InP-InGaAsP high-speed traveling-wave electroabsorption modulatorswith integrated termination resistors

Traveling-wave electroabsorption modulators for operation at 1.55 μm have been designed and fabricated. Devices of different lengths were characterized. Modulators with integrated termination resistors showed wide modulation bandwidths and excellent bandwidth-length products. A bandwidth of 43 GHz was measured for a 450-μm-long device, which corresponds to a 19.3-GHz·mm bandwidth length product. For a device length of 250 μm, a bandwidth of 67 GHz is extrapolated from measurements up to 45 GHz     

Double-bonded InP-InGaAsP vertical coupler 1:8 beam splitter

A novel three-layer double-bonded InP-InGaAsP waveguide vertical coupler 1:8 beam splitter is demonstrated. The strongly coupled waveguides allow a 583-μm device length, more than 100 times shorter than that of the equivalent horizontal coupler. The device illustrates the use of multiple vertical-layer optical interconnects for three-dimensional routing of optical signals     

Coding performance of hybrid ARQ schemes

We develop a unified performance metric and detailed analysis for hybrid automatic repeat request (HARQ) schemes based on incremental redundancy (IR) and Chase combining (CC). The general result is applicable to both symbol-based and bit-interleaved coded modulations, to HARQ processes based on rateless and fixed-rate mother codes, and IR schemes with and without a self-decodability restriction. The analysis shows that IR over CC coding gains tend to increase with the initial coding rate, but decrease with the signal-to-noise (SNR) variation between retransmissions. The gains can also be diminished when a fixed-rate mother code is used or when the self-decodability criterion is imposed. The theoretical prediction is compared with observed gains at 10% codeword error rates based on turbo-coding simulations. For scenarios with moderately varying SNR between retransmissions, the analytical model tracks actual simulation results very well. However, when the SNR varies widely and the systematic part of the turbo codeword is effectively erased, the CC scheme could, in fact, outperform some IR schemes. For these scenarios, which can be induced by fast time-varying fading or long retransmission delays, the self-decodable IR and the CC schemes prove to be more robust without much performance comprise. Finally, we discuss adaptive improvement to the conventional IR schemes based on the analytical result.     

Detailed study of AlAs-oxidized apertures in VCSEL cavities foroptimized modal performance

We present a numerical optical model for calculating threshold material gain in vertical-cavity surface-emitting lasers. It is based on a vectorial solution of Maxwell's equations and therefore gives exact results where other approaches fail, e.g., in the case of oxide-confined devices, which have high lateral index contrasts. Results are given concerning the influence of oxide window thickness and position on threshold gain and modal stability. We also propose an intuitive plane-wave model to enhance the physical understanding of these effects     

Fabrication of sidelobe-suppressed InP-InGaAsP vertical coupleroptical filter using pair grating structure

In this letter, we report -19-dB suppression of sidelobes in a grating-assisted codirectional coupler (GACC) optical filter, which is the lowest to the best of our knowledge. Pair grating structures has been employed to control the coupling strength with a raised cosine functional form. A unit pair grating is composed of two unit conventional gratings and the fundamental period of pair gratings is fixed at 2Λ, where Λ is the grating period of conventional GACC filter. The distance between the two gratings inside a pair grating is linearly shifted to control the coupling strength. This structure provides a spatially weighted coupling strength without any change of averaged effective optical index or propagation constant     

On the Graphical Method of Drawing APD's for Atmospheric Radio Noise

It has been found that an amplitude probability distribution (APD) of a defined form factor cannot be drawn on a Rayleigh graph by the well-known graphical method using the three statistical moments for a significant part of a large number of samples of atmospheric radio noise in VLF-LF bands. An attempt has been made to approximate an individually measured APD for a sample of atmospheric radio noise using the concept of the form factor. It has been found that the great majority of measured APD's for the noise at a few frequencies can be approximated with reasonable accuracy. Based upon a large number of pairs of APD's, measured and approximated, each pair being obtained for a single noise sample, various parameter relations are obtained for the purpose of comparison with the original parameter relations associated with the graphical method. The results of the comparison show that some agreements as well as some disagreements exist between the two groups of the parameter relations. It is worthy of note that the agreements and disagreements are due to two types of atmospheric radio noise with different characteristics.     

Low-loss polarization-insensitive InP-InGaAsP optical space switches for fiber optical communication

High-performance InP-InGaAsP optical space switches are reported, which in monolithic four switch arrangements reach fiber-to-fiber losses as low as 5 dB. Polarization insensitivity is within /spl plusmn/0.5 dB. On-off ratios throughout the 1.53-1.56 /spl mu/m wavelength range exceed 15 dB. Switch rearrangement times are below 200 ps.     

Transient characteristics of n-channel hybrid Schottky injectionFETs

Theoretical transient characteristics of hybrid Schottky injection FETs (HSINFETs) are considered. The theoretical analysis is based on two-dimensional numerical simulations, in which the entire turn-off process and the effects of minority-carrier injection levels on the transient performance of the HSINFET device are analyzed. The analysis shows that the fast turn-off speed in the HSINFET device occurs because (1) only a small number of minority carriers is injected into the drift region, (2) a current path, provided by the Schottky contact, effectively removes electrons from the drift region during turn-off, and (3) Schottky clamping at the anode is effective during turn-off and prevents the p⁺ portion of the hybrid anode from significantly injecting holes. Experimental results compared the DC and transient performance of the lateral double-diffused MOS transistor (LDMOST), lateral insulated-gate transistor (LIGT), Schottky injection field-effect (SINFET), and HSINFET are presented     

Observation of the surface degradation mode of InP/InGaAs APD's during bias-temperature test

We report the surface degradation mode observed during a bias-temperature (BT) test for InP/InGaAs APD's. Failure analyses using the light-beam-induced current (LIBIC) method clarify that the degradation is caused by local avalanche multiplication in the guard-ring periphery. Based on the analyses, we propose a failure mechanism.     

Scalable performance evaluation of a hybrid optical switch

This paper provides new loss models for a hybrid optical switch (HOS) combining optical circuit switching (OCS) and optical burst switching (OBS). Exact blocking probabilities are computed when 1) no priority is given to either circuits or bursts and 2) circuits are given preemptive priority over bursts. Because it is difficult to exactly compute in realistic scenarios, computationally scalable approximations are derived for the blocking probability. The sensitivity of the analytical results to burst length and circuit holding-time distributions is quantified by simulation. It is demonstrated how the proposed approximations can be used for multiplexing-gain evaluation of a hybrid switch. In addition, the extension of the proposed single-node model to a network model composed of OCS, OBS, and hybrid switches is outlined.     

有机电解液聚苯胺-炭混合电容器性能研究

采用化学氧化法合成盐酸掺杂聚苯胺,经NaOH溶液去掺杂后制得本征态聚苯胺(PANI)。以PANI为正极材料,活性炭为负极材料,使用1 mol/L LiPF6/(DMC+EC)有机电解液组装了混合电容器。通过循环伏安、交流阻抗、恒流充放电、循环寿命及漏电流等手段,对混合电容器的电化学性能进行了测试。结果表明,充电截止电压在1.5 V时,电容器比容量最高可达36.0 F/g,1 100次充放电循环后比容量保持在初始容量的94.2%。     

Suppression of modal birefringence in InP-InGaAsP waveguides through use of compensated tensile strain

We show that the modal birefringence of InP-based planar guides can be significantly reduced through the action of compensated tensile strain. By using low bandgap tensile and higher bandgap compressive layers, the material birefringence of the former may be made to dominate and provide significant modal birefringence suppression. The suppression attained is much greater than can be achieved through the application of tensile strain alone.     

AM/OFDM混合光传输系统误码特性

本文分析了在限幅噪声和高斯噪声环境下,在ＨＦＣ网中混合传输ＡＭ／ＯＦＤＭ信号时的误码特性,并与单载波ＡＭ／ＱＡＭ系统进行比较,结果表明ＯＦＤＭ系统由于多个子通道的稀释作用,其抗限幅噪声性能比单载波系统好。     

The performance of hybrid adaptive beamforming algorithm forjammers suppression

Adaptive array processing is of growing importance in the fields of communications, radar, and sonar, where the designer almost invariably faces the problem of interference suppression. In general, under some situations, the conventional Frost's (1972) beamforming algorithm may have some problems associated with performance degradation in multiple jammers environment. It causes the convergence time to be essentially dependent on the jammer powers ratio. A new hybrid adaptive beamforming algorithm is derived in the transformed domain for multiple jammers suppression. Here, three popular orthonormal transformations-i.e., discrete Hartley, discrete cosine, and discrete Fourier transforms-are considered. Overall performance improvement, in terms of convergence rate and the computational requirement, is investigated. From the simulation results, we observed that the new presented beamforming algorithm is more robust than the conventional Frost's beamforming algorithm in terms of jammers suppression and the convergence rate     

Design and performance of VQ-based hybrid digital-analog jointsource-channel codes

A joint source-channel hybrid digital-analog (HDA) vector quantization (VQ) system is presented. The main advantage of the new VQ-based HDA system is that it achieves excellent rate-distortion-capacity performance at the design signal-to-noise ratio (SNR) while maintaining a "graceful improvement" characteristic at higher SNRs. It is demonstrated that, within the HDA framework, the parameters of the system can be optimized using an iterative procedure similar to that of channel-optimized vector quantizer design. Comparisons are made with three purely digital systems and one purely analog system. It is found that, at high SNRs, the VQ-based HDA system is superior to the other investigated systems. At low SNRs, the performance of the new scheme can be improved using the optimization procedure and using soft decoding in the digital part of the system. These results demonstrate that the introduced scheme provides an attractive method for terrestrial broadcasting applications     

On the architecture and performance of a hybrid image rejectionreceiver

This paper describes a hybrid image rejection receiver. The hybrid image rejection receiver contains a modified Hartley (1928) image rejection mixer and a digital image rejection processor. The modified Hartley image rejection mixer performs similarly to an original Hartley image rejection receiver but provides two digital outputs. In one output it enhances the desired signal and in the other output it enhances the image signal. The digital image rejection processor first measures the mismatching effect in the analog devices and then suppresses the image signal by compensating for the mismatching effect. We also propose a simplified implementation method for the hybrid image rejection receiver to reduce its computation complexity. Computer simulation was used to evaluate the performance of this simplified implementation method to include the quantization effect introduced by the A/D converters. Simulation results show that the proposed hybrid image rejection receiver achieves much better performance than the original Hartley image rejection receiver. This architecture greatly relaxes the matching requirements of the analog devices and has a low complexity for an IC implementation     

Improvement for low power high performance hybrid type CAM

Based on the analysis of typical hybrid-type content addressable memory （CAM） structures, a hybrid-type CAM architecture with lower power consumption and higher stability was proposed. This design changes the connection of a N-type metal-oxide-semiconductor （NMOS） transistor in the control circuit, which greatly reduces the power consumption during comparison by making the match line simply discharge to the NMOS threshold voltage. A comparative study was made between conventional and the proposed hybrid-type CAM architecture by semiconductor manufacturing international corporation （SMIC） 65 nm complementary metal-oxide-semiconductor （CMOS） technology. Simulation shows that the power consumption of the proposed structure is reduced by 23%. Furthermore, the proposed design also adjusts the match line （ML） discharge path. In case that, the not and type （NAND-type） block is matched and the not or type （NOR-type） block is mismatched, the jitter voltage on the match line can be decreased largely.     

Locking characteristics of a subharmonically hybrid mode-locked multisection semiconductor laser

Locking characteristics of a subharmonically hybrid mode-locked (SH-ML) semiconductor laser are investigated experimentally. The locking bandwidths under the second- and third-order SH-ML operation, as well as under fundamental hybrid mode-locking (FH-ML) condition, are characterized with a variety of microwave power and reverse bias voltage applied to the saturable absorber of the laser. Unique locking characteristics are observed for the third-order SH-ML where the locking bandwidth increases with increasing reverse bias, which is opposite to the FH-ML case. This leads to a locking bandwidth of 56 MHz, 2.3 times broader than that for the FH-ML under the shortest pulse condition.