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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.
Jie Lin Junping Zhang Fow-Sen Choa Xiangjun Zhao J. Khurgin 《Photonics Technology Letters, IEEE》2004,16(2):392-394
A new type of semiconductor optical amplifiers (SOAs) that can have a very low-channel crosstalk is proposed and demonstrated. By arranging the order of the gain materials with different saturation power, the SOA crosstalk is greatly reduced. This new type of SOA can be an ideal gain material for wavelength division multiplexed (WDM) amplification and integration in the access and metro environment. 相似文献
3.
Liwei Cheng Jenyu Fan Douglas Janssen Dingkai Guo Xing Chen Fred J. Towner Fow-Sen Choa 《Journal of Electronic Materials》2012,41(3):506-513
We investigated the effect of deep-etched mesa sidewall profile and oxide overhang length on the regrowth structural characteristics
for buried- heterostructure (BH) quantum cascade lasers (QCLs) grown by metalorganic chemical vapor deposition (MOCVD). The
relationship between etched mesa sidewall geometry, oxide overhang length, oxide thickness, and growth uniformity was examined
and is extensively discussed. In particular, anomalous growth in the vicinity of the oxide edge resulting from insufficient
oxide overhang length was identified and studied. An ideal ratio of mesa height to oxide overhang length between 2.5 and 3.0
is proposed and experimentally justified to yield satisfactory planar regrowths without anomalous growth. Mesas in the [ 0 1[` 1] ] [ 0 1\overline{ 1} ] direction with smoothly etched entrant profile yield a higher degree of growth uniformity than mesas in the [011] direction
with the re-entrant profile. 相似文献
4.
Zhijun Liu D. Wasserman S.S. Howard A.J. Hoffman C.F. Gmachl Xiaojun Wang T. Tanbun-Ek Liwei Cheng Fow-Sen Choa 《Photonics Technology Letters, IEEE》2006,18(12):1347-1349
We report on room-temperature continuous-wave (CW) operation of /spl lambda//spl sim/8.2 /spl mu/m quantum cascade lasers grown by metal-organic chemical vapor deposition without lateral regrowth. The lasers have been processed as double-channel ridge waveguides with thick electroplated gold. CW output power of 5.3 mW is measured at 300 K with a threshold current density of 2.63 kA/cm/sup 2/. The measured gain at room temperature is close to the theoretical design, which enables the lasers to overcome the relatively high waveguide loss. 相似文献
5.
Chen-Chia Wang Trivedi S.B. Feng Jin Khurgin J. Temple D. Hommerich U. Gad E. Fow-Sen Choa Yu-Sung Wu Corder A. 《Lightwave Technology, Journal of》2001,19(5):666-672
A new coherent optical detection technique employing coherent frequency-domain reflectometry and a novel optical frequency sensor is demonstrated for high-precision optical path-length measurements. Using pulsed laser sources, an improvement of more than two orders of magnitude in spatial resolution over conventional optical coherent frequency domain reflectometry techniques is demonstrated. Varying degrees of spatial resolution ranging from several centimeters to a few hundred nanometers are achieved. High-precision distance measurement with long baseline is also presented 相似文献
6.
Slow-wave finite-difference beam propagation method 总被引:3,自引:0,他引:3
Pao-Lo Liu Qida Zhao Fow-Sen Choa 《Photonics Technology Letters, IEEE》1995,7(8):890-892
By invoking the slow-wave approximation, the wave equation resumes the form of the Fresnel equation. Codes developed previously for the paraxial beam propagation can be extended to simulate the backward reflection and diffraction at any angle. Results of planar waveguide gratings and a beveled corner bend are presented 相似文献
7.
An optical packet switch based on WDM technologies 总被引:6,自引:0,他引:6
Fow-Sen Choa Zhao X. Xiuqin Yu Lin J. Zhang J.P. Gu Y. Ru G. Guansong Zhang Longjun Li Huiping Xiang Hadimioglu H. Chao H.J. 《Lightwave Technology, Journal of》2005,23(3):994-1014
Dense wavelength-division multiplexing (DWDM) technology offers tremendous transmission capacity in optical fiber communications. However, switching and routing capacity lags behind the transmission capacity, since most of today's packet switches and routers are implemented using slower electronic components. Optical packet switches are one of the potential candidates to improve switching capacity to be comparable with optical transmission capacity. In this paper, we present an optically transparent asynchronous transfer mode (OPATM) switch that consists of a photonic front-end processor and a WDM switching fabric. A WDM loop memory is deployed as a multiported shared memory in the switching fabric. The photonic front-end processor performs the cell delineation, VPI/VCI overwriting, and cell synchronization functions in the optical domain under the control of electronic signals. The WDM switching fabric stores and forwards cells from each input port to one or more specific output ports determined by the electronic route controller. We have demonstrated with experiments the functions and capabilities of the front-end processor and the switching fabric at the header-processing rate of 2.5 Gb/s. Other than ATM, the switching architecture can be easily modified to apply to other types of fixed-length payload formats with different bit rates. Using this kind of photonic switch to route information, an optical network has the advantages of bit rate, wavelength, and signal-format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic, including even analog signals. 相似文献
8.
David Eisen ;Kevin Zhang ;Linh Pham ;Fow-Sen Choa ;Nicole Armstrong ;Phillip Aye ;Ricardo Aye ;George Bennett ;Robert Hawthorne ;Huguens Jean ;Kimberly Brown 《能源与动力工程:英文版》2014,(11):1942-1951
Windbelt generators have been proposed as small, green power sources for battery charging applications. Some of the reported results lack detailed information about how key parameters influence the output power of the generator. In this work, we built prototypes with different architectures to study the voltage generation and power delivery as functions of belt tension, length, and electrical load at various wind speeds. We also studied the maximum power delivery conditions before the breakdown of the belt oscillation occurs. Our results are obtained from windbelt generators with two types of architectures: a conventional design with an adjustable belt that uses weight for tension control, and a revised design with a belt oscillation perpendicular to the coil axis. We have concluded that the breakdown of the belt oscillation at lower output resistances is a primary bottleneck that will limit windbelt systems to only very low power applications. 相似文献
9.
Liming Wang Fow-Sen Choa Jye-Hong Chen Yanjie Chai Mei-Hao Shih 《Lightwave Technology, Journal of》1999,17(10):1724-1731
Low-cost simple structure integrated transceivers are the key components toward future applications of coherent technology in access networks. In this paper, we propose a novel counterreceiving heterodyne detection (CRHD) scheme of a monolithically integrated four-section coherent transceiver. The CRHD scheme can lead to further simplification of the design of integrated coherent transceivers, and facilitates duplex transmissions with a single terminal device. Error free detection at 100 Mb/s with a 215-1 pseudorandom pattern is achieved. Flexible partitioning of channel capacity between the up- and downstream traffic on the same wavelength channel is proposed and demonstrated based on the CRHD scheme. The functions of signaling and multichannel operations are performed to demonstrate a proof-of-concept bandwidth-on-demand access network with integrated coherent transceivers 相似文献
10.
We report in this paper the architectural design and implementation of all-optical packet networks. Using photonic switches to route information, an all-optical network has the advantages of bit rate, wavelength, and signal format transparencies. Within the transparency distance, the network is capable of handling a widely heterogeneous mix of traffic. We will describe our research on the implementation of all-optical backbone switches. The switch components including frame synchronizers, frame delineation units, frame header over-writing units, wavelength converters, frame concentrators, and WDM buffers were constructed at 2.5 Gb/s. Their subsystem and device structure as well as preliminary performance are reported. 相似文献
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