Showing papers on "Step-index profile published in 1979"
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TL;DR: In this article, the theoretical basis and experimental realization of the refracted near-field technique for the direct measurement of optical fiber profiles are presented, which requires minimal sample preparation, no computation and is applicable to both single and multimode fibres.
Abstract: Both the theoretical basis and experimental realization of the refracted near-field technique for the direct measurement of optical fibre profiles are presented. The technique requires minimal sample preparation, no computation and is applicable to both single and multimode fibres. Both the core and the cladding are profiled. After outlining the problems associated with other techniques, the use of this method for the measurement of fibre profile, numerical aperture and geometry is discussed. Leaky mode rejection and resolution are treated in detail. A fitting procedure for determining theα-value of a profile is given. The experimental apparatus is fully discussed. Results are presented to illustrate both the applicability of the technique to single and multimode fibres and also the rejection of leaky modes. The experimental sensitivity is shown sufficient to reveal an index fluctuation having a wavelength < 1μm and an amplitude of < 0.0001.
152 citations
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TL;DR: It is shown that it is possible to determine the refractive index distribution of a fiber or preform with slight index variation by observing the power distribution of the light field that is focused by the core acting as a lens.
Abstract: We show that it is possible to determine the refractive index distribution of a fiber or preform with slight index variation by observing the power distribution of the light field that is focused by the core acting as a lens. This method requires index matching of the cladding and illumination of the core at right angles to its axis with a broad beam of incoherent collimated light. The refractive index distribution is obtained after two numerical integrations to be performed by computer. The first integration establishes the relation between the output and input ray positions from the observed power distribution, the second uses this information to determine the refractive index distribution. However, it is not necessary to solve a large system of simultaneous equations. The sensitivity of the method to measurement inaccuracies was tested by computer simulation. It was found that the method has a builtin smoothing effect that attenuates rather than amplifies measurement errors.
90 citations
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TL;DR: A new exit-radiation pattern method for measuring the refractive-index profile of a single-mode fiber is proposed and used experimentally, and shows a good agreement with that obtained from the interference fringe pattern measured before drawing the fiber.
Abstract: A new exit-radiation pattern method for measuring the refractive-index profile of a single-mode fiber is proposed and used experimentally. In this method the profile is computed from the far-field exit-radiation pattern of the HE11 mode at the end of the single-mode fiber. This method can be applied to a cabled fiber, and the propagation constant, field profile, and group delay of the HE11 mode, and the single-mode limit can be obtained as well as the index profile. The principle, computer simulations, experimental setup, and experimental results are first described. The profile obtained shows a good agreement with that obtained from the interference fringe pattern measured before drawing the fiber. Computations of the group delay of the HE11 mode and the single-mode limit from the measured exit-radiation pattern are discussed.
64 citations
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TL;DR: Comparison between the experimental results and the ray trace calculations using an interative curve-fitting procedure gave nondestructive determinations of the refractive index ratio Delta and index gradient profile parameter alpha as well as measurement of the core dimensions.
Abstract: A technique is described which permits the determination of geometric and refractive index characteristics of graded-index preforms from measurements of the refraction of rays traced through the preform perpendicular to the preform axis. A computer program was developed to trace rays through graded-index preforms to display the refracting effect of the index properties and relate the ray incidence angle to its deflection in traversing the preform. An experimental apparatus has been developed in which a narrow beam of laser radiation is directed at the preform and its deflection angle measured. Comparison between the experimental results and the ray trace calculations using an interative curve-fitting procedure gave nondestructive determinations of the refractive index ratio Delta and index gradient profile parameter alpha as well as measurement of the core dimensions.
60 citations
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TL;DR: An automatic and nondestructive focusing method to determine the refractive index distributions of optical fiber preforms is presented, and excellent agreement is obtained with profiles determined interferometrically using slab samples from the tips of the same preforms.
Abstract: An automatic and nondestructive focusing method to determine the refractive index distributions of optical fiber preforms is presented. The preform is immersed in index matching oil, and collimated light is passed transversely through it. The intensity distribution of the transmitted light is detected with a vidicon camera equipped with a low f-number lens focused just outside the core boundary. Recording and processing of the light distribution follow with the aid of a computer-controlled video-analysis system. The refractive index profile of the preform is computed from the intensity distribution, plotted, and fitted with a power-law curve within several minutes time. The repeatability of the index measurement is better than 1%, and excellent agreement is obtained with profiles determined interferometrically using slab samples from the tips of the same preforms.
40 citations
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39 citations
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TL;DR: In this paper, the authors show that the low propagation losses and the diffusion profile are related to the interaction between the two alkalis and propose a waveguide that approximates a step-index profile in soda-lime glass.
Abstract: Optical waveguides approximating a step-index profile have been fabricated in soda-lime glass by ion-exchanging rubidium or caesium for sodium. We show that the low propagation losses and the diffusion profile are related to the interaction between the two alkalis.
38 citations
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TL;DR: This paper presents error estimates and shows how well the focusing method agrees with the interferometric slab method, an error which is easily attributable to incident light level fluctuations.
Abstract: A new method to determine the refractive-index distributions of the cores of optical fibers is presented. The fiber is immersed in index matching oil to eliminate light refraction at the outer core boundary. Collimated light is passed transversely through the fiber core and is detected with a microscope focused just above the plane of the core boundary. The intensity distribution in the image plane is recorded with the aid of a computer-controlled video-analysis system. The refractive-index profile of the fiber core is then computed from this intensity distribution. In this paper we present error estimates and show how well the focusing method agrees with the interferometric slab method. The repeatability of the index measurement is approximately 2%, an error which is easily attributable to incident light level fluctuations.
35 citations
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TL;DR: It was found that in spite of the fact that rather complicated coupling behavior is observed when multimodes exist, total guide power still exchanges among the fibers in a periodic manner, and the coupling length still increases monotonically as a function of the separation distance between the fibers.
Abstract: A numerical technique to obtain the wave behavior in tightly coupled multimode fibers with inhomogeneous indices is introduced in this paper. The specific problem of the coupling characteristics of two parallel multimode fibers whose index profile is parabolic is treated in detail. It was found that in spite of the fact that rather complicated coupling behavior is observed when multimodes exist, total guide power still exchanges among the fibers in a periodic manner, and the coupling length still increases monotonically as a function of the separation distance between the fibers. It has also been demonstrated that by simply specifying the index profiles of the coupling structure (provided that the profiles are slowly varying), the coupling characteristics can be generated with our technique.
34 citations
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TL;DR: In this paper, the composition dependence of the refractive index and its photo-induced variation have been calculated for the Ge1−xSex and As 1−xsex binary glass systems, using the random network model.
Abstract: The composition dependence of the refractive index and its photo-induced variation have been calculated for the Ge1−xSex and As1−xSex binary glass systems, using the random network model. It is found that the refractive index has a minimum in Ge1−xSex at x = 0.8, while it shows a monotomic increase with increasing As content in As1−xSex glasses. The refractive index of the Ge1−xSex system decreases with illumination and the variation Δn of GeSe2 is −0.0316, while the refractive index of the As1−xSex system increases with illumination and the variation of As2Se3 is 0.01. These results are in agreement with the experimental results reported by several workers.
24 citations
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TL;DR: A new nondestructive technique is presented for determining the refractive index profile of an optical fiber from its backscattered pattern arising from a normally incident laser beam to the fiber axis.
Abstract: A new nondestructive technique is presented for determining the refractive index profile of an optical fiber from its backscattered pattern arising from a normally incident laser beam to the fiber axis. The proposed method requires no sample preparation or index matching liquid. The principle of the method is to construct a deflection function from the measured pattern. The index profile can then be determined by the inversion of an Abel integral equation. Good agreement is obtained between the index profile determined by this technique and that measured by the near-field scanning technique.
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TL;DR: In this paper, a non-destructive method for determining the refractive index profile of an elliptic optical fiber or preform was proposed. But the method was not suitable for the case of the preform.
Abstract: A nondestructive method of determining the refractive-index profile of an elliptic optical fibre or preform is reported. For the fibre, the pathlength data obtained from interference microscopic measurement are used. For the preform, the ray exit angles are used. These data are put into an integral that can be inverted numerically to obtain the reconstructed profile.
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TL;DR: In this article, a plane wave is made to impinge on the preform laterally and the power distribution of the scattered pattern is recorded, from the recorded power, the ray path length difference is calculated.
Abstract: A nondestructive method is presented to determine simultaneously the refractive-index profile and the cross-sectional geometry of a preform. In this method, a plane wave is made to impinge on the preform laterally and the power distribution of the scattered pattern is recorded. From the recorded power, the ray pathlength difference is calculated. After the preform has been rotated through 360° and the necessary data collected, a numerical inversion is performed to obtain the index profile and cross-sectional geometry.
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TL;DR: In this article, the refractive index depression that exists along the axis in modified chemical vapor deposited (MCVD) preforms and fibers doped mainly with GeO2 or P2O5 is studied by interference microscopy.
Abstract: The refractive index depression that exists along the axis in modified chemical vapor deposited (MCVD) preforms and fibers doped mainly with GeO2 or P2O5 is studied by interference microscopy. The index profile of a preform, determined as a function of its transition from the uncollapsed to the fully collapsed state, shows that this central region is fully depleted of dopant and has an index value corresponding to that of the pure fused silica cladding. The same results are found in samples taken from six preform tips and from a relatively large fiber, indicating that this effect is a general property of an uncompensated fabrication process. Implications for its influence on the fiber's transmission properties are discussed.
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TL;DR: This paper considers the signal bandwidth of germanium- and phosphorus-doped fibers with ideal power law refractive index profiles and investigates how the bandwidth as a function of wavelength (bandwidth spectrum) is changed as the ideal index profile is distorted.
Abstract: This paper presents some thoughts on how to improve the bandwidth spectrum of multimode optical fibers. We consider the signal bandwidth of germanium- and phosphorus-doped fibers with ideal power law refractive index profiles and investigate how the bandwidth as a function of wavelength (bandwidth spectrum) is changed as the ideal index profile is distorted. We also study what happens if two fibers with different undistorted power law profiles are used in cascade. Examples are also given of bandwidth calculations of fibers made with a mixture of germanium and phosphorus dopants. It is shown that such fibers are capable of realizing a bandwidth which exceeds 5 GHz·km over a wavelength range from 0.8 μm to 1.45 μm. Finally, bandwidth vs wavelength curves are computed for several real fibers whose refractive index profiles were measured.
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TL;DR: In this article, an experimental system for nondestructive measurement of the refractive index profile of an optical fiber preform was presented, and it was shown that the profile does not significantly change from the preform stage to the fiber stage.
Abstract: An experimental system for nondestructive measurement of the refractive-index profile of an optical fibre preform is reported. The result shows that the profile does not significantly change from the preform stage to fibre stage.
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16 Mar 1979TL;DR: In this paper, the effect of fluctuations superimposed upon the index profile are minimized by introducing an odd number of phase reversals in the fluctuations equally spaced along the fiber, such that the average value of α is equal to αopt.
Abstract: Increased mode dispersion in graded-index, multimode optical fibers due to defects in the index profile can be significantly reduced if the average defect is caused to vanish over the length of the fiber. For fibers with non-optimum α-values, minimum impulse response can be approached provided α varies along the fiber, such that the average value of α is equal to αopt. The effect of fluctuations superimposed upon the index profile are minimized by introducing an odd number of phase reversals in the fluctuations equally spaced along the fiber.
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TL;DR: In this paper, the effects of changing the shape of the refractive-index profile of the fiber core on the secondary maxima were investigated, and the power distribution of the light propagating in the core region is compared to the refraction-index distribution.
Abstract: Photoelectric and photographic techniques have been used to measure and display the intensities and positions of as many as six secondary maxima in the far-field radiation patterns of a variety of low V-number optical fibers. The effects of changing the shape of the refractive-index profile of the fiber core on the secondary maxima are investigated. The power distribution of the light propagating in the core region is compared to the refractive-index distribution.
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07 Mar 1979
TL;DR: In this article, the refractive index gradient is produced by interdiffusion of T1 + and K + ions between core and cladding glasses which are selected to contain substantial proportions of thallium oxide and potassium oxide respectively.
Abstract: Gradient refractive index fibers or rods are formed of leachable glass clad glass core preforms drawn to a desired diametral size, bundled together, fused under high compressing forces and rapidly interdiffused at a temperature above their deformation point. Cooling, annealing and separation of the fibers or rods by leaching provides the end product devices which may be cut into lengths required for the lens power desired and end polished. The refractive index gradient is produced by interdiffusion of T1 + and K + ions between core and cladding glasses which are selected to contain substantial proportions of thallium oxide and potassium oxide respectively.
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08 Oct 1979
TL;DR: In this paper, an intermediate layer 3 having a refractive index n3 smaller than refractive indexes n1, n2 is provided between a core and a clad, and these are so constituted that these are mutually equal and of opposite polarities.
Abstract: PURPOSE:To expand a band width of transmittable light and improve transmission characteristics by providing an intermediate layer of a refractive index smaller than that of a core and a clad between the core and the clad. CONSTITUTION:An intermediate layer 3 having a refractive index n3 smaller than refractive indexes n1, n2 is provided between a core 1 having the refractive index n1 and a clad 2 having the refractive index n2 enclosing this, and these are so constituted that the refractive index difference DELTA1 between the core 1 and the clad 2 and the refractive index difference DELTA2 between the intermediate layer 3 and the clad 2 become mutually equal and of opposite polarities. With such constitution, the entire dispersion is made <=+ or -1ps/Km/nm in a wide band including the wavelengths at which the transmission losses of a quartz optical fiber becomes minimum; therefore, super wide band and super long distance transmission can be performed by WDM (wavelength multiplexing).
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TL;DR: A convenient refractive index profile, which is based on the Morse potential function and is similar to that which is observed in practically fabricated optical waveguides, is introduced in order to study the propagation characteristics of the 2-D buried optical waveguide.
Abstract: A dielectric waveguide, whose guiding region is located beneath the substrate surface, will be a useful configuration to connect optical functional devices fabricated in the same substrate. A convenient refractive index profile, which is based on the Morse potential function and is similar to that which is observed in practically fabricated optical waveguides, is introduced in order to study the propagation characteristics of the 2-D buried optical waveguide.
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TL;DR: In this paper, the authors compare two computational methods by which the propagation characteristics of a fiber, hence the impulse response and system bandwidth, may be determined, based on a knowledge of the refractive-index profile and source geometry.
Abstract: The use of graded-index fibers for optical communication systems is now under consideration for numerous civil and military applications, and in these either LED or laser sources can be developed. The bandwidth of the system depends on the source linewidth, the dispersion of refractive index in the fiber, the strength of excitation of the modes by the source, and the extent of mode mixing caused, by example, by microbending. In fibers with refractive-index profiles that have a nearly parabolic dependence upon radius, pulse broadening is a slight, but small departures from an optimum profile can cause a dramatic decrease in bandwidth. It is of considerable importance to predict the bandwidth of fibers from a knowledge of the refractive-index profile and source geometry. The purpose of the first part of this paper is to compare two computational methods by which the propagation characteristics of a fiber, hence the impulse response and system bandwidth, may be determined. In the second part, we sha...
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TL;DR: In this paper, a method for calculating the modal delay characteristics of multimode optical fibres with arbitrary refractive index profiles is described, which is quick, accurate, and can be used with either an analytical or an experimentally measured profile.
Abstract: A method for calculating the modal delay characteristics of multimode optical fibres with arbitrary refractive index profiles is described, which is quick, accurate, and can be used with either an analytical or an experimentally measured profile.
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TL;DR: In this article, an experimental investigation was made of the dependence of the effective refractive indices of the TM and TE modes on the depth of waveguides fabricated in glass by ion exchange in an AgNO3 melt.
Abstract: An experimental investigation was made of the dependence of the effective refractive indices of the TM and TE modes on the depth of waveguides fabricated in glass by ion exchange in an AgNO3 melt. It is shown that approximation of the refractive index profile by the function n(x)=n0–Δn[(x/d)+b(x/d)2] (d and b are the profile parameters) gives a high degree of accuracy and permits waveguides with the required parameters to be fabricated. The results of direct measurements of the profile n(x) are presented. A method is proposed for determining the effective thickness of diffused waveguides having an arbitrary profile n(x). This method is based on measurements of the effective refractive indices of only the TM or only the TE modes. It is shown that as a result of the anisotropy of diffused waveguides, the proposed method of determining the effective thickness from the difference n*TE – n*TM may be used for few-mode waveguides.
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01 Oct 1979
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TL;DR: In this article, a profile function that compensates for a broad class of profile dispersions is presented, which may become a design criterion for fibres in the future, although its practical applicability is presently restricted by the limited variety of available glasses.
Abstract: As the profile dispersion parameter P of graded-index fibres is wavelength-dependent. Marcatili's condition for achieving high bandwidth is usually satisfied only in a narrow wavelength range, if at all. This behaviour can be compensated by a wavelength-dependent refractive-index profile. This letter presents a profile function that compensates for a broad class of profile dispersions and may become a design criterion for fibres in the future, although its practical applicability is presently restricted by the limited variety of available glasses.
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TL;DR: In this paper, a novel dielectric waveguide that simulates optical graded index fiber is proposed for millimetre-wave applications, which is shown that a gradually varying refractive index across the guide can result in a well confined, single-mode propagation even in a guide several wavelengths wide.
Abstract: A novel dielectric waveguide that simulates optical graded index fibre is proposed for millimetre-wave applications. It is shown that a gradually varying refractive index across the guide can result in a well confined, single-mode propagation even in a guide several wavelengths wide. The desired index profile is achieved by varying the thickness or height of the waveguide. The effective-dielectric-parameter concept is introduced and used in generating the thickness profile which is approximated by a roof-top. Experimental results for a trial guide are presented and discussed together with the relative merits of this guide.
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TL;DR: In this article, it was shown that the fonnation of vapor bubbles around absorbing centers in a liquid illuminated with a laser beam not only enhances light scattering but also alters the refractive index of the medium.
Abstract: It is shown that the fonnation of vapor bubbles around absorbing centers in a liquid illuminated with a laser beam not only enhances light scattering but also alters the refractive index of the medium. Equations describing the dynamics of the refractive properties of a liquid are obtained and solved. The results are given of experiments which are in agreement with the proposed mechanism of the appearance of optical inhomogeneities.