Abstract
Polarization gratings (PGs) enable a novel architecture for dynamic non-mechanical steering of light over large angles and with large clear apertures. This beam steering approach has many applications in active sensing and optical communications. In this review, we describe some of the defining characteristics of this beam steering architecture and highlight several applications of the technology.
Highlights
Crystals 2021, 11, 361 we present demonstrations of polarization gratings (PGs) beam steering in three compelling use cases: a time-of-flight camera, a coherent Doppler lidar, and a midwave infrared (MWIR)
In the infrared, increasing absorption of many transparent conductors, such as indium tin oxide (ITO) and indium molybdenum oxide (IMO) gradually decreases per-stage efficiency as the design wavelength increases beyond 1 μm [36]
Long wave infrared (LWIR) for many liquid crystals [37], though these bands can be shifted through chemical modifications to the LC mixtures [38,39]
Summary
In the pursuit of a comparatively less expensive and more producible approach, there were researchers working with patterned polymer plates that formed blazed grating structures that could be switched on or off through index matching with a LC layer to null out the grating [6] These LC-based devices were composed of thin films and could be scaled to large apertures but relied on 0 to 2π phase wrapping. Unlike optical path delay (OPD) modulators and Bragg gratings, this type of phase shift made the deflector plates less sensitive to the steered light’s wavelength, because the phase shift depends only on the relative optic-axis orientation of the birefringent material These theoretical advantages eliminated some difficult fabrication issues and provided a means for achieving a practical non-mechanical scanner with a large angle-aperture product.
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