Characterization of microstructured optical fibers for wideband dispersion compensation

Microstructured optical fibers (MOFs) with small hole-to-hole spacing and large airholes are designed to compensate the anomalous dispersion and the dispersion slope of single-mode fibers. The geometrical parameters that characterize triangular MOFs are chosen to optimize the fiber length and the compensation over a wide wavelength range. A proper design of the photonic crystal fiber geometry allows us to achieve dispersion values of approximately -1700 ps nm(-1) km(-1) at 1550 nm and to compensate the dispersion of standard fibers within +/- 0.5 ps nm(-1) km(-1) over a 100-nm range. The MOF dispersion properties have been studied by means of a numerical simulator for modal analysis based on the finite-element method.     

High numerical aperture in multimode microstructured optical fibers

Microstructured or "air-clad" fibers, with air holes surrounding a large core, have recently demonstrated much wider light-acceptance angles than conventional fibers. An original and accurate method is presented for determining the numerical aperture of such fibers using leaky modes. The dependence on length, wavelength, and various microstructure dimensions are evaluated for the first time for a class of fibers that exhibit exceptionally high numerical apertures. These results show excellent agreement with published measurements on similar fibers and verify that bridge thicknesses much smaller than the wavelength are required for high numerical apertures.     

Nanoparticle layer deposition for plasmonic tuning of microstructured optical fibers

Plasmonic nanoparticles with spectral properties in the UV-to-near-IR range have a large potential for the development of innovative optical devices. Similarly, microstructured optical fibers (MOFs) represent a promising platform technology for fully integrated, next-generation plasmonic devices; therefore, the combination of MOFs and plasmonic nanoparticles would open the way for novel applications, especially in sensing applications. In this Full Paper, a cost-effective, innovative nanoparticle layer deposition (NLD) technique is demonstrated for the preparation of well-defined plasmonic layers of selected particles inside the channels of MOFs. This dynamic chemical deposition method utilizes a combination of microfluidics and self-assembled monolayer (SAM) techniques, leading to a longitudinal homogeneous particle density as long as several meters. By using particles with predefined plasmonic properties, such as the resonance wavelength, fibers with particle-adequate spectral characteristics can be prepared. The application of such fibers for refractive-index sensing yields a sensitivity of about 78 nm per refractive index unit (RIU). These novel, plasmonically tuned optical fibers with freely selected, application-tailored optical properties present extensive possibilities for applications in localized surface plasmon resonance (LSPR) sensing.     

Prediction of light-transmission losses in plastic optical fibers

A theoretical expression is derived, based on a geometrical optics approach, with which to predict light-transmission losses in multimode plastic optical fibers for office or home lighting. Two types of optical ray arrangement, meridional ray and skew ray, are evaluated, and five loss mechanisms are identified and considered. The meridional arrangement results in a lower overall loss of light than the skew ray arrangement. The theoretical results were compared with experimental measurements taken for a 0.5-cm-diameter polymer optical fiber. For optical rays entering the fiber at incident angles of less than 20 degrees, the theoretical results are in good agreement with the empirical results.     

Power losses in bent and elongated polymer optical fibers

This study performs experimental and numerical investigations into the power losses induced in bent, elongated polymer optical fibers (POFs). The theoretical analysis is based on a three-dimensional elastic-plastic finite-element model and makes the assumption of a planar waveguide. The finite-element model is used to calculate the deformation of the elongated POFs such that the power loss can be analytically derived. The effect of bending on the power loss is examined by considering seven different bend radii ranging from 10 to 50 mm. The results show that bending and elongation have a significant effect on the power loss in POFs. The contribution of skew rays to the overall power loss in bent, elongated POFs is not obvious at large radii of curvature but becomes more significant as the radius is reduced.     

Power losses in deformed graded-index polymer optical fibers

We investigate the power losses in bent and elongated graded-index polymer optical fibers (GI POFs). The variations of power losses in deformed GI POFs for various radii of curvature and elongations are measured. A simple tensile test result is used to calculate the average plastic energy density (APED) in a deformed GI POF at various elongations. The results indicate that the APED accumulated in a deformed GI POF can be considered as a key index to study the power loss in POF. Based on the experimental results, a curve-fitted equation is proposed to estimate the power loss using the APED for various radii of curvature. The maximum difference between the proposed equation and the experimental results is less than 3% for the deformed GI POFs.     

Simple method of measuring scattering losses in optical fibers

A simple method of measuring the scattering losses of optical fibers was developed. The method permits the measurement of the scattering-loss spectra by use of photon counting. Measurement is based on right-angle scattering, which is dominated by Rayleigh scattering, a material-intrinsic loss. A reference fiber for which the scattering loss is known is used to cancel out the unknown factors that are dependent on the optical setup. The scattering-loss measurement was demonstrated by use of two different low-loss fibers and was found to agree with predetermined figures to within 10% over the wavelength range 0.44-1.0 mum. Finally, the method was applied to a new high-numerical-aperture optical fiber to find its material scattering loss.     

Effect of metal coating on the optical losses in heated optical fibers

The effect of heating in air on the optical losses in metal-coated fibers has been studied. Two fibers were drawn from the same silica preform and coated by different metals (copper and aluminum). Dependences of a change in the optical losses on the temperature were measured in a 20–400°C range at a 50°C step. The optical losses of metal-coated fibers heated to temperatures below 300°C change mostly due to the microbending contribution. At temperatures above 300°C, the main contribution to increasing optical losses is due to the absorption on OH groups. It is established for the first time that the contribution to optical losses due to the OH groups is much more pronounced in Al-coated fibers than in Cu-coated ones. In addition, the Al-coated fibers exhibit growth in the optical losses above 300°C due the absorption on molecular hydrogen.     

Modal field deformation and transition losses in UV side-written optical fibers

The asymmetry of the UV-induced refractive-index profile in photosensitive optical fibers causes a deformation of the modal fields, resulting in transition losses between UV-exposed and unexposed fiber sections up to 0.1 dB for UV-induced index changes of the order of 相似文献   

Determination of modal effective indices and dispersion of microstructured fibers with different configurations: a variational approach

A simple semi-analytical model based on the variational method is developed for determining the effective indices of the fundamental modes and consecutively the dispersion properties of microstructured optical fibers (MOFs) with different lattice geometries without resorting to any numerical tool. We consider an equivalent step-index (ESI) profile of the MOF and the fundamental mode shape is approximated as a simple Gaussian function in the core. Effective index data and dispersion obtained from the proposed variational method offer reasonable agreement with numerically derived data using the Finite Element Method (FEM). The proposed model offers an alternative and swift way for reasonably precise determination of the effective index of the fundamental mode and dispersion properties of MOF designs with different lattice geometries. Finally, as a major application, the dispersion property of a fabricated MOF, derived through the proposed variational method, is directly used in order to model experimental supercontinuum (SC) spectra with satisfactory agreement.     

Circular fourier analysis of modes of microstructured optical fibers with complex channel cross sections

A method for calculating the properties of microstructured optical fibers (MOFs) with complex channel cross sections has been developed and applied to studying leaky modes in MOFs with elliptical channels. It is demonstrated that MOFs can exhibit significantly anisotropic damping of the modes with orthogonal polarization.     

The properties of modes in microstructured optical fibers in the vicinity of critical conditions

A new method based on the analysis of integral equations is proposed for calculating the properties of microstructured optical fibers (MOFs) and used for the analysis of modes in MOFs in the vicinity of critical conditions. Slow leaky modes are found that can influence the MOF transmission.     

Effect of elongation deformation on power losses in polymer optical fibers

We investigate the effect of fiber elongation on power loss as rays propagate along deformed polymer optical fibers (POFs). Variations in core diameter, incident angle, stress and strain distributions, and necking of the POFs during fiber elongation are studied. The power losses in the deformed POFs are analyzed both experimentally and numerically. Theoretical analysis based on an elastic-plastic finite-element model and a planar waveguide assumption is proposed. It is found that fiber elongation significantly affects the power loss in POFs, particularly at higher values of elongation. Good agreement between the measured results and the results simulated from the proposed model is obtained. The maximum difference is less than 5%. Results indicate that the proposed theoretical analysis based on an elastic-plastic finite-element model and a planar waveguide assumption is feasible to predict the power loss variation introduced by elongated deformations. A curve-fitted equation is also proposed to estimate the power loss of POFs under different fiber elongation conditions.     

Dependence of bending losses on cladding thickness in plastic optical fibers

Our main goal is to provide a comprehensive explanation of the existing differences in bending losses arising from having step-index multimode plastic optical fibers with different cladding thickness and under different types of conditions, namely, the variable bend radius R, the number of fiber turns, or the fiber diameter. For this purpose, both experimental and numerical result of bending losses are presented for different cladding thicknesses and conditions. For the measurements, two cladding thicknesses have been considered: one finite and another infinite. A fiber in air has a finite cladding thickness, and rays are reflected at the cladding-air interface, whereas a fiber covered by oil is equivalent to having an infinite cladding, since the very similar refractive index of oil prevents reflections from occurring at the cladding-oil interface. For the sake of comparison, numerical simulations based on ray tracing have been performed for finite-cladding step-index multimode waveguides. The numerical results reinforce the experimental data, and both the experimental measurements and the computational simulations turn out to be very useful to explain the behavior of refracting and tunneling rays along bent multimode waveguides and along finite-cladding fibers.     

Amplification of frequency-modulated pulses in graded dispersion erbium-doped optical fibers

The possibility of effective amplification of self-similar frequency-modulated pulses in longitudinally nonuniform erbium-doped optical fibers has been studied. A general expression is obtained for the coordinate dependence of the normal dispersion of group velocities that ensures ??fast?? amplification of the frequency-modulated pulses. It is shown that, at an optimum choice of the dispersion profile, subpicosecond pulses can be amplified up to energies above 1 nJ and peak powers above 50 kW.     

Numerical analysis of modal dispersion in graded-index plastic optical fibers

Modal dispersion properties of a fabricated plastic optical fiber are numerically calculated through a finite-element method. The modal index, group delay, impulse response, and output pulse shape are compared with those for the power-law profile plastic optical fiber; the influence of index profile deviations from the power-law profile is described. It is shown that index profile fluctuations in the actual index profile strongly affect the group delays, even though they are relatively small. On the other hand, they have little effect on the modal indices.     

New phospho-tellurite glasses with optimization of transition temperature and refractive index for hybrid microstructured optical fibers

The glass formation and compositional dependences of glass thermal properties and optical properties were investigated in TeO₂–ZnO–Na₂O–P₂O₅ system. The refractive index at 1.55 μm and glass transition temperature varied in a wide range from 1.513 to 2.036 and from 265 °C to 376 °C by controlling of the TeO₂/P₂O₅ and ZnO/Na₂O content, respectively. These properties enable phospho-tellurite glasses with large freedom in designing and fabrication of hybrid microstructured optical fiber. The structures of glasses were investigated by Raman spectra to understand their dependence of structure on composition. Using the present glasses, some hybrid microstructured optical fibers with various dispersion profiles were designed.     

Mechanical properties of microstructured high-purity silica fibers

We have studied the effect of drawing conditions and process environment on the mechanical strength of microstructured optical fibers. The results indicate that, even at reduced drawing temperatures, high-strength fibers with few “weak” points can be produced provided that the walls of the holes in the preform are sufficiently clean. The effects of air humidity and different liquids in the holes on the strength of microstructured fibers are shown to be similar to those for standard fibers.     

Polarization-maintaining optical fibers with low dispersion over a wide spectral range

The total dispersion characteristics of the doubly clad Panda (or bow-tie) fibers have been investigated. It is shown that the contribution of the photoelastic effect to the total dispersion becomes of the order of several psec/km x nm in the 1.5-1.7-microm wavelength region. By careful adjustment of the cutoff wavelength, the total dispersion is reduced to within +/- 1 psec/km x nm over the 1.38-1.70-microm wavelength region for the HE(11)(x) mode and 1.38-1.68 microm for the HE(11)(y) mode, respectively.     

Bright and dark solitons in the normal dispersion regime of inhomogeneous optical fibers

In this letter, under investigation is a nonlinear Schrödinger equation with varying dispersion, nonlinearity and loss for the propagation of ultra-short optical pulses in the normal dispersion regime of optical fibers. By virtue of the modified Hirota's method and symbolic computation, the analytic two-soliton solution is explicitly obtained. Both the bright and dark solitons are observed in the normal dispersion regime of optical fibers with dispersion management. An asymptotic analysis to verify the elastic collision between solitons is performed and the stability of the soliton solutions is investigated. Besides, a new bright solitonic generator for generating high-power and narrow bandwidth pulses is advised. Furthermore, possible applicable soliton control techniques which might be used for the design of optical switch and dispersion-managed systems are proposed.