Ultrafast all-optical switching with an asymmetric Fabry-Perotdevice using low-temperature-grown GaAs: material and device issues

For future telecommunications systems to take full advantage of the optical fiber bandwidth, it will be necessary to have components responding at picosecond speeds. The only way currently known to achieve these speeds is using all-optical switching. By using low-temperature-grown GaAs (LT-GaAs) in a compact asymmetric Fabry-Perot device, we have achieved ultrafast all-optical switching with large bandwidth, high contrast ratio, low insertion loss, and low switching energy. In this paper, we discuss the dependence of the switch performance on the mirror bandwidth and reflectivity, and the LT-GaAs layer thickness and growth conditions. We develop guidelines for the optimization of the device design to maximize the bandwidth and contrast ratio     

Ultrafast all-optical switching in an asymmetric Fabry-Perot deviceusing low-temperature-grown GaAs

We report the first ultrafast all-optical switching using low-temperature-grown bulk semiconductor material (LT-GaAs) in a compact asymmetric Fabry-Perot device. We obtain 3-ps response times, 2.8-dB insertion loss, 40-nm bandwidth, and 15-dB contrast ratios using 200-fJ/μm² average switching energy flux     

Optical CDMA for All-Optical Sub-Wavelength Switching in Core GMPLS Networks

Generalized multi-protocol label switching (GMPLS) is a multipurpose control-plane paradigm that extends the MPLS scheme allowing switching without recognizing packet boundaries. In this paper, we present a novel extension that exploits a new physical layer for switching in optical GMPLS. The proposed extension is achieved through adding an optical code switching layer, or code switch capable (CSC) layer, to the existing label mapping layers. Our proposal enables finer granularity at sub-wavelength level in all-optical GMPLS core switches, resulting in significant enhancements to traffic isolation capabilities for all-optical GMPLS core switches. We employ mathematical analysis to derive performance bounds for the proposed scheme, from both the labeling capacity and network throughput points of view. We use our analytical model to derive several optimum operating points for the network, and show that our techniques significantly improve the overall performance of all-optical core networks     

Photonic packet switches: architectures and experimentalimplementations

Photonic packet switches offer high speed, data rate and format transparency, and flexibility required by future computer communications and cell-based telecommunications networks. In this paper, we review experimental progress in state-of-the-art photonic packet switches with an emphasis on all-optical guided-wave systems. The term all-optical implies that the data portion of a packet remains in optical format from the source to the destination. While the data remain all-optical, both optical and optoelectronic techniques have been used to process packet routing functions based on extremely simple routing protocols. An overview of the design issues for all-optical photonic packet switching is given and contrasted with electronic packet switch implementations. Low-level functions that have been experimentally implemented include routing, contention resolution, synchronization, and header regeneration. System level demonstrations, including centralized photonic switching and distributed all-optical multihop networks, will be reviewed     

Subpicosecond carrier response of unannealed low-temperature-grown GaAs vs temperature

The subpicosecond carrier lifetime of an unannealed molecular beam epitaxial layer of GaAs grown at ∼210°C has been demonstrated between 10 and 290K through optoelectronic switching and all-optical pump-probe measurements. The low room-temperature resistivity of the as-grown layers, believed to arise from hopping conductivity through defect sites, has been observed to increase as the sample temperature was lowered, allowing ultrafast switching measurements to be performed using the low-temperature-as-grown GaAs as a photoconductive element. After illumination by 100 femtosecond optical pulses, photogenerated carriers in the sample have rapidly relaxed, returning the material to its high-resistivity state in less than 1 ps. This indicates that the precipitates present in post-annealed samples are not required for the fast relaxation of photoexcited carriers in low-temperature-grown GaAs. Ultrafast switching measurements on a post-annealed version of the GaAs film also resulted in the generation of similar, 0.6 ps full width at half maximum pulses.     

Analytical study of crosstalk propagation in all-optical networks using perturbation theory

The performance of current optical networks is inherently limited by the speed of electronic components and, in particular, by electronic switches. A new generation of optical networks, referred to as all-optical networks, overcomes this limitation by switching data entirely optically using all-optical crossconnects (OXCs). However, all-optical networks are prone to phenomena that are unknown to current optical networks with electrical regeneration: OXCs are subject to optical leaks, called crosstalk, resulting in unwanted components being added to transmitted signals, and this crosstalk is transmitted over very long paths without any signal regeneration. In this paper, we consider the interplay between fiber nonlinearity and crosstalk signals over long distances as the source of performance degradation, measured in terms of Q factor. We present an analytical crosstalk model for all-optical networks and give expressions for the performance degradation resulting from the joint propagation of a signal [using a continuous-wave (CW) assumption and perturbation theory] and crosstalk in large networks. Analytical calculations required by this model are shown to be much less computationally intensive than simulations. Simulations are carried out to validate our analytical model and good agreement is found between the analytical model and simulations for wide ranges of parameters.     

Defects in molecular beam epitaxial GaAs grown at low temperatures

We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction band.     

光码分多址全光网络实现方案

本文提出一种利用时域编码的光码分多址(OCDMA)技术构造全光通信网络的实现方案.给出了OCDMA全光接入网,OCDMA光交叉连接、光交换、光上下路、光复用的具体实现方法,给出了OCDMA全光网络体系结构.     

Hybrid State Engineering of Phase-Change Metasurface for All-Optical Cryptography

Chalcogenide material Ge₂Sb₂Te₅ (GST) has bistable phases, the so-called amorphous and crystalline phases that exhibit large refractive index contrast. It can be reversibly switched within a nanosecond time scale through applying thermal bias, especially optical or electrical pulse signals. Recently, GST has been exploited as an ingredient of all-optical dynamic metasurfaces, thanks to its ultrafast and efficient switching functionality. However, most of these devices provide only two-level switching functionality and this limitation hinders their application to diverse all-optical systems. In this paper, the method to expand switching functionality of GST metasurfaces to three level through engineering thermo-optically creatable hybrid state that is co-existing state of amorphous and crystalline GST-based meta-atoms is proposed. Furthermore, the novel hologram technique is introduced for providing the visual information that is only recognizable in the hybrid state GST metasurface. Thanks to thermo-optical complexity to make the hybrid state, the metasurface allows the realization of highly secured visual cryptography architecture without the complex optical setup. The phase-change metasurface based on multi-physical design has significant potential for applications such as all-optical image encryption, security, and anti-counterfeiting.     

Demonstration and performance analysis for the off-ramp portion ofan all-optical access node

Ultrafast processing of packets is demonstrated and the performance analyzed for the off-ramp portion of an all-optical access node. The off-ramp consists of synchronized fiber lasers driving an all-optical header processor that includes nonlinear optical loop mirrors (NOLM), electrooptic router, and demultiplexer in the form of a two-wavelength NOLM. We achieve switching contrasts of 10:1 for the header processor and demultiplexer with switching energies of 10 pJ and 1 pJ, respectively. Also, a proposed measurement technique to obtain eye diagrams is used to analyze the all-optical header processor using the synchronized lasers. Using this technique, we obtain an eye diagram with a Q value of 7.1±0.36, which corresponds to a worst case BER value of 8.8×10^-12 for a 95% confidence level. Finally, simulation models are used to verify and compare the experimental results, and we find good agreement. We also use the model to study the various causes for the degradation of the Q value through our system     

支持灵活谱利用的超大容量全光网体系结构研究

随着超高速光传输技术的发展,支撑100Gbit/s以及更高速率的组网应用成为全光网研究的关键。文章提出支持灵活谱利用的超大容量全光网体系结构。该结构根据端口实际需要编程配置光通道带宽并实现全光交换,突破波分复用（WDM）对通道带宽的限制,解决超高速率光信号的传送问题。同时,支持面向精细颗粒带宽的全光谱域分割和疏导控制与管理,实现光层资源虚拟化与按需配置,提高光纤带宽利用率。     

Performance analysis and dimensioning of multi-granular optical networks

Recent years have demonstrated the limited scalability of electronic switching to realize transport networks. In response, all-optical switching has been identified as a candidate solution to enable high-capacity networking in the future. One of the fundamental challenges is to efficiently support a wide range of traffic patterns, and thus emerges the need for equipment that is both practical and economical to construct and deploy. We have previously proposed the use of multi-granular optical cross-connects (MG-OXC), which support switching on both the wavelength and sub-wavelength level. To this end, the MG-OXCs are equipped with cheap, highly scalable slow switching fabrics, as well as a small number of expensive fast switching ports. The goal of this work is two-fold: first to demonstrate that a small number of fast switching ports suffices to support a wide range of traffic requirements, and second that multi-granular optical switching can offer cost-benefits on a network-wide scale. The first objective is studied through simulation analysis of a single switching node, and results indicate that a limited number of fast switching ports can significantly improve burst blocking performance over slow only switches. Furthermore, under certain circumstances, the MG-OXC can even approach the performance of a fast only switch design. Secondly, we introduce an Integer Linear Programming model for the total network installation cost, and our evaluation indicates that multi-granular optical switching can be a cost-effective solution on the network level, in comparison to slow only or fast only approaches. Furthermore, we can achieve reduced costs of individual OXC nodes, which allows us to minimize scalability problems corresponding to emerging fast switching fabrics.     

All-optical bistable switching dynamics in 1.55-μm two-segmentstrained multiquantum-well distributed-feedback lasers

All-optical bistable switching dynamics of 1.55-μm two-segment strained multiquantum-well (MQW) distributed-feedback (DFB) lasers were systematically studied both experimentally and theoretically. Some fundamental optical functionalities, including all-optical set-reset (flip-flop) operations, were demonstrated. The switching responses of these bistable lasers were studied, for the first time, with optical injection from a single-mode DFB laser, indicating that the switching dynamics based on gain quenching and absorption saturation are inherently different. A theoretical model including optical injection was developed to study these all-optical bistable switching characteristics in segmented bistable lasers. It was found that the nonuniform distribution of the photon density in the bistable laser cavity induced by optical injection was essential to perform the time-domain switching operations. Simulations showed a good agreement with experimental observations and indicated design improvements. Although the switching responses in the range of tens of picoseconds can be obtained with these bistable lasers, the maximum repetition frequency of the bistable systems would still be limited to the hundreds of megahertz due to the slow carrier recovery time (5 ns) of the lasers     

长波长垂直腔面发射激光器开关及双稳特性

为了研究垂直腔面发射激光器偏振转换特性,基于自旋反转模型,数值研究了正交光注入下1550nm垂直腔面发射激光器频率诱导偏振开关及双稳特性。结果表明,在正交光注入下,连续改变注入光与激光器光场内x线性极化模的频率失谐可诱导产生两类偏振开关和偏振双稳现象,且注入光强与偏振电流的变化都显著影响双稳宽度和激光器的输出特性;合理选择操作条件,可实现对1550nm垂直腔面发射激光器频率诱导偏振开关及双稳的控制。这一结果对垂直腔面发射激光器在全光开关和全光存储等领域的应用具有参考价值。     

Optical networks with hybrid routing

All-optical switching or wavelength routing has the benefit of optical bypass that can eliminate expensive high-speed electronic processing at intermediate nodes and reduce significantly the cost of high-bandwidth transport. But all-optical switching has the limitations of coarse granularity, lack of multiplexing gain, and scarcity of wavelength resources, which do not mesh well with Internet traffic that has many small and diverse flows and emphasizes the importance of resource sharing. In particular, wavelength routed light paths have difficulty to seamlessly converge with multiprotocol label switching label-switched paths that have arbitrary bandwidth granularity and relatively abundant labels. In this paper, we propose a hybrid wavelength and subwavelength routing scheme that can preserve the benefits of optical bypass for large traffic flows at the same time provide multiplexing gain for small traffic flows. We first study the hybrid routing scheme using static optimization that produces an optimal path set and a partition between wavelength and subwavelength routing. We then present a dynamic heuristic that tracks the static optimization closely. During the process, we proposed a traffic arrival process called incremental arrival with sporadic random termination to more accurately model practical optical network traffic generation process.     

全光网中光码流性能的整体监控

波分复用(WDM)多粒度交换可重构全光网是当前光通信网发展的方向,该文构造了一种实际试验网,提出了一种 眼图法对网中数字光信号进行全面监控的方法,并在自建WDM多粒度交换可重构全光网试验床上进行了演示,结果显示在网络重构等各种条件下均可对网中各波长通道数字信号的信噪比、定时抖动、功率、误码率等进行实时监测控制,该方法对光信号的协议和速率透明且能对各种光性能劣化进行鉴别。     

Tree-net architecture for integrated all-optical arithmetic operations and data comparison scheme with optical nonlinear material

In the field of optical interconnecting network the tree architecture has already taken the significant roles. Nonlinear optics has drawn a great interest in all-optical signal processing for its high speed photonic activity. Optical nonlinear materials (ONLM) may provide a major support to optical switching-based all-optical logic and algebraic operations. Here operational speed is extremely high (far above GHz). In this paper, an ONLM-based switching system is extensively used to design tree architecture for developing some arithmetic operational system in an all-optical domain. An alternative scheme of all-optical addition and subtraction and comparison of binary data is also proposed exploiting the above optical tree.     

Overspill routing in optical networks: a true hybrid optical network design

To efficiently support the highly dynamic traffic patterns of the current Internet in large-scale switches, we propose a new hybrid optical network design: Overspill Routing In Optical Networks (ORION). By taking advantage of the reduced (electronic) processing requirements of all-optical wavelength switching, the electronic bottleneck is relieved. At the same time, ORION achieves a level of statistical multiplexing comparable to the more traditional point to point WDM solutions, circumventing the bandwidth inefficiencies of all-optical wavelength switched networks, caused by dynamic traffic patterns. The result is a true hybrid optical network design, forming a bridge between these two switching concepts. In this paper the generic concept of ORION is described. An example node design, based on current advanced optical technologies, is described in detail. The ORION concept is also evaluated, comparing it with its two composing technologies, optical wavelength switching and point to point WDM, as well as a third, more trivial, hybrid one, through several case studies.     

Optical bistability and all-optical switching in novel waveguidejunctions with localized optical nonlinearity

We propose novel all-optical guided-wave devices using the structure with localized third-order optical nonlinearity where only a selected part of a waveguide both in a cross section and along a propagation direction is made from a Kerr-like nonlinear material and the rest are made from linear ones. Optical bistable devices and all-optical switching devices are realizable by utilizing bistable like nonlinear dispersion characteristics in selectively nonlinear guided-wave systems. Optical bistability and all-optical switching characteristics are analyzed in waveguide Y-junctions adopted the scheme by using a modified BPM combined with the normal mode analysis. The method to realize the guided-wave structure with localized nonlinearity is also discussed     

未来光因特网中的光交换方式及其发展趋势

Internet的业务流量正以每六个月翻一番的速度快速增长,未来网络中,数据业务超过话音业务只是时间问题,因此,基于电路交换的电信网升级到支持基于分组交换的数据业务是不可避免的,但是对因特网来说,由于光逻辑与光存储等器件不成熟,发展全光分组交换,技术上异常困难。另一方面,近来新提出的光突发交换,技术上相对简单,性能特点优异,因而成为更理想的选择,本文介绍了全光分组交换和光突发交换的研究现状,比较了两者的优缺点,最后指出改进光突发交换性能的两种方式。