Step-index profile

About: Step-index profile is a research topic. Over the lifetime, 3104 publications have been published within this topic receiving 53199 citations.

Measurement of CO2-laser-irradiation-induced refractive index modulation in single-mode fiber toward long-period fiber grating design and fabrication.

Abstract: We report a new method to measure the CO2-laser-irradiation-induced refractive index modulation in the core of a single-mode optical fiber for the purpose of design and fabrication of long-period fiber gratings (LPFGs) without applying tension. Using an optical fiber Fabry-Perot interferometer, the laser-induced axial refractive index perturbation was measured. We found that the CO2-laser-irradiation-induced refractive index change in the fiber core had a negative value and that the magnitude was a sensitive function of the laser exposure time following almost a linear relation. Under the assumption of a Gaussian-shaped refractive index modulation profile and based on the first two terms of Fourier series approximation, the measured refractive index perturbations were used to simulate the LPFG transmission spectra. LPFGs with the same laser exposure parameters were fabricated without applying tension, and their spectra were compared with those obtained by simulations.

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.

Measurement of the refractive index dispersion of As2Se3 bulk glass and thin films prior to and after laser irradiation and annealing using prism coupling in the near- and mid-infrared spectral range.

Abstract: The prism coupling technique has been utilized to measure the refractive index in the near- and mid-IR spectral region of chalcogenide glasses in bulk and thin film form. A commercial system (Metricon model 2010) has been modified with additional laser sources, detectors, and a new GaP prism to allow the measurement of refractive index dispersion over the 1.5-10.6 μm range. The instrumental error was found to be ±0.001 refractive index units across the entire wavelength region examined. Measurements on thermally evaporated AMTIR2 thin films confirmed that (i) the film deposition process provides thin films with reduced index compared to that of the bulk glass used as a target, (ii) annealing of the films increases the refractive index of the film to the level of the bulk glass used as a target to create it, and (iii) it is possible to locally increase the refractive index of the chalcogenide glass using laser exposure at 632.8 nm.

Theoretical and experimental study of refractive index sensors based on etched fiber Bragg gratings

Abstract: In this work, a theoretical and experimental study of the effect of the etching process on the properties of fiber Bragg gratings (FBGs) used as refractive index sensors is presented. The theoretical study addresses the dependence of the effective refractive index on the cladding thickness of the etched FBG. The results of this study show that as the cladding thickness is reduced, the effective refractive index decreases exponentially. Based on this result, a simple analytic expression between the effective refractive index and the radius of the etched FBG was developed. Thus, the radius of the FBG after the etching process can be determined directly from the shift of the Bragg wavelength, without the need of extensive numerical simulations. Also, the sensitivity of the FBG sensor in characteristic environments of practical interest has been calculated as a function of the fiber radius, and found to be described by simple analytic functions. The time evolution of the Bragg wavelength during the etching process has also been investigated, both experimentally and theoretically. By means of detailed theoretical analysis of the experimental results, the heating and the etching rate of the FBG was calculated. Finally, the etched FBGs have been used as liquid level sensors for water and oil, having refractive indices lower and higher than the fiber core respectively. The analysis of the experimental results was based on the shift of the diffracted wavelength in the case of water and on the reduction of the reflected power in the case of oil.