Index Profile Of Fiber Research Articles

Determining of Refractive Index Profile of Optical Fibers from Measured Intensity in Near-Field Zone

Determining of Refractive Index Profile of Optical Fibers from Measured Intensity in Near-Field Zone

Nondestructive analysis of the transverse structure of novel optical fibers by third-harmonic-generation microscopy

We demonstrate the suitability of the third-harmonic-generation technique as a new nonlinear microprobe for nondestructive determination of the index profile of optical fibers. Photonic bandgap (Bragg-type) and air-silica microstructure (ASM) fibers were tested. The complete spatial characteristics, such as hole diameter and spacing into ASM fibers or sandwiched layer thickness into Bragg fibers, were demonstrated to be attainable anywhere along a bare fiber.

Characterization of refractive index distribution of polymer optical fiber

A focusing method is developed to characterize the refractive index profile of polymer optical fiber (POF). Based on the refractive index profile the theoretical bandwidth and the core index exponent α (α > 0) of POF are calculated. The results show that the value of theoretical bandwidth agrees well with the experimental data.

Multiple‐beam Fizeau fringe‐pattern analysis using Fourier transform method for accurate measurement of fiber refractive index profile of polymer fiber

AbstractIn this article the Fourier transform method is applied to analyze multiple‐beam interference Fizeau fringes. The real part of the inverse Fourier transform is used to estimate a theoretical pattern. This pattern coincides with the experimental one. A derivative‐sign binary image of the interference pattern is also used in automated determination of the contour line of the fringe pattern, regardless of the quality of this pattern. A correlation between the pixel size and the accuracy of the measured fiber refractive index is presented. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 475–484, 2002

Automatic Characterization of the Refractive Index Profile of Fibers by Interferometry

Interferometry provides a non-destructive method for examining the refractive index profile or the radial birefringence distribution within fibers. The key step in the interference data reduction involves the extraction of the refractive index profile along the axial direction of the fiber. The profile is due to the path difference between the fiber and the immersion liquid when a fiber is oriented perpendicular to the fringe field in an interference microscope. The refractive index provides a measure of the degree of optical anisotropy and is indicative of the degree of orientation of the structure. This is of particular interest to nonwovens because in thermally bonded nonwovens, the orientation plays a major role in how well the fibers are bonded and the ultimate properties of the fabric. Despite its long history, however, the interpretation of the interference fringe shift is not precisely defined. Consequently, the data are not reproducible from one laboratory to the next. We outline below an objective and quantitative method for precisely measuring a fiber's refractive index profile from a digitized image of the interference fringe. This new algorithm uses the Fast Fourier Transform (FFT) to remove the inherent noise present in the fiber interferogram and to aid in extracting the profile.

Automatic refractive index profiling of fibers by phase analysis method using Fourier transform

Automatic fringe pattern analysis is a powerful and inexpensive digital image-processing technique. It is used to analyze the fringe pattern obtained by different optical techniques, such as multiple-beam Fizeau fringes. To perform accurate and fast automatic measurement of fiber refractive index profile, phase analysis method has been used with the Fourier transform technique. In this paper, the refractive index profiles of polyethylene fibers with different draw ratios are presented by two methods, fringe shift method and phase analysis method. A comparison between the results obtained is presented.

Design and fabrication of a nonzero-dispersion fiber with a maximally flat dispersion spectrum

Using a general-purpose multivariate optimization program that we have developed for the design of the fiber-index profile for a given set of several fiber optimization parameters, we have designed and fabricated nonzero-dispersion fibers with a maximally flat chromatic dispersion spectrum, which have shown improved dispersion-spectrum curves compared to those of commercially available fibers developed for the same purpose.

Intermodal interference in optical fibres

In this paper the results of a theoretical analysis and practical investigation of mode interference in single mode optical fibres are described. It is shown that inter-modal interference is a sensitive parameter depending on the quality of an index profile or geometrical parameters of optical fibre. The comparison of experimental and theoretical values of mode interference indicates that the measurement of interference could be used for testing how the real refractive index profile of investigated fibre corresponds with the refractive index profile assumed at the calculation (step-index profile).

Analysis of the Fiber Bragg Gratings using the Lattice Filter Model

We propose a new method for analyzing fiber Bragg gratings with an arbitrary index profile and an arbitrary individual grating length. The proposed method is based on the lattice filter model which is widely used in applications ranging from digital filtering to speech synthesis and explosive seismic signal processing. Lattice filter interpretation provides us with an accurate and simple tool for analyzing an arbitrary index profile and arbitrary aperiodic fiber grating structures, and gives us further insight into the understanding of fiber Bragg gratings. To verify the validity of the proposed model experimentally, we have fabricated two grating structures; the short-period (periodic) fiber Bragg grating structure and the chirped fiber Bragg grating structure. We have observed that the calculated transmission spectrum and the calculated reflectivity using our lattice filter model match very closely to the corresponding measured spectrum in the wavelength band of interest.

Comparison between optical fiber birefringence induced by stress anisotropy and geometric deformation

A variational formulation-based vector perturbation model is used to compare the contribution of stress anisotropy and geometric deformation toward optical fiber birefringence. We show that relative impact of stress on birefringence and differential group delay depends significantly on the exact fiber index profile.

Two-dimensional index profiling of fibers and waveguides

We have constructed a two-dimensional refracted-ray scanner that can resolve index-of-refraction increments of approximately 4 x 10(-5). This resolution is an order of magnitude finer than the uncertainty of the measurement. The scanner can be adapted to evaluate either fibers or planar waveguides. The two-dimensional scan and the high precision allow visualization of features, such as deposition layers, that are difficult if not impossible to see in conventional one-dimensional scans.

Determination of Refractive Index Profile and Material Dispersion of Step Index Optical Fibers using Tow-beam Interferometric Method

Determination of Refractive Index Profile and Material Dispersion of Step Index Optical Fibers using Tow-beam Interferometric Method

Precision fiber-optic sensor based on an optoelectronic recirculation system

It is proposed that an optoelectronic recirculation system can be used as an instrument for measuring the length of optical fibers and as a temperature sensor. The measured quantity is identified from the recirculation frequency, which is recorded with comparative ease and high accuracy. The optoelectronic recirculation system can be used to monitor the quality of optical fiber connections and other optical elements, and also to estimate the refractive index profile of multimode graded-index optical fibers.

A comprehensive ray approach for teaching intermodal dispersion of a parabolic index profile fiber

A simple and comprehensive ray approach for teaching intermodal dispersion of a parabolic index fiber is proposed. The result is the same as that by using the conventional approach. Because the approach here only uses the ray concepts with very simple mathematics, it can be easily understood by sophomore students. A simple perturbation idea adopted in this paper makes the calculation easier and the distinction between the concepts of near axial and far-axial rays makes the solution have more physical significance.

Inverted-graded index fiber structures for evanescent-wave chemical sensing

The paper deals with a novel multimode fiber-optic structure, the inverted-graded index profile (IGI) fiber, and its feasibility for evanescent-wave chemical sensing. Results of the theoretical analysis of the sensitivity of the IGI fiber to changes of the refractive index and light absorption coefficient of its cladding are shown. Fabrication of IGI fibers doped in the core with GeO 2 or B 2O 3 is described. The evanescent-wave sensitivity of the prepared IGI fibers to changes of the cladding refractive index and light absorption coefficient is given showing its increase in comparison with reference fibers with cores of pure silica and with the same polymer claddings as the IGI fibers.

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

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.

Optical fibers and amplifiers for WDM systems

The development of optical-fiber amplifiers allowed a dramatic increase in the capacity of optical transmission systems while reducing system costs. Capacity increases are possible because the high output powers afforded by optical-fiber amplifiers support higher bit rates, while their broad bandwidth and slow gain dynamics allow multichannel operation. This benefit comes at the expense of having to manage signal-to-noise ratio degradations due to the accumulation of amplifier noise and dispersion distortions accumulated over the total system link. Furthermore, nonlinear optical effects become significant with the use of high power signals over long lengths of fiber, causing cross talk among the different channels and increasing signal distortions. To fully exploit the potential capacity of wavelength division multiplexing systems, the optical characteristics of the fibers and optical-fiber amplifiers must be optimized. The optical amplifiers should have low noise and flat gain, which can be achieved by using 980-nm pump lasers, optimized fiber glass composition, and gain-flattening filters. The optical fibers should have a small nonzero dispersion and large effective area. Both features can be achieved by optimizing the fiber index profile. This paper summarizes the state of the art in these components and points to directions for future exploration.

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

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.

Optical fibers profiling by phase-stepping transverse interferometry

The phase-stepping technique for data acquisition from transverse interferograms is proposed in the refractive index profiling of optical fibers. The advantages for automatic data extraction are pointed out. Experimental results are presented. >

Scattering of the fundamental modes from graded-index fibers into semi-infinite space

The scattering of the fundamental linearly polarized (LP)01 mode of a weakly guiding graded-index fiber (n1 − n2 ≪ 1) that is abruptly terminated in a dielectric half-space with index of refraction n3 is rigorously investigated. By using Marcuse’s Gaussian beam approximation for the incident and the reflected fiber modes and continuous distributions for the E and H modes in the half-space and by matching the transverse E field at the termination, as well as imposing the conservation-of-complex-power condition, a closed-form expression for the load admittance Y of a Gaussian beam is obtained. From Y. the associated transmitted-power coefficient T can easily be determined. Numerical results for T are presented for a variety of fiber-index profiles.