New tuning technique paves way for nanophotonic advances
European researchers have drawn on radio frequency tuning technologies to develop a new way of controlling light on the nanoscale. The novel method could find application in the development of sensitive biosensors for use in medical diagnostics, or in extremely fast photodetectors designed for use in information processing. 'By extending circuit theory to visible and infrared frequencies, the design of novel photonic devices and detectors will become more efficient. This bridges the gap between these two disciplines,' commented Javier Aizpurua of the Center of Material Physics and the Donostia International Physics Center in Spain. Antennae are devices that transmit or receive electromagnetic waves. Optical antennae, meanwhile, are designed to receive or transmit visible or infrared light. They are also able to focus light onto tiny areas just nanometres across (a nanometre is a billionth of a metre). In this study, published in the journal Nature Photonics, scientists from Germany, Spain and the USA studied so-called gap antennae. These consist of two nanoscale gold bars placed next to each other in a line, separated by a minute gap. These gap antennae are extremely efficient, but their performance can be impaired by the presence of molecules or semiconductors in the gap. Previous work had suggested that this phenomenon, known as gap loading, could be harnessed to fine tune the response of the optical antennae. The researchers put these ideas to the test by placing metal bridges of different sizes across the gap. They used a near-field microscope to see how the bridges affected the performance of the antennae. 'By monitoring the near-field oscillations of the different antennas with our novel near-field microscope, we were able to directly visualise how matter inside the gap affects the antenna response,' explained Rainer Hillenbrand, leader of the Nanooptics group at the newly established Nanogune research institute in Spain. 'The effect could find interesting applications for tuning of optical antennas.' Their experiments confirmed the theory that gap loading can be used to effectively manipulate and control the fields of gap antennae. 'Targeted antenna loading provides an excellent means of engineering complex antenna configurations in coherent control applications, adaptive nanooptics and metamaterials,' the scientists write. They conclude that: 'This opens the door for designing near-field patterns without the need to change antenna length, which could be highly valuable for the development of compact and integrated nanophotonic devices.'
Countries
Germany, Spain, United States