Superconducting Sub-Terahertz Oscillator with Continuous Frequency Tuning

Abstract

The development and approbation of a superconducting local oscillator based on a long Josephson junction made it possible to create a fully superconducting integrated receiver in sub-terahertz frequency range, which was successfully tested both on board a high-altitude balloon and in the laboratory. In order to expand the frequency range of a superconducting integrated local oscillator, it is necessary to ensure the continuous tuning of its frequency at an arbitrary bias current, including a so-called resonant mode regime. The resonant mode regime takes place for high-quality tunnel junctions with low leakage; in this regime, stable generation is possible only at Fiske steps, the distance in frequency between which is tens of GHz. A method for suppressing resonances has been proposed and implemented; this method is based on the introduction of normal metal layers into the region near the long Josephson junction. Modeling of the propagation of electromagnetic waves in the proposed integrated structure was carried out; experimental samples were fabricated, and their comprehensive study was performed. The complete suppression of resonances and the possibility of the continuous tuning of the frequency of a superconducting local oscillator in the range of 200–700 GHz have been demonstrated. The linewidth of the FFO radiation does not exceed 15 MHz over the entire frequency range, which makes it possible to implement the phase locked loop mode in an integrated receiver intended for spectral studies.

A distributed active patch antenna model of a Josephson oscillator

“…The factor [λ 0 /b] 2 in Eqs. (12) and (49) leads to a very large R rad Z 0 . (ii) The smallness of junction resistance, R QP Z 0 .…”

“…FFO was used in the first direct demonstration of Josephson emission by Yanson, et.al., back in 1965 [13,14]. State of the art FFOs, developed by Koshelets and co-workers show a remarkable performance in terms of tunability and linewidth [6,9,12]. However, 1 they emit very little power into free space [11,13,15,16].…”

“…Flux-flow oscillator (FFO) is the most well studied Josephson source of high-frequency electromagnetic waves (EMW) [1][2][3][4][5][6][7][8][9][10][11][12]. FFO was used in the first direct demonstration of Josephson emission by Yanson, et.al., back in 1965 [13, 14].…”

“…The corresponding cavity mode resonances are manifested by Fiske steps in the currentvoltage (I-V ) characteristics [16,[28][29][30][31][32]. FFOs exhibit * Vladimir.Krasnov@fysik.su.se sharp emission maxima at Fiske steps [9,12,13]. Such a conditional emission indicates that several additional and equally important phenomena (apart from the ac-Josephson effect) are involved in FFO operation [10].…”

A distributed active patch antenna model of a Josephson oscillator

“…A flux-flow oscillator (FFO) is the most extensively studied Josephson source of high-frequency electromagnetic waves (EMW) [1][2][3][4][5][6][7][8][9][10][11][12]. A FFO was used in the first direct demonstration of Josephson emission by Yanson et al, back in 1965 [13,14].…”