小孔径蝴蝶型光电导天线太赫兹辐射源的研究

研究了5种小孔径光电导天线的太赫兹发射特性,并且对它们所发射的太赫兹波进行了对比,为研制高效率的太赫兹波发射源提供了参考依据。利用太赫兹时域光谱技术测量了光电导天线发射的太赫兹（THz）脉冲,得到了时域发射光谱,并通过快速傅里叶变换得到相应的频域光谱。结果表明,太赫兹信号强度随偏置电压的增大而增强;随着泵浦激光功率的增大而增强并出现饱和现象。偏置电压与泵浦激光功率相同时,我们对比5种光电导天线产生的太赫兹信号,从中找到了一种发射效率较高的小孔径光电导天线,并且研究了电极形状、电极间距对光电导天线发射效率的     

小孔径螺旋型光电导天线的太赫兹辐射特性研究

研究了小孔径螺旋型光电导天线的太赫兹辐射特性.利用太赫兹时域光谱技术测量了螺旋型光导天线辐射的太赫兹波谱,得到了其时域发射光谱.通过快速傅里叶变换得到相应的频域光谱,同时对两种不同孔径螺旋天线的太赫兹辐射特性进行了比较.实验结果表明,太赫兹信号强度会随偏置电压的增大而增强;在偏置电压和泵浦光功率相同的情况下,较小孔径的...     

低温生长砷化镓光电导天线产生太赫兹波的辐射特性

研究了低温生长砷化镓光电导天线(LT-GaAs PCA)产生太赫兹(THz)波的辐射特性。利用太赫兹时域光谱(TDS)技术测量了光电导发射极在飞秒激光作用下辐射的太赫兹脉冲,得到了时域发射光谱,并通过快速傅里叶变换(FFT)得到相应的频域光谱。结果表明,低温砷化镓光电导天线产生的太赫兹波信号比飞秒激光激发半导体表面产生的太赫兹波信号具有更高的强度和信噪比;太赫兹波信号与光电导天线的偏置电压成线性关系;随着抽运激光功率的增强,太赫兹波信号增大并出现饱和。     

太赫兹折叠波导慢波结构止带振荡器

为实现太赫兹新频段的开拓,满足太赫兹应用对实用化功率源的需求,研发了太赫兹折叠波导慢波结构止带振荡器。器件工作在慢波结构的止带附近,利用高耦合阻抗的特点,完成强注波互作用,实现大功率、小尺寸的太赫兹源。实验验证的振荡器样管采用了折叠波导慢波结构,工作电压为23.1 kV,工作电流为150 mA,在振荡频率为124.45 GHz时,最大脉冲输出功率达到32 W。实验结果表明,该器件适于作为开拓新频段的探索,能够满足高功率、窄带宽需求的太赫兹应用。     

折叠波导结构的THz振荡辐射源研究

 以折叠波导为基本结构的真空电子器件,具有大功率、宽频带和制造成本低的优点,本文通过深入研究折叠波导振荡器的冷腔结构、色散方程和耦合阻抗,给出了可以产生THz的折叠波导振荡器的基本结构.并利用三维PIC粒子模拟软件进行了三维模拟计算,结果显示,在输入电子注电压为20.6kV,电流为0.12A,磁场为3000高斯时,可得到频率为0.1THz,平均输出功率174W,互作用效率大于7%.     

共振声子THz QCL有源区结构设计

利用Airy函数代换与传输矩阵方法精确计算了有外加偏压下电子在共振声子太赫兹量子级联激光器有源区单个周期内的透射系数与波函数,得到了不同偏压下的电子波函数分布以及准束缚态能级位置与外加偏压的关系曲线.在仿真计算的基础上设计了一种共振声子太赫兹量子级联激光器的有源区结构.计算结果表明,对于设计的结构,当单个周期两端的外加...     

Terahertz detector utilizing two-dimensional electronic fluid

We report on the first implementation of a terahertz detector utilizing two-dimensional (2-D) electronic fluid in a high electron mobility transistor (HEMT) operating at 2.5 THz. The terahertz radiation induced a dc drain-to-source voltage proportional to the radiation intensity. The measured dependencies of the detector responsivity on the gate bias are in good agreement with the gate bias dependence of the normalized responsivity predicted by the detector theory. This result shows the potential for developing a new family of electronics devices-plasma wave electronics devices-operating at terahertz frequencies     

0.6 THz三次谐波回旋管的研究

 太赫兹回旋管是一类基于电子回旋受激辐射机理的快波器件,同时也是目前最具发展前景的高功率太赫兹辐射源.本文根据回旋管的线性理论和自洽非线性理论对三次谐波、工作频率0.6 THz的回旋管进行了研究,重点讨论了引导中心分别为0mm的实心回旋电子注和0.315mm的空心回旋电子注的模式竞争.通过分析比较,发现工作在0.6THz 、三次谐波的众多模式中TE37模是一比较理想的工作模式,它不仅有相对较高的功率输出,而且还有相对较少的模式竞争.本文中的设计采用55kV/1.0A,电子注的速度横纵比为1.5,在工作磁场7.86T下,数值计算结果表明输出功率达4.73kW.     

Room-Temperature AlGaN/GaN Terahertz Plasmonic Detectors with a Zero-Bias Grating

In this paper, we present sensitivity measurement as well as measured and calculated absorption spectra for AlGaN/GaN THz plasmonic detector made of a metallic grating in-between two ohmic contacts. Detectors with different grating patterns have been fabricated and their sensitivity, reaching 1.9 μA/W at 77 K and 0.7 μA/W at 300 K, measured with a voltage applied between the ohmic contacts. It is the first time that such a detector shows THz detection with no voltage applied on the grating, namely with a bidimensional electron gas (2DEG) having a homogeneous electron density. These results are consistent with detection by drag-effect rectification. Measurements held between 0.648 and 0.690 THz show that the dependence of the sensitivity on the frequency follows the absorption spectrum, indicating that absorption is a crucial step in the detection process. Further simulations of absorption spectra show the tunability offered by such detector and allow us to predict frequency behavior for grating-biased detectors as well, in which the rectification is mainly governed by ratchet effect.     

Terahertz Imaging Detectors in CMOS Technology

Square-law power detection circuits with on-chip antennas and amplifiers are presented for the detection of 0.65-THz radiation in a low-cost 0.25-μm CMOS technology. The circuit architecture combines metal-insulator-metal (MIM) coupling capacitors with NMOS transistors to facilitate self-mixing in a resistive mixer. A low-frequency (quasi-static) and a high-frequency (non-quasi-static) analysis of the broad-band circuit is presented. Current and voltage readout techniques of non-amplified detectors are compared, and exhibit a measured responsivity of 5.3 mA/W and 150 V/W respectively. A monolithic integrated 3×5 pixel focal-plane array has been used for single-pixel and multi-pixel imaging of concealed objects at 0.65 THz.     

基于铟镓砷材料的新型太赫兹/亚毫米波探测器研究

对一种基于生长在半绝缘InP衬底上InGaAs外延材料的新型太赫兹室温探测器进行研究。首先在HFSS理论计算的基础上对器件天线阻抗、驻波比、辐射方向图等特性参数进行分析。其次,通过光刻、腐蚀、溅射、点焊等工艺制作出对称金属电极天线耦合的太赫兹探测器件。结合自己搭建的0.037 5 THz器件响应测试系统,得到铟镓砷太赫兹探测器件在不同偏置电流和不同调制频率下的器件响应曲线。结果表明器件具有明显的光电信号和快的响应速度。通过利用高莱探测器进行标定,得到器件在0.037 5 THz时的电压灵敏度优于6 V/W,器件噪声等效功率NEP优于1.610-9 W/Hz1/2,器件响应时间优于300 s。     

基于肖特基势垒二极管的太赫兹固态倍频源和检测器研制

本文基于GaAs肖特基势垒二极管以及混合集成电路工艺,对太赫兹固态倍频和检测技术开展了研究.文章结合肖特基势垒二极管物理结构,采用电磁场仿真软件和电路仿真软件相结合的综合分析方法,对各模块电路进行优化设计,研制出了高倍频效率的倍频源和高灵敏度的检测器(检波器和谐波混频器).0.15THz检波器测得最高检波电压灵敏度1600mV/mW,在0.11~0.17THz灵敏度典型值为600mV/mW,切线灵敏度优于-29dBm.0.15THz二倍频器测得最高倍频效率7.5%,在0.1474~0.152THz效率典型值为6.0%.0.18THz二倍频器测得最高倍频效率14.8%,在0.15~0.2THz效率典型值为8.0%.0.15THz谐波混频器测得最低变频损耗10.7dB,在0.135~0.165THz变频损耗典型值为12.5dB.0.18THz谐波混频器测得最低变频损耗5.8dB,在0.165~0.2THz变频损耗典型值为13.5dB,在0.21~0.24THz变频损耗典型值为11.5dB.     

Terahertz radiation of a butterfly-shaped photoconductive antenna (invited)

The terahertz(THz) far-field radiation properties of a butterfly-shaped photoconductive antenna (PCA) were experimentally studied using a home-built THz time-domain spectroscopy(THz-TDS) setup. To distinguish the contribution of in-gap photocurrent and antenna structure to far-field radiation, polarization-dependent THz field was measured and quantified as the illuminating laser beam moved along the bias field within the gap region of electrodes. The result suggests that, although the far-field THz radiation originates from the in-gap photocurrent, the antenna structure of butterfly-shaped PCA dominates the overall THz radiation. In addition, to explore the impact of photoconductive material, radiation properties of butterfly-shaped PCAs fabricated on both low-temperature-grown GaAs(LT-GaAs) and semi-insulating GaAs(Si-GaAs) were characterized and compared. Consistent with previous experiments, it is observed that while Si-GaAs-based PCA can emit higher THz field than LT-GaAs-based PCA at low laser power, it would saturate more severely as laser power increased and eventually be surpassed by LT-GaAs-based PCA. Beyond that, it is found the severe saturation effect of Si-GaAs was due to the longer carrier lifetime and higher carrier mobility, which was confirmed by the numerical simulation.     

用飞秒激光触发GaAs光电导体产生THz电磁波的研究

报道了用半绝缘GaAs材料研制的光电导偶极天线在飞秒激光脉冲触发下辐射THz电磁波的实验结果.GaAs光电导偶极芯片的两个欧姆接触电极间隙为3mm,采用Si3N4薄膜绝缘保护,在540V直流偏置下被波长800nm,脉宽14fs,重复频率75MHz,平均功率130mW的飞秒激光脉冲触发时产生THz电磁波.用电光取样测量得到了THz电磁脉冲的时域波形和频谱分布.THz电磁波的辐射峰值位于0.5THz左右,频谱宽度大于2THz,脉冲宽度约为1ps.     

Generation of CW terahertz radiation using two-colour laser with Fabry-Perot etalon

A simple scheme for generating continuous-wave (CW) terahertz (THz) radiation from a two-colour laser is reported. A Ti-sapphire laser is forced to oscillate on two modes by placing a Fabry-Perot etalon in the laser cavity. THz radiation is generated by photomixing in a biased photoconverter. The THz frequency is determined by the separation of the etalon plates     

Characteristics of the Beam-Steerable Difference-Frequency Generation of Terahertz Radiation

We have investigated the characteristics of a terahertz (THz) beam steering method based on a combination of difference-frequency generation (DFG) with the principle of the phased array antenna. In the DFG of THz radiation from a nonlinear optical crystal pumped by optical beams, the phase front of the THz radiation is indirectly tilted by adjusting the relative incidence angle between the pump beams to the crystal. A magnification of the steering angle with a factor of 193 is demonstrated as the most important effect provided by the method. The effect allows the use of a high-speed optical deflector for adjusting the incidence angle, accelerating the steering more than a hundred times compared with mechanical methods. The phase mismatching between the THz radiation and the pump beams as well as the refraction at the crystal surface limit the steering angle of the THz radiation to 56°, full width at half maximum.     

缓慢上升快速下降的飞秒激光脉冲与气体等离子体作用的太赫兹辐射产生研究

飞秒激光脉冲与气体等离子体作用可以产生宽带、强的太赫兹脉冲辐射。采用一种缓慢上升、快速下降的飞秒激光脉冲与气体等离子体作用产生太赫兹辐射,并基于等离子体电流模型计算了这种太赫兹辐射的特性。由于这种特殊整形的激光脉冲能够对电子的加速产生较大的速度,从而可以产生较大的等离子体电流和较强的太赫兹辐射。计算结果显示:尽管这种特殊整形的飞秒激光脉冲能量有所损失,它能够比普通双色飞秒激光脉冲产生更强、更宽的太赫兹脉冲辐射。该项研究为基于激光等离子体作用的太赫兹辐射源提供了新的思路。     

Far-Infrared Spectrum Analysis Using Plasmon Modes in a Quantum-Well Transistor

Excitation of resonant plasmon modes by far-infrared (FIR) radiation in a quantum-well transistor is used to analyze the spectral content of FIR illumination at frequencies between 0.58 and 0.99 THz. A split grating gate design that allows localized pinch-off of the transistor channel greatly enhances FIR response and allows completely electrical tuning of the plasmon resonance, enabling broadband FIR spectrum analysis without moving parts. A voltage ramp applied to the gate can generate a spectrum at video rate.     

基于合成超构材料的太赫兹调制器设计

为了研究利用新型器件提高辐射控制的能力,利用合成超构材料演示了一种太赫兹有源调制器的设计。该结构采用三维设计,除通过电压调节基底耗尽层载流子复合之外,还通过悬臂结构调节该结构的等效电磁参数,最终达到有效调节器件响应的目的。研究表明该器件能够实时、有效地对太赫兹辐射进行控制和操作。其对透射率的调制可达75%,频移0.1 THz,优于目前基于二维平面方法设计的太赫兹调制器件。     

THz Thermal Radiation Enhancement Using an Electromagnetic Crystal

Thermal radiation in the terahertz (THz) range only occupies a tiny portion of the whole blackbody power spectrum at room temperature. We demonstrate that a thermal radiator, which is constructed from an electromagnetic (EM) crystal, can be designed so that its photon density of states (DOS) is enhanced in the THz frequency range. We also demonstrate, as a consequence, that this source may lead to large enhancements of the radiated power over the values associated with normal blackbody radiation at those frequencies. The THz thermal radiation enhancement effects of various EM crystals, including both silicon and tungsten woodpile structures and a cubic photonic cavity (CPC) array, are explored. The DOS of the woodpile structures and the CPC array are calculated, and their thermal radiation intensities are predicted numerically. These simulations show that the radiated power can be enhanced by a factor of 11.8 around 364 GHz and 2.6 around 406 GHz, respectively, for the silicon and tungsten woodpile structures in comparison to the normal blackbody radiation values at those frequencies. It is also shown that an enhancement factor of more than 100 may be obtained by using the CPC array. A silicon woodpile EM crystal with a band gap around 200 GHz was designed and fabricated. The transmission property of this woodpile structure was verified using the THz time-domain spectroscopy (TDS). Thermal emissions from the fabricated silicon woodpile and a control blackbody sample were measured. Enhancements of the woodpile source radiation over the blackbody were observed at several frequencies which are consistent with the theoretical predictions.