Showing papers on "Step-index profile published in 1997"

Displacements of the resonant peaks of a long-period fiber grating induced by a change of ambient refractive index.

Abstract: We present a graphic method of analyzing the spectral displacements of a long-period fiber grating as a function of ambient index. Mode dependence of the maximum displacement, disappearance of a particular resonance peak, and spectral behavior when the ambient index is larger than that of the cladding material are investigated and compared with experimental results.

Broadband spectral generation with refractive index control

Abstract: We describe a method for generating a wide spectrum and at the same time improving propagation through a model inhomogeneous gaseous medium. The method is based on using a small two-photon detuning from a Raman resonance to adiabatically establish an appropriate molecular superposition state. This state, in turn, generates a broad spectrum of sidebands whose refractive index, Rayleigh scatter, and accumulated phase delay are much less than those of a single spectral component, if propagating alone. @S1050-2947~97!50606-8#

Dispersion compensating single mode waveguide

Abstract: A dispersion compensating single mode optical waveguide fiber designed to change the wavelength window of operation of a link from 1310 nm to 1550 nm. The dispersion compensating waveguide fiber is characterized by a core glass region refractive index profile comprised of at least three segments. The segment on the waveguide center has a positive relative refractive index. At least one segment, spaced apart from, the waveguide centerline has a negative relative refractive.

Optical waveguide with photosensitive refractive index cladding

Abstract: An optical fibre (1) comprises a core (2) and a cladding (3) that includes an inner cladding region (3a) with a refractive index that is photosensitive to UV light, surrounded by a non-photosensitive outer cladding region (3b). Refractive index gratings can be written into the cladding region (3a). Also, the refractive index of the inner region (3a) can be altered by exposure to UV light to achieve mode matching at a splice between fibres with different core diameters. An optical fibre laser is disclosed with integral refractive index gratings (33, 34, 36) in the cladding of a fibre with an optically active core.

Formation of the refractive index profile in the graded index polymer optical fiber for gigabit data transmission

Abstract: Bandwidth characteristics of the large core graded index polymer optical fiber (GI-POF) are theoretically and experimentally clarified. The refractive index profile of the GI-POF was controlled by interfacial-gel polymerization to investigate the relation between the index profile and the bandwidth characteristics. It was experimentally confirmed that the maximum bandwidth of the poly methyl methacrylate (PMMA) base GI-POF is at most 3 GHz for 100 m transmission using a typical laser diode emitting at 650-nm wavelength (3 nm source spectral width) when its refractive index profile is optimized. The maximum bandwidth theoretically estimated by considering both modal and material dispersions is approximately 3 GHz which is exactly the same as the measured value, while higher than 10 GHz for 100 m was expected if only modal dispersion was taken into account. The optimum refractive index profile of the PMMA base GI-POF is theoretically and experimentally clarified by considering the profile dispersion further.

Optical fiber having a low-dispersion slope in the erbium amplifier region

Abstract: An optical fiber is disclosed that is suitable for use in wave-division-multiplex (WDM) systems served by Erbium-doped fiber amplifiers. The fiber has a chromatic dispersion whose absolute magnitude is at least 0.8 ps/(nm-km) over the wavelength region 1530-1565 nm, and has a dispersion slope that is less than 0.05 ps/(nm 2 -km). This optical fiber exhibits a loss that is less than about 0.20 dB/km and is relatively insensitive to bending; moreover, its effective area exceeds 50 μm 2 . The optical fiber includes a core of transparent material having a maximum refractive index n 1 , and a layer of transparent cladding material on the outer surface of said core having a refractive index n 2 . The core includes an annular region of transparent material whose minimum refractive index, n 3 , is depressed with respect to n 2 . These indexes are constrained by the following equations: 0.50<(n 1 -n 2 )/n 2 <0.70; and -0.30<(n 3 -n 2 )/n 2 <-0.05.

Optical fiber with enhanced light collection and illumination and having highly controlled emission and acceptance patterns

Abstract: An optical fiber, including a cylindrical core of light conducting material having a first refractive index, surrounded by a cladding having a second refractive index that is lower than the first refractive index. The optical fiber includes at least one endface formed with a cone tip for controlling the characteristics of light entering or exiting the fiber. The polish angle of the cone tip can be selected according to the desired emergence/acceptance properties of the fiber.

Optical fibre and optical fibre grating

Abstract: An optical fiber comprises a glass core having a core refractive index; a glass primary cladding at least partially surrounding said core, said primary cladding having a primary cladding refractive index lower than said core refractive index; a glass secondary cladding at least partially surrounding said primary cladding, said secondary cladding having a secondary cladding refractive index lower than said core refractive index but higher than said primary cladding refractive index; said glass of said core and said glass of at least part of said primary cladding containing one or more photosensitizing dopants.

Optical fibers for optical attenuation

Abstract: Optical fibers are provided for optical attenuation comprising a core (1) and a cladding (2, 3). The cladding comprises two or more parts different from each other in their refractive indices and/or in the presence of an attenuating dopant. Using the opical fibers, an optical attenuator can effectively reduce the effect of the cladding mode and excellent stability can be achieved.

Atomic force microscopy for the determination of refractive index profiles of optical fibers and waveguides: A quantitative study

Abstract: The use of preferential etching and atomic force microscopy to measure refractive index profiles of optical fibers is investigated. Both the etch rate and the position of lateral features are shown to be independent of etch time. An elliptical core fiber was studied and the resultant profile was found to be in qualitative agreement with the preform index profile. It is shown, however, that the ellipticity of the core has changed during the drawing process. The method was extended to fluorine and germanium doped planar waveguides and the results correlated with the fabrication process.

Origin of high bandwidth performance of graded-index plastic optical fibers

Abstract: Observations in high bandwidth graded-index plastic optical fibers (GI POFs) are reported of strong mode coupling and its characteristic square root-like fiber length dependence of the optical pulse broadening. We have further found that the measured refractive index profile is not parabolic, but consists of two markedly different regions. Analysis of the index profile reveals that strong mode coupling increases the GI POF bandwidth from its profile-determined value of 0.43 GHz to its measured value of 3.0 GHz for 100 m.

Depressed cladding fiber design for reducing coupling to cladding modes in fiber gratings

Abstract: A waveguide, such as an optical fiber waveguide for guiding light waves, which can provide a strongly reflective grating (e.g., a Bragg grating) at a specified wavelength while maintaining very low losses at adjacent wavelengths. The waveguide includes a core, an inner cladding laterally surrounding the core, an outer cladding laterally surrounding the inner cladding, and a grating pattern. The core has a refractive index nco and a first transverse dimension 2A. The inner cladding has a width W and a refractive index nic. The outer cladding has a refractive index noc. The relation between the refractive indexes, nco⊃noc⊃nic and 0,5∫A/(A+W)∫1, define a narrow depressed well region for limiting cladding losses.

Method and apparatus for submicroscopic particle sizing, and probe therefor

Abstract: An apparatus for determining the size or other physical properties of particles executing Brownian motion is provided. An integrated fiber optic probe, including a length of a gradient index multimode optical fiber fusion spliced to a monomode optical fiber, delivers laser light to a scattering medium such that the light scattered in the backward direction is collected by another integrated fiber optic probe mounted into the same cylindrical housing. A step index fiber may be fusion spliced between the monomode and gradient index multimode fibers. The axes of the fibers may be collinear or offset. The scattered light, after conversion to a series of photoelectron pulses, is processed to determine the mean particle diameter. The temporal coherence of the scattered field from submicroscopic particles illuminated by laser light is a function of both the integration time and the particle diameter. The temporal degree of coherence of the time averaged scattered intensity decreases as the integration time increases. Statistical processing of the scattered photons leads to a new method of particle sizing, which circumvents the need for digital autocorrelation.

Extracting concentrated guided light

Abstract: The maximum concentration of radiation is proportional to the square of the refractive index of the medium in which it propagates. A medium with a high refractive index can also serve as a lightguide for concentrated radiation. However, if concentrated radiation is extracted from one medium, with a high refractive index, to another, whose index is lower (e.g., from fused silica into air), part of the radiation may be lost because of the total internal reflection at the interface. We present polygonal shapes suitable for efficient extraction of the concentrated radiation in a controllable way, without increasing the cross-section area (or diameter) of the lightguide. It is shown analytically and experimentally that the use of a secondary concentrator, followed by such a light extractor, both having a high refractive index, can provide considerably more power to a solar receiver with a specific aperture.

Measurement of the Refractive Index of Glass Fibers by the Christiansen-Shelyubskii Method

Abstract: The Christiansen principle was employed to measure the refractive index of borosilicate glass fibers (13–41 μm diameter) over the visible range. The refractive index for glass fibers at 589.3 nm was measured by temperature and wavelength scan and values obtained were in close agreement. The refractive index for glass fibers as a function of wavelength was measured to an accuracy of < 10−4. The uniformity of the refractive index for a bundle of fibers of slightly different diameter was calculated using the modified Shelyubskii method and compared to experimental values. Theoretical calculations of the transmission by the present work suggest that, for high optical clarity and transmission of Christiansen cell (or transparent composite consisting of glass fiber and polymer), the refractive index must be controlled to the fifth decimal place. For example, the maximum transmission of a fiber/liquid mixture cell at 25°C can increase from 89 to 97% when the standard deviation is reduced from 13 × 10−5 to 9 × 10−5.

Stimulated brillouin scattering suppressed optical fiber

Abstract: The invention provides a stimulated Brillouin scattering suppressed optical fiber which is easy to be produced, has an almost zero chromatic dispersion over the entirety of an optical fiber in the lengthwise direction, and has a low light loss. That is, in an optical fiber having a property, by which the chromatic dispersion with respect to optical communication signals becomes zero, obtained by changing the relative refractive index difference of the optical fiber and core diameter in the same increase or decrease direction, the relative refractive index difference of the core and the core diameter R are changed in the lengthwise direction of the optical fiber, and the core diameter R is made smaller in line a decrease the relative refractive index difference of the core while the core diameter R is made larger in line with an increase of the refractive index difference, whereby the chromatic dispersion the designated wavelength band is made nearly equal to zero in the entirety of the optical fiber in the lengthwise direction.

Reflection preventive film and manufacture thereof

Abstract: PROBLEM TO BE SOLVED: To prevent the reflection of the light of a surface of a transparent base board, and clearly read internal visual sense information by laminating a medium refractive index layer, a high refractive index layer and a low refractive index layer in order. SOLUTION: A reflection preventive film 10 is formed by laminating a medium refractive index layer 3, a conductive high refractive index layer 2 and a low refractive index layer 1 composed of an SiOx layer in order on a transparent base material film 5 through a hard coat layer 4. The medium refractive index layer 3 is constituted on the hard coat layer 4 by a coating of paint composed of a binder and ultrafine particulates having a refractive index not less than 1.5. There is the relationship of (2.20 > the high refractive index layer 2 of a refractive index > the medium refractive index layer 3 of a refractive index > the low refractive index layer 1 of a refractive index > 1.40). In a thickness of the respective refractive index layers, the low refractive index layer is 80 to 100nm, and the high refractive index layer 2 is 80 to 110nm, and the medium refractive index layer 3 is 55 to 70nm. An optical film thickness D(iD =n.d and (n) is a refractive index of the medium refractive index layer 3, and (d) is its thickness) is constituted so as to be set not more than a wave length of visible radiation.

Optical surface analysis of graded index coatings on glass

Abstract: A method for the determination of the refractive index close to an interface, valid for inhomogeneous films, is presented as an extension of the Abeles—Hacskaylo technique used for homogeneous films. Consistent refractive index values, with precision in the third decimal place, are determined for Ag + (1.550 ± 0.001) and K + (1.522 ± 0.002) ion-exchange films on glass, as well as for bare glass substrates (1.509 ± 0.002), in the neighborhood of their interface with air. The validity of the method is discussed in simple fundamental terms, which, along with the experimental evidences, indicates applicability to any graded index film, provided an index discontinuity is present at one of its extremes.

Mach-Zehnder interferometric devices with composite fibers

Abstract: A Mach-Zehnder wavelength selective device is made using one or more composite optical fibers each incorporating a phase shift region having one effective refractive index spliced between coupling regions having a different effective refractive index. The optical path length difference or phase delay induced by each such composite fiber is a linear function of the length of the phase shift region.

Semiconductor laser diode including ridge and partially disordered active layer

Abstract: A ridge type laser diode with a stabilized horizontal transverse mode and little variation in peak output power and a method for producing the laser. The ridge type laser diode includes a semiconductor substrate; an active layer on the semiconductor substrate, the active layer being interposed between a lower cladding layer and an upper cladding layer; and a ridge waveguide having a width, the ridge waveguide being part of the upper cladding layer so that the active layer located directly opposite the ridge waveguide is a first high refractive index region having a first refractive index; and a second high refractive index region in the central part of the first high refractive index region, having a second, higher refractive index than the first refractive index, and formed by disordering a region other than the central part and having a width less than the width of the ridge waveguide.

Waveguide device and a method of producing the same

Abstract: A waveguide device having a waveguide layer provided with a core and a cladding, and having a mode filter function of propagating either of TE mode polarized light and TM mode polarized light, wherein the core and the cladding are formed of a variable anisotropic refractive index material or a material in which a variable anisotropic refractive index material is dispersed in a matrix Upon photoirradiation, the refractive indices (n o , n e ) of the core and the cladding can be changed to satisfy the formulae: one of n o and n e of the core is greater than that of the cladding, and the other of n o and n e of the core is less than or equal to that of the cladding, wherein n o is the ordinary refractive index and n e is the extraordinary refractive index This waveguide device can be an important constitutional component in a compact optical system A method of producing the waveguide device is also disclosed

Bottom antireflective coatings through refractive index modification by anomalous dispersion

Abstract: This invention provides a process for the generation of an antireflective bottom layer with effective reduction of substrate reflectivity and swing curve effects in lithographic applications. It involves the use of a suitably selected monomeric and/or polymeric dye which brings the real part of the refractive index into a range which is optimal for the suppression of reflection-related effects. The refractive index change is effected via anomalous dispersion, i.e., by utilizing changes in the real part of the refractive index caused by the bottom layer's absorption.

Optical fiber preform and its fabrication process

Abstract: A process of fabricating an optical fiber preform, preferably a multimode optical fiber preform, having a maximum refractive index along an axis of the fiber and a lower refractive index at its periphery. The process includes the following steps: depositing successive layers onto the interior of the tube with the refractive index increasing from the first, larger diameter layer to the central layer, each layer being formed from gases which react with each other inside the tube, and varying the proportions of the gases from one layer to another to vary the index. The gases are introduced into the tube at a velocity such that the radial index profile is homogenized in the longitudinal direction. This velocity is advantageously maintained substantially the same for the fabrication of all the layers. This process produces preforms having a homogeneous index profile in the longitudinal direction.

Refractive index profile of GRIN optical fibre considering the area under the interference fringe shift: I. The matching case

Abstract: An expression has been derived to determine the refractive index profile of a graded index (GRIN) optical fibre using and . This expression considers the area enclosed under the interference fringe shift when using a liquid of refractive index exactly matching the cladding one. Multiple-beam Fizeau fringes are used to obtain the profile shape constant and the refractive index difference between the fibre centre and its cladding. Another two methods are applied to compare the results. The suggested method has the advantage that it gives the exact solution and it provides a simple relation between the measured quantities.

Measurement of pump-induced refractive index changes in erbium-doped optical fibre

Abstract: A novel technique for measuring the pump induced change in refractive index in erbium-doped optical fibre is reported. A saturated peak-to-trough change in index of 6.7 × 10-8 /(dB/m) of absorption was measured and the technique was verified by showing excellent agreement with a Kramers-Kronig transform of the measured change in absorption.

Low nonlinearity dispersion-shifted fibers employing dual-shaped core profile with depressed cladding

Abstract: Recently, dispersion-shifted fibers (DSFs) with large effective core areas have been widely studied and demonstrated by employing various index profiles. In the paper, we show that DSFs with effective core areas >85 /spl mu/m/sup 2/ and excellent bending loss performance can be realized by properly optimizing the dual-shaped core profile, which is one of the major refractive index profiles employed by the currently mass-produced standard DSFs.

Characterization of refractive index change induced by electron irradiation in amorphous thin As2S3 films

Abstract: Binary diffraction gratings in As2S3 films were prepared with the aid of an electron beam. The dose of the electrons was varied. The gratings were read with a HeNe laser, and the zero-order and first-order diffraction efficiencies were noted. Rigorous diffraction theory was used to give a homogeneous approximation for the refractive index change. Reactive ion etching was applied to reduce the thickness of the film, and a new value for the refractive index change was evaluated. The refractive index change versus film thickness dependence was found to be linear at low electron doses and Gaussian shaped at higher doses. Through a simple mathematical analysis, the absolute value of the refractive index was determined as a function of the position inside the film. At higher doses, the refractive index change was found to have a maximum value of 3%, approximately 1.2 μm from the film surface.

Cathode ray tube with multilayered high- and low-refractive index films thereon

Abstract: A cathode ray tube comprising a vacuum enclosure including a glass panel 1 whose inner face is coated with a phosphor film 4 to form a screen; a neck portion housing an electron gun; and a funnel portion connecting the glass panel and the neck portion. A multi-layered anti-reflection, anti-electrostatic charge film formed on the outer face of the glass panel is constructed of a high refractive index film having a refractive index of 1.6 to 2.2 and a low refractive index film having a refractive index of 1.3 to 1.58. The high refractive index film is sandwiched between the outer face of the glass panel and the low refractive index film, and an unevenness having an average diameter of 5 to 80 μm is provided at the interface between the high refractive index film and the low refractive index film. The interface has a height of 10 to 40 nm. The unevenness of the surface of the low refractive index film is made smaller than the average roughness Rz of the unevenness of the interface between the high refractive index film and the low refractive index film, or the surface of the low refractive index film is flat.

Reflection reducing coating

Abstract: The coating has a layer with a low refractive index (14) applied to a substrate (20) and a layer of higher refractive index (12) applied on top of the low refractive index layer. A roughened surface scatters and reflects the incident light entering the layer of low refractive index. The roughened surface (18) is applied to the layer with a low refractive index. It is applied at the boundary between the low refractive index layer and the substrate.