Showing papers on "Step-index profile published in 2001"

GRIN fiber lenses

Abstract: A GRIN fiber lens has a silica-glass core whose refractive index has a radial profile. The profile has a radial second derivative whose average magnitude in the core is less than about 1.7×10 −6 microns −2 times the value of the refractive index on the axis of the GRIN fiber lens.

Modelling of long-period fibre grating response to refractive index higher than that of cladding

Abstract: In this paper we introduce a new mathematical model, which can be used to investigate the response of a long-period fibre grating to changes in ambient refractive indices of values both greater and less than that of the cladding. A numerical method to calculate the HE core and cladding modes is presented. The results show that even when the ambient refractive index is higher than that of the cladding, the coupling (resonance) wavelengths experience a measurable shift (a few nm). The result obtained suggests that LPGs coated with a material of higher refractive index than the cladding may be used as index sensors.

Optical waveguide sensors having high refractive index sensitivity

Abstract: An optical waveguide sensor having high refractive index sensitivity over a range of ambient refractive indices is provided. The sensor comprises a core having at least one long period gating disposed therein. An inner and outer cladding region, each cladding region having an effective refractive index. The total effective refractive index of the inner cladding region and the outer cladding region is approximately equal to but not greater than the effective refractive index of an environmental parameter to be sensed. These optical waveguide sensors are useful for measuring changes in a variety of environmental parameters.

Graded index waveguide

Abstract: A planar waveguide that has a graded index layer at the core/cladding interface to reduce scattering losses due to core/classing interfave roughness. The refractive index at the core/cladding interface is changed from that of the core to that of cladding gradually by having a graded index layer. The graded index layer reduces the scattering of light traveling in the waveguide by reducing the effect of the roughness at the abrupt interface between the core and the cladding. Using a proper design, the graded index layer also minimizes the modal and polarization dispersion of the optical mode traveling in the waveguide.

Cladding-pumped 3-level fiber laser/amplifier

Abstract: An optically active fiber (30) is disclosed for making a fiber laser (18) or an amplifier (16). This double-clad structured active fiber (30) has a core (34), doped with an optically excitable ion having a three-level transition. The core (34) has a core refractive index and a core cross-sectional area. An inner cladding (32) surrounds the core (34). The inner cladding (32) has an inner cladding refractive index less than the core refractive index, an inner cladding cross-sectional area between 2 and 25 times greater than that of the core cross-sectional area, and an aspect ratio greater than 1.5:1. An outer cladding (36) surrounds the inner cladding (32) and has an outer cladding refractive index less than the inner cladding refractive index.

Refractive index sensor with a guided-mode resonant grating filter

Abstract: This paper describes a novel refractive index sensor with a guided-mode resonant grating (GMRG) filter. The GMRG filter is a narrowband wavelength reflection filter. The incident light is reflected at a resonance condition of incident angle and wavelength. When the grating filter is covered by a liquid to be tested, the resonant condition depends upon its refractive index. The refractive index of the liquid can be determined from the resonance angle for a known wavelength. Since a full-half width of incident angle for the resonance is very narrow (less than 0.1 degree(s)), a high resolution is expected. We designed the GMRG filters for the refractive index sensor. And the resonance angle of incidence was investigated experimentally for the mixture of water and ethyl alcohol.

Large effective area optical fiber

Abstract: An optical waveguide fiber having a relatively large effective area which exhibits low attenuation, low PMD and low microbending sensitivity. A step-index refractive index profile is advantageously used.

Dispersion-compensating fiber having a high figure of merit

Abstract: Disclosed is a dispersion-compensating (DC) optical fiber 10 that is designed to support only the fundamental mode of radiation at 1550 nm. The DC fiber is fabricated from silica glass and has a refractive index profile that includes a core region 51 surrounded by a cladding region 52 having a nominal refractive index n 4 . The core region includes a central core 511 having a nominal refractive index n 1 , a “trench” 512 surrounding the central core having a nominal refractive index n 2 , and a “ridge” 513 surrounding the trench having a nominal refractive index n 3 . A range of refractive index profiles has been found that provides figures of merit that are greater than 300 ps/(nm·dB) and relative dispersion slopes that are greater than 0.01 nm −1 . The range is conveniently expressed in terms of index differences and radial dimensions: central core: radius=1.5±0.5 μm, and 0.015

Optical fiber having extended single-mode capability

Abstract: An optical fiber having extended single-mode capabilities is described in which subwavelength microstructural voids are introduced into the core and/or cladding to allow a fine tuning of the difference between their effective refractive indices. The introduction of subwavelength microstructures into the optical material, preferably through a photolithographic process at the preform stage, allows for control of the effective refractive index difference between the core and the cladding that is more precise than the control afforded by chemical doping processes (e.g., flame hydrolysis) alone. Accordingly, the specified effective refractive index difference between the core and the cladding may be made smaller than that allowed by chemical doping processes alone, thereby allowing the optical fiber to exhibit single-mode properties for larger core diameters. In one preferred embodiment, for example, an optical fiber having a diameter of 25 microns and a single-mode cutoff wavelength of 1500 nm is provided. In another preferred embodiment, for example, an optical fiber having a diameter of 20 microns and a single-mode cutoff wavelength of 1100 nm is provided. Advantageously, lower-cost optical sources, optical coupling components, and optical splicing components can then be used due to the larger core size. Alternatively, for a given core size, the optical fiber will provide single-mode propagation over a larger range of wavelengths due to the smaller specified effective refractive index difference between the core and the cladding.

Optical fiber and optical fiber device

Abstract: An optical fibre has a cladding layer surrounding a core, the cladding layer comprising at least a first, relatively inner generally cylindrical region, a third, relatively outer generally cylindrical region, and a second region disposed between the first and third regions, the second region having a higher refractive index than the first and third regions; and the peak difference in refractive index between the first cladding region and the core being less than about 0.0030.

Microstructured multimode fiber

Abstract: A new type of multimode fiber is provided, capable of being constructed without the need for chemical doping The fiber contains a core region comprising a first material and one or more axially oriented elements disposed in the first material The axially oriented elements (which typically extend throughout the length of the fiber) are configured to provide a graded effective refractive index profile or to provide more focused interaction with selected modes The fiber further contains a cladding region surrounding the core region, where the cladding region exhibits a refractive index less than the effective refractive index of the portion of the core immediately adjacent the cladding region, ie, there exists an index step at the core/cladding interface

Sensitivity of slanted fibre Bragg gratings to external refractive index higher than that of silica

Abstract: The influence of external refractive index higher than that of silica on the transmission spectra properties of slanted fibre Bragg gratings is investigated. An analytical method is presented for their potential use as refractometers for refractive index ranges beyond 1.45.

Parameters affecting bending losses in graded-index polymer optical fibers

Abstract: Radiation losses that occur when bending graded-index polymer optical fibers (POFs) are analyzed as a function of the profile exponent, the light wavelength, the fiber core radius, and the length of the bent section. For this purpose, a ray-tracing model is used, which combines both the generalized Fresnel power transmission coefficients for curved graded-index media and the differential equations that govern the ray paths in highly multimode graded-index fibers. This model is applied to the most recent types of graded-index POF, for which the choice of the core radius and profile exponent is discussed from the point of view of bending losses (the greater the profile exponent and the core radius, the greater the bending losses). The influence of profile exponents different from two is included for the first time.

The refractive index profile of highly-oriented fibres

Abstract: A new method is suggested for measuring the refractive index profile of homogeneous highly-oriented fibres. This method depends on the principle of the variable wavelength interferometric technique. A numerical fitting is used to determine the fringe shift profile at a certain wavelength. The refraction of the light beam by the fibre is taken into consideration in the mathematical treatment. Poly(ethylene terephthalate) and poly(ethylene 2,6-naphthalene-dicarboxylate) fibres are used as examples of these highly-oriented fibres. The diffraction of a He-Ne laser beam is used to determine the diameter and the cross sectional shape of these fibres. Also, a two-beam interference microscope (Pluta microscope) is used for measuring the refractive index profile of these fibres, at the same wavelength, for light vibrating perpendicular to the fibre axes to confirm the results of the new method. Microinterferograms are given for illustration.

Diffusion-Assisted Coextrusion Process for the Fabrication of Graded-Index Plastic Optical Fibers

Abstract: The diffusion-assisted coextrusion process is introduced as a method to fabricate graded-index plastic optical fibers (GI-POFs). In this process, two or more polymeric materials containing additives for refractive index modification are fed separately into a coextrusion die where a concentric multilayer structure is formed. Subsequently, the diffusion of additives takes place in a diffusion zone, creating a nonequilibrium concentration profile, and hence the refractive index profile. A theoretical analysis for the prediction of the refractive index profile obtainable by this process indicates that it is difficult to obtain a near-parabolic refractive index profile unless a very large residence time in the diffusion zone is provided. However, significant changes in the refractive index profile can be induced by adopting a multilayer approach. Furthermore, the bandwidth estimated by the ray analysis indicates that a small variation of the refractive index profile created by the additive diffusion can result...

Semiconductor laser element having excellent light confinement effect and method for producing the semiconductor laser element

Abstract: A semiconductor laser element including: a three-dimensional photonic crystal structure which has a light confining effect and includes alternating first and second refractive index changing layers, where refractive index of light periodically changes in a first direction in each first refractive index changing layer and periodically changes in a second direction in each second refractive index changing layer; and an active unit which is disposed in a portion having a predetermined refractive index inside the three-dimensional photonic crystal structure, and generates a laser beam in response to reception of electric power.

Optical fiber, method of making optical fiber preform, and method of making optical fiber

Abstract: An optical fiber comprising a core region 100 doped with C1 which raises the refractive index; and a cladding region 200, provided at the outer periphery of the core region 100, having a cladding layer 201 doped with F which lowers the refractive index is formed. The cladding region 201 to become the outermost cladding layer is configured such that the doping amount of F successively decreases within an outer peripheral part 205 including the outer periphery thereof to a predetermined doping amount which is the minimum doping amount of F within the cladding layer 201. Therefore, the stress within the optical fiber is dispersed into the outer peripheral part 205 having an enhanced viscosity, whereby the stress concentration into the core is suppressed. Since the favorable tension range at the time of drawing the optical fiber becomes wider at this time tension control is facilitated.

Low-dispersion optical fiber and optical transmission system using the low-dispersion optical fiber

Abstract: A lower-dispersion optical fiber achieving both low wavelength dispersion in the usable wavelength region and enlarged effective core cross-section The outer peripheral face of a center core (1) of the lower dispersion optical fiber is covered with a first side core (2) the outer peripheral face of the first side core (2) is covered with a second side core (3), and the outer peripheral face of the second side core (3) is covered with a clad (5) If the maximum refractive index of the center core (1) is n1, the minimum refractive index of the first side core (2) is n2, the maximum refractive index of the second side core (3) is n3, and the refractive index of the clad (5) is nc, a relation n1 > n3 > nc > n2 is satisfied The relative refractive-index differences Δ1, Δ2, and Δ3 of the maximum refractive index of the center core (1), and the minimum refractive index of the first side core (2) to tose of the clad (5) are, respectively, in the ranges of 04 % ≤ Δ1 ≤ 07 %, -030 % ≤ Δ2 ≤ -005 %, and 02 % ≤ Δ3

Method for making gradient refractive index optical components

Abstract: A method for making gradient refractive index optical components includes mixing a molten basic material ( 11 ) with a refractive index modifying material ( 21 ) in continuously changing proportions. The mixture is changed into a plurality of semi-molten fibers ( 41 ), and the fibers are rolled to form a continuous plate ( 51 ). The plate has a continuously changing refractive index along a lengthwise direction thereof. The plate is wound around a spindle ( 57 ) to obtain a wound preformed rod ( 58 ). The preformed rod is integrally fused by local heating, and drawn to form a draw ( 61 ) having a predetermined diameter. The draw is cut into pieces. Each piece can then be made into an optical component having a continuously changing refractive index in a radial direction. The method allows precise control of all steps, and such control is achieved with relative ease throughout.

Propagation characteristics of single-mode optical fibers with arbitrary complex index profiles: a direct numerical approach

Abstract: We present here a rapidly converging numerical procedure for the evaluation of the propagation characteristics of a single-mode optical fiber with an arbitrary complex refractive index profile. To illustrate the procedure, we have first applied it to a fiber with a complex step index profile. As an application, we have used it to evaluate the gain in a typical 980-nm pumped erbium-doped fiber.

Universal conditions for estimating the nonlinear refractive index n 2 of dispersion-compensating fibers by the CW-SPM method

Abstract: We investigated universal conditions for measuring the nonlinear refractive index n/sub 2/ of dispersion-compensating fibers by the continuous wave self-phase modulation (CW-SPM) method both theoretically and experimentally. We showed that the required fiber length and the minimum power for n/sub 2/ estimation can be expressed as simple functions in terms of chromatic dispersion D. Moreover, we confirmed experimentally that the present conditions for n/sub 2/ estimation are reasonable.

Light-induced variation in the refractive index in a polyimide-fullerene system

Abstract: Light-induced variation in the refractive index of the polyimide-C70 system is studied. This process makes a contribution to the nonlinear transmission of this system in the study of the optical limitation of laser radiation and determines the prospects of using this system as a nonlinear holographic medium for reversible data storage. The nonlinear optical coefficients n2 and χ(3) of fullerene-sensitized polyimides are determined for the first time by the methods of dynamic holography.

Optical fiber coupler and optical fiber for optical fiber coupler

Abstract: In a single mode optical fiber employed in an optical fiber coupler, letting r be the radial distance from the optical axis center, Δn(r) be the relative refractive index difference at the position r within a core portion with reference to the refractive index of a cladding portion placed about the core portion, Δn peak be the peak value of the relative refractive index difference Δn(r) at the position r peak , and a be the core radius, the relative refractive index difference Δn (r) satisfies the relationship of Δn(r)≦Δn peak [1−(r/a) 3 ] in the range of r peak ≦r≦a; and the refractive index of the cladding portion gradually decreases outward in its radial direction.

Antireflective hard coat sheet, optical element and image display device

Abstract: PROBLEM TO BE SOLVED: To provide an antireflective hard coat sheet which shows a high surface antireflective effect when used for a polarizing plate or the like and which prevents interference fringes of the reflected light SOLUTION: The antireflection hard coat sheet has layers on a transparent base film The layers are, from the base film side, a medium refractive index layer having 15 to 17 refractive index, a high refractive index layer having 16 to 18 refractive index, and a low refractive index layer made of a material having a refractive index lower than that of the high refractive index layer

Diffraction grating body, optical pick-up, semiconductor laser apparatus and optical information apparatus

Abstract: A transmission diffraction grating body including a base material being substantially transparent with respect to wavelength λ 1 and having a refractive index n 0 ; another base material being substantially transparent with respect to wavelength λ 1 and having a refractive index n 1 , which is formed on the base material having a refractive index n 0 ; and a relief diffraction grating formed on the base material having a refractive index n 1 ; wherein the refractive indexes n 1 and n 0 satisfy the relationship: n 1 >n 0 . Thus, the base material having a refractive index n 1 can be formed of a high refractive index material, and when the depth of grating of the diffraction grating is set so that the diffraction grating diffracts the light with wavelength λ 1 and does not diffract the light with wavelength λ 2 , the depth of grating of the diffraction grating can be made to be shallow, thus preventing the loss of the amount of the light with wavelength λ 1 . Furthermore, since base materials each having a different refractive index are bonded to each other to form a diffraction grating body, it is possible to minimize the use amount of the relatively expensive material having a high refractive index. Furthermore, since the most of the diffraction grating body can be formed of a material having a low refractive index, it is possible to lower the height of the diffraction index body.

Multimode optical fiber having a structure to reduce scattering loss

Abstract: Disclosed is a multimode optical fiber having a structure to reduce scattering loss which includes a core divided into a central region having the optimal refractive index according to an optimal core shape index minimizing the scattering loss of the multimode optical fiber, and a peripheral region having the refractive index lower than that of the central region; and a cladding enclosing the core and having the refractive index lower than the lowest refractive index of the core.