共查询到20条相似文献,搜索用时 15 毫秒
1.
Zhijun Liu Gmachl C.F. Liwei Cheng Fow-Sen Choa Towner F.J. Xiaojun Wang Jenyu Fan 《Quantum Electronics, IEEE Journal of》2008,44(5):485-492
Temperature-dependent optical gain and waveguide loss have been measured for continuous-wave operated quantum-cascade lasers with wavelengths between 8.2 and 10.2 mum up to room temperature using the Hakki-Paoli method. The gain coefficient decreases with increasing temperature, and is close to the designed value for vertical transition lasers, but smaller than the designed value for diagonal transition lasers. The waveguide loss, however, is two to three times higher than calculated from free carrier absorption, and can be nearly constant, increase or decrease with temperature depending on sample design, which indicates that it is dominated by another mechanism other than plain free carrier absorption. One likely factor resulting in high waveguide loss is intersubband resonant absorption into higher lying states. 相似文献
2.
Soliton-effect compression of femtosecond optical pulses in a silicon photonic nanowire at 1.5 mum is numerically investigated. A region of anomalous group velocity dispersion, small third-order dispersion, and large nonlinearity of silicon is used to show compression of 30-fs input pulses to 1 fs. Large nonlinearity of silicon allows for compression of input pulses with subnanojoule energies. 相似文献
3.
Polynkin P. Polynkin A. Panasenko D. Peyghambarian N. Moloney J. V. 《Photonics Technology Letters, IEEE》2006,18(21):2194-2196
Amplification of ultrashort pulses in doped fibers is limited by an onset of nonlinear effects in the fiber. At the 1.5-mum wavelength, single-mode fibers typically have anomalous dispersion. The self-phase modulation combined with dispersion leads to instability of multinanojoule pulses in such fibers. Various techniques developed to amplify pulses beyond the nonlinearity limit typically rely on a delicate balance between dispersive and nonlinear effects in different parts of the laser system. We report a simple all-fiber alternative to these complex techniques that utilizes a rapid amplification of pulses in a short and heavily doped phosphate-glass active fiber. In our preliminary experiments, picosecond pulses at 1.5 mum generated by a passively mode-locked fiber oscillator at a repetition rate of 70 MHz are amplified in a 15-cm-long heavily Er-Yb codoped fiber amplifier to the average output power of 1.425 W. The pulse energy and peak power reach 20.4 nJ and 16.6 kW, respectively, while the pulse distortion is minimal in both temporal and spectral domains. Further power up-scaling is possible by using active phosphate fiber with a large mode area, in the amplifier stage 相似文献
4.
Chun-Lin Kuo Bo-Jr Huang Che-Chung Kuo Kun-You Lin Huei Wang 《Microwave and Wireless Components Letters, IEEE》2008,18(7):455-457
10-35 GHz doubly balanced mixer using a 0.13-mum CMOS foundry process is presented in this letter. Using the bulk-driven topology, the number of transistors of the doubly balanced mixer is reduced; thus the mixer can achieve a low supply voltage and low power consumption. This bulk-driven mixer exhibits a measured conversion gain of -1 plusmn 2 dB from 10 to 35 GHz of radio frequency (RF) with a fixed intermediate frequency (IF) of 100 MHz. The measured local oscillation (LO) to IF and RF-IF isolations are better than 30 dB. The chip area of the mixer is 0.6 times 0.4 mm2. The total power consumption included output buffer is only 6 mW. 相似文献
5.
Dagens B. Make D. Lelarge F. Rousseau B. Calligaro M. Carbonnelle M. Pommereau F. Accard A. Poingt F. Le Gouezigou L. Dernazaretian C. Le Gouezigou O. Provost J.-G. van Dijk F. Resneau P. Krakowski M. Duan G.-H. 《Photonics Technology Letters, IEEE》2008,20(11):903-905
The modulation bandwidth has been identified as a specific limitation of quantum-dot or quantum-dash (QDash) lasers for direct modulation application. Solutions using tunnel injection and p-doping have already been demonstrated to increase the modulation bandwidth above 10 GHz, but with complex tunnel injection design and p-doping induced high internal losses. We show in this letter that the use of optimized QDashes and waveguide structure is sufficient to reach such high bandwidth at 1.55 mum. The device is validated by a large signal modulation demonstration at 10 Gb/s. 相似文献
6.
Recent theoretical studies have shown that circular patch antennas loaded by an inhomogeneous substrate partially filled with a mu-negative (MNG) metamaterial may in principle support a resonant radiating mode, even if the total size of the radiator is significantly smaller than the wavelength of operation. In those theoretical analyses, MNG metamaterials have been assumed as continuous, isotropic and readily available materials, characterized by a proper dispersion in frequency and by inherent ohmic losses. The fabrication of such compact antennas, however, would require the major effort of designing proper subwavelength inclusions that realize the MNG behavior of the substrate, and consequently a careful design of their geometry, location and orientation. The fabrication of a fully isotropic MNG sample to reside underneath the sub-wavelength patch, moreover, may be challenging with the current technological limitations. In this paper, we first show that the proposed sub-wavelength radiator may operate even when the fabricated MNG sample is not isotropic, due to the specific polarization of the magnetic field in the MNG region. Then, we propose a complete design of the magnetic inclusions, presenting full-wave numerical simulations of the structure, which effectively supports the expected resonant mode, despite the small size of the antenna. The comparisons among analytical results of the patch loaded by: (a) the ideal MNG sample applying a simple cavity model; (b) full-wave numerical simulations of the same antenna considering the presence of the feed; and (c) full-wave numerical simulations of the antenna loaded by the proposed magnetic inclusions, show how our design effectively simulate the presence of an MNG sample, allowing the realistic design of a sub-wavelength metamaterial patch antenna with satisfactory matching and radiating features. This may open up new venues in the realization of efficient metamaterial radiating components for practical purposes. 相似文献
7.
Zhigang Tian Yam R.C.M. Zuo M.J. Hong-Zhong Huang 《Reliability, IEEE Transactions on》2008,57(1):53-58
Algorithms have been available for exact performance evaluation of multi-state k-out-of-n systems. However, especially for complex systems with a large number of components, and a large number of possible states, obtaining "reliability bounds" would be an interesting, significant issue. Reliability bounds will give us a range of the system reliability in a much shorter computation time, which allow us to make decisions more efficiently. The systems under consideration are multi-state k-out-of-n systems with i.i.d. components. We will focus on the probability of the system in states below a certain state d, denoted by Qsd. Based on the recursive algorithm proposed by Zuo & Tian [14] for performance evaluation of multi-state k-out-of-n systems with i.i.d. components, a reliability bounding approach is developed in this paper. The upper, and lower bounds of Qsd are calculated by reducing the length of the k vector when using the recursive algorithm. Using the bounding approach, we can obtain a good estimate of the exact Qsd value while significantly reducing the computation time. This approach is attractive, especially to complex systems with a large number of components, and a large number of possible states. A numerical example is used to illustrate the significance of the proposed bounding approach. 相似文献
8.
《IEEE transactions on circuits and systems. I, Regular papers》2008,55(9):2584-2594
9.
《IEEE transactions on circuits and systems. I, Regular papers》2009,56(8):1576-1589
10.
Koudymov A. Shur M.S. Simin G. Kanin Chu Chao P.C. Lee C. Jimenez J. Balistreri A. 《Electron Devices, IEEE Transactions on》2008,55(3):712-720
A compact analytical model of short-channel AlGaN/GaN HEMTs in the presence of a current collapse is presented. The model is based on an experimentally established trapping mechanism at the gate edges and relies on significant differences between the characteristic carrier capture-escape times and typical RF signal periods. For the first time, we implement the theory describing electric field distributions in the HEMT gate-to-drain spacing region, with and without trapped charge distributions. By consequently accounting for velocity saturation effects in gated and trapped regions of the device, the presented model shows good agreement with the experimental data. The model uses a minimal number of fitting parameters, most of which are physical parameters describing velocity-field dependence of the carriers. 相似文献
11.
Many communication systems require a two-way, or three-way handshaking process to improve their dependability & authenticity in order to achieve a more successful operation. In this paper, we present a new two-way handshaking reliability model based upon threshold-based cryptography systems. Such systems require a two-way handshaking process to i) establish a group of participated servers in the first handshaking process, and ii) calculate a cipher with successfully connected servers collaboratively in the second handshaking process. When the servers are attempted, each server has three known connection probabilities in the following three states: i) successful, ii) breakdown, and iii) congested. These connection probabilities are unchanged in both handshaking processes. During the first handshaking process, we establish connections that more than servers are willing to participate. For the second handshaking process, the system becomes successful as soon as we can connect these servers successfully again. Because we need to connect servers successfully in the second handshaking process, we would rather connect additional servers besides the servers required to be connected successfully in the first handshaking process. This preference will minimize the chance that the system breaks down when fewer than servers can be reconnected successfully in the second handshaking process. We refer to this system as a Two-Way Handshaking Circular Sequential-out-of-Congestion (TWHCSknC) system. In this paper, we derived analytical formulas for the system's successful probability & average stop length, and we showed that the TWHCSknC system is a communication system with an efficient two-way handshaking process. 相似文献
12.
《Quantum Electronics, IEEE Journal of》2010,46(2):272-276
13.
Kuang-Sheng Lai Ji-Chen Huang Hsu K.Y.-J. 《Electron Devices, IEEE Transactions on》2008,55(3):774-781
In this paper, without altering any step of the commercial 0.35-mum SiGe BiCMOS process, a novel photodetector named phototransistor photodetector (PTPD) has been realized and demonstrated. The PTPD shows high photoresponsivity and its structure relaxes the tradeoff between sensitivity and speed. Responsivities of 9.5 A/W for 670 nm light and of 5.2 A/W for 850 nm light were achieved. The operation details of the PTPD are introduced in this paper. The device can be readily integrated with other on-chip circuits to form a high-performance optoelectronic IC. The low cost, the high performance, and the flexibility in optical-electrical design allow the SiGe PTPD to be used in many demanding applications. 相似文献
14.
Probe-corrected spherical near-field antenna measurements with an arbitrary probe set certain requirements on an applicable scanning technique. The computational complexity of the general high-order probe correction technique for an arbitrary probe, that is based on the Phi scanning, is O(N4), where N is proportional to the radius of the antenna under test (AUT) minimum sphere in wavelengths. With the present knowledge, the computational complexity of the probe correction for arbitrary probes in the case of the thetas scanning is O(N-6), which is typically not acceptable. This paper documents a specific double Phi-step thetas scanning technique for spherical near-field antenna measurements. This technique not only constitutes an alternative spherical scanning technique, but it also enables formulating an associated probe correction technique for arbitrary probes with the computational complexity of 0(N4) while the possibility for the exploitation of the advantages of the thetas scanning are maintained. 相似文献
15.
《Electron Devices, IEEE Transactions on》2008,55(9):2429-2436
16.
Saab R. Yilmaz O. McKeown M.J. Abugharbieh R. 《Signal Processing, IEEE Transactions on》2007,55(8):4004-4017
In this paper, we address the problem of underdetermined blind source separation (BSS) of anechoic speech mixtures. We propose a demixing algorithm that exploits the sparsity of certain time-frequency expansions of speech signals. Our algorithm merges lscrq -basis-pursuit with ideas based on the degenerate unmixing estimation technique (DUET) [Yiotalmaz and Rickard, "Blind Source Separation of Speech Mixtures via Time-Frequency Masking," IEEE Transactions on Signal Processing, vol. 52, no. 7, pp. 1830-1847, July 2004]. There are two main novel components to our approach: 1, our algorithm makes use of all available mixtures in the anechoic scenario where both attenuations and arrival delays between sensors are considered, without imposing any structure on the microphone positions, and 2, we illustrate experimentally that the separation performance is improved when one uses lscrq-basis-pursuit with q < 1 compared to the q = 1 case. Moreover, we provide a probabilistic interpretation of the proposed algorithm that explains why a choice of 0.1 les q les 0.4 is appropriate in the case of speech. Experimental results on both simulated and real data demonstrate significant gains in separation performance when compared to other state-of-the-art BSS algorithms reported in the literature. 相似文献
17.
Hongming Zhao Qihong Lou Jun Zhou Fangpei Zhang Jingxing Dong Yunrong Wei Guohua Wu Zhijun Yuan Zujie Fang Zhijiang Wang 《Photonics Technology Letters, IEEE》2008,20(12):1009-1011
A simple actively Q-switched double-clad fiber laser combining an amplifying cavity is reported by using a dynamic acoustooptic Q-switching as a beam splitter. Sub-100-ns pulses independence of the repetition rate of acoustooptic modulator are almost changeless with repetition rate varied from 50 kHz to 1.5 MHz. With 4.5-W absorbed power, 9.4-W peak-power pulses at 1.5-MHz repetition rate with 75-ns pulse duration are generated. 相似文献
18.
《Advanced Packaging, IEEE Transactions on》2008,31(3):473-478
19.
《Semiconductor Manufacturing, IEEE Transactions on》2008,21(2):180-185
20.
《Electron Devices, IEEE Transactions on》2009,56(1):116-125