JEOS:RP - Journal of the European Optical Society Rapid publications
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Optical metrology for immersed diffractive multifocal ophthalmic intracorneal lenses
Get PDFThis paper deals with the optical characterization of diffractive multifocal Intra-Corneal Lenses (ICLs) that we have developed in order to correct presbyopia. These diffractive multifocal lenses are made of a very soft material (permeable to oxygen and nutrients), with a thickness smaller than 100 µm and require liquid immersion. As a consequence, most of the conventional metrology methods are unsuited for their characterization. We developed specific setups to measure diffractive efficiencies and Modulation Transfer Function (MTF) adapted to such components. Experimental results are in good agreement with Zemax® simulations. For the best of our knowledge, it is the first time that optical characterization is devoted to the ICLs. Furthermore, most of the IOL’s optical characterizations are focused on far vision MTF and don’t assess the near vision MTF, which we study in this paper
Modeling and measurements of angular truncation for an aerosol albedometer
Get PDFIn this work, we examine the angular truncation behavior and present correction factors for the aerosol albedometer previously developed in our laboratory. This new instrument makes simultaneous measurement of extinction and scattering coefficients (bext and bscat) on dispersed aerosol samples. The aerosol extinction coefficient is measured with cavity ring-down spectroscopy (CRDS), and the scattering coefficient is determined through the integrating sphere nephelometer. However, all nephelometers are not able to collect light scattered from an aerosol sample very near the forward (0°) and reverse (180°) directions, due to the geometrical constraints. This can result in systematic underestimation of scattering coefficient known as truncation error. In order to account for this problem and describe scattering by aerosols more precisely, correction factors (C) for this angular non-ideality have been theoretically developed. Truncation angles (q) were calculated upon consideration of the geometry of the sphere nephelometer. As truncation error largely depends on particle size and refractive index, C values were computed for a series of spherical, homogeneous aerosol particles with different known particle sizes and refractive indices by Lorenz-Mie theory. Measurements on size-selected, laboratory generated aerosols of known size and composition allowed empirical measurement of truncation correction factors to compare with the Mie model results. Results indicate the model we built overestimates the fraction of light not collected by the sphere. Empirically observed correction factors of ≤ 1.12 for particles with size parameters (a) < 6 were determined. In addition, the effect of number of particles within the probe beam on the suitability of correction factors was also examined. Observations support the hypothesis that particles are rapidly transported / mixed through the probe beam, and measurement integration times as short as 52 s yield data that is indistinguishable from the probe region being homogeneously filled with aerosol, even at very low particle concentrations
Novel concept for three-dimensional polymer waveguides for optical on-chip interconnects
Get PDFWe present a simulation study and first experimental implementations for a novel polymer three-dimensional waveguide design. The structures described here allow for new concepts of on-chip communication. By using direct laser writing, free-formed polymer structures can be realized directly on the surface of integrated circuits on wafer- or die-level. Further photonic structures like waveguides, resonators, splitters and couplers can be realized with an extended freedom of design to the third dimension. Our approach opens new possibilities for optical interconnects and routing for on-chip signal transmission with a high fill factor and CMOS compatibility
Refractive index sensor based on slot waveguide cavity
Get PDFThe experimental study of a gold slot waveguide cavity is presented. The resonance of this cavity working in the telecom wavelength range is highly dependent on the refractive index of the medium located in or around the slots array, because of the high confinement of the electromagnetic field in the structure. We will demonstrate the application of this structure to local refractive index sensors at the nanoscale. The measured sensitivity of this device is S = 730 nm/RIU (refractive index unit). The structure has been optimized by adding another array of slots cascaded with the first one. The consequence is an improvement in the time efficiency of the experiments. A discussion about the effect of the volume of liquids used and the filling percentage of the slots by the liquids is also presented as parameters affecting the measurements and the sensitivity of the sensor
Subwavelength resolution of the annular photonic crystal with negative refraction
Get PDFIn this paper, negative refraction in the two-dimensional (2D) hexagonal lattices annular photonic crystal (APC) was theoretically studied. The annular photonic crystal was obtained by introduced circular-air-hole in the core of the Si-rod. The properties of the designed APC, such as photonic band structure, equal-frequency contours (EFCs) and the electric field distribution are analyzed by using Plane Wave Expansion (PWE) method and Finite-Difference Time-Domain (FDTD) method. Numerical simulations show that negative refraction and super-lens imaging can be realized in the designed annular photonic crystal for the normalized frequency from 0.2983(2Ï€c/a) to 0.347(2Ï€c/a). And it was also found that the resolution decreases linearly with the increasing of the inner radius
An integrated Young interferometer based on UV-imprinted polymer waveguides for label-free biosensing applications
Get PDFWe demonstrate a polymer rib waveguide Young interferometer sensor fabricated by UV-imprinting. An inverted rib waveguide structure was utilized in order to simplify the fabrication process. In this configuration grooves are formed on the under cladding layer by UV-imprinting and core material is spin coated on top to fill the grooves. Glucose water solution was used to characterize the sensor response against ambient refractive index changes. The sensing responses correspond linearly with the refractive index change of glucose solutions with a detection limit of about 10-5. To verify the capability of the polymer sensor for biosensing, an immunoassay was performed with c-reactive protein (CRP) and human CRP specific antibody adsorbed on the waveguide surface as a receptor. The CRP solution in PBS (phosphate buffered saline) buffer with a concentration of 2 µg/ml (16 nM) resulted in an obvious response which was over a couple hundred times of the noise level. Based on these values, a detection limit of about 2.4 pg/mm2 was found for the surface sensing of molecular adsorption. With the proposed waveguide configuration, the fabrication of polymer sensors can be ultimately transferred to roll-to-roll mass production to produce low-cost disposable sensors
Investigation on nonlinear-optical properties of palm oil/silver nanoparticles
Get PDFWe have investigated the spatial self phase modulation of palm oil containing silver nanoparticles (palm oil/Ag-NPs). The study carried out using continuous wave diode pumped solid state laser with wavelength of 405 nm and power of 50 mW. The strong spatial self phase modulation patterns were observed that suggest the palm oil/Ag-NPs have a relatively large nonlinear refractive index. The obtained values of nonlinear refractive index were increased with the increment in the volume fractions. The observed experimental patterns were also theoretically modeled which are in good agreement with experimental results
Microsized subsurface modification of mono-crystalline silicon via non-linear absorption
Get PDFWe introduce a novel method of optically inducing microsized subsurface structures using non-linear absorption of near infrared light in mono-crystalline silicon. We discuss the physical processes such as multi-photon absorption and self focussing in the material. The results presented in this paper demonstrate a new method of subsurface modifications in silicon and may open up novel avenues for optical devices embedded in silicon and optical process for the separation of wafers from their ingots
Detection of inter-hemispheric functional connectivity in motor cortex with coherence analysis
Get PDFFunctional near-infrared spectroscopy (fNIRS) is showing promise as an alternate method to fMRI for studying cortical function. Resting state studies in both methods are showing functional linkages. The strength of functional connections is typically quantified by the level of significance of the temporal synchrony between brain regions, termed resting-state functional connectivity. Coherence analysis of resting state allows for phase insensitive and frequency specific analysis. This paper provides a detailed method for undertaking fNIRS in combination with resting-state coherence analysis. We show that maps of inter-hemispheric resting-state functional connectivity between the motor cortices can be reliably generated, and the frequency responses (to 50 Hz) for both oxy- and deoxyhemoglobin. Frequencies of 0-0.1 Hz provide robust data as have been shown previously. Higher frequencies (up to 5 Hz) also exhibit high coherence. Deoxyhemoglobin also shows high coherence above 10Hz. Coherence is similar during both resting and task activated states. fNIRS allows for mapping cortical function and, in combination with coherence analysis, allows one to study variations in frequency response
Measurement accuracy of the pulse repetition interval-based excess fraction (PRIEF) method: an analogy-based theoretical analysis
Get PDFWe describe a novel approach for a theoretical analysis of the measurement accuracy of the pulse repetition interval-based excess fraction8 (PRIEF) method, which is expected to be useful for high-precision length measurement. The proposed approach is introduced by focusing on an analogy between the PRIEF method and the conventional length-measurement method. The theoretical analysis results show that the absolute accuracy achievable by the PRIEF method is nanometer-order, and the relative accuracy achievable by the PRIEF method is 10^-8-order, which is affected mainly by the measuring accuracy of the refractive index of air. We conclude that our analysis is useful for further development of the PRIEF method