Frequency response of a unidirectional-output optical frequencyconversion device with an asymmetrical-κ DBR laser structure

The frequency response of a unidirectional-output optical frequency conversion device is measured. The device has a saturable absorber region within the active region, which acts as an optical gate for converted light. The 3-dB bandwidth of the device with saturable absorber region is measured up to 800 MHz, and is found to be limited by the frequency response of the saturable absorber region. To operate the device faster, lasing mode intensity modulation by input light is attempted by using the device in a laser diode mode. In this case, the electrodes of the saturable absorber and the gain regions are connected electrically, and the saturable absorber region is also biased far above the threshold condition at the same time with the gain region. The 3-dB bandwidth of the device increases to over 10 GHz, and the 10-Gb/s nonreturn-to-zero (NRZ) eye pattern can be observed when the input TM-polarized light intensity is modulated by a 10-Gb/s NRZ pseudorandom signal     

High-speed signal wavelength conversion using aunidirectional-output wavelength conversion device withasymmetric-κ DBR structure

The wavelength conversion device whose frequency response is evaluated analytically and experimentally in this work has a saturable absorber region, which acts as an optical gate, within the active region. The 3-dB bandwidth of this device was measured to be 800 MHz and found to be limited by the frequency response of the saturable absorber region. To speed up this device, the electrodes of the saturable absorber and the gain regions were connected electrically so that the device would act as a unidirectional-output distributed Bragg reflector (DBR) laser. When the active region (saturable absorber and the gain regions) of this DBR laser were biased above threshold condition, the 3-dB bandwidth was more than 10 GHz, and clear eye patterns were observed when the input TM-polarized light intensity was modulated by a 10-Gbit/s pseudo-random NRZ signal. These results show that high-speed wavelength conversion can be achieved when the device is operated as a laser diode     

谐振腔增强型光探测器的高速响应性能研究

高速长波长光探测器是高速光纤通信系统和网络的关键器件，它要求光探测器具有宽的频率响应带宽和高量子效率。常用的PIN光探测器由于量子效率和高速性能均受到吸收层厚度的牵制，使得二者相互制约，成为一对矛盾。谐振腔增强型(RCE)光探测器为这一矛盾的解决提供了有效的方案。基于谐振腔增强型光探测器的实际设计和制作模型，分析了器件吸收层中的光场分布，并将其运用于载流子的连续方程，从理论上详细地分析了器件的高速响应特性，给出了计算结果。针对研制的高速长波长谐振腔增强型光探测器，进行了理论分析和实际器件测试的结果比较，得到了比较一致的结果。     

Analysis of balanced active doubler for broad-band operation - thefrequency-tuning concept

A comprehensive analysis of an active balanced frequency doubler is described and proposed as a new concept: tuning the center frequency at which the doubler exhibits its highest performance to extend the usable bandwidth of the device. The concept is validated using a fabricated V-band pseudomorphic high electron-mobility transistor frequency doubler. For this device, a substantial improvement in the usable bandwidth (more than double) is achieved, demonstrating that the proposed concept is particularly suitable for the realization of high spectral purity and widely tunable V-band frequency sources     

High-speed optical Fourier transformer

A new type of high-speed signal processing or analyzing device-the picosecond Fourier transformer-is proposed. The device can be used to obtain the Fourier transform of the time-dependent intensity of an optical signal. The device makes use of the spatially distributed electrooptic modulator or deflector, and has the potential for terahertz bandwidth and picosecond time resolution. Practical devices are considered and their performances (bandwidth, frequency resolution, etc.) are discussed. The operation of the proposed device is demonstrated in the microsecond range by a preliminary experiment using LiTaO3e-o deflectors.     

Graphene Microstrip Patch Ultrawide Band Antennas for THz Communications

Future generation local communication systems will need to employ THz frequency bands capable of transferring sizable amounts of data. Current THz technology via electrical excitation is limited by the upper limits of device cutoff frequencies and by the lower limits of optical transitions in quantum confined structures. Current metallic THz antennas require high power to overcome scattering losses and tend to have low antenna efficiency. It is shown here via calculation and simulation that graphene can sustain electromagnetic propagation at THz frequencies via engineering the intra‐ and interband contributions to the dynamical conductivity to produce a variable surface impedance microstrip antenna with a several hundred GHz bandwidth. The optimization of a circular graphene microstrip patch antenna on silicon with an optimized return loss of ?26 dB, a ?10 dB bandwidth of 504 GHz, and an antenna efficiency of ?3.4 dB operating at a frequency of 2 THz is reported. An improved antenna efficiency of ?0.36 dB can be found at 3.5 THz but is accompanied by a lower bandwidth of about 200 GHz. Such large bandwidths and antenna efficiencies offer significant hope for graphene‐based flexible directional antennas that can be employed for future THz local device‐to‐device communications.     

Wavelength Filter and Converter by NDFWM in Strained Quantum Wells

A novel kind of wavelength filter and converter using nondegenerate four-wave mixing (NDFWM) in an optical amplifier with tensile and compressively strained quantum wells (T/C SQW) is reported in this paper. The configuration of the T/C SQW converting filter is designed first, followed by the establishment of the coupling model of the device. The influences of the property parameters of the optical amplifier with T/C SQW on the output efficiency, 3dB bandwidth, and the frequency shift are mainly discussed. The device can serve as both filter and wavelength converter with high conversion efficiency and narrow bandwidth on the order of 0.01 nm. Meanwhile, the frequency conversion range, which is decided by the gain bandwidth of the semiconductor media, is up to 5000 Ghz in the considered case.     

应变量子阱光放大器NDFWM波长转换和滤波

报告了一种新型的波长转换滤波器，它产生于拉伸/压缩应变量子阱（T/CSQW）光放大器中的非简并四波混频（NDFWM）。提出T/CSQW转换滤波器的结构，并由器件的耦合模式实现了波长的转换滤波。讨论了T/CSQW光放大器的特征参数对输出效率，输出带宽及频移的影响。在0.01量级，该器件可用作具有高转换效率及窄带的滤波器和波长转换器，其频率转换的范围取决于半导体介质的增益带宽，可达到5000GHZ。     

声表面波式指宽变长小波变换处理器的设计

为消除声表面波式小波变换处理器压电基片对频率特性的影响,以及输出换能器的指条数对带宽的影响和解决衍射问题,研制了声表面波式指宽变长小波变换处理器。该处理器选取机电耦合系数为0.64%的X-112°Y LiTaO_3压电基片,输出换能器指条数为36,输入换能器采用指宽变长且声孔径均匀的叉指换能器。设计和制作了尺度2-2声表面波式指宽变长小波变换处理器样品。实验结果表明,声表面波式指宽变长小波变换处理器频率特性曲线光滑,-3dB实验带宽为1.072 MHz,与理论带宽值一致,且不存在衍射问题。     

Microwave frequency division using transferred-electron devices

Transferred-electron devices (t.e.d.s), when biased above threshold (Vth) exhibit transit-time or circuit-controlled oscillations. This property of t.e.d.s is used to achieve dynamic division at microwave frequencies. The device is biased at 0.9?0.95 Vth using a d.c. power source, and an input signal of 0.1?0.3 Vth, is used to raise the device bias above threshold level. The division occurs when the input frequency is an integral multiple of the oscillator frequency. We observed dynamic division by 2, 3 and 4 with the output frequency 4.0 GHz. The bandwidth for division by two is 560 MHz referred to the input.     

基于紫外光刻的双轴张应变Ge/SiGe多量子阱电吸收调制器北大核心CSCD

采用紫外光刻工艺(ultraviolet lithography technique,UVL),在互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)兼容的硅基平台上制作了基于悬空微桥结构在Ge/SiGe多量子阱材料中引入双轴张应变的低偏振相关电吸收调制器。利用拉曼光谱测试了器件引入双轴张应变的大小,并对器件在横电(transverse electric,TE)偏振和横磁(transverse magnetic,TM)偏振下的光电流响应、调制消光比和高频响应等性能进行了测试。器件的低偏振相关消光比在0 V/4 V工作电压下可达5.8 dB,3 dB调制带宽在4 V反向偏置电压时为8.3 GHz。与电子束光刻工艺(electron beam lithography technique,EBL)相比,采用UVL制作的器件在调制消光比、高频响应带宽等性能上略差一点,但具有曝光时间短、成本低和可大批量生产等优势,应用前景广阔。     

基于GaN HEMT 多倍频程高效率功率放大器设计

使用GaN HEMT 功率器件,设计了一款多倍频程高效率功率放大器。利用负载牵引技术分析输入功率、偏置电压、工作频率对功率器件输出阻抗的影响,从而寻找出满足宽带性能的最优阻抗区域;输入、输出匹配网络采用了切比雪夫多节阻抗变换器的综合设计方法,很好地拓展了匹配网络的带宽性能,从而实现了0. 8 ~4. 0 GHz(相对带宽133%)多倍频程高效率功率放大器电路。连续波大信号测试结果表明:在0. 8 ~ 4. 0 GHz 的频率范围内输出功率为39. 5 ~42. 9 dBm,漏极效率为54. 20% ~73. 73%,增益为9. 4 ~12. 0 dB。在中心频率2. 4 GHz 未利用线性化技术的情况下使用5 MHz WCDMA 调制信号测试得到邻近信道泄漏比(ACLR)为-27. 2 dBc。设计的工作频率能够覆盖目前主要的无线通信系统GSM900M、WCDMA、DCS1800 LTE、PCS1900 LTE、3. 5GHz WiMAX 以及下一代移动通信系统(5G)等。     

A hybrid phase shifter circuit based on TlCaBaCuO superconductingthin films

A superconductor-semiconductor hybrid reflection-type phase shifter circuit has been designed, fabricated, and characterized for 180° phase bit with center frequency of 4 GHz and bandwidth of 0.5 GHz for operation at 77 K. All of the passive components of the phase shifter circuit such as input/output feed lines, 3 dB Lange coupler, impedance matching networks, and transmission lines consisted of thallium based superconducting TlCaBaCuO thin films of 4000 Å thickness on lanthanum aluminate substrate. Metal-Schottky field-effect-transistors (MESFET's) on GaAs semiconductor were used as active devices for switching action (on-state and off-state) in the phase shifter circuit. The phase shift and insertion losses were investigated as a function of frequency from 3.6 to 4.6 GHz at 77 K. The circuit exhibited a fairly flat response of 180° phase shift with a maximum deviation of less than 2° and a maximum insertion loss of 2 dB for on-state and 2.2 dB for off-state conditions over 0.5 GHz bandwidth at 4 GHz. The insertion losses were also fairly flat within the bandwidth. The insertion losses were constant between 50 and 80 K, giving the circuit a large range of operation at or below 77 K. The performance of this circuit as compared to a gold microstrip-semiconductor circuit designed identically was superior by a factor of 1.5, and may be due to lower conductor losses and lower surface resistance in the superconducting microstrips     

External-Q factor measurement of an oscillator by the injection locking ellipse

The usual relation between the external Q factor and the locking bandwidth of an oscillator is not valid when the device reactance is nonlinear. The correct value of the Q factor is then obtained by using a certain frequency interval that can be easily read on the locking ellipse in this relation, rather than the locking bandwidth.     

GaAs PIN electro-optic travelling-wave modulator at 1.3 ?m

A GaAs PIN travelling-wave modulator operated at 1.3 ?m has been fabricated from material grown by organometallic vapour phase epitaxy (OMVPE) on an n+ (100) GaAs substrate. The device has a constant V? of 8 V from DC to 10 GHz and an optical extinction ratio of 13 dB. The optical insertion loss of the device is 3.5 dB, and the 3 dB frequency bandwidth is measured to be 4.1 GHz, which is limited by the microwave slowing induced by the n+ substrate.     

电容加载对频率选择表面传输特性的影响

有源频率选择表面,是指在频率选择表面中加入变容二极管或PIN二极管等有源器件构成的FSS结构,通过有源器件的可调性来实现对FSS性能的控制。文中根据有源器件的电容等效原理,设计了一种方形缝隙FSS结构,研究了电容加载对FSS传输特性的影响。仿真结果表明,加载电容后其谐振频点向低频偏移,带宽减小,且加载电容对FSS传输特性有较好的可控性。     

Temperature optimization for broad-band quasi-phase-matched difference frequency generation

The temperature-tuning prosperities of quasi-phase-matched (QPM) difference frequency generation (DFG) in a uniform periodically poled LiNbO/sub 3/ (PPLN) device are studied theoretically in the near degeneracy limit. Combining the theoretical and numerical analysis results, the paper shows that through the tuning of temperature, the conversion efficiency and bandwidth can be changed considerably. This paper proposes a PPLN device consisting of several segments of different temperature to obtain a more desirable performance for the QPM-DFG. The optimizations for temperature are studied in detail by the use of a cascading technique, and they show that broadening of the conversion bandwidth will reduce the conversion efficiency. A better performance of uniform PPLN can be obtained owing to the reconfigurable and adjustable abilities of multisection temperature tuning.     

Design considerations for acousto-optic devices

The design and fabrication of wide-band bulk acousto-optic modulators (temporal modulation) and beam deflectors (spatial modulation) are described. Optimized device parameters can be obtained systematically for given specifications of the desired modulation bandwidth, throughput efficiency and number of resolvable elements. As the device operating frequency goes beyond a few hundred megahertz, the acoustic transducer response becomes sensitive to the intermediate metal layers between the piezoelectric transducer and the acoustooptic interaction medium. Transducer bandwidth and impedance matching can be optimized using computer modeling programs. Criteria for material selection based on performance requirements and propagation loss are presented. Practical considerations for the fabrication of high performance devices and specific device parameters are discussed.     

Numerical analysis of traveling-wave photodetectors' bandwidth using the finite-difference time-domain method

We present full-wave analysis of traveling-wave photodetectors (TWPDs) using the finite-difference time-domain (FDTD) method. Impulse response in the frequency domain is obtained after time-domain data are calculated by the FDTD method. The impulse response includes the optical field profile, carrier transit time, microwave loss, microwave dispersion, and velocity mismatch all together. Three-decibel bandwidth is analyzed with the thickness of an i-layer and waveguide width as the design parameters. It is shown how transit time and microwave characteristics affect the bandwidth according to the TWPD's length. Three-decibel bandwidth is dominated by carrier transit time in case the device length is shorter than 300-500 /spl mu/m under the conditions given in this paper. However, if the device length gets longer, microwave characteristics affect the bandwidth.     

反常声电光频谱分析器

介绍了一种新型的反常声电光频谱分析器，它可以采用外加电压的办法改变器件的中心频率，扩大器件的频带宽度，并改善器件在频带宽度范围内的频率响应特性。用ＬｉＮｂＯ３制作了一个６０ＭＨｚ的反常声电光频谱分析器件，测试结果表明，器件中心频率可以由５０ＭＨｚ变到７０ＭＨｚ，频带宽度由原来的２６ＭＨｚ扩大到３７ＭＨｚ。