Recent advances on multiple channel unequally spaced optical phased array for ultrafast LADAR

In this paper, we experimentally verify that previously proposed idea of unequally spaced optical phased array can greatly reduce grating-lobes. As the verification purpose of our previous numerical design, a laser beam is passed through unequally-spaced slits, whose spacings are the same as the previous design. Interference patterns formed after both 4- and 8-channel slits clearly show that the grating-lobes can be greatly minimized. To realize the beam steering possible, optical waveguides array, which has unequally spaced design at the output ends is fabricated. The phase of each beam can be varied using fibers array wound around PZT tubes before each beam is coupled into the waveguides array. Interference patterns formed after the outputs of both 4- and 8-channel waveguides array show that the gratinglobes can be greatly reduced using unequally spaced optical phased array technique.