Electrically Addressed Bragg Grating in Optical Delay Line for Phased Array Radar

Optical delay lines are key components for steering phased array radar and are also widely in demand for synchronization, multiplexing, security, etc. in commercial optical communication systems. The proposed device is a very compact electrically controlled optical delay line capable of delays up to 1 10 ns. It has been made practical by the continued advance of below 0.5 Fm feature size submicron lithography. The device consists of a circulator followed by an electro optic waveguide with an interdigitated electrode pattern of period equal to the Bragg spacing on top. An electro optic Bragg grating is created at only those electrodes to which voltage is applied. Light enters through the circulator and travels down the waveguide until it reaches the selected electrodes, at which point it is reflected back to the circulator. The delay is equal to the time of flight to the selected electrodes and back. Note that no 1 x n splitter is necessary. DARPA applications are anticipated in phased array radar and high speed optical communication.