Photonic Technique for Phase Control of Microwave to Terahertz Signals

We present a simple linear photonic technique to achieve fixed or time-varying phase shifts in microwave to terahertz frequency band signals. We show that the wavelength change of an RF modulated optical carrier within the operational band of a photonic filter with a step in the group-delay spectrum results in a broadband linear phase change in the RF signals. We demonstrate the concept experimentally using a simple fiber Bragg grating filter implementation in the microwave K- and Ka-bands, achieving up to 1500° continuously tunable linear phase shifts within a 20-GHz bandwidth (15-35 GHz).