Showing papers on "Guided wave testing published in 1981"

Coupled wave analysis of obliquely incident waves in thin film gratings.

Abstract: The problem of a guided wave obliquely incident on a grating etched in a thin film guide is considered. Two-dimensional coupled wave equations for the incident and reflected beams are derived for the cases of TE–TE, TE–TM, and TM–TM coupling. Two methods, a ray optic approximation and a coupled beam method, are proposed for the numerical solution of the coupled wave equations. Both methods are illustrated by a number of calculated examples.

Hybrid mode analysis of end effects of planar microwave and millimetrewave transmission lines

Abstract: The phase shift associated with the reflection of a guided wave at the abrupt open end of planar strip and slot waveguides is determined numerically by solving the relevant frequency-dependent hybrid mode boundary-value problem. In addition, nonideally short-circuted ends are considered, i.e. those where the planar guiding structure terminates in a metallisation layer. The method of analysis employed is a Galerkin approach in conjunction with a spectral-domain Green's function interpolation technique and especially suited expansion functions. Its main features are described, and numerical results are presented for most of the technically important types of planar waveguides (microstrip, suspended substrate, slot/fin and coplanar line). The results are compared with published measured data and quasistatic compuations, as far as these are available. The frequency-dependent behaviour of the different end effects is discussed. In an Appendix, it is shown how the numerical approach of this paper can be extended to the analysis of planar n-ports.

Scattering of optical guided waves by waveguide surface roughness: a three-dimensional treatment.

Abstract: The scattering of optical guided waves by waveguide surface roughness has been analyzed in three dimensions. The scattered fields were determined by satisfying the boundary conditions to first order in the height of the surface roughness. The utility of the theory for practical problems is illustrated by developing explicit formulas for the power radiated by a TE guided wave into the medium above the planar waveguide. These formulas are expressed in terms of the surface autocorrelation function.

A Comparison of Thin Film Measurement by Guided Waves, Ellipsometry and Reflectometry

Abstract: The optical properties of thin dielectric films prepared by vacuum deposition and r.f. sputtering have been measured using guided waves, ellipsometry and reflectometry to assess the relative merits and disadvantages of the three techniques. Particular attention has been given to the effect on these measurements of typical film imperfections, for example refractive index inhomogeneity and anisotropy. The guided wave technique is shown to possess the highest precision of measurement, to be relatively insensitive to film inhomogeneity and to provide the most suitable method for studying film birefringence. Ellipsometry has a high sensitivity of measurement that can be usefully applied to thinner films than those required by the other techniques. The method is well suited for studying inhomogeneity, but because of its sensitivity to this film defect, ellipsometric measurements must always be interpreted with care. Reflectometry, although only of limited accuracy in measuring film properties, is widely applica...

Theoretical Investigation of the Electromagnetic Wave Propagation Tool

Abstract: A theoretical investigation of the electromagnetic wave propagation tool (EPT)® is presented. An asymptotic analysis, using contour integration, was utilized to derive approximations for the waves at the receivers of the EPT tool. The waves at the receivers are decomposed into a guided wave and a lateral wave. When the mudcake layer is thin, the lateral wave nearly satisfies the guidance condition of the mudcake layer, and its algebraic decay is diminished from the negative of the three-halves power with distance (thick mudcake) to the negative one-half power with distance. In this case, the guided wave and the lateral wave both propagate with a wave number close to the wave number of the invaded zone. Indeed, plots of the directional dependence of the transmitted wave in the invaded zone demonstrate that more power is directed along the planar boundary in the invaded zone when the mudcake layer is thin. Plots of the total magnetic field and the magnetic field from the guided wave at the receiver locations are presented as a function of mudcake thickness. These plots show the dominance of the guided wave for increasing mudcake thickness. Travel times are also computed, using both asymptotic approximations and a plane-wave assumption. These results are then compared with the results of Freedman and Vogiatzis. Excellent agreement with the plane wave assumption is found for a thin mudcake layer. This analysis validates the schemes used by Schlumberger for interpreting the EPT tool log.

Guided-wave holographic grating beam expander-fabrication and performance

Abstract: A novel realisation is presented of an established optical component_a beam expander which diffracts guided optical waves using an ion-etched holographic grating.

Multimode propagation in anisotropic optical waveguides

Abstract: Using far from cutoff approximation (2a/λ0 ≫ 1) we have derived elegant expressions for the characteristic equations and their relevant solutions to determine the guided wave features of an optical waveguide having an axial dielectric anisotropy. Also, the attenuation constant has been calculated following the concept of a complex permittivity in a lossy medium. For TE and TM, as well as hybrid modes studied here, the results computed by the approximate method show very good agreement with those of the exact analytical solutions. The dependence of the power carrying capacity and attenuation on the waveguide parameters highlights the usefulness of the dielectric anisotropy in optical waveguides.

Submillimeter Guided-Wave Experiments with Dielectric Rib Waveguides

Abstract: The transmission characteristics of rib waveguides are examined in the submillimeter-wave region at Lambda/sub 0/ =337 µm. A number of miniature polyethylene rib waveguides are fabricated by means of a die-cast technique. The mode launching into such a waveguide is performed by focusing a laser beam directly on the end face of the waveguide, while the transmitted power is detected at any point on a waveguide through a movable grating coupler which can couple selectively with one of propagating modes. The measured phase constants show good agreement with the theoretical ones calculated by our analytical method, while the attenuation constants, typicafly alpha lambda /sub 0/ = 4.5 X 10/sup -3/ are found to be about 1.8 times as much as theoretical ones. Finally, the good confinement of fields in the rib portion is proved by means of two simple methods.

500 MHz bandwidth guided wave L-band Bragg cell

Abstract: A 530 MHz bandwidth, 1.74 GHz centre frequency, guided optical wave-SAW Bragg cell is reported on Ti-difiused LiNbO3 substrates.

Guided-Wave Optical Interferometer Using Periodic Structures

Abstract: An important area in integrated optics application is optical interferometer which may benefit from the rigidity of guided-wave optical construction and the precision of optical alignment using photolithographic procedures. Both the mirror reflectors, beam splitter/ combiners can be made of periodic structures. The design aspects of periodic gratings in planar optical waveguide and a sagnac interferometer using periodic gratings are described.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Integration Of Photodetectors And Optical Guided Wave Structures Formed On Silicon Substrates

Abstract: Various configurations of integrated photodetectors and optical guided wave structures will be discussed. Channel waveguide arrays integrated with charge-coupled devices (CCDs) formed on silicon have been used to perform transversal filtering, log detection, high quantum efficiency detection of X = .82μm, and high resolution imaging without requiring small detector array spacings. The latter is accomplished through use of a fan-out channel waveguide array. We shall also describe how computer simulation is utilized to predict crosstalk in linear imaging arrays. The simulation is based on analysis which includes the effects of focusing of the input light, the use of Kettler's equations to describe propagation in a lossy medium, and a solution of the generalized diffusion equation for excited carriers. Crosstalk for a conventional linear image array and one employing a fan-out channel waveguide array is evaluated and compared.

Implementation of photomasks for guided wave optical components by a step-and-repeat process

Abstract: The fabrication of photomasks for integrated optical (i.o.) components presents the particular difficulty of an extreme aspect ratio. It is shown that this problem can often be solved by a synthesizing procedure using a photorepeater. This method is demonstrated for two different versions of i.o. directional couplers (total length 20 mm, width of waveguides 3 μ, width of coupling gap between waveguides 3 μ). Single characteristic parts of the masks, which are composed on the reticle, are joined together by a step-and-repeat process. Residual imperfections of junctions can be neglected for diffused waveguides. Further advantages of the method (constant width of the waveguide and of the separating gap along the total length) are explained. Finally, the i.o. directional couplers produced are examined, and some of their characteristic parameters are described.

Polarization-independent optical guided-wave devices

Abstract: Offset waveguides connected by a transition form an integral part of optical circuits such as interferometric modulators and analog-to-digital converters where directional changes in channel waveguides often occur. Also offset waveguides are needed to connect high density integrated optical circuits to a group of optical fibers. The ends of these optical waveguides, displaced both horizontally and vertically, are usually connected by a transition. These transitions could be a straight section’ or made up of a number of smaller sections.2 On the other hand, the transition can be a smooth curve made up of two curved bends having a constant radius of c~rva ture .~ The reported loss of 1.5 dB, for a transition whose separation length as well as height is 40 mm, is still rather high. In this paper, we report transition losses as low as 0.3 ! C 0.3 dB. The average loss per bend is (0.15 dB and is the lowest so far reported. The shape of the transition is a smooth S-shaped curve,4 represented by a raised cosine function resulting in lower tilt radiation loss. However, the masks were produced by the electron beam exposure system (EBES) where the pattern was written by moving the e-beam in discrete amounts in both the x and y direction but not at arbitrary angles to these directions. The resolution was limited to a quarter micron. Thus instead of a smooth raised cosine curve connecting the offset waveguides, we obtain a staircase structure as illustrated in Fig. 1. The staircase step is 0.25 pm, and the offset height His 100 pm, which represents very nearly the value of the 0.d. of a single-mode fiber. This then will be the minimum separation required between offset waveguides when connecting a closely packed set of fibers to an integrated optical circuit. Several sets of curves were written in the mask, and each set consists of three S-shaped raised cosine transitions, connecting straight waveguides on either side. Each curved section was widely separated (400 pm) to avoid coupling of radiated power from the bends in the case of sharp transitions. The offset length L ranged from 0.1 to 8 mm. For reference purposes, straight sections were written in the mask after every set of waveguides with transitions. Using standard photolithographic techniques, the waveguide patterns were replicated onto LiNb03 substrates. All our experiments were carried out with Z-cut Y-propagating Ti-diffused strip waveguides of 3and 5-pm widths. We report the results of the 3-pm waveguides, fabricated by depositing 300-A thick Ti strips and diffusing them at 98OoC for 4 h. The transition losses were arrived at by subtracting the throughput of the offset waveguides from that of the straight waveguides. The absorption losses in the additional linear length of the curved section can always be neglected for all values of L . Radiation loss through the transition for the TE mode as a function of L was measured. Our results indicate that the loss is primarily due to radiation losses at the bends, since the Ti diffusion seems to eliminate the sharp edges and the loss contribution associated with the quasi-periodic staircase structure. Thus we find a minimum useful transition length rather than an optimum length as previously expected. To achieve an average radiation loss of 0.3 dB through the transition, the separation length must be at least 3 mm in our case. (13 min)

Open Guided Wave Structures for Millimeter-Wave Circuits

Abstract: Open guided wave structures for millimeter-wave integrated circuit applications are reviewed. Analytical and design techniques for various functional circuits are discussed. Some of the important problems to be solved are identified.