Showing papers on "Step-index profile published in 1980"
TL;DR: The method makes it possible to characterize a fiber from a simple measurement of the HE(11) mode spot size without making difficult index profile and core radius measurements, and it is found that the step-index distribution is suitable for single-mode fibers.
Abstract: A method is proposed whereby the propagation characteristics of a single-mode fiber having an arbitrary refractive-index profile may be expressed in terms of a newly defined equivalent step-index profile. The theory is based on the fact that the field distribution of the HE11 mode of a fiber closely resembles the Gaussian profile. The method makes it possible to characterize a fiber from a simple measurement of the HE11 mode spot size without making difficult index profile and core radius measurements. It is also found that the step-index distribution is suitable for single-mode fibers.
61 citations
TL;DR: A modified focusing method for measuring simultaneously the refractive-index profile and the cross-sectional geometry of an optical fiber preform is presented and it was found that the error of the index profile measurement was <1%.
Abstract: A modified focusing method for measuring simultaneously the refractive-index profile and the cross-sectional geometry of an optical fiber preform is presented. In this method the preform is immersed in index-matching liquid, and collimated light is made to impinge on the preform laterally. The intensity distributions of the transmitted light are detected on two planes inside the preform core. From the recorded light intensity distributions, the deflection function is calculated. After the preform has been rotated through 180° and the necessary data have been collected, a numerical inversion is performed to obtain the 2-D index profile. In this paper, the principle, the experimental setup, and results are described. The sensitivity of the method to measurement errors and the accuracy of the inversion formula were investigated by computer simulations. It was found that the error of the index profile measurement was <1%.
33 citations
01 Jun 1980
TL;DR: In this paper, the authors discuss methods for measuring the refractive index distribution in optical fibers and for predicting their impulse response and signal bandwidth from the measured profiles, and some attention is also given to preform and single-mode fiber profiling.
Abstract: The refractive index distribution in the core of a multimode optical-fiber waveguide plays an important role in determining the transmission properties of the guide. The closer the index profile is to the required ideal distribution, the greater the resulting information carrying capacity of the fiber. This review paper discusses methods for measuring the refractive index distribution in optical fibers and for predicting their impulse response and signal bandwidth from the measured profiles. Some attention is also given to preform and single-mode fiber profiling.
32 citations
Patent•
08 Sep 1980TL;DR: In this article, the authors measured the profile and the core diameter of an optical fiber using a focused beam of ultraviolet radiation, which induced a fluorescence along a thin pencil-like region of the preform core whose intensity varies in proportion to the concentration of the dopant.
Abstract: Shaping of the refractive index profile of an optical fiber is typically achieved by changing the concentration of an index-modifying dopant within the glassy matrix preform. To measure the profile and the core diameter of the preform, in accordance with the present disclosure, the preform (10) is illuminated with a focused beam of ultraviolet radiation (15) whose beam width (w) is small compared to the preform core diameter (d). This induces a fluorescence along a thin pencil-like region (16) of the preform core whose intensity varies in proportion to the concentration of the dopant. Inasmuch as the latter is proportional to the refractive index, the intensity profile gives the index profile directly. A similar measure can also be made on fibers using microscopes for focusing the uv and observing the induced fluorescence. Use of this technique for controlling the rate at which a fiber is drawn is also described.
27 citations
TL;DR: In this article, the authors measured group delay differences of time-resolved discrete pulses of the LP(01) and LP(11) modes as a function of wavelength in the 1.06- to 1.6-μm region.
Abstract: We study propagation characteristics of double-mode fibers by measuring group delay differences of time-resolved discrete pulses of the LP(01) and LP(11) modes as a function of wavelength in the 1.06- to 1.6-μm region. The technique has been used to make the first measurements of zero intermodal dispersion in the zero material dispersion region of graded-index double-mode fiberguides that can have larger diameters than standard single-mode fibers. The results can also be used to deduce information about the fiber's refractive-index profile, such as δ, the normalized peak refractive index difference.
27 citations
26 citations
TL;DR: A nondestructive refractive-index profile measurement of optical-fiber preform rods by means of a transverse-differential-interference method is given, and it almost coincided with that of the fiber drawn from the rod.
Abstract: A nondestructive refractive-index profile measurement of optical-fiber preform rods by means of a transverse-differential-interference method is given. The error resulting from the data reading of a fringe center is investigated by computer simulation and is confirmed to be less than about 1% of the index difference between the core and the cladding. The refractive-index profile of a preform rod was measured, and it almost coincided with that of the fiber drawn from the rod. The elliptic deformation of the core and its variation along the longitudinal axis were measured.
23 citations
TL;DR: In this article, a simple and accurate method is presented for experimental characterisation of graded-index single-mode fibres using their far-field radiation patterns and the equivalent-step? method.
Abstract: A simple and accurate method is presented for experimental characterisation of graded-index single-mode fibres using their far-field radiation patterns and the `equivalent-step? method
22 citations
TL;DR: By comparing theoretical results of various correlation functions to measured excess losses of the cabled fibers, it is verified that the correlation function of random bends of single-mode and multimode cabled fiber fibers is estimated to be Gaussian.
Abstract: Excess losses of single-mode and multimode cabled optical fibers due to random bends of the Gaussian correlation function are discussed theoretically. By comparing theoretical results of various correlation functions to measured excess losses of the cabled fibers, it is verified that the correlation function of random bends of single-mode and multimode cabled fibers is estimated to be Gaussian. Using the estimated Gaussian correlation function, random-bend loss formulas of the single-mode and the graded-index multimode fiber cables are given. To use a cabled single-mode fiber over a wider wavelength region intended for a wavelength-division-multiplexing system, the relative refractive-index difference between core and cladding should be made larger to reduce the random-bend loss substantially. Cabling losses of graded-index multimode fibers depend strongly on the relative refractive-index difference and the diameter of the core.
22 citations
20 citations
TL;DR: In this paper, the optical transmission spectra of thin GaAs thin films is analyzed and the photon energy range from 0.5 eV to the fundamental gap energy is determined for CuInSe2, CuInTe2 and CuGaTe2.
TL;DR: A method is presented for calculating the profile of the refractive index of an optical waveguide from the measured coupling angles for any physically justified functional form of f(x), for a Ti in-diffused LiNbO(3) waveguide that fits the sum of two Gaussians.
Abstract: A method is presented for calculating the profile of the refractive index of an optical waveguide, n(x) = n0 + f(x), from the measured coupling angles for any physically justified functional form of f(x). As an example, we present the results of a Ti in-diffused LiNbO3 waveguide for which f(x) fits the sum of two Gaussians.
Patent•
13 Aug 1980
TL;DR: An optical component having a gradient refractive index produced by multiple windings of a glass fiber over a glass mandrel is described in this article, where the windings have a radial index gradient of predetermined profile, which varies from an approximate match with the mandrel to selected lower values along its length.
Abstract: An optical component having a gradient refractive index produced by multiple windings of a glass fiber over a glass mandrel. The fiber is provided with a refractive index gradation which varies from an approximate match with the mandrel to selected lower values along its length thereby causing refractive index in the depth of windings to vary accordingly. Fusion and drawing of the mandrel and windings provide a rod (or fiber) of solid cross-section having a radial index gradient of predetermined profile.
Patent•
28 Jan 1980TL;DR: In this paper, a method for directly drawing a glass optical waveguide or waveguide blank from two or more reservoirs of molten glass wherein a relatively high refractive index glass core member is clad with a relatively low refractive indices glass cladding is presented.
Abstract: In a method for directly drawing a glass optical waveguide or waveguide blank from two or more reservoirs of molten glass wherein a relatively high refractive index glass core member is clad with a relatively low refractive index glass cladding, control over the refractive index variations occurring due to the migration of dopants between the core and cladding is obtained by providing one or more glass diffusion layers between the core and cladding.
TL;DR: In this article, a modified bounded-mode near-field scanning method for determining the refractive index profiles of optical fibres is described, which is simple to implement and allows the fibre numerical aperture and geometry to be measured.
Abstract: A modified bounded-mode near-field scanning method for determining the refractive-index profiles of optical fibres is described. The technique is simple to implement and allows the fibre numerical aperture and geometry to be measured.
TL;DR: In this paper, a non-destructive computer-aided measurement of the arbitrary two-dimensional refractive index distribution of an optical fiber preform is described, where the angle of refraction of rays in the preform was measured by an optical set-up which features the use of a triangular mask for converting the angles of rays to their displacement and the index distribution was computed from the information on these refraction angles.
Abstract: A nondestructive computer-aided measurement of the arbitrary two-dimensional refractive-index distribution of an optical fibre preform is described The angle of refraction of rays in the preform is measured by an optical set-up which features the use of a triangular mask for converting the angle of rays to their displacement The index distribution is computed from the information on these refraction angles
TL;DR: In this paper, the temperature coefficient of the refractive index, (∂n/∂T)p, has been measured for deuterium oxide and the observed values are considered together with those previously obtained for water.
Abstract: Abstract The temperature coefficient of the refractive index, (∂n/∂T)p, has been measured for deuterium oxide. The observed values are considered together with those previously obtained for water. The experimental data cannot be explained with the best known models of molecular polarizability, at least in the approximation generally used in these models. Therfore they are discussed on the basis of a different approximation, suggested by a well-known structural model of liquid water. It is shown that the experimental results are very well explained, in a wide range of temperature, with the hypothesis of the existence of \"structural voids\".
Patent•
14 Nov 1980TL;DR: In this article, a fiber is inserted into a body of transparent liquid held by surface tension in a surrounding capillary tube also made of light-transmissive material, which is axially coextensive with the inserted fiber.
Abstract: To facilitate determination of the refractive-index profile of an optical fiber by the near-field technique, the fiber to be examined is inserted into a body of transparent liquid held by surface tension in a surrounding capillary tube also made of light-transmissive material. The tube, which is axially coextensive with the inserted fiber, has a refractive index less than the minimum index of the fiber core and cladding whereas the liquid has a refractive index exceeding the maximum index of the fiber core.
TL;DR: A complete computational procedure operating within the framework of geometric optics is presented for obtaining the pulse response of multimode graded-index fibers, which have circular cross sections but arbitrary refractive-index profiles.
Abstract: A complete computational procedure operating within the framework of geometric optics is presented for obtaining the pulse response of multimode graded-index fibers, which have circular cross sections but arbitrary refractive-index profiles. The profile is approximated by parabolic sections, thus reducing the ray transit time calculation to an exact procedure, which involves only the solution of quadratic equations, and the analytical evaluation of standard integrals. The effect of material dispersion, absorption, and tunneling rays can be incorporated exactly within the adopted profile approximation and computational procedure.
TL;DR: In this article, microbending losses in single-mode fibers with several types of core refractive index profiles are compared and the effects of fiber curvature statistics and index profile parameters are investigated in detail.
Abstract: Microbending losses in single-mode fibers with several types of core refractive index profiles are compared. Numerical calculations were carried out to characterize fibers with step, power-law, W and ring-shaped index profiles. Step-index and W fibers exhibit a small excess loss near the single-mode operation upper limit. However, permissible offset misalignment in fiber splice at constant microbending loss is nearly identical for step, power-law, and W fibers. An index dip at the core center has an undesirable influence on the required splicing accuracy. The effects of fiber curvature statistics and index profile parameters are investigated in detail.
Patent•
22 Jul 1980
TL;DR: In this article, the authors proposed to connect two fibers different in refractive index of the cores with a low loss by heating more strongly a fiber with higher this article than a fiber having lower this article.
Abstract: PURPOSE:To connect two fibers different in refractive index of the cores with a low loss by heating more strongly a fiber with higher refractive index of a core than a fiber with lower refractive index of a core. CONSTITUTION:A fiber 6 with higher refractive index of a core is allowed to contact with a fiber 7 with lower refractive index of a core and the connection. Central line 8 and an electrode central line 9 of discharging electrodes 1, 2 are shifted in their positions such that the fiber 6 having higher refractive index of a core is more strongly heated. When an optical fiber is heated, the refractive index becomes generally small, so by an execution of a discharge connection with such arrangement a refractive index change near a connection point becomes gentle, thus a connection with a low loss becomes possible. Further constitution in the invention can be also used for connecting optical fibers different in melting temperature.
TL;DR: In this article, a simple method is proposed to calculate the real index of refraction for a Lorentzian type absorption band, which does not require the value of the oscillator strength of the absorption.
Abstract: A simple method is proposed to calculate the real index of refraction for a Lorentzian type absorption band. According to this method we need not to know the value of the oscillator strength of the absorption.
TL;DR: In this article, a nondestructive method for obtaining information about the refractive index profiles of diffused channel waveguides of the type used in integrated optics is described, where the index profile can be approximated as a product of two functions each of which depends on one of the two transverse coordinates.
Abstract: A nondestructive method is described for obtaining information about the refractive index profiles of diffused channel waveguides of the type used in integrated optics. The method assumes that the index profile can be approximated as a product of two functions each of which depends on one of the two transverse coordinates. By observing the focusing effect, which the waveguide has on collimated light passing through it transversely to its axis, the shape of the index profile in a direction parallel to the surface of the substrate can be obtained. From measurements of the reflection coefficients we obtain the refractive index at the upper surface of the waveguide. By combining the two measurements the effective depth of the waveguide can be calculated. Results of measurements on multimode and single-mode waveguides formed in glass and lithium niobate are presented.
TL;DR: In this paper, a simple method is proposed for measuring the refractive index at the surface of a diffused waveguide whereby the profile n(x) can be reconstructed uniquely from the mode spectrum of the waveguide.
Abstract: A simple method is proposed for measuring the refractive index n(x) at the surface of a diffused waveguide whereby the profile n(x) can be reconstructed uniquely from the mode spectrum of the waveguide. A description is given of a method of measuring effective refractive indices of the waveguide modes using a grating element for coupling radiation into the waveguide. The profile n(x) in single-mode waveguides is discussed.
TL;DR: In this article, a holographic method of measuring the refractive index profile of an optical fiber preform is presented, which uses the principle of shearing interferometry and allows measurements to be repeated even after the preform has been withdrawn for fibre drawing.
Abstract: A holographic method of measuring the refractive-index profile of an optical fibre preform is presented. It uses the principle of shearing interferometry. The method is simple and allows measurements to be repeated even after the preform has been withdrawn for fibre drawing.
01 Oct 1980
TL;DR: In this paper, the authors present a review of methods that can be used to measure the index profiles of preforms, both multi-mode and single mode, and the effects of profile perturbations and means of eliminating them.
Abstract: The information carrying capacity of multimode optical fibers is mainly determined by the quality of the refractive index distribution of their cores which, in turn, is determined by the distribution existing in the fiber's parent--the preform. This paper reviews methods that can be used to measure the index profiles of preforms--both multi-mode and single mode. Attention is also given to the effects of profile perturbations and means of eliminating them, as well as to applications of the techniques to fiber profiling.
TL;DR: In this Letter a simple method is presented that is particularly suitable for solvent-coated materials, enabling measurement of n to the third decimal place, used for simultaneous measurement of RIs of several layers in a stack of materials coated on top of each other on a prism.
Abstract: Several methods have been published recently for measurement of refractive indices (RI) of nearly transparent films. In this Letter a simple method is presented that is particularly suitable for solvent-coated materials, enabling measurement of n to the third decimal place. It can be used for simultaneous measurement of RIs of several layers in a stack of materials coated on top of each other on a prism. The thickness of the layers is not critical. For explanation of the principles of the method, consider a stack of dielectric films 1...N with RIs n1 . . .nN , where n1 is the RI of the substrate. Let the interfaces (i – 1,i) i = 2...N be planes parallel to each other and a collimated light
TL;DR: In this article, the optimal distribution of refractive index with respect to pulse broadening is found for multilayer multimode fibres by means of the ray theory, and it is concluded that even with a low number of layers we can reduce pulse broadens significantly.
Abstract: Multilayer multimode fibres are considered by means of the ray theory, and the optimal distribution of refractive index with respect to pulse broadening is found. It is concluded that even with a low number of layers we can reduce pulse broadening significantly. Low sensitivity to the variations of refractive index distribution is predicted.
TL;DR: In this article, an air bearing linear guide has been developed for the precision linear guide of CCD camera, which is used to measure the core pitch at multiple-fiber connector end using CCD (charge coupled devices) line scanner and He-Ne laser interferometer.