OPTICAL PHASED-ARRAY TECHNOLOGY

Optical phased arrays represent an enabling new technology that makes possible simple, affordable, lightweight, optical sensors offering ver y precise stabilization, random-access pointing, programmable multiple simultaneous beams, a dynamic focus/defocus capability, and moderate to excellent optical power handling capability. These new arrays steer or otherwise operate on an already formed beam, as compared to modem microwave phased arrays which both generate a beam and direct it in a specific direction. A phase profile is imposed on an optical beam as i t is either transmitted through or reflected from the phase shifter ar ray. The imposed phase profile steers, focuses, fans out, or corrects phase aberrations on the beam. The array of optical phase shifters is realized through lithographic patterning of an electrical addressing n etwork on the superstrate of a liquid crystal waveplate. Refractive in dex changes sufficiently large to realize full-wave differential phase shifts can be effected using low (<10 V) voltages applied to the liqu id crystal phase plate electrodes. High efficiency large-angle steerin g with phased arrays requires phase shifter spacing on the order of a wavelength or less; consequently addressing issues make I-D optical ar rays much more practical than 2-D arrays. Orthogonal oriented 1-D phas ed arrays are used to deflect a beam in both dimensions. Optical phase d arrays with apertures on the order of 4 cm by 4 cm have been fabrica ted for steering green, red, 1.06 mu m, and 10.6 mu m radiation. Steer ing efficiencies of about 60% at 4 degrees and 85% at about 20 have be en achieved to date with switching times as short as a few millisecond s in the visible. Fluences of several hundred W/cm(2) have been demons trated at 10.6 mu m with nonoptimally engineered devices. Higher fluen ces can be handled at shorter wavelengths. Larger apertures are feasib le, as is operation at other wavelengths and significantly faster swit ching times System concepts that include a passive acquisition sensor as well as a laser radar are presented.