High-speed III-V semiconductor intensity modulators

A description is given of a GaAs-AlGaAs, loaded-line traveling-wave modulator which has achieved bandwidths up to 36 GHz to date with low (<6 V) drive voltage into a 50 Ω device. The loaded-line design concept is able to combine the high efficiency of vertical p-i-n-type phase modulators with a velocity-matched 50 Ω structure to obtain very high bandwidth/voltage ratios. At 1150 nm, a bandwidth of 25 GHz for V_π=4.85 V typically represents the performance. At 1300 nm, the bandwidth is unchanged but the drive voltage is higher by the expected wavelength-ratio factor. Reduced drive voltage can be obtained without bandwidth sacrifice by choosing a wavelength close to the material band edge. Threefold enhancement in AlGaAs at short wavelength is demonstrated (lumped only, to date)