Lenses

This chapter presents the Integrated Lens Antenna (ILA) technology as it evolved since its introduction aiming to respond to the needs of emerging applications such as high-data-rate communication, intelligent transport, and mm-wave imaging. The topics covered include the ILA design concepts as well as the electromagnetic phenomena intrinsic to dielectric lenses that may affect ILA performance. The aspects of the ILA technology related to selection of the primary feeds, lens materials, and fabrication methods are also revised. A few practical examples are provided to illustrate the current and future trends of this technology.

Dielectric lens antennas are attracting a renewed interest for millimetre-and sub-millimetre wave applications where they become compact, especially for configurations with integrated feeds usually referred as integrated lens antennas. Lenses are very flexible and simple to design and fabricate, being a reliable alternative at these frequencies to reflector antennas. Lens target output can range from a simple collimated beam (increasing the feed directivity) to more complex multi-objective specifications. This chapter presents a review of different types of dielectric lens antennas and lens design methods. Representative lens antenna design examples are described in detail, with emphasis on homogeneous integrated lenses. A review of the different lens analysis methods is performed, followed by the discuss ion of relevant lens antenna implementation issues like feeding options, dielectric material characteristics, fabrication methods and a few dedicated measurement techniques. The chapter ends with a detailed presentation of some recent application examples involving dielectric lens antennas.

A computer program has been created to simulate a ray diagram on a thin lens using the Python programming language. The program is a ray diagram simulation on a convex lens and a concave lens. The program is built using the canvas, create line, button and motion functions in the object-oriented programming language Python. The object being simulated is a convex and concave lens with a focal length of 10 cm and an object's height of 4 cm. The simulation results are in the form of an interface with the user using computer graphic media and interaction via a touch screen. The program can run on Android mobile phones. The results of ray diagrams on computers and Android cellular phones show that they are in accordance with theory, so that the program can be used as a virtual laboratory material.

Nematic liquid crystals (NLCs) of achiral molecules and racemic mixtures of chiral ones form flat films and show uniform textures between circular polarizers when suspended in sub-millimeter size grids and immersed in water. On addition of chiral dopants to the liquid crystal, the films exhibit optical textures with concentric ring patterns and radial variation of the birefringence color. Both are related to a biconvex shape of the chiral liquid crystal film; the rings are due to interference. The curvature radii of the biconvex lens array are in the range of a few millimeters. This curvature leads to a radial variation of the optical axis along the plane of the film. Such a Pancharatnam-type phase lens dominates the imaging and explains the measured focal length of about one millimeter. To our knowledge, these are the first spontaneously formed Pancharatnam devices. The unwinding of the helical structure at the grid walls drives the lens shape. The relation between the lens curvature and material properties such as helical pitch, the twist elastic constant, and the interfacial tensions, is derived. This simple, novel method for spontaneously forming microlens arrays can also be used for various sensors. Microlenses are a topic of considerable interest in applications ranging from biomimetic optical systems 1 to security printing 2 and solar concentrators 3. The most commonly-used solid microlenses are made through delicate fabrication processes 4, 5 and require mechanical adjustments to focus the image. In liquid lenses, the focal length is varied by electrowetting 6–10. Liquid crystals (LC) can also be used to make lenses either by filling 11 or imprinting LCs in curved substrates 12, 13 ; by using a LC film with constant thickness, but spatially-varying refractive indices 14–16 ; by creating focal-conic defects in smectics 17, 18 and by using short pitch cholesteric liquid crystal polygo-nal textures 19. The common feature of all these microlenses is the requirement for delicate fabrication processes. Thus, a simpler means of forming well-defined microlenses is highly desirable. Carefully patterned LCs have been used to form Pancharatnam lenses. Unlike conventional phase or amplitude gratings, Pancharatnam phase 20 devices operate by locally modifying the polarization state of light waves passing through them. Recently, the unique optical properties of Pancharatnam devices have been utilized in making high efficiency compact optical lenses by providing an appropriate profile across an aperture 21, 22. In such lenses the optical axis is in the plane of the film with an azimuthal angle β that spatially varies along the radial direction. Here, we demonstrate assembly-driven microlenses with size controlled by the grid in which chiral nematic liquid crystal films are suspended. Upon immersion in water, the suspended films spontaneously form converging spherical microlenses, which operate primarily as Pancharatnam lenses. We characterize the geometry and imaging properties of such lenses, and show that the lens shape is induced by molecular chirality and is driven by the liquid crystal-grid interaction. Materials and Methods The molecular structures of the studied materials and the experimental arrangements are shown in Fig. 1. Chiral nematic LC (N*) materials were obtained by adding chiral dopants CD1 or CD2 to the nematic LC (NLC) material 4-cyano-4′-pentylbiphenyl (5CB) obtained from Sigma-Aldrich and used without further purification. The nematic phase of 5CB is observed from 21.5 °C to 33.2 °C. Chiral dopant CD1 was obtained from Kent Displays, Inc., and (S)-and (R)-CD2 (code: ZLI 811 and ZLI 3786, respectively) were purchased from Merck. To measure the helical twisting power (HTP) of the chiral dopants, a concentration gradient was created by putting the pure 5CB in contact with a c = 5 wt% mixture of CD1 or CD2 in 5CB. Only integer numbers of the half pitch (p/2) can be accommodated within the cell thickness, d, so that bands with half-pitch jumps in twist form