Modal attenuation in metal-clad graded-index slab optical waveguides

The paper presents the influence of refractive profile shape on the distribution of modal attenuation in planar metal-clad optical waveguide structures. A calculation method has been presented in which we applied the Snyder–Love expression on modal attenuation coefficients and matrix method 4 × 4 for the analysis of planar waveguides. The obtained results are almost identical with the exact results for refractive profiles: the parabolic, exponential, Gaussian and linear ones. It has been demonstrated that the applied calculation method can be used in waveguides of any profiles of the refractive index.     

New method for calculating the spectra and radiation losses of leaky waves in multilayer optical waveguides

The efficiency of a new method for calculating the spectrum and attenuation coefficient of leaky electromagnetic modes is demonstrated with multilayer planar optical waveguides the guiding properties of which are determined by antiresonant reflection from the multilayer cladding (antiresonant reflecting optical waveguides) rather than by total internal reflection from the core-cladding interface as in standard optical waveguides. The new method applies to calculation of both electromagnetic modes in dielectric waveguides and electron quantum states in multibarrier semiconductor heterostructures. The characteristics of multilayer waveguides calculated by the new method are compared with published data obtained from a complex dispersion relation by the transfer matrix method. As an example, the wavelength dependence of the radiation losses for the first TE mode of a planar optical waveguide containing 52 pairs of layers is calculated.     

K-Na离子交换单模平面波导的制备及其表征

通过K-Na离子交换技术制备了多模玻璃平面波导.采用棱镜耦合技术测量了波导的有效折射率,用IWKB方法拟合得到K-Na离子交换波导的折射率分布符合高斯分布,由色散曲线得到单模波导的制备条件(即扩散深度范围),从而得出单模波导的离子交换时间范围,制备出单模波导,并通过求解WKB色散方程得出单模波导的表面折射率.用普通数码相机,通过对离子交换平面玻璃光波导传输线进行数字成像,根据传输线上的光强分布拟合出光强传输衰减曲线,计算出单模波导的传输损耗大约为0.4 dB/cm.     

数码照相法测量离子交换平面光波导损耗特性

利用数码相机对离子交换平面玻璃光波导传输线进行数字成像,根据传输线上的光强分布拟合出光强传输衰减曲线,计算出波导的传输损耗.对光波导进行退火处理,研究了波导退火前后的传输损耗特性.退火后0阶模式下传输损耗由2.148 9 dB·cm－1降为0.746 0 dB·cm－1.结果表明,波导的传输损耗是随着模阶数的增加而递增,适当的退火处理明显改善了离子交换波导的质量.     

Optical Characterization of Optofluidic Waveguides Using Scattered Light Imaging

The use of scattered light images is shown to be an attractive method for the characterization of optofluidic waveguides. The method is shown to be capable of measuring waveguide propagation losses and transmissions between solid and liquid-core structures. Measurement uncertainties are considered and characterized and were typically less than 15%.     

Structural and optical properties of waveguides in YbVO4 crystals formed by 3.0 MeV Cu-ions implantation

We report on the structural and optical characterization of waveguides formed in YbVO₄ crystals by Cu²⁺-ion implantation with an energy of 3.0 MeV and doses of 3.0×10¹⁴-1.0×10¹⁵ ions/cm². The damage properties are determined by RBS/Channeling measurements with the help of simulation code RUMP. The m-line method is used to characterize the dark-mode spectroscopy in the planar waveguides. According to the reconstructed refractive index profile of the waveguide cross section, a numerical simulation is carried out to investigate the confinement of the light in the waveguides based on the beam propagation method.     

Discrete diffraction of light in optically induced bulk and planar photonic superlattices in photorefractive lithium niobate

Experimental multielement planar and channel waveguide structures induced by coherent radiation in bulk samples of photorefractive lithium niobate and planar waveguides on their basis including those formed in a projection scheme with scaling of image dimensions are described. The possibility of linear and nonlinear light localization in optically-induced bulk and planar one-dimensional photorefractive photonic superlattices is demonstrated. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 57–62, September, 2008.     

溶胶-凝胶法制备SiO2-TiO2平板光波导工艺研究

采用溶胶-凝胶法制备了SiO₂-TiO₂平板光波导,计算了平板光波导通光条件,分析了硅/钛溶胶-凝胶材料的热性能,观测了平板光波导的结构形貌,并测试了其通光损耗。结果表明：经过200℃,30 min干燥处理的凝胶薄膜呈疏松多孔状态,对于非对称平板波导,存在芯层通光截止厚度,而且当SiO₂-TiO₂芯层厚度为0.5 μm时,SiO₂下包层厚度至少有6 μm才能防止1550 nm波长光泄露入单晶硅衬底中。制备的光波导对于1550 nm波长光传输损耗最小值为0.34 dB/cm。     

Silicon-based rectangular hollow integrated waveguides

This paper describes the simulation, fabrication and characterization of silicon-based rectangular hollow waveguides. Numerical evaluation of such structures has been done using both modal propagation and ray tracing, low total losses and multimodal behavior, even for small core sizes, are predicted. Since light propagation in rectangular hollow waveguides strongly depends on the Fresnel coefficients at the facets, the technological processes have been optimized to obtain wall angles close to 89° and wall and base average roughness of 57 nm and <5 nm, respectively. Hence, roughness is negligible to the working wavelength (678 nm). Measured waveguides show total losses close to 6.0 dB for 3.0 cm length. The non-lineal response due to mode filtering in hollow waveguides has also been experimentally observed. Finally, loss simulations and measurements are in agreement, especially for the widest waveguides. For thinner structures, the reduction of the depth due to the DRIE process, together with the blundering of the vertices, causes a dramatic attenuation increase. All these effects should be taken into consideration when defining hollow structures.     

Fs-Laser structuring of ridge waveguides

Thin films made by PLD from Er:ZBLAN and Nd:Gd₃Ga₅O₁₂ are micro machined to form optical wave guiding structures using Ti:sapphire and Yb:glass fiber laser radiation. For the manufacturing of the ridge waveguides grooves are structured by ablation using femtosecond laser radiation. The fluence, the scanning velocity, the repetition rate, and the orientation of the polarization with respect to the scanning direction are varied. The resulting structures are characterized using optical microscopy and scanning electron microscopy. Damping and absorption coefficients of the waveguides are determined by observing the light scattered from the waveguides due to droplets in the thin films and the surface roughness of the structured edges. To discriminate between damping due to droplets and the structured edges, damping measurements in the non-structured films and the structured waveguides are performed. Ridge waveguides with non-resonant damping losses smaller than 3 dB/cm are achieved. Due to the high repetition rate of the Yb:glass fiber laser, the manufacturing time for one waveguide has been decreased by a factor of more than 100 compared to earlier results achieved with the Ti:sapphire laser.     

Nonlocality in PT-symmetric waveguide arrays with gain and loss

We demonstrate that light propagation in waveguide arrays that include PT-symmetric structures can exhibit strongly nonlocal sensitivity to topology of the array at fixed other parameters. We consider an array composed of lossless waveguides, that includes a pair of PT-symmetric waveguides with balanced gain and loss, and reveal that PT-symmetry breaking thresholds are different for planar and circular array configurations. These results demonstrate that PT-symmetric structures can offer new regimes for optical beam shaping compared to conservative structures.     

Packing density of conventional waveguides and photonic crystal waveguides

We compare coupling between parallel waveguides within one-dimensional photonic crystals and coupling between conventional waveguides. We consider the situation in which coupling between the waveguides is minimized, so that light in the waveguides propagates essentially independently. Subject to this condition, we compare the minimum mutual distance between conventional planar waveguides and waveguides in one-dimensional photonic crystals. We find that the packing densities of the conventional and periodic structures are comparable.     

Impressing technology of optical Bragg’s gratings on planar optical sol-gel waveguides

The aim of the presented investigations was to develop a technique of producing Bragg’s grating couplers on planar waveguides. Waveguides are obtained by means of the sol-gel technology. The introduction of a light beam into the structure of the waveguide is in the case of planar or strip optical systems always an essential technical problem, requiring simple and reproducible solutions without extending excessively the waveguide structure. The paper presents a technology of producing grating couplers by impressing the pattern of the network while forming the planar waveguide structure applying the sol-gel method. Some remarks concerning the sol-gel technology are also presented. The results of investigations on grating couplers obtained in such a way have been discussed, too. Attention has been drawn to the possibility of using such structures in optoelectronic sensors, particularly gas sensors, including sensors of water vapour as well as toxic gases.     

Mode analysis of realistic optical waveguide structures and microstructured holey fibers by modal field evolution

In this article, we describe a useful technique for calculating modes of practical optical waveguides having two-dimensional arbitrary transverse refractive index profile. The method uses a finite difference platform for evaluating Helmholtz's equation in scalar and semivectorial forms through a field evolution algorithm. The method is straightforward, easy to handle and does not involve any complex analysis or matrix formulation. We tested the accuracy of our analysis approach by applying it on a large number of realistic waveguide problems having known results or results available in the literature. The formulation has facilitated us to study the modal properties, viz., field distribution, birefringence, dispersion and mode effective area, of a variety of practical two-dimensional structures namely, planar structure, coupler, semiconductor optical waveguides, optical fibers and arbitrary profile microstructured fibers which are uniquely important in photonics and guided-wave devices. The algorithm will therefore be very useful in designing and studying any arbitrary-structure waveguides, and to explore new geometry and properties.     

Flow measurements based on Rayleigh scattering and Fabry-Perot interferometer

Flow diagnostics based on molecular Rayleigh scattering are discussed along with the results of a feasibility study to non-intrusively measure flow properties in a small supersonic wind tunnel. The technique uses an injection seeded, frequency doubled Nd:YAG laser tuned to an absorption band of iodine. The molecular Rayleigh scattered light is filtered with an iodine cell to block light at the laser frequency. The Doppler-shifted Rayleigh scattered light that passes through the iodine cell is analyzed with a planar mirror Fabry-Perot interferometer used in a static imaging mode. An intensified CCD camera is used to record the images. The images are analyzed at several subregions, where the flow properties are determined. Each image is obtained with a single laser pulse, giving instantaneous measurements.     

Forward and backward wave propagation in multilayer planar waveguide using metamaterials layer

In this study, an efficient method is discussed to analyze the multilayer planar waveguides with double negative guided (DNG) and double positive material as guiding film. Here, among various lossless multilayer planar waveguide structures, only three layer and five layer structures are discussed. For these structures, guided dispersion characteristic, along with electric field distribution of TM modes are numerically analyzed and compared. This analysis enables an effective comparison of guided modal properties of various modes and results in a better understanding of the multilayer planar waveguide with DNG as guiding film.     

Models of non-linear waveguide excitation by non-stationary light beam

The propagation of a non-stationary light beam through a linear/non-linear discontinuity in a planar waveguide is considered by using an approximate approach based on the Generalised Non-Linear Schrodinger Equation (GNLSE) and the rigorous Transmission Line Modelling (TLM) Method. The objective is to compare the different theoretical approaches that can be used for the design of guiding structures with pulse shaping and signal processing functionality. Reflection and transmission of the light beam propagating through the junction of linear and non-linear waveguides are studied with respect to a dimensionless parameter that defines the increase of the refractive index induced by high-intensity radiation. In conclusion, the routes to efficient modelling are discussed.     

Experimental demonstration of electromagnetic tunneling through an epsilon-near-zero metamaterial at microwave frequencies

Silveirinha and Engheta have recently proposed that electromagnetic waves can tunnel through a material with an electric permittivity (epsilon) near zero (ENZ). An ENZ material of arbitrary geometry can thus serve as a perfect coupler between incoming and outgoing waveguides with identical cross-sectional area, so long as one dimension of the ENZ is electrically small. In this Letter we present an experimental demonstration of microwave tunneling between two planar waveguides separated by a thin ENZ channel. The ENZ channel consists of a planar waveguide in which complementary split ring resonators are patterned on the lower surface. A tunneling passband is found in transmission measurements, while a two-dimensional spatial map of the electric field distribution reveals a uniform phase variation across the channel--both measurements in agreement with theory and numerical simulations.     

Simple low-loss waveguide bends using ARROW effect

A new concept for reducing bend loss in dielectric planar waveguides is presented. It is based on the introduction of a set of antiresonant reflecting optical waveguides (ARROWs) on the outside of the bent core and defined in the same fabrication step as the main bend. It has been ascertained by simulation that the bending loss can be significantly reduced. The method is compatible with other bend-lossreduction strategies, as well as with different waveguiding structures, such as rib and buried waveguides and fibers.This revised version was published online in August 2005 with a corrected cover date.     

SBN:Cr晶体中孤子诱导的实时平面光波导及其导光特性分析

通过数值模拟和实验对SBN:Cr晶体中的（1+1）维亮屏蔽空间孤子及其诱导的实时平面光波导的导光特性进行了研究.采用分步束传播法和Petviashvili迭代法对（1+1）维亮屏蔽空间孤子的特性进行了模拟.通过求解本征方程,对孤子诱导平面波导中存在的导波模式进行了数值求解.采用633 nm的He-Ne激光作为孤子诱导光束,532 nm的半导体泵浦的固体激光作为探测光,在固液同成分的SBN:Cr晶体中进行了实验研究.实验结果和数值模拟的结果符合的很好.而且结果表明SBN:Cr晶体中红光诱导的波导可以作为实时光波导.