Large Quadratic Electro-optic Effect in GaAs/AlGaAs Multiple Quantum Wells (MQWs).

We simultaneously measure the intensity modulation level and the optical spectrum of the output of an MQW modulator, and use these data to deduce the electro-optic coefficients. The effect is quadratic, with a measured |S sub(33)| = 4.6 x 10 sup (-13) cm sup 2 / V sup 2 at a wavelength 12 meV below the band-gap. This is approximately 800 times the coefficient measured further from the band-gap. We are able to achieve a fractional change in the refractive index of 3.7%. Despite the size of this effect, when we operate the device as an intensity modulator, we observe a linewidth-enhancement factor of proportional to = 1.0, which means the chirp induced in the device's output will be small.