Showing papers on "Step-index profile published in 1986"

Pressure or strain sensitive optical fiber

Abstract: Pressure or strain sensitive optical fiber having a core, at least a portion of which has a predetermined refractive index for transmitting light therethrough, a cladding adjacent the core having a refractive index which is less than that of the core, and a concentric light transmissive layer adjacent the cladding having a refractive index which is greater than that of the cladding. The light transmissive layer has an internal diameter which is greater than the unperturbed mode boundary diameter of the core, such that all light passes through the core when the fiber is unperturbed. When the optical fiber is subjected to pressure forces in the form of stress or strain, light passes through the light transmissive layer in proportion to the amount of stress or strain acting upon the fiber. Also, pressor sensors and methods for measuring forces or pertubations utilizing such optical fiber.

X‐ray refractive index: A tool to determine the average composition in multilayer structures

Abstract: We present a novel and simple method to determine the average composition of multilayers and superlattices by measuring the x‐ray refractive index. Since these modulated structures exhibit Bragg reflections at small angles, by using a triple axis x‐ray spectrometer we have accurately determined the peak shifts due to refraction in GaAs/AlxGa1−xAs and Nb/Ta superlattices. Knowledge of the refractive index provides the average fractional composition of the periodic structure since the refractive index is a superposition of the refractive indices of the atomic constituents. We also present a critical discussion of the method and compare the values of the average fractional composition obtained in this manner to the values obtained from the lattice parameter change in the GaAs/AlxGa1−xAs superlattices due to the Al.

Optical transmission system comprising a radiation source and a multiple-clad monomode optical transmission fibre with a negative-step index profile

Abstract: An optical transmission is described which comprises a radiation source (30) and a multiple-clad monomode optical transmission fibre (10) with a negative-step index profile. In order to improve the efficiency of coupling the radiation from the source into the transmission fibre a single-clad- monomode transmission fibre (20), whose end portion which faces the source is tapered, is arranged between the source and said fibre.

Fiber taper particularly useful for coupling a monomode fiber to a semiconductor laser

Abstract: A fiber taper in the form of a fiber with a conically tapering at one end and having a step-shaped refractive index profile which is particularly used for coupling a single-mode fiber to a semiconductor laser. The fiber will have a core with a high index of refraction surrounded by an intermediate core layer with an index of refraction being lower by a defined index of refraction difference than the index of refraction of the core. The intermediate core layer is surrounded by a jacket or cladding layer of a lower refractive index which is lower than the refractive index of the core layer by a defined refractive index difference. An expanding beam is established given such a taper and an adiabatic mode matching from one to the other core can be achieved along the taper.

Critical-angle measurement of refractive index of absorbing materials: an experimental study

Abstract: Critical-angle measurements of the refractive index of dilute dye solutions are presented. These provide experimental support for a recent theoretical assertion that optical absorption in a refractometric sample can give rise to large errors in critical-angle measurements of refractive index. The error in the transmission mode is shown to be much larger than the corresponding reflection mode error.

Refractive index changes formed by N+ implants in silica

Abstract: Optical waveguides may be formed in silica by an increase in refractive index resulting from a compaction of the glass network caused during radiation damage. An additional index enhancement had been ascribed to chemical changes during nitrogen implantation. The present work confirms this higher level of index enhancement of up to 4%. Measurements of the refractive index profile before and after annealing suggest that whereas electronically generated damage is annealed by 450°C, the changes in the region of the implanted nitrogen are stable. In the region of maximum nitrogen concentration the presence of a glass phase resembling silicon oxynitride is proposed. However a comparison of the refractive index profile with computer simulations of impurity and defect profiles suggests that radiation damage induced by nuclear collisions contributes to the refractive index profile even in the annealed samples.

Optical multiconductor of silica glass type

Abstract: OF THE DISCLOSURE1. An optical multiconductor of the silica glass type chracterized in that the multiconductor comprises 102 to 107 optical fibers of the silica glass type fused to one another, each of the optical fibers comprising a core made of doped silica glass and occupying at least 20% of the fiber in cross sectional area, and a cladding layer made of a kind of silica glass and formed on the core, the core having a refractive index distribution satisfying the following expression:n2?n1 -1 0.50(n1 - n1) where-in n0 is the refractive index of the core at its center, n1 is the refractive index of the core at its outermost portion, and n2 is the refractive index of the core at a position centered about the axis of the core and having an average radius of 0.65r1, the r1 being an average radius of the core. The multiconductor is suited to use as the image trans-mitter of an image scope for industrial, medical or other uses.

Refractive index profiles of ion implanted optical waveguides

Abstract: The refractive index of insulators may be changed by ion implantation and for several crystalline materials such as quartz, LiNbO3 and LiTaO3 this is thought to be associated with the production of regions of high defect density or even amorphisation of the lattice. Analyses of the refractive index profiles using reflectivity and waveguide mode spacing have been compared. These reveal distinct differences in the profiles of n0 and n e for LiNbO3 and LiTaO3. These data will be discussed in terms of the contributions to the damage from electronic excitation and nuclear collision damage.

Preform with graded refractive index and method for construction of the same

Abstract: A preform with a graded refractive index of synthetic material, i.e. optically clean polymer compounds, constructed by means of a technique where monomers with additives are supplied to a rotating tube (1) with end pieces (2' and 2'') via a cannula (4) in a continuous or discontinuous flow and so that the monomer composition is changed from a lower refractive index toward a higher refractive index from the periphery of the preform toward its rotation axis. Monomered material which is deposited during the rotation of the tube (1) is caused to polymerize by means of radiation with UV beams and/or by means of radical polymerization.

Distributed index lens

Abstract: PURPOSE: To obtain a single small-sized lens, with which a refractive index distribution can be easily formed and which is excellent in aberration correction and usable for an image pickup system, by forming the lens to an almost spherical form and providing the lens with a spherically symmetric refractive index distribution which continuously changes from the center of the sphere. CONSTITUTION: This distributed index lens is a single lens having an almost spherical form and provided with an almost spherically symmetric refractive index distribution, with its center being set at the center of the sphere. When the refractive index distribution is expressed in the following formula: Nρ=N 0 + N 2 ρ 2 +N 3 ρ 3 +N 4 ρ 4 +N 5 ρ 5 +..., where the N 0 is the refractive index at the center, N k (k=2, 3...) are refractive index distribution factors, and ρ is the distance from the center, at least one is a positive value among the refractive index distribution factors N k of k≥3 and satisfies the inequalities. Therefore, a distrib uted index lens which is small in refractive index difference and has an ordinary refractive index can be obtained. Moreover, sufficient aberration correction can be performed practically on the lens and the lens has a wide picture angle and wide numerical aperture (NA). COPYRIGHT: (C)1988,JPO&Japio

Methods for reducing the fresnel reflection in an optical-fiber connector with index matching material.

Abstract: If there is a discontinuity of the refractive index in optical fibers connected with an optical connector, the light is reflected from this part to the light source, creating a problem in its light transmission characteristic. The main causes of the discontinuity are: (1) the gap between the endfaces of the optical fibers; and (2) the change of the refractive index at the end-face of the fibers due to their polishing. Solutions to these problems are investigated in this paper, using silica-based graded index multimode optical fibers. For (l), a refractive-index matching material is employed, and the method for selecting the central value of the refractive index and the temperature coefficient from the reflected light in the visual-light wavelength region is investigated. It has been confirmed that the refractive-index matching material made of silicone resin and chosen by this method can obtain the required reflection loss greater than 40 dB, in each of the transmission wavelengths of 0.85 pm and 1.3 μm, and in the temperature range of −30°C to +60°C. For (2), the relationship between the polishing conditions and the reflected light power was investigated. It has been found that the refractive index of the endface of an optical fiber changes slightly when polished. The conditions of polishing for suppressing this change have been determined, and the property of the polished endface has been clarified.

Characteristics Of KRS-5 Fiber With Crystalline Cladding

Abstract: KRS-5 polycrystalline fibers having a core-cladding structure have been fabricated by complex extrusion. The core material is KRS-5 (T1Br-TlI), and the cladding material is KRS-6 (T1Br-T1C1). Through thermal treatment after fiber fabrication, the refractive index profile is changed to the graded index (GI) type. The attenuation loss of these core-cladding GI fibers is 0.2 dB/m at about 10.6 μm (lauching NA = 0.05). Fibers with this core-cladding structure will enable wide applications using far infrared wavelength light, for example in CO 2 , laser processing machines and spectroscopy equipment, because of their ease in handling.

Round birefraction dielectric wave-guide

Abstract: A round birefraction dielectric wave-guide has in section a central round zone with a constant, or substantially constant, refractive index n1, an outer zone preferably with a constant refractive index n2 and an intermediate zone divided into 8 (or multiples of 8) angular sectors. Respective alternate sectors have refractive indices n3 and n4. Refractive index n3 may be constant but index n4 varies in inverse proportion to the square of the distance from the axis of the waveguide. N1 is greater than n2, n1 is greater tha n3 and n4 lies between n1 and n2. The wave-guide is subjected to torsion around the longitudinal axis of symmetry thereof and/or is spirally wound around a cylinder.

Non-ambiguous Evanescent-wave Fibre Refractive Index and Temperature Sensor

Abstract: The dependence of the leakage of the LP01 mode of a polished single-mode fibre section on the refractive index of an external medium provides non-ambiguous intensity modulation of the guided wave and a single-point in situ calibration of a sensor based on this refractive index, or temperature, transducing mechanism. Refractive index and temperature resolution of 10m4 and 0·1°, has been obtained over an adjustable range of 0·02 and 80°, respectively.

Parameter optimization in graded-index dispersion-shifted single-mode fibers

Abstract: The characteristics of graded-index single-mode nonsegmented-core fibers with a single cladding region, in which the wavelength of zero dispersion is shifted to 1.55 μm, are studied analytically. It is found that for a given relative index difference above a certain value, there are two core sizes at which this zero dispersion shifting is realized. The larger core has certain advantages and has been invariably used in practice. For fibers in which the core is Ge-doped and the index of refraction has a triangular or a parabolic profile, we calculate the rate of change of dispersion with wavelength, the sensitivity of the zero dispersion wavelength to small changes in the core radius and in the refractive index difference, and the outer radius of the cladding needed to limit microbending losses in the cabled fiber. There is a doping level at which the wavelength of zero dispersion is not sensitive to the exact level of doping. The factors involved in choosing a doping level are expounded.

Polarisation characteristics of graded-core stress-applied polarisation-maintaining fibres

Abstract: Polarisation characteristics of stress-applied polarisation maintaining fibres having graded-index cores with α-power profile are investigated. It is found that when the stress-applying parts approach the core, the dependence of modal birefringence B on the normalised frequency v for the triangular profile is considerably different from that for the step-index profile, and the absolutely single-mode operation can be easily realised compared with the conventional step-index profile.

Dual core single mode optical fiber with refractive index groove

Abstract: PURPOSE:To suppress an increase in transmission loss due to bending and microbend loss by using dual cores with a refractive index groove, making the refractive index of the 2nd core larger than that of a clad, and making the refractive index of the 1st core at the center part larger than that of the 2nd core. CONSTITUTION:An optical fiber is constituted by arranging the 1st core, the 2nd core 2, an intermediate layer 3, and the clad 4 concentricaly in order from the center and the refractive indexes of the respective layers are denoted as n1, n2, n3, and n4 respectively. The refractive index n1 of the 1st core 1 is largest and the refractive index n3 of the intermediate layer 3 is smallest. The refractive index n2 of the 2nd core 2 is an intermediate value between the refractive index n4 of the clad 4 and the refractive index n1 of the 1st core 1. Consequent ly, the optical fiber has a wide wavelength band of 1.5mum in wavelength where the smallest loss is expected, and the dual core single core optical fiber which is tolerant to bending loss and microbend loss is obtained.

The nonlinear and thermal effects of refractive index of optical fibre material

Abstract: The refractive index including linear and nonlinear terms, the zero dispersion wavelength and their relation to the temperature have been calculated by using semi-classical method. The theoretical results are consistent with experiment results.

Interference Measurement Of Waveguide Preform Refractive Index Distribution - Destructive Method With Plane Wave Of Interference

Abstract: Interference measurement of waveguide preform refractive indexdistribution- destructive method with plane wave of interferenceWaldemar Kowalik, Adam HeimrathInstitute of Physics, Technical University of Wroclaw,Wyb. Wyspiariskiego 27, Wroclaw, PolandIntroductionExploitation parameters of a waveguide mostly depend on the distribution of the refracti-ve index in it. Therefore, control over the distribution of the refractive index in thewaveguide preforms out of which the waveguides are drawn is necessary in waveguide produc-tion and in working out a proper technology of preform production. Interference methodsprevail in refractive index distribution measurements because of their great measurementaccuracy. Observation of the preform along its axis provides us with information about theactual refractive index distribution in this preform. In order to obtain this information,it is necessary to cut a slice out of the preform and to place it in the measurement setupso that the light beam goes along the symmetry axis of the preform slice. Owing to the factthat the refractive index does not change along the run of the beam parallel to the preformaxis, this method makes it possible to determine the actual refractive index distribution.The method of three interferograms is a destructive method and i makes it possible to mea-sure the refractive index distribution with an accuracy of 1x10- for a slice of 1mm thick-ness as well as the sample thickness distribution. Although the method presented here issimpler, it constitutes a model method for nondestructive methods. This method makes itpossible to make measurements of varying accuracy whether we take into account the distribu-tion of the thickness of the examined slice based on other measurements , or whether theslice wedge alone is considered, or whether the slice thickness is assumed as constant.Measurement setup

Characterisation Of Optical Fibres By Measurement Of The Transmitted Near Field

Abstract: Methods of deriving propagation parameters of optical fibres from measurements of the transmitted near field are described. The transmitted near field of an optical fibre is dependent on the illumination wavelength spectrum and this is used to determine refractive index and mode spot profiles. When an optical fibre is multimoded by illuminating with white light the transmitted near field intensity distribution is directly related to the refractive index profile. This can be used to achieve a reasonably accurate measure of the refractive index profile of both multimode and monomode fibres. Both the theoretical considerations and the practical conditions for performing this measurement are described. When the optical fibre is single-moded the transmitted near field intensity distribution is the mode spot distribution. Many of the propagation characteristics can be determined from this distribution. For standard single mode fibres, such as step index or depressed cladding, the spot size and hence the equivalent step index are easily derived from this distribution. Advanced single mode fibres can be characterised from a more detailed knowledge of this distribution. Other techniques have been suggested and used for these measurements, they are all theoretically interrelated. By considering the relationship between the refractive index profile, the transmitted near field intensity distribution and the far field intensity distribution it is possible to estimate the relative merits and errors of these techniques.

Refractive index distribution type meniscus lens and optics

Abstract: A refractive index distribution type meniscus-shaped single lens characterized in that it has a refractive index distribution in which the refractive index decreases along the optic axis thereof from a convex surface to a concave surface and the difference ΔN in refractive index between the convex surface and the concave surface on the optic axis satisfies ΔN≧0.15.

Dispersion shift type optical fiber

Abstract: PURPOSE: To decrease the chances of the incorporation of an OH group into a fiber in actual production and to obviate the increased absorption loss by the OH group by forming the fiber in such a manner as to have the low- refractive index part where the refractive index is not lower than the refractive index of the pure quartz glass sandwiched by plural high-refractive index parts and to have a clad part where the refractive index is lower than the refractive index of the pure quartz glass enclosing the core part. CONSTITUTION: This fiber has the high-refractive index part 2 doped with germanium in the central part of the core part 1, the low-refractive index part 3 around the same and further the high-refractive index part 4 doped with germanium around the low-refractive index part 3. The clad part 5 of the low refractive index is provided around the core part 1 so as to enclose the same. The low-refractive index part 3 sandwiched by the two high-refractive index parts 2, 4 in the core part 1 consists of the pure quartz glass or the quartz glass doped with a small amt. of the germanium and the refractive index thereof is not lower than the refractive index of the pure quartz glass. The clad part 5 has the refractive index lower than the refractive index of the pure quartz glass by doping fluorine thereto. COPYRIGHT: (C)1988,JPO&Japio

Improved optical fiber

Abstract: An optical communications fiber is made from a core of high refractive index glass, a cladding of lower refractive index glass, and an edge cladding of a high refractive index glass. This optical fiber does not depend upon the refractive index of the polymeric coating to function properly, because the edge cladding refracts the errant light away from the core and cladding.

Low loss dispersion shifted fiber with fluorine doped cladding and step like index profile

Abstract: Various types of dispersion shifted fibers for 1.55 μm operation have been proposed with variety of refractive index profiles such as triangle, trapezoidal, segmented core1), quadruple clad. Dispersion characteristics of these fibers were well analized and good reproducibility has been reported.

Determination of chromatic dispersion in single-mode fiber waveguides by an interference method

Abstract: A determination was made of the spectral dependence of the chromatic dispersion in a single-fiber waveguide by an interference method. The same dependence was calculated for the parameters of an equivalent fiber waveguide with a step index profile deduced from the spectral dependence of the size of the spot formed by a mode in the investigated waveguide. A comparison of the experimental and calculated data demonstrated the validity of such calculations in the case of waveguides with a nominal step index profile.

The effect on mode propagation of a depressed refractive index along the axis of an optical fibre core

Abstract: Any depression of the refractive index along the axis of the core of a conventional optical fibre tends to confine waves transmitted along it to the concentric layer of higher-refractive-index material. Moreover, the inner radius, in the transverse plane of this layer, proves to be a particularly important factor in determining propagation behaviour and this paper shows how the HE11, the EH11, the TE01 and the TM01 modes are affected. The EH11 mode is found to be extremely sensitive to a minute filament of depressed refractive index along the axis and this apparently can provide for limited propagation of that mode at the bottom end of the frequency scale. The implication is that single-mode operation in the HE11 pattern is only surely established when the core is of uniform refractive index extending right to the axis of the fibre.