8mm波段Fabry-Perot谐振腔及其在约瑟夫森结特性测量中的应用

 通过三维电磁仿真技术设计并制作了8mm波段Fabry-Perot谐振腔,并建立起一套Fabry-Perot谐振腔高温超导约瑟夫森结特性测试系统.用它测量了Tl₂Ba₂CaCu₂O₈(Tl-2212)高温超导薄膜双晶约瑟夫森结的毫米波辐照特性,得到高质量的夏皮罗台阶,并与在U形波导测试系统中测得的结果进行了比较,发现利用Fabry-Perot谐振腔测量技术可显著提高外加电磁场与约瑟夫森结的耦合效率,为进一步研究毫米/亚毫米波信号检测、THz波信号源等研究打下坚实的基础.     

0.67 THz高分辨力成像雷达

为达到厘米甚至亚厘米级的成像分辨力,从电子学角度出发,设计并构建了0.67 THz线性调频连续波(FMCW)成像实验平台。平台通过将Ka波段带宽1.2 GHz、功率2 W的线性调频信号24倍频,获得0.66 THz~0.688 8 THz的发射信号,功率约为1.2 mW,接收端的回波经过谐波混频完成去斜(Dechirp)形成2.4 GHz中频信号,二次变频后经高速采样送入信号处理机箱完成成像。雷达发射信号带宽为28.8 GHz,经系统非线性校正处理后,成像分辨力达到1.3 cm,验证了太赫兹雷达的高分辨成像能力。     

基于虚拟仪器的频谱监测技术研究

首先介绍了对信号进行频谱分析的原理,并根据软件无线电和虚拟仪器的思想,基于NI(National Instruments)的PXI硬件模块和LabVIEW软件平台,实现了100 kHz~2.7 GHz频率范围内的宽带频谱扫描、频率测量、带内功率测量、邻波道功率测量、信号带宽测量等功能。最后,利用该测试平台对实际信号进行测量,并与频谱分析仪的测量结果进行比较,验证了该方案的有效性。     

高速太赫兹时域光谱系统中平衡探测器的设计

平衡探测器是直接探测太赫兹信号的器件,位于高速太赫兹时域光谱(THz-TDS)系统末端光信号检测部分,是将光学信号转变为模拟电信号的关键器件,其性能决定了测量出的THz信号的精确度。利用2个低噪声光电二极管串联,直接探测出2束激光的差值光电流,降低了探测噪声;选用增益带宽乘积为4 GHz的运算放大器对差值光电流进行两级放大,得到高动态范围的THz信号,提高了THz信号的探测速度,并测量了α-乳糖一水合物吸收峰,得到了和文献中相同的吸收峰。     

高端信号和频谱分析仪实现最小相位噪声和最大工作带宽

日前,罗德与施瓦茨(ROHDE&SCHWARZ;R&S)正式面向中国市场推出第四代信号和频谱分析仪R&S FSW,其频率范围覆盖为2Hz～8GHz、13GHz和26.5GHz。在10kHz载波频偏上,FSW实现了小于-137dBc(lHz)的相位噪声,此指标比市场上同类的仪表还要低10dB。高达160MHz的解调带宽性能,使其可以测量宽带、跳频及线性调频信号。据悉,在射频性能和     

基于肖特基变容二极管的0.17 THz 二倍频器研制

研制了一种基于肖特基变容二极管的0.17 THz 二倍频器, 该器件为0.34 THz 无线通信系统收发前端提供了低相噪、低杂散的本振信号.倍频器结构基于波导腔体石英基片微带电路实现, 其核心器件是多结正向并联的肖特基变容二极管.文中采用结参数模型和三维电磁模型相结合的方式对二极管进行建模, 通过两种电路匹配方式实现了0.17 THz 二倍频器的最优化设计, 最终完成器件的加工及测试.测试结果表明, 在输入80~86 GHz, 20 dBm 的驱动信号下, 倍频器的最大输出功率达12.21 mW, 倍频效率11%, 输出频点为163 GHz;当前端输入功率达到饱和状态时, 该频点输出功率可达21.41 mW.     

迈克尔逊干涉法精确测量太赫兹频谱及目标速度

搭建了一套迈克尔逊干涉仪,对CO2激光的9P36和9R10谱线泵浦CH3OH气体所产生的频率分别为2.52 THz和3.11 THz的太赫兹激光器输出频谱进行了精细测量。测量系统频率分辨率约为1 GHz,测量结果显示CO2激光泵浦的太赫兹源为单色源并具有极窄的线宽,波长与激光器标称值进行对比具有很好的一致性。基于这套系统实现了对干涉仪动臂目标的运动速度准确测量,提出了两种分别适用于匀速运动和变速运动情况下的速度反演方法,反演结果与设定值均相符。结论表明,迈克尔逊干涉仪不但可以精确测量太赫兹波源的频谱,同时配合单色太赫兹源可以准确测量目标速度,为太赫兹波段光谱、成像等领域的应用奠定基础。     

一种0.34 THz站开式三维成像安检仪

介绍了一种太赫兹站开式大视角三维成像雷达系统。系统可用于人体隐藏危险品的成像检测,采用二维非均匀逐点扫描的工作方式,视场范围达到0.6 m×1 m,成像速度达到2 s。系统工作于0.34 THz,采用直径450 mm椭球镜聚焦,在5.8 m的成像距离实现了2 cm的方位分辨力。为了改善回波动态范围,采用相位噪声相消的系统结构。系统采用调频连续波(FMCW)雷达线性调频信号作为工作波形,工作带宽达到12 GHz。成像结果显示,系统校正后的距离分辨力可达到2 cm,能够实现隐藏危险品的有效检测。     

超导微波源的仿真、设计与制备

本文主要介绍了采用超导约瑟夫森结实现的超导微波源的基本原理及实现方法。文中我们通过电路仿真得到了输入为直流信号,输出为幅值可调的4.2GHz微波信号,然后根据相应仿真参数绘制了芯片版图,并对实验室原有的自对准剥离工艺进行了改进,完成了超导微波振荡器的制备,为将来利用超导材料实现具有实用价值的太赫兹源奠定了理论以及实验研究基础。     

约瑟夫森结跳变电流统计分布测量系统

本文详细介绍了一种通过对时间的测量来获得单个约瑟夫森结(JJ)跳变电流统计分布P(I)的测量系统,包括致冷系统和测量方案.我们还在测量电路中采取了电磁屏蔽、低通滤波、接地等一系列的降噪措施,使得实验所能测量到的约瑟夫森结的最低等效温度进一步的降低至300mK.     

Comparison of CW THz Wave Spectrometer with Laser Diode Excitation and Pulsed THz Wave Spectrometer with Cr:forsterite Sources Based on Difference Frequency Generation of Near-infrared Lasers in GaP

We constructed two types of terahertz (THz) spectrometers with automatic scanning control based on the difference frequency generation method by the excitation of the phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were based on an optical parametric oscillator and Nd: YAG laser sources having a frequency resolution of 1.5 GHz, and on Cr:fosterite sources with a resolution of 20 GHz. Following these, we recently constructed a continuous wave (CW) THz wave spectroscopic system with laser diode excitation. One of the advantages of the CW THz wave spectrometer is its wide frequency tuning range with fine frequency resolution of < 8 MHz. In this study, we compare both types of spectrometers (pulsed versus CW) to show the characteristics of each system in terms of frequency resolution. The absorption spectra of a non-deformed white polyethylene crystal and ultra-high molecular weight polyethylene with/without deformation are measured by using the CW THz wave spectrometer and pulsed THz wave spectrometer. The effect of the high-resolution CW THz wave spectrometer is shown based on the THz spectroscopic results.     

Superconducting bandpass /spl Delta//spl Sigma/ modulator with 2.23-GHz center frequency and 42.6-GHz sampling rate

This paper presents a superconducting bandpass /spl Delta//spl Sigma/ modulator for direct analog-to-digital conversion of radio frequency signals in the gigahertz range. The design, based on a 2.23-GHz microstrip resonator and a single flux quantum comparator, exploits several advantages of superconducting electronics: the high quality factor of resonators, the fast switching speed of the Josephson junction, natural quantization of voltage pulses, and high circuit sensitivity. The modulator test chip includes an integrated acquisition memory for capturing output data at sampling rates up to 45 GHz. The small size (256 b) of the acquisition memory limits the frequency resolution of spectra based on standard fast Fourier transforms. Output spectra with enhanced resolution are obtained with a segmented correlation method. At a 42.6-GHz sampling rate, the measured SNR is 49 dB over a 20.8-MHz bandwidth, and a full-scale (FS) input is -17.4 dBm. At a 40.2-GHz sampling rate, the measured in-band noise is -57 dBFS over a 19.6-MHz bandwidth. The modulator test chip contains 4065 Josephson junctions and dissipates 1.9 mW at T=4.2 K.     

High-speed experiments on a QFP-based comparator for ADCs with18-GHz sample rate and 5-GHz input frequency

The authors report on the high-speed operation of a superconducting comparator circuit, based on coupling the quantum flux parametron (QFP) to an RF SQUID, which can be used to build a flash-type analog-to-digital converter (ADC). Simulations of this circuit show that it is expected to achieve operation with input signal bandwidths greater than 4 GHz and with a dynamic range equal to at least 4 b of resolution. A QFP-based comparator fabricated with a process using NbN/Pb-alloy Josephson junctions of 5 μm by 5 μm and a current density of 100 A/cm² has been examined to evaluate the properties of the QFP-ADC. Analog-to-digital conversion of the comparator has been observed with a QFP activation frequency up to 18.2 GHz. By employing a sampling method, input signals with frequencies up to 5.4 GHz have also been digitized     

Terahertz and Millimetre Wave Imaging with a Broadband Josephson Detector Working above 77 K

A high-T_c superconducting (HTS) broadband Josephson detector has been developed and applied to millimetre wave (mm-wave) and terahertz (THz) imaging. The detector is based on a YBa₂Cu₃O_7-x (YBCO) step-edge Josephson junction, which is coupled to a thin-film log-periodic antenna, designed for operation at 200–600 GHz, and a hemispheric silicon lens. The junction parameters have been optimised to achieve a high I_cR_n value so that the detector responds well to the specified frequencies at liquid nitrogen temperature (77 K). Images at ∼200 GHz and ∼600 GHz were acquired with the same detector; each demonstrated their unique properties. The results demonstrate the potential of achieving a cheaper, compact and portable multi-spectral imager based on a HTS detector.     

Josephson array oscillator with microstrip resonators for submillimeter wave region

Shunted tunnel junctions with a small parasitic inductance have been developed for improving the operating frequency of Josephson array oscillators. The inductance was minimized by reducing the inductive length to 1 μm and was estimated to be about 40 fH. The analysis of resonant properties for the shunted junctions gave a high resonant frequency up to 1.4 THz. Josephson array oscillators were designed and fabricated to operate at near Nb gap frequency (700 GHz) using 11 shunted Nb/AlOx/Nb tunnel junctions with Nb microstrip resonators. Shapiro steps induced by Josephson oscillation were clearly observed above the Nb gap frequency (up to 830 GHz). By fitting the step height to the simulation result using the RLCSJ model, the output power of the Josephson oscillator to the load resistor was estimated to be about 0.1 μW at 680 GHz.     

超导微波源的仿真、设计与制备

本文主要介绍了采用超导约瑟夫森结实现的超导微波源的基本原理及实现方法。文中我们通过电路仿真得到了 输入为直流信号，输出为幅值可调的4.2GHz 微波信号，然后根据相应仿真参数绘制了芯片版图，并对实验室原有的自对 准剥离工艺进行了改进，完成了超导微波振荡器的制备，为将来利用超导材料实现具有实用价值的太赫兹源奠定了理论 以及实验研究基础。     

Resonance-free low-pass filters for the AC Josephson voltage standard

We have designed and characterized superconducting integrated circuits for the ac Josephson voltage standard that demonstrate significantly improved performance. The typical circuit consists of an array of superconductor-normal metal-superconductor Josephson junctions, which are placed in a transmission line and biased with a broad-band (dc-to-15 GHz) pulse-drive waveform. Additional low-speed (dc and audio frequency) bias and output leads contain on-chip inductors that act as low-pass filters. The operating margins of the array were improved by adding resistive shunts across these inductors to damp their intrinsic resonances. These resonances had previously degraded the integrity of the broad-band signal driving the array. We present simulations and measurements of these improved circuits that demonstrate no resonances in the range of 0.1-20 GHz. Moreover, the operating margins of the ac Josephson voltage standard were improved.     

Noise and mixing properties of high-Tc Josephson junctions at W-band frequencies

We report on the noise and Josephson mixing properties of high-T_c superconductor (HTS) Josephson junctions. Direct radiation measurements and heterodyne mixing experiments in the frequency range 45–141 GHz have been performed by using YBa₂Cu₃O_7−x (YBCO) step-edge junctions (SEJ) on LaAlO₃ and MgO and bicrystal junctions (BCJ) on MgO substrates. Junctions with current voltage characteristics (CVC) close to predictions of the resistivity shunted junction (RSJ) model were mounted into a high sensitive radiometer system. From linewidth measurements we calculated an effective noise temperature of our junctions. In heterodyne mixing experiments we obtained conversion efficiencies around −14 dB in the 11 GHz intermediate frequency (IF) band under the radiation of two monochromatic signals. In the fundamental mixing regime we observed response at IF at working temperatures up to 72 K. The measured receiver and mixer noise temperature of the Josephson mixer at 94 GHz local oscillator (LO) frequency, an IF of 1.4 GHz and at a working temperature of 10 K was 4700 and 3400 K, respectively.     

基于声表面波色散延迟线的频谱探测系统

利用声表面波(SAW)技术设计的Chirp变换频谱仪(CTS)具有低功耗、高稳定性等优势,特别适用于深空探测领域。该文提出了一种大带宽的CTS系统。由数模转换器(DAC)和四倍频器产生2 GHz带宽的展宽线Chirp信号,其色散特性与1 GHz带宽的声表面波色散延迟线特性匹配。搭建了实时处理带宽为1 GHz、频率分辨率为100 kHz的频谱分析仪,并对在大带宽下CTS出现的响应不均衡展开探讨。分析了系统各部分对CTS的影响,通过实验验证了响应不均衡出现的原因。测试结果表明,该文设计搭建的1 GHz带宽CTS系统的频率分辨率可达115.512 kHz。