Showing papers on "Step-index profile published in 1983"

Simultaneous determination of refractive index and size of spherical dielectric particles from light scattering data.

Abstract: The diameter and refractive index of micrometer sized spherical dielectric particles are simultaneously deduced using the wavelength dependence of backscattering data from optically levitated particles. The accuracy of the results is set by experimental errors in the determination of the wavelength of backscatter resonance peaks and the ratio of slopes of specified peaks. At present the refractive index and diameter can be deduced with relative errors of 5 x 10(-5). This represents the most accurate determination of absolute size and refractive index yet made by light scattering. A reduction of these errors by an order of magnitude is possible. We assume a priori knowledge of diameter and refractive index with accuracy of 10(-1) and 5 x 10(-3), respectively.

Refractive index dispersion and related properties in fluorine doped silica

Abstract: Refractive index dispersion has been determined for fluorine doped fused silica containing 1 and 2% fluorine. Addition of fluorine is found to reduce the refractive index and material dispersion. Fibers modeled for minimization of modal dispersion having fused silica cores and fluorine doped silica cladding show a strong composition dependence of the optimum refractive index profile. Comparison of results with those in the literature based on N.A. vs λ measurements reveal minor discrepancies probably due to the drawing process.

Characterization of proton‐exchange slab optical waveguides in z‐cut LiNbO3

Abstract: We report the results of a systematic study on planar optical waveguides fabricated in z‐cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single‐mode waveguide at a 633‐nm wavelength was 2.4 dB/cm.

Refractive index and spectral models for gradient-index materials.

Abstract: Models are presented which describe the refractive index and spectral variation of gradient-index materials. Classes of gradient which exhibit little or no variation with wavelength are predicted. These are termed achromatic gradients. Experimental verification of the models is presented in a following paper.

Measuring refractive index and thickness of thin films: a new technique

Abstract: Properties of a leaky quasi-waveguide formed by a thin film of refractive index smaller than the substrate are described. By exciting these leaky waves through the substrate, we have demonstrated a convenient and accurate method of measuring both the refractive index and thickness of thin films. Experimental results are given for polystyrene, with a demonstrated accuracy comparable with both that of prism coupling into a waveguiding film and with ellipsometry.

Refractive-Index measurements of liquids used in conjunction with optical fibers

Abstract: Refractive-index measurements of ten liquids were made at nine discrete wavelengths over the 589–1674-nm spectral range using a Hilger-Chance refractometer with a modified viewing system. The total error in refractive-index measurement was considered to be ±3 × 10−4. In all cases, the variation in refractive index with increasing wavelength was found to be a smooth monotonically decreasing function that could be accurately fitted by the Cauchy formula. Constants for the latter have been given.

Dispersionless single-mode fibers with trapezoidal-index profiles in the wavelength region near 1.5 microm

Abstract: The transmission performance of trapezoidal-index profile single-mode fibers that can operate with zero dispersion in the 1.5-microm region has been investigated. The exact numerical calculations of propagation characteristics for these lightguides established a variety of relationships in terms of the parameters of a trapezoidal-index profile. One of the profile parameters that defines the shape of a trapezoid is the aspect ratio S, which ranges between 0 and 1. It was found that as the aspect ratio decreases from 1.0 to 0.3 the optimum core radius of the fiber gradually increases. But when S is <0.3, it approaches a constant equal to the value of the triangular-index profile (S = 0).

Refractive index profiles of LiNbO3: Ti waveguides

Abstract: Eight LiNbO3: Ti waveguides have been fabricated under differing conditions The effective refractive indices of guided modes have been measured and successfully fitted to Gaussian index profiles The change of refractive index and titanium concentration are related by a power law, the exponents being different for the extraordinary and the ordinary beam

Characterisation of single-mode fibres by near-field measurement

Abstract: A new technique for the determination of the refractive-index profile of single-mode optical fibres from a simple near-field measurement is proposed. This permits one to deduce accurately all the important parameters of the fibre.

Large bandwidth optical fibers

Abstract: Multimode optical fibers are described comprising a cylindrical core with a radius a o exhibiting an index of refraction n o surrounded by a cladding having an outer radius a in which the index of refraction varies continually from the core to the periphery from a value of n 1 to a lower value n e . Between the core and cladding there is a step change Δn in their respective indices of refraction whose value is a function of the ratio a o /a. Such fibers have both slight attenuation and slight dispersion and can be manufactured using processes similar to those used in making step-index optical fibers.

Simple Method For Measuring The Refractive Index Of A Liquid Or Glass Wedge

Abstract: This paper describes a simple method of measuring the refractive index of a liquid. The basic element is a thin wedge cell, and the source of light is a low power He-Ne laser. Conditions are derived to obtain the best possible accuracy using this setup. The same setup can also be used for the determination of the refractive index of a solid medium such as glass.

Method and apparatus for determining index of refraction profiles of optical fibers

Abstract: A photodetector (42) having a passageway (47) therethrough is employed in practicing the refractive nearfield method of determining the index of refraction profile of an optical fiber (45) as a technique of eliminating leaky mode (55) contribution to detected power.

Determination of Single-Mode Fiber Refractive Index Profiles by a Propagation Mode Near-Field Scanning Technique

Abstract: The characteristics of an optical fiber, such as spot size, single-mode condition, and dispersion characteristics, are principally determined by its refractive index profile It is important to establish an efficient and accurate method for measuring the refractive index profile For a single-mode fiber, however, the measurement of the profile is very difficult because of its small core diameter and low refractive index difference Several methods were proposed for the measurement of the refractive index profile of single-mode fibers, such as the far-field radiation pattern technique [1],[2], the scattering pattern method [3], the reflection method [4], the focusing method [5], the refracted near-field technique [6], and the interferometric slab method [7]

Coupling an elliptical Gaussian beam into a multimode step-index fiber.

Abstract: The power coupling efficiency of an elliptical-spot-size Gaussian beam into a multimode step-index fiber is derived using a full-wave analysis. Numerical results indicate that the power coupling efficiency increases not only with decreasing index mismatch but also with increasing spot size of the Gaussian beam at its waist and the relative core–cladding refractive-index difference of the fiber. The coupling loss due to beam spread is found to be large when the spot size at the beam waist is small. The coupling loss is also found to increase with increasing wavelength of the Gaussian beam. A slight difference of power coupling efficiency is found with the different direction of electric polarization for a Gaussian beam of large spot size at its waist.

Empirical evaluation of profile variations in an MCVD optical waveguide fiber using modal structure analysis

Abstract: This paper presents a computer modeling evaluation of the effect on mode propagation of typical perturbations in the refractive index profile produced as a result of the MCVD process. Certain profile variations were eliminated, singly and/or collectively, and the resultant changes in modal structure analyzed. The most important factor in the deterioration of the bandwidth is the presence of a refractive index dip at the core center. Small shifts in the level of dopant were seen to broaden pulse shapes and thus reduce bandwidth. Much less effect on bandwidth is associated with the ripples in the profile, as is also true for dips in refractive index below the index of the cladding near the core-cladding interface. A perpendicular rise, or step, in index of refraction at the core-cladding interface reduces the number of altered modes near the cladding.

Production of optical element with a varying refractive index

Abstract: An optical element, consisting essentially of an amorphous compound and having a varying refractive index, is prepared by introducing a melt of the material into a mold and cooling it in such a manner that the material gradually solidifies, while simultaneously applying a programmed pressure to the cooling melt. When the material is fully solidified, it possesses a refractive index gradient. An element manufactured by this method has a capacity for guiding and focusing light.

Resolution improvement in refracted near-field index measurement by a lens-shaped liquid cell

Abstract: The resolution of the refracted near-field measurement method for optical-fibre refractive-index profiles has been improved by a factor of about three by simply using a lens-shaped liquid cell and an oil immersion objective. The resulting optimum resolution is below 0.2 ?m and at 0.633 ?m wavelength with polarisation normal to the refractive index gradient.

Measuring cylindrically symmetric refractive-index profiles: a method.

Abstract: This paper describes a new nondestructive method to measure cylindrically symmetric refractive-index profiles of transparent cylinders. The technique is based on the measurement of the axial displacement of rays that are refracted within the cylinder. Three different types of index profile were experimentally determined. Profile errors of better than one part in 103 were achieved using very modest equipment. The effects of certain experimental parameters on the profile accuracy are noted. The technique may be applied to the characterization of optical fiber preforms and graded-index rod lenses.

Method of and apparatus for determining the refractive-index profile of optical fibres and optical-fibre preforms

Abstract: The invention allows the refractive - index profile to be obtained by phase - difference measurements. A Zeeman- effect laser (1) generates a light beam of plane waves comprising two radiations with slightly different frequencies. The beam is split into the component radiations (2d, 2e); the beats between the first radiation, which is made to follow a path outside the fibre or preform (6), and the second radiation, which is made to follow a path crossing the fibre or preform (6), are generated by a photodetector; the phase differences between said beats and a reference beat are measured, and the refractive - index profile is obtained from the phase difference values by suitable computing means.

Refractive Index Measurement During The Deposition Of Dielectric Coatings

Abstract: Refractive indices and index profiles of dielectric coatings have been measured during their deposition. The measurements can be applied in the case of single layers as well as complex layer systems with arbitrary layer thicknesses. The refractive index of homogeneous layers is investigated using transmission measurements of monochromatic light, whereas inhomogeneous layer profiles are measured at different wavelengths.With an accurately determined index, the production of special dielectric multilayer stacks as steep edge filters or antireflection coatings with low residual reflection can be realized. Thus it is possible to reach the theoretical steepness by monitoring the actual refractive index and correcting the layer thickness accordingly. Considering inhomogeneities the performance of antireflection coatings can be improved.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical body provided with thin interference film

Abstract: PURPOSE:To obtain a thin interference film having a high refractive index and low heterogeneity by forming a layer having a high refractive index and contg. zirconium oxide, titanium oxide and aluminum oxide as at least one layer of a thin interference film for an optical body. CONSTITUTION:A layer 2 of Al2O3, SiO, CeF3 or MgO having 1.6-1.7 medium refractive index and lambda/4 optical thickness, a layer 3 consisting of 81wt% ZrO2, 9wt% TiO2 and 10wt% Al2O3 and having 1.9-2.3 high refractive index and lambda/2 optical thickness, and a layer 4 of SiO2, MgF2 or Na3AlF6 having 1.35-1.47 low refractive index and lambda/4 optical thickness are successively laminated on a glass substrate to obtain an optical body 5 provided with a three-layered antireflection film. Thus, a uniform thin interference film having a high refractive index is obtd.

One Dimensional Linear Refractive Index Profiles From Angular Reflectivity Measurements At One Wavelength

Abstract: One dimensional linear refractive index profiles from angularreflectivity measurements at one wavelengthM. N. Grimbergen* and R. B. GoldnerDepartment of Electrical EngineeringTufts UniversityMedford, Massachusetts 02155 USAAbstractA technique has been developed to determine one -dimensional linear refractive indexprofiles for planar thin films from angular reflectivity measurements at one wavelength.The technique uses a nonlinear least- squares fitting algorithm, together with amultilayer characteristic matrix model. The fitting error is examined as a function ofadjustable parameters using a three -dimensional graphing routine. From synthetic data itis demonstrated that, within the domain of chosen adjustable parameters and realisticexperimental uncertainties, a best linear profile fit can be obtained. The technique isdemonstrated using reflectance data on laboratory samples of In2O3:Sn.IntroductionThe determination of refractive index gradients in optical materials has received muchattention in recent years. The increased ability to design and fabricate such materialsas graded index optical fibers and graded index planar waveguides has required thedevelopment of techniques to measure index gradients. Also, the need to createantireflection coatings by implementing graded index layers has been recognized since theearly 1930's. More recently, solar energy conversion applications for antireflectioncoatings and selective absorbers have created renewed interest in obtaining graded indexlayers.This paper addresses the problem of determining the refractive index profile normal tothe surface of a nonuniform layer as shown in Figure 1. A plane wave is incident upon

A Sensitive Technique for Fibre Profile Characterization

Abstract: A technique has been developed that permits the detection of fluctuations as small as 1 part in 105 in the refractive index of graded index fibres. It consists of measuring the derivative of the profile rather than the profile itself. The procedure enables small defects on the profile to be emphasized in a smooth background.