Propagation losses in metal-film-substrate optical waveguides

The propagation losses in metal-film-substrate two-dimensional optical waveguides are calculated. Losses for confined modes may become large and are at least an order of magnitude larger for TM than for TE modes. Higher order modes suffer more loss than the fundamental mode. Such mode-dependent loss can make efficient mode analyzers, useful for integrated optics modulation schemes.     

Low-loss bends in planar optical ridge waveguides

Bending losses lower than 0.7 dB for 90° bend sections with radii of curvature as small as 75 μm were measured on silicon-based Al₂O₃ ridge waveguides with SiO₂ cladding layers at a wavelength of 632.8 nm. These values, which are close to the calculated values, are the lowest thus far reported     

Propagation characteristics of trapezoidal-cross-section ridge optical waveguides

A detailed experimental and theoretical study has been carried out on the dispersion characteristics of narrow-ridge glass-film optical waveguides formed by ion etching of photoresist. Agreement between experiment and finite-element numerical calculations varies from moderately good to excellent.     

Splicing losses between dissimilar optical waveguides

A simple computational formalism has been derived for the analysis of splicing and return losses between different optical waveguides. It has been found that the splicing loss can be approximated by the overlap integral method as long as total reflectance is negligible. The reciprocity of splicing loss between two single-mode waveguide is theoretically confirmed while return loss is found nonreciprocal. The return loss can be tolerably approximated by simple Fresnel formula except near the resonance. When close to the resonance, the deviation from Fresnel approximation is found to be strongly dependent on the structure of the waveguide and the refractive index difference between the core and clad     

WKB analysis of bend losses in optical waveguides

A more complete Wentzel-Kramers-Brillouin (WKB) analysis of bend losses is given for a circularly curved waveguide. Using the WKB approximation with a conformal transformation of a curved optical waveguide, is shown to give more accurate bend loss results     

Bend losses in GaAs/AlGaAs optical waveguides

Circular bends with low excess bend loss (? l dB) and radii of a few millimetres were fabricated using GaAs/AlGaAs single-heterostructure rib waveguides with propagation loss ? 1 dB/cm. The effect of rib geometry and roughness due to bend pattern quantisation on the excess bend loss at 1.52/?i was investigated.     

用于光互连的聚硅氧烷脊型光波导研究

采用软成型和图案转移技术,制备了可用于高速芯片间光互连的大尺寸聚硅氧烷脊型光波导,光波导长度达23cm.利用有效折射率法,对芯层残留层和传输模场的关系进行了分析.采用截断和数字化散射两种方法,测得输入光波长为633nm时的平均传输损耗小于0.14dB/cm.研究结果表明,波导的长度和损耗指标满足高速芯片间光互连的要求.     

Radiation losses from sinusoidal serpentine bends in optical waveguides

Radiation losses due to curvature in optical waveguides with sinusoidal bends are found in terms of the amplitude and period of the fluctuation. For tolerable loss, the critical factor is the minimum radius of curvature, i.e. the radius of curvature at a point of maximum deviation.     

Scattering losses in single and double heterostructure semiconductor optical rib waveguides

The relative scattering losses due to rough rib sidewalls in GaAs/AsGaAs single and double heterostructure rib waveguides are investigated theoretically. The authors find that double heterostructures exhibit at least as much scattering loss as single heterostructures, provided that such comparisons are made among structures with comparable bend performance.<>     

Wide Y-junctions with low losses in three-dimensional dielectric optical waveguides

This paper proposes a simple structure (antenna coupledY- junction) which reduces radiation losses ofY-junctions in 3-D optical waveguides by decreasing refractive indexes near the branching regions. A principle to reduce radiation losses and a design theory are presented for the newY-junction by using geometrical optics. It is theoretically shown that losses of the properly designed 3-DY-junctions can be reduced by around an order of magnitude compared to those of conventional ones when the branching angles are large.     

Radiation losses of tapered dielectric waveguides: a finitedifference analysis with ridge waveguide applications

The finite-difference third-order simplified wave equation method is used to study the radiation losses of optical waveguides with step (abrupt) and parabolic tapers, including the radiation losses of the tapered ridge waveguides used as electro-optic phase modulators for tuning the frequencies of infrared lasers. The radiation losses of the parabolic taper given by Burns et al. is found to be under 5%. The results of a step taper are compared with Marcuse's; and found to be in good agreement. The numerical results are also compared with those from the coupled wave equations used by Sporloder and Unger     

A novel self-aligned fabrication process for nickel-indiffusedlithium niobate ridge optical waveguides

A novel self-aligned fabrication process for LiNbO₃:Ni ridge waveguides has been proposed. By using the self-aligned trilayered structure composed of Ni-Ti-Si, the fabrication process is significantly simplified, and takes advantage of suppression of the unwanted planar waveguides and high-coupling efficiency to a single-mode fiber as compared to the conventional processes. Detailed investigations into the characteristics of the ridge waveguides have also proved to be informative under different fabrication parameters. Moreover, the novel self-aligned fabrication process was applied to fabricate a ridge waveguide Mach-Zehnder modulator. The measured half-wave voltage and extinction ratio mere 20.5 V and 12 dB (@1.3 μm), and were 4.2 V and 8 dB (@0.6328 £gm)     

RTA removal of E-beam-induced damage in GaAs-AlGaAs heterostructures as determined by magnetotransport characterization

Measurement was made of the effect of electron energy on the 2D EG transport properties of high electron mobility transistor (HEMT) structures at low temperatures. The structures were grown by molecular beam epitaxy (MBE) with a 2D EG approximately 850Å below the surface. A Cambridge EBMF 10.5 was used for electron irradiation with electron energies between 2.5 and 20 keV. The HEMTs were fabricated into Hall bars, and damage was assessed by changes in the 2D EG concentrations as determined from Shubnikov-de Haas oscillations and changes in the mobility as determined from the zero magnetic-field resistivity. For electron energies from 5.0 to 12.5 keV, the electron dose produced a degradation of the Hall mobility. No damage was observed for electron energies outside this range; this result is attributed to the penetration depth and damage distribution. The effect of performing RTA on all samples simultaneously at 450° C for 30 sec was to remove damage and in some cases restore the sample to its original mobility.     

Finite curvature and corrugations in dielectric ridge waveguides

The authors present a technique based on the concept of local modes that is capable of handling finite, tight bends in open dielectric waveguides of the LSE-mode or LSM-mode type, together with step discontinuities along the arc. By analytical manipulation of the continuum, the approach results in a small system of coupled integrodifferential equations, one for each discrete propagating mode. The latter system is solved analytically by means of an iterative approach to the point where it can be implemented on a desktop computer. The method was applied to the curved, corrugated, dielectric ridge waveguide, yielding numerical results in general agreement with published experimental points. The technique is equally applicable to other curved open transmission media in the microwave, millimetric, and integrated optics ranges     

Wet-etched ridge waveguides in y-cut lithium niobate

By the technique of nickel indiffusion proton exchange (NIPE) and the technique of buffered proton exchange (PE) melt, wet-etched ridge waveguides in y-cut LiNbO₃ are fabricated for the first time. The fabricated ridge waveguides have smooth surfaces and are good enough for low-loss waveguides. Moreover, a ridge waveguide Mach-Zehnder modulator in y-cut LiNbO₃ is fabricated. The measured half-wave voltage is about 30% lower than that of a conventional modulator. The wet-etched ridge waveguides in y-cut and z-cut substrates are also characterized for comparison     

Determination of bending losses in rectangular waveguides

This paper details an accurate method for computation of bending losses in rectangular optical waveguides which we combine with perturbation theory to account for the fields in the (outer) corner regions of the guiding channel. In the case of the weakly guiding channels of interest in optical signal processing, the correction to the loss coefficient due to the corner fields is shown to be in excess of 50%     

Low transition losses in bent rib waveguides

We reduce the transition losses that occur between curved and straight rib waveguides, by offsetting the guides and placing isolation trenches. Using a three-dimensional (3-D) semivectorial beam propagation program, we also can investigate more novel effects such as rib heights and sidewall slopes. Our consideration of all these effects results in an optimized design     

Optically CW-induced losses in semiconductor coplanar waveguides

The authors present a quasi-static analysis of photoinduced wave attenuation in a continuously illuminated coplanar waveguide transmission line on a semiconductor substrate, using a conformal mapping technique. The relevant effects of charge carrier diffusion and surface recombination on photoconductivity and plasma penetration depth have been incorporated into the theory. This allows a quantitative estimate of optically induced losses as a function of the various light-source and substrate parameters by means of numerically calculated diagrams. In the particular case of small-plasma-depth excitation, an appropriate, analytical expression for the light-controlled attenuation constant is presented. Initial experimental results are in relatively good agreement with the theory     

Low-loss straight and curved ridge waveguides in LPE-grown GaInAsP

Loss measurements on ridge waveguides in LPE-grown GaInAsP at a wavelength of 1.3 mu m are presented. An attenuation of 4.5 dB/cm has been obtained for straight waveguides, and for curved waveguides an excess loss at low as 0.7 dB was found for a 20.8 degrees S-bend with a radius of 300 mu m ( approximately=1.5 dB/90 degrees ).<>