Progress and opportunities in the development of nonmechanical beam steering for electro-optical systems

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 2πn 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.

Liquid Crystal Devices for Beam Steering Applications

“…Due to silicon's high reflectivity, such LCoS devices can only operate in reflection mode, whereas Liquid Crystal on Poly Silicon (LCoPS) can work in transmission mode leads to larger minimum pixel sizes [21,109]. The optical loss in efficiency associated with w fb can be approximated as [21,22,102,106],…”

“…Conversely, a grating can be considered "thick" or of the Bragg type if d > 10Λ gr (22) is satisfied [129]. Bragg diffraction physically manifests significantly differently to the RN type.…”

“…LCs are used widely in the field of adaptive optics due to their refractive index anisotropy, the variety of alignment methods that are available, and the ability of liquid crystals to reorient when subjected to relatively low energy stimuli. Over the decades, a broad range of liquid crystal beam steering devices has been created utilizing both refractive and diffractive optics [13][14][15][16][17][18][19][20][21][22]. Various methods have been employed in creating new LC beam steering devices, depending on the requirements for the proposed application.…”

Effect of the fill factor on microlens array scanning systems

“…The scanning of optical beams has various applications, such as in laser radar, optical communications, and imaging system [1]. Several conventional methods of beam scanning with mechanical, electro-optic, and acousto-optic structures suffer from many limitations, the disadvantages of mechanical scanners are that the system is large, bulky and consumes a lot of power.…”

Analysis of fill factor and diffraction influence on micro-lens array imaging system

“…With the rapid development and production needs of the optoelectronics industry, micro-lens arrays are rapidly emerging in the industry due to their advantages of miniaturization and integration, which can solve the problems of difficult adjustment and high cost of traditional large-diameter lenses to a certain extent. There are many applications in the field of optics, such as beam imaging [1][2] , beam shaping [3] , and beam scanning [4][5] .The micro-lens array is composed of multiple lenses with small apertures arranged in a certain period. However, due to the small aperture of a single lens, its size and wavelength are of the same order of magnitude, and then the light wave will be diffracted on the optical element during the transmission process, which will widen the image point in a certain direction and affect the imaging quality [6][7] .…”