Liquid crystals (LCs) are a versatile class of materials capable of modulating their effective refractive index for specific light polarization when subjected to an external electric field. This unique feature positions LCs as valuable components in the creation of electronically reconfigurable optical elements by eliminating the need for mechanical components. This study presents LC-based Fresnel diffractive elements, with spiral shaped phase profiles, that convert planar light beams into vortex beams. The devices feature directly addressable electrodes, facilitating dynamic adjustment of the vortex beam generation. Consequently, a single device may be configured to introduce an arbitrary orbital angular momentum (OAM) into a passing planar light beam. The devices may be calibrated to any desired wavelength within the visible and NIR light spectrum. The developed devices are characterized by high fill factor, low operating voltages, and are suitable for various applications, including optical trapping or OAM multiplexing, due to their lack of moving parts, reconfigurability, and ease of integration. The control of these optical devices is accomplished by an in house developed electronic driver that generates pulse width modulation (PWM) signals to independently address each element electrode. In this way, the element phase profile can be precisely controlled. The devices are fabricated through Direct Laser Writing (DLW) ablation on glass substrates coated with Indium-Tin Oxide (ITO), utilizing nematic LCs for phase modulation of incident light beams.
In this talk, we’ll discuss our latest findings on cascaded spiral diffractive lenses (cSDL) based on liquid crystal (LC) technology. Our lenses are notable for their low voltage requirements (less than 10Vrms), direct addressing capabilities, and wide aperture (greater than 25mm OD). They also boast high fill factors (over 98%) and a broad tunable focal range (over 4 Diopters). Each of the two cascaded devices are standard LC cells, created using a single direct laser writing lithographical process on a conventional transparent ITO covered glass substrate.
We’ll also share our recent work with dual frequency materials and the application of these lenses in zoom systems and dynamic achromatic image capture, highlighting our progress in reducing the haze often present in diffractive liquid crystal lenses, and other high resolution devices.
We’ll showcase implementations with both 24 and 72 electrodes, which allow for quasi analogue tuning across the entire tuning range.
Keywords: Liquid Crystal, flat lens, adaptive optics, diffractive optics, optical vortex, orbital angular momentum
Cascaded spiral diffractive lenses (cSDL) based on liquid crystal (LC) technology, offer low voltage (⪅10Vrms) direct addressing, for wide aperture (>25mm OD) transparent lenses with very high fill factors (>98%), and broad tunable focal range (>4 Diopters). The two cascaded devices are conventional LC cells, manufactured using a single direct laser writing lithographical process on a transparent ITO covered glass substrate. In this presentation we will present our latest results, employing dual frequency materials, the use of the lenses in zoom systems, and in dynamic achromatic image capture. We will present implementations with both 24 and 72 electrodes, allowing for quasi analogue tuning in the whole tuning range. We will also present the employed direct addressing electronics.
Reconfigurable diffractive lenses manufactured in liquid crystal are presented. The lenses show an unprecedented performance in terms of active diameter and focal distance range when compared to any other transparent adaptive lens. The lenses are characterized by an active area free of electronic components, with a fill factor of 98% which combined with a low operating voltage (⪅10Vrms), open for applications ranging from eye contact lenses to space applications. The addressing of the liquid crystal is done exclusively from the periphery of the device. The lenses are based on tunable spiral diffractive lenses (SDL) for which the focal length may be changed by changing the topological charge, i.e. twist of the spiral in the lens. The twist in the resulting wavefront is eliminated by cascading two spiral plates with opposite twists emulating a conventional diffractive lens. The presented lenses have a tuning range from -2 to +2 diopters and an active diameter of 25mm.
A project-based teaching course for postgraduate students in the field of Photonics Engineering is based on the implementation of a Spectrophotometer. Hard and soft skills are evaluated in the implementation with an auto-evaluation criteria.
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