Low-Loss Fiber-Optic True Time Delay Generator for RF Signal Processing andPhased Array Antenna Control (TTD)

摘要

The work established the viability of a fiber-optic approach for low-loss truetime delay of wideband RF signals for phased-array antenna (PAA) beamsteering. In this approach an optical carrier modulated by the RF signal of interest is launched into a delay-line fiber composed of optical Bragg reflection gratings written holographically into the core of a single-mode fiber. The beam is steered by tuning the optical carrier wavelength for reflection from the appropriate grating. The fiber Bragg grating writing performance meets and exceeds PAA requirements. We demonstrated: (1) a time delay accuracy of approximately 2 ps (20 Ps verified); (2) a wavelength writing accuracy for Bragg gratings of 0.04 microns absolute, 0.01 nm relative; (3) a sidelobe suppression of 50 dBe at 2 nm channels and 60 dBe at 3 nm channels. We produced a 4-bit, 16 grating true time delay element which includes an optical circulator. An analytical model, which includes chirp, was developed that predicts both the optical and RF response for the fiber optic Bragg grating.