Highly tunable broadband RF photonic fractional Hilbert transformer based on a Kerr soliton crystal microcomb source

TL;DR

This paper presents a highly tunable, broadband RF photonic fractional Hilbert transformer utilizing a Kerr micro-comb source with a record low free spectral range, enabling flexible bandwidth, center frequency, and fractional order control.

Contribution

It introduces a novel integrated Kerr micro-comb source with 75 lines across the C-band for programmable RF photonic Hilbert transformation with broad tunability.

Findings

Achieved tunable bandwidths from 1.2 to 15.3 GHz.

Demonstrated switchable center frequencies from baseband to 9.5 GHz.

Validated good agreement between experimental results and theoretical predictions.

Abstract

We demonstrate an RF photonic fractional Hilbert transformer based on an integrated Kerr micro-comb source featuring a record low free spectral range of 48.9 GHz, yielding 75 microcomb lines across the C-band. By programming and shaping the comb lines according to calculated tap weights, we demonstrate that the Hilbert transformer can achieve tunable bandwidths ranging from 1.2 to 15.3 GHz, switchable centre frequencies from baseband to 9.5 GHz, and arbitrary fractional orders. We experimentally characterize the RF amplitude and phase response of the tunable bandpass and lowpass Hilbert transformers with 90 and 45-degree phase shift. The experimental results show good agreement with theory, confirming the effectiveness of our approach as a powerful way to implement the standard as well as fractional Hilbert transformers with broad and switchable processing bandwidths and centre frequencies, together with high reconfigurability and greatly reduced size and complexity.