Phased array antenna system based on few-mode fiber mode interferometer delay lines

This paper proposes a delay line (DL) based on a few-mode fiber (FMF) mode interferometer utilizing few-mode long-period fiber grating (FM-LPFG), and constructs a 1 × 4 phased array antenna (PAA) system. Current phased array systems based on FMFs primarily rely on few-mode fiber gratings (FMFGs) for delay tuning, offering advantages including low power consumption, compact structure, and the requirement of only a single-wavelength light source. However, their performance is constrained by discrete tuning mechanisms. To address this limitation, this work introduces dynamic adjustment of the coupling ratio between the LP₀₁ mode and a degenerate state of the LP₁₁ mode via a few-mode polarization controller (FM-PC), achieving the first demonstration of continuously tunable delay in a DL based on FMFG. Simulations and experiments validate this capability, while the impact of fusion splice lateral core offset distance on delay characteristics and errors induced by carrier frequency offset are also analyzed. Finally, the 1 × 4 PAA system is constructed using four experimentally fabricated DLs, and the results of far-field radiation pattern testing demonstrate that the system can achieve non-skewed beam steering.