Phased array beam controller using integrated electro-optic circuits

DETAILED DESCRIPTION The invention is a photonic device for controlling phased array beam direction using optical heterodyning techniques, polarization mixing, and integrated optical circuits to perform high-speed, continuous beam steering of a phased array antenna.
In a preferred embodiment, it includes an electro-optic substrate; a plurality of waveguides formed in the substrate, each of which is capable of simultaneously propagating light signals with orthogonal polarizations; an input waveguide for inputting into each one of the plurality of waveguides a pair of co-propagating polarized light signals having orthogonal polarizations and offset frequencies; a plurality of electrodes on the substrate configured to differentially phase shift the signals on each polarization traveling through each waveguide by a different amount in response to a common applied voltage, thereby creating a differential phase shift between the two polarized signals; and means for combining the phase shifted polarized signals within each one of the waveguides.
Each of these combined signals are then propogated to an antenna element.
With the invention, photonics technology can be used to control both phase and amplitude of the microwave radiation in the optical domain to achieve compact, broadband operation.
The basic operating principle of the invention is based on the differential phase shift between optical waves of orthogonal polarizations traveling in an electro-optic optical waveguide.
This differential phase shift is directly proportional to the voltage applied to a control electrode and to the length of that electrode.
The outputs from the waveguide are passed through a polarizer oriented at an angle (such as 45 degrees) to the orthogonal polarizations, so as to effectively combine components from each signal.
The optical signals at different frequencies are, in effect, coherently combined and detected by an array of high speed optical detectors, thereby generating a set of microwave outputs.
These heterodyne beat signals have a beat frequency when photodetected equal to the difference in the optical laser frequencies and phase equal to the optical differential phase shift