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11 August 2009 A new beam steering concept: Risley gratings
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We introduce a new beam steering concept of the "Risley grating" that consists of independently rotating inline polarization gratings (PGs). The Risley grating concept replaces the bulky prismatic elements of the Risley prisms with thin plates containing polarization gratings, and employs their highly polarization-sensitive diffraction. As rotating two PGs, the output beam tracks within a field-of-regard (FOR), which is determined by the grating period and their relative orientations. Since PGs are typically patterned in thin liquid crystal layers (a few μm thick), the system can be implemented with far less thickness and weight. In addition, these thin gratings can be placed with virtually zero proximity and the beam walk-off becomes negligible. We demonstrate the Risley grating that performs continuous steering with 62° FOR and 89-92% transmittance at 1550 nm wavelength. The governing equations for the steering angles of the Risley grating in the direction cosine space are also presented.
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Chulwoo Oh, Jihwan Kim, John F. Muth, and Michael J. Escuti "A new beam steering concept: Risley gratings", Proc. SPIE 7466, Advanced Wavefront Control: Methods, Devices, and Applications VII, 74660J (11 August 2009);

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