A Terahertz Source of Radiation to Open Space Based on a Long Josephson Junction
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A Terahertz Source of Radiation to Open Space Based on a Long Josephson Junction N. V. Kineva, *, K. I. Rudakova, L. V. Filippenkoa, V. P. Kosheletsa, and A. M. Barysheva a Kotel’nikov
Institute of Radio Engineering and Electronics, Russian Academy of Sciences, Moscow, 125009 Russia * e-mail: [email protected] Received March 26, 2020; revised March 26, 2020; accepted April 2, 2020
Abstract—An electromagnetic source of terahertz radiation on the basis of a tunnel long Josephson junction was proposed and experimentally studied. Output radiation was transmitted to open space by means of a slot antenna, which was located on the same microcircuit with the junction and matched with the collecting lens. Several Oscillator structures designed for operation within the frequency ranges of 250–410, 330–530, and 390–700 GHz with the possibility of continuous frequency tuning were manufactured and tested. The amplitude-frequency characteristics of output radiation with a spectral resolution of nearly 0.1 MHz were studied with the use of a terahertz-spectrometer based on a superconducting receiver. The study of transmitting antenna characteristics throughout the entire bandwidth was performed with the use of a cooled highly sensitive silicon based bolometer. The experimental results correspond to numerical calculations. Keywords: terahertz radiation sources, Josephson effect, slot antenna, harmonic mixer DOI: 10.1134/S1063783420090140
1. INTRODUCTION Terahertz radiation sources are currently demanded in a number of scientific problems, such as heterodyne detection of ultraweak signals for radioastronomic studies and high-resolution terahertz spectroscopy. Spectroscopy of gases and living tissues is widely used in biology, medicine, environmental monitoring, and security systems. A long Josephson junction (LJJ) operates as a source of electromagnetic terahertz radiation [1], whose frequency f can be uniquely determined from the direct-current bias voltage Vdc on the junction by the Josephson relationship
hf = 2eVdc, where h is the Planck constant, and e is the charge of an electron. Applying an external local magnetic field and specifying the LJJ bias voltage, it is possible to create a unidirectional flux of magnetic vertices (magnetic flux quanta)—fluxones—inside a tunnel junction. In recent decades, the structure of such a junction has been appreciably improved with the purpose of its application just as a widely tunable terahertz oscillator [2], and its spectral characteristics were thoroughly studied [3] with the use of a harmonic mixer to decrease the output radiation frequency to the range of 0.1–1 GHz and stabilize radiation on the basis of a phase locking loop (PLL). The signal within a frequency range of up to 1 GHz can be immediately measured with the use of a laboratory spectrum analyzer
with a resolution of nearly 1 Hz. The LJJ based source output characteristics attained by now are the following: the generation frequency variates from 300 to 700 GHz with the possibility of continuous tuning
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