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Tunable Picosecond Pulse Generation from an Actively Mode-locked Laser Diode Array with Intracavity Chirp Compensation
No full text[[abstract]]Wavelength-tunable picosecond pulses have been generated from an actively mode-locked laser diode array in an external cavity. The cavity incorporated a folded dispersive delay line which provided functions of pulse compression, wavelength tuning and spatial mode control. By varying the group velocity dispersion inside the cavity, the laser pulse width was intra-cavity compressed from 44 to 25 ps. The laser wavelength was tuned from 794 to 806 nm by translating a stripe end mirror horizontally with respect to the optical axis. The side mode suppression ratio was better than 10 dB over the entire tuning range. The spatial mode was a quasi-single-lobe[[fileno]]2010144010058[[department]]物理
Sub femto-joule sensitive single-shot OPA-XFROG and its application in study of white-light supercontinuum generation
Get PDF[[abstract]]We report a new design of single-shot cross-correlation frequency-resolved optical gating (XFROG) with sub femto-joule sensitivity for complete field characterization of ultrashort optical pulse using a 400-nm-pumped type-I noncollinear optical parametric amplifier. Optical parametric gain as high as 10(8) with 0.8-0.9 femto-joules sensitivity had been demonstrated with an un-cooled CCD in this study. The experimental FROG traces have been successfully retrieved with an error no worse than 0.0014. The device had been to be useful for studying the generation mechanism of white-light supercontinuum (WLS)[[fileno]]2010144010108[[department]]物理
Ultrabroadband terahertz field detection by proton-bombarded InP photoconductive antennas
Get PDF[[abstract]]Photoconductive (PC) antennas fabricated on InP bombarded with 180 keV protons of different dosages (InP:H+) all exhibit a useful bandwidth of about 30 THz, comparable to that of the LT-GaAs PC antenna. The peak signal current of the best InP: H+ device (dosage of 10^15 ions/cm^2) is slightly higher than that of the LT-GaAs one, while the signal-to-noise ratio (SNR) of the former is about half of that of the latter due to lower resistivity. This suggests that InP: H+ can be a good substrate for THz PC antennas with proper annealing and/or implantation recipe.[[fileno]]2010144010113[[department]]物理
Gap-Dependent Terahertz Pulses from Mid-Gap Biased Multi-Energy Arsenic-Ion-Implanted GaAs Antennas
No full text[[abstract]]We investigated the characteristics of sub-picosecond radiation pulses from mid-size-gap multi-energy arsenic-ion-implanted GaAs photoconductive antennas in terahertz time-domain spectroscopy experiments. At fixed fluence excitation, both the bandwidth and the negative peak of terahertz waveform minimum reveal increasing trends with increases in the antenna's gap. We reproduce both the measured terahertz waveforms and increasing trends numerically, by calculating a model that incorporates the trap-enhanced bias field with wave equation. We deduce from our simulation that the gap-dependent behavior stems from the fact that an antenna with a larger gap has a stronger trap-enhanced bias field near the anode edge and thereby induces a larger space-charge screening effect and bandwidth.[[fileno]]2010144010166[[department]]物理
Optimizing the Extinction Ratio and Error Bit Penalty of the On-Off-Keying Pulse Data With Gain-Constrictive SOA
No full text[[abstract]]On/off extinction ratio and receiving power penalties of a 10-Gb/s all-optical on-off-keying pulse data generated from a multiwavelength dark-optical-comb injected semiconductor optical amplifier (SOA) is analyzed. Such an SOA with a temporally constricted gain window is employed to offer an on-off-keying (OOK)-generated data stream with on/off extinction ratio of 17 dB and bit error rate (BER) of 10-13 at a receiving optical power of -18 dBm. With an input nonreturn-to-zero (NRZ) power as low as - 15 dBm and an injected dark-optical-comb power of 16.5 dBm, the generated OOK pulse data reaches a BER 10-13 at receiving power as low as -18.5 dBm. The OOK operation in the SOA also exhibits a decision-gate function with improved negative power penalty of 1.5 dB as compared with the back-to-back NRZ transmission condition. The injection via a multiwavelength dark-optical-comb source further benefits from a lower noise level as compared with single-wavelength laser or broadband spontaneous emission source. Such a system exhibits a tolerance for detuning timing of > 65% period with power penalties on the on/off extinction ratio and the receiving power of 3 and 1 dB, respectively. Even after 25-km propagation in a single-mode fiber spool, there is only a power penalty of 0.5 dB at a BER of 10-13 obtained for the generated pulse data stream.[[fileno]]2010144010169[[department]]物理
Characterization and Comparison of GaAs/AlGaAs Uni-Traveling Carrier and Separated-Transport-Recombination Photodiode Based High-Power Sub-THz Photonic-Transmitters
No full text[[abstract]]We describe in detail the characterization of two high-power photonic transmitters based on two different kinds of high-power photodiodes, one a GaAs/AlGaAs based uni-traveling-carrier photodiode (UTC-PD) and the other a separated-transport-recombination photodiode (STR-PD). The diodes operate under optical pulse excitation at the 800 nm wavelength. Both PDs have the same total depletion layer thickness (same theoretical RC-limited bandwidth) and are m integrated with the same broadband micro-machined circular disk monopole antennas to radiate strong sub-THz pulses. However the STR-PD based transmitter exhibits very different dynamic and static performance from that of the UTC-PD based transmitter due to the existence of a low-temperature-grown GaAs (LTG-GaAs) based recombination center inside the active region, and the much thinner thickness of effective depletion layer. Under optical pulse excitation (similar to 480 pJ/pulse), the STR-PD based transmitter exhibits a much lower maximum averaged output photocurrent (1.2 mA versus 0.3 mA) than that of the UTC-PD transmitter, although the radiated electrical pulse-width and maximum peak-power, which are measured by the same THz time-domain spectroscopic (TDS) system, of both devices are comparable. These results indicate that although the recombination center in the STR-PD degrades its DC responsivity, it effectively improves the high-speed and output power performance of the device and eliminates the DC component of the photocurrent, which should minimize device-heating problem during high-power operation. The radiated waveforms of both devices under intense optical pulse illumination also exhibit excellent linearity and strong bias dependent magnitude. This suggests their suitability for application as photonic emitters and possibly as a data modulator in sub-THz impulse-radio communication systems.[[fileno]]2010144010185[[department]]物理
Evaluation and Application of Bounded Generalized Pareto Analysis to Fault Distributions in Open Source Software
No full text[[abstract]]In general, one of the most important aspects of software development and project management is how to make predictions and assessments of quality and reliability for developed products. Project data usually will be systematically collected and analyzed during the process of software development. Practically, it would be helpful if developers could identify the most error-prone modules early so that they can optimize testing-resource allocation and increase fault detection effectiveness accordingly. In the past, many research studies revealed the applicability of the Pareto principle to software systems, and some of them reported that the Pareto distribution (PD) model can be used to predict the fault distribution of software. In this paper, a special form of the Generalized PD model, named the Bounded Generalized Pareto distribution (BGPD) model, is further proposed to investigate the fault distributions of Open Source Software (OSS). It can be seen that the BGPD model eliminates the issue which occurred in the classical PD model. Three methods of parameter estimation will be presented, and related experiments are performed based on real OSS failure data. Experimental results show that the BGPD model presents high fitness to the actual failure data of OSS. Finally, the possibility of using early limited fault data to predict the later software fault distribution is also studied. Numerical results indicate that the BGPD model can be trusted to consistently produce accurate estimates of fault predictions during the early stages of development. The findings can provide an effective foundation for managing the necessary activities of software development and testing.[[fileno]]2030240010043[[department]]資訊工程學
多方透視歷史：學科觀點在歷史教學中所扮演的角色
No full text[[abstract]]壹、歷史個概念，貳、因果關係，參、歷史扮演的角色，肆、學科觀點的影響，伍、教學認證的途徑，陸、後記[[fileno]]204_JA04_2005_n16_p6
如何在一學期內教完中國歷史
Get PDF[[abstract]]中國歷史的教學，普遍說來成效不彰。許多地方需要改進，教育改革需要熱情，更需要合作，一個人的力量有限，集合眾人，力量就很可觀。有些人做課程設計，有些人做閱讀精選，又有些人做命題研究，集合起來，就可以做出許多中國歷史教學的輔助資料，可以供許多老師用於課堂教學。這樣的話，就是時間很少，我們也可以讓學生認識中國歷史，甚而也會喜歡中國歷史。[[fileno]]204_JA04_2007_n18_p
