Characteristics of Multi-Beam Module Using Waveguides for Laser Scanning Optical Systems

A multi-beam module using optical waveguides has been studied for a laser scanning optical system. Laser diodes with a wavelength of 780 nm are assembled on a silicon substrate. The beams emitted from the laser diodes are directly coupled into waveguides. This multi-beam module is assembled on a metal substrate with a photodiode. The photodiode controls the power of each laser diode on the silicon substrate. The multi-beam module is able to increase the output speed of high-density image printings, and the speed for high-speed color printings. We have developed the four-beam module with beam divergence angles of 11 degrees and spatial beam interval of 24 μm. Additional heat sink and optimizing tip-bonding between the laser diode and solder pad on the silicon substrate is useful to stabilize laser power against rising temperature.     

Planar waveguides in multicomponent glasses fabricated by field-driven differential drift of cations

The fabrication of planar waveguides by a constant-current thermal poling procedure in multicomponent glasses rich in alkali or alkaline earth ions is described. Near the anode, the dc electric field applied to the substrate separates the mobile cations into regions according to their mobility. Each region presents a different refractive index, allowing a waveguide to be formed. This method produces waveguides with an index increase greater than 10(-2) in soda-lime glass with no external ion source, and the waveguides are buried beneath the substrate surface without an additional step.     

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.     

A simple variational analysis of diffused channel waveguides

The variational analysis of Ti:LiNbO₃ strip waveguides is resolved into two related one-dimension problems, which provides a new iterative approach for the calculation of the mode parameters and the propagation constant. The analytical expressions of the local effective index profiles can be obtained from the variational analysis. The parameters of four trial solutions for the fundamental mode in a diffused-channel waveguide have been determined by using the present method. Comparison with results using the effective method shows that these four approximate expressions are accurate enough. It is also shown that this method converges very quickly and is suitable for both diffused channel waveguides and optical waveguides with rectangular cross-section.     

扩散沟道光波导的条形传递函数解

利用条形传递函数方法分析了二维扩散沟道光波导的传播特性,对两种典型折射率分布计算的数值结果与精确解及其它方法的结果进行了比较,表明该方法具有优于其它数值方法的精度.     

Dispersion properties of silicon nanophotonic waveguides investigated with Fourier optics

We experimentally investigate the dispersion relation of silicon-on-insulator waveguides in the 1.5 microm wavelength range by using a technique based on far-field Fourier-space imaging. The phase information of the propagating modes is transferred into the far field either by linear probe gratings positioned 1 microm away from the waveguide core or by residual gratings located on the sidewalls of the waveguide. As a result, the dispersion curve of rectangular and slot waveguides as well as the group index dispersion are accurately determined.     

全硅矩形截面脊形波导的研制及其损耗分析

运用有效折射率法和微分法分别对全硅矩形截面脊形波导的模式特性和模吸收损耗系数作了分析，通过乙二胺－邻苯二酚水溶液（ＥＰＷ）各向异性腐蚀的方法，研制成了矩形截面脊形全硅光波导，并对其损耗特性进行了研究和讨论。     

Fully three-dimensional accurate modeling of scattering loss in optical waveguides

Scattering loss in high-index-contrast optical waveguides has been modeled by a rigorous 3D numerical algorithm based on volume current method. The electromagnetic field generated by the wire current distribution simulating sidewalls roughness has been calculated by 3D finite element method. The developed modeling technique does not introduce any approximation in radiated power estimation. Numerical results obtained by our model have been compared with some experimental results reported in literature for four typical sub-micrometer high-index-contrast waveguides realized by different technologies and a very good agreement (relative error less than 3%) has been demonstrated. Closed-form expressions for scattering loss in low-index-contrast waveguides have been also derived and discussed. Developed modeling technique has been compared with other three-dimensional algorithms for scattering loss estimation and its advantages in terms of accuracy, computation time and generality have been pointed out. Scattering loss dependence on the parameters of the roughness distribution has been finally discussed.     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Charge Flow and Plasma Behavior in Intense Ion Beam Diodes

Intense ion beams are produced in high-power vacuum diodes of various configurations and are believed to be useful for applications in inertial confinement fusion and plasma confinement. Using magnetically insulated diodes, we investigated spatial nonuniformities of the diode plasmas, plasma expansion, ion transverse velocities in the diode gap, electron flow to the anode, and the charge distribution in the gap. Various time-dependent diagnostic techniques including recently developed spectroscopic methods have been used. We observed rapid closure of the diode gap, resulting from fast expansion of the electric field-excluding anode plasma early in the pulse. This contributes significantly to the measured ion current density enhancement. The electron cloud in the gap was seen to spread towards the anode beyond the region of the theoretical electron sheath. This is consistent with observed ion current densities being larger than the values calculated using the actual diode gap. The ion angular spread was found to increase locally due to nonuniform expansion of the cathode plasma for one class of phenomena and of the anode plasma for the other two classes. Part of these phenomena were associated with electron flow to the anode. The ion divergence angle in the gap was observed to be independent of the ion mass and to be significantly smaller than angles previously observed outside the diode.     

Small-bore fluorocarbon polymer-coated silver hollow glass waveguides for Er:YAG laser light

Several types of fluorocarbon polymer (FCP)-coated silver hollow glass waveguides have been fabricated for Er:YAG laser delivery by using the improved wet chemical technique and dynamic coating procedure. The straight losses of 2 m long 700 μmØ and 540 μmØ waveguides are 0.4 and 1.0 dB, respectively. The transmission losses of these waveguides are below 1.5 dB even when the waveguides are bent to 180° with the bending radius of either 20 or 15 cm. The waveguides with the small diameters of 320 and 200 μm have also been developed for clinical treatment, which exhibit low enough transmission losses for Er:YAG laser light.     

Determination of dynamic characteristics of rectangular plates with cutouts using a finite difference formulation

The paper describes a method for the prediction of dynamic characteristics of rectangular plates with cutouts. The method is based on the use of variational principles in conjunction with finite difference technique. A concept of interlacing grids has been developed to express the strain energy of nodal subdomains into which the plate is divided. The use of this idea has been demonstrated in relation to internal and boundary nodes. Natural frequencies and corresponding mode shapes of rectangular plates with one and two cutouts have been predicted and experimentally verified.     

L波段高功率波导缝隙阵设计与数值模拟

设计了一种基于宽边纵缝驻波阵的高功率射频微波辐射系统,系统由四路矩形波导以及聚四氟乙烯天线窗组成。天线内采用真空绝缘实现天线高功率容量,天线窗真空侧采用周期刻三角槽技术抑制高功率微波介质表面击穿。在波导缝隙阵与天线窗之间设计支撑板,除支撑天线窗外还可抑制表面波电流。采用HFSS数值模拟软件对辐射系统进行了优化设计。数值模拟结果表明,设计的辐射系统在频率为1.575 GHz时,增益为22.7 dBi,天线口径效率为98.3%,反射系数为-25 dB,带宽达到5%,带宽内天线增益波动小于等于0.4 dB、天线口径效率大于等于98%、主瓣指向偏差小于等于1.2。系统功率容量达到1.92 GW。     

A variational mode expansion mode solver

A variational approach for the semivectorial modal analysis of dielectric waveguides with arbitrary piecewise constant rectangular 2D cross-sections is developed. It is based on a representation of a mode profile as a superposition of modes of constituting slab waveguides times some unknown continuous coefficient functions, defined on the entire coordinate axis. The propagation constant and the lateral functions are found from a variational principle. It appears that this method with one or two modes in the expansion preserves the computational efficiency of the “standard” effective index method while providing more accurate estimates for propagation constants, and well-defined continuous approximations for mode profiles. By including a larger number of suitable trial fields, the present approach can also serve as a technique for rigorous semivectorial mode analysis.     

Single fiber model of particle retention in an acoustically driven porous mesh

A method for the capture of small particles (tens of microns in diameter) from a continuously flowing suspension has recently been reported. This technique relies on a standing acoustic wave resonating in a rectangular chamber filled with a high-porosity mesh. Particles are retained in this chamber via a complex interaction between the acoustic field and the porous mesh. Although the mesh has a pore size two orders of magnitude larger than the particle diameter, collection efficiencies of 90% have been measured. A mathematical model has been developed to understand the experimentally observed phenomena and to be able to predict filtration performance. By examining a small region (a single fiber) of the porous mesh, the model has duplicated several experimental events such as the focusing of particles near an element of the mesh and the levitation of particles within pores. The single-fiber analysis forms the basis of modeling the overall performance of the particle filtration system.     

Fundamental nonlinear-optical interactions in photonic fibers: Time-spectral visualization

The nonlinear dynamics of optical signals propagating in fibers or waveguides can be quite complex. Many nonlinear regimes manifest themselves in spectral transformations observed at the output of the fiber. Such time-integrated measurements are severely limiting, however, and, thus, a number of time spectrally resolved techniques have been developed in the past. One of the simplest and most versatile appears to be the cross-correlation frequency-resolved optical gating (X-FROG), because it offers high sensitivity, broad bandwidth, and produces very intuitive two-dimensional spectrograms showing relative temporal positions of various frequency components comprising the output signal. Indeed, certain experiments described in this article can only be performed with X-FROG. For others, X-FROG offers better insight into the fundamental physics of nonlinear interactions; yet others yield beautiful and visually stunning images. Some of the fundamental non-linear-optical interactions in waveguides, such as soliton formation and propagation, soliton stabilization and the emission of Cherenkov continuum, resonant scattering of continuous waves on solitons, and the supercontinuum generation have been visualized with X-FROG and are summarized in this article.     

Hybrid Modes in Highly Oversized Corrugated Rectangular Waveguides

Using a scattering matrix formalism the relative TE/TM eigenmode contents of hybrid modes in oversized corrugated rectangular waveguides has been calculated. The influences of slot depth and corrugation period on the eigenmode mixture have been examined.     

Analysis of current-voltage characteristics of inhomogeneous Schottky diodes at low temperatures

Two approaches of Gaussian distribution of barrier heights in inhomogeneous Schottky diodes have been analyzed by comparing the results for consistency between the two. For this the current-voltage characteristics of inhomogeneous Schottky diodes have been generated by using analytically solved thermionic-emission diffusion equation incorporating Gaussian distribution of barrier heights and by direct numerical integration over a barrier height range. The differences in the results obtained in two approaches are discussed and it is shown that the two approaches yield current-voltage characteristics with slightly different features. The discrepancies in the results obtained in two approaches are attributed to the same series resistance assumed for all elementary barriers of the distribution. It is shown that assigning same series resistance to all barrier of the distribution in numerical integration approach causes current saturation at low bias and inhibits intersection of current-voltage curves from being observable which otherwise occurs in the curves obtained using analytical equation. The paper deals with these aspects in details.     

Characteristic Analysis of Bending Coupling Between Two Optical Waveguides

By means of the coupled mode theory and transfer matrix technique, a method is presented for analyzing the bending coupling between straight and bent rectangular waveguides, or between two bent rectangular waveguides. Calculations show that an effective coupling region exists around the central coupling point, in which the bending coupling appears, beyond which the bending coupling is very weak, and the propagation power in each waveguide becomes constant. When the bending radius becomes larger or the central coupling gap becomes smaller, this effective coupling region becomes wider, in which the coupling behavior becomes stronger.     

Low-loss polymeric optical waveguides with large cores fabricated by hot embossing

A simple low-cost method of fabricating polymeric optical waveguides with large core sizes for plastic optical fibers is presented. The waveguides are fabricated by hot embossing with an ultraviolet-cured epoxy resin stamper. The stamper is fabricated by replication of a rectangular groove mold that is made from silicone rubber replicated from a ridged original silicon master. The master is fabricated by anisotropic etching of (110) single-crystal silicon. Optical waveguides with large core sizes of 100-500 microm have been fabricated, and a low propagation loss of 0.19 dB/cm at 650 nm was achieved.