Novel photonic true-time-delay beamformer based on the free-spectral-range periodicity of arrayed waveguide gratings and fiber dispersion

A novel optical beamformer based on the spectral periodicity of arrayed waveguide gratings (AWGs) and dispersive fiber is proposed. This architecture uses multiple sets of wavelengths with a spectral spacing among the signals on each set equal to the free spectral range of the AWG in such a way that all the wavelengths of each set are routed to the same AWG port and pass through the same fiber length in order to obtain multiple simultaneous delays. A wavelength-to-antenna element correspondence is established so fiber dispersion will introduce an equal delay amongst signals of the array elements. This architecture presents straightforward multibeam capability. Experimental results demonstrating the feasibility of the delay line are presented.

I. Introduction

Phased-Array antennas (PAAs) have been proposed for different applications due to their higher flexibility and better performance over mechanical steering antennas. Traditionally, beamforming networks in PAA have been electronically implemented. However, over the last years, optical beamforming for PAAs has been intensely studied to ease some of the problems related with traditional electronic steering systems [1]. Optical beamforming offers many advantages such as small size, low weight, no susceptibility to electromagnetic interference, and especially, wide instantaneous bandwidth and squint-free beam steering. Nevertheless, many optical beamforming architectures present high overall system cost and complexity. In order to achieve a significant cost reduction, the use of the wavelength-domain parallelism is the most promising option. In Fig. 1. AWG loop-back configuration [2], a switched-dispersion-based delay-line architecture was presented, which uses multiple simultaneous wavelengths to obtain multiple simultaneous proportional delays with a fixed wavelength-to-antenna element correspondence. In this beamformer, the beam is discretely steered by switching between different lengths of dispersive fiber. However, this scheme does not provide an easy multibeam capability, which is required in many applications.