Implementing optical phased array beam steering with cascaded microlens arrays

A cascade of microlens arrays that are decentered with respect to each other is one potential method for beam steering; the magnitude of the steering angle depends on the amount of decenter. A simple argument is presented that shows that the output of such a system is analogous to the output of an optical phased array. The periodic nature of the exiting wavefront restricts allowed steering angles to values that are determined by the grating equation and the pitch of the microlens arrays. The efficiency of steering into a desired diffraction order of the phased array is determined by the amount of decenter of the microlens arrays, the coherence of the arrays, and the fill-factor at the output of the array. Maximum fill-factor is desired, which can be achieved through the addition of an intermediate microlens array that acts like a field lens. An experimental implementation of such a triplet cascade of microlens arrays, suitable for steering short wave infrared laser light, is described. The extension of such a cascade to steering broad spectral band light is also discussed.