Improved method for loss measurements in planar waveguides

A method employing an isosceles prism and a right-angle one is developed for loss measurement in planar waveguides. During the measuring process, the isosceles prism is fixed and the right-angle prism fixed on the waveguide slides by following the waveguide. Only by adjusting the gap thickness we can realize the loss measurement in planar waveguides. The method is demonstrated with an Ag/Na ion-exchanged waveguide fabricated on BK7 glass from AgNO₃ melt diluted with NaNO₃ (mass ratio 1:9), with the condition of 4 h and . The experimental results show that the method has the advantages on convenient operation, accurate results and no required end polishing.     

New method for loss measurements in optical waveguides

A new three-prism method for measuring losses of optical waveguides is presented. It has a high accuracy and is comparatively simple, both in construction and during the measurement process. The method can be applied to all kinds of planar waveguides and enables one to obtain results which are independent of the coupling efficiencies of the middle movable prism and laser radiation fluctuations.     

The third-order electric susceptibilities of NaCl and KCl monocrystals

The dispersion of the third-order electric susceptibilities(; , , –) and(; , 0, 0) of NaCl and KCl monocrystals has been calculated by means of experimental data on the electro-optic Kerr effect. The result has been obtained by using semi-classical models of anharmonic oscillators. An ionic contribution to the electro-optic coefficients has been presented. From the result obtained it follows that the third-order electric susceptibilities are of the order of 10^–22 m² V^–2.     

Measurement of third-order nonlinear susceptibilities by non-phase matched third-harmonic generation

The third-order susceptibilities χ _xxxx ⁽³⁾ (?ω₃;ω₁,ω₁,ω₁) of some liquids, solids and air are determined by third-harmonic generation. The samples are placed behind the focal region of a laser beam in an evacuated environment to avoid third-harmonic generation of the surroundings. For fluid media the sample cell is made out of two thin fused quartz plates and oriented to an angle of zero net third-harmonic production in each window (minimum Maker fringe position).     

The complex Jacobi iterative method for non-paraxial beam propagation in nonlinear optical waveguides

The recently introduced beam propagation method using complex Jacobi iteration adapted for modeling of non-paraxial beam propagation in nonlinear optical waveguides is presented in this paper. The beam propagation equation is based on our recently proposed modified Padé(1,1) approximant operator. The resulting approach is very efficient and well-suited for large structures with long propagation paths.     

Absolute measurements of third order susceptibilities

We determined the third-order susceptibility of quartz by comparing third harmonic generation and a two-step process: second harmonic generation and two-wave mixing. The value of χ_xxx⁽³⁾ is given as a function of [χ_xxx⁽²⁾]². The values of χ_xxx⁽³⁾ of LiF and benzene are determined by comparison with quartz.     

The nonlinear refractive indices and nonlinear third-order susceptibilities of quadratic crystals

The third-order nonlinear susceptibilities and nonlinear refractive indices of KDP, BBO, and LiNbO₃ crystals at wavelengths of 1064 and 532 nm are measured using the Z-scan technique. The measurements are made for different energies of incident radiation and different focusing conditions and crystal lengths. It is found that, as the angle between the light beam and the principal optic axis of a KDP crystal increases, the nonlinearity drops, with its magnitude at a wavelength of 1064 nm being higher than at 532 nm. For a BBO crystal, the nonlinearity dispersion is normal. The mechanisms of nonlinear losses in KDP, BBO, and LiNbO₃ crystals are identified. The values of the nonlinear susceptibilities thus obtained are analyzed and compared with the results of calculations based on an empirical model and with the data of other authors.     

一种水平变化波导中声传播问题的耦合模态法

针对介质参数及海底边界水平变化波导中的声传播问题,本文基于多模态导纳法提出一种能量守恒且便于数值稳定求解的耦合模态方法.将声压表示为一组正交完备的本地本征函数之和,对声压满足的Helmholtz方程在本地本征函数上作投影,推导出关于声压模态系数的二阶耦合模态方程组.耦合矩阵直观描述水平变化因素对模态耦合的贡献.为避免直接求解二阶耦合模态方程组可能遇到的数值发散问题,将其重构为两个耦合的一阶演化方程组,引入导纳矩阵并使用Magnus数值积分方法获得稳定的声场解.利用该耦合模态方法数值计算水平变化波导中的声场,并与COMSOL参考解比较,结果表明该耦合模态理论能够精确求解水平变化波导中的点源及分布源传播问题.     

High-intensity third-harmonic generation in beta barium borate through second-order and third-order susceptibilities

The azimuthal dependence of third-order and cascaded second-order nonlinear coupling was used to measure the relative contributions of each to direct third-harmonic generation in beta-barium borate. This permitted the measurement of the values of tensor elements chi(3)(10) , chi(3)(11) , and chi(3)(16) relative to the known chi(2)(ij) . Finally, conversion efficiencies to 3 omega of up to 6% were achieved with a femtosecond chirped-pulse amplification laser with 200 GW/cm(2) in collimated beams.     

A deep learning method for solving third-order nonlinear evolution equations

It has still been difficult to solve nonlinear evolution equations analytically. In this paper, we present a deep learning method for recovering the intrinsic nonlinear dynamics from spatiotemporal data directly. Specifically, the model uses a deep neural network constrained with given governing equations to try to learn all optimal parameters. In particular, numerical experiments on several third-order nonlinear evolution equations, including the Korteweg–de Vries (KdV) equation, modified KdV equation, KdV–Burgers equation and Sharma–Tasso–Olver equation, demonstrate that the presented method is able to uncover the solitons and their interaction behaviors fairly well.     

An FDTD analysis of photonic crystal waveguides comprising third-order nonlinear materials

A finite difference time domain (FDTD) study of two-dimensional photonic crystals containing nonlinear materials is presented in this paper. An appropriate Z-transform oriented formulation of the FDTD method for the simulation of third-order nonlinear Kerr- and Raman-type media is analyzed and applied to model nonlinear photonic crystal waveguide structures. For their reflectionless termination a novel perfectly matched layer (PML) is proposed and evaluated comparatively to other periodic and inhomogeneous absorbers. Furthermore, the absorbing efficiency of the proposed PML is investigated varying its parameters.     

A model for sonar interrogation of complex bottom and surface targets in shallow-water waveguides

Many problems of current interest in underwater acoustics involve low-frequency broadband sonar interrogation of objects near the sea surface or sea floor of a shallow-water environment. When the target is situated near the upper or lower boundary of the water column the acoustic interactions with the target objects are complicated by interactions with the nearby free surface or fluid-sediment interface, respectively. A practical numerical method to address such situations is presented. The model provides high levels of accuracy with the flexibility to handle complex, three-dimensional targets in range-independent environments. The model is demonstrated using several bottom target scenarios, with and without locally undulating seabeds. The impact of interface and boundary interactions is considered with an eye toward using the sonar return signal as the basis for acoustic imaging or spectral classification.     

A pulse-resonance method for the determination of frequency-dependent magnetic susceptibilities in the microwave region

A simple set-up for the determination of non-diagnonal elements of the magnetic susceptibility tensor in the microwave region is given. The change of the magnetization during microwave absorption (MMA) is detected and leads directly to the susceptibilityχ′ _yx (ω). The method is applicable to magnetic systems having longitudinal relaxation times larger than 10^?6 sec. The MMA-method enables one to decide whether the sample is para-, ferro- or antiferromagnetic and from this magnetic transition temperatures can be measured.     

A new semi-analytical method for the analysis of tapered optical waveguides

Tapered waveguide are used in number of integrated optic devices such as directional couplers, modulators, switches mode converters, etc. Most of the methods analyzing tapered waveguide are numerical in nature. In this paper we present a simple, fast and accurate semi analytical method for z-varying waveguide. However, very few idealized structures can be analyzed directly. The present method consists of separating transverse and longitudinal variation in the wave equation, leading to a differential equation with z-varying coefficients for the field variation along z-axis. For the transverse variation local normal theory is applied. Now this equation is applied to specific taper geometries like linear down taper. Computational are done assuming typical values. We observe variation of power mode profile and mode width. Waveguide loss is also including in the analysis. Finally the analytical simulation results have been verified by the commercial Opti-BPM software.     

Unidirectional sensitive flexible sensor for bending measurements

The measurement of bending direction and bending angles is essential in the multiaxial servo-controlled system, especially for collaborative robots. However, most flexible sensors developed for bending measurements cannot distinguish bending directions due to their sensitivity to both positive and negative bending. Also, these sensors usually exhibit simultaneous response to normal pressure, which results in additional calibration. Here, a unidirectional-sensitive flexible capacitive sensor is proposed. A simple asymmetric pyramidal microstructure was designed to create uneven responses to positive and negative bending and minimum response to normal pressure based on the fringe effect. The fabricated sensor shows a relative capacitance change of nearly 0.9 in the sensitive direction and only 0.05 in the other direction as the sensor bends from flat to the curvature radius of 10 mm. Also, the sensor shows negligible sensitivity even under a normal pressure force as high as 16 N, either in planar or bending condition.     

A collective variable approach for optical solitons in the cubic-quintic complex Ginzburg-Landau equation with third-order dispersion

Considering the theory of electromagnetic, especially from the Maxwell equations, a basic equation modeling the propagation of ultrashort optical solitons in optical fibers is derived, namely a cubic-quintic complex Ginzburg-Landau equation (CQGLE) with third-order dispersion (TOD). Considering this one-dimensional CQGLE, we derive the equations of motion of pulse parameters called collective variables (CVs), of a pulse propagating in dispersion-managed (DM) fiber optic-links. Equations obtained are investigated numerically in order to view the evolution of pulse parameters along the propagation distance. A fully numerical simulation of the CQGLE finally tests the results of the CV theory. It appears chaotic pulses, attenuate pulses and stable pulses under some parameter values.     

A capacitive method for hall effect measurements

A new, simple and reliable method for Hall effect measurements is introduced. The method employs a capacitive probe technique and requires neither special shaping of samples nor probing Hall contacts. With this method, Hall effect measurements onp-Ge have been first extended to high electric fields up to 3kV/cm at 4.2 K. The wide applicability of this method is discussed.     

A time-resolved method for nonlinear ultrasonic measurements

We describe a time-resolved method for measuring nonlinear ultrasonic phenomena. Current approaches rely on a narrowband measurement of harmonic generation to identify and characterize nonlinearity. Concomitant with these techniques is poor time resolution. We address this limitation with a hybrid narrowband/broadband approach that provides simultaneous time resolution and harmonic isolation for the measurement of weak nonlinearites. We discuss applications and present demonstrative results showing harmonic generation both in water and at a dry contact aluminum-aluminum interface.     

A complex sum method of quantifying susceptibilities in cylindrical objects: the first step toward quantitative diagnosis of small objects in MRI

A complex sum method of quantifying the magnetic susceptibility of a long, narrow cylinder embedded in a uniform medium has been developed. The radius of the cylinder can be as small as one pixel. The susceptibility inside the object is extracted from the magnetic resonance complex images, using two concentric circles around the axis of the cylinder. The numerical simulations of this complex sum method are in good agreement with the phantom studies. Specifically, the method was tested with a susceptibility difference of -9 ppm to mimic air/tissue interface in the human body at 1.5 T with an echo time of 5 ms. Phantom studies using an air-filled cylinder in a solidified gel have shown that the susceptibility of the gel cannot be determined by the usual least-squares-fit method but can be determined by the complex sum method to within 5-10% of the expected value.     

Scalar FD-TD method for circularly symmetric waveguides

A scalar finite-difference time-domain (FD-TD) method is formulated in order to analyse a circularly symmetric waveguide with longitudinal discontinuities. The second-order absorbing boundary condition originally developed in rectangular coordinates is extended to cylindrical coordinates. The propagating fields in a tapered step-index fibre with a facet and in a distributed feedback reflector are calculated, and the power reflectivities are evaluated. This revised version was published online in November 2006 with corrections to the Cover Date.