Showing papers on "Step-index profile published in 1994"

Analysis of vectorial mode fields in optical waveguides by a new finite difference method

Abstract: An important class of dielectric optical waveguides has stepped refractive index profiles. For these waveguides we present a new finite-difference approach free of spurious modes. The coupled difference equations are formulated in terms of the transverse magnetic field components H/sub x/ and H/sub y/. We show how the boundary conditions can be formulated and included in the finite difference scheme to obtain a unique set of equations. For a step-index fiber a comparison of the numerical results with the analytical solution shows that the relative error in the propagation constant is as low as 4.4/spl times/10/sup /spl minus/7/ for an index difference of 7.3%. For a rib waveguide, we compare our results with previously published data based on other methods. Field plots of the dominant and the weak transverse field components of the magnetic field for the fundamental mode of a buried rib waveguide are also given. >

Method and apparatus for forming aperiodic gratings in optical fibers

Abstract: A method and apparatus for simultaneously exposing an optical fiber (32), made of a material which has a refractive index that can be permanently changed by exposure to light of a predetermined intensity at a predetermined wavelength, to two writing light beams (268, 272) which intersect and interfere in a predetermined region (30) of the fiber (32) so as to create an interference pattern along a longitudinal axis of the fiber (32), for a time long enough to form a permanent refractive index variation in the waveguide. Each of said two writing beams have a predetermined number of wavelengths, each wavelength being sufficiently different from each other so as to cause said refractive index variation to be an aperiodic variation. Also, each wavelength represents a Fourier component of the desired aperiodic refractive index variation.

Article comprising a dispersion-compensating optical waveguide

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 1.3 μm to 1.55 μm operating wavelength (λ op ). The fiber typically has a power law core refractive index profile, a refractive index "trench" surrounding the core, and a refractive index "ridge" surrounding the trench. The refractive index profile of the fiber preferably is designed such that the fiber supports the fundamental mode (LP 01 ), does not support the LP 11 mode but does support the LP 02 mode, all at λ op . At λ op , LP 01 has dispersion more negative than -150 ps/nm·km and, in a preferred embodiment, LP 01 also has negative dispersion slope at λ op . In a further embodiment of the invention the refractive index profile is designed such that the cut-off wavelength of the LP 11 mode is less than that of the higher order mode, typically LP 02 , and less than λ op , such that the fiber does not support propagation of the LP 11 mode. In some preferred embodiments the fiber is designed to have dispersion more negative than about -90 ps/nm·km and loss less than about 0.5 dB/km at λ op ˜1.55 μm.

Control of the dynamic range and sensitivity of a surface plasmon resonance based fiber optic sensor

Abstract: The refractive index sensitivity and dynamic range of a recently developed fiber optic based surface plasmon resonance sensor have been investigated. The sensor response was studied using a set of aqueous refractive index standards. The sensitivity to refractive index was found to be between 5.0×10−4 and 5.0×10−5 index of refraction units. The dynamic range of an unmodified sensor was between 1.25 and 1.40 index of refraction units. The dynamic range was tuned for ranges between 1.00 and 1.40 index of refraction units with the addition of thin high refractive index overlayer films. This range is significant since it includes both gas and aqueous chemical sample refractive indices. The upper limit of the refractive index dynamic range was extended to 1.70 by use of a sapphire fiber core material.

Polarization beam splitter and projection display apparatus

Abstract: A polarization beam splitter which includes a first prism, a second prism, and a dielectric multilayer film which is sandwiched between the first and second prisms is disclosed. The dielectric multilayer film comprising: a plurality of high refractive index layers having a refractive index higher than refractive indices of the first and second prisms; a plurality of intermediate refractive index layers having a refractive index lower than the refractive index of the high refractive index layers; and a plurality of low refractive index layers having a refractive index lower than the refractive index of the intermediate refractive index layers, a reference incident angle θ 0 of light which is incident on the dielectric multilayer film through the first or second prism being within a range of the following expression: θ.sub.1 <θ.sub.0 <θ.sub.2 where ##EQU1## where n H indicates the refractive index of the high refractive index layers, n M indicates the refractive index of the intermediate refractive index layers, n L indicates the refractive index of the low refractive index layers, and n 0 indicates the refractive indices of the first and second prisms.

Multilayer antireflective coating with a graded base layer

Abstract: An antireflectance coating is disclosed comprising a first graded layer wherein the composition is varied throughout the thickness of the layer such that the refractive index of the graded layer varies from a low refractive index approximately matching the refractive index of the substrate at the interface of the graded layer and the substrate to a higher refractive index at the surface of the graded layer opposite the interface with the substrate, and a second substantially homogeneous layer of a composition selected to have a refractive index which is approximately the square root of the product of the higher refractive index of the graded layer and the refractive index of the incident medium at the surface of the second layer opposite the interface of the second layer with the graded layer, having an optical thickness of approximately at least one quarter of a selected design wavelength. The antireflectance properties of the coating of the present invention can be expanded to a broader range of reflected wavelengths by incorporating, between the graded layer and the second substantially homogeneous layer, an intermediate layer having a relatively high refractive index and an optical thickness of about half the design wavelength.

Guided optical waves in fibers with negative dielectric constant

Abstract: We classify and discuss all optical guided modes able to propagate in ideal metallic-dielectric structures having the symmetry of a step index fiber. The cases of a metallic core with a dielectric cladding and a dielectric core with a metallic cladding are considered. In each case, the intensity profile of the allowed guided modes is shown. The geometric and frequency dispersion of the effective index of the modes is discussed as a function of the optogeometrical parameters of the fibers. >

Achromatic overclad fiber optic coupler

Abstract: An achromatic fiber optic coupler of the type wherein a plurality of 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. The propagation constants of the fibers are preferably equal; however if the fiber claddings have different refractive indices, the lowest cladding refractive index is n 2 . A matrix glass body of refractive index n 3 surrounds the coupling region, n 3 being lower than n 2 by such an amount that the value of Δ 2-3 is less than 0.125%, wherein Δ 2-3 equals (n 2 2- n 3 2 )2n 2 2 .

Neutral, low emissivity coated glass articles and method for making

Abstract: A coated article and method of producing it are disclosed wherein the iridescence caused by the difference between the refractive index of a transparent substrate and the refractive index of a metal oxide coating is reduced by means of two intermediate layers, the first of which, closest to the substrate, has a refractive index higher than the refractive index of the substrate but lower than the refractive index of the second, and the second has a refractive index higher than the refractive index of the first but lower than the refractive index of the metal oxide coating. The thicknesses of the two intermediate layers for optimizing a neutral appearance are determined by the thickness and refractive index of the metal oxide coating.

Total-reflection type refractive index sensor

Abstract: A refractive index sensor of a total-reflection type comprises a waveguiding layer of a cladding/core/cladding waveguide structure formed on a substrate. The waveguiding layer has an input face connected to either a single optical fiber or a plurality of optical fibers for injecting a light(s) into the layer, a detection face which, obeying Snell's law, totally reflects/transmits the light beam or beams that have arrived there with an expansion angle from the optical fiber or fibers and which constitutes a surface with which a material whose refractive index is to be measured comes in contact, and an output face which outputs the light reflected from the detection face and is connected to an optical detector. The refractive index of the material of interest is detected from a bright-dark boundary of the presence of the corresponding total reflected light from the detection face. With no need of a bulk prism or lamp-type light source, the sensor is small in size and high in sensitivity.

Polyimide optical waveguide and method of manufacturing the same

Abstract: A polyimide optical waveguide comprising a core made of polyimide whose refractive index is controlled to a predetermined value by electron beam irradiation, and a cladding set in contact with the core and having a refractive index lower than that of the core.

Surface plate treatment film and display device and its manufacture

Abstract: PURPOSE: To form a reflection preventive/static preventive/leakage electromagnetic field reducing film on a surface base body of a display device. CONSTITUTION: A high refractive index layer 2 and a low refractive index layer 3 are formed in this order between a surface board (a base body) 1 of a display device and an air layer 4, and reflection prevention of external light and static prevention or reduction in a leakage electromagnetic field are performed. The high refractive index layer 2 has the density distribution becoming small in order toward the low refractive index layer 3 from the surface board 1 side, and forms a graded film structure whose refractive index becomes continuously small between it and the air layer 4 from the display panel 1 side together with the low refractive index layer 3.

Epifilm thickness measurements using fourier transform infrared spectroscopy : effect of refractive index dispersion and refractive index measurement

Abstract: Procedures and results of refractive index measurements using a Fourier transform infrared spectrometer are reported. These measurements were performed on both lightly and heavily doped silicon samples over the midinfrared (2.5–25 μm) spectrum region. A strong dependence of refractive index as a function of substrate dopant concentration was observed. Moreover, it was observed that the refractive index of heavily doped silicon also varies significantly with wavelength. Furthermore, it was also observed that the refractive index of silicon decreases with increasing wafer temperature for long wavelengths. Finally, the effect of refractive index dispersion on epifilm thickness measurement was examined. The results suggest that the spectral dispersion of the refractive index cannot be neglected for epifilm thickness measurements.

Injection efficiency from a side-excited thin-film fluorescent cladding of a circular waveguide

Abstract: Experiments were conducted to verify a theoretical model on the injection efficiency of sources in the cladding of an optical fiber. The theoretical results predicted an increase in the injection efficiency for higher differences in refractive indices between the core and cladding. The experimental apparatus used consisted of a glass rod 50 cm long, coated at one end with a thin film of a fluorescent substance. The fluorescent substance was excited with side illumination, perpendicular to the rod axis, using a 476-nm argon-ion laser. Part of the excited fluorescence was injected into the core and guided to a detector. The signal was measured for several different cladding refractive indices. The cladding consisted of sugar dissolved in water, and the refractive index was changed by varying the sugar concentration in the solution. The results indicate that the power injected into the rod, due to evanescent wave injection, increases with the difference in refractive index, which is in qualitative agreement with theory.

Optical device with a pig tail optical fiber and its production method

Abstract: The present invention relates to an optical waveguide with a specific refractive index difference .DELTA.1, has a construction in which a core having a high refractive index having a rectangular section is built in a cladding layer with a low refractive index formed on a substrate. A pig tail optical fiber comprising a first fiber serially connected to a second fiber each of which has a different specific refractive index difference is connected to an input terminal of the optical waveguide. The second fiber with a specific refractive index difference .DELTA.2 (.DELTA.2 (.DELTA.1) is connected to a terminal of the first fiber with a specific refractive index difference nearly equal to .DELTA.1. A diffusion region at the neighbourhood of the connection between the first and the second fiber is formed by diffusing the dopant for refractive index control in the core of the second fiber by heat addition. By the diffusion region, both diameters of the first and the second fiber are adjusted so as to be nearly equal in diameter.

Determination of monomode fiber buffer properties

Abstract: Observations of oscillations in bending loss as a function of illuminating wavelength in monomode optical fibers are presented. A model is developed based on the interference between the core-guided mode, and a "whispering gallery" (WG) mode established by reflection at the buffer-air interface. It is shown that the relative phase of the modes is a function of the dimensions and refractive index of the buffer coating. The phase is determined in experiments where the bend radius and wavelength of illumination are varied, allowing the buffer diameter and refractive index to be determined by a best fit to experimental data. The practicality of this method for the characterisation of buffer properties is discussed. >

Measurement of the refractive index of alxga1-xas and the mode indices of guided modes by a grating coupling technique

Abstract: We have determined the index of refraction of AlxGa−xAs over the wavelength range 0.76–1.15 μm, and the composition range 0≤x<0.33, using a grating to couple light into waveguides. We find the mode indices of multimode slab waveguides from the coupling angle and grating period, then calculate the bulk indices of the core and cladding materials by a root searching technique using the analytical formula for the effective index of a guided mode. The method gives the core index within ±0.001, and the cladding index within ±0.01. We are in agreement with high precision index values for GaAs in the literature, confirming the method. We are in substantial agreement with literature values for AlGaAs but find a significant systematic difference in the composition dependence. An analysis of measurement uncertainties shows that the determination of composition is the dominant variable.

Method of manufacturing a polyimide optical waveguide

Abstract: A polyimide optical waveguide comprising a core (2) made of polyimide whose refractive index is controlled to a predetermined value by electron beam irradiation, and a cladding (1, 3) set in contact with the core and having a refractive index lower than that of the core.

Errors in film refractive-index determinations from interference fringes

Abstract: An analysis of interference fringes (channel spectra) in transmission or reflection spectroscopy of optical films can provide an accurate method for determining the refractive index or thickness of the film. If the index is changing and the common equation n = 1/(2tΔν) determined from the positions of two adjacent maxima in the interference pattern is employed, the resulting refractive index does not lie between the correct values at the frequencies of the two maxima as intuitively expected but well outside this range. This error can be large and is not restricted to the previously discussed case of an index with a linear dependence on wavelength.

Characteristics of the changes in the refractive index due to interaction of a radiation pulse with an inverted medium

Abstract: An allowance is made of the influence of various processes on the dynamics of the changes in the refractive index during amplification of radiation in a CO2 — N2 inverted medium. It is shown that a transient focusing lens can form as a result of the amplification of the radiation by resonant interaction with the R branch of the 0001 → 1000 transition in the CO2 molecule. It is demonstrated that in cases of practical interest the macrotransport processes, associated with a nonequilibrium distribution of the energy between the vibrational degrees of freedom of the CO2 and N2 molecules have only a slight influence on the refractive index.

Polarization beam splitter and optical head device using the same

Abstract: PURPOSE: To contrive a cost reduction by forming rugged periodic gratings on a surface and packing a material having the refractive index equal to either of the ordinary ray refractive index or extraordinary ray refractive index of a double refractive material into the recessed parts. CONSTITUTION: For example, a rock crystal 32 is formed as the double refractive material on the surface of an optically isotropic substrate 11 consisting of soda glass. The periodic gratings are formed by ruggedness at this rock crystal 32. The bases of the recessed parts of the rock crystal 32 are dug down until the bases arrive at the surface of the glass substrate 11. For example, an acrylic resin having the refractive index n c =1.48a equal to the refractive index n e for the extraordinary ray of the rock crystal 32 is packed into the recessed parts of the rock crystal 32, namely, the regions enclosed by the side faces of the projecting parts of the rock crystal 32 and the surface of the glass substrate 11. Then, there is no difference in the refractive index for the extraordinary ray and, therefore, diffracted light is not generated but the difference in the refractive index acts as a phase grating of 0.04 and generates the diffracted light for the ordinary ray. The optically isotropic substrate 11 is more inexpensive than the double refractive material and the reduction of the cost of the polarization beam splitter is possible. COPYRIGHT: (C)1995,JPO

Waveguiding Characteristics of Optical Waveguide with Claddings Having Negative Nonlinear Refractive Coefficient

Abstract: Waveguiding characteristics of the optical waveguide with claddings having a negative nonlinear refractive coefficient are investigated theoretically. The relationship between the total light intensity and the effective refractive index is obtained by means of numerical computation based on the multisegmentation procedure. As the result, an anomalous optical power-limiting action of this nonlinear waveguide is revealed.

Production method and apparatus for plastic optical fiber base material

Abstract: Plastic layers, containing a polymer A (refractive index: Na) and a refractive index adjusting agent having a refractive index different from that of the polymer A, are applied on the surface of a rod rotating on its axis by using CVD (Chemical Vapor Deposition) or a coating method so as to obtain a base material wherein the refractive index gradually decreases with the distance from the center toward the periphery. The proportions of the polymer A and the refractive index adjusting agent in the plastic layers can be varied so that the refractive index may gradually decrease.

Dispersion compensating fiber

Abstract: PURPOSE: To provide a dispersion compensating fiber which compensates 1.55μm- length dispersion and its wavelength dependency as to a transmission system of a 1.3μm-band zero-dispersion fiber. CONSTITUTION: The dispersion compensating fiber has a 1st clad which is formed principally out of SiO 2 glass and has a refractive index n 1 at its center part and a refractive index n 2 at the periphery of the core and a 2nd clad which surrounds the 1st clad and has a refractive index n 3 lower than the refractive index of the core and higher than the refractive index of the 1st clad, and, the core external diameter (2a) is 3-4μm, the ratio a/b of the core external diameter and the 1st clad external diameter (2b) 0.6, the radio (n 1 -n 3 )/n 3 of the refractive indexes of the respective parts 0.02-0.03, and (n 3 -n 2 )/n 3 0.004-0.01. COPYRIGHT: (C)1995,JPO

Correlation of index changes with stress changes in fibers containing UV-written Bragg gratings

Abstract: Strong correlation between index change and stress change in irradiated optical fibers is reported. The stress increases with fluence. Stress changes and hence index changes seem to be due to a compaction of the fiber core

Optical system including a distributed index optical element in combination with a lens having a homogeneous refractive index

Abstract: An optical system includes a refractive index distribution type optical element which configuration is formed to be a parallel plane plate. The refractive index distribution is provided in the radial direction perpendicular to an optical axis of the optical system, in which the refractive index is increased and a color dispersion value νd is decreased as a location on the optical element is farther away from the optical axis. The optical element is combined with a lens or a plurality of lenses, the refractive index of which is homogeneous, so that a chromatic aberration generated by the homogeneous refractive index lens can be compensated. When the refractive index distribution in the radial direction perpendicular to the optical axis is expressed by the following expression, n=n.sub.0 i+n.sub.1 ih.sup.2 +n.sub.2 h.sup.4 where h is the height from the optical axis and i is the wave length respectively illustrated by lines d, F and C, then the following expression is satisfied, νdG=n.sub.1 d/(n.sub.1 F-n.sub.1 c)<20.

Method for measuring refractive index profile

Abstract: The invention relates to a method for measuring the refractive index profile in preferably macroscopic objects, in particular preforms for optical fibres, and a shearing interferometer for carrying out the method, having the following procedural steps: - making a thin section of defined thickness, - making a section edge on the thin section along the line of the refraction coefficient profile of interest, - introducing the thin section into an immersion liquid having a refractive index which essentially corresponds to the average refractive index of the thin section, - sampling along the section edge by means of a shearing interference microscope, - in known fashion, determining the position-dependent refraction coefficient from the position-dependent path difference of the formed double images of the section edge, the thickness of the thin section and the refraction coefficient of the immersion medium.

Germanium implantation into substrates for integrated optics

Abstract: Germanium and helium implantations have been performed in LiNbO3, SiO2 quartz and silica. The agreement between calculated and experimental doping profiles is excellent. The index profiles coincide with the calculated collision profiles but we have observed a surface effect in quartz and LiNbO3. In the first material, Ge implantation yields a larger decrease of the refractive index at the surface than He, as it is predicted by calculation if we assume the refractive index and the disorder profile to be connected. In contrast, in LiNbO3 a reverse observation is made with respect to the refractive index. It is accompanied by chemical perturbation which interferes with the structural modification at the origin of the refractive index change. One advantage of the method is that implanted Ge is in a reduced state.