Chen et al. have demonstrated a multiplexed volume Bragg grating (VBG)-based angular amplifier for non-mechanical optical beam steering. Laser-based imaging technologies such as LIDAR require some means of continuously steering the beam over a large field of view quickly and repeatably. At RF frequencies, this is easily accomplished with phased arrays, but in the optical domain, it is harder to control the phase of the signal. Diffractive optical elements like VBGs can direct a beam over a wide range, but only at discrete angles. One known scheme to overcome this is to sandwich VBGs between two liquid crystal optical phased arrays (LCOPAs), which provide near-continuous tuning with high efficiency, but only over a narrow angular range. The input LCOPA defines the incident angle to a VBG, which in turn amplifies the diffraction angle, and a second LCOPA provides fine angular tuning at the output. In this paper, the authors design and fabricate a VBG that covers twelve discrete angles between -45° and 45°. In order to get good diffraction efficiency and angle selectivity, they are limited to two grating periods per VBG, and so a stack of three gratings is needed to cover the full desired angular range. Measurements of the VBG stack show diffraction efficiencies >80% for all angular channels, and very little polarization dependence.
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