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

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

A comprehensive review of integrated circuit antennas suitable for millimeter and terahertz applications is presented. A great deal of research was done on integrated circuit antennas in the last decade, and many of the problems associated with electrically thick dielectric substrates, such as substrate modes and poor radiation patterns, have been understood and solved. Several antennas, such as the integrated horn antenna, the dielectric-filled parabola, the Fresnel plate antenna, the dual-slot antenna, and the log-periodic and spiral antennas on extended hemispherical lenses, which have resulted in excellent performance at millimeter-wave frequencies, are covered in detail. A review of the efficiency definitions used with planar antennas is included. >

Millimeter-wave and terahertz integrated circuit antennas

Basic principles of heterodyne techniques are introduced and the various components of a heterodyne system are summarized. Special applications in ECE, interferometry and reflectometry are discussed after introducing the diagnostic principles. Realized systems as described in the literature are briefly outlined. Ordering principles are radiometer types in the case of ECE, mixing scheme and generation and stabilization of local oscillator and intermediate frequency signals in the case of interferometry and reflectometry. Special techniques and their impact on the performance of the diagnostic instruments are discussed.

https://iopscience.iop.org/article/10.1088/0741-3335/39/11/001/pdf

Heterodyne methods in millimetre wave plasma diagnostics with applications to ECE, interferometry and reflectometry

Tunable, CW, far-infrared radiation has been generated by nonlinear mixing of radiation from two CO2 lasers in a metal-insulator-metal (MIM) diode. The FIR difference-frequency power radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO2 lasers. The combination of lines from a waveguide CO2 laser, with its larger tuning range, with lines from CO2, N2O, and CO2 isotopic lasers promises complete coverage of the entire far-infrared band from 100 to 5000 GHz (3-200 per cm) with stepwise-tunable CW radiation. To demonstrate the usefulness of the technique, the J = 4-5 line of CO was observed at 567 GHz.

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Tunable far-infrared spectroscopy

We have made heterodyne radiometric measurements with GaAs Schottky diode mixers, mounted in a corner‐reflector configuration, over the spectral range 170 μm to 1 mm. At 400 μm, system noise temperatures of 9700 K DSB (NEP=1.4×10−19 W/Hz) and mixer noise temperatures of 5900 K have been achieved. This same quasioptical mixer has also been used to generate 10−7 W of tunable radiation suitable for spectroscopic applications.

Far‐ir heterodyne radiometric measurements with quasioptical Schottky diode mixers

Radiometric sensitivity measurements have been made on a quasi-optical receiver in the spectral range 170 mu m to 1 mm. Using GaAs Schottky mixer diodes in a corner reflector configuration, a total system noise temperature of 9,700 K (DSB) has been obtained at 447 mu m. This same quasi-optical mixer has also been used for harmonic generation of tunable radiation suitable for spectroscopic applications.

W. D. Fitzgerald

Papers

Far‐ir heterodyne radiometric measurements with quasioptical Schottky diode mixers

High Sensitivity Submillimeter Heterodyne Receiver