Thermal stress induced birefringence in double cladding fiber with non-circular inner cladding

Thermal stress induced birefringence due to the thermoelastic difference between the outer cladding and the non-circular inner cladding of a double cladding fiber (DCF) is theoretically investigated. A modified slab model is proposed to estimate the influence of the outer cladding on the birefringence property of the core. Numerical simulation is carried out to investigate the thermoelastic and geometric contributions of the cladding to thermal induced birefringence in rectangular and D-shaped ytterbium-doped DCFs. The thermoelastic relations deduced in the modified slab model are also qualitatively verified. Research shows that the influence of the outer cladding on the thermal-induced birefringence in DCF varies greatly depending on the choice of outer cladding materials, inner cladding shapes and temperature variation.     

Measurement of low-frequency ultrasonic wave in water using an acoustic fiber

An acoustic fiber sensor for measurement of ultrasonic waves, which used the approximate Raman-Nath diffraction effect where light diffraction waves were generated in an optical fiber by strain due to the ultrasonic waves, was proposed and examined. In order to characterize the acoustic fiber sensor as a basic study, measurements of low-frequency ultrasonic waves in water were examined using a step index fiber operating as a detection sensor. The results showed that characteristics of detected signals agreed with the theoretical prediction based on Fraunhofer diffraction. This indicates that our proposed fiber sensor can be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.     

Interaction of torsional waves with an annular crack in an infinitely long cylinder

The Hankel transform is used to obtain a complete solution for the dynamic stresses and displacements around a flat annular surface of a crack embedded in an infinite elastic cylinder, which is excited by normal torsional waves. The curved surface of the cylinder is assumed to be stress free. Solution of the problem is reduced to three simultaneous Fredholm integral equations. By finding the numerical solution of the simultaneous Fredholm integral equations the variations of the dynamic stress-intensity factors are obtained which are displayed graphically.     

Surface plasmon resonance in a bent single-mode fiber with a metallized cladding experimental research

The processes of surface plasmon resonance excitation in a bent single-mode optical fiber with a metallized cladding have been studied experimentally. It is shown that, for a certain combination of the bending radius of an optical fiber and the thickness of a metal film, a strong coupling between the fundamental and plasmon–polariton mode is achieved through a whispering gallery mode supported by the fiber cladding, which leads to the formation of a resonance dip with a depth of ~30 dB or more in the transmission spectrum of an optical fiber loop. The position of the dip depends strongly on the ambient refractive index, which provides the possibility of refractometric measurements with a spectral sensitivity of ~5 μm/RIU and a resolution of ~4 × 10^–6. Limits of measurement of the refractive index are determined by the operating spectral range and the bending radius of the optical fiber and are 1.42–1.44 for the setup used.     

Measurement of low-frequency ultrasonic wave in water using an acoustic fiber sensor.

An acoustic fiber sensor for measurement of ultrasonic waves, which used the approximate Raman-Nath diffraction effect where light diffraction waves were generated in an optical fiber by strain due to the ultrasonic waves, was proposed and examined. In order to characterize the acoustic fiber sensor as a basic study, measurements of low-frequency ultrasonic waves in water were examined using a step index fiber operating as a detection sensor. The results showed that characteristics of detected signals agreed with the theoretical prediction based on Fraunhofer diffraction. This indicates that our proposed fiber sensor can be used for the detection of low-frequency ultrasonic waves as well as the transmission of light diffraction signals.     

Interaction of axially symmetric waves with an annular crack in an infinitely long hollow cylinder

In this paper an analysis of the interaction of longitudinal waves with an annular crack in an infinitely long hollow cylinder is presented. Using Fourier sine and cosine as well as Hankel integral transforms, formal complete solutions to the governing equations are given. By means of Abel integral transform, the problem is reduced to the solution of a Fredholm integral equation of the second kind which is, then, solved numerically for a range of values of the frequencies of the incident waves. The numerical values of the dynamic stress intensity factor at the rim of the crack have been calculated.     

Characterization of broadband amplified spontaneous emission of erbium-doped tellurite fiber with D-shape cladding

In this presentation, we report the results of spectral characteristics of amplified spontaneous emission (ASE) from a newly Er3⁺-doped tellurite fiber with D-shape cladding. When pumped at 980 nm, an erbium ASE source that has nearly a flatten FWHM bandwidth of 100 nm is obtained in the D-shape cladding erbium-doped tellurite fiber with 30–60 cm length. The changes in ASE with regard to pumping power and fiber lengths were measured. Output power up to 2.0 mW is obtained with a total pump power of 660 mW.     

Characteristics of a long-period fiber grating with reduced cladding for refractive index sensing

The sensitivity to surrounding refractive index (SRI) of a long-period fiber grating (LPFG) can be effectively improved by decreasing the cladding radius. When the cladding is reduced, a three-layer model is necessary to evaluate the effective refractive index (ERI) of the core mode. A variation of SRI can induce a greater resonant wavelength shift when the core mode is coupled to a higher-order cladding mode. However, as the cladding is reduced further, the highest-order cladding mode would be cut off, i.e. the number of cladding modes that a given fiber structure can support would be less; thus, the higher-order cladding modes that can be used for higher sensitivity are limited. Hence, the implementation of high sensitivity for SRI sensing with cladding-reduced LPFGs is dependent on the proper combination of cladding radius and cladding mode order. Based on the vector coupled-mode theory, the transmission spectrum and sensitivity are numerically analyzed with respect to the cladding radius, which shows that the SRI sensitivity of the HE₁₂ mode with cladding radius a ₂?=?20?µm is 32 times as high as that with a ₂?=?62.5?µm and the SRI resolution is available to the order of 10^?7.     

InP薄膜内包层光纤放大性的理论计算

将纳米技术和光纤技术相结合，对研制出的纳米级InP薄膜内包层光纤进行光放大性能的测试，测试结果表明该光纤在很短的长度上具有比较好的放大性能，单位长度放大系数在906-1044nm的波段上为1．40-5．12dB／m，在1080-1491nm的波段上为1．40-15．35dB／m，在1524-1596nm的波段上为1．86-7．44dB／m。根据氢原子模型计算了InP微粒产生量子尺寸效应的相对粒径αB=8．313nm，以及纳米级InP微粒的粒径与能级改变的关系得到，当厚度d=16nm，△E=0.071eV,满足当d≤2aB时的强限域，量子尺寸效应明显，光纤具有光放大性,计算结果与实验测试结果相符。     

Coupling characteristics of cladding modes in tilted optical fiber bragg gratings

We have studied both theoretically and experimentally the effect of grating tilting on the coupling between the fundamental core mode and the cladding modes in an optical fiber Bragg grating. The coupling is shown to be very sensitive on the tilting angle. It is also shown that tilting angle has to be minimized in fibers with designs to suppress the coupling between the fundamental core mode and the cladding modes. We have also studied the single, strong loss peak accompanying the Bragg reflection peak in depressed-cladding fibers, thus showing a good agreement between behavior that is measured and that is predicted theoretically.     

The detection of an external acoustic impact on an optical fiber using a scattered-light interferometer

The results of a study of a scattered-light interferometer for detecting external acoustic impacts on optical fiber are presented. A method of scattered field demodulation using the phase diversity technique is proposed. The demodulated signal is shown to contain regions of fading, the causes of which are analyzed.     

Elastic wave propagation in a microstructured acoustic fiber

Elastic wave propagation along the structure of hollow cylinders in a linear isotropic medium is investigated. The multipole method for modeling elastic waves propagation in such structures is formulated and implemented. Using the multipole method, dispersion dependencies of the structures (microstructured fibers) containing 3, 6, and 7 hollow cylinders are calculated. Comparison with wave dispersion properties along one cylinder is made. Also, an approximate physical model based on an equivalent coaxial waveguide and multipole method is proposed. Exploiting this model, wave dispersion of the wave propagating along a structure with 18 hollow cylinders is calculated. Validation of the model is also proposed.     

Bending-loss studies of a single-mode triangular-index fiber with a depressed cladding ring with a vector-mode method

Attention is directed to the bending-loss properties of a triangular-index fiber with a depressed cladding ring, which can be advantageously used to obtain either a dispersion-shifted or a dispersion-flattened feature. Both cases are studied to search for the set of ring parameters that yield the lowest bending loss while ensuring a low dispersion. Near-optimal designs are proposed and compared with other well-known dispersion-shifted and dispersion-flattened fiber designs. The numerical methods used in our computations are the vector-mode power-series expansion method for fields and dispersion calculations and the volume-current method for bending-loss predictions.     

Non‐reflecting boundary conditions for acoustic propagation in ducts with acoustic treatment and mean flow

We consider a time‐harmonic acoustic scattering problem in a 2D infinite waveguide with walls covered with an absorbing material, in the presence of a mean flow assumed uniform far from the source. To make this problem suitable for a finite element analysis, the infinite domain is truncated. This paper concerns the derivation of a non‐reflecting boundary condition on the artificial boundary by means of a Dirichlet‐to‐Neumann (DtN) map based on a modal decomposition. Compared with the hard‐walled guide case, several difficulties are raised by the presence of both the liner and the mean flow. In particular, acoustic modes are no longer orthogonal and behave asymptotically like the modes of a soft‐walled guide. However, an accurate approximation of the DtN map can be derived using some bi‐orthogonality relations, valid asymptotically for high‐order modes. Numerical validations show the efficiency of the method. The influence of the liner with or without mean flow is illustrated. Copyright © 2011 John Wiley & Sons, Ltd.     

Interaction of shear waves with a griffith crack situated in an infinitely long elastic strip

This paper deals with the propagation of shear waves in a wave guide which is in the form of an infinite elastic strip with free lateral surfaces. This strip contains a Griffith crack. An integral transform method is used to find the solution of the equation of motion from the linear theory for a homogeneous, isotropic elastic material. This method reduces the problem into an integral equation. It has been observed that only shear waves with frequencies less than a parameter-value, depending on the width of the wave guide, can propagate. The integral equation is solved numerically for a range of values of wave frequency and the width of the strip. These solutions are used to calculate the dynamic stress intensity factor, displacement on the surface of the crack and crack energy. The results are shown graphically.     

Problem in electromagneto thermoelasticity for an infinitely long solid conducting circular cylinder with thermal relaxation

The problem of an infinitely long solid conducting circular cylinder whose lateral surface is traction free and subjected to known surrounding temperatures in the presence of a uniform magnetic field in the direction of the axis is considered. The problem is in the context of generalized magneto-thermo-elasticity theory with one relaxation time. The solution is obtained by a direct approach without the customary use of potential functions. Laplace transform techniques are used to derive the solution in the Laplace transform domain. The inversion process is carried out using a numerical method based on Fourier series expansions.Numerical computations for the temperature, the displacement and stress distributions as well as for the induced magnetic and electric fields are carried out and represented graphically. Comparison is made with the results obtained when using the coupled equation of heat conduction.     

A stochastic thermoelastic diffusion interaction in an infinitely long annular cylinder

In this work, we study the effect of a stochastic heating on an elastic solid in the form of an infinitely long circular cylinder under the existence of a permeating substance in contact with the outer surface. The stochastic heating is driven by an additive Gaussian white noise. Random elastic, thermal and diffusive properties are obtained in terms of the induced noise. The model is considered in the context of the generalized thermoelastic diffusion theory with one relaxation time. The Laplace transform technique is used to obtain the analytical solution in the transformed domain, while a numerical inversion method for Laplace transform is used to obtain an approximate solution for the temperature, displacement, stress, concentration of the diffusive material and chemical potential. Statistically, first and second moments of the physical properties are derived analytically and discussed.