Optical phase feed network and ultra-wideband phased array

Abstract

An optically addressed phase feed network for an ultra-wideband RF phased array is proposed. The architecture leverages recent advances in the development of optical RF source generation and coherent optical system in the fiber optics. By using polarization maintaining (PM) fibers two coherent optical tones can be encoded in two orthogonal states and transmitted to a high-speed photomixer at the antenna head for RF signal transmission. The copropagation in the same fiber enables two optical signals experience same environmental impact, thereby significantly minimizing phase fluctuation. To phase the antenna array, electro-optic z-cut LiNbO3 phase modulators are used, in which phase modulation is dominated at one of the polarizations, consequently leading to electrically addressed phase shift at the mixer. In addition, dynamic polarization control is also investigated to compensate the polarization fluctuation due to bending, thermal and mechanical stresses. A 1×2 array is implemented to demonstrate the feasibility and robustness of the proposed system.