Showing papers on "Step-index profile published in 2010"

Overcoming Losses with Gain in a Negative Refractive Index Metamaterial

Abstract: On the basis of a full-vectorial three-dimensional Maxwell-Bloch approach we investigate the possibility of using gain to overcome losses in a negative refractive index fishnet metamaterial. We show that appropriate placing of optically pumped laser dyes (gain) into the metamaterial structure results in a frequency band where the nonbianisotropic metamaterial becomes amplifying. In that region both the real and the imaginary part of the effective refractive index become simultaneously negative and the figure of merit diverges at two distinct frequency points.

High-Bandwidth Multimode Optical Fiber Having Reduced Bending Losses

Abstract: The present invention embraces a multimode optical fiber that includes a central core having an alpha-index profile, an inner cladding, a depressed trench, and an outer cladding (e.g., an outer optical cladding). Typically, the central core's alpha-index profile has a minimum refractive index at the central core's radius that corresponds to a refractive index difference with respect to the outer cladding. The optical fiber achieves reduced bending losses and a high bandwidth with a reduced cladding effect for high-data-rate applications.

Multimode Optical Fiber with Low Bending Losses and Reduced Cladding Effect

Abstract: The present invention embraces an optical fiber that includes a central core having an alpha-index profile with respect to an outer cladding. The optical fiber also includes an inner cladding, a depressed trench, and an outer cladding. Typically, the alpha-index profile of the central core is interrupted at a point having a positive refractive index difference with respect to the outer cladding. The optical fiber achieves reduced bending losses and a high bandwidth with a reduced cladding effect for high-data-rate applications.

Large numerical aperture bend resistant multimode optical fiber

Abstract: Bend resistant optical fibers which are multi-moded at 1300 nm include a core, an inner cladding, a low index ring and an outer cladding. The core has a graded index of refraction with a core alpha profile where 1.9≦αC≦2.1, a maximum relative refractive index percent Δ1Max%, and a numerical aperture NA of greater than 0.23. The inner cladding surrounds the core and has a maximum relative refractive index percent Δ2Max%, a minimum relative refractive index percent Δ2Min%, and a radial thickness ≧0.5 microns, wherein Δ1Max%>Δ2Max%. The low index ring surrounds the inner cladding and has a relative refractive index percent Δ3%, a radial thickness of at least 0.5 microns, a profile volume with an absolute magnitude of greater than 50%-μm2, wherein Δ2Min%≧Δ3%. The outer cladding surrounds the low index ring and has a relative refractive index percent Δ4%, such that Δ1Max%>Δ4%≧Δ2Max%.

Auto-cladded large-core optical fibers

Abstract: Embodiments of auto-cladded optical fibers are described. The fibers may have a refractive index profile having a small relative refractive index change. For example, the fiber may include an auto-cladded structure having, e.g., a trough or gradient in the refractive index profile. A beam of light propagating in the fiber may be guided, at least in part, with the auto-cladded structure. In some embodiments, the optical fiber may be all glass. In some embodiments, the optical fiber may include a large-core or an ultra large-core.

Plasmon resonances on gold nanowires directly drawn in a step-index fiber

Abstract: We report the successful production of high-quality gold wires, with diameters down to 260nm, by direct fiber drawing from a gold-filled fused-silica cane. The stack-and-draw technique makes it straightforward to incorporate a conventional step-index core, adjacent to the gold wire, in the cane. In the drawn fiber, strong coupling of light from the glass core to SPP resonances on the gold wire is observed at specific well-defined wavelengths. Such embedded wires have many potential applications, for example, as nanoscale electrodes, in nonlinear optical plasmonics, and as near-field scanning optical microscope tips.

Optical band gap and refractive index dispersion parameters of As x Se 70 Te 30− x (0≤ x ≤30 at.%) amorphous films

Abstract: Amorphous As x Se70Te30−x thin films with (0≤x≤30 at.%) were deposited onto glass substrates by using thermal evaporation method. The transmission spectra T(λ) of the films at normal incidence were measured in the wavelength range 400–2500 nm. A straightforward analysis proposed by Swanepoel based on the use of the maxima and minima of the interference fringes has been used to drive the film thickness, d, the complex index of refraction, n, and the extinction coefficient, k. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model (WDD). Increasing As content is found to affect the refractive index and the extinction coefficient of the As x Se70Te30−x films. With increasing As content the optical band gap increases while the refractive index decreases. The optical absorption is due to allowed indirect transition. The chemical bond approach has been applied successfully to interpret the increase of the optical gap with increasing As content.

A Novel Nanometeric Plasmonic Refractive Index Sensor

Abstract: A novel surface plasmon-polariton (SPP) refractive index sensor based on the coupling of a split waveguide mode with a cavity mode in the metal is proposed and studied in this paper. Both analytic and simulated results show that the resonant wavelength of the sensor has a linear relationship with the refractive index of materials under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of the resonant wavelength. The resolution of refractive index of the nanometeric sensor can reach as high as 10-6, given the wavelength resolution of 0.01 nm. It can be applied to high-resolution biosensor.

Microstructured optical fiber refractive index sensor.

Abstract: We describe a dual-core microstructured optical fiber designed for refractive index sensing of fluids. We show that by using the exponential dependence of intercore coupling on analyte refractive index, both large range and high sensitivity can be achieved in the one device. We also show that selective filling of the microstructure with analyte can increase the device sensitivity by approximately 1 order of magnitude.

Linear and nonlinear refractive index of As-Se-Ge and Bi doped As-Se-Ge thin films

Abstract: The present work reports the linear and nonlinear refractive index for (As2Se3)90Ge10 and [(As2Se3)90Ge10]95Bi5 thin films. The formulation proposed by Fournier and Snitzer has been used to predict the nonlinear behavior of refractive index. The linear refractive index and Wemple–DiDomenico parameters were used for the determination of nonlinear refractive index in the wavelength region 0.4 to 1.5 μm. Linear refractive index has been determined using the well known Swanepoel method. This is observed that nonlinear refractive index increases linearly with increasing linear refractive index. With Bi addition this has been found that nonlinear refractive index increases by 2.4 times, while on comparing with pure and doped silica glasses results are 2–3 orders higher. Density and molar volume has also been calculated. The obtained results may lead to yield more sensitive optical limiting devices and these glasses may be used as an optical material for high speed communication fibers.

Multimode Optical Fiber Having Improved Bending Losses

Abstract: The present invention embraces a multimode optical fiber that includes a central core having an alpha refractive index profile with respect to an outer optical cladding and a depressed trench positioned between the central core and the outer optical cladding. The central core's refractive index at its periphery is the same as the outer cladding's refractive index. Typically, an inner cladding is positioned between the central core and the depressed trench. The optical fiber achieves reduced bending losses without significantly increasing numerical aperture.

Large bandwidth multimode optical fiber having a reduced cladding effect

Abstract: A multimode optical fiber includes a central core having a radius (r 1 ) and an alpha-index profile. The multimode optical fiber further includes a depressed trench, which surrounds the central core, that has a width (w t ) and a refractive index difference (Δn t ) with an outer optical cladding. Typically, the central core's diameter is between about 47 and 53 microns, and the depressed trench's width (w t ) is between 0.5 micron and 2 microns. The depressed trench's refractive index difference (Δn t ) with the outer optical cladding is typically between −4×10 −3 and −1×10 −3 .

Temperature dependence of refractive characteristics of optical plastics

Abstract: In this study we investigate the variation of refractive characteristics of optical plastics with temperature in the range of 10 to 50 oC. We have measured the indices of several optical polymers as Optorez 1330, Zeonex E48R, Polymethyl methacrylate, S-low styrene and Bayer by means of the deviation angle method. The obtained refractive index data is presented at five standard spectral lines in the visible region. A decrease of refractive index values with increasing temperature is observed. Dependence on measuring wavelength is also noticed. We have calculated the temperature coefficients of refractive indices of the studied optical plastics. Charts of refractive index of some of the materials versus temperature are presented. Temperature dependence of dispersion curves based on Cauchy-Schott's approximation and Abbe numbers is also considered.

High-bandwidth multimode optical fiber with reduced cladding effect

Abstract: The present invention embraces an optical fiber that includes a central core having an alpha refractive index profile with respect to an outer cladding. The optical fiber also includes an inner cladding, a depressed trench, and an outer cladding. The optical fiber achieves reduced bending losses and a high bandwidth with a reduced cladding effect for high-data-rate applications.

Fiber amplifier utilizing an Yb-doped large-mode-area fiber with confined doping and tailored refractive index profile

Abstract: Power scaling of Yb-doped large-mode-area fibers drives the scaling of the mode area in order to suppress nonlinearities. Two Yb-doped large-mode-area fibers were manufactured using the Direct Nanoparticle Deposition process: one with a step refractive index profile and active ion confinement, and another with a tailored refractive index and active ion confinement. The index tailoring and doping profiles were designed based on literature to enhance the beam quality of the fibers. Both fibers exhibited a mode field diameter comparable to a 40μm step index fiber with 0.07 NA. The fibers were characterized for their geometries, index profiles, and material composition profiles. Additional testing for beam quality and nonlinearities in pulsed operation was conducted using a power amplifier setup. The beam quality enhancement capability of the tested fibers was inconclusive due to incomparable launching conditions of the signal to the fibers.

Tunable two-dimensional liquid gradient refractive index (L-GRIN) lens for variable light focusing.

Abstract: We report a two-dimensional (2D) tunable liquid gradient refractive index (L-GRIN) lens for variable focusing of light in the out-of-plane direction. This lens focuses a light beam through a liquid medium with a 2D hyperbolic secant (HS) refractive index gradient. The refractive index gradient is established in a microfluidic chamber through the diffusion between two fluids with different refractive indices, i.e. CaCl2 solution and deionized (DI) water. The 2D HS refractive index profile and subsequently the focal length of the L-GRIN lens can be tuned by changing the ratio of the flow rates of the CaCl2 solution and DI water. The focusing effect is experimentally characterized through side-view and top-view image analysis, and the experimental data match well with the results from ray-tracing optical simulations. Advantages of the 2D L-GRIN lens include simple device fabrication procedure, low fluid consumption rate, convenient lens-tuning mechanism, and compatibility with existing microfluidic devices. We expect that with further optimizations, this 2D L-GRIN lens can be used in many optics-based lab-on-a-chip applications.

Sensitivity of Plasmonic Nanostructures Coated with Thin Oxide Films for Refractive Index Sensing: Experimental and Theoretical Investigations

Abstract: This paper reports on the use of the Lorentz−Drude model to investigate the refractive index sensitivity, S (change of nanometer per refractive index unit, in nm RIU−1) of multilayered localized surface plasmon resonance (LSPR) interfaces. The investigated interface consists of an array of gold nanostructures (Au NSs) on glass (n1 = 1.51) coated with dielectric overlayers of different refractive index (n2 = 1.45−2.63) and varying thickness (0−300 nm). These interfaces are in contact with solvents of different refractive index (n3 = 1.000−1.630). The refractive index sensitivity for architectures with n1≤ n2 is found to be proportional to the amplitude of the oscillation of the wavelength at maximal absorption (λmax). It reaches its maximal value when the amplitude of the oscillation is maximal and its minimal value when the amplitude is null. The amplitude of the oscillations increases with an increase in refractive index of the dielectric. For n1 > n2, all the curves oscillate in phase leading quickly (d...

Multi-mode bending-resistant fiber and production method thereof

Abstract: A multimode fiber including a core and a cladding. The core has a radius (R1) of 24-26 μm, the refractive index profile thereof is a parabola, and the maximum relative refractive index difference (Δ1) is 0.9-1.1%. The cladding surrounds the core and includes from inside to outside an inner cladding, a middle cladding, and an outer cladding; a radius (R2) of the inner cladding is 1.04-1.6 times that of the core, and a relative refractive index difference (Δ2) thereof is −0.01-0.01%; the middle cladding is a graded refractive index cladding whose radius (R3) is 1.06-1.8 times that of the core, and a relative refractive index difference thereof is decreased from Δ2 to Δ4; and a radius (R4) of the outer cladding is 2.38-2.63 times that of the core, and a relative refractive index difference (Δ4) thereof is between −0.20 and −0.40%. The invention reduces the additional bending loss of the fiber, improves the bending resistance and mechanical properties, basically eliminates the internal stress, and ensures the service life even working for a long term under the condition of low radius. The method for producing the fiber is simple, effective, and suitable for mass production.

Avoided-crossing-based ultrasensitive photonic crystal fiber refractive index sensor

Abstract: We propose and demonstrate an ultrasensitive photonic crystal fiber refractive index sensor by introducing the avoided-crossing effect in a bent-controlled fluid-filled photonic-bandgap fiber (FF-PBGF). By controlling the bend radius of the FF-PBGF, resonant couplings between the fundamental core mode and the cladding modes are realized and transmission notches are observed in the transmission band of the FF-PBGF. By changing the refractive index or temperature of the bent FF-PBGF, a sensitivity of 32,400 nm per refractive index unit (or 13.1 nm/degrees C) is achieved, which is the highest for a fiber device to date, to our best knowledge.

Investigation of defects of refractive index profile of silica graded-index multimode fibers

Abstract: In this article present results of measurements for refractive index profile of silica graded multimode optical fibers are presented. The measurement technique is described. Estimation of parameters for profile defects of investigated samples of multimode optical fibers is received. Analysis data for effect of profile defects of graded multimode optical fibers (MMF) on differential mode delay (DMD) is presented.

In-series double cladding fibers for simultaneous refractive index and temperature measurement

Abstract: A fiber-optic sensor for simultaneous measurement of refractive index (RI) and temperature was proposed and demonstrated. It was fabricated by cascading two sections of specialty double cladding (DC) fibers which presented a pair of well-separated resonant spectra dips. The sensing properties of temperature and ambient RI were investigated theoretically based on the coupled mode theory. Experimental results indicated that these two resonant spectra shifts were linearly dependent on the variation of the RI in the range of 1.3333~1.4118 and on the temperature in the range of −10°C~ + 80°C. Such a fiber-optic sensor is simple and easy for mass production and has potential applications for biosensors or chemical sensors.

Equalizing modal delay of high order modes in bend insensitive multimode fiber

Abstract: PROBLEM TO BE SOLVED: To provide multimode optical fibers in which the differential in the mode delay of a high order mode is reduced for bending insensitive MMF. SOLUTION: The result is preservation of low differential mode delay and high bandwidth is achieved, while low bend loss is achieved. The designs are based on choosing a combination of a core profile and a cladding structure with a negative trench positioned at a radius position related to the core profile. The feature of the preferable embodiments is a core with a hybrid refractive index profile. The hybrid refractive index profile is essentially a combination of a standard alpha profile and a step-like profile at the outer edge of the alpha profile. COPYRIGHT: (C)2011,JPO&INPIT

Long period fiber grating formed by periodically structured microholes in all-solid photonic bandgap fiber.

Abstract: A new type long period fiber grating is fabricated in all-solid photonic bandgap fiber by periodically drilling microholes using femtosecond laser pulse irradiation. Such a structure introduces a strong refractive index modulation in the waveguide structure and hence exhibits a compact grating dimension. Both the simulation and the experimental results confirm the existence of the light coupling from core mode to the LP11 cladding mode. The refractive index sensing capability of the device has been investigated and the resonant wavelength shift corresponding to the refractive index change from 1.30 to 1.35 is 23.7nm. The average refractive index sensitivity obtained is 537nm/RIU (refractive index unit).

Transverse radiation force in a tailored optical fiber

Abstract: We show, by means of simple model calculations, how a weak laser beam sent though an optical fiber exerts a transverse radiation force if there is an azimuthal asymmetry present in the fiber such that one side has a slightly different refractive index than the other. The refractive index difference {Delta}n needs only to be very low, of order 10{sup -3}, to produce an appreciable transverse displacement of order 10 {mu}m. We argue that the effect has probably already been seen in a recent experiment by W. She et al. [Phys. Rev. Lett. 101, 243601 (2008)], and we discuss the correspondence between these observations and the theory presented. The effect could be used to bend optical fibers in a predictable and controlled manner and we propose that it could be useful for micron-scale devices.

Influence of tapering process on changes of optical fiber refractive index distribution along a structure

Abstract: Investigations of internal structure changes along an optical fiber during the manufacture of biconical taper have been described. Basing on the constant volume theory, classification of biconical structures manufactured on a special set-up is presented and discussed. The interferometric tomography method has been used for determination of 3D geometry and refractive index distribution in manufactured optical fiber tapers. The experiments provide detailed information on external (diameter of cladding) as well as internal (core diameter and refractive index profile) changes along the taper region. The results have been discussed in relation to the parameters of the manufacturing process.

Extrinsic fiber-optic Fabry–Perot interferometer sensor for refractive index measurement of optical glass

Abstract: A simple fiber-optic sensor based on Fabry-Perot interference for refractive index measurement of optical glass is investigated both theoretically and experimentally. A broadband light source is coupled into an extrinsic fiber Fabry-Perot cavity formed by the surfaces of a sensing fiber end and the measured sample. The interference signals from the cavity are reflected back into the same fiber. The refractive index of the sample can be obtained by measuring the contrast of the interference fringes. The experimental data meet with the theoretical values very well. The proposed technique is a new method for glass refractive index measurement with a simple, solid, and compact structure.

Single mode optical fiber with depressed trench

Abstract: The invention relates to an optical fiber comprising an outer optical cladding and an optical core. The optical core comprises, from the center towards the periphery: a central core having a radius and a refractive index difference with respect to the outer optical cladding; and a depressed inner cladding. The depressed inner cladding includes at least a first portion having a radius and a refractive index difference with respect to the outer optical cladding, the first portion preferably being adjacent to the central core; a second portion adjacent to the first portion constituting a depressed trench having a radius, and a refractive index difference with respect to the outer optical cladding. The first portion of the inner cladding has a refractive index below the refractive index of the outer optical cladding, and the depressed trench - i.e. the second portion - has a refractive index that is lower than - i.e. more negative than - the refractive index of the first portion of the depressed inner cladding. The outer radius of the depressed inner cladding of the optical fiber is between 28 µm and 40 µm, the LP01 mode leakage losses at a wavelength of 1550 nm are less than 0.01 dB/km and the cable cut-off wavelength is less than 1530 nm.

Single-mode fiber and production method thereof

Abstract: A single mode fiber having a core, an inner cladding, a depressed cladding, and an outer cladding composed of pure silica glass. The core is surrounded in sequence with the inner cladding and the depressed cladding. The core has silica glass doped with germanium and fluorine, with a diameter (a) of 8.0-8.8 μm, a relative refractive index difference (Δ 1 ) of 0.35-0.38%, and the contribution of fluoride (Δ F ) is −0.09±0.02%. The inner cladding has silica glass doped with germanium and fluorine, with a diameter (b) of 18-21 μm and a relative refractive index difference (Δ 2 ) of 0±0.02%. The depressed cladding has silica glass doped with fluorine, with a diameter (c) of 26-36 μm and a relative refractive index difference (Δ 32 ) at the external interface thereof is between −0.22 and −0.35%, and a relative refractive index difference (Δ 31 ) at the internal interface thereof is between −0.20 and −0.35%, and Δ 32 ≦Δ 31 . The fiber has a good bending resistance, good mechanical properties, and extended service lifetime, and prevents the additional stresses generated by bending from passing on to the core, thereby reducing attenuation.