Showing papers on "Step-index profile published in 2009"

Tapered fiber Mach–Zehnder interferometer for simultaneous measurement of refractive index and temperature

Abstract: An approach to achieve simultaneous measurement of refractive index and temperature is proposed by using a Mach–Zehnder interferometer realized on tapered single-mode optical fiber. The attenuation peak wavelength of the interference with specific order in the transmission spectrum shifts with changes in the environmental refractive index and temperature. By utilizing S-band and C/L-band light sources, simultaneous discrimination of refractive index and temperature with the tapered fiber Mach–Zehnder interferometer is demonstrated with the corresponding sensitivities of −23.188 nm/RIU (refractive index unit) and 0.071 nm/ °C, and −26.087 nm/RIU (blueshift) and 0.077 nm/°C (redshift) for the interference orders of 169 and 144, respectively.

Ultrasensitive photonic crystal fiber refractive index sensor

Abstract: We introduce a microfluidic refractive index sensor based on a directional coupler architecture using solid-core photonic crystal fibers. The sensor achieves very high sensitivity by coupling the core mode to a mode in the adjacent fluid-filled waveguide that is beyond modal cutoff, and with strong field overlap. We demonstrate the device through the selective infiltration of a single hole with fluid along a microstructured optical fiber. A detection limit of 4.6x10(-7) refractive index units has been derived from measurements with a sensitivity of 30,100 nm per refractive index unit, which is the highest for a fiber device to date.

Bend insensitive single mode fiber

Abstract: This invention discloses a bend insensitive single mode fiber, which is composed by a bare glass fiber with a round cross section and two resin protective layers with circular cross sections surrounding the outer of the bare glass fiber. It is characterized in that the bare glass fiber is composed by a core layer with a round cross section and two claddings with circular cross sections. The refractive index of the core layer is higher than the index of the two claddings and the refractive index difference between the core layer and the first cladding is larger than the difference between the first and second claddings. The second cladding is made of pure SiO2. The refractive index profile of the core layer follows a power function, and the refractive index profile of the two claddings follow a ladder-type distribution. The loss of the invented fiber is insensitive to the bending of the fiber, which meets the requirements of ITU.T G.657.A and G.657.B standards, respectively. It is applicable to the Fiber To The Home (FTTH) and other local area network and the access network systems.

Limit of Effective Area for Single-Mode Operation in Step-Index Large Mode Area Laser Fibers

Abstract: Step-index (SI) fiber designs are commonly used in achieving large mode area (LMA) and single-mode (SM) operation in fiber lasers. These fibers can either be intrinsically single-moded fibers or few-moded fibers, which can be forced into SM operation through bending. In this paper we evaluate the limitation of the effective area for SM operation by taking into account the effects of practical constraints such as fiber bending loss, laser performance, and fiber mechanical reliability on these LMA fiber designs. It is shown that the effective area of these fibers cannot be arbitrarily scaled up with the size of the fiber core. We also use the modeling result to provide estimated upper limits to the core diameters and corresponding effective areas for conventional SI fiber designs taking into account fiber parameters that are achievable nowadays.

Refractive index sensor based on surface-plasmon interference

Abstract: We propose a refractive index sensor based on the interference of two surface-plasmon waves on both surfaces of a gold film with a two-slit structure. The phase of the interference was solved, and the dispersion relation of the real part of Au dielectric function was considered. The sensor was performed with NaCl-H2O solutions of different concentrations and exhibited a linear response and a high sensitivity of 4547 nm/RIU (refractive index unit) to the refractive index change.

High numerical aperture multimode optical fiber

Abstract: Multimode optical fibers with a large core diameter and high numerical aperture are disclosed herein Multimode optical fibers disclosed herein comprise a core region having a radius greater than 30 microns and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular portion comprising a depressed relative refractive index The depressed cladding region is surrounded by a titania doped cladding region The fiber has a total outer diameter of less than 120 microns, and exhibits an overfilled bandwidth at 850 nm greater than 200 MHz-km

Side-emitting step index fiber

Abstract: Side-emitting step index fibers. Between core and cladding, the side-emitting step index fibers have scattering centers that ensure the coupling out of light from the fiber. The side-emitting step index fibers are produced by preforms that contain inlay rods, in which the scattering centers are embedded and which are applied to the outer region of the fiber core during fiber drawing. Alternatively, at least one inlay tube can be used.

Optical film, method for producing the same, polarizing plate and image display device

Abstract: An optical film, includes: a transparent support; and an optical functional layer as the outermost layer of the optical film, the optical functional layer being provided on or above the transparent support, wherein the optical functional layer has a thickness of 50 nm or more and not more than 250 nm; the optical functional layer contains low refractive index fine particles having a refractive index of not more than 1.45, high refractive index fine particles having a refractive index of 1.55 or more, and a fluorine-containing compound; the low refractive index fine particles are arranged substantially in a line on a surface of the optical functional layer on the opposite side of the transparent support; and the high refractive index fine particles are unevenly distributed in a lower part of the optical functional layer on the side of the transparent support.

Corrections to “Beam Quality Factor of Higher Order Modes in a Step-Index Fiber”

Abstract: The beam quality factor (or M2-parameter) for linearly polarized (LP)-modes of a step-index fiber is calculated in a closed form, as a function of the fiber V-number. It is shown that M2 sharply peaks for all fiber modes when they are close to cutoff. Particularly simple expressions are derived in the limit Vrarrinfin. Two practically important coherent superpositions of modes are considered for which the degree of degradation of the beam quality due to the higher order mode content is calculated. The reported results can be useful for designing large-core high-power fiber lasers, amplifiers, and fiber-based beam delivery systems, when preservation of the spatial beam quality is important

Investigations on the Bragg grating recording in all-silica, standard and microstructured optical fibers using 248 nm 5 ps, laser radiation

Abstract: The fabrication of Bragg reflectors in hydrogenated, all-silica, fluorine cladding depressed and microstructured optical fibers using 248 nm, 5 ps laser radiation, is investigated here. Comparative Bragg grating recordings are performed in both optical fibers, for investigating effects related to the scattering induced by the capillary micro-structure, to the photosensitivity and index engineering yield. Further, finite difference time domain method is employed for simulating the scattering from the above capillary structure and the nominal intensity reaching the fiber core for side-illumination. The maximum modulated refractive index changes inscribed in the standard, step-index fiber were of the order of 8.3x10-5, while the maximum refractive index changes inscribed in one of the microstructured optical fibers was 32% lower and 5.7x10-5, for nominal pulse intensities of 20 GW/cm2 and modest accumulated energy densities.

Simultaneous Measurement of Refractive Index and Temperature Using a Hybrid Fiber Bragg Grating/Long-Period Fiber Grating Configuration

Abstract: A fiber optic sensing system for simultaneous measurement of refractive index and temperature, based on a hybrid fiber Bragg grating/long-period grating arrangement is described. The experimental results show that this setup has a good performance in terms of linearity and sensitivity, the ratiometric output changes 4%/0.001 RIU and 3.6%/°C, respectively. The sensor resolution for the refractive index is ≈2 × 10−5 RIU. The simultaneous measurement of the refractive index and temperature was demonstrated. The sensing configuration has the ability to be read-out in reflection and works in the telecommunications window.

Optical article and method for manufacturing the same

Abstract: An optical article includes an anti-reflection layer on a substrate, wherein the anti-reflection layer is formed of nine layers obtained by alternately stacking low refractive index layers and high refractive index layers, the layer closest to the substrate among the high and low refractive index layers that form the anti-reflection layer is called a first layer and the numbers of the following layers are incremented by one so that the odd-numbered layers are low refractive index layers and the even-numbered layers are high refractive index layers, and at least one of the following equations is satisfied: 0.8λ 0 ≦λ 1 ≦1.2λ 0 (1) 0.8λ 0 ≦λ 3 ≦1.2λ 0 (2) where λ 0 represents a design primary wavelength greater than or equal to 480 nm but smaller than or equal to 550 nm, and λ k represents the optical thickness of the corresponding one of the high and low refractive index layers (k represents the layer number).

Holey metal films: From extraordinary transmission to negative-index behavior

Abstract: In this paper we study the common physical background of the phenomenon of extraordinary optical transmission in holey metal films and the emergence of the negative refractive index behavior in double fishnet structures. Here we provide further evidence that the resonant magnetic response of the latter structures is associated with the excitation of gap surface plasmon modes. The evolution of the optical response with the number of double fishnet layers is also addressed, finding that the effective refractive index reaches a converged value for a moderate number of layers.

Multimode fiber with at least dual cladding

Abstract: Multimode optical fiber is disclosed herein having a core surrounded by first and second annular cladding regions. The second annular cladding region has a maximum relative refractive index that is at least 0.05% higher than the minimum relative refractive index of the first annular cladding region.

Refractive index dependence of the coupling characteristics between long-range surface-plasmon-polariton and dielectric waveguide modes

Abstract: The coupling characteristics of a hybrid coupler comprised of a long-range surface-plasmon-polariton (LRSPP) waveguide and a dielectric waveguide is analyzed with different detecting layers. Calculation results show that the coupling strength between the LRSPP mode and the dielectric-waveguide mode is rather sensitive to the refractive index of the detecting layer. This is promising to realize an integrated refractive index senor with high resolution better than 4×10−7 refractive index units or a modulator with rather low driving power and insert loss.

Double-clad optical fibers and devices with double-clad optical fibers

Abstract: A double-clad optical fiber includes a core, an inner cladding and an outer cladding of silica-based glass. The core may have a radius of less than about 5 μm, a first index of refraction n1 and does not contain any active rare-earth dopants. The inner cladding may surround the core and includes a radial thickness of at least about 25 μm, a numerical aperture of at least about 0.25, and a second index of refraction n2 such that n2

Graded index multimode optical fiber

Abstract: Disclosed is a GI multimode optical fiber (10) comprising a core (11) having an outer diameter of 45-65 μm, a first cladding (12) so formed as to cover the core (11), a second cladding (13) so formed as to cover the first cladding (12) and composed of a material having a lower refractive index than that of the first cladding (12), and a third cladding (14) so formed as to cover the second cladding (13) and composed of a material having a higher refractive index than that of the second cladding (13). The ratio of the outer diameter of the first cladding (12) to the outer diameter of the core (11) is 1.15-1.25.

Determination of refractive indices of liquids by Fresnel diffraction

Abstract: We demonstrate an easy, reliable, applicable, and sensitive method to measure refractive index of liquids by using Fresnel diffraction. In this method a cylindrical glass rod, in general, or an optical fiber in special case, is immersed into a liquid. Physical parameters of the rod, like radius and refractive index, should be well known. Then, the normalized intensity distribution on the Fresnel diffraction pattern of a plane wave diffracted from the immersed fiber is measured. Thereafter, refractive index of the liquid is evolved by the least-square method. This method applied to determine the refractive index of four liquids; pure water, 2-propanol (isopropanol), acetone and methanol. Index of refraction of each one has been acquired for four visible wavelengths. A theoretical approach and experimental results is presented.

Effective refractive index for determining ray propagation in an absorbing dielectric particle

Abstract: The ray-tracing technique can be employed to simulate the scattering of light by a dielectric particle whose characteristic dimension is much larger than the incident wavelength. When a scattering particle is absorptive, a localized electromagnetic wave refracted into the scatterer is inhomogeneous, which requires the use of an effective refractive index to determine the propagation direction of the refracted ray. The effective refractive index for the first-order reflection–refraction event (i.e., the case for the ray-transmission from air into a particle) has been previously derived by the authors. In this study, we further develop recurrence formulae for the effective refractive indices associated with higher-order reflection–refraction events when the ray-transmission is from a particle to air. It is shown from the new formulae that effective refractive indices in this case depend upon ray history. Numerical results indicate that the real and imaginary parts of the effective refractive index are larger and smaller, respectively, than the real and imaginary parts of the inherent complex refractive index of an absorbing particle. Furthermore, if the particle faces associated with two sequential internal reflections are parallel to each other, the corresponding effective refractive indices are the same.

Diffractive optical element and manufacturing method thereof

Abstract: A diffractive optical element according to the present invention includes: a body 1 being composed of a first optical material containing a first resin, and having a diffraction grating 2 on a surface thereof; and an optical adjustment layer 3 being composed of a second optical material containing a second resin, and provided on the body 1 so as to cover the diffraction grating 2. The first optical material has a refractive index which is smaller than a refractive index of the second optical material; the refractive index of the first optical material has a wavelength dispersion which is greater than a wavelength dispersion of the refractive index of the second optical material; and a difference in solubility parameter between the first resin and the second resin is no less than 0.8 [cal/cm3]1/2 and no more than 2.5 [cal/cm3]1/2.

Refractive index sensing characteristics of dual resonance long period gratings in bare and metal-coated D-shaped fibers.

Abstract: We present a theoretical study of the ambient refractive index sensing characteristics of long period gratings in bare and metal-coated D-shaped fibers. An equivalent rectangular core waveguide method based on the first-order perturbation theory has been used to study the modal behavior of the waveguide. Power coupling corresponding to dual resonance in both cases has been investigated, and an optimum metal thickness giving maximum sensitivity has been found to exist. The study shows that the dual resonances can be shifted to lower wavelengths by increasing (decreasing) the metal thickness (core to flat surface separation). Further, an optimum combination of metal thickness and core to flat surface separation, corresponding to maximum sensitivity, has been presented for different cladding modes and their relative performance has been discussed. It has been shown theoretically that detection of refractive index changes as small as 1.67×10−7 RIU in the ambient region is possible using the optimized parameters. The study should find application in realizing highly sensitive biochemical sensors.

Fabrication of Photonic Bandgap Fiber Gas Cell Using Focused Ion Beam Cutting

Abstract: In this paper, we present a novel low-loss splice for use between the photonic bandgap fiber (PBGF) and the conventional step index fiber to make PBGFs more functional. The gap between the butt-coupled fibers is the most important parameter for maintaining good output coupling efficiency and allowing gas diffusion. To achieve the small gap, a focused ion beam (FIB) milling technique was developed to clean the fiber surface. The gap is adjustable from 0 to 400 µm, and the typical connection loss at a gap of 20 µm is 1.6 dB. A measurement system for low gas concentrations based on the PBGF cell has been developed and implemented. Experiments for measuring ammonia gas at the ppm level were performed. The basic peak agreed well with the database of the Pacific Northwest National Laboratory (PNNL), meaning that this method can be used to accurately and effectively measure gas concentration.

Optical fiber cable and optical cable

Abstract: Provided is an optical fiber that has a small bending loss, can be securely prevented from being fractured due to accidental bending during installation or other operations, and is compliant with the G 652 standard. An optical fiber 1 includes a core 11, a first cladding 12, a second cladding 13, and a third cladding 14. The relative refractive index difference Δ1 of the core 11 is in the range of 0.3% to 0.38%, the relative refractive index difference Δ2 of the first cladding 12 is equal to or smaller than 0%, and the relative refractive index difference Δ3 of the second cladding 13 is in the range of -1.8% to -0.5%. The inner radius r2 and the outer radius r3 of the second cladding 13 satisfy the expression "0.4r2 + 10.5 < r3 < 0.2r2 + 16", and the inner radius r2 of the second cladding 13 is equal to or greater than 8 µm. The bending loss at a wavelength of 1550 nm and at a radius of curvature of 7.5 mm is smaller than 0.1 dB/turn, and the bending loss at a wavelength of 1625 nm and at a radius of curvature of 4 mm is greater than 0.1 dB/turn.

Temperature-insensitive refractive index sensor based on tilted fiber Bragg grating

Abstract: Short-period fiber Bragg gratings with gratings planes tilted at an angle 8° corresponding to the fiber axis show core mode and a large number of cladding-mode resonances in transmission. The differences between the cladding-mode resonance and the core-mode resonance are used to detect the variation of the surrounding refractive index; this refractive index sensor is immune to temperature effects by experimental demonstrations. After the cladding of the tilted fiber, Bragg grating was etched by the hydrofluoric, TFBGs with different diameters and different-order cladding modes were investigated; the sensitivity of a TFBG to the external index can be significantly improved by reducing the cladding radius. Enhanced sensitivity and accuracy are achieved when the changes between 1.333 and 1.4532. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 479–483, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24057

Laterally emitting step index fiber

Abstract: The invention relates to laterally emitting step index fibers, preforms and methods for the production thereof and to fiber bundles and sheet material comprising laterally emitting step index fibers and to the use thereof. The laterally emitting step index fibers comprise scatter centers (3) between the core (1) and jacket (2) that ensure light decoupling from the fiber. The laterally emitting step index fibers are produced from preforms that comprise inlay rods, in which the scatter centers are embedded and which coat the outside region of the fiber core during fiber drawing. Alternatively, at least one inlay tube can be used.

Photonic bandgap fiber

Abstract: A photonic bandgap fiber of the present invention functions as a polarization maintaining fiber, and includes: a core made from a solid material; a cladding provided around the core; a periodic structure region which is provided in a part of the cladding in a vicinity of the core and in which a plurality of high refractive index parts with a refractive index higher than that of the cladding are arranged in a periodic structure; a low refractive index region which is provided in another part of the cladding in a vicinity of the core and has an average refractive index lower than that of the core; and stress applying parts which are provided in a part of the low refractive index region close to the periodic structure region and have a thermal expansion coefficient different from that of another part of the low refractive index region.