3-bit substrate-guided-mode optical true-time-delay lines operating at 25 GHz

We report a high packing density true-time-delay lines based on substrate guided wave propagation combined with slanted volume phase grating fanout couplers. Three-bit delay lines with delay step of 42 ps are fabricated on quartz substrates with a substrate bouncing angle of 45 degrees. A fanout power fluctuation of around 10% is experimentally achieved. A 25-GHz optical heterodyned signal has been detected through the device with a S/N ratio of 20 dB. Compared with similar devices, the true-time-delay lines reported herein achieves both high packing density per unit substrate area (similar to 5 delay lines/cm(2)) and ultrawide microwave bandwidth.