A Photonic crystal fiber with large effective refractive index separation and low dispersion.

A photonic crystal fiber (PCF) structure with a ring-core and 5 well-ordered semiellipse air-holes has been creatively proposed. Through a comparison between the structures with a high refractive index (RI) ring-core and the structure without, it conclude that a PCF with a high RI ring-core can work better. Schott SF57 was elected as the substrate material of ring-core. This paper compares the effects of long-axis and short-axis changes on the PCF and selects the optimal solution. Especially TE0,1 mode's dispersion is maintained between 0 and 3 ps / (nm · km) ranging from 1.45 µm to 1.65 µm. This property can be used to generate a supercontinuum with 200 µm long zero dispersion wavelength (ZDM). In addition, Δneff reaches up to 10-3, which enables the near -degeneracy of the eigenmodes to be almost neglected. The proposed PCF structure will have great application value in the field of optical communications.

Refractive index of human red blood cells between 290 nm and 1100 nm determined by optical extinction measurements.

The knowledge of optical properties of biological cells is essential to interpret their interaction with light and to derive morphological information and parameters associated with cell function like the oxygen transport capacity of human red blood cells (RBCs). We present a method to determine the dependence between the refractive index (RI) of human RBCs and their intracellular hemoglobin (Hb) concentration from spectral extinction measurements of a cell suspension. The procedure is based on the analysis of the corresponding ensemble averaged extinction cross section [Formula: see text]. Thus far two complementary approaches have been taken to derive RIs of RBCs. The first one uses homogeneous macroscopic samples prepared by hemolysis for the destruction of the RBCs' membranes and subsequent centrifugation. A second approach is the determination of RIs of single intact cells by microscopic investigation. These techniques are limited to a few discrete wavelengths or a rather narrow wavelength range. In addition most of these techniques require additional information about the concentration dependence. In contrast, our approach yields the RI increment with Hb concentration of intact, reversibly isovolumetrically sphered, oxygenated RBCs over a wide wavelength range from 290 nm to 1100 nm from macroscopic measurements.

Ultrasensitive refractive index sensor based on a Mach-Zehnder interferometer created in twin-core fiber.

We proposed and experimentally demonstrated a twin-core fiber (TCF)-based Mach-Zehnder interferometer (MZI) to develop an ultrasensitive refractive index (RI) sensor. This fiber MZI was constructed by splicing a short section of TCF between two sections of single mode fibers. A microchannel was drilled through one core of the TCF by means of femtosecond laser micromachining to create one arm of the proposed interferometer, and the other core worked as the second arm. Such a fiber interferometer exhibits an ultrahigh RI sensitivity of -10981 nm/RIU and a low temperature cross-sensitivity of 3.96×10(-6) RIU/°C. Moreover, the ultra-compact device size and all-fiber configuration make it very suitable for highly sensitive RI sensing at precise location.

Ultra-broadband wide-angle unidirectional plasmonic coupler based on joint effects of plasmonic critical angles and subwavelength metallic gratings.

A unidirectional plasmonic coupler with ultra-broadband and wide-angle coupling efficiency is proposed and demonstrated. Employing the plasmonic critical angle (PCA) phenomenon in conjunction with the effect of subwavelength metallic gratings, a wide incident angular full-width-half-maximum (AFWHM >28°) coupling efficiency larger than 50% and extinction ratio better than 15 dB over an ultrabroad wavelength range 725-985 nm (bandwidth >260 nm) are achieved. The operation principle and performance of the structure are clarified and theoretically illustrated.

Refractive index of solutions of human hemoglobin from the near-infrared to the ultraviolet range: Kramers-Kronig analysis.

Because direct measurements of the refractive index of hemoglobin over a large wavelength range are challenging, indirect methods deserve particular attention. Among them, the Kramers-Kronig relations are a powerful tool often used to derive the real part of a refractive index from its imaginary part. However, previous attempts to apply the relations to solutions of human hemoglobin have been somewhat controversial, resulting in disagreement between several studies. We show that this controversy can be resolved when careful attention is paid not only to the absorption of hemoglobin but also to the dispersion of the refractive index of the nonabsorbing solvent. We present a Kramers-Kroning analysis taking both contributions into account and compare the results with the data from several studies. Good agreement with experiments is found across the visible and parts of near-infrared and ultraviolet regions. These results reinstate the use of the Kramers-Kronig relations for hemoglobin solutions and provide an additional source of information about their refractive index.

Ultimate resolution for refractometric sensing with whispering gallery mode microcavities.

Many proposed microfluidic biosensor designs are based on the measurement of the resonances of an optical microcavity. Fluorescence-based resonators tend to be simpler and more robust than setups that use evanescent coupling from tuneable laser to probe the cavity. In all sensor designs the detection limits depend on the wavelength resolution of the detection system, which is a limitation of fluorescence-based devices. In this work, we explore the ultimate resolution and detection limits of refractometric microcavity sensor structures. Because many periodic modes are collected simultaneously from fluorescent resonators, standard Fourier methods can be best suited for rapid and precise analysis of the resonance shifts. Simple numerical expressions to calculate the ultimate sensor resolution and detection limits were found, and the results compared to experiments in which the resonances of fluorescent-core microcapillaries responded to various sucrose concentrations in water.

Influence of linear birefringence in the computation of scattering phase functions.

Birefringent media, like biological tissues, are usually assumed to be uniaxial. For biological tissues, the influence of linear birefringence on the scattering phase function is assumed to be neglectable. In order to examine this, a numerical study of the influence of linear birefringence on the scattering phase function and the resulting backscattering Mueller matrices was performed. It is assumed that the media consist of spherical scattering particles embedded in a nonabsorbing medium, which allows us to employ the Lorenz-Mie theory. In the Monte Carlo framework, the influence of linear birefringence on the components of the electric field vector is captured through the Jones N-matrix formalism. The Lorenz-Mie theory indicates that a given linear birefringence value Δn has a bigger impact on the scattering phase function for large particles. This conclusion is further supported by Monte Carlo simulations, where the phase function was calculated based on the refractive index once in the ordinary direction and once in the extraordinary one. For large particles, comparisons of the resulting backscattering Mueller matrices show significant differences even for small Δn values.

Medición comparativa de la densidad urinaria: tira reactiva, refractómetro y densímetro / Comparative measurement of urine specific gravity: reagent strips, refractometry and hydrometry

La densidad urinaria se utiliza enla clínica para evaluar la capacidad renal de concentrar y diluir la orina. Se puede medir mediante tres métodos: urodensímetro (UD), refractómetro(RE) y tiras reactivas (TR).Objetivo. Evaluar la exactitud de diferentes métodos de medición de la densidad urinaria.Diseño del estudio. Transversal, comparativo, con recolección prospectiva de datos.Material y métodos. Se analizaron 156 muestras de orina de pacientes pediátricos, durante abrily mayo de 2007. Se determinó, en forma simultánea, la densidad urinaria mediante UD, RE y TR, y se midió osmolaridad por punto de congelación;la osmolaridad urinaria fue el métodode referencia. Se calculó la correlación entre los distintos métodos (UD, TR y RE) contra la osmolaridad mediante el coeficiente de correlación lineal de Pearson.Resultados. Se encontró una correlación positiva y aceptable con la osmolaridad tanto del RE como del UD (r= 0,81 y r= 0,86 respectivamente).Las tiras reactivas presentaron baja correlación (r= 0,41). También, observamos buena correlaciónentre las mediciones por UD y RE (r= 0,89).Las mediciones obtenidas por TR, en cambio, tuvieron mala correlación cuando se compararoncon UD (r= 0,46). Se encontraron valores más altos de densidad medidos con RE con respecto al UD.Conclusiones. Las TR no constituyen un método confiable para la determinación de la densidad urinaria y debería ser abandonada como prueba de rutina. En cambio, tanto el UD como el RE sonalternativas aceptables para determinar la densidad urinaria, siempre y cuando el seguimiento del paciente se realice con el mismo método.(AU)

Temperature performance of a macrobending single-mode fiber-based refractometer.

We present, theoretically and experimentally, an investigation of temperature dependence of a macrobending single-mode fiber-based refractometer utilizing a ratiometric scheme. The conventional scalar approximation method is utilized for predicting the temperature dependent loss of the proposed fiber refractometer. An all-fiber ratiometric measurement system is built to allow the comparison of modeled and measured results. Calculated and measured results for an SMF28 refractometer are in good agreement and confirm the effect of temperature on refractive index measurements. Both calculated and measured ratio responses monotonically change with temperature, which allows for a temperature correction process.

[Setting the individual file of ocular refractive development of children is the primary procedure in the prevention of myopia].

The purpose of setting the file of ocular refractive development is to record the process of eye development in children with plan. Set the individual file and begins at 3 years old till 12. Examination is done every 6 months. Parameters are recorded including power of cycloplegic refraction, visual acuity, keratometer, anterior chamber depth, axial length, intraocular pressure, body height and weight. In this way, can provide very important information as to the prompt intervening in myopia control. It is also the effective and practical way in myopia prevention.

Towards automated classification of clinical optical coherence tomography data of dense tissues.

The native contrast of optical coherence tomography (OCT) data in dense tissues can pose a challenge for clinical decision making. Automated data evaluation is one way of enhancing the clinical utility of measurements. Methods for extracting information from structural OCT data are appraised here. A-scan analysis allows characterization of layer thickness and scattering parameters, whereas image analysis renders itself to segmentation, texture and speckle analysis. All fully automated approaches combine pre-processing, feature registration, data reduction, and classification. Pre-processing requires de-noising, feature recognition, normalization and refining. In the current literature, image exclusion criteria, initial parameters, or manual input are common requirements. The interest of the presented methods lies in the prospect of objective, quick, and/or post-acquisition processing. There is a potential to improve clinical decision making based on automated processing of OCT data.

Inherent homogenous media dispersion compensation in frequency domain optical coherence tomography by accurate k-sampling.

Depth dependent broadening of the axial point spread function due to dispersion in the imaged media, and algorithms for postprocess correction, have been previously described for both time domain and frequency domain optical coherence tomography. We show that homogeneous media dispersion artifacts disappear when frequency domain samples are acquired with uniform spacing in circular wavenumber, as opposed to uniform sampling in optical frequency. We further explicate the source of this point spread broadening and simulate its magnitude in aqueous media. We experimentally demonstrate media dispersion compensation in high dispersion glass by choosing sample frequencies at equal intervals of media index of refraction divided by vacuum wavelength, and we recover unbroadened reflections without an additional postprocessing step.

Laser spectral characterization in multiphoton microscopy.

Spectral and temporal characterization is a fundamental task when a tunable Ti:sapphire ultrafast laser system is operated for multiphoton microscopy applications. In the present paper simple procedures are reported that perform laser-peak-emission wavelength and bandwidth measurements without the need of any further instrumentation but a simple and inexpensive diffraction grating, by taking advantage of the confocal microscope imaging capabilities.

Variation during autorefraction: influence of two different target types.

An investigation was performed on seven subjects of varying ages in order to determine the influence of two different target types on autorefractor results. A single autorefractor capable of presenting two different targets was used. Multivariate statistical methods which only recently have become available in optometry are used to illustrate graphically the results obtained and formal hypothesis tests further demonstrate that most of the eyes in the sample display similar variation or behaviour with both targets. The mean refractive state likewise is not significantly different for both targets for five of the seven eyes at a 99% confidence level. Departures from multivariate normality (such as resulting from outliers) are shown to be of great importance in order to reach appropriate decisions with respect to target influence on autorefractor measurements and an example is provided to illustrate this point. In the absence of departures from normality it is believed that this study exhibits only weak evidence for differences in variation or mean refractive state with the different target types.

Refractometría automática: análisis y aplicación práctica / Automatic refractometry: analysis and practical use

Con el fin de establecer la confiabilidad de la técnica se realizó un estudio prospectivo de refracción automatizada durante un período de 12 meses en diversos centros de atención clínica logrando refraccionar objetivamente 7000 pacientes. El rango de edades fluctuó entre los 6 a los 94 años con una media de 66.3 años de los cuales el 42,7 por ciento fue de sexo masculino y el 57,3 por ciento de sexo femenino. Las ametropías más frecuentes fueron la hipermetropía y el astigmatismo miópico compuesto. El componente esférico resultó altamente confiable (76,3 por ciento), no así el componente cilíndrico (23,7 por ciento) que debe ser interpretado cuidadosamente. La refracción expresada en términos de componente cilíndrico negativo es mejor tolerada que en valores positivos cuando es a favor de la regla (86,7 por ciento). La confiabilidad de la variación esférica por sobre o bajo el promedio fue de 0,25 dioptrías (71,1 por ciento), en cambio la variación cilíndrica resultó más segura al disminuirla en 0,5 dioptrías (52,3 por ciento). El rendimiento de la técnica es mejor en edades entre los 20 a los 60 años (67,8 por ciento). Las mujeres manifestaron mayor tolerancia con la prescripción (76,3 por ciento). La confiabilidad según el eje del astigmatismo es ligeramente mejor cuando es a favor de la regla (36,9 por ciento). Diversas patologías, entre ellas diabetes y cataratas, son las que más errores causan durante la medición y la falta de discriminación entre un astigmatismo corneal o residual es el error más frecuente en la interpretación. La sensación de desnivel fue la causa más frecuente de intolerancia con la prescripción (11,3 por ciento). Finalmente la confiabilidad de la técnica fue de 97,4 por ciento