Showing papers on "Step-index profile published in 1993"

Variable Refractive Index Effects on Radiation in Semitransparent Scattering Multilayered Regions

Abstract: A simple set of equations is derived for predicting the temperature distribution and radiative energy flow in a semitransparent layer consisting of an arbitrary number of laminated sublayers that absorb, emit, and scatter radiation. Each sublayer can have a different refractive index and optical thickness. The plane composite region is heated on each exterior side by a different amount of incident radiation. The results are for the limiting case where heat conduction within the layers is very small relative to radiative transfer, and is neglected. The interfaces are assumed diffuse, and all interface reflections are included in the analysis. The thermal behavior is readily calculated from the analytical expressions that are obtained. By using many sublayers, the analytical expressions provide the temperature distribution and heat flow for a diffusing medium with a continuously varying refractive index, including internal reflection effects caused by refractive index gradients. Temperature and heat flux results are given to show the effect of variations in refractive index and optical thickness through the multilayer laminate.

Enhancement of optical-amplifier noise by nonlinear refractive index and group-velocity dispersion of optical fibers

Abstract: The influence of the nonlinear refractive index and the group-velocity dispersion of optical fibers on optical-amplifier noise is studied. A new method is used to calculate the spectrum of the amplified spontaneous emission. The result shows that the positive dispersion is favorable for suppressing the enhancement of the amplifier noise. >

Low bend loss singlemode optical waveguide fiber

Abstract: An optical waveguide fiber with improved bend loss performance while maintaining cutoff wavelength, λc, and zero dispersion wavelength, λ0, in practical operating ranges. The fiber includes an inner core region with a refractive index delta higher than the rest of the core and a reduced diffusion tail at the core/cladding interface. Optionally, a ring at the outer portion of the core is provided to compensate for increased λ0 which results from the higher inner core refractive index delta. This ring also contributes to the reduced diffusion tail at the core/cladding interface.

Optical fiber for soliton transmission and method of making

Abstract: A single-mode optical fiber suitable for the transmission of solitons has a refractive index profile that changes along the length of the fiber to provide a fiber dispersion that monotonically decreases along the fiber from one end thereof to the other. The fiber includes a core of maximum refractive index n 1 and a radius a, surrounded by cladding material having a refractive index n 2 which is less than n 1 . The fiber core includes a central region that extends to the longitudinal axis of the fiber and an outer region, the inner and outer regions being separated by a region of depressed refractive index. The inner radius a 1 of the region of depressed refractive index is greater than zero and the maximum radius a o of the region of depressed refractive index is less than a. The fiber preform can be made by depositing layers of glass particles on an elongated mandrel, the composition of glass particles being varied with respect to longitudinal position along the preform during the deposition of some of the layers.

Method of refractive index profile reconstruction from effective index of planar optical monomode waveguides: Application to potassium ion-exchanged waveguides

Abstract: A simple nondestructive method for determination of refractive index profile of single-mode waveguides using the measured effective refractive indexes is proposed. The method is based on the extraction of the additional data about the waveguide profile from the investigation of its evolution with the duration of fabrication process. The profile reconstructions are carried out using an appropriate algorithm in the frames of the WKB approximation. The method is applied for few- and single-mode waveguides, obtained by K/sup +/-Na/sup +/ field assisted ion exchange. The results are corroborated with the reconstruction from the effective refractive indexes measured at a shorter wavelength, as well as with profile study by means of step-by-step etching. >

Multimode optical fiber coupling apparatus and method of transmitting laser radiation using same

Abstract: A laser radiation source apparatus comprises a laser source means for producing laser radiation; a stepped-index optical fiber; first coupling means for coupling the laser source means with one end of the stepped-index optical fiber; and second coupling means for coupling the other end of the stepped-index optical fiber with another fiber suitable for transmission of laser radiation. The stepped-index fiber optic includes a core suitable for transmission of laser radiation, which is encompassed by at least one cladding layer and a buffer layer, in which the refractive index value for the core is greater than the refractive index value for the cladding layer, and the refractive index value for the cladding layer is greater than the refractive index for the buffer layer, so that laser radiation transmitted into the cladding layer is transmitted through the fiber. Single index fibers having several diameters may be coupled to the apparatus.

Fast nonlinearity of the refractive index of solid-state dielectric active media

Abstract: Research on the nonlinear refractive indices of solid dielectric active media is reviewed. The review is restricted to media for which the nonlinear refractive index is fast, i.e., has a relaxation time τ < 10−9 s. The nature of the nonlinear refractive index, its relaxation time, and its dispersion are discussed. Measurements of the parameters of the nonlinear refractive index of more than 160 laser and optical glasses and crystals are collected.

Negative dispersion optical fiber

Abstract: Disclosed is optical fiber that can advantageously be used to compensate chromatic dispersion in an optical fiber communication system, typically a system that is upgraded from 1.3µm to 1.55µm operating wavelength (λop). The fiber typically has a power law core (11) refractive index profile, a refractive index "trench" (12) surrounding the core, and a refractive index "ridge" (13) surrounding the trench. The refractive index profile of the fiber preferably is designed such that the fiber supports the fundamental mode (LP₀₁), does not support the LP₁₁ mode but does support the LP₀₂ mode, all at λop. A λop, LP₀₁ has dispersion more negative than -150 ps/nm·km and, in a preferred embodiment, LP₀₁ also has negative dispersion slope at λop.

Interference modulation of Q values in a cladded-fiber whispering-gallery-mode laser.

Abstract: We examine numerically the Q values of some of the core whispering-gallery resonances of a fiber clad with a material of lower refractive index, which differ from those of a homogeneous fiber of the same relative refractive index The enhancement and reduction of the Q values are explained in terms of interference effects caused by internal reflection from the surface of the fiber cladding; a simple model gives the period of the interference modulation The effect of this modulation has been observed in the whispering-gallery-modelaser spectra from a dye-doped highly refractive solvent flowing in a normally illuminated fused-silica capillary

Low loss coupler

Abstract: A low loss fiber optic coupler of the type wherein a plurality of single-mode optical fibers are fused together along a portion of the lengths thereof to form a coupling region. Each fiber includes a core and a cladding, the lowest refractive index of the fiber claddings being n 2 . Each of the output fibers of the coupler further includes a surface region of refractive index n 4 that inhibits the coupling of light to lossy composite modes, n 4 being lower than n 2 .

Surface refractive index of the eye lens determined with an optic fiber sensor

Abstract: The use of a fiber-optic sensor for measurement of the refractive index on the surface of eye lenses is described. The technique makes use of the fact that the amount of light reflected at the interface of two media (Fresnel reflectance) depends on the refractive-index difference between them. The sample is probed with a single-mode fiber, and the refractive index is calculated from the proportion of light reflected at the probe-sample interface.

Optical fiber type diffraction grating

Abstract: PURPOSE:To increase the reflectivity and to make it possible to change a selection wavelength by applying periodic refractive index changes to a specific core by irradiation with light to form diffraction gratings. CONSTITUTION:An optical fiber structure having the core consisting of a polymer or polysilane dispersed with a low molecular compd. is constituted by imparting the periodic refractive index changes to the core by irradiation with light, thereby forming diffraction gratings. The optical fiber structure in such a case means a structure obtd. by covering the core having a high refractive index with a clad having a low refractive index and includes not only such a three-dimensional optical waveguide as represented by an optical fiber in a narrow sense but a two-dimensional optical waveguide as well. As the low molecular compd., a compound which generates, for example, charges and a charge transfer with the polymer to change the refractive index when the compd. is irradiated with the light of the prescribed wavelength, is used. The polymer is not particularly limited and various kinds of the polymers are usable.

Optical fiber for connection to waveguide type optical device and method of manufacturing the same

Abstract: An optical fiber for connection to waveguide type optical device has a core having a flat cross-section, a first clad which is formed along a greater diameter of the core and which has a refractive index smaller than that of the core, and a second clad which is formed outside of the core and the first clad and which has a refractive index smaller than that of the core and greater than that of the first clad, wherein a²·Δ2 = b²·Δ1 , where a is the greater diameter of the core, b is the smaller diameter of the core, Δ1 is the difference in specific refractive index between the core and the first clad, and Δ2 is the difference in specific refractive index between the core and the second clad.

Light diffusing body

Abstract: PURPOSE: To provide a light diffusing body suppressing the diffusion of light in the reverse direction to the direction of light propagation, mainly diffusing the light only in the direction of light propagation and optically controlled by composing the body of a transparent body having the specified distribution of refractive index. CONSTITUTION: A light diffusing body is composed of a transparent body having the specified distribution of refractive index. Namely, the difference Δn between the maximum value and the minimum value of the refractive index is ≥0.005 and the difference of the refractive index at two arbitrary points 500Å apart is ≤0.01 or ≤Δn/2. The average of the refractive index within a circle of 5mm in diameter at an arbitrary position is nearly equal to the average of the whole refractive index. The material of the transparent body is suitably a transparent solid body and capable of substantially continuing the refractive index and e.g. it is a glass, transparent polymer or resin composition. Consequently, the discontinuous part of refractive index within the light diffusing body is removed and the reflection of light in the reverse direction is prevented. COPYRIGHT: (C)1994,JPO

Surface emission led

Abstract: PURPOSE: To achieve high emission efficiency by interposing a low refractive index layer, having relatively lower refractive index than an active layer on the light take out face side, between the active layer and the light take out face. CONSTITUTION: A LED 10 is constituted by laminating a clad layer 14, an active layer 16, a clad layer 18, a low refractive index layer 20, a cap layer 22, and an ohmic electrode 24 sequentially on a substrate 12. The refractive index n 20 of the low refractive index layer 20 is set at 3.20 by setting the mixed crystal ratio (x) of P-Al x Ga 1-x As compound at 0.6, i.e., it is set lower than the refractive index n 18 =3.29 of an adjacent clad layer 18. Since the light emitted upward is totally reflected over a relatively wide angular range of 63.04°-78.7° with respect to the thickness direction of the chip on the border face 25 and taken out from the side face 30 of the chip to the outside, the light emission efficiency is enhanced. COPYRIGHT: (C)1994,JPO

Determination of monomode fiber buffer properties from bend-loss measurements

Abstract: Bend loss in monomode optical fibers exhibits oscillations as a function of wavelength due to a whispering gallery mode. The period of these oscillations has been used to measure the mean refractive index and thickness of the buffer material on two optical fibers in situ. The mean refractive index of the buffer material was measured to an accuracy of ±0.0025, which is sufficient to distinguish two nominally identical fibers with buffer surface cures of 86% and 96%.

UV-induced Bragg gratings in optical fibers and thin-film waveguides

Abstract: The side-writing of Bragg gratings in fibers by exposure to a periodic UV intensity pattern is discussed. The spectral characteristics of gratings in depressed index fiber are described including the formation of higher-order reflection bands and coupling to cladding modes. Exposure requirements are compared with photosensitivity measurements of the refractive index change induced by individual KrF laser pulses. Commercial germaosilicate thin film waveguides are also found to be photosensitive. Results are presented on UV-induced lateral wave confinement in H 2 -loaded film and grating formation in standard buried channel guides.

Shaped articles of graduated refractive index exhibiting low dispersion

Abstract: A monolithic, thermoplastic article with a continuously graded refractive index is formed by polymerizing a fluorinated matrix polymer in the presence of a low molecular weight, substantially unreactive guest molecule of different refractive index than the matrix polymer. The thermoplastic articles may be used to produce shaped articles such as optical waveguides, fibers or lenses of low attenuation and high bandwidth.

Shaped articles of graduated refractive index

Abstract: A monolithic, thermoplastic article with a continuously graded refractive index is formed by polymerizing a fluorinated matrix polymer in the presence of a low molecular weight, substantially unreactive guest molecule of different refractive index than the matrix polymer. The thermoplastic articles may be used to produce shaped articles such as optical waveguides, fibers or lenses of low attenuation and high bandwidth.

Axial strain insensitivity of weakly guiding optical fibers

Abstract: A numerical model has been developed to calculate the modal phase shift of circular step index profile weakly guiding fibers under axial strain. Whenever an optical fiber is under stress, the optical path length, the index of refraction, and the propagation constants of each mode change. In consequence, the phase of each mode is also modified. A relationship for the modal phase shift is presented. This relation is applied to both single mode and two-mode fibers in order to determine the sensitivity characteristics of strained fibers. It was found that the phase shift is strongly dependent on the core refractive index, n(co). It was also found that it is possible to design fibers which are insensitive to axial strain. Practical applications of strain insensitive fibers are discussed.

On the discretization process involved in the staircase-approximation technique for analyzing radially inhomogeneous optical fibers

Abstract: The accuracy of staircase-approximation techniques that are used for analyzing optical fiber properties depends on how certain discretization parameters are chosen. In this work we discuss and develop criteria for the choice of those parameters. Particular emphasis is placed on a physics-based criterion we suggest be followed for the specification of the refractive index of the layers into which the fiber core is discretized. © 1993 John Wiley & Sons, Inc.

Multilayer antireflection film and optical system provided with the same

Abstract: PURPOSE: To provide a multilayer antireflection film which can give the required antireflection effect regardless of the refractive index of optical parts such as a lens by successively forming a specified medium refractive index layer, high refractive index layer, and low refractive index layer on a substrate. CONSTITUTION: Three layers are successively formed on a substrate comprising an optical material when λ is the standard wavelength in the wavelength range for the antireflection effect. These layers are, from the substrate side, (a) medium refractive index layer having λ/4 optical film thickness and refractive index (n) satisfying 1.72≤n≤1.74, (b) high refractive index layer having λ/2 optical film thickness and satisfying 1.97≤n≤2.13, and (c) low refractive index layer of MgF 2 having λ/4 optical film thickness. The reflection characteristics are shown in the figure when layers with the following refractive indices are formed. Namely, n=1.73 in the medium refractive index layer (Al 2 O 3 /Pr 2 O 3 ), n=2.03 in the high refractive index layer (TiO 2 /La 2 O 3 ), and n=1.38 in the low refractive index layer (MgF 3 ). The leader lines in the figure show refractive indices of- substrates. Thus, good antireflection characteristics are obtd. regardless of the refractive index of the substrate. COPYRIGHT: (C)1994,JPO&Japio

Equivalent step-index-fiber method for multicladding fibers

Abstract: An equivalent step-index-fiber method (ESFM) has been extended to multicladding fibers. Upon defining the refractive-index profile for the multicladding preform, the transmission parameters, especially the cutoff wavelength of the fiber drawn from the preform, can be predicted directly before fiber-drawing, saving time and energy. Comparison between the theory and results from experimental fibers shows an accuracy of 5% in predicted cutoff wavelengths. >

An efficient method for analyzing graded-index optical fibers

Abstract: We describe a method for analyzing graded index optical fibers using a stepwise function approximation to model the core refractive index profile. For each homogeneous shell uncoupled radial equations for the longitudinal field components Ez and Hz are considered. Relationship between field solutions corresponding to core adjacent shells is established with the help of appropriate boundary conditions. Numerical results obtained with this method are presented and discussed, with special attention being focused on the analysis of the number of discretization steps necessary for achieving satisfactory core modeling. © 1993 John Wiley & Sons, Inc.

Atomic-coherence-induced enhancement of refractive index

Abstract: The influences of lower-level coherence in atomic medium of Ξ-type energy-level scheme on the absorption and dispersion are studied in dressed states. It is found that a weak probe light of a certain frequency can be free of atomic absorption, and at the same time has a large index of refraction.

Detection and refractive index identification of submicron particles on surfaces

Abstract: Inspection for contaminant particles on surfaces is of major interest in the semiconductor industry as well as many others. We have developed an optical inspection instrument which detects particles as small as 65 nm and give information about the refractive index as well. Such information can be used to identify contaminant particles leading to more rapid identification of the source. The instrument is based on a scanned laser Nomarski interferometer, and measures differential phase and amplitude over an inspected area. We have previously shown that the forward scattered light from a small particle (in this case in liquid) interferes with the incident beam to produce a phase shift and amplitude change (extinction) dependent on the particle size and refractive index. This method is also applicable to surfaces by using a reflection mode. Similar to ellipsometry, plotting phase shift against extinction can provide information on both size and refractive index. We have analyzed particles on a silicon surface for a range of compositions, and found that particles can be sorted into refractive index classes such as low index, moderate index and metals.

Characterization of proton-exchanged planar waveguides on z-cut lithium tantalate

Abstract: We have characterized proton-exchanged z-cut LiTaO3 planar waveguides fabricated with pyrophosphoric acid. A step index profile was assumed. Following proton-exchange the waveguides were annealed at temperatures from 300 degree(s)C to 500 degree(s)C. Interestingly, the surface index n, increased instead of decreasing. The waveguide depth d, (Delta) ns, and shape of the index profile were closely monitored throughout annealing, and the results are presented. The mechanism of the surface index increase with annealing is explained and the results support this theory.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Dependence of immunoassay fluorescence signal on the index of refraction outside the fiber

Abstract: The dependence of fluorescence signal in optic-fiber immunoassay detection on the index of refraction outside the fiber has been studied both theoretically and experimentally. Studies show an enhancement of factor 7 can be obtained in index matching condition.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.