Propagation of p-polarized waves in a linearly graded index film surrounded by negative index materials

The theory of step-index waveguides is well-established. Most practical slab waveguide structures have a graded-index profile. The basic properties of graded-index planar waveguide structures are similar to those of step-index waveguides with subtle differences. The most common types of graded-index slab waveguides are linearly and exponentially graded-index profiles. We here treat linearly graded-index slab waveguide. In this work, a three-layer waveguide structure with linearly graded-index film is considered. We assume three structures: the first structure comprises a left-handed material (LHM) cladding, the second structure contains a LHM substrate layer and the third has a LHM cladding and substrate. Closed-form expressions for electric and magnetic fields and the characteristic equation are derived. The three normalized parameters: the asymmetry coefficient (a), the normalized film thickness (V) and the normalized guide index (b) are used to study the dispersion properties of the proposed slab waveguide structure.     

偏振态对飞秒激光加工石英玻璃表面质量的影响

为研究线偏振和圆偏振对飞秒激光烧蚀加工石英玻璃表面质量的影响,开展不同扫描速度的线烧蚀试验和不同线重叠率的面烧蚀试验。研究了线、圆偏振光对烧蚀线宽度的影响,利用光学显微镜和环境扫描电子显微镜观察烧蚀形貌,并使用三维表面轮廓仪进行烧蚀面粗糙度分析。结果表明:线偏振光烧蚀线宽度大于圆偏振光,且激光功率越大,线宽差异越明显;当线重叠率在65%~90%时,线偏振光烧蚀表面粗糙度随重叠率增大而增大,在重叠率为65%时达到1.33μm;线轮廓算术平均偏差随重叠率增大先减小后增大,并在重叠率为80%时达到较小值1.05μm;当重叠率不到80%时,线偏振光烧蚀面线轮廓算术平均偏差比圆偏振光小;重叠率为90%时,其线轮廓算术平均偏差反而比圆偏振光大。     

Vectorial vortex mode transformation for a hollow waveguide using Pancharatnam-Berry phase optical elements

Transformation and inverse transformation between a free-space linearly polarized beam and the vectorial vortex mode of a circular hollow waveguide by use of Pancharatnam-Berry phase optical elements is proposed. Demonstration was achieved by fabricating GaAs subwavelength gratings and utilizing a 300 microm diameter hollow metallic waveguide for 10.6 microm wavelength CO(2) laser radiation. The mode transformations and the excitation of a single vectorial mode inside the hollow waveguide were verified by full polarization measurements. In addition, the inverse mode transformation of the single vectorial mode excitation in the waveguide enabled us to experimentally obtain a linearly polarized bright spot with a high central lobe.     

The Influence of Defects on the Propagation Light within Polymeric Optical Waveguides Studied by Polarized Near-Field Scanning Optical Microscopy

We have developed a polarization-preserving near-field scanning optical microscopy (NSOM) optical fiber probe and with it observed the influence of defects and weak stresses on a propagation light within polymeric optical waveguides. To characterize the influence, we intentionally printed an indentation in the vicinity of the waveguide and then evaluated the resulting influence using polarized guide-collection-mode NSOM images taken around the indentation. When transverse magnetic polarized light enters a waveguide, the light intensity becomes greater on the near side of the indentation than on the far side, as measured by a linearly polarized component perpendicular to the direction of light propagation. The most probable cause of this phenomenon is microdefects generated by the printing of the indentation. The polarized NSOM technique is useful in searching for small defects or stresses within integrated photonic devices.     

Quasi-TEM mode propagation in twin-wire THz waveguides

We numerically investigate the trade-offs between the dispersion properties,coupling efficiency,and geometrical constraints in dual-wire (twin-lead) terahertz (THz) waveguides.In particular,we show that their inherent linearly polarized quasi-transverse electromagnetic (TEM) modes exist for waveguide transverse dimensions comparable with the wavelength,enabling significant end-fire coupling (>10%) for numericalaperture limited Gaussian beams while supporting a relatively low-dispersion propagation of below 0.5 ps 2 /m,as desired for short-pulse time-domain spectroscopy applications.Starting from the dual-wire structure,we also demonstrate that low-dispersion tapers can be designed to improve coupling efficiency.     

Second-harmonic generation in He+-implanted gadolinium calcium oxoborate planar waveguides

What is believed to be the first investigation of second-harmonic generation (SHG) in Ca(4)GdO (BO(3))(3) waveguides is reported. A planar waveguide was formed by 2-MeV-helium implantation. We cut the sample to achieve type I noncritical phase matching of an 823-nm fundamental wave for fundamental light propagating along the y axis and polarized along the z crystallophysic axis of the crystal. SHG was achieved with a relatively low pumping power of a cw Ti:sapphire laser. The results indicate that the nonlinearity of the material remains in the guiding region after ion implantation.     

Optically pumped distributed feedback thin film waveguide lasers with multiwavelength and polarized emissions

Zirconia titania organically modified silicate (ZrO₂-TiO₂-ORMOSIL) thin film waveguides of thickness from 0.4 to 7.0 μm were synthesized using low temperature sol–gel method. Narrow linewidth distributed feedback (DFB) lasing was demonstrated in rhodamine 6G-doped ZrO₂-TiO₂-ORMOSIL waveguides. Simultaneous tuning of multiple-output wavelengths was achieved in the dye-doped waveguides by varying the period of the gain modulation generated by a nanosecond Nd:YAG laser at 532 nm. As many as eight separate output wavelengths were observed for a planar ZrO₂-TiO₂-ORMOSIL waveguide of thickness 7.0-μm. The output polarizations of the DFB waveguide lasers can be tuned by varying the polarization of the crossing pump beams. TE and TM optical waves belonging to the same propagation mode were generated by crossing two polarized pump beams, resulting in an effective double of the number of output wavelengths. Continuous tuning of the polarized laser outputs was also achieved by varying the crossing angle.     

Novel waveguide components based on complementary electrically small resonators

In this paper, we present a new class of waveguide components based on the use of complementary electrically small resonators etched on metallic sheets. We first show a rectangular-to-circular waveguide transition that allows to effectively match waveguides with different cross-sections and to transform the linearly polarized TE₁₀-mode of a rectangular waveguide into a circularly polarized TE₁₁-mode of a circular waveguide. Then, using similar structures, we present the design and the numerical results of two power dividers and of an orthomode transducer. All these components, employing only thin metallic sheets with properly shaped slits, can be integrated in waveguide transmission systems without increasing their space occupancy. A proper set of full-wave numerical simulations proves the validity of the proposed approach.     

Optical properties of a waveguide written inside a LiTaO3 crystal by irradiation with focused femtosecond laser pulses

Optical waveguides were fabricated by modifying the optical properties inside a LiTaO₃ crystal by irradiation with femtosecond laser pulses, and the performance and optical properties of the waveguide were investigated. On the basis of near-field pattern of the light guided through the waveguides, the optimum writing conditions such as the pulse energy and the pulse duration were determined. The waveguide written inside a LiTaO₃ crystal had a strong polarization dependence of guided light. Observation by a polarized microscope suggested that the stress distribution around the photoexcited region should be responsible for the polarization dependence of guided light. In addition, the second harmonic generation from a laser beam passing through the waveguide was observed, which suggests that the ferroelectric properties of LiTaO₃ were preserved after the photoexcitation.     

Polarized Emission of an Eu^3＋ Doped Azo-Polymer Waveguide

We investigate the polarized emission behaviour of an Eu^3 doped azo-polymer waveguide. Affected by the azobenzene groups in the photoinduced orientation process by the 532nm linearly polarized laser, the ligands were realigned orderly perpendicular to the direction of the orientation direction. This leads to the polarized absorption and emission of the waveguide in the orientation direction. By an m-line apparatus based on the prism coupling technique, two guided propagation modes were observed in the waveguide, and the refractive index at 650hm in TE polarizations is 1. 7505.     

Designing arbitrary nanoscale patterns by a nanocavity waveguide with omnidirectional illumination

We report one- and two-dimensional arbitrary patterns which are achieved by nanocavity waveguides made of a quasi-metal?Cdielectric-metal heterostructure with omnidirectional illumination. This proposed heterostructure supports the surface plasmon polaritons whose phase and group velocities have opposite sign for given frequency. Negative refraction and reflection in the waveguide result in imaging nanolithography and the omnidirectional property can be well understood by the dispersive relation of the nanocavity waveguide. Numerical results demonstrate that such an omnidirectional nanolithography scheme is feasible for arbitrary 1D gratings and 2D linearly chirped gratings with TM and circular polarized incidence, respectively, at 365?nm.     

Directly laser-written integrated photonics devices including diffractive optical elements

Femtosecond laser-written integrated devices involving Fresnel Zone Plates (FZPs) and waveguide arrays are demonstrated as built-in optical couplers. These structures were fabricated in borosilicate glass using a direct laser writing technique. The optical properties of these integrated photonic structures were investigated using CW lasers and high-resolution CCDs. For a single FZP coupled to a single waveguide, the overall coupling efficiency was 9%. A multiplexed optical coupler composed of three FZP layers was demonstrated to couple three waveguides simultaneously in a waveguide array. Structures of this type can be used as platforms for multichannel waveguide coupling elements or as microfluidic sensors that require higher light collecting efficiency.     

Buried ion-exchanged glass waveguides: burial-depth dependence on waveguide width

A detailed theoretical and experimental study of the depth dependence of buried ion-exchanged waveguides on waveguide width is reported. Modeling, which includes the effect of nonhomogeneous time-dependent electric field distribution, agrees well with our experiments showing that burial depth increases linearly with waveguide width. These results may be used in the proper design of integrated optical circuits that need waveguides of different widths at different sections, such as arrayed waveguide gratings.     

Design and comparison of single-mode planar and ridge type electro-optic waveguide modulators

Electro-optic waveguide modulators utilizing phase retardation of two orthogonally polarized optical modes in LiNbO₃ and LiTaO₃ waveguides have been designed taking into consideration the optical field distribution in the waveguides and the electrical properties of the electrodes. The analysis has revealed that a driving-voltage to frequency-bandwidth ratio of 1 V/GHz is attainable at the wavelength of 1.05 m using presently available embedded and ridge waveguides. Improvement in waveguide fabrication techniques may reduce the ratio by at least a half. Thus, LiNbO₃ and LiTaO₃ waveguide modulators are considered to be promising candidates for practical application to single-mode optical-fibre transmission systems of higher than 1 Gbit/s.     

Second-harmonic generation in periodically poled nonlinear polymer waveguides

We demonstrate quasi-phase-matched (QPM) second-harmonic generation (SHG) at the optical communication wavelengths with side-chain polymer waveguides. A ridge waveguide structure is designed to support fundamental mode guiding at both the pump and the second harmonics, leading to a high field overlap integral of the guided modes. The nonlinearity contrast in the +/0 type QPM waveguide is maximized under a QPM poling electrode width of nearly half the coherence length. Using these configurations, we record a normalized SHG efficiency of 2.2% W(-1) cm(-2) in the polymer waveguide.     

Efficient yellow-light generation by frequency doubling a narrow-linewidth 1150 nm ytterbium fiber oscillator

A linearly polarized, narrow-linewidth, diode-pumped, Yb-doped silica-fiber oscillator operating at 1150 nm was frequency doubled to produce 40 mW of 575 nm radiation. The oscillator generated 89 mW of cw linearly polarized output power and was tunable over 0.80 nm. The laser output was coupled to a periodically poled LiNbO3 waveguide that converted 67% of the coupled power to the yellow. The system was fully integrated, with no free-space optics, and had an overall optical-to-optical efficiency of 7.0% with respect to the incident diode-laser pump power.     

Ar+激光和532 nm激光及其线偏振激光辐照光学模型下人正常小肠组织光学特性

采用双积分球系统和光辐射测量技术的基本原理以及运用生物组织的光学模型 ,研究了 4 76 5 ,4 88,4 96 5 ,5 14 5 ,5 32nm激光及其线偏振激光辐照人正常小肠组织的光学特性。结果表明 :组织对激光及线偏振激光的衰减系数和散射系数随着波长的减小而增大 ,而 5 14 5～ 5 32nm波长之间 ,线偏振光与非线偏振光入射则开始有明显差异。吸收系数是随着波长的减小而缓慢地增大 ,而 5 14 5～ 5 32nm波长之间吸收系数的改变则明显变小 ,与是否线偏振光入射无明显差异。平均散射余弦也是随着波长的减小而增大 ,光学穿透深度则是随着波长的增大而增大 ,折射率在这五个波长范围内的值在 (1 38～ 1 4 8)之间。Kubel ka Munk二流模型下组织对同一波长的激光及其线偏振激光的吸收系数、散射系数、总衰减系数、有效衰减系数没有显著性差异 (P >0 0 5 )。组织对不同波长的激光或其线偏振激光的吸收系数、散射系数、总衰减系数、有效衰减系数是有差异的。而在 5 14 5～ 5 32nm波长之间其光学特性参数有较为明显的差异。     

5个不同波长的激光及其线偏振激光辐照人正常膀胱组织光学特性

采用双积分球系统和光辐射测量技术的基本原理以及运用生物组织的光学模型,研究了476.5, 488, 496.5, 514.5和532 nm激光及其线偏振激光辐照人正常膀胱组织的光学特性。结果表明：组织对激光及线偏振激光的总衰减系数和散射系数均随着波长的增大而减小,而且线偏振激光与非线偏振激光入射是有明显的差异。吸收系数是随着波长的增大而缓慢地减小,但有一些起伏,而与是否线偏振光入射无明显差异。平均散射余弦也是随着波长的增大而减小,而且线偏振激光与非线偏振激光入射是有明显的差异。光学穿透深度则是随着波长的增大而增大,而有一些起伏。折射率在这5个波长范围内的值在(1.37～1.44)之间。Kubelka-Munk二流模型下组织对同一波长的激光及其线偏振激光的吸收系数、散射系数、总衰减系数和有效衰减系数没有显著性差异(P＞0.05)。组织对不同波长的激光或其线偏振激光的吸收系数、散射系数、总衰减系数和有效衰减系数则有些是有明显的差异。     

Planar waveguide lasers and structures created by laser ablation — an overview

The parameters of planar and channel waveguide lasers fabricated by different techniques are reviewed. Materials and properties of thin films used for creation of planar waveguide lasers are summarized. The parameters of active and passive planar waveguides created by the method of pulsed laser deposition and problems of laser deposition are described. The aspects of laser generation of planar waveguide lasers, resonators and channel waveguides are presented. The results of our experiments of laser deposition of thin Ti:sapphire layers and thin layers of Nd:YAG and Nd:YAP are briefly discussed. This work was supported by the grant of Czech Grant Agency No. 102/96/0429.     

Measurement of birefringence in thin-film waveguides by Rayleigh scattering

A method of measuring birefringence in slab and ridge waveguides based on the coherent superposition of Rayleigh light scattering from TE and TM polarized modes is described and demonstrated in silica-on-silicon waveguides. A measurement accuracy of approximately 10(-6) has been achieved. This method is used to determine the evolution of waveguide birefringence with annealing temperature in phosphorous-doped glass waveguides. The measured birefringence increases rapidly with annealing temperatures up to 800 degrees C but remains unchanged for higher-temperature anneals. We interpret this threshold as the temperature above which glass can flow.