Continuously tunable photonic fractional Hilbert transformer using ring resonators for on-chip microwave photonic signal processing

We propose and demonstrate a wideband photonic fractional Hilbert transformer implemented using a ring resonator-based optical all-pass filter. The full programmability of the ring resonators allows variable and arbitrary fractional order of the Hilbert transformer. The implemented all-pass filter performs a good approximation to the ideal Hilbert transform response, and it can be used as a building block to construct on-chip complex microwave photonic signal processors.