Showing papers on "Step-index profile published in 2018"

A yttrium aluminosilicate glass fiber with graded refractive index fabricated by melt-in-tube method

Abstract: A graded-index fiber with yttrium aluminosilicate (YAS) glass core was fabricated by a “Melt-in-Tube” method. The refractive index and stress profiles of the fibers exhibit a highly symmetrical gradient tendency along the radial axis which is in accordance with the results of element migration. Based on the formation mechanism of YAS glass core, the relationships between the refractive index/stress profile and the spontaneous migration are discussed. A linear all-fiber laser based on the obtained fiber shows a laser output threshold of 11.48 mW and slope efficiency of 8.3%. The near-field beam intensity distribution of fiber laser with spectrum FWHM of 0.24nm indicates the good laser beam quality. The facile “Melt-in-tube” method was proved to be reliable in designing graded-index fiber through the dissolution and diffusion process, which is more advanced than commonly used “Rod-in-tube” method. This article is protected by copyright. All rights reserved.

Fabrication of Yb2O3–Al2O3–P2O5–SiO2 Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

Abstract: An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb2O3–Al2O3–P2O5–SiO2 multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P2O5 losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.

Excitation of epsilon-near-zero resonance in ultra-thin indium tin oxide shell embedded nanostructured optical fiber

Abstract: We report a novel optical waveguide design of a hollow step index fiber modified with a thin layer of indium tin oxide (ITO). We show an excitation of highly confined waveguide mode in the proposed fiber near the wavelength where permittivity of ITO approaches zero. Due to the high field confinement within thin ITO shell inside the fiber, the epsilon-near-zero (ENZ) mode can be characterized by a peak in modal loss of the hybrid waveguide. Our results show that such in-fiber excitation of ENZ mode is due to the coupling of the guided core mode to the thin-film ENZ mode. We also show that the phase matching wavelength, where the coupling takes place, varies depending on the refractive index of the constituents inside the central bore of the fiber. These ENZ nanostructured optical fibers have many potential applications, for example, in ENZ nonlinear and magneto-optics, as in-fiber wavelength-dependent filters, and as subwavelength fluid channel for optical and bio-photonic sensing.

High-sensitivity refractive index sensor with normal incident geometry using a subwavelength grating operating near the ultraviolet wavelength

Abstract: A high-sensitivity refractive index sensor is demonstrated for the first time, near the ultraviolet (UV) wavelength region using a Si3N4-subwavelength grating (SWG) with a normal incident optical geometry. Using the eigenmode within the Si3N4-SWG, a high sensitivity for the refractive index is expected by finite-difference time-domain calculation, without an oblique incident geometry. The proposed SWG is fabricated and the high-sensitivity refractive index sensor operating near the UV wavelength is experimentally and successfully developed. The normal transmitted intensity through the fabricated SWG varies considerably with slight changes in the refractive index. The experimental sensitivity of the SWG attained 1240 % per refractive index unit (RIU) and the sensitivity shows good agreement with the calculation. These experimental results suggest that our refractive index sensor with a normal incident geometry can measure a refractive index change of 8.06 x 10-4 RIU, if the optical detection system can measure an intensity change of 1%.

On the possibility of mid-IR supercontinuum generation in As-Se-Te/As-S core/clad fibers with all-fiber femtosecond pump source

Abstract: We propose and optimize theoretically a supercontinuum (SC) laser source in the mid-IR based on using As-Se-Te/As-S core/clad step-index fibers and a femtosecond all-fiber laser system at 2 μm. Numerically simulated spectra extending from ~ 1 μm to > 8 μm are demonstrated for pump energy of order 100 pJ in a fiber with a core diameter of 2 μm. To the best of our knowledge, the possibility of such long-wavelength spectral conversion of pump pulses at the wavelength of 2 μm in optical fibers is demonstrated for the first time. The theoretical calculations are performed on the base of real low loss step-index As-Se-Te/As-S glass fibers with various core-clad diameter ratios.

Sensitivity-enhanced single-mode fiber-tapered hollow core fiber-single-mode fiber Mach-Zehnder interferometer for refractive index measurements

Abstract: In this paper, a sensitive-enhanced single-mode fiber—tapered hollow core fiber—single-mode fiber Mach–Zehnder interferometer is demonstrated for refractive index sensing. The sensitivity was improved by forming an up-taper at the two splicing joints and concave cone in hollow core fiber. The up-tapered regions served as a more effective mode splitter/combiner, and the tapered hollow core fiber was used to generate a stronger evanescent field to enhance the interaction of light with the analyte. According to the principles of interference between the cladding and fundamental modes, we performed refractive index measurements. The experiments indicated that the proposed sensor has a high refractive index sensitivity of 214.97 nm/RIU in the refractive index range of 1.333–1.379, with a minimum refractive index measurement resolution of 9.3 × 10−5. In addition, the sensor had a low temperature response of 2.96 pm/°C in the range from 50 to 85°C and a low cross sensitivity of 1.377 × 10−5 RIU/°C. The p...

All-Optical Mode Conversion and Temperature Sensing via Transient Grating in Step-Index Fiber

Abstract: We demonstrate the formation of Kerr-induced transient long period grating in a standard single-mode fiber (SMF28) using sub-nanosecond laser pulses, which can be used to realize an efficient all-optical mode conversion and temperature sensing. The fiber supports $LP_{01}$ and $LP_{11}$ spatial modes at 1064-nm wavelength. The beating between two guided modes induces refractive index grating exploiting the Kerr effect. The probe beam co-propagating with the pump at the same wavelength but with different polarization exhibits efficient mode conversion efficiency from $LP_{01}$ to $LP_{11}$ mode. Temperature sensitivity is measured owing to the change in mode conversion efficiency due to the shift in resonant peak wavelength with the increase in temperature. The change in temperature is manifested by the change in spectral power of probe beam at the output. The experimental result demonstrates an average temperature sensitivity of 0.15 Watt/°C. The transient nature of the grating with high sensitivity makes our approach unique from the existing results and can open a route for potential applications.

Study of the linearly polarized modes and power analysis of double-clad refractive index profile of a dispersion flattened step index fiber

Abstract: Design of double-clad or W refractive index profile of a dispersion flattened step index fiber which enables the understanding of various LP modes and their 2D as well as radial, intensity and amplitude plots. This index profile results in achieving high power in core for different values of core radius and waist radius of incident Gaussian beam. A comparative study is presented in this paper at three operating wavelengths. Optimal power in core (99.4 %) is observed at 1550nm for dispersion flattened fibers considering Fresnel reflection at the input end of the fiber.

Finite element BPM fiber modal instability modeling

Abstract: Two approaches are presented for detailed analysis of transverse mode instability in fiber amplifiers based on a scalar finite element beam propagation method (BPM). The first employs two beams: one propagating at a fundamental frequency and one de-tuned to the middle of the stimulated thermal Rayleigh scattering (STRS) gain peak. This method was found to suffer from a computational artifact causing it to converge in some cases to an unphysical solution. The second was based on the steady periodic method. This required more computational resources but was found to be reliable and not susceptible to the artifact mentioned above. This method was used to simulate step-index fiber amplifiers, large pitch photonic crystal fiber amplifiers, and a hybrid large pitch photonic bandgap fiber amplifier with reduced symmetry. Results for reference step index fiber amplifiers were found to be consistent with those obtained by other methods. The simulated instability threshold values all fell between 200 and 310 Watts showing relatively little variation among designs. Some areas for improvement in the method are discussed.

15-dB Raman Amplification of an Optical Orbital Angular Momentum Mode in a Step-Index Fiber

Abstract: We experimentally demonstrate 15-dB Raman amplification of 1115-nm, 20-ns pulses of charge l =+2 orbital angular momentum mode in a 5-m multimode-pumped step-index fiber with measured mode purity of 83.2%.

High-Power Gaussian Beam Amplification of a Large-Mode-Area Inverse-Step-Index Fiber by Thermally Induced Parabolic-Index Guide

Abstract: We propose a method for high-power Gaussian beam amplification of an active-ion-doped inversestep- index fiber. Our method is to induce a strong thermal parabolic index distribution on a fiber core cross section. We show that a single Gaussian beam can be guided by the thermally induced parabolic index formed on an inverse-step-index fiber cross section while maintaining a very low propagation loss coefficient. To prove this numerically, we use the parameters of a laser glass with a high thermo-optic coefficient. Thus, we numerically demonstrate kilowatt-level Gaussian beam amplification of an inverse-step-index fiber amplifier by thermally inducing a high refractive index with a parabolic shape.

Analysis of Noiseless Static Optical C 2 DMA Correlation Receivers Using Fiber Bragg Grating or Multimode Step Index Fiber under the Effect of Pulse Broadening

Abstract: Optical communications is becoming an increasingly popular technique to transmit data. In our daily life we share useful data by using optical networks. However, a common problem that system face is dispersion. In this work, we discuss some forms of dispersion in ordinary fibers and Fiber Bragg Grating (FBG). In optical communication systems, FBG plays a vital role as filters, dispersion compensators and flatteners gain. The performance analysis of static 1D/2D wavelength hopping/time spreading CDMA static is introduced. The probability of error is computed for general systems based on asymmetric prime-hop codes (APHCs). A comparison between FBG and multimode step index fibers reveals, in general, that FBG is one of the most applicable components to compensate dispersion losses in optical communication systems. Furthermore, it is better than multimode and single-mode fibers.