Continuously tunable silicon waveguide optical switched delay line based on grating-assisted contradirectional coupler.

The integrated optical delay line plays a crucial role in microwave photonic chips. Continuous tunability is a growing trend in filtering and beamforming techniques of microwave photonics. Based on the silicon platform, we present and experimentally demonstrate an integrated continuously optical tunable delay line (OTDL) chip, which contains a 4-bit optical switched delay line (OSDL) and a thermally tunable delay line based on grating-assisted Contradirectional coupler (CDC). The OSDL can achieve stepwise optical delays, while the CDC is introduced to improve delay tuning resolution within one step delay of the OSDL. The combination of the two modules can realize tuning delays from 0 to 160 ps. Additionally, it is easy to increase the maximum delay by cascading more optical switches. The experimental results demonstrate that the proposed OTDL shows outstanding performance and good expansibility.