Tunable microwave Hilbert transformer based on a dispersion-engineered few-mode fiber

Beyond optical communications, the inherent spatial parallelism of space-division multiplexing fibers offers a unique avenue for implementing sampled true-time delay lines based on time-discrete architectures in a compact platform, with a considerable reduction of size, weight, and power-consumption. We present the first experimental demonstration of a microwave fractional Hilbert transformer in a few-mode fiber using a transversal filtering method. Our approach is based on a tunable true-time delay line implemented in a dispersion-engineered double-clad step-index few-mode fiber. By adjusting tap coefficients and optical wavelength, both the fractional order and operational bandwidth can be continuously tuned.