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.

Antennas for light

1. Introduction 2. Quantum confined systems 3. Transmission in nanostructures 4. Quantum dots and single electron phenomena 5. Interference in diffusive transport 6. Temperature decay of fluctuations 7. Non-equilibrium transport and nanodevices.

Transport in Nanostructures

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

1 Introduction 2 Quantum confined systems 3 Transmission in nanostructures 4 Quantum dots and single electron phenomena 5 Interference in diffusive transport 6 Temperature decay of fluctuations 7 Non-equilibrium transport and nanodevices

/pdf/transport-in-nanostructures-2pr7vx7rmr.pdf

Transport in nanostructures

Resonant tunneling through a single quantum well of GaAs has been observed. The current singularity and negative resistance region are dramatically improved over previous results, and detecting and mixing have been carried out at frequencies as high as 2.5 THz. Resonant tunneling features are visible in the conductance‐voltage curve at room temperature and become quite pronounced in the I‐V curves at low temperature. The high‐frequency results, measured with far IR lasers, prove that the charge transport is faster than about 10−13 s. It may now be possible to construct practical nonlinear devices using quantum wells at millimeter and submillimeter wavelengths.

Resonant tunneling through quantum wells at frequencies up to 2.5 THz

This paper introduces a proposed imaging system suitable for millimeter and submillimeter wavelengths, based on heterodyne mixing at the focal plane of an optical system. We have designed a prototype planar antenna array and quasi-optical system and present measurements at 9 GHz and at 140 GHz of beam patterns and sensitivity for a single two-element, full-wave, printed dipole array incorporating a GaAs beamlead diode. Scale model studies were carried out in the 8-10 GHz range, where the design was optimized. Subsequent measurements were made with a tunable carcinotron at 128-140 GHz on an appropriately scaled array.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Printed Dipole-Schottky Diode Millimeter Wave Antenna Array

Laser heterodyne observations of submillimeter emissions from carbon monoxide in the Orion molecular cloud are reported. High frequency and spatial resolution observations were made at the NASA Infrared Telescope Facility on Mauna Kea by the use of an optically pumped laser local oscillator and quasi-optical Schottky diode mixer for heterodyne detection of the J = 6 - 5 rotational transition of CO at 434 microns. Spectral analysis of the 434-micron emission indicates that the emitting gas is optically thin and is at a temperature above 180 K. Results thus demonstrate the potential contributions of ground-based high-resolution submillimeter astronomy to the study of active regions in interstellar molecular clouds.

http://science.sciencemag.org/content/sci/211/4482/580.full.pdf

Submillimeter heterodyne detection of interstellar carbon monoxide at 434 micrometers.

Enhancement of optically pumped far infrared lasing by stark modulation

Planar antenna arrays have been developed at 140 GHz using twin-dipole elements. The initial systems have been fabricated using a hybrid approach with beam lead Schottky GaAs diodes mounted on quartz substrates. Heterodyne measurements of subelement sensitivities have yielded DSB noise temperatures of 12,000 K. Subsequently implementation of completely monolithic systems has been demonstrated using SIS technology.

P. E. Tannenwald

Papers

Printed Dipole-Schottky Diode Millimeter Wave Antenna Array

Submillimeter heterodyne detection of interstellar carbon monoxide at 434 micrometers.

Enhancement of optically pumped far infrared lasing by stark modulation

Printed dipole millimeter wave antenna for imaging array applications

CO/J = 6-5/ distribution in Orion and detection in other galactic sources