Showing papers on "Step-index profile published in 1996"

Compaction- and photoelastic-induced index changes in fiber Bragg gratings

Abstract: The tension on the core of single‐mode fibers is strongly increased by the formation of a Bragg grating. This tension increase lowers the refractive index because of the photoelastic effect. On the other hand, the compaction of the core network results in an increased refractive index. The two contributions are evaluated from axial stress measurements, from the determined index modulation amplitude, and from the mean index change of the Bragg gratings. The total Bragg grating index modulation is smaller than the compaction‐induced index modulation by 30%–35% because of the photoelastic effect.

An improved procedure to calculate the refractive index profile from the measured near-field intensity

Abstract: Refractive index profile of optical waveguides is reconstructed from the measured transmitted near-field intensity. A Butterworth low-pass digital filter is employed in the frequency domain to remove impulsive and high frequency fluctuations which have severe effects on the procedure to calculate the index profile from the measured power intensity. The proposed method has been applied to measure the index profile of monomode optical fiber, Ti:LiNbO/sub 3/ and buried MgTi:LiNbO/sub 3/ channel waveguides.

Dispersion compensating optical fiber

Abstract: A dispersion compensating optical fiber is proposed for application in a wavelength optical signal transmission system This dispersion compensating fiber has a W shaped refractive index profile, and has a first core layer, a second core layer formed around the outside of the first core layer, and a cladding layer made of substantially pure silica formed around the outside of the second core layer The first core layer is doped with germanium, so that its refractive index s increased by a proportional refractive index difference of about 2% The second core layer is uniformly doped with fluorine, so that its refractive index is decreased by a proportional refractive index difference of about 058% The ratio of the outer radius of the second core layer to the outer radius of the first core layer is about 25 The wavelength dispersion slope is in the negative region, the dispersion is made to be high negative dispersion, and moreover the dispersion slope compensation ratio from a wavelength of 1530 nm to a wavelength of 1570 nm is made to be a value close to the perfect dispersion ratio and about 075 to 125 thereof

Measurement of normalization factor of n(2) for random polarization in optical fibers.

Abstract: The 8/9 normalization coefficient for the nonlinear refractive index in nonpolarization-maintaining optical fibers is confirmed directly by measurement of the ratio of the self- and cross-phase modulation coefficients for two orthogonal polarizations. The nonlinear phase shift is accurately measured with a dual-frequency beat signal as a pump source.

Thermal dependence of the refractive index of InP measured with integrated optical demultiplexer

Abstract: The temperature dependence of the refractive index of InP in the wavelength range from 1.2 to 1.6 μm has been determined. The method is based on the measurement of the transmission wavelengths of a n−/n+‐InP optical demultiplexer as a function of device temperature. The refractive index of InP is found to depend linearly on temperature with a temperature coefficient between 2.3 and 1.9×10−4/K. The measured absolute value and the dispersion of the refractive index of InP are in agreement with data from the literature.

Low frequency corrections to the static effective dielectric constant of a two-dimensional composite material

Abstract: We derive the first dynamic correction to the effective refractive index for a square array of cylinders (of finite or infinite refractive index), subject to a low frequency in­cident radiation. This correction also imposes constraints on the wavenumber region for which the Lorentz-Lorenz formula in two dimensions is accurate.

Optical semiconductor device for changing a beam diameter

Abstract: An optical semiconductor device has a greatly reduced transmission constant even when a reduction rate in the thickness of a core layer is small so that a relatively high beam-diameter increasing efficiency is obtained. The optical semiconductor device has a multilayered structure with a first end surface perpendicular to an optical axis of the optical semiconductor device and a second end surface opposite to the first end surface. A core layer has a first refractive index. A lower cladding layer is provided on a lower side of the core layer, the lower cladding layer having a second refractive index. An upper cladding layer is provided on an upper side of the core layer, the upper cladding layer having the second refractive index. A transmission constant reduction enhancing layer is provided between the lower cladding layer and the upper cladding layer, the transmission constant reduction enhancing layer having a third refractive index less than the first refractive index and the second refractive index. The optical semiconductor device includes a first area and a second area, a portion of the core layer in the first area having a uniform thickness, a portion of the core layer in the second area having a thickness gradually decreasing toward the first end surface of the optical semiconductor device.

LP(01)-LP(02) interference using a spectrally extended light source: measurement of the non-step-refractive-index profile of optical fibers.

Abstract: LP(01)-LP(02) interference over an extended wavelength region is used to describe a new spectroscopic technique for determining the refractive-index profile of non-step-index optical fibers. The technique is illustrated with a fiber that shows an alpha-profile variation of the refractive index.

Single-mode optical fiber with plural core portions

Abstract: The present invention relates to a single-mode optical fiber having a configuration which enables lowering of dispersion slope while securing a sufficient MFD. This single-mode optical fiber has a refractive index profile in which an indent with a sufficient width is provided at the center of its core region. In particular, this indent satisfies the following relationship: a·(Δn.sub.2 -Δn 1 )/(b·Δn 2 )≧0.04 when the first core portion in the single-mode optical fiber has a mean relative refractive index difference of Δn 1 with respect to the cladding portion and an outer diameter of a while the second core portion has a mean relative refractive index difference of Δn 2 with respect to the cladding portion and an outer diameter of b.

At least penta-layered optical device

Abstract: The present invention is in the field of optical components, more particularly, polymeric optical components, even more particularly, thermo-optical components, electro-optical components or passive components. The present invention pertains to an optical component having an at least penta-layered polymer structure on a substrate comprising: A) a low refractive index lower cladding layer, B) a core-matching refractive index lower cladding layer, C) a core layer, D) a core-matching refractive index upper cladding layer, and E) a low refractive index upper cladding layer. With this specific layer structure an optimal transversal confinement can be obtained, which results in less loss of light and an improved switching efficiency.

Improved near-field method for refractive index measurement of optical waveguides

Abstract: Refractive index profiles of waveguides are deduced from near-field intensity distributions of guided modes. To improve the accuracy of refractive index profiles, some measurements are taken with the center peak of the mode intensity profile blocked, allowing the increase of the optical power at the waveguide boundaries with a corresponding increase in the signal-to-noise ratio. Additional improvements reported here are related to the subsequent signal processing, which is performed mainly in the spatial frequency domain. Smooth and reliable profiles of channel waveguides are obtained, the method being very general and not presuming the functional dependence of n(x, y).

Geo2 concentration dependence of nonlinear refractive index coefficients of silica‐based optical fibers

Abstract: The nonlinear refractive index coefficient n2 dependence on the GeO2 concentration in optical fibers is quantitatively shown for SiO2 core fibers and GeO2-SiO2 core/SiO2 clad fibers with Δ = 0.35–2.2% using an XPM measurement method where the phase change in the fiber of a probe signal caused by a pump signal is found from the delay self-heterodyne spectrum. The GeO2 concentration distribution which determines the n2 distribution in the fiber is not uniform, and the measured n2 is the average of the product of the local n2 and the fourth power of the electric field in the fiber. In this work, this relationship of the measured n2, the cross sectional distribution of n2, and the electric field distribution in the fiber is used to define an effective GeO2 concentration, ηeff. This effective GeO2 concentration level is used to evaluate n2. The measured n2 increases proportionally to ηeff by the relationship n2[x 10–20 m2/W] = 0.0552°eff[mol%] + 2.44. Furthermore, the measured n2 in the fiber agrees well with the n2 of bulk glass obtained a semiempirically for the nonlinear refractive index coefficient derived from linear refractive index data.

Two-dimensional/three dimensional image display screen

Abstract: PROBLEM TO BE SOLVED: To provide a two-dimensional/three-dimensional display screen which is provided with and not provided with optical directivity by changing the electric field to be impressed on a refractive index change layer by transparent electrodes, thereby changing the refractive index of this refractive index change layer to the value nearly same as the value of a lens layer or a value different therefrom. SOLUTION: A lenticular lens plate 1 for changing the progressing direction of light and a refractive index variable material 2 variable in the refractive index are superposed on each other. Whether the refractive index of this refractive index variable material 2 is made the same as the refractive index of the lenticular lens plate 1 or the value different therefrom is embodied by switching the magnitude of the electric field to be impressed on the refractive index variable material 2, i.e., the magnitude of the voltage to be impressed on the transparent electrodes 3. As a result, a lens effect is developed by the voltage impression when the refractive indices of both are varied and a transparent plate, such as mere glass plate, is obtd. if the refractive indices are the same.

Dispersion-flattened single-mode optical waveguide with large effective mode surface area

Abstract: A single-mode optical waveguide comprises an optical core and a cladding surrounding the optical core having a predetermined refractive index. The core comprises a central area that has a refractive index lower than the predetermined refractive index and annular area around the central area that has a refractive index higher than the predetermined refractive index. Between the peripheral annular area and the cladding is at least one composite annular area made up of two successive annular areas respectively having refractive indices lower than and higher than the predetermined refractive index.

Optical fibre for improved power coupling

Abstract: An optical fibre having a single mode absorptive core (10) whose position, relative to the cross-sectional plane of the inner multimode cladding (12), varies along the length of the fibre. The periodicity and the magnitude of the relative displacement of the core (10) with respect to the cladding (12) are such that the transfer of radiation from the inner multimode cladding (12) to the core (10) is substantially improved over conventional fibres.

Optical fiber waveguide

Abstract: Optical waveguide of the type comprising a core (10) presenting a refractive index (n1), maximal at least at its center; an optical cladding (20) involving core (10) and presenting a refractive index (n2) constant along its diametral extension and lower than the maximum refractive index (n1) of core (10) and further including a region defined by at least a stress-relieving intermediate portion (30) disposed between core (10) and the optical cladding (20), said intermediate portion presenting: a refractive index (n3), maximal along its diametral extension, at the maximum equal to the refractive index (n1) of core (10) and at least equal to refractive index (n2) of optical cladding (20), so as to provide an increase in the cutoff wavelength; a thermal expansion coefficient and a viscosity adequate to reduce the internal stress levels at least in core (10) of the optical waveguide to values which permit the obtention of acceptable attenuation and chromatic dispersion for a wavelength region.

Electro-optic modulator with voltage tunable quantum well waveguide cladding layer

Abstract: An electro-optic modulator (300) comprises a multiple quantum well core layer (320) in which the band gap and refractive index are adjusted to make the core layer (320) transparent to light at a selected wavelength and a voltage tunable, multiple quantum well cladding layer (330) in which an exciton absorption provides the cladding layer (330) with a first refractive index that is less than the core refractive index when a first voltage is applied and a second refractive index that approaches or exceeds the core refractive index when a second voltage is applied. The exciton absorption also provides the voltage tunable cladding layer (330) with a substantially greater absorption coefficient at the selected wavelength than that of the core layer (320). The core and voltage tunable cladding layers (320, 330) are combined with a second cladding layer (310) to form a waveguide in which light is confined to the low loss core layer (320) in the first voltage state and diverted into the highly absorbing voltage tunable cladding layer (330) in the second voltage state. In a preferred embodiment of the modulator (300), the multiple quantum well core and cladding layers (320, 330) comprise GaAs quantum wells and AlGaAs barriers. The small effective absorption coefficient of the core layer (320) and the large difference between this absorption coefficient and that of the voltage tunable cladding layer (330) in the off state provide a modulator (300) characterized by a higher contrast ratio and, simultaneously, a lower insertion loss than are available from conventional electro-absorption or electro-refraction based modulators.

Large effective area dispersion-shifted fibers with dual-ring index profiles

Abstract: Summary form only given. In summary, we have designed and fabricated single mode dispersion-shifted fibers, using the dual-ring index profile, with effective area as large as 90 /spl mu/m/sup 2/. The large effective area can greatly reduce the performance degradation caused by fiber nonlinearities for long-haul terrestrial and submarine applications. Furthermore, these fibers show lower bending losses than standard step-index single-mode fibers.

Refractive index profile and geometry measurements in multicore fibres

Abstract: The refracted near-field technique (RNF) has been applied to the measurement of the refractive index profiles in multicore fibres (MCF). The fibre core diameter and the intercore distances have been determined.

Iterative simplex-finite difference method for the characterization of optical waveguides

Abstract: A new method is presented for reconstructing smooth refractive index profiles of optical waveguides from measured effective indexes. It is based on the semivectorial finite difference method to solve the polarized wave equation for a given refractive index profile. An iterative simplex algorithm is used to find the best refractive index parameters that give, as a solution, effective indexes close to the measured ones. The method is applied successfully to Ag/sup +/-Na/sup +/ ion-exchanged glass slab waveguides and to diffused Mg/Ti:LiNbO/sub 3/ slab waveguides. Dopant concentration profiles are obtained by using secondary ion mass spectrometry. The relationship between the refractive index change and the dopant concentration is determined for both cases. The iterative simplex algorithm-finite difference method (ISA-FDM) is compared to other index profile reconstruction methods, and the advantages with respect to WKB-based methods are pointed out.

Refractive index modulation device and method of refractive index modulation

Abstract: A refractive index modulation element made of a refractive index modulation material. The refractive index can be thermally modulated. The refractive index modulation material can be a silicone resin represented by the following formula R n SiO.sub.(4--n)/2,where the average value of n is 0.5 to 3 and where K is an aliphatic or aromatic group with 1 to 18 carbon atoms or other functional group. The silicone resin has a spectral transmission factor that on average is higher than 80%, within the wavelength range of 350 nm to 1,600 nm, and a refractive index temperature dependence of -0.001/°C. to -0.00005/°C.

Design of subpicosecond dispersion-flattened fibers

Abstract: Dispersion flattened (DF) fibers are required for wide-band WDM systems. The DF fibers designed in the past have dispersion in the range of 2.0-3.0 ps/km-nm. In this letter, we define a generalized refractive index profile that can be characterized by few controlling parameters. An optimum refractive index profile is obtained by minimizing the maximum dispersion over the wavelength range of 1300-1600 nm with respect to profile parameters. The designed fiber gives dispersion less than 1.0 ps/km-nm over 1350-1590 nm wavelength range. Sensitivity of the dispersion performance to the profile parameters is also discussed.

Manufacturing method for an optical waveguide

Abstract: A method of manufacturing an optical waveguide whose refractive index distribution exhibits a step index profile comprises: forming a first layer (2) of fine glass particles to serve as a lower cladding on a substrate (1) by flame hydrolysis deposition; heat-treating the first layer (2) at 800 DEG C or more; forming a second layer (3) of fine glass particles and a refractive index increasing material e.g. P2O5 or GeO2, on the first layer (2) by flame hydrolysis deposition; heat-treating the first and second layers (2, 3) together, thereby converting the layers into transparent glass layers; applying photolithography and then dry-etching layer (3) to form a core (5) on the layer (2A); burying the core (5) by forming a third layer (6) of fine glass particles to serve as an upper cladding by flame hydrolysis deposition; and a step of heat-treating the third layer (6), to convert it into a transparent glass layer.

Single mode optical fiber and its production

Abstract: PROBLEM TO BE SOLVED: To provide a structure which embodies the decrease of dispersion slopes in the state of assuring a sufficient MFD(mode field diameter). SOLUTION: The refractive index profile 600 of this optical fiber 1 is provided with a recess of a sufficient width and depth at center of a core region so as to satisfy the relation a.(Δn2 -Δn1 )/(b.Δn2 )>=0.04 when the average of the specific refractive index difference to the clad part of the first core apart 110 is An, the outside diameter thereof is (a), the average of the specific refractive index difference to the clad part of the second core part 120 is Δn2 and the outside diameter thereof is (b).

Grating light reflection spectroscopy for determination of bulk refractive index and absorbance.

Abstract: An optical sensing technique is described and evaluated for sensitivity to changes in refractive index and absorbance of model sample matrices. A binary dielectric/metal transmission diffraction grating is placed in contact with a sample and utilized in reflection mode; thus, the light captured and analyzed does not pass through the sample. This particular condition creates thresholds at which a particular transmitted diffraction order is transformed from a traveling wave to an evanescent one. The positions of these thresholds depend upon the complex dielectric function of the sample, the period of the grating, and the wavelength and incident angle of light striking the grating. Experimental evidence directly supports the theoretical predictions regarding responses to both the real and imaginary portions of the refractive index: the reflection coefficient derivative wavelength peak position shifts linearly with changes in the real part of the refractive index, and the derivative peak amplitudes exhibit a square-root dependence on absorbance. Refractive index sensitivity to a series of ethanol/water solutions is demonstrated with detectable changes in index as small as 2 × 10(-)(6). Absorbance sensitivity is shown via the differentiation of methylene blue samples having equivalent 1 cm path length absorbances between 0.459 and 244 AU. In a single reflection measurement, GLRS offers a large dynamic range for absorbance detection, allows simultaneous determination of bulk refractive index in optically dense media, and provides a platform for performing continuous process analysis.

Improved dispersion shifted optical waveguide

Abstract: A novel optical waveguide fiber having low total dispersion slope, relatively large mode field diameter, larger effective area, and a relatively simple core profile design is disclosed. The core refractive index profile comprises three segments (2,4,6). The adjustability of the height, width and location of the three core index profile segments, provides sufficient flexibility to meet a specification which calls for a dispersion shifted waveguide fiber capable of limiting four photon mixing or self phase modulation. The novel waveguide is characterized by a mode field diameter 7.5 microns and a total dispersion slope 0.070 ps/nm 2 -km.

Thermal reliability of Bragg gratings written in hydrogen-sensitized fibers

Abstract: Summary form only given. In this work, the thermal reliability of gratings in hydrogen-loaded fibers is studied. It is known that the refractive index modulation in the fiber core is caused by UV-generated defects in the fiber core. It may, hence, be expected that a thermally induced decrease in concentration of the defects that are responsible for the refractive index change would also reduce the UV-induced index modulation, which in turn would decrease the spectral width in strong gratings.