R.S. Burton

Design and simulation of waveguide electrooptic beam deflectors

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. >

Wet thermal oxidation of AlxGa1−xAs compounds

Results are presented on the wet thermal oxidation of AlxGa1−xAs. The growth of wet thermal oxides of AlxGa1−xAs is shown to be linear with time. An O2 carrier gas was found to form a self‐terminating oxide for compositions investigated (x≳0.4), but required elevated temperatures for substantial growth. The use of a medium oxygen concentration (∼20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al0.6Ga0.4As from 1.9 to 1.0 eV while increasing the activation energy of Al0.8Ga0.2As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.

Self‐aligned native‐oxide ridge‐geometry AlxGa1−xAs‐GaAs quantum well heterostructure laser arrays

Process conditions for fabricating ridge geometry AlxGa1−xAs‐GaAs quantum well heterostructure laser arrays utilizing a high quality self‐aligned native oxide of AlxGa1−xAs are presented. Wet oxidation is performed, after etching ridges, via H2O vapor in a N2 or N2/H2(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.

Comparative analysis of the method-of-lines for three-dimensional curved dielectric waveguides

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.

Semiempirical relation for curved optical waveguide design in the edge-guided mode regime

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 Maxwells equations in two dimensions for lateral index steps 0.01 >

An investigation of the modal coupling of simple branching semiconductor ring lasers

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. >

High‐performance diffusion disordered AlxGa1−xAs lasers via a self‐aligned process and conventional open‐tube annealing

Process conditions for fabricating Si‐O impurity‐induced layer disorder defined AlxGa1−xAs‐GaAs buried heterostructure quantum well lasers utilizing a fully self‐aligned planar process and conventional As free open‐tube‐furnace annealing are presented. An SiO2 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 AlxGa1−xAs 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.

Microelectromechanical tuning of electrooptic devices

The wavelengths of separate-confinement quantum-well heterostructure semiconductor lasers have been tuned by applying mechanical stress through a piezoelectric transducer. In addition, photoluminescence measurements have been made on GaAs samples stressed with piezoelectric bimorphs. It is shown that measurable shifts in the energy gap can be obtained by mechanically stressing the semiconductor with a microelectromechanical system (MEMS) transducer. The authors demonstrate MEMS-induced wavelength tuning with four independent phenomena: photoluminescence, photoresponse, lasing, and electroluminescence.<<ETX>>

Ridge waveguide analysis for integrated optoelectronic devices

The effective index method has been used to calculate eigenmodes of A1GaAs optical waveguides to determine optimal process parameters for their fabrication and to compare the advantages and disadvantages of several different fabrication technologies for the integration of waveguides and lasers.

Spatial-filtered expanded-window lasers for high-power operation of single-stripe lasers

We have investigated, via the beam propagation method, waveguide designs for wide window single-mode single-stripe lasers. The expanded window allows for higher power operation of the laser diode owing to the lower power density at the facets. Higher-order transverse mode suppression is achieved by incorporating a spatial filter in the waveguide that preferentially allows propagation of the fundamental mode. These devices can be fabricated using existing laser diode fabrication technologies such as reactive-ion-etching, native oxidation, or impurity- induced-disordering, and buried heterostructure processes. In our design and analysis of these devices we compare several expanding waveguides to determine the effects on mode selection. Additionally, the catastrophic optical damage power limit for these devices is expected to be significantly greater than for simple fundamental-mode single-stripe lasers.