sub-THz Waves Research Articles

Photodiode-integrated microstrip antenna array for subterahertz radiation

The radiation characteristics of subterahertz (sub-THz) electromagnetic waves emitted from an antenna array integrated with photodiodes are investigated. The element of the fabricated array antenna was a 300-GHz microstrip antenna integrating a uni-traveling carrier photodiode. It was observed that the beamwidth of a 3 × 1 antenna array is about half that of the single microstrip antenna. We also confirmed that the radiation direction changed by 20/spl deg/ when 2/spl pi//5 of phase difference was added to the input optical signal for each antenna element. These results demonstrated that sub-THz waves emitted by each element of the array were coherently superimposed and the power combining of the sub-THz radiation occurred in the microstrip antenna array. The measured output power of each radiation element is about 120 μW, and a total output power of 1 mW can be estimated for a fabricated 3 × 3 array in an ideal radiation condition.

Frequency detection of focused sub-THz waves using a high-Tc Josephson junction

We have proposed a new type of frequency detection system of sub-terahertz electromagnetic waves using a photomixing technique and a Josephson junction detector. The photomixer illuminated by two lasers with different wavelengths generates coherent electromagnetic waves that include a frequency component corresponding to the frequency difference of the two lasers. The generated electromagnetic waves were radiated from a horn antenna and focused to the Josephson junction detector with Si lens. The high-Tc Josephson junction operates as a frequency detector for electromagnetic waves. Using this system, we observed the Shapiro steps of 188μV that correspond to the frequencies of 90.8GHz.

Generation of sub-terahertz waves using a semiconductor photomixer

A low-temperature-grown GaAs (LT-GaAs) photoconductive switch has been utilized as a photomixer in the sub-terahertz (sub-THz) region. The usefulness of the switch has been demonstrated by detecting the radiated sub-THz wave with a high-TC Josephson junction detector consisting a series of nine junctions and a gold-coated log-periodic antenna. The sub-THz waves are radiated from the photoconductive switch by introducing the optical heterodyne signal of two semiconductor lasers. Although the radiation power of the photoconductive switch is three orders of magnitude lower than a conventional photodiode, the sub-THz waves from the switch were successfully observed in the difference voltage response of the junctions. This result suggests that the LT-GaAs switch can be used as the photomixer in the optical-microwave converter for superconductive electronics. We have also studied the properties of a radiated sub-THz frequency spectrum using a Martin–Puplett interferometer.