Reconfigurable photonic molecules with independently tunable external coupling and mode splitting on thin-film lithium niobate

Microcavity photonic molecules (PM) provide a versatile platform for optical-field manipulation and photonic Hamiltonian engineering, but their spectral programmability is typically limited by fixed coupling. Here, we report a programmable photonic molecule on thin-film lithium niobate with independently tunable external coupling and mode splitting enabled by two integrated Mach-Zehnder interferometers. Experimental results show that the mode splitting can be tuned up to 17.2 GHz, while the coupling depth can be widely tuned from under-coupling to over-coupling while maintaining a preset splitting. This work provides a compact solution for programmable photonic molecules and reconfigurable lithium-niobate microcavity networks.