Cladding Of Optical Fiber Research Articles

Investigation on characteristics of W-type fiber with an inner cladding made of negative refractive index materials

A doubly clad optical fiber with an inner cladding made of negative refractive index material was proposed and the modes distribution, dispersion and time delay were investigated by fully vectorial numerical method. The results indicate that HE12 mode can be operated as a single mode, the cut-off frequency of modes shifts to low normalized frequency with increasing thickness of inner cladding made of negative index materials, large negative dispersion and time delay can be obtained and tailored by the inner cladding. These results provide theoretical basis for designing novel fibers or optical devices.

Feasibility study on fiber-optic goniometer for measuring knee joint angle

In this study, we fabricated a fiber-optic goniometer using a plastic optical fiber, a light-emitting diode, and a photodiode. The cladding of the plastic optical fiber was removed at 0.5–3mm intervals regularly to increase the bending loss of the plastic optical fiber. Also, the output voltages of the photodiode based on light intensity that measured using the fiber-optic goniometer were measured light intensities using the fiber-optic goniometer were measured to evaluate the linearity of the fiber-optic goniometer. Finally, we measured the responses of the fiber-optic goniometer for gait speeds of 3, 5, and 10 km/h using a data acquisition board and a LabVIEW program.

Analysis of surface plasmon resonance in bent single-mode waveguides with metal-coated cladding by eigenmode expansion method.

A numerical study is presented of surface plasmon waves excitation in a metal film applied to the cladding of a standard bent single-mode optical fiber. It was shown that by adjusting the bend radius and metal film thickness one can achieve effective coupling between the fiber fundamental mode and symmetric surface plasmon mode through the intermediary of whispering gallery modes supported by the cladding of the bent fiber. This effect is demonstrated to allow for refractometric measurement both in the wavelength and intensity-modulated regimes with a resolution of up to 10⁻⁸ RIU. Usage of standard noise reduction techniques for intensity-modulated optical signals promises further increase in accuracy.

An optical amplifier having 5 cm long silica-clad erbium doped phosphate glass fiber fabricated by “core-suction” technique

We have fabricated an erbium-doped phosphate glass fiber with a silica cladding and used 5cm length of it to form an optical amplifier. A bulk erbium phosphate glass called MM2 was used as a core glass in a silica cladding tube to prepare a preform using “core-suction” technique. This MM2 glass preform was drawn to a fiber and the resultant fiber was of good optical quality, free from air bubbles and major defects. The fiber was mechanically strong enough to allow for ease of handling and could be spliced to conventional silica fiber using commercial fusion splicer. This fiber was then used to setup an EDFA. Our work demonstrates the potential to form silica clad optical fibers with phosphate cores doped with very high levels of rare-earth ions. It is demonstrated that the core suction technique can be used to make a high-gain erbium phosphate fiber amplifier that is compatible with conventional silica fibers.

A simple small size and low cost sensor based on surface plasmon resonance for selective detection of Fe(III).

A simple, small size, and low cost sensor based on a Deferoxamine Self Assembled Monolayer (DFO-SAM) and Surface Plasmon Resonance (SPR) transduction, in connection with a Plastic Optical Fiber (POF), has been developed for the selective detection of Fe(III). DFO-SAM sensors based on appropriate electrochemical techniques can be frequently found in the scientific literature. In this work, we present the first example of a DFO-SAM sensor based on SPR in an optical fiber. The SPR sensing platform was realized by removing the cladding of a plastic optical fiber along half the circumference, spin coating a buffer of Microposit S1813 photoresist on the exposed core, and finally sputtering a thin gold film. The hydroxamate siderophore deferoxamine (DFO), having high binding affinity for Fe(III), is then used in its immobilized form, as self-assembled monolayer on the gold layer surface of the POF sensor. The results showed that the DFO-SAM-POF-sensor was able to sense the formation of the Fe(III)/DFO complex in the range of concentrations between 1 μm and 50 μm with a linearity range from 0 to 30 μm of Fe(III). The selectivity of the sensor was also proved by interference tests.

Polarization-selective excitation of plasmonic resonances in silver nanocube random arrays by optical fiber cladding mode evanescent fields

Silver nanocubes provide polarization resolved enhancement of the evanescent waves of optical fiber cladding modes.

Effective Permittivity of Ultrathin Chemical Vapor Deposited Gold Films on Optical Fibers at Infrared Wavelengths

The geometry- and size-dependent effective medium properties of ultrathin gold films deposited on the bare cladding of single mode optical fibers by chemical vapor deposition are characterized by measuring the polarized transmission spectra of in-fiber gratings at wavelengths near 1550 nm. The real part of the complex refractive indices of films with average thicknesses ranging from 6 to 65 nm are about 10 times higher than that of bulk gold at these wavelengths, while the imaginary part values are 2 orders of magnitude lower. The films are essentially isotropic, apart from a small increasing dichroism between the in-plane and out-of-plane component of the imaginary part of the refractive index at thicknesses larger than 25 nm. Unlike gold films prepared by other means, the optical properties of the coatings do not converge rapidly toward bulk values at thicknesses larger than 10 nm but remain characteristic of gold films prepared by very slow physical deposition processes. The modified Clausius–Mossotti ...

Evolution of modes in double-clad Raman fiber amplifier

Stimulated Raman scattering in a double cladding optical fiber is studied with a continuous wave laser used as a pump source. Under various launch conditions, pump modes are differently excited. Considering the mode coupling effect among the pump modes, the evolution of the power in the Stokes modes is studied. The results show that the scattered waves (the Stokes waves) in the fiber core with 9-μm diameter and 0.14 NA could propagate predominantly in the fundamental mode of the fiber by carefully adjusting the pump light launching conditions.

Refractive index sensitivity enhancement of optical fiber cladding mode by depositing nanofilm via ALD technology

The atomic layer deposition (ALD) technology is introduced to enhance the sensitivity of optical fiber cladding mode to surrounding refractive index (SRI) variation. The highly uniform Al2O nanofilm was deposited around the double cladding fiber (DCF) which presents cladding mode resonant feature. With the high refractive index coating, the cladding mode resonant spectrum was tuned. And the sensitivity enhancement for SRI sensor was demonstrated. Through adjusting the deposition cycles, a maximum sensitivity of 723 nm/RIU was demonstrated in the DCF with 2500 deposition cycles at the SRI of 1.34. Based on the analysis of cladding modes reorganization, the cladding modes transition of the coated DCF was investigated theoretically. With the high performance nanofilm coating, the proposed SRI sensor is expected to have wide applications in chemical sensors and biosensors.

Selective Excitation of Radially and Azimuthally Polarized Optical Fiber Cladding Modes

The dominant polarization properties of the cladding modes excited by tilted fiber Bragg gratings are investigated. Even in conventional cylindrically symmetric fibers, by orienting the input core mode polarization with respect to the tilt plane of the grating cladding modes with near complete radial or azimuthal polarization can be excited at well separated wavelengths, as confirmed by experiments.

Sensors based on surface plasmon resonance in a plastic optical fiber for the detection of trinitrotoluene

The objective of this study is to present an optical chemical sensor based on surface plasmon resonance (SPR) in a plastic optical fiber (POF) for the selective detection and analysis of trinitrotoluene (TNT) in aqueous solution.The fabricated optical chemical sensor was realized removing the cladding of a plastic optical fiber along half the circumference, spin coating on the exposed core a buffer of Microposit S1813 photoresist, and finally sputtering a thin gold film. A molecularly imprinted polymer (MIP) film was, then, deposited on the thin gold film to allow the selective detection of TNT. The film was a methacrylic acid-divinyl benzene copolymer obtained by radicalic polymerization at high temperature.The experimental results show that the use of MIP layer is suitable for highly selective detection of TNT, down to about 50μM (i.e. ∼11μg/ml). This shows that the direct detection of a low molecular mass substance is possible by SPR transduction, even at low concentration. Furthermore, the proposed sensing head is low cost and relatively easy to realize, and may be very attractive for the detection and analysis of trinitrotoluene (TNT), in particular considering that it does not involve the use of any electrical devices and it can be used for remote/online monitoring exploiting, f.i., a fiber optic link.

Visible and near infrared up-conversion luminescence in Yb3+/Tm3+ co-doped yttria-alumino-silicate glass based optical fibers

We report blue light up-conversion (UC) emission in Yb–Tm co-doped nano-phase separated yttria-alumino-silicate (YAS) glass based D-shaped with low-index cladding optical fibers. Y2O3 creates an environment of nano structured YAS glass phases with Yb and Tm rich zone into the core glass which confirmed from TEM analyses. This kind of glass host assists in distributing of Yb and Tm rich zone uniformly throughout the core region. Yb and Tm doped regions exist mainly into nano YAS phases, defined as RE rich nano YAS-RE phases. All samples exhibit UC luminescence peaks at 483nm, 650nm and 817nm for Tm3+ and 1044nm for Yb3+ under excitation by 975nm laser light. In such type of nano-engineered glass–ceramic based host, almost all the Yb ions transferred its energy to the nearer Tm ions. In particular 483nm emission is attributed to 1G4→3H6 transition through a three step resonance energy transfer (ET) from excited Yb3+. The highest emission intensity is obtained with a concentration of 0.5wt% Tm3+ and 2.0wt% Yb3+. The ET between Yb3+ and Tm3+ is increased with increase of Yb3+ concentration with respect to Tm3+. The experimental fluorescence life-times of Tm3+ upconversion emission at visible wavelengths into such kind of fiber is reported under 975nm pump excitation. The present study is important for development of an efficient tunable 483nm fluorescence light source.

Synthesis and characterization of spinel MgAl2O4 thin film as sapphire optical fiber cladding for high temperature applications

Spinel MgAl2O4 thin films have been coated on ϕ75-μm single crystal sapphire fibers and sapphire wafers by low-temperature (700°C) firing of (Mg2+,Al3+)-chelated polymeric precursor films. The MgAl2O4 coating was demonstrated to be chemically stable on sapphire substrate at temperatures as high as 1200°C. No evidences of solid state reactions or ion diffusion between the MgAl2O4 and sapphire layers were found by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy examinations for the samples annealed at 1200°C for 672h. The refractive indices of the MgAl2O4 films fired at 1000°C and 1200°C were close to the index of MgAl2O4 single crystal but slightly smaller than that of the sapphire fiber. The MgAl2O4 thin film-coated sapphire fiber exhibited a dramatically reduced numerical aperture and improved preservation of transmitting light intensity as compared to the uncoated fiber. Results of this study demonstrate that the MgAl2O4 thin film is suitable for sapphire fiber cladding for high temperature applications.

Modal characteristics analysis of a doubly clad optical fiber with semi-weakly guiding approximation

Modified characteristic equations for doubly clad multimode fibers were rigorously derived under semi-weakly guiding approximation in this article. The analytical expressions of the power flows distributed in the three regions of fiber cross section are also given. Different from previous works, results in this paper elucidate that, other than the inner cladding, the refractive indices also hold a non-ignorable influence on the modal power distribution and mode behaviors. By comparing the results of two models, this article demonstrates that the singly clad fiber model may not be suitable for analyses of common doubly clad fibers.

Femtosecond Laser Structuring in Optical Fiber and Transparent Films

Femtosecond laser processing is optimized for writing optical circuits, optical resonators, and microfluidic devices inside the cladding of single-mode optical fiber that couple efficiently with the fiber core waveguide. The laser processes open new directions towards Lab- on-a-Fiber.

Calculation and simulation of optical fiber core and cladding mode effective refractive index

The accurate computation of effective refractive index of optical fiber core and the cladding mode are needed for the fiber structure design, mode dispersion analysis and fiber grating mode coupling research. In this paper, based on three layered optical fiber waveguide model and its accurate eigenvalue equation, by using the cut string algorithm the effective refractive index of core mode is solved. At the same time the computation results are verified by using COMSOL software. By using interval traversal algorithm the effective refractive index of cladding mode is computed. Compared with the existing algorithms, this method can avoid the loss of root during the calculation. It can also avoid the generation of odd point and can keep the normality of each mode. The simulation is based on Mathematica software. The curves relating effective refractive index of core and cladding mode to wavelength are obtained.

Multifocal multiphoton endoscope

We report a miniaturized resonant/non-resonant multi-fiber raster scanner that is paired with a gradient-index lens assembly to achieve a compact and flexible multifocal multiphoton endoscope capable of longitudinal parallel image acquisition. Multiphoton images are obtained simultaneously at three axial depths, separated by ≥4.8 μm, by incorporating three axially offset double clad optical fibers into the miniaturized scanner. The fabricated endoscope has an outer diameter of 3 mm, a rigid length of 4 cm, and acquires images at 4 frames/s per focal plane, with lateral and axial resolutions for two-photon imaging of 0.8 and 10 μm, respectively.

Light focusing at the end-face of a high-index cladding optical fiber

Modal analysis of a high-index cladding optical fiber reveals that it supports the radially polarized TM0r electromagnetic mode. Full-wave simulations of the electromagnetic fields of this mode emerging from the fiber end-face into free-space predict a light focusing effect. This focusing effect occurs at a characteristic distance from the end-face and it keeps its shape as it propagates in free-space.

A long-period grating written in the cladding of an optical fiber

A long-period grating (LPG) written in the cladding of an optical fiber is demonstrated.The optical fiber is specially designed and manufactured, which cladding is photosensitive, and core is not. The cladding LPG is written in by illuminating a cladding photosensitive fiber with an UV lamp through an amplitude grating mask. The cladding LPG is compared with a core LPG manufactured in the same way, and the property of the cladding LPG is different from that of the core LPG. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2425–2427, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26269

A Feasibility Study on the Use of Optical Fibers for the Transfer of Scintillation Light to Silicon Photomultipliers

Integrated PET/MRI units with simultaneous acquisition capability are set to play an important role in studies of human breast and prostate imaging and brain function. However, to take advantage of existing MRI units in hospitals and institutions, minimally modified combined PET MRI is highly desirable. In addition, the current MRI trend is to utilize powerful body coils to transmit radio-frequency (RF) waves and local RF coils to receive signals. The authors propose a silicon photomultiplier (SiPM) PET equipped with optical fiber bundles that transfer photons from scintillation crystal to SiPM. To investigate the feasibility of SiPM PET using optical fiber bundles, the authors studied the performances of SiPM/scintillator couplings using single optical fibers and a fiber bundle. GEANT4 Monte-Carlo simulation was used to study scintillation photon transfer from scintillation crystals to the SiPM. This simulation showed that light loss, due to the bending of an optical fiber, is not significant for a fiber with a diameter of 2.0 mm and a bending radius of greater than 25 mm. To validate the GEANT4 Monte-Carlo simulation, several simple detectors were assembled and tested. Simulation results agreed reasonably well with experimental results. Two Hamamatsu multi-pixel photon counters (MPPCs) were tested using double clad optical fibers of 1.5 mm and 2.0 mm diameter, and 25 mm and 50 mm bending radius, respectively. When two MPPCs were directly attached to 2.0 × 2.0 × 10.0 mm3 LYSO crystals, a ~14% energy and a ~1.3 ns coincidence timing resolution were obtained at full width half maximum (FWHM). With one of the MPPCs attached to an optical fiber of 1.5 mm diameter, 50 mm bending radius, and length 300 mm, energy and coincidence timing resolutions were 27% and 2.2 ns, respectively. With an optical fiber bundle made of bare fibers with 1.5 mm diameter and length 100 mm, an ~ 26% energy resolution was obtained. Even though the Monte-Carlo simulation showed light loss was not significant for a single 90° turn of bending, the mechanical integrity of the optical fiber, especially the absence of cracks which can be caused by sharp bending, seemed to be a far more important constraint on sharp bending. These initial results are encouraging with respect to the use of combined SiPM PET using optical fibers.