Ralph Spickermann

Experimental analysis of millimeter wave coplanar waveguide slow wave structures on GaAs

Microwave coplanar waveguide slow wave structures suitable for use in traveling wave electrooptic modulators were experimentally investigated to 40 GHz. Velocity slowing is achieved by introducing periodic slots in the ground planes. Structures both on semiinsulating GaAs substrates and on epitaxial layers grown by molecular beam epitaxy on semiinsulating GaAs substrates were examined. In the measurements the thru-reflect-line calibration method was used and its limitations are discussed. The characteristic impedance, phase velocity and loss coefficient of these lines were extracted from measured S-parameters. Effects of various dimensions on these line properties are presented and discussed. Results indicate that significant phase velocity slowing without dispersion at least up to 40 GHz is possible with this approach. This is true both on semi-insulating GaAs substrates and specially designed epitaxial layers. A design approach to achieve a specified phase velocity and characteristic impedance is given. >

In traveling wave modulators which velocity to match

Optical modulators with very wide electrical bandwidths are essential components for optical control of microwaves and millimeter waves as well as high speed optical communication systems. A very desirable approach to obtain very wide electrical bandwidths is the so-called traveling wave design. In such a design electrode is designed as a transmission line. Therefore, electrode capacitance is distributed and does not limit the modulator speed. In this summary we will only concentrate on the measured small signal modulation response of the GaAs-AlGaAs electro optical modulator device at 1.3 and 1.55 /spl mu/m.

A low-loss beam splitter with an optimized waveguide structure

Novel beam splitters with optimized waveguide structures are designed and fabricated using reactive ion etching. At 1.15 mu m the excess loss of the beam splitter is measured to be 1.2 dB for TE and 1.8 dB for TM polarizations, respectively.<<ETX>>

A polarization independent GaAs-AlGaAs electrooptic modulator

Two designs for polarization independent GaAs-AlGaAs interferometric electrooptic modulators are described. One design uses the linear electrooptic effect to couple degenerate TE/TM eigenmodes of a single-mode waveguide. In the other design the eigenmodes need only be near degenerate. The design using the coupling between near degenerate TE/TM modes utilizes a novel biasing scheme. A novel polarization independent GaAs-AlGaAs interferometric optical modulator based on this design has been fabricated and characterized at 1.3 /spl mu/m. This modulator is fabricated as a traveling wave modulator incorporating 50 /spl Omega/, phase velocity matched, low microwave loss electrodes for maximum electrical bandwidth.

GaAs/AlGaAs traveling-wave electro-optic modulators

A GaAs/AlGaAs traveling wave Mach-Zehnder electro-optic modulator with novel slow wave electrodes was fabricated on undoped epitaxial layers. Using appropriate electrode engineering velocity matching with matched impedance and low microwave loss was achieved. Device had a measured electrical bandwidth greater than 40 GHz at 1.55 micrometer. The measured bandwidth at 1.3 micrometer was 37 GHz. The mechanism limiting the bandwidth was identified as phase velocity matching rather than group velocity matching.

Distributed microwave effects in high speed semiconductor lasers

In this paper we analyze and experimentally show that high speed semiconductor lasers approximately 300 /spl mu/m long and operating at frequencies above 25 GHz should be treated as distributed electrical elements. The analysis and experiments indicate that the microwave propagation is lossy, slow wave and dispersive, and that these distributed effects have important implications for the use of directly modulated lasers in high speed optical links.<<ETX>>

Ultra wide electrical bandwidth GaAs/AlGaAs electrooptic modulators

A high speed GaAs/AlGaAs traveling wave Mach-Zehnder electrooptic modulator has been fabricated. The device uses a novel slow wave electrode design to achieve phase velocity matching and has a measured electrical bandwidth greater than 40 GHz. An improved electrode design has been characterized and is currently being integrated into a modulator to increase the bandwidth further.<<ETX>>

GaAs/AlGaAs electrooptic modulator with novel electrodes and bandwidth in excess of 40 GHz

This abstract reports the latest results of our ongoing effort on GaAs/AlGaAs traveling wave Mach-Zehnder electrooptic modulators. Previously we reported >40 GHz electrical bandwidths but with rather large on/off voltage V/sub /spl pi//. By introducing a completely different electrode design we have reduced the V/sub /spl pi// from 28 V to 10 V while keeping the measured bandwidth >40 GHz. Furthermore the new design reduces the microwave loss, which determines the bandwidth, from 4.6 to 3.2 dB/cm at 35 GHz. Additionally, this new electrode geometry has the potential for further V/sub /spl pi// reduction while maintaining low loss.

Effect of electrode gap variation on high speed traveling wave electro-optic modulators

Summary form only given. We report our results on GaAs-AlGaAs traveling wave Mach-Zehnder electro optical modulators. We measured the phase velocity, matched modulators with electrode /spl mu/m gaps. This paper discusses the effect of this gap variation on modulator characteristics.