Velocity-matched electrodes for compound semiconductor traveling-wave electrooptic modulators: experimental results

Abstract

Abstruct-Coplanar strips, capacitively loaded with fins and pads and capable of achieving the microwavdoptical wave velocity-match condition in GaAs-and InP-based electrooptic modulators, are described. Measurements on electrodes, fabricated to have dimensions appropriate for use in conventional, Mach-Zehnder-type modulators in the 5 4 0 GHz range, show that these electrode structures can be made to obtain the desired match between the microwave effective index and the effective indexes of AlGaAs and InGaAsP optical waveguides, while having loss coefficients -0.7 Npkm at 40 GHz.

Analysis of Segmented Traveling-Wave Optical Modulators

“…In the past, microwave properties of segmented traveling-wave electrodes have been studied experimentally [15], [16], as well as by using some simple inductance-ca- pacitance (LC) circuit model [17], [18]. These studies did not involve the analysis of modulation frequency response.…”

General equations for the induced phase shift in resonant electrooptic modulators

“…The agreement between both traces is quite good and the estimated maximum value using the numerical technique of [4] is only 3% greater than that from (6). The inset shows the relative error between both methods as a function of , showing that the proposed formulation is a very good approximation for the usual values of losses in a conventional transmission line.…”

“…This conclusion is especially important for GaAs modulators where the velocity of the electrical signal is usually greater than that of the optical signal. For example, [6] gives and for a conventional coplanar strip, which implies a walkoff parameter closer to the optimal walkoff of most topologies of Table I than the velocity matching condition . Therefore, designing the electrodes to match velocities could be unnecessary, even counterproductive.…”

“…Otherwise, if the losses are very high, the accuracy of (5) decreases since the voltage distribution deviates from the assumed standing wave pattern in (2). To illustrate this effect and give an estimate of the error, we particularize (5) for a open-ended resonator ( and ) (6) In this equation, the parameter of (5) has been replaced by , being a term which accounts for (5) the frequency response of the resonator (see the Appendix). The addition of this term extends (5)-we denote instead of -and gives the response of the induced phase shift around the resonance frequency.…”

Investigation of Temperature Dependence in the Dark Current of InAs Diode Detectors

“…The microwave index for conventional, thin, coplanar electrodes on GaAs is -2.6 whereas the effective index for the lightwave guided by typical AlGaAs/GaAs optical waveguides is in the range 3.2 -3.4. Higher microwave indices (larger than 2.6) can be achieved by incoprating capacitive fins, and/or capacitive f m with pads on their ends, in the gaps between the coplanar electrodes [1], [3]. Here, we compare SW coplanar strips (SW-CPS) with SW coplanar waveguides (SW-CPW).…”