Pumping planar waveguide amplifiers using a coupled waveguidesystem

A novel scheme is presented that can be used to efficiently pump optical waveguide amplifiers. It is based on the coupling between two adjacent waveguides, where pump light is gradually coupled from a nonabsorbing pump waveguide into the amplifier waveguide. The coupling between the waveguides in such a configuration is calculated using an improved coupled mode theory (CMT). The proposed distributed coupling scheme can enhance the optical gain in systems that exhibit a reduced pumping efficiency at high pump power. A numerical example is given for a sensitized neodymium-doped polymer waveguide amplifier, in which the optical gain increases from 0.005 dB to 1.6 dB by changing from conventional butt-coupling to distributed coupling     

等离子体在强电磁脉冲防护中的应用

为了提高屏蔽腔对强电磁脉冲的屏蔽效能,分析了在屏蔽腔中引入等离子体的理论基础,建立了一种加载等离子体的双层屏蔽腔模型,采用时域有限差分法计算了强电磁脉冲耦合进入双层屏蔽腔的耦合系数。计算结果表明:加载等离子体的双层屏蔽腔可使强电磁脉冲耦合进入腔体的能量大大降低,在2～14GHz内耦合系数降低了近30dB,即使屏蔽效能也提高了近30dB,为新的屏蔽腔设计提供了重要的理论依据。     

Simple technique to improve the spectral quality of gain-switchedpulses from a DFB laser

The authors show that by coupling the output from a gain-switched DFB laser to a fibre loop mirror the spectral quality of the gain-switched pulse can be greatly improved. The SMSR of a gain-switched 1.5 μm DFB has been increased by 25 dB, and also the chirp has been reduced, by using this technique. This spectral improvement is vitally important in systems where the gain-switched pulses will pass an optical filter     

Improving the characteristics of rectangular waveguide branchingsby cylindrical obstacles

The scattering matrix of a transition between one or two parallel rectangular waveguides and a larger rectangular waveguide which contains two metallic or dielectric cylinders is investigated by means of the orthogonal expansion method. Mathematical programming is applied in order to improve the characteristics of the branchings. Reflection at a rectangular step discontinuity can be reduced by 30 dB using metallic or dielectric obstacles. Using Teflon cylinders, coupling of a transition can be reduced by 40 dB without debasing reflection. Physical interpretations are given with the help of field patterns     

小型化高方向性的微带双定向耦合器设计

为解决弱耦合时微带平行耦合线定向耦合器方向性低的问题,提出了适用于大功率场合的小型化高方向性微带双定向耦合器。基于传统四分之一波长平行耦合三线微带双定向耦合器结构,采用扇形微带电容加载可明显减小耦合器尺寸并增大隔离度,通过耦合边缘引入锯齿结构进一步提高了方向性。负载电阻采用扇形微带短截线接地设计,避免电气化过孔,使得加工更加简单。设计了一个中心频率为915 MHz、耦合度为20 dB 的微带双定向耦合器,利用HFSS 仿真软件对耦合器结构进行优化设计,并做了实物加工和测试。实测结果表明,在中心频率处耦合度为20.2 dB,方向性达到32.1 dB;在0.74~1.35 GHz 频带内,输入匹配良好,耦合度波动小于0.5 dB,方向性高于20 dB。     

基于基片集成波导(SIW)的低副瓣阵列天线设计

基片集成波导(SIW)因其低插损、易于加工等特性,在微波天线领域受到了广泛关注.本文应用SIW技术设计了一个Ku波段20元并联馈电的低副瓣线阵天线.实测结果表明在6%的带宽内,其VSWR＜1.5,可以实现-27dB以下副瓣电平及高于18.7dB的增益.此天线应用了改进的维尔瓦迪辐射单元,有效抑制了单元间的互耦,其功分器...     

Image guide couplers with dielectric coupling elements and radiation reduction

Directional couplers in image guide technique for millimeter-wave circuits are discussed, and steps to improve their properties are demonstrated. The simple two-line-9 dB coupler with periodical coupling is compared to a design with an intermediate dielectric coupling element to reduce the frequency dependence. Radiation from the waveguide bends can be reduced significantly by inserting absorber materials at critical points. Experimental results for a-3 dB coupler are also given.     

红外探测系统三重相关峰值检测技术研究

将三重相关峰值检测技术用于对红外探测系统亚像元或点目标图像的信号处理。研究表明，该技术在峰值信噪比为０．８、功率信噪比为－９．７３ｄＢ时可获得的信噪比改善约为２３ｄＢ。提出了一种可供实用的三重相关的二维图形表示法，该方法在峰值信噪比低至０．４８、功率信噪比低至－１４．２ｄＢ时仍可以从噪声中有效地提取点目标信号的幅度信息。     

新型的平面双模椭圆函数带通滤波器

根据传统的方形贴片双模滤波器,提出了一种新颖的带有两个切角的平面双模带通滤波器结构.该结构使用单个贴片谐振器并且没有耦合缝隙,通带两端各有一个衰减极点,有效减小了滤波器的辐射损耗.对该滤波器结构进行改进,又提出了一种带有两个相互正交、长度不等槽线的双模椭圆函数带通滤波器结构.该滤波器在中心频率1.8GHz处,回波损耗达到31.53 dB,通带内最小插损达到0.01 dB,3 dB相对带宽为19.44%.采用Ansotf公司的En-sem ble 8.0仿真软件进行的仿真研究.仿真结果表明该结构可以更加有效地减小辐射损耗,增加带宽,且体积比传统滤波器减小了约40%,有利于小型化.     

低损耗双模微带贴片带通滤波器研究

首先提出了一种新颖、简单的带有两个切角的双模微带带通滤波器结构。该结构使用单个贴片谐振器并且没有耦合缝隙,通带两端各有一个衰减极点,可以有效减小滤波器的辐射损耗。对该滤波器结构进一步改进,又提出了一种中心频率1.8GHz相互正交槽线的新型双模微带带通滤波器结构。该滤波器在中心频率1.8GHz处,回波损耗达到31.65dB,通带内最小插损为0.01dB,3dB带宽为19.44%。研究结果表明该结构可以进一步减小辐射损耗,并且可以减小滤波器的体积,有利于小型化。     

A novel noise efficient feedback DAC within a switched capacitor /spl Sigma//spl Delta/ ADC

Efficient sampling of the reference noise within a bilinear switched capacitor /spl Sigma//spl Delta/ analog-to-digital converter (ADC), resulting in improved thermal noise performance is presented. Bilinear integrators contain a zero at the Nyquist frequency, with the result that no charge is transferred from the reference when a transition occurs in the modulator output. The average noise power added by the reference digital-to-analog converter (DAC) can be reduced substantially if the reference DAC is sampled only when charge is to be transferred. For midscale inputs, the sampled noise from a single bit reference DAC is reduced by more than 5 dB. When multibit quantization and feedback is used the reference noise can be further suppressed, in the case of 5 bits of feedback the reference noise is reduced by more than 20 dB.     

Wafer-fused optoelectronics for switching

Wafer fusion technique for realization of compact waveguide switches and three-dimensional (3-D) photonic integrated circuits is investigated theoretically and experimentally. Calculations based on beam propagation method show that very short vertical directional couplers with coupling lengths from 40 to 220 μm and high extinction ratios from 20 to 32 dB can be realized. These extinction ratios can be further improved using a slight asymmetry in waveguide structure. The optical loss at the fused interface is investigated. Comparison of the transmission loss in InGaAsP-based ridge-loaded waveguide structures with and without a fused layer near the core region, reveals an excess loss of 1.1 dB/cm at 1.55 μm wavelength. Fused straight vertical directional couplers have been fabricated and characterized. Waveguides separated by 0.6 μm gap layer exhibit a coupling length of 62 μm and a switching voltage of about 2.2 V. Implications for GaAs-based fused couplers for 850 nm applications will also be discussed     

一种带功率检测和自适应偏置的CDMA功率放大器

设计了一款包含功率检测和自适应线性化偏置电路的CDMA功率放大器,功率检测器能根据输入信号的大小来调整功率管的偏置点,大幅提升低功率输出时的效率,从而提升系统整体效率;自适应线性化偏置能有效抑制功率放大器的增益压缩和相位失真,改善其线性度.采用2 μm InGaP/GaAs HBT晶体管工艺成功流片,测试结果表明,与普...     

A multi-stage sigma-delta modulator based on noise-coupling and digital feed-forward techniques

This paper presents a new structure for high-resolution, low-power and wideband discrete time multi-stage (DT-MASH) sigma-delta (ΣΔ) modulators. It uses multi-bit digital input feed forward path (DFF) and noise coupling (NC) techniques. With the DFF technique, the modulator does not need a power-consuming analog adder at the quantizer input, and the number of comparators of the quantizer will be reduced significantly. Also, because of the reduced swing of the modulator’s integrators, low power integrators can be used. Using a second-order NC technique with no extra active block, the order of the modulator, which uses some paths between analog stages, is increased, and its performance is improved with zero-optimization of the modulator’s noise transfer function (NTF). Behavioral simulations and extensive mathematical analyses confirm the effectiveness of the proposed structure. The effect of the non-idealities in the DFF and NC paths were considered in the behavioral simulations. To examine its performance, a MASH 2–1 modulator was designed in the circuit level with a 180-nm CMOS technology and 1.8 V power supply. The integrators use a new op-amp switching technique to reduce total power consumption. With an over-sampling ratio (OSR) of 8 for the 10 MHz signal bandwidth, the proposed structure improves the signal-to-noise and distortion ratio (SNDR) by 28 dB compared with a conventional MASH 2–1 structure at approximately the same power consumption and very low complexity.

     

Development of linear traveling wave tubes for telecommunicationsapplications

Traveling wave tubes (TWTs) designed for telecommunications applications in multichannel power amplifiers (MCPAs) are required to have high linearity, low intermodulation distortion, high efficiency and high power outputs. The linearity of the TWT can be greatly improved by operation of the tube significantly backed off from saturation and by optimization of the design of the helix circuit. This results in two tone intermodulation products that are 25 to 40 dB below the carrier level, depending on the amount of back-off selected. However, operation backed off from saturation results in a greatly reduced efficiency of the TWT, which must be compensated for by optimal circuit and collector design. Several L-band and S-band Hughes TWTs have been developed for telecommunications applications and feature saturated power levels of up to 2 kW and average power of over 600 W with overall efficiencies of over 20% at 10 dB back-off and 40% at 6 dB back-off. These tubes provide high average power, high efficiency amplification with modest size and reduced cooling requirements compared to solid state amplifiers     

Improvement of the design of 180° rat-race hybrid

An innovative and simple design for a 180° rat-race hybrid is proposed which has a substantially improved phase shift characteristic over a large bandwidth compared with that of a conventional rate-race hybrid. The proposed hybrid has been fabricated with a three-dimensional technology to benefit from a high level of integration. It exhibits a bandwidth of 31% from 28.8 to 39.4 GHz with -15 dB input and output matching, a coupling loss of 4.6 dB with a power dividing balance better than 1.1 dB, and a phase balance better than 2     

小孔耦合型双通道太赫兹波导定向耦合器设计

提出了一种小孔耦合型双通道太赫兹波导定向耦合器,采用新颖的阶梯结构,将两个单通道耦合器结合,可在双通道内实现相同的耦合输出。研究结果表明,在180~260 GHz的频率范围内,该耦合器的耦合度为10 dB,输出最大误差小于1.6 dB,回波损耗大于25 dB,隔离度大于35 dB,相对带宽达到36%。与传统的太赫兹波导定向耦合器相比,该耦合器能够实现双通道的耦合输出,在太赫兹系统中可用于双通道的功率检测、功率合成与分配。     

非对称马赫-曾德尔干涉型低串扰聚合物光开关

针对对称马赫-曾德尔干涉(MZI)型光开关工艺制备中形成的光栅结构所引起的导模与辐射模耦合是恶化光开关串扰特性的一个重要因素,提出一种采用非对称的MZI结构来抑止光栅导模和辐射模间耦合的新型聚合物电光开关设计方案。研究结果表明,光开关的串扰可以从-20dB改善到-50dB以上;同时,器件的开关电压也从传统MZI型结构开关电压的1.5Vπ减小到了1.0Vπ。     

A 16-channel frequency selection switch for optical FDMdistribution systems

The performance of a 5-GHz-spaced, 16-channel frequency selection switch (FS-SW) for optical frequency division multiplexing (FDM) distribution systems is described. The silica waveguide-type FS-SW is constructed with four serially connected periodic filters integrated on a silicon chip. The required crosstalk level for each periodic filter of the FS-SW was estimated to be -21.0 dB for a 16-channel FS-SW and 23.6 dB for a 128-channel FS-SW. Crosstalk can be independent of the power coupling ratio of the 3-dB-coupler regions by choosing suitable connecting configurations for the periodic filters. A controller for the switch is also described and the desired channel can be selected successfully from among 16 optical carriers under an average crosstalk level of less than -20 dB     

Optical directional coupler using deposited silica waveguides (DS guides)

A new optical directional coupler using embedded single-mode glass waveguides is presented. The glass waveguides, called deposited silica waveguides (DS guides), were fabricated by depositing doped glass on a silica substrate after forming grooves by reactive sputter etching. Waveguide transmission loss was measured to be 1.3 dB/cm, and fiber-to-waveguide coupling loss was 0.1 dB. Using a tunable monochromatic light source, 96 percent power transfer or 14 dB isolation was measured. The DS guide directional coupler is compatible with single-mode fiber and is expected to be a useful component for future wavelength division multiplexing transmission systems.