A Review of Phased Array Steering for Narrow-Band Electrooptical Systems

Nonmechanical steering of optical beams will enable revolutionary systems with random access pointing, similar to microwave radar phased arrays. An early approach was birefringent liquid crystals writing a sawtooth phase profile in one polarization, using 2 pi resets. Liquid crystals were used because of high birefringence. Fringing fields associated with voltage control required to implement the 2 pi resets have limited the efficiency and steering angle of this beam steering approach. Because of steering angle limitations, this conventional liquid crystal steering approach is usually combined with a large angle step-steering approach. volume holograms, birefringent prisms or sawtooth-profile birefringent phase gratings, and circular-type polarization gratings are the large angle step steering approaches that will be reviewed in this paper. Alternate steering approaches to the combined liquid crystal and step-steering approach exist. Microelectromechanical system mirrors, lenslet arrays, electrowetting, and a variable birefringent grating approach will be reviewed and compared against the conventional liquid crystal and step-steering approaches. Step-steering approaches can