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ABSTRACT: We discuss the effects of waveguide geometry on the radiation loss
of tightly curved multimode dielectric waveguides. Three waveguide
geometries are investigated: a ridge waveguide, a buried waveguide, and
an interdiffused waveguide. We compare the effective index method with
both semi- and full-vectorial method-of-lines analyses for these
waveguide geometries. This comparison shows that the effective index
method is accurate for curved waveguides except where the outer
confinement region is in cut-off or, in the case of TM-polarization, for
the ridge waveguide. In the latter case, the full-vectorial
method-of-lines predicts a resonant feature of the TM-mode radiation
loss of curved ridge waveguides; this is not predicted by either the
semivectorial method-of-lines or the effective index method
Journal of Lightwave Technology 03/1996; · 2.78 Impact Factor
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ABSTRACT: Numerical simulation based on the scalar beam propagation method,
was used to investigate the performance of waveguide electrooptic beam
deflectors. The deflectors under investigation consist of a stack of
electrooptically controlled prisms in a waveguide. The results were
compared to earlier simplified analysis. It was found that for given
overall device dimensions, the number of interfaces between prisms in a
prism-type electrooptic deflector has significant influence on the
device performance when it is small. To avoid wavefront distortion,
unwanted reflection from the interfaces, and asymmetry in the deflection
angles caused by small number of interfaces, one should use more than
about ten interfaces in a typical deflector. Additional insights of
device operation and design issues are discussed
Journal of Lightwave Technology 11/1995; · 2.78 Impact Factor
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ABSTRACT: The radiation loss of curved ridge dielectric waveguides can show
an oscillatory dependence on radius for the TM-polarisation. This effect
is predicted only by a three-dimensional full vectorial analysis and is
confirmed experimentally in S-bend dielectric ridge waveguides
Electronics Letters 08/1995; · 0.96 Impact Factor
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ABSTRACT: The authors present an improvement to the method-of-lines
technique which significantly decreases the computations required to
achieve accurate solutions for the propagating modes of
three-dimensional dielectric waveguides. This method is applied to a
circular dielectric waveguide to assess its advantages
Electronics Letters 07/1994; · 0.96 Impact Factor
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ABSTRACT: The authors present a novel design for a Y-junction splitter for
ring waveguides based on the principle of mode conversion by
self-interference. Power in the device is diverted from an edge-guided
ring mode into a straight guide with little loss to radiation modes. The
power injected into the fundamental modes of both the straight and ring
guides is maximised relative to higher order modes
Electronics Letters 07/1994; · 0.96 Impact Factor
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ABSTRACT: We have investigated, by simulation, the coupling efficiencies of
a ring laser into a straight guide in terms of the power splitting ratio
between the fundamental modes of the ring and straight output guide, as
well as the proportion of power lost to higher-order excitations of the
straight guide. The results show that the typical design for a branching
ring laser can be optimized by offsetting the output guide position and
choosing the proper guide width. This analysis also shows that the
symmetrical dual output port design (i.e. tangential straight guide) can
result in very poor output coupling efficiencies as compared to the
single output port design
Journal of Lightwave Technology 06/1994; · 2.78 Impact Factor
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ABSTRACT: A semiempirical relation has been developed for determining the
minimum allowable radius of curvature of a circular waveguide with an
edge-guided fundamental mode. The specified parameters are the
wavelength, the effective refractive index of the waveguide, the lateral
index step, and the allowable radiation loss coefficient. This relation
was fitted and verified against numerically evaluated solutions of
Maxwell's equations in two dimensions for lateral index steps
0.01<ΔN<0.1, for effective indices of refraction 3<N<4
(appropriate for the GaAs/Al<sub>x</sub>Ga<sub>1-x</sub>As system), and
for radiation losses of 10<sup>-4</sup> <α<sub>r</sub><100
cm<sup>-1</sup>. The difference between the results of solving Maxwell's
equations and the semiempirical relation over these parameter ranges was
determined to be less than 2%
Journal of Lightwave Technology 01/1994; · 2.78 Impact Factor
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ABSTRACT: Process conditions for fabricating Si‐O impurity‐induced layer disorder defined Al x Ga 1-x As‐GaAs buried heterostructure quantum well lasers utilizing a fully self‐aligned planar process and conventional As free open‐tube‐furnace annealing are presented. An SiO 2 layer, deposited by sputtering, was used as a diffusion source for Si and O impurities as well as a source for Ga vacancies that enhance impurity diffusion and allow for a reduction in the required annealing temperature and time. A self‐aligned native oxide of the Al x Ga 1-x As cladding layer was used to form a Zn diffusion mask and dielectric layer. Lasers fabricated using this process exhibited threshold currents as low as 2.72 mA and external differential quantum efficiencies of 79% at room temperature in continuous operation.
Journal of Applied Physics 03/1993; · 2.17 Impact Factor
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ABSTRACT: Process conditions for fabricating ridge geometry Al x Ga 1-x As‐GaAs quantum well heterostructure laser arrays utilizing a high quality self‐aligned native oxide of Al x Ga 1-x As are presented. Wet oxidation is performed, after etching ridges, via H 2 O vapor in a N 2 or N 2 /H 2 (10%) carrier gas at 435–445 °C for 15–20 min. The formation of a uniform smooth oxide was found to be critically dependent on the crystal environment prior to the oxidation process. Characteristics of devices fabricated by this process are presented.
Applied Physics Letters 05/1992; · 3.84 Impact Factor
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ABSTRACT: A unified process for integrating lasers, detectors, modulators, and waveguides for optoelectronic integrated circuits (OEICs) on a single substrate is described. The devices are fabricated from a quantum well heterostructure (QWH). Initial efforts have been directed toward fabricating these devices in a ridge waveguide form because of the simplicity of fabrication. A QWH is grown by metalorganic chemical vapor deposition (MOCVD) and modified as necessary to produce detectors, modulators, and waveguides. The detector is essentially given, because the laser structure can be operated with no bias (no dark current) and photogenerated carriers will be swept out of the quantum well by the large built-in field. The waveguides are produced by etching a ridge to induce an effective lateral index step, as are the other devices, and the GaAs quantum well can also be slightly disordered using Ga vacancy diffusion to shift the absorption edge of the waveguide to a longer wavelength than the emission wavelength of the laser. The modulator regions may be Ga vacancy diffused or not, depending on the modulator type and function. The characteristics of an inline laser-modulator-detector structure are reviewed. Results of modeling ridge waveguide structures for Δβ modulators are discussed. Several self-aligned fabrication processes that have the best prospects for reliable integration of lasers, detectors, modulators, and waveguides are introduced
High Speed Semiconductor Devices and Circuits, 1991., Proceedings IEEE/Cornell Conference on Advanced Concepts in; 09/1991
