–Huckel approximation. Because the extent of second- and third-order contributions to the nonlinear polarization can vary with ionic strength, but not with the angle of incidence, we perform a global fit to the experimental data using our proposed model to extract the relative magnitude of the two susceptibi...

Measurement of the refractive index of whole blood and its components for a continuous spectral region.

Abstract: The refractive index of blood is a key biophysical parameter, which can reflect the physiological state. We measured the refractive index of whole blood and other components, such as serum, plasma, and hemoglobin, based on internal reflection by using a homemade apparatus in the spectral range of 400 to 750 nm. In addition to the hemoglobin solution, which has a Soret band about 420 nm and two Q-bands between 500 and 600 nm, the measurements of other samples are the normal dispersion curve. The results are approximated by the Cauchy equation and Sellmeier equation, and the correlation coefficients are more than 0.997.

Dual-focal waveguide see-through near-eye display with polarization-dependent lenses

Abstract: A waveguide near-eye display (NED) with a dual-focal plane using a polarization-dependent lens device is proposed. The novel optical device is composed of a geometric phase holographic lens, a wave plate, and a circular polarizer, which is operating as a concave lens or a see-through optical window, depending on the polarization state of the input beam. Such property and ultra-thinness of about 1.5 mm can be applied to a combiner-eyepiece lens for augmented reality. This optical device attached to the waveguide provides two depth planes with polarization multiplexing. We have demonstrated that our proof-of-concept system has image planes at infinity and 20 diopters. The devised system can be expected to offer a better immersive experience, compared to a NED system with a single-focal plane.

Bound States in the Continuum in Fiber Bragg Gratings

Abstract: Optical fibers typically confine light through total internal reflection or through photonic band gaps. Here, we show that light can be perfectly guided in optical fibers through a different mechan...

V-shaped micro-structure optical fiber surface plasmon resonance sensor for the simultaneous measurement of the refractive index and temperature

Abstract: We propose and demonstrate a novel and compact optical fiber surface plasmon resonance (SPR) sensor for the simultaneous measurement of the refractive index (RI) and temperature. The sensor is fabricated by employing the eccentric-core fiber (ECF), which is polished to a V-shaped micro-structure optical fiber (MOF). One side of the MOF is used as the RI sensing channel, and the other side is used as the temperature sensing channel. Two sensing channels are independent without crosstalk. The sensor has high RI sensitivity up to the maximum of 3376 nm/RIU from 1.333 to 1.385 RIU, and high-temperature sensitivity up to −2.65 nm/°C from 20°C to 60°C. In addition, owing to the few-mode light in the ECF, the full width at half-maximum is smaller than other SPR sensors based on multimode fiber. This sensor will be extremely helpful to improve the RI measurement uncertainty caused by temperature disturbance.

Gradual cross polarization conversion of transmitted waves in near field coupled planar terahertz metamaterials

Abstract: In this work, we examine gradual cross polarization conversion using two coupled circular split ring resonators (SRRs) in the terahertz (THz) frequency regime. In the proposed geometry, a metamolecule (unit cell) is comprised of two circular split ring resonators having a single split gap. One resonator is rotated with respect to the other from 0° to 180° in the steps of 15° and thereby, co- and cross-polarization components of the transmitted terahertz are investigated. The cross polarization component is observed to be maximum when resonator split gaps are orthogonal to each other; however, in the co polarization resonance, a strong split is observed. Based upon the angle of rotation between the resonators, the study reveals that the cross polarization conversion can be tuned from minimum to maximum and then back to the minimum. We have employed a semi-analytical model to understand the polarization conversion arising from the coupling between the resonators and found that it corroborates numerical findings. The ability to control linear polarization conversions can be significant in the development of THz polarimetric devices.

Simultaneous measurement of refractive index and temperature for prism-based surface plasmon resonance sensors

Abstract: A detailed theoretical model is provided to analyze the effects of temperature on prism-based surface plasmon resonance (SPR) sensors, including temperature dependence of the metal and prism. A complete sensitivity matrix simultaneously measures variations in refractive index (RI) and temperatures using measurements at two wavelengths for the angular-interrogation mode, or at two angles of incidence for the wavelength-interrogation mode. Correction of matrix coefficients improves accuracy of the two modes. Validation is performed using a self-designed wavelength SPR system with an adjustable incident angle perform. This method provides a new way to detect the RI and may lead to the better design and fabrication of prism-based SPR sensors.

Experimental studies on the sensitivity of the propagating and localized surface plasmon resonance-based tapered fiber optic refractive index sensors

Abstract: In the present study, the sensitivities of the fiber optic propagating surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR)-based refractive index sensors have been evaluated experimentally for a tapered probe of different taper ratio. The tapering of the fiber probe has been carried out via a heating and stretching technique. The SPR probe has been fabricated by coating a thin film of silver over the core of the tapered optical fiber, while the LSPR probe has been prepared by the coating of the gold nanoparticles over the core of the tapered optical fiber. The increase in the taper ratio increases the sensitivity of both kinds of the probes. The experimentally obtained sensitivity has been compared with the sensitivity of the SPR-based fiber optic refractive index sensors fabricated using various techniques and reported in the literature.

Total Internal Reflection-Based Extinction Spectroscopy of Single Nanoparticles.

Abstract: Herein we report a reflection-mode total internal reflection microscopy (TIRM) to measure the extinction spectrum of individual dielectric, plasmonic, or light-absorbing nanoparticles, and to differentiate absorption and scattering components from the total optical output. These capabilities were enabled via illuminating the sample with evanescent wave of which the lightpath length was comparable with the size of single nanoparticles, leading to a dramatically improved reflectance change (ΔI/I0 ) up to tens of percent. It was further found that scattering and absorption of light contributed to bright and dark centroids, respectively, in the optical patterns of single nanoparticles, allowing to distinguish scattering and absorption components from the extinction spectrum by the use of an appropriate image processing method. In addition, wide-field feature of TIRM enabled the studies on tens of nanoparticles simultaneously with gentle illumination.

Angular color variation in micron-scale light-emitting diode arrays.

Abstract: A simulation scheme was developed to explore the light distribution of full-color micron-scale light-emitting diode (LED) arrays. The influences of substrate thickness, patterning, and cutting angle of the substrate on several important features, such as light field pattern, light extraction efficiency, and color variation, were evaluated numerically. An experiment was conducted; the results were consistent with simulation results for a 225 × 125 µm2 miniLED and those for an 80 × 80 µm2 microLED. Based on the simulation results, the light extraction efficiency of LED devices with a substrate increases by 67.75% over the extraction efficiency of those without a substrate. The light extraction efficiency of LED devices with a substrate increases by 113.55% when an additional patterned design is used on green and blue chips. The calculated large angle Δu′v′ can be as low as 0.015 for miniLED devices.

INVITED) Monolithic total internal reflection resonators for applications in photonics

Abstract: Monolithic total internal reflection resonators confine light through traveling waves that can feature high quality factors and small mode volumes. Such resonators have emerged as rigid and compact platforms to explore high-efficiency laser-matter interactions and their related applications in photonics technology. In this review, we focus on monolithic ring resonators based on total internal reflection, with a particular emphasis on nonplanar ring oscillators and whispering-gallery mode lasers. We also discuss resonantly enhanced nonlinear photonic systems based on these resonators, using both non-centrosymmetric and centrosymmetric optical materials.

Weak measurement of magneto-optical Goos-Hänchen effect.

Abstract: As a lateral shift of reflected light beam from the optical interface, the Goos-Hanchen (GH) effect led to various practical applications in biosensing and optical field manipulations. Magneto-optical (MO) effect of dielectric or metal may bring flexible modulation for GH effect, which can be regarded as the magneto-optical Goos-Hanchen (MOGH) effect. In this paper, the GH and MOGH effects in a BK7 prism/Fe/Au waveguide enhanced by surface plasmon resonance (SPR) are demonstrated experimentally for the first time. By weak measurement, the GH and MOGH shifts are further amplified to facilitate their applications. By contrast, the results of theory and experiment are basically consistent. The maximum MOGH shift of the proposed BK7/Fe/Au waveguide achieves 120 μm when optimum thicknesses are chosen. As MOGH effect exhibits a higher sensitivity to the refractive index of sample than GH shift, it can be applied in refractive index detection. The demonstrated MOGH effect with advantages of high sensitivity and convenient control opens avenues for future applications with biosensors and functionally optical devices.

Compact head-mounted display system

Abstract: There is provided an optical system, including a light-transmitting substrate ( 20 ) having at least two major surfaces ( 26 ) and edges, an optical prism ( 54 ) having at least a first ( 58 ), a second ( 56 ) and a third ( 60 ) surface, for coupling light waves having a given field-of-view into the substrate by total internal reflection, at least one partially reflecting surface located in the substrate, the partially reflecting surface being orientated non-parallelly with respect to the major surfaces of the substrate, for coupling light waves out of the substrate, at least one of the edges ( 50 ) of the substrate is slanted at an oblique angle with respect to the major surfaces, the second surface of the prism is located adjacent to the slanted edge of the substrate, and a part of the substrate located next to the slanted edge is substantially transparent, wherein the light waves enter the prism through the first surface of the prism, traverse the prism without any reflection and enter the substrate through the slanted edge.

Large in-plane asymmetric spin angular shifts of a light beam near the critical angle.

Abstract: The photonic spin Hall effect (SHE) manifests itself as the transverse and in-plane spin-dependent shifts of a light beam. Normally, the spin shifts are tiny due to the weak spin-orbit coupling. Therefore, it is very important and interesting to explore some effective methods for enhancing this phenomenon. In this Letter, we theoretically propose and experimentally verify a simple method for obtaining large and asymmetric in-plane spin angular shifts when an arbitrary linearly polarized beam reflects near the critical angle (for total internal reflection). The universal expressions of spatial and angular shifts are deduced. Remarkably, by modulating the incident and polarization angles, the left- and right-handed circularly polarized components can be distinguished directly.

Bloch surface waves at the telecommunication wavelength with lithium niobate as the top layer for integrated optics

Abstract: Lithium niobate (LN)-based devices are widely used in integrated and nonlinear optics. This material is robust and resistive to high temperatures, which makes the LN-based devices stable, but challenging to fabricate. In this work, we report on the design, manufacturing, and characterization of engineered dielectric media with thin-film LN (TFLN) on top for the coupling and propagation of electromagnetic surface waves at telecommunication wavelengths. The designed one-dimensional photonic crystal (1DPhC) sustains Bloch surface waves (BSWs) at the multilayer–air interface at 1550 nm wavelength with a propagation detected over a distance of 3 mm. The working wavelength and improved BSW propagation parameters open the way for exploration of nonlinear properties of BSW-based devices. It is also expected that these novel devices potentially would be able to modify BSW propagation and coupling by external thermal–electrical stimuli due to the improved quality of the TFLN top layer of 1DPhC.

A Total Internal Reflection Photoconductive Switch

Abstract: We demonstrate a novel illumination technique for extrinsic photoconductive switches based on the creation of a total internal reflection trap to increase the optical path length. The optimal geometry is a square substrate illuminated from one of the corners along the diagonal, ensuring that the total internal reflection condition is maintained after any reflection off the device lateral sides. The optical absorption uniformity throughout the device bulk was improved by designing the entry window to have a cylindrical shape and by using a square core optical fiber as an illumination source. The concept is experimentally validated on a vanadium-doped silicon carbide device that shows approximately four-fold improvement in responsivity compared to normal illumination.

Broadband Terahertz Polarizing Beam Splitter Based on a Graphene-Based Defective One-Dimensional Photonic Crystal

Abstract: Seeking operative terahertz (THz) devices has always stimulated considerable attention. Of particular interest is the THz beam splitter. Here, a tunable THz polarizing beam splitter (PBS) is proposed based on a graphene-embedded quarter-wave stack with a central defect layer of air. The spectral performance of the structure is investigated by the transfer matrix method. It is found that the electromagnetic waves can be decomposed into two separate polarized waves at incident angles greater than the critical angle. Furthermore, it is shown that a new kind of Brewster angle is found at the low THz frequencies due to the existence of the graphene nano-layers. The appearance of this angle which we call it the graphene induced Brewster angle results in the separation of TM- and TE- polarized waves at the low THz frequencies (f 200 dB) for TM waves with frequency f <; 2 THz is achieved by increasing the chemical potential to 0.5 eV. Moreover, this structure can exhibit extremely high extinction ratio for TE waves with high THz frequencies. Finally, the degree of polarization equals to one is reported for the PBS proposed here. This structure offers the opportunity to realize a high-efficiency PBS with very high extinction ratios at the broadband THz frequency.

Double-pump technique - one step closer towards efficient liquid-based THz sources.

Abstract: By irradiating a water jet with double pulses, we demonstrate 4-fold higher THz wave generation than for a single pump pulse. The dependence of the enhanced THz signal on the temporal delay between two collinear pulses reveals the optimal time for launching signal pulse is near 2-4 ps, which corresponds to the time needed to create the complete pre-ionization state when sufficient electron density is already induced, and there is no plasma reflection of the pump pulse radiation. The increase in THz waves generation efficiency corresponds to the case of water jet excitation by the pulses with an optimal duration for a certain jet thickness, which is determined by the spatial pulse size. Using a theoretical model of the interaction of a high-intensity sub-picosecond pulse with an isotropic medium, we held a numerical simulation, which well describes the experimental results when using 3 ps value of population relaxation time. Thus, in this work, double pump method allows not only to increase the energy of the generated THz waves, but also to determine the characteristic excited state lifetime of liquid water. The optical-to-terahertz conversion efficiency in case of double pulse excitation of water column is of the order of 0.5⋅10 −3, which exceeds the typical values for THz waves generation during two-color filamentation in air and comparable with the achievable values due to the optical rectification in some crystals.

Multifunctional weak measurement system that can measure the refractive index and optical rotation of a solution

Abstract: In this study, we propose a multifunctional weak measurement system that can measure the optical rotation and the refractive index of solution. The center wavelength of the output spectrum of such a system is sensitive to the optical rotation and the phase difference produced by total internal reflection. The optical resolution and refractive index resolution of the solution determined by the proposed method were 3.26 × 10–5° and 3.93 × 10–7 RIU, respectively, by measuring different concentrations of glucose solution. As the optical rotation and refractive index of the solution are important properties of the solution, this system can be used to determine the type of solute in the solution in the future.

Direct Inscription of on-surface waveguides in polymers using a mid-ir fiber laser

Abstract: A detailed study of photo-inscribed optical waveguides in PMMA and polycarbonate using a mid-IR laser is presented. The wavelength of the laser is tuned near the absorption peaks of stretching C-H molecular bonds and the focused beam is scanned onto the surface of planar polymer samples. For the first time, we report the formation of optical waveguides in both polymers through resonant absorption of the laser beam. The optical properties of the waveguides were thoroughly assessed. An elliptic Gaussian mode is guided at the surface of both polymers. Insertion losses of 3.1 dB for a 30 mm long on-surface waveguide inscribed in PMMA were recorded. Such waveguides can interact with the external medium through evanescent coupling. As a proof of concept, the surface waveguides are used as highly sensitive refractometric sensors. An attenuation dynamical range of 35 dB was obtained for a liquid that matches the index of the PMMA substrate. Our results pave the way for large scale manufacturing of low cost biocompatible photonic devices.

Anomalous Brewster effect and evanescent modes at an achiral/chiral dielectric boundary under planar electromagnetic propagation

Abstract: Fresnel coefficients are examined for electromagnetic (EM) propagation across an achiral/chiral (ACC) boundary. It is found that upon both transmission and reflection, the incident plane (specifica...