Abstract: Optical antennas are devices that convert freely propagating optical radiation into localized energy, and vice versa. They enable the control and manipulation of optical fields at the nanometre scale, and hold promise for enhancing the performance and efficiency of photodetection, light emission and sensing. Although many of the properties and parameters of optical antennas are similar to their radiowave and microwave counterparts, they have important differences resulting from their small size and the resonant properties of metal nanostructures. This Review summarizes the physical properties of optical antennas, provides a summary of some of the most important recent developments in the field, discusses the potential applications and identifies the future challenges and opportunities.

Abstract: Round spiral antennas are generally designed by using Archimedean spiral geometries which have linear growth rates. To obtain smaller antennas with nearly the same performance, square spiral Archimedean geometries are also widely used instead. In this study, novel square antennas are proposed, designed and examined. At first two similar but different approaches are employed to design new antennas by considering the design procedure used to obtain log-periodic antennas. Then, the performance of these antennas is improved by considering another property of log-periodic antennas. Simulations are performed by using two different numerical methods which are Finite Difference Time Domain Method (FDTD) and Method of Moments (MoM). The results obtained from the simulations are compared with those of the Archimedean spiral antennas in terms of the frequency dependency of fundamental antenna parameters such as antenna gain and radiation pattern. The simulation results are compared with the ones obtained from the experimental study.

Abstract: This article provides a review of early work and developments in the field of near-field optics. The roots trace back to the letters exchanged between Edward Hutchinson Synge and Albert Einstein in 1928 and, because of the analogy to antenna theory and lightning rods, the origins project back to the time of Benjamin Franklin who discovered the wonderful Effect of Points both in drawing off and throwing off the Electrical Fire. The modern interest was mainly inspired by the invention of scanning probe microscopy and by the first optical near-field measurements by Dieter W. Pohl and co-workers at the IBM Research Laboratory in R¨uschlikon, Switzerland, and also by parallel developments of other groups. Near-field optics received inspiration from the fields of surface enhanced spectroscopy and from studies of energy transfer. While optical near-fields were extensively exploited for overcoming the diffraction limit in optical imaging the study of their physical aspects revealed unique properties which cannot be imitated by free propagating radiation.