Quantum Well Optical Modulator With Circular Patch Antenna for Millimeter-Wave Radio Over Fiber System

A circular patch antenna-coupled quantum well optical modulator for 1550 nm is proposed for the incident millimeter-wave polarization angle-independent phase modulation. The core layer of the modulator is composed of a multiple five-layer asymmetric coupled quantum well structure. The design and theoretical millimeter wave reception characteristics of circular and rectangular patch antennas with a gap structure are theoretically discussed for comparison. The circular antenna with an outer radius of 330 μm and a gap radius of 310 μm is designed. The optical phase modulators with both types of antennas are fabricated, and their modulation characteristics in the 60 GHz millimeter wave band are demonstrated and compared. The phase modulation independent of the incident millimeter-wave polarization angle is successfully realized. The CSR of 55.0 dB (3.56 mrad of phase shift) is obtained when irradiated with 60 GHz millimeter waves. The phase shift of 3.0 to 3.6 mrad is obtained at any polarization angle of the radio waves at an incident power density of 4.4 W/m².