Photonic Microwave True-Time Delay Using Tapered Fiber Bragg Gratings

A photonic microwave true-time delay based on uniform and chirped fiber Bragg gratings having a tapered structure in the light propagation direction has been proposed and fabricated. It requires only a single-wavelength light source. A resistive heating electrode coated on the tapered fiber was incorporated to control the time delay continuously without any mechanical perturbation and moving. This was achieved by adjusting the reflection positions of the optical signal carrying the microwave signal from within the tapered grating via the thermooptic effect. The measured time delay was ∼120 ps with the electrical power consumption of 250 mW.