The use of a resonant tunnelling diode buried in the centre of an opti
cal waveguide to achieve optoelectronic modulation through the Franz-K
elydsh effect is demonstrated. The response of the modulator to both a
pulsed and CW electrical signal is described in detail. It has been s
hown that owing to the nonlinear response of the RTD it is possible to
switch the modulator with a 0.1V electrical pulse.