Wavelength tunable phase-locked laser diodes for true-time delay beamforming

Abstract

Photonic true-time delay (TTD) beamforming has been considered a promising technique for wideband phased-array antenna (PAA) systems. An efficient way to achieve optical TTD beamforming is through the use of fiber Bragg grating (FBG) delay lines. In an FBG-based TTD beamforming system, a microwave signal carried by an optical carrier is required, which is usually obtained by modulating the microwave signal on the optical carrier using an external modulator. In this paper, we propose a novel approach to economically generate high-frequency microwave signals using two wavelengths from two phase-locked laser diodes through optical heterodyning. Since no optical modulator is required, the cost is significantly reduced. In addition, since the system uses only two wavelengths, the power-penalty problem caused by chromatic dispersion is minimized. In the proposed approach, the two phase-locked wavelengths are generated using an optical phase-locked loop (OPLL). A TTD beamforming system using an OPLL in combination with FBG-based delay lines to achieve tunable time delays is investigated. Experimental results are provided.