Abstract
We discuss over three decades of progress in nonmechanical beam steering, provide a comparison of approaches being developed, and comment on promising approaches not yet fully developed. Most of the work in nonmechanical beam steering has been for narrowband optical systems, but a brief discussion is provided of broadband. The majority of the nonmechanical approaches to beam steering create a tilted optical path delay (OPD) to change the wavefront, but some directly create a phase delay. OPD-based approaches may be true time delay, with no resets or modulo 2π n optical phased arrays that have resets. Most of the nonmechanical optical beam steering approaches tilt an existing wavefront and are called space fed approaches, because the beam is already formed when the wavefront is tilted. For the majority of radar nonmechanical beam steering, the tilted wavefront is formed by individual transmit/receive modules. Periodic structures (gratings) spread different wavelengths of light in angle, thus steering light, and are also used for nonmechanical steering. Our paper is derived from a conference paper presented at Photonics West in February 2019.
Highlights
This paper explores the history of the development of electro-optical nonmechanical beam steering since 1985.1 Most of the paper discusses nonmechanical beam steering for narrow band systems
Active EO materials, such as liquid crystals (LCs) have limitations on how quickly the index can change in space, which can act similar to fringing fields in limiting steering efficiency by causing a region that steers the wrong direction, when the optical path delay (OPD) is reduced by an amount that will cause modulo 2πn reduction in phase
Nonmechanical beam steering has come a long way since the mid-1980s
Summary
This paper explores the history of the development of electro-optical nonmechanical beam steering since 1985.1 Most of the paper discusses nonmechanical beam steering for narrow band systems. The most common way to build optical phased arrays (OPAs) is by dynamically creating an optical path delay (OPD). Phase automatically returns to zero each time 2π phase is completed Both modulo 2πn OPD-based beam steering and the phased-based approach use periodic structures. The modulo 2πbased OPD approach allows use of a much thinner active medium than true time delay but requires OPD resets, which cause dispersion, making the OPA narrow band unless something is done eliminate this dispersion. True time delay OPA approaches are broadband but require a much larger OPD if a moderate or larger aperture is steered to a moderate or large angle. Gratings act as point scatterers, and different wavelengths will have constructive inference at different angles, where the path to a given spot from multiple scatterers is a multiple of the specific wavelength
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