Compact super-wideband optical antenna

Abstract

We present progress on advanced optical antennas, which are compact, small size-weight-power units capable to receive super wideband radiated RF signals from 30 MHz to over 3 GHz. Based on electro-optical modulation of fiber-coupled guided wave light, these dielectric E-field sensors exhibit dipole-like azimuthal omni directionality, and combine small size (<< λ_RF) with uniform field sensitivity over wide RF received signal bandwidth. The challenge of high sensitivity is addressed by combining high dynamic range photonic link techniques, multiple parallel sensor channels, and high EO sensing materials. The antenna system photonic link consists of a 1550 nm PM fiber-pigtailed laser, a specialized optical modulator antenna in channel waveguide format, a wideband photoreceiver, and optical phase stabilizing components. The optical modulator antenna design employs a dielectric (no electrode) Mach-Zehnder interferometer (MZI) arranged so that sensing RF bandwidth is not limited by optical transit time effects, and MZI phase drift is bias stabilized. For a prototype optical antenna system that is < 100 in³, < 10 W, < 5 lbs, we present test data on sensitivity (< 20 mV/m-Hz^1/2), RF bandwidth, and antenna directionality, and show good agreement with theoretical predictions.