Tunable holographic components in WDM optical networks

This paper describes the applications of a multipurpose holographic device in optical networks with Coarse and Dense Wavelength Division Multiplexing (CWDM/ DWDM) technologies. In its basic structure, it can operate as a tunable wavelength filter, wavelength multiplexer or λ router. By using a more complex structure, the device works as OADM (Optical Add Drop Multiplexer) or OS (Optical Switch). Some simulations of the basic devices, from the optical transmission point of view, are made to match the transmission parameters for the application in optical networks. Performance parameters of the device, like switching time, losses, cross-talk or polarization insensitivity are analyzed and compared with other multiplexing or switching technologies. To complete the review of these components, a study of computer generated holograms (CGH) design is carried out. The results are used in the design of holographic devices to perform different applications: in Metro networks, where a design of a holographic device with wavelength conversion and routing is analyzed, or, in Access Networks like a tunable filter or demultiplexer in Fiber to the Home/Business (FTTH/FTTB) topologies.     

Investigation of wavelength division multiplexing ring network topology to enhance the system capacity

In this paper, we have investigated the wavelength division multiplexed (WDM) system using ring network topology. This network is used to increase the capacity with eight optical add/drop multiplexers (OADMs) by using dispersion compensating fiber and semiconductor optical amplifier (SOA) to achieve a distance up to 1600 km. It is observed that network shows the acceptable results at 15 Gbps data rate with 100 GHz channel spacing. The OADM nodes are also varied to investigate the network performance in the term of BER and Q-factor.     

Wavelength conversion in optical transport networks

The introduction of optical technology in the path layer of a transport network is analyzed; in particular, the impact of all-optical wavelength conversion is examined. Two basic optical cross-connect schemes based on space switching and on wave-length switching, respectively, and two types of wavelength converters are considered. The wavelength converters are, respectively, based on four-wave miring (FWM) in semiconductor optical amplifiers (SOAs) and on cross-phase modulation (XPM) obtained by two SOAs put in an interferometric configuration. An analysis of transmission performances of optical transport networks employing both types of wavelength conversion and both the node architectures is reported. The performances are evaluated by means of a system modeling that facilitates considering physical phenomena occurring during transmission and all the important transmission impairments. The analysis reveals that both the types of converters can be employed with different features and limitations, according to the considered network and switching architecture.     

Distributed control based routing and wavelength assignment strategy for WDM optical networks

Wavelength-division-multiplexing (WDM) is emerging as the dominant technology for the next generation optical networks. The control strategy can be either centralized or distributed. In centralized control, there is a central controller to keep track of the state of the network. It is also responsible for selecting the path for data transmission. Most of the work done in this field is based on centralized control. For large networks, distributed control is preferred over centralized control because of low control overhead. Distributed control strategy requires exchange of control messages among nodes. The distributed control generally results in the possibility of resource reservation conflicts among simultaneous path establishments and poor resource utilization. In this paper, we have proposed one distributed control based routing and wavelength assignment strategy that avoids the problem of resource reservation conflicts along with the efficient utilization of resources.     

RSOA-basRSOA-based distributed access long reach hybrid WDM-TDM PON with OADMs

A distributed access scheme using optical add/drop multiplexers （OADMs） for long reach hybrid wavelength division multiplexing and time division multiplexing passive optical networks （WDM-TDM PONs） is proposed and demonstrated. Colorless operations are implemented by using commercially available reflective semiconductor optical amplifiers （RSOAs） at both the center office （CO） and the customer side. Four 1.25-Gb/s channels are successfully transmitted over 80-km single-mode fiber with four OADMs. The dynamic input power range of the RSOA is also investigated. Compared with traditional access schemes, the proposed scheme could cover the area along the feed fiber with no blind zone. The experimental results show that it could be an ideal solution for the next generation access networks.     

智能光网络中一种新型的分布式恢复方法

提出了一种基于固定备用路由和目的端触发的智能光网络中的分布式恢复方法,所选择的任一对源端节点和目的的端节点之间的固定备用路由包括该节点对之间的k条最短路径路由和基于部分链路无关的路由.目的端节点一旦探测到业务通道的失效将立即启动恢复进程,根据网络当前的资源使用情况,在这些备用路由中按照一定的次序选择一条恢复路由并为此分配一条可用的波长(对于没有波长变换器的光网络),然后将恢复通道的建立请求消息发送给该恢复通道的相关节点,这些相关节点可以锁定相关的网络资源,以避免来自其他恢复通道的竞争.所提出的算法增加了固定备用路由的数量,从仿真结果可以看出,该方法明显改善了失效连接的阻塞性能.     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

Analysis of Wavelength-Routed Optical Burst-Switched Network Performance

This paper studies a novel scalable network architecture combining optical burst switching (OBS) with dynamic wavelength allocation to guarantee quality of service (QoS), forming a wavelength-routed optical burst-switched network. All processing and buffering functions are concentrated at the network edge and bursts are assigned to fast tuneable lasers and routed over a bufferless optical transport core using dynamic wavelength assignment. Different burst aggregation mechanisms are evaluated for a range of traffic statistics in terms of delay and packet loss rate. New network performance parameters in an analytical model quantify the advantages of dynamic wavelength allocation. The results define the operational gain achievable with dynamic wavelength assignment compared to quasi-static wavelength routed optical networks.     

Performance enhancement of optical burst switched networks

Optical burst switching (OBS) is an optical switching paradigm which offers a good tradeoff between the traditional optical circuit switching (OCS) and optical packet switching (OPS) since it has the relatively easy implementation of the first and the efficient bandwidth utilization of the second. Hence, OBS is a promising technology for the next generation optical Internet. A buffer-less OBS network can be implemented using ordinary optical communication equipment without the need for either wavelength converters or optical memories. In an OBS network, burst-loss performance is a critical concern. In OBS, the data-burst transmission is delayed by an offset time (relative to its burst control packet (BCP), or header) and the burst follows its header without waiting for an acknowledgment for resource reservation. Thus, a burst may be lost at an intermediate node due to contention, which is generally resolved according to the local routing and bandwidth information. The routing table maintained in each OBS node is generally pre-computed and fixed to forward the data bursts. Such a static forwarding feature might have limited efficiency to resolve contentions. Moreover, a burst may be lost and the network may be congested when a network element (e.g., fiber link) fails. In this paper, an efficient integrated scheme based on dynamic routing and burst segmentation has been proposed to improve reliability of data transport and network load balancing in optical burst switched networks. Simulation results demonstrate that the proposed approach reduces effectively blocking probability and hence contention. Further, it provides end-to-end throughput performance also. Hence, it establishes an appropriate tradeoff between loss rate and end-to-end throughput.     

An optimal protection and restoration scheme (OPARS) for optical networks

Protection and restoration are critical network design issues for optical networks since even a single failure for a short duration may result in huge data loss due to the large capacity of optical fibers. However, few studies have been done on these issues for optical burst switching (OBS) networks. Protection and restoration are essential mechanisms for guaranteeing more reliable traffic delivery services. But it is not easy to apply existing mechanisms to optical burst switching (OBS) networks due to its one-way reservation signaling and the statistical burst multiplexing. Thus, to achieve the high transmission performance and reliability simultaneously, unique properties of OBS must be considered in the design of protection scheme. In this paper, an optimal protection and restoration scheme (OPARS) has been introduced that not only optimizes the number of provisioned protection wavelengths adaptively based on the traffic load as well as the quality of service (QoS) requirements of bursts in high speed networks but also minimizes burst loss rates. In addition, the proposed scheme has been used as an efficient contention resolution technique. The simulation results verify that the proposed scheme improve the network resource and channel utilization while guaranteeing the targeted protection reliability and QoS requirements of bursts.     

Multi-soliton generation with extremely narrow free spectrum range for multiplexed sensors via optical network

We propose a new system of multiplexer sensors using the localized soliton pulse generated by a microring resonator in optical networks. A large bandwidth signal is generated by a soliton pulse propagating within the microring resonator, which is allowed to form the multiplexed sensors. Two forms of soliton pulses are generated and localized, i.e. temporal and spatial solitons. The required soliton pulses with specified wavelengths can be localized and formed the sensing. This is formed by using an optical add/drop multiplexer incorporating in the optical network, where the localized soliton pulses are available for add/drop signals to/from the optical network. The change in physical parameter measured the change in soliton wavelength, which formed the measurement.     

Design of a device with wavelength multiplexing and routing functions using dynamic holography on SLMs

This work describes the theory and design of a generic multipurpose device that can operate as a tunable wavelength filter, wavelength multiplexer and wavelength router. This device could be especially useful in optical network applications based in both coarse and dense wavelength division multiplexing technology. The enabling component is a ferroelectric liquid crystal spatial light modulator (SLM) where dynamic holograms are implemented in real time. As a consequence, the device will be able to carry out different functions according to the hologram recorded onto the SLM. The great advantage of this device is a polarization insensitivity operation, allowing low crosstalk and simple handling.     

Penalty Evaluation Due to the Cascade and Frequency Misalignment of AWG-Based Optical Add-Drop Multiplexers in 10 Gb/s Metro Core Ring Networks

The performance evaluation of AWG-based OADMs due to filter cascade in 10 Gb/s WDM metro core networks is presented. The penalty for the through optical channels is investigated versus the laser wavelength drift and OADM temperature stabilization failure. Results are measured and extrapolated with simulation results to obtain the maximum allowable number of OADMs in the metro network.     

Penalty Evaluation Due to the Cascade and Frequency Misalignment of AWG-Based Optical Add-Drop Multiplexers in 10 Gb/s Metro Core Ring Networks

The performance evaluation of AWG-based OADMs due to filter cascade in 10 Gb/s WDM metro core networks is presented. The penalty for the through optical channels is investigated versus the laser wavelength drift and OADM temperature stabilization failure. Results are measured and extrapolated with simulation results to obtain the maximum allowable number of OADMs in the metro network.     

An optimal burst assembly approach employing traffic shaping (OBATS) for OBS

Optical burst switching (OBS) aims at combining the strengths of packet and circuit switching and is considered as a promising technology for implementing the next generation optical Internet, required to cope with the rapid growth of Internet traffic and the increased deployment of new services. In this paper, an optimal burst assembly approach employing traffic shaping (OBATS) for OBS networks has been proposed in order to improve network performance in terms of reduced blocking probability, congestion control and better utilization of bandwidth. Particularly, the proposed scheme aims at reducing the average delay experienced by the packets during the burstification process in optical burst switched (OBS) networks, for a given average size of the bursts produced. Reducing the packet burstification delay, for a given average burst size, is essential for real-time applications; correspondingly, increasing the average burst size for a given packet burstification delay is important for reducing the number of bursts injected into the network and the associated overhead imposed on the core nodes. Simulation results show that the proposed burst assembly approach gives better network performance in terms of burst drop, resource contention and delay as compared to conventional burst assembly approaches.     

Survivable WDM-PON with self-protection and in-service fault localization capabilities

In this paper, we analyze the survivability of wavelength division multiplexed (WDM) passive optical network (PON). We propose and experimentally demonstrate a novel survivable WDM-PON architecture with self-protection and in-service fault localization capabilities. Two WDM-PONs are combined together and multiple sub-ring architecture is formed. Protection switching is achieved automatically at optical network units (ONUs) when failure occurs. Fiber loss, fiber fault localization and automatic protection switching in each ONU are real-time monitored in central office (CO) without interrupting customer service. No signaling for failure notice or protection switching is required for either CO or ONUs. Extra fibers required for protection are minimized compared with previous protection schemes. The self-protection and in-service fault localization capabilities of the proposed WDM-PON architecture are experimentally verified.     

用于WDM光网络的一种低串扰无损耗光开关矩阵

提出了一种低串扰无损耗的光开关矩阵.该结构是在扩展Benes（DB）结构的基础上通过改进得到的称为改进的扩展Benes（IDB）结构,并通过进一步的改进得到各级改进的扩展Benes（GIDB）结构.理论分析了IDB结构和GIDB结构中串扰产生的机理和对信号的影响，比较了几种结构的信噪比和光交换容量之间的关系.发现随着光交换规模的扩大，GIDB结构相对于DB结构信噪比明显提高.实验研究了4×4的IDB、GIDB结构中串扰引起的误码率降低以及眼图的恶化情况.结果表明GIDB结构能有效减少串扰的影响.     

用于WDM光突发交换网的改进JIT信令协议

提出了一种用WDM光突发交换网的良好时间通信协议(MJIT-SP)该协议结合了光线路交换和光分组交换的优点与用于光突发交换的其他信令协议相似,MJIT-SP的特点也是采用带外控制信号处理来排除核心节点处对光缓存器的需求然而,与其它协议如JIT-SP相比,它能最小化数据源端的建立时间和最大化交叉连接的带宽利用率而且,MJIT-SP还能支持光网络中无连接和面向连接的数据包传递并介绍了MJIT-SP的基本结构并从三个方面分析了它的基本性能,即建立时间、端到端延时和信道占用时间然后,对本协议与JIT-SP的性能进行了比较,结果显示:MJIT-SP不仅优于JIT-SP,而且还克服了JIT-SP的一个缺点,即过长的信道占用时间此外,还给出了MJIT-SP的信令信息,尤其是非常关键的信号与脉座电平差(SETUP)消息MJIT-SP中的SETUP与JIT-SP中的SETUP不同,它需要给出数据包路由和交换所需的信息,包括数据包长度、比特率、SETUP与数据包之间的偏置时间以及数据业务的质量控制系统(QoS)要求等最后讨论了MJIT-SP两种可能的变化并且分析了它们的优缺点.     

ATMOS (ATM optical switching)—system perspective

The expected traffic growth from new broadband services will require network capacities that can be beneficially provided by optical WDM transport networks. Optical packet techniques are essential for large networks to provide flexibility and granularity. A layered network architecture with a transparent optical layer and optical packet layers has been elaborated. Four switching concept options for large optical ATM switch fabrics in the public network and small access nodes are presented. The technology for the related key functions of space and wavelength switching was developed in the RACE ATMOS project and the feasibility of concepts and technologies was verified in four system demonstrators.     

Reconfigurable optical multiplexer based on liquid crystals for polymer optical fiber networks

In this work, different novel 3×1 multiplexer structures for being used in polymer optical fiber networks are proposed. Designs are compact, scalable, and of low consumption, capable of operating in a large wavelength range simultaneously 660, 850, and 1300 nm, due to the use of nematic liquid crystal cells. Light that comes from each input port is handled independently and eight operation modes are possible. Control electronics has been made using a programmable integrated circuit. Electronic system makes available the managing of the optical stage using a computer. An additional four optical sensors have been included for allowing the optical status checking. Finally, a polarization independent multiplexer has been implemented and tested. Insertion losses less than 4 dB and isolation better than 23 dB have been measured. In addition, 30-ms and 15-ms setup and rise times have been obtained. The proposed multiplexer can be used in any polymer optical fiber network, even in perfluorinated graded index one, and it can be specially useful in optical sensor networks, or in coarse wavelength division multiplexing networks.