Fully Programmable Microwave Photonic Filter Based on Manageable Two-Soliton Microcombs

Integrated dissipative Kerr soliton (DKS) frequency combs have shown great promise in microwave photonics applications due to their versatile merits. For example, the smooth sech
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-shaped spectral envelope of single soliton states enables a microwave photonic filter (MPF) without the need for additional pulse shaping. The reconfiguration of the MPF can be further realized by leveraging the intrinsically rich soliton states. However, deterministic access of different soliton states remains challenging, which limits the reconfiguration of MPFs. In this work, we demonstrate a programmable MPF based on two-soliton microcombs (TSMs) with in situ tunability from a dual-cavity coupled microresonator structure. The optical signal of TSM can be mapped to an electrical filtering response, and the resulting filter passband frequency is proportional to the relative angle between two solitons. The relative angle between the solitons is manipulated by the avoided mode crossing (AMX). The solitons are trapped by AMX-induced background modulation field whose amplitude and spectral position can be tuned by the coupled microresonator. The tunable coupler can turn off the coupling to stabilize the solitons’ intracavity positions. By adjusting the AMX to certain states, the relative angle between two solitons can be arbitrarily chosen between 11° and 180°. MPF with passband frequency from 0.5 GHz to 9 GHz can be obtained without the help of pulse shapers or other auxiliary off-chip tunable devices. The sech-shaped narrow optical pulse provides a filter response with a 3-dB bandwidth of ∼0.1 GHz. The proposed scheme provides a simple and programmable filtering solution for radar and 5G communication applications. The soliton angle controlling method can also be enlightening to other applications.