Design of double-coated optical fibers to minimize long-term hydrostatic-pressure-induced microbending losses

The design of double-coated optical fibers to minimize long-term hydrostatic-pressure-induced microbending losses is investigated. Microbending loss in these fibers is dominated by compressive radial stress at the interface between the glass fiber and the primary coating, which is a function of the material properties of the polymeric coatings and their thickness. To minimize long-term hydrostatic-pressure-induced microbending losses, one should decrease the Young's modulus and Poisson ratio of the primary coating but increase the radius, Young's modulus, Poisson ratio, and relaxation time of the secondary coating. Alternatively, the radius and relaxation time of the primary coating have their optimum values.     

Minimization of low-temperature microbending losses in initially curved tightly jacketed double-coated optical fibres

Thermally induced microbending losses in initially curved tightly jacketed double-coated optical fibres at low temperature are investigated. The initial deflections are described by a more general formula. The deflections in an initially curved fibre increase gradually with increasing thermally induced compressive axial force, and result in an increase of microbending loss. In order to minimize such a microbending loss, the Young's modulus and Poisson's ratio of the primary coating should be increased. The best value of the Poisson's ratio of the primary coating is 0.5. On the other hand, the thickness of the primary coating, the Young's modulus and effective thermal expansion coefficient of the secondary coating, and the thickness, Young's modulus and effective thermal expansion coefficient of the jacket should be decreased. These results are compared to those of double-coated optical fibres. Thermally induced lateral pressure in the glass fibre can also produce microbending loss. When the effects of axial force and lateral pressure on the microbending losses are both considered, the optimum selection of polymeric coatings is to let the lateral pressure be less than zero, and the magnitude of lateral pressure and the ratio of the final-initial deflection be as small as possible. When the material properties of polymeric coatings and their thicknesses are selected, there are two ways to achieve the optimum design.     

Design guidelines and characteristics of beam-shaping microstructure optical fibers

Microstructure optical fibers with flat-top fundamental mode are first proposed by introducing a low-index inner core into the core of index-guiding microstructure optical fibers. The design guidelines and characteristics of beam-shaping microstructure optical fibers are demonstrated. The interrelationships of inner-core index with laser wavelength, air hole diameter and size of inner core are investigated. The influence of the relative size of inner core on the spatial profile of the fundamental mode is demonstrated. Moreover, sensitivity of the flat-top fundamental mode profile from the slight change of the optimum inner-core index value is studied. Starting from these results we deduce that it is possible to fabricate beam-shaping microstructure fibers with nowadays technique.     

Hydrostatic pressure and thermal loading induced long-term optical effects in tightly jacketed double-coated optical fibers

By the viscoelastic theory, the hydrostatic pressure and thermal loading simultaneously induced optical effects in tightly jacketed double-coated optical fibers in the long term are analyzed. Using the Laplace transformation method, close-form solutions for the microbending loss and refractive index changes are obtained in the transform domain. The results of the microbending loss are initially identical to those obtained by the elastic analysis, and then decrease gradually as time progresses. The microbending loss and refractive index changes of the glass fiber are functions of material properties of the coating layers and jacket. To minimize the microbending loss and refractive index changes in the long term, the viscosity ratio η₃/η₁, Young’s modulus ratio E₂/E₁ and E₃/E₁, and ratio of Poisson’s ratio ν₃/ν₁ should be increased. Nevertheless, the ratio of Poisson’s ratio ν₂/ν₁ should be decreased. PACS 42.79.Wc; 61.20.Lc; 68.65.Ac     

Structured electrodes on optical fibers

We have investigated three different techniques for electrode production directly on surfaces of D-shaped optical fibers. All three techniques were capable of producing suitable structural shapes and structural sizes for different metallic electrodes. The produced electrodes differ, however, in their electrical insulation properties and in the reproducibility of the electrode structures. Best results were achieved by a photolithographic structuring process.     

Calculation of nonlinear waves guided by optical fibers with an inhomogeneous nonlinear core

A circular optical fiber consisting of an inhomogeneous nonlinear core bounded by a linear cladding medium is considered here. In this case, the calculation of the nonlinear modes is of practical importance because of the joint effects of nonlinearity and inhomogeneity on the field concentration and the achievable optical confinement. Numerical results indicate that the combination of this type of inhomogeneity along with the characteristics of nonlinearity may play a significant role towards the optical confinement in the core.     

Diverse chirped optical solitons and new complex traveling waves in nonlinear optical fibers

This paper studies chirped optical solitons in nonlinear optical fibers. However, we obtain diverse soliton solutions and new chirped bright and dark solitons, trigonometric function solutions and rational solutions by adopting two formal integration methods. The obtained results take into account the different conditions set on the parameters of the nonlinear ordinary differential equation of the new extended direct algebraic equation method. These results are more general compared to Hadi et al(2018 Optik 172 545–53) and Yakada et al(2019 Optik197 163108).     

Analysis of Long-Term Optical Effects in Double-Coated Optical Fibers Induced by Hydrostatic Pressure and Thermal Loading

The hydrostatic pressure and thermal loading simultaneously induced optical effects in double-coated optical fibers in the long-term are analyzed by the viscoelastic theory. Using the Laplace transformation method, close-form solutions for the microbending loss and refractive index changes are obtained. The results of the microbending loss are initially identical to those obtained by the elastic analysis, and then decrease gradually as time progresses. The microbending loss and refractive index changes of the glass fiber are functions of the material properties of the primary and secondary coatings. To minimize the microbending loss and refractive index changes in the long-term, the Young's modulus of the primary coating, and the viscosity and Poisson's ratio of the secondary coating should be increased. Nevertheless, the viscosity and Poisson's ratio of the primary coating, and the Young's modulus of the secondary coating should be decreased.     

Numerical calculation of cutoff frequencies of optical fibers by a variational technique

A numerical method for calculating cutoff frequencies of modes of weakly guiding optical fibers is described. Starting from a properly constructed field representation, the method follows a variational approach to obtain an eigenvalue problem for the cutoff frequencies which can be easily solved by a standard numerical routine. The field representation uses an expansion in terms of the Laguerre–Gauss functions in the fiber core and limiting form for small arguments of modified Bessel functions in the fiber cladding. Fibers with power-law refractive index profiles and fibers with a profile showing a dip on the axis are analyzed. Results obtained for modes of arbitrary order (both azimuthal and radial) show that our method is very efficient and accurate.     

光纤1/f热噪声的实验研究

光纤热噪声是限制光纤传感、测量系统性能的最终因素.但是低频区域呈1/f谱特性的光纤热噪声的形成机制迄今仍然存在争论.实验研究了光纤1/f热噪声水平与光纤内杂质离子浓度和光纤施加张力的关系,验证了这类热噪声来源于光纤内部的机械耗散引起的长度自发抖动,符合热机械噪声的理论假设.     

光纤技术在近红外光谱仪中的应用

探讨了光纤在近红外光谱技术应用中光纤材料选择、能量损耗和使用注意事项等问题。通过把光纤与近红外光谱技术相结合,使得近红外光谱仪从实验室走向现场,可适用于军事恶劣、危险和复杂的环境。为在军事条件下近红外光谱技术的应用提供了更大的空间。     

Parametric amplification and processing in optical fibers

We review recent progress made in parametric amplification and signal processing using high confinement fibers. In contrast to crystalline and semiconductor devices, fiber parametric amplifiers offer interaction lengths that can vary from 10 m to 1 km and are not limited by waveguide losses. The operation, design and impairment physics of general fiber parametric devices are reviewed. The technology prospects for advanced signal processing are discussed.     

Self-organized parametric down conversion and photoinduced reflectivity in optical fibers

We report new experimental results concerning self-organized nonlinear optical interactions in optical fibers. A self-organized parametric down conversion was observed if the second-harmonic seeding radiation had been above the saturation level. If furthermore increasing the second-harmonic input power a nearly total photoinduced reflectivity for the second-harmonic green light and about 50% reflectivity for the fundamental infrared radiation were observed.     

Modulation instabilities in randomly birefringent two-mode optical fibers

Modulation instabilities in the randomly birefringent two-mode optical fibers(RB-TMFs) are analyzed in detail by accounting the effects of the differential mode group delay(DMGD) and group velocity dispersion(GVD) ratio between the two modes, both of which are absent in the randomly birefringent single-mode optical fibers(RB-SMFs). New MI characteristics are found in both normal and anomalous dispersion regimes. For the normal dispersion, without DMGD,no MI exists. With DMGD, a completely new MI band is generated as long as the total power is smaller than a critical total power value, named by Pcr, which increases significantly with the increment of DMGD, and reduces dramatically as GVD ratio and power ratio between the two modes increases. For the anomalous dispersion, there is one MI band without DMGD. In the presence of DMGD, the MI gain is reduced generally. On the other hand, there also exists a critical total power(Pcr), which increases(decreases) distinctly with the increment of DMGD(GVD ratio of the two modes) but varies complicatedly with the power ratio between the two modes. Two MI bands are present for total power smaller than Pcr, and the dominant band can be switched between the low and high frequency bands by adjusting the power ratio between the two modes. The MI analysis in this paper is verified by numerical simulation.     

Sensing ammonia with ferrocene-based polymer coated tapered optical fibers

Abstract

The application of ferrocene-based polymers as variable index materials is discussed. The refractive index of thin film of a particular polymer known as poly(methylphenylsilyeneferrocenylene) is examined during exposure to ammonia, nitrous oxide, nitric oxide, nitrogen, carbon dioxide, carbon monoxide, and argon. A maximum of 9% deviation in the refractive index of the polymer upon exposure to ammonia is observed. The theory of operation and fabrication of polymer-coated tapered optical fiber gas sensors are explained. Experimental data is presented showing qualitative response to ammonia and other gases.     

Sensing ammonia with ferrocene-based polymer coated tapered optical fibers

The application of ferrocene-based polymers as variable index materials is discussed. The refractive index of thin film of a particular polymer known as poly(methylphenylsilyeneferrocenylene) is examined during exposure to ammonia, nitrous oxide, nitric oxide, nitrogen, carbon dioxide, carbon monoxide, and argon. A maximum of 9% deviation in the refractive index of the polymer upon exposure to ammonia is observed. The theory of operation and fabrication of polymer-coated tapered optical fiber gas sensors are explained. Experimental data is presented showing qualitative response to ammonia and other gases.     

Optical characterization of quantum dots entrained in microstructured optical fibers

We present a study of the basic optical properties of colloidal CdSe/ZnS core/shell quantum dots entrained in a microstructured optical fiber. Quantum dots suspended in heptane were pulled into the holes surrounding the solid core of a microstructured optical fiber of the holey fiber class via capillary action and are found to remain in the fiber. In this experiment, a laser coupled into the fiber photoexcited quantum dots along the length of the fiber. Quantum dot emission was observed to couple into the fiber core and propagate along the fiber. To investigate the use of such a system in fiber-based light generation or amplification, a second laser overlapping the low-energy portion of the quantum dot emission was simultaneously coupled into the fiber. We observed apparent amplification of this light when photoexciting the quantum dots well above their bandedge.     

A rigorous analysis of the power distribution in plastic clad annular core optical fibers

Using Maxwell's field equations, an analytical investigation is presented of the relative power distributions in the different sections of a step-index plastic clad annular core optical fiber (ACF) operating in the infrared region of the electromagnetic (EM) spectrum. It is assumed that the fiber cross-section is made of two concentric circles, and the EM waves propagate through the annular region. The chosen fiber materials are widely used in low cost optical links. The wave equations are solved in the different sections of the fiber, and the general expressions for power in the core and the cladding regions are finally deduced. Plots are shown of the variation of fractional power (or the power confinement factor) in all the fiber sections against the propagation constants of sustained modes. The cases of three lowest azimuthal modal indices (i.e. meridional as well as skew modes) are described. It is observed that the confinement of power in the core section is increased for ACFs of larger cross-sectional dimensions. Also, a fairly uniform distribution of power over the sustained modes remains for large sized fibers, and this uniformity is greatly affected in ACFs of smaller dimensions. It is suggested that, because of strong evanescent fields, ACFs can be of potential use in chemical sensing. Apart from this, it is also presumed that these may be useful in the areas of communications. The improved mechanical strength adds the potentiality of ACFs.     

Design theory and experiment of acousto-optical tunable filter by use of flexural waves applied to thin optical fiber

Spectral response of acoustically induced microbending through thin optical fiber is discussed from mode-coupling of core and cladding modes. The thin fiber is analyzed in three-layered structure (core-cladding-air) to gain insights into acousto-optic modulation. We explained the dependence of core and/or cladding diameters on acoustic source parameters from numerical calculations. According to the calculations, we successfully fabricated all-optical tunable filter using this thin fiber that yields an efficient mode-coupling at flexural wave frequencies less than 1MHz. To increase the acousto-optic effect, we used a specially designed thin optical fiber (80 μm of cladding diameter) in the section where flexural wave is produced, and spliced both ends of the thin fiber to the tapered 125 μm fibers. The frequency and voltage tuning of fabricated filter is also confirmed by changing the driven frequency and applied voltage of the PZT, respectively. This result suggests a possibility of fiber-optic device application as all-optical tunable filter at 1.55 μm.