Total Internal Reflection Mode Research Articles

Photonic crystal-connected bidirectional micro-ring resonator array for duplex mode and wavelength channel (de)multiplexing

The progress of on-chip optical communication relies on integrated multi-dimensional mode (de)multiplexers to enhance communication capacity and establish comprehensive networks. However, existing multi-dimensional (de)multiplexers, involving modes and wavelengths, face limitations due to their reliance on single-directional total internal reflection and multi-level mode conversion based on directional coupling principles. These constraints restrict their potential for full-duplex functionality and highly integrated communication. We solve these problems by introducing a photonic-like crystal-connected bidirectional micro-ring resonator array (PBMRA) and apply it to duplex mode-wavelength multiplexing communication. The directional independence of total internal reflection and the cumulative effect of the subwavelength-scale pillar within the single-level photonic crystal enable bidirectional mode and wavelength multiplexed signals to transmit among multi-pair nodes without interference, improving on-chip integration in single-level mode conversion. As a proof of concept, we fabricated a nine-channel bidirectional multi-dimensional (de)multiplexer, featuring three wavelengths and three TE modes, compactly housed within a footprint of 80 μm×80 μm, which efficiently transmits QPSK-OFDM signals at a rate of 216 Gbit/s, achieving a bit error rate lower than 10−4. Leveraging the co-ring transmission characteristic and the orthogonality of the mode-wavelength channel, this (de)multiplexer also enables a doubling of communication capacity using two physical transmission channels.

Precise refractive index measurement of fused silica optics

Abstract We have developed an experimental platform that non-destructively and precisely measures the Refractive Index (RI) and dispersion of ultra-polished fused silica optics. Using Total Internal Reflection Digital Holographic Microscopy (TIRDHM), we exploit the phase change of reflected light in Total Internal Reflection (TIR) mode. This phase change depends on the incident angle at the TIR interface and the refractive indices of the involved media. We have optimized a combination of higher TIR phase sensitivity, considerable penetration depth, and minimized phase measurement inaccuracies through simulations to design our experiment. Key features include a custom-made precision Right-Angle Prism (RAP) of Astrositall material, a seamless interface with fused silica optics on TIR interface through optical contact, and single-shot measurement. We have demonstrated the accuracy of measuring fused silica optics through proof of concept and experimental results. Our measurements on two different samples show accuracy better than ±3 × 10−4 compared to those obtained using a commercially available critical angle Refractometer (Metricon). Importantly, the setup offers the advantage of spatially mapping the refractive index, unlike point measurements by available Refractometers.

Towards interfacial nanothermometry in chemical reactions by total internal reflection wide-field diamond microscopy

In situ monitoring interfacial temperatures at microscopic scale is crucial in chemical reactions involving two immiscible phases. However, such measurement is challenging for most sensing methods due to harsh chemical conditions. Nanodiamond (ND) containing nitrogen-vacancy centers provides a promising method for sensitive temperature monitoring at nanoscale in a chemical reaction zone without perturbing the ongoing reactions. In this study, we developed a total internal reflection (TIRF) wide-field microscopy combined with ND quantum sensors for interfacial temperature monitoring in chemical reactions. The stability and measurement uncertainty of this method were demonstrated by monitoring the interfacial temperature in zinc electrodeposition with dendrite growth induced internal short circuit (ISC). For the first time, the surface scattering of growing Zn dendrites was revealed, which would induce significant photon counts fluctuations of NDs when the surface morphology of Zn dendrite dynamically changed. Fluorescence stability maintained by adopting TIRF mode wide-field microscope, which enabled real time monitoring of the interfacial temperature at intervals of hundreds of seconds with a measurement uncertainty of ∼1 K during the entire process of zinc dendrite induced ISC. This work represents a critical advancement in the investigation of surface optical properties and thermal dynamics across a wide range of chemical reactions.

Self-supervised machine learning pushes the sensitivity limit in label-free detection of single proteins below 10 kDa

Interferometric scattering (iSCAT) microscopy is a label-free optical method capable of detecting single proteins, localizing their binding positions with nanometer precision, and measuring their mass. In the ideal case, iSCAT is limited by shot noise such that collection of more photons should extend its detection sensitivity to biomolecules of arbitrarily low mass. However, a number of technical noise sources combined with speckle-like background fluctuations have restricted the detection limit in iSCAT. Here, we show that an unsupervised machine learning isolation forest algorithm for anomaly detection pushes the mass sensitivity limit by a factor of 4 to below 10 kDa. We implement this scheme both with a user-defined feature matrix and a self-supervised FastDVDNet and validate our results with correlative fluorescence images recorded in total internal reflection mode. Our work opens the door to optical investigations of small traces of biomolecules and disease markers such as α-synuclein, chemokines and cytokines.

Chalcogenide Thin Films—Holographic Media for Augmented Reality Devices

Holographic characteristics of chalcogenide film materials with a typical thickness of 0.5–1.5 µm of a number of Ge-S and As-S compositions have been studied theoretically and experimentally with the aim of using them in augmented reality waveguide devices. The possibility of controlling the spectral and holographic properties of materials by varying their composition is shown. The recording of both volume and surface holographic elements operating in the total internal reflection mode was carried out. The operation of holograms in the “periscope mode” with a diffraction efficiency of about 10% is demonstrated. It is concluded that the recording of high-performance holographic elements on chalcogenide films requires significant values of exposure energy when recording in the near UV range (325–355 nm), which makes holographic recording currently ineffective for creating such elements.

Design and simulation of liquid infiltrated photonic crystal fibre in terahertz frequencies

Since ethanol, methanol, and water are polar solvents with similar physical properties albeit contrasting chemical properties, it is essential to have a method of accurately and reliably detecting and differentiating the liquids. In this paper, a unique-structured liquid infiltrated photonic crystal fibre (PCF) for sensing ethanol, methanol and water, has been introduced. The structure has been modelled, simulated and analysed in the terahertz (THz) region using the full vectorial finite element method. It has been shown that the THz light, which is guided using modified total internal reflection (M-TIR), is confined within the infiltrated analytes with negligible losses. For the detection of infiltrated liquids at 1.6 THz operating frequency, the proposed PCF shows sensitivity levels above 99% and effective material losses (EMLs) in the order of 10−4 dB m−1. Manufacturing of the proposed fibre has been shown to be feasible using the existing PCF fabrication technologies. It is envisaged that the proposed PCF will provide a solution to the existing challenges in detecting common polar solvents.

Effect of Psychostimulants on the Subunit Stoichiometry of the Dopamine and Serotonin Transporter

Objective and hypothesis Monoamine transporters control extracellular monoamine levels in the brain by mediating their reuptake from the synaptic cleft, thereby terminating signal transduction in monoaminergic neurons. Previous studies of our lab have revealed that these transporters co-exist as monomers and oligomers at the plasma membrane. Transporter oligomerization has been suggested to play a role in transporter trafficking, drug-induced monoamine efflux, and drug tolerance development. However, many aspects regarding monoamine transporter oligomerization remain poorly understood. The objective of the present study was to investigate how psychostimulants affect monoamine transporter oligomerization for the first time on a single molecule level. Based on findings of other studies, the hypothesis was that substrate-type psychostimulants dissociate monoamine transporter oligomers whereas transporter inhibitors have no effect. Methods Transporter oligomerization was measured using single molecule microscopy in live transporter-transfected Chinese hamster ovary cells. The oligomeric state of fluorescently-labeled dopamine and serotonin transporter (DAT and SERT, respectively) was assessed in total internal reflection mode one hour after exposure to various transporter inhibitors and substrates. Results The substrates 3,4-methylenedioxymethamphetamine and mephedrone dissociated higher-order SERT oligomers, resulting in a statistically significant decrease in average oligomeric state (Student's t-test, P<0.05). Furthermore, both substrates reduced the kinetic trapping of SERT oligomers by phosphatidylinositol 4,5-bisphosphate (PIP2). In contrast, none of the tested transporter inhibitors altered SERT oligomerization. Furthermore, none of the tested transporter substrates or inhibitors altered the oligomeric state of DAT. Conclusion The effect of psychostimulants on DAT and SERT oligomerization was for the first time investigated on a single molecule level in live cells. Substrate-type stimulants dissociated SERT higher-order oligomers whereas transporter inhibitors had no effect. None of the psychostimulants affected DAT oligomers. The effect of substrate-type psychostimulants therefore resembles that of direct phospholipase C agonists.

Investigation of the stability of spatial modes in quarter-disk resonators

In this work, the stability of short-wavelength spatial modes in quarter-disk cavities was studied. It was found that in such resonators, short-wave modes (with wavelengths λ smaller than the radius R of the quarter-disk λ<<R) in space form figures similar to folded twice m-polygons. The m-order of allowed stable modes decreases rapidly with an increase in the δ/R parameter of deviation from the ideal quarter-disk shape. Unlike half-disk resonators, quarter-disk resonators with δ/R>0.1 lack total internal reflection modes.

Study of human colorectal Mucosa by SPR biosensor using admittance Loci method

Biological tissues have the refractive index that may be used as a marker of colorectal pathological. Which can be study by using the theoretical design of Surface Plasmon Resonance (SPR), we have compared the refractive index of healthy with those of pathological human Colorectal Mucosa at different wavelengths. It was observed a higher sensitivity for refractive index for pathological tissues. The design of SPR study using different thickness of Gold thin film in attenuated total internal reflection mode has been reported in this paper. Different refractive index of colorectal Mucosa were investigated by discussing their effect on the SPR sensing and validated by the use of admittance Loci method.

Interfacial polymerization of a thin film on contact lenses for improving lubricity

Hypothesis: A large number of contact lens wearers drop out each year due to end of day discomfort, which could possibly be reduced by designing lenses with highly lubricious surfaces. We hypothesize that polymerizing a thin film of dimethyl acrylamide (DMA) on the surface of the lenses will improve lubricity.Experiments: The thin film is polymerized by loading a commercial contact lens (1-DAY ACUVUE® TruEye®) with N,N,N′,N′-Tetramethylethane-1,2-diamine (TEMED) and soaking it in a solution of DMA and ammonium per sulfate (APS). The two components of the redox couple (APS and TEMED) mix near the surface of the lens due to diffusion and react rapidly to form free radicals. The free radicals lead the polymerization of the DMA monomer near the surface resulting in the formation of the thin hydrogel layer that is attached to the lens matrix through activation of unreacted vinyl groups or possibly through formation of entanglements with the lens polymer.Findings: The thickness of the layer is controlled by the polymerization time which is limited to 30 s to create a layer of DMA only at the surface. The presence of the DMA layer is confirmed through measurements of Fourier-transform infrared spectroscopy (FTIR) spectra in total internal reflection mode. The layer is determined to be about 3–5 µm thick with a water content of about 285%. The presence of the layer significantly improves lubricity as is evident through the qualitative rubbing test and quantitative measurement of the friction coefficient. A preliminary one-week safety study in rabbits show that lens wear does not cause any toxicity.

Optical anisotropy of black phosphorus by total internal reflection

Although abundant research on the anisotropy of van der Waals (vdW) materials has been published, we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional (2D) nanospace. As an example, we study the reflectance of few-layered black phosphorus (BP) in the total internal reflection (TIR) mode in detail. We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles, polarization states, and the in-plane rotation angles of the BP samples. Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals, so these conclusions can be widely applied to other anisotropic 2D materials. This research furthers the current understanding of the properties of BP more comprehensively, and provides guidance for developing new optoelectronic applications, especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.

Room-temperature high-performance CsPbBr3 perovskite tetrahedral microlasers.

With the goals of faster coherent light sources with lower power consumption, laser miniaturization has been intensively pursued in the past four decades. Novel microscale cavities with efficient feedback and distinct emission profiles are essential for excellent performance of laser devices and for exploring their new functionalities. Here, for the first time, well-defined high-quality tetrahedron-shaped CsPbBr3 perovskite microcavities with smooth surfaces were synthesized via the vapor growth method. A room-temperature high-performance tetrahedral microlaser was realized based on CsPbBr3 perovskite single crystals. The three-dimensional total internal reflection mode inside the tetrahedral cavity led to a high-performance microlaser with a linewidth of only ∼0.3 nm at 538 nm emission wavelength and a unique profile with three emission beams into free space with triangular symmetry. In addition, the perovskite tetrahedral microlasers could be pumped by two-photon absorption with threshold only about 2.5 times higher than that of a one-photon laser. The high-performance tetrahedral microlaser with a distinct emission profile enriches the microscale laser family and may find exceptional applications in optical manipulation, communication and on-chip beam steering.

Spectral characteristics of a photonic bandgap fiber

With the help of numerical simulation, we study the propagation of light in an all-glass photonic crystal fiber. A comparison of the spectral characteristics of a fiber with the idealized hexagonal structure and a fiber with transverse profile deformations is conducted. The calculations use methods based on a spatial Fourier transform. It is shown that total internal reflection modes and the fundamental mode of the photonic bandgap can be excited simultaneously. Structural deformation of a photonic crystal fiber results in the shifting and narrowing of the photonic bandgap. Excitation of the total internal reflection modes leads to increased absorption on the boundaries of the spectral band of the fiber.

LSPR Biosensor Based on Nanostructured Gold Films: Detection of Mycotoxins

This work focuses on the development of optical sensors based on the LSPR phenomenon in nano-structured gold films suitable for detection of mycotoxins. A simple technology of annealing thin gold films was utilized for the formation of gold nano-islands exhibiting the LSPR effect. The morphology of gold nano-structures produced was studied with SEM and AFM while their optical properties were analysed with UV-vis absorption spectroscopy and spectroscopic ellipsometry (SE). A blue spectral shift of LSPR band caused by changes in the refractive index of medium constitutes the main principle of LSPR sensing. Bio-sensing tests were attempted using SE in total internal reflection mode (TIRE); a noticeable spectral shift was recorded on course of immune binding of aflatoxin B1 to specific antibodies immobilized on the surface of gold.

Förster Resonance Energy Transfer to Study TCR-pMHC Interactions in the Immunological Synapse.

T-cell antigen recognition is remarkably efficient: when scanning the surface of antigen-presenting cells (APCs), T-cells can detect the presence of just a few single antigenic peptide/MHCs (pMHCs), which are often vastly outnumbered by structurally similar non-stimulatory endogenous pMHCs (Irvine et al., Nature 419(6909):845-849, 2002; Purbhoo et al., Nat Immunol 5(5):524-530, 2004; Huang et al., Immunity 39(5):846-857, 2013). How T-cells achieve this is still enigmatic, in particular in view of the rather moderate affinity that TCRs typically exert for antigenic pMHCs, at least when measured in vitro (Davis et al., Ann Rev Immunol 16:523-544, 1998). To shed light on this in a comprehensive manner, we have developed a microscopy-based assay, which allows us to quantitate TCR-pMHC interactions in situ, i.e., within the special confines of the nascent immunological synapse of a T-cell contacting a planar-supported lipid bilayer functionalized with the costimulatory molecule B7-1, the adhesion molecule ICAM-1, and pMHCs (Huppa et al., Nature 463(7283):963-967, 2010) (Fig. 1). Binding measurements are based on Förster resonance energy transfer (FRET) between site-specifically labeled pMHCs and TCRs, which are decorated with recombinant site-specifically labeled single-chain antibody fragments (scFV) derived from the TCRβ-reactive H57-597 antibody (Huppa et al., Nature 463(7283):963-967, 2010). FRET, a quantum-mechanical phenomenon, involves the non-radiative coupling of dipole moments of two adjacent fluorophores, a donor molecule and an acceptor molecule. FRET efficiency is inversely proportional to the sixth power of the inter-dye distance. Hence, it can be employed as a molecular ruler (Stryer and Haugland, Proc Natl Acad Sci, USA 58(2):719-726, 1967) or, as is the case here, to score for interactions of appropriately labeled molecules. To facilitate both quantitative and single-molecule readout, it is important to conjugate donor and acceptor dyes in a site-specific manner.While SLBs mimic some but certainly not all properties of a plasma membrane of a living cell, their use features a number of operational advantages: SLBs can be prepared in a fluid state, thereby facilitating the spatial rearrangements that accompany the formation of an immunological synapse (Grakoui et al., Science 285(5425):221-227, 1999). The imaging of a three-dimensional binding process is reduced to two dimensions, which saves time and fluorophore-emitted photons and allows for fast measurements. Furthermore, images can be acquired in noise-attenuated total internal reflection (TIR) mode, so far a necessity for single-molecule detection within the immunological synapse. Importantly, the stimulatory potency of pMHCs is very well preserved compared to cell surface-embedded pMHCs. Hence, while in principle artificial, SLBs are still a good approximation of the physiologic scenario a T-cell encounters when approaching an APC. Vice versa, the reconstitutive approach offers unique opportunities to interrogate the influence of accessory molecules on T-cell antigen recognition in a highly quantitative manner.In this chapter we will provide recommendations for the production of proteins used for SLB decoration as well as hands-on protocols for the production of SLBs. We will describe in detail how to perform and analyze FRET-based experiments to determine synaptic binding constants. In the "Notes" section, we will provide some information regarding the microscope setup as well as the mathematical and biophysical foundation underlying data analysis.

High-Speed Surface Plasmon Resonance (SPR) Reflectance Imaging of Drop Coalescence during Condensation and Evaporation

Drop condensation and coalescence is visualized using high-speed Surface Plasmon Resonance (SPR) reflectance microscopy. SPR microscopy is a label-free technique that can characterize thin films (less than 1µm) by detecting the changes in the refractive index of the test medium. The sensing surface is a 50 nm thick gold film on a 2.5 nm thick Ti layer is deposited on a borosilicate substrate. P-polarized monochromatic light (632 nm) is incident on the gold film in a total internal reflection mode. Free electrons in the gold film are excited by the incident light when a resonance condition is met. The result is a decrease in the reflected intensity. Resonance depends upon wavelength, incident angle, and refractive index of prism and test medium. To induce condensation, a water bridge is created between the SPR gold film and an ITO coated glass slide. When the ITO coated slide is heated water evaporates from the bridge and condenses on the gold film. The sequence of images on the process of droplet deposition and drop coalescence are captured at 1500 frames per second. Experiments were conducted at an SPR angle of 44o, which is slightly above the minimum intensity angle for air at 43.8o. Therefore, the brightest and darkest regions correspond to the areas on the gold film covered with bulk water and a very thin film of water, respectively. The thickness of the film is proportional to the intensity of reflected light.

Analysis of Silicon Based Surface Plasmon Resonance Sensors with Different Amino Acids

A semiconductor prism coupler based nano-plasmonic sensor consisting of a high refractive index (RI) silicon prism, a gold (Au) metal film and different amino acids was used as a dielectric sample for sensing in the in the Attenuated Total Internal Reflection (ATIR) mode. An additional silicon nano-layer has been used for increasing stability and sensitivity of the surface plasmon resonance-sensor which causes enhancement of the evanescent field near the metal-analyte interface compared to the traditional three layer structure. Positional swap of the silicon nano-layer from above the metal surface to below the metal surface causes further enhances of the evanescent field near the metal-analyte interface. Performance of the nano-plasmonic sensors depending upon the high refractive index silicon prism, additional silicon nano-layer and swapping mechanism is discussed with the help of sensing performance for different amino acids with corresponding image response for the proposed nano-plasmonic sensor in a MATLAB environment.

Interface modes for monolithic nonlinear photonics

A design methodology for obtaining versatile interface modes in monolithic structures is discussed. These modes are then utilized in conjunction with total internal reflection modes for phase-matching second-harmonic generation (SHG) in periodic layered media in AlxGa1&#x2212;x As material system. Typical loss values of 2.71&#x2009;&#x2009;cm&#x2212;1 for a TE-polarized pump and 4.26&#x2009;&#x2009;cm&#x2212;1 for a TM-polarized pump around 1550&#xA0;nm were obtained. Nonlinear characterizations are carried out using 2&#xA0;ps, 30&#xA0;ps, and a continuous wave pump for type-I and type-II interactions. Maximum SHG conversion efficiency of 1.14&#xD7;104&#x2009;%&#x2009;&#x2009;W&#x2212;1&#x2009;cm&#x2212;2 is observed for the type-II process with a pump power of 0.52&#xA0;mW in a sample with a length of 2.0&#xA0;mm.

Surface plasmon resonance structures in spectral interrogation using high refractive index prism materials for sensing of different amino acids

A prism coupler-based nano-plasmonic sensor consisting of a high refractive index (RI) prism (2S2G-prism, LASF9-prism), gold (Au) metal film, and different amino acids as the dielectric sample is used for sensing in attenuated total internal reflection mode. An additional semiconductor (silicon) nano-layer over the gold surface has been used for increasing the stability and sensitivity of the surface plasmon resonance sensor. A comparative analysis of performance of the nano-plasmonic sensors in the spectral regime using these two high RI prism materials with an additional semiconductor nano-layer has been presented. The sensing performance of the proposed nano-plasmonic sensors in terms of evanescent field enhancement, spectral sensitivity, detection accuracy, figure of merit, and Q-factor with different amino acid samples has been discussed along with supporting theoretical simulations in a MATLAB® environment.

Slot Spiral Silicon Photonic Crystal Fiber With Property of Both High Birefringence and High Nonlinearity

A photonic crystal fiber (PCF) made of silicon is proposed and numerically optimized with both ultrahigh birefringence and nonlinearity. By introducing an elliptical low-index slot in the core region, one of the orthogonally polarized fundamental modes can be confined in the low-index region due to the discontinuity of its electric field at the interface of the slot and the surrounding material, while the other fundamental mode is dominated by the modified total internal reflection (MTIR) induced by air holes of the cladding, leading to a birefringence as high as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> order. On the other hand, benefiting from the tight field confinement and highly nonlinear material, nonlinear coefficients up to 1068 W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 162 W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> can be achieved for the slot mode and the MTIR mode, respectively.