On-chip tunable photonic delay line

An on-chip tunable photonic delay line is a key building block for applications including sensing, imaging, and optical communication. However, achieving long and tunable delay lines within a small footprint remains challenging. Here, we demonstrate an on-chip tunable photonic delay line using ultralow loss high confinement Si3N4 waveguides with integrated microheaters. As an example of potential application, we embed a 0.4 m delay line within an optical coherence tomography (OCT) system. We show that the delay line can extend the OCT imaging range by 0.6 mm while maintaining a high signal to noise ratio. Our tunable photonic delay line is achieved without any moving parts which could provide high stability, critical for interference based applications.