Terahertz electro-optic modulation in biased GaAs quantum wells

Terahertz-optical mixing is studied in biased GaAs quantum wells for voltage-controlled wavelength conversion. The mixing produces sidebands, which appear at ω_sideband=ω_optical+ncω_{Teraher tz}, where n=±1, ±2,... sidebands are strong when the optical beam or the sum of the two laser beam excite resonances of the quantum well. Their intensity is found to depend strongly on the electric bias and on terahertz frequency. The n=±1 sideband intensity is zero when the sample is unbiased and increases significantly with bias. The sideband is strong when the terahertz laser frequency is tuned in resonance with an intersubband transition and also at low terahertz frequencies. At low frequencies the system is equivalent to quantum well modulators. We show how the response extends into the terahertz range.