InGaAs/InAlAs multiple-quantum-well optical modulator integrated with a planar antenna for a millimeter-wave radio-over-fiber system

An InGaAs/InAlAs multiple-quantum-well (MQW) optical phase modulator integrated with a planar antenna for a millimeter-wave (MMW) radio-over-fiber (RoF) system is fabricated, and its high-speed modulation under irradiation of MMW signals is experimentally demonstrated. The modulator exhibits a carrier-to-sideband ratio (CSR) of 62.7 dB, corresponding to a phase shift Δϕ of 1.46 mrad under irradiation of MMW signals with an RF power density P of ∼77 W/m2 at a frequency of 57.5 GHz. The modulator is operated over the C band in optical communications. The modulation operation was attributed to the large change in refractive index caused by the quantum-confined Stark effect in the MQW. This is the first case where the refractive index change of a semiconductor was used as an antenna-coupled optical modulator.