Sluggish light and its applications in true-time-delay beam forming for wideband RF phased-array antennas

Abstract

In this paper, we present a new photonic technique for producing large time delay of radio-frequency (RF) modulated optical signals and its application in a novel true-time-delay (TTD) multiple beam-forming system for wideband RF phased-array antennas using Fourier optics. The RF signal to be delayed is modulated onto a broadband optical carrier in a frequency-mapped manner by an acousto-optic tunable filter (AOTF). Due to the phased-matched acousto-optic interaction and the moving nature of the acoustic waves in the AOTF, di.erent frequency components of the optical carrier are only modulated and Doppler-shifted by the corresponding frequencies of the modulating RF signal. Heterodyne detection between the modulated optical beam and a timealigned reference beam from the same light source can recover the modulating RF signal. When a small optical path length di.erence is introduced between the heterodyne beams, a large RF time delay magnified by the frequency ratio between the optics and the RF will be generated, which we refer to as the sluggish-light effect. Sluggish light has potential applications in TTD beam forming for wideband RF phased-array antennas and proof-of-concept experiments of the sluggish-light based TTD beam forming for an emulated 2- and 4-channel RF array will be presented in this paper.