A degradation mode in Mach-Zehnder semiconductor optical modulators wi
th InGaAs/InAlAs MQWs is investigated. The main accelerating factors a
re the input optical power and the applied voltage in high stress test
s. The main cause of degradation is found to be the destruction of the
p-n junction on the side wall of the ridge waveguide. The time to fai
lure is consequently expected to be >10(5)h under practical operating
conditions in optical fibre transmission systems.