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Applied Physics Letters

Radiation linewidth of phase-locked distributed array in the submillimeter wave range

Baokang Bi, Siyuan Han, James E. Lukens

Published May 31, 1993• 18 citations
Publisher

Abstract

The radiation linewidth of a phase-locked distributed Josephson junction array source at 250 GHz has been measured as a function of temperature using an integrated submillimeter wave receiver/source. The measured total linewidth (including signal and local oscillator arrays, having 10 junctions each) is 10 MHz at 1.6 K. The measured data agree, within 50% uncertainty, with the linewidth obtained from computer simulation assuming the Nyquist noise current spectral density generated by the junction shunt resistors.

DOI
10.1063/1.109248

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The radiation linewidth of a phase-locked distributed Josephson junction array source at 250 GHz has been measured as a function of temperature using an integrated submillimeter wave receiver/source. The measured total linewidth (including signal and local oscillator arrays, having 10 junctions each) is 10 MHz at 1.6 K. The measured data agree, within 50% uncertainty, with the linewidth obtained from computer simulation assuming the Nyquist noise current spectral density generated by the junction shunt resistors.
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The power and linewidth of the radiation, near 250 GHz, of small distributed Josephson junction array sources have been measured using a single-chip integrated source and receiver. The intermediate frequency (IF), coupled off the chip to a room-temperature spectrum analyzer, permitted a direct measurement of the oscillator linewidth. The one-dimensional arrays were of a novel design with junctions placed in 1/4 wavelength lumps separated by one half wavelength. The measured power ( approximately=2 mu W) and linewidth ( approximately=10 MHz) for the 10 junction sources were in reasonable agreement with those obtained from computer simulations.>
A reliable technique for wide band measurements of the spectral linewidth of superconducting oscillators integrated on-chip with superconductor-insulator-superconductor (SIS) detectors has been developed. The spectral linewidth of flux-flow oscillators (FFO) based on the unidirectional and viscous flow of magnetic vortices in a long overdamped Josephson tunnel junction was measured in the frequency range 250–580 GHz, and a linewidth as low as 200 kHz was obtained at 450 GHz. Also stable frequency locking of a FFO to very high (≤60th) harmonics of an external microwave reference source has been demonstrated. The proposed technique may improve the sensitivity, frequency resolution, and stability of the fully superconducting integrated submillimeter wave receiver.
We have developed resistively shunted tunnel junctions with a small parasitic inductance (/spl equiv/100 fH) to improve the high-frequency performance of Josephson array oscillators. Josephson array oscillators with 11 such junctions and Nb microstrip resonators were designed and fabricated to operate at 690 GHz. Shapiro steps induced by Josephson oscillation were clearly observed at the submillimeter frequency region. By comparing the step height with the numerical simulation, we estimated the power of the Josephson oscillator delivered to the load resistor to be about 10 /spl mu/W at 625 GHz. The linewidth of the Josephson array oscillator was also measured using an integrated receiver consisting of two Josephson array oscillators and an SIS mixer. The designed frequency of the receiver was set at 550 GHz. IF output power spectrum was observed when both the oscillators were biased at about 1.17 mV which corresponds to 566 GHz. The composite linewidth of Josephson oscillation was measured about 8 MHz at 4.2 K.
A submillimeter wave source based on a new design using Josephson junction arrays has been developed and tested. The maximum rf power, delivered to a 68Ω load and detected on chip, was 47 μW at 394 GHz. Significant power was detected at a number of frequencies from 300 to 500 GHz where the power was 10 μW. The observed power at the designed operating frequency near 400 GHz is consistent with all 500 junctions in the series biased array delivering current in phase to the loads. This is in agreement with simulations of smaller arrays of the same design. The linewidth, inferred from the measured resistance at the point of maximum power, with T=4.2 K, is less than 1 MHz. The minimum inferred linewidth near 400 GHz, at somewhat lower power, is about 100 kHz.