Showing papers on "Step-index profile published in 1990"

An effective attenuation coefficient for evanescent wave spectroscopy using multimode fiber

Abstract: An attenuation coefficient for evanescent wave spectroscopy on the core of a multimode step index fiber in contact with an absorbing species is derived in terms of the range of incident angles of the meridional rays to the interface. An expression, for the fractional power outside the core as a function of incident angles is also given. Their ratio is discussed for the case of a fiber sensor having a porous cladding in contact with a gaseous absorbing species and one in which a section of cladding has been removed and replaced by an absorbing liquid.

Achromatic fiber optic coupler

Abstract: An achromatic fiber optic coupler of the type wherein first and second single-mode optical fibers, each having a core and a cladding, are fused together along a portion of the lengths thereof to form a coupling region. A matrix glass of lower index than the fiber claddings surrounds the coupling region. The fiber diameters are smaller in the coupling region than in the the remainder of the fibers. The refractive index n2 of the cladding of the first fiber is different from the refractive index n~ of the cladding of the second fiber, the difference between the refractive indices n2 and n~ being such that the coupler exhibits very little change in coupling ratio with wavelength over a band of wavelengths.

Ultraviolet light photosensitivity in Ge-doped silica fibers: wavelength dependence of the light-induced index change.

Abstract: A novel technique is reported for detecting permanent and transient light-induced refractive-index changes (photosensitivity) in optical fibers. The index change is detected by irradiating one arm of an unbalanced Mach–Zehnder fiber interferometer with UV light, thereby changing its optical path length. From a measurement of the change in the spectral response of the Mach–Zehnder interferometer, the change in the fiber core index as a function of wavelength can be determined. The equilibrium change in the core index is found to have an almost constant value of approximately 2.3 × 10−5 over the measured wavelength range of 700 to 1400 nm.

Refractive index measurements on single-mode fiber as functions of product parameters, tensile stress, and temperature

Abstract: This paper describes results of a recent study that characterizes effective index of refraction for commercially available matched-clad, single-mode optical fibers. Effects of product parameter, stress, and temperature ranges on the index are reported. Direct measurements of flight times, fiber lengths, tensile loads, elongations, and temperatures provide index of refraction accuracy to four decimal places. Nominal effective index of refraction values found for unshifted fiber were 1.4675 and 1.4681 at 1300 nm and 1550 nm wavelengths, respectively; values for dispersion-shifted fiber were 1.4718 and 1.4711. Both fiber types at each wavelength displayed index versus stress slopes of -0.000024/kpsi, and index versus temperature slopes of 0.000012/°C.

Uniform refractive index cladding for LiNbO3 single‐crystal fibers

Abstract: A uniform refractive index cladding for LiNbO3 single‐crystal fibers has been achieved using a Mg ion indiffusion process. This cladding has a uniform MgO concentration of ∼20 mol %, resulting in a uniform refractive index. The refractive indices of the cladding material have been evaluated to be ne=2.08 and no=2.09 at 0.6328 μm by using the light reflection technique.

Chlorine-doped optical component

Abstract: A fiber optic coupler of the type wherein first (F₁) and second (F₂) single-mode optical fibers, each having a core and a cladding, are fused together along a portion of the lengths thereof to form a coupling region (N). The fiber diameters are smaller in the coupling region (N) than in the the remainder of the fibers. The cladding of the second fiber contains an amount of chlorine sufficient to increase the refractive index n ' ₂ thereof to a value greater than the refractive index n₂ of the cladding of the first fiber.

Measurement of the electrically induced refractive index change in silicon for wavelength λ=1.3 μm using a Schottky diode

Abstract: We report the results of measurements of the electrically induced refractive index change caused by the free‐carrier effect in a silicon Schottky diode. We find that for the wavelength λ=1.3 μm, the real part of the refractive index changes by as much as ‖Δn‖∼0.01 for current densities less than 1 A/cm2. This refractive index change produced changes in the input‐coupling efficiency as large as 75% in our sample geometry.

Determination of two-dimensional optical waveguide index distribution function parameters from effective indexes

Abstract: The method described is based on the least-squares method and gives the maximum-likelihood estimate of the parameters. Its practicality is demonstrated by application to waveguides with three types of refractive index distribution. First, the convergence of the method is shown by computer simulations of a waveguide with an exponential refractive index distribution. Second, a Ti-diffused LiNbO/sub 3/ waveguide is considered as an example of a Gaussian refractive index distribution. The computed refractive index distribution agrees with computational results obtained by S. Fouchet et al. (1987). Third, a proton-exchanged LiNbO/sub 3/ waveguide is considered as an example of a step refractive index distribution. The computed depth of the waveguide agrees with the measured depth. >

Thin-film optical element, production thereof and head up display using the same

Abstract: PURPOSE: To enhance the uniformity of film thicknesses and to obtain a large area by using high-polymer composition as dielectrics varying in refractive index. CONSTITUTION: High-refractive index materials 3 having the thickness of 1/4 wavelength and low-refractive index materials 2 of 1/4 wavelength are laminated on a base material. The reflected light on the surface of the low-refractive index layers is offset by the reflected light on the boundary between the low- refractive index layers and the high-refractive index layers shifted in phase by 1/2 wavelength and on the boundary between the high-refractive index layers and the base material 1 in this case. The high-polymer composition varying in the refractive index are alternately laminated by ≥1 layers each respectively as the low-refractive index layers and the low-refractive index layers on the base material 1 in such a manner and, therefore, the thin-film optical element having the large area is easily obtd. COPYRIGHT: (C)1992,JPO&Japio

Achromatic fiber optic coupler and method of making it

Abstract: An achromatic fiber optic coupler of the type wherein first (F1) and second (F2) single-mode optical fibers, each having a core and a cladding, are fused together along a portion of the lengths thereof to form a coupling region (N). A matrix glass (10) of lower index than the fiber claddings surrounds the coupling region (N). The fiber diameters are smaller in the coupling region than in the the remainder of the fibers. The refractive index n₂ of the cladding of the first fiber is different from the refractive index n'@2 of the cladding of the second fiber, the difference between the refractive indices n₂ and n'@2 being such that the coupler exhibits very little change in coupling ratio with wavelength over a band of wavelengths.

Narrow-band directional couplers made of dissimilar single-mode fibers with different cladding refractive indexes

Abstract: A wavelength-selective directional coupler, consisting of two polished single-mode fibers with different cladding refractive indexed, has been fabricated. In contrast to symmetrical couplers, where the power transfer characteristic is a quasiperiodic function of the wavelength, couplers made of dissimilar fibers show a true bandpass-filter characteristic. They consist of two fibers with different core diameters and refractive-index profiles, having the same cladding refractive index. The parameters of the fibers must be chosen in such a way that if their propagation constants beta /sub 1/, beta /sub 2/ are plotted over the wavelength, the curves intersect at a cross-over wavelength lambda /sub 0/ equal to the center wavelength of the filter. The 3-dB bandwidth of the coupler's power transfer characteristic is 13.6 nm, the best value achieved up to now. >

Modeling variation in the refractive index of optical glasses

Abstract: Experimental measurements that describe the dispersive behavior of production samples of optical glasses are fit with models of minimum complexity for the purpose of in terpolation and extrapolation. Software to perform this procedure on a regular basis is presented, and shown to dis tinguish between models of inappropriate complexity. Two degrees of freedom usually provide a statistically optimum fit to the data contrary to the widespread practice of fit ting a general, six term model to such measurements. Using specially developed analysis tools, it is concluded that annealing does not significantly change the partial dis persion of the sample. Partial dispersion is established at the time the ingredients are combined in a melt and is in variant from one annealing to another. This is an important result to consider when planning the fabrication of optical systems whose prescription changes with changes in materi al characteristics.

Flexible optical fibre transmitting polychromatic beams - has refractive profile such that convergence angle at input and divergence angle at output are practically independent of wavelength

Abstract: The flexible optical fibre consists of a core and a cover and is intended for a region of the spectrum in which the ratio of the largest to the smallest wave length is 1.2. The profile of the refractive index in the core is defined by a set of equations, depending on the value of the radius from the centre of the core and the variation of the index with this value as shown on simple graphs. USE/ADVANTAGE - Simple design with simple refractive index profile. Suitable for optical communuications systems.

Stress-induced refractive index inhomogeneity in fluoride glass fibers: origin of wavelength independent scattering loss.

Abstract: Inhomogeneous distribution of refractive index in fluoride glass fibers was found. The inhomogeneity results from stress in the fiber and can be an origin of wavelength independent scattering which is the dominant loss factor present in fluoride glass fibers.

Graded-index lens

Abstract: A graded-index lens for focusing an erect unmagnified image out of the lens has a refractive index varying radially in a cross-sectional plane normal to the optical axis thereof. The graded-index lens comprises a cylindrical medium whose refractive index at a radial distance r from an optical axis within a cross-sectional plane normal to the optical axis, is expressed by: n.sup.2 (r)=n.sub.0.sup.2 [1-(gr).sup.2 +h.sub.4 (gr).sup.4 ] where n 0 is the refractive index on the optical axis, g is a parameter indicating the gradient of the varying refractive index, and h 4 is a fourth-order refractive index distribution coefficient, the fourth-order refractive index distribution coefficient h 4 being in the range of: 0.6

Determination of refractive index of a simple negative, positive, or zero power lens using wedged plated interferometer

Abstract: Measurement of the refractive index of a simple negative lens is presented. The technique is also useful for measuring the refractive index of a simple convex and zero power lens.

Fast Measurement Of Parameters ▵ And ∝ Of Refractive Index Profile In Preforms And Waveguides. Lateral Shearing Interference Method

Abstract: It became possible to make the measurements of parameters u and ∝ of preforms and waveguides faster by satisfying the following assumptions: 1. Sufficient and accurate approximation of the real profile is description by the formula.

Measurement Of Refractive Index Profiles Of Preforms And Waveguides By Means Of Higher-Order Approximation And Interference With Plane Wave Of Reference

Abstract: There are described the methods of wave front reconstruction by means of optical path difference fringe shift method, interfringe linear interpolation, and polynomial approximation. By way of example, the results of measurements of refractive index profiles for waveguide preforms are given. These results were obtained using higher order approximation methods (of the first and second orders). The method in question, together with computer programs that have been worked out, also permits correction of errors caused by discontinuity of refractive index profile, mismatching of the immersion liquid refractive index to preform clad or waveguide, as well as by core ellipticity (partial correction). The measuring accuracy of 0.1 per cent was obtained.

Method of measuring the refractive index of glass plates

Abstract: The diagram of the wavelength meter is presented in Fig. 1 (i is the telescope mirror, 2-4 are light dividers; 5 is a lightguide; 6-8 are interferometers, 9-11 are photodetecting matrices; 12-14 are photodetector control apparatus; 15 is a commutator; 16 is an ADC; 17 is a controller; 18 is the central computer). Its basis is three Fizo interferometers with bases on the order of 3 mm that permit measurements of laser wavelengths with approximately 0.02 nm radiation linewidth, which is an order of magnitude higher than the meter described in [2], say, assures.

Interferometric Measurement Of Refractive Index Differences In Optical Fibres

Abstract: This paper will discuss measurements of refractive index differences in optical fibres using an image shearing interference microscope. The technique has been used to characterise a multi-step index fibre suitable as a transfer standard to calibrate other more convenient fibre profiling instruments, eg refracted near-field. The technique of axial interferometry, where a thin slice of the fibre about 100 pm thick is viewed along its axis, has been developed so that uncertainties of about ±1% in refractive index differences are considered possible. The implementation of the technique, sources of error and interferometric measurements of slice thickness will be discussed along with the measurement uncertainties. Finally, an intercomparison of results obtained from interferometry, refracted near field, phase contrast microscopy and far-field measurement of light emerging from the fibre end, will be discussed.

Automatic Measurement Of Gradient Index Fiber Profile By Transverse Differential Shearing Interferometry

Abstract: A measurement of gradient index optical fiber profile by means of transverse differential shearing interferometry is described By incorporating an automatic fringe processing system the accuracy of the fringe shift data reading equal to D/140 ( D - interfringe spacing) is obtained Due to the accurate method of reconstruction of the profile from interferometric data the refraction of the probing beam is completely compensated The immersion - cladding index mismatch is considered and it is shown that the immersion of refractive index higher then cladding refractive index can be used

Determination of thickness and of refractive index of material with “silver” cracks

Abstract: Reflection of light on “silver” cracks was theoretically analysed for the case of attenuated total reflection. The field of the reflected light wave on the wedge-like crack was found. An expression for the integral intensity of the reflected wave as a function of the angle of incidence was derived. Formulae for the determination of the thickness and refractive index of the crack material are presented.

Refractive index measurement of ion‐exchanged glass waveguides by reflection method

Abstract: It is important to measure the refractive index profile in an optical waveguide. In particular, there has been a demand for the development of simple methods to measure precisely the refractive index profile in a waveguide with a small number of propagation modes. One of the methods which can provide relatively high resolution is the edge reflection method using an optical fiber as a probe. This method has been used to evaluate a rod lens. In this study, the edge reflection method was used to evaluate a diffused-type glass waveguide with small dimensions. To increase the sensitivity to reflected light, the fibers for incident light and reflected light detection were located with a certain angle, that is, an oblique incident light system was used. In addition, to increase the spatial resolution, the refractive index profile in the direction of interest was expanded by angle lapping of the edge of the test fiber. By using this method, it was possible to measure easily the refractive index profile in a silver-diffused glass optical waveguide with two propagating modes.

Inverse analysis of refractive index profile of optical waveguide from propagation‐mode near field pattern including noise

Abstract: To estimate the transverse refractive index distribution of optical waveguides, comparison of the measured light intensity and that calculated from the assumed refractive index distribution is proposed as a new method. The assumed refractive index distribution is corrected to give the best agreement between the two intensity distributions [5, 6]. This is the reverse procedure of the previous method in which the refractive index distribution is extracted directly from the field intensity distribution [1–4] and, therefore, the present method can be called the “inverse analytical method”. In this paper, simulated numerical investigations of the inverse analytical method are carried out when the intensity distributions are noise proofed. The true step and graded refractive index distributions of buried and diffused types are assumed and Gaussian noises with two standard deviations are added to their corresponding light intensity distributions. Then the present method is applied to assess their refractive index distributions. Numerical simulations of the previous differential method [2] also are carried out for buried-type graded refractive index distribution. As the result of comparison, it is shown that the results do not depend on the smoothing process of the intensity distributions as they do in the case of the differential method. Therefore, it is quite possible to assess the refractive index distribution even without any smoothing process.

Development And Characterization Of Ag+-Na+ Exchanged Waveguides In Glass

Abstract: Field assisted Ag+-Na*-exchange in a newly developed glass is investigated in order to optimize the refractive index profile to multimode fibres. Two methods are considered to match the refractive index profile to step-index (Sl-)fibres and graded-index (Gl-)fibres, respectively. The typical insertion loss of first samples of y-branches for 50 y-cm-GI-fi- bre for bidirectional operation is 4.6 dB including 3 dB splitting loss. 1. INTRODUCTION Ion exchanged waveguides in glass form the basis for passive integrated optical compo­ nents, such as y-branches, star couplers, multiplexers and demultiplexers. The refractive index profile has to be matched to that of the fibre used, in order to minimize fibre-wa­ veguide-fibre coupling losses. We investigate field assisted Ag -Na exchange in a newly developed glass in order to optimize the refractive index profile to multimode fibres, es­ pecially 50 ^/tm-GI- and 200 yU.m-SI-fibre.For a field assisted exchange through a small (xyy = 10 /