Investigation of Frequency Tunable Superconducting Submillimeter Oscillator

作为紧凑型亚毫米振荡器的候选器件，我们制作了通过微带四分之一波长阻抗变压器与领结天线连接的磁通流振荡器（FFO）。该器件采用Nb/A10_x/Nb隧道结技术制备。在项目期间，我们制作了两种类型；FFO版本1和FFO版本2。每个装置都是在一个4毫米正方形的晶石英衬底上制造的。版本1比版本2更加集成。Ver. 1由四个部分组成：两个长约瑟夫森结，两个微带变压器，一个领结天线和一个监视SIS（超导体绝缘体超导体）探测器。在第1版中还集成了沿长约瑟夫森结产生磁通量的电流电路。Ver. 2由一个长约瑟夫森结、一个微带变压器和一个领结天线组成。磁通量是由外部磁铁产生的。实验将每一种元素浸泡在4.2 K的液氦中。在静态电流-电压测量过程中，观察到两种版本的速度匹配步骤。利用第1版SIS的光子辅助隧穿（PAT）检测模式监测振荡功率。基于速度匹配阶跃所处电压计算的振荡频率与PAT阶跃得到的频率吻合较好。在160 GHz到310GHz的频率范围内证实了振荡。在第2版中，振荡功率从领结天线辐射到超半球面透镜准直的自由空间。辐射功率通过金属锥聚焦到校准的InSb热电子辐射热计上。在140GHz-490GHz范围内确认振荡。在测试装置中，振荡功率最大时达到-1 muW。这个功率水平在实际应用中并不那么稀缺。为了使该装置达到实际应用水平，必须继续进行振荡线宽的测量和振荡频率的稳定。少

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 … More 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. Less