An acoustooptical directional coupler for an optical time-domain reflectometer

An optical directional coupler in which a TeO2acoustooptical deflector (AOD) is employed has been designed and developed for use in an optical time-domain reflectometer (OTDR). A low round-trip insertion loss of 4.6 dB and low crosstalk of below -48 dB were attained for the fabricated coupler. Signals of large amplitude, such as Fresnel reflection, could be suppressed to less than - 33 dB by switching of the optical directional coupler. Amplitude fluctuation of the back-scattered signal due to polarization fluctuation in single-mode fibers is reduced to a negligible extent.     

GaAs/AlGaAs directional coupler switch with submillimetre device length

A GaAs/AlGaAs directional coupler switch, for the first time with a device length shorter than 1 mm, has been fabricated by utilising the good controllability of molecular beam epitaxy and reactive ion beam etching. The switching voltage is as low as 5V. The extinction ratio is 17dB for a crossover state and 14dB for a straight-through state.     

Optical bistability in a nonlinear directional coupler

In the nonlinear directional coupler, the optical field and the nonlinear material usually interact in a spatially and temporally local fashion and the device exhibits a nonlinear transmission characteristics, but it is not bistable. In this paper, it is shown theoretically that optical bistability in the input optical power is possible for the nonlinear directional coupler if the local phase change of the optical mode propagating through tile coupler is influenced by the excitation over the whole coupler. This condition can be satisfied in a coupler based on biased-pin-diodes comprising coupled asymmetric quantum wells in the i-region, Calculations show that in this configuration, the nonlinear directional coupler can exhibit sharp switching characteristics, low switching optical powers, optical bistability or bifurcation     

飞秒弧子脉冲在非线性定向耦合器中的传输控制研究

本文研究了超短脉冲在非线性定向耦合器中的传输控制。在飞秒级超短脉冲情况下 ,三阶色散效应变得很重要 ,需对在耦合器中的皮秒级脉冲传输控制方程进行修正。用对称分步傅里叶变换方法进行数值模拟分析 ,结果表明通过选择不同强度的正交极化同步控制脉冲 ,可对在NLDC中超短信号弧子脉冲的传输方向进行控制     

Very low power nonlinear directional coupling in a p-i (MQW)-nvertical coupler using an electrooptic feedback

An optically controlled 1×2 optical switch based on a vertically arranged directional coupler in which the guiding regions are GaAs/GaAlAs multiple quantum wells is discussed. The device can be switched electrically in a very efficient way (5-V driving voltage for a 330-μm-long sample) as well as optically. When connected to a constant-current source, the system shows high optical nonlinearities and can be all-optically switched with very low incident optical power on the order of 0.1 mW     

4*4 directional coupler switch matrix with an InGaAlAs/InAlAs multiquantum well structure

A 4*4 directional coupler switch matrix is developed which uses, for the first time, the quantum confined Stark effect of InGaAlAs/InAlAs multiquantum well structures. The rearrangeable nonblocking 4*4 network with six 2*2 switches is shown to be perfectly functional with switching voltages between 5 and 6 V and crosstalk below -17 dB in all the operation states.<>     

All-optical bistable switching in nonlinear directional couplerloaded with Bragg reflector

A GaInAsP nonlinear directional coupler loaded with a Bragg reflector has been fabricated. All-optical bistable switching in the fabricated device is demonstrated at a wavelength of 1.55 μm     

Optical FM signal amplification and FM noise reduction in an injection locked AlGaAs semiconductor laser

Optical frequency. modulation index suppression in FM signal amplification and FM signal generation in an injection locked semiconductor laser are experimentally studied by injecting coherent FM signals and CW light, respectively. Experimental results are in good agreement with a simple theory using the van der Pol equation with an external signal term. The FM noise accumulation in cascade injection locked amplifiers is calculated and an optimum design for an injection locked repeater system is discussed.     

All-optical time-division demultiplexing of 160 Gbit/s signal using cascaded second-order nonlinear effect in quasi-phase matched LiNbO/sub 3/ waveguide device

Using the cascade of the second-harmonic generation and the difference frequency mixing in a 30 mm-long quasi-phase matched LiNbO/sub 3/ waveguide device, all-optical time-division demultiplexing of a 160 Gbit/s signal into 10 Gbit/s channels is demonstrated. The power penalty is as small as 2.5 dB at the bit error rate of 10/sup -9/, which is attributed to crosstalk of the switch.     

Coupling properties in a 2-D photonic crystal slab directional coupler with a triangular lattice of air holes

Two-dimensional (2-D) photonic crystal (PC) directional couplers (DCs) that have a triangular lattice pattern of air holes in a planar dielectric slab are theoretically and experimentally analyzed. Unlike the 2-D PC DC structure with a dielectric rod in air, which is frequently used in theoretical studies, more practical PC DCs tend to be multimode in nature and exhibit a large group velocity dispersion, thus creating decoupling points in the dispersion relation without any additional modifications to the structure. The multimode nature and large dispersion lead to interference which degrades the coupling properties. By inserting three rows of air holes between neighboring line-defect waveguides in order to separate them, we have successfully reduced the multimode region and obtained a single-mode region. In this case, the large dispersion allows the creation of a PC DC with wavelength selectivity and a coupling length as short as 30 a,/spl sim/10 /spl mu/m for a=345 nm, where a is the lattice constant. The transmission spectra obtained experimentally showed good agreement with the theory whereas their transmission ranges were restricted to those of bent waveguides. These results are encouraging for practical application to optical communications.     

A 1.3-/spl mu/m wavelength laser with an integrated output power monitor using a directional coupler optical power tap

A 1.3-/spl mu/m Fabry-Perot laser with a directional coupler power tap inside the laser cavity, used for diverting optical power to an integrated waveguide monitoring photodetector is demonstrated. The monitoring detector provides photocurrent which is linear with the front facet output power, with responsivity as high as 0.37 mA/mW, depending on the length of the directional coupler coupling region.     

偏分复用系统中直接解复用反馈信号建模及验证

在采用直接解复用的偏分复用(PDM)系统中,反馈信号是决定系统解复用性能的关键因素,因此反馈信号的选取与正确建模至关重要。本文详细分析了两偏振态信号光相干性对基于光功率差和射频(RF)功率两种直接解复用反馈信号的影响,完善了相关的理论模型,建立了100Gbit/s的PDM-DQPSK传输系统仿真平台,对两种反馈信号的解复用效果进行了验证。结果表明,无论两偏振态信号光的相干性如何,基于光功率差的反馈信号都适用,而RF功率反馈信号只适用于信号光相干度较大的情况;在两种反馈信号均可以使用的情况下,它们的解复用效果基本相同,引入的光功率代价均约为0.1dB。     

Improvement of optical nonlinear response in GaAs/AlGaAs nipi-MOW structure with Au ohmic contact

Experiments demonstrate that the optical nonlinear response in a GaAs/AlGaAs nipi-MQW structure can be improved by introducing ohmic contacts, which electrically connect n- and p-layers. The response time is reduced by more than two orders of magnitude because of the enhanced recombination rate of photoexcited carriers, whereas the figure of merit for absorptive nonlinearity sigma /sub eh/ is kept constant and is an order of magnitude larger than that in a conventional GaAs/AlGaAs MQW structure.<>     

Efficient transport of packets with QoS in an FSAN-aligned GPON

The standardization of passive optical networks capable of transporting Ethernet frames at gigabit-per-second speeds, currently in progress in both ITU-T and IEEE, constitutes a major milestone toward cost-effective photonization of the last (aka first) mile. The article presents an Ethernet gigabit PON (GPON) system aligned with the philosophy of the evolving FSAN (full service access network) ITU-T specification, which focuses on the efficient support of any level of quality of service. The intelligence of this system, in terms of traffic quality guarantees, lies in the MAC protocol, which controls the distributed multiplexing/concentration function by allocating variable length slots to every user of the shared upstream (toward the network) medium. The way transport of information is organized in an ITU-T GPON system and the operation of a MAC protocol that preserves all QoS guarantees are presented and evaluated.     

Multigigabit/s pulse source based on the switching of an optical beat signal in a nonlinear fibre loop mirror

A novel technique for the generation of a high repetition rate train of transform-limited pulses is demonstrated. A 32 GHz train of 4.2 ps pulses has been generated.<>     

Exciton waveguide and lasing in structures with superfine GaAs quantum wells and InAs submonolayer inclusions in an AlGaAs host

The optical properties of structures with InAs islands and narrow GaAs quantum wells in an AlGaAs host have been investigated. The InAs islands were formed by depositing a layer of InAs with an effective thickness less than one monolayer. The effect of an exciton waveguide and the onset of lasing due to optical pumping in the red spectral range are demonstrated in structures without external optical confinement by layers with a lower refractive index. Fiz. Tekh. Poluprovodn. 33, 488–491 (April 1999)     

The effect of partial conversion and fiber delay lines in an OBS switch with a large number of wavelengths

In this paper, we analyze an optical burst switching (OBS) switch endowed with both wavelength converters (WCs) and fiber delay lines (FDLs) to resolve contention. We consider the case where the number of wavelengths is large by introducing a mean field model that provides exact results when the number of wavelengths tends to infinity. We have confirmed through simulations that the mean field model provides accurate approximations for switches with a large but finite number of wavelengths, which are of interest in view of wavelength division multiplexing (WDM). Furthermore, our model allows a very general behavior for the arrival process and the packet size distribution, as well as two different wavelength allocation policies: minimum horizon and minimum gap. Our results include a detailed analysis of the effect that these parameters have on the burst loss rate, and on the minimum number of WCs required to attain a zero loss rate as the number of wavelengths becomes large. We have found that at high loads there is little value in adding FDLs and, if included, shorter granularities result in fewer WCs required to achieve a zero loss rate. The inclusion of FDLs becomes more significant under mid loads and bursty traffic, where the addition of several FDLs may reduce the conversion requirements. Also, increasing the number of WCs under the minimum horizon policy may worsen the loss rate, while this is never the case for the minimum gap policy.     

An AlGaAs laser with high-quality dry etched mirrors fabricatedusing an ultrahigh vacuum in situ dry etching and deposition processingsystem

Highly reliable AlGaAs lasers with dry etched mirrors have been successfully fabricated with an ultrahigh-vacuum in situ processing system, equipped with reactive ion-beam etching (RIBE) and dielectric film deposition chambers. Etched mirror surfaces are protected against air-exposure contamination and nonvolatile-reaction-products adsorption with in situ Al₂O₃ passivation subsequent to the CI₂ RIBE mirror formation. Ion-bombardment-induced damage is repaired by thermal annealing. The annealing effect is enhanced by a contamination-free interface between the etched mirror surface and Al ₂O₃ passivation film. The lasers exhibit an increase in catastrophic optical damage (COD) level and long-life operation. Their COD levels are twice as high as that for as-etched lasers and are almost the same as those for conventional cleaved lasers     

WiNoC中无线节点和无线链路级拥塞避免的高效路由器设计

无线片上网络中,无线网络拥塞可以分为无线节点级的拥塞和无线链路级的拥塞,这两种拥塞都会造成网络性能下降.针对无线节点和无线链路级拥塞,本文设计了一种拥塞避免的高效无线路由器,首先提出了节点级的拥塞避免机制,无线节点通过广播本地拥塞信息相互感知拥塞程度,避免向拥塞程度较高的无线节点发送数据包;其次提出了链路级拥塞避免机制,在无线接口中设计了并行FIFO,允许无线接口以流水的方式,在单个时钟周期内传输一个拥塞信息数据包和三个数据微片,数学建模证明使用并行FIFO至少降低50%无线信道竞争频率,从而避免了无线链路级拥塞,提高了无线资源利用率.实验表明本文方案相较普通无线路由器增加了少量的面积,但是在网络整体性能、无线路由器性能以及功耗方面都取得了不错的优势.