Investigation of Frequency Tunable Superconducting Submillimeter Oscillator

1990 Fiscal Year Final Research Report Summary

• Project/Area Number: 01550035
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: 物理計測・光学
• Research Institution: Osaka University
• Principal Investigator: SAKAI Kiyomi Osaka University, Faculty of Engineering, Department of Applied Physics, Associate Professor, 工学部, 助教授 (00029109)
• Project Period (FY): 1989 – 1990
• Keywords: Flux-flow Oscillator / Superconducting Oscillator / Tunable Oscillator / Submillimeter Oscillator / Velocity Matching step

Research Abstract

As a candidate for compact submillimeter oscillators, we have fabricated the flux-flow oscillator (FFO) connected with a bow-tie antenna through a microstrip quarter-wavelength impedance transformer. The Nb/A10_x/Nb tunnel junction technology has been used for the fabrication of the device. In the term of project, we have fabricated two types ; FFO Ver. 1 and FFO Ver. 2. Each device is fabricated on a crystalline quartz substrate in a cell of 4mm squares. The Ver. 1 is more integrated than the Ver. 2. The Ver. 1 is composed of four parts : two long Josephson junctions, two microstrip transformers, a bow-tie antenna and a monitor SIS (Superconductor Insulator Superconductor) detector. Current circuits to generate the magnetic flux along the long Josephson junctions are also integrated in Ver. 1. The Ver. 2 is composed of a long Josephson junction, a microstrip transformer and a bow-tie antenna. The magnetic flux is generated by use of an external magnet.
Experiments were done immersing e ach element in liquid helium (4.2 K). Velocity-matching steps were observed in both versions in the course of static current-voltage measurements. The oscillation power was monitored by means of PAT (Photon-Assisted-Tunnelling) detection mode of the SIS in Ver. 1. The oscillation frequency calculated based on the voltage where the velocity-matching step stands coincides well with the frequency obtained from the PAT step. The oscillation was confirmed in the frequency range between 160 GHz and 310GHz. In Ver. 2 the oscillation power was radiated from the bow-tie antenna into the free space collimated with a hyper-hemispherical lens. The radiated power was focused by a metallic cone onto a calibrated InSb hot electron bolometer. The oscillation was confirmed over the range of 140GHz-490GHz. The oscillation power of -1 muW was obtained at maximum in the tested devices. This power level is not so scarce for practical applications. In order to push up this device to the practical application level, measurements of oscillation line width and the stabilization of oscillation frequency have to be continued.