Continuously tunable broadband adiabatic coupler for programmable photonic processors.

Programmable integrated photonic circuits are poised to drive a new revolution in information systems by synergizing with high-speed digital signals. Central to this vision is the ability to reconfigure optical signal processing for multi-functional photonic integration. Here, we design and experimentally demonstrate a thermo-optically reconfigurable adiabatic coupler monolithically integrated on a silicon photonics platform. The device combines adiabatic directional couplers with titanium nitride (TiN) micro-heaters embedded in the adiabatic transition region, enabling dynamic coupling ratio tuning via the localized thermo-optic modulation. Experimental results confirm continuous coupling ratio adjustment from 50:50 to 70:30 across 80-nm bandwidth (1,520-1,600 nm), with insertion loss kept below 0.25 dB. Leveraging its tunability, the device enables programmable spectral routing with free spectral ranges (FSR) of 20 nm and 40 nm. The proposed approach offers enhanced flexibility and scalability for high-density photonic systems, providing a promising pathway toward next-generation programmable photonic circuits and optical computing architectures.