Transparent Two-Fiber Optical Channel Shared Protection Ring

A two-fiber optical channel shared protection ring including node architecture, signaling protocol, control hardware, and software is designed and implemented experimentally. For a ring with four nodes and two wavelengths, a total protection switching time of 6.8 ms is demonstrated along with a revert-to-working switching time of 1.6 ms. Experimental results show that the switching time scales linearly with number of nodes and number of wavelengths. The system can protect a ring with 16 nodes, 1200 km circumference, and 40 wavelengths in less than 50 ms.     

Use of spare wavelengths for traffic restoration in a multiwavelength transport network

This article describes three network protection strategies for a single link failure using spare wavelengths in multiwavelength all-optical transparent networks. The use of spare wavelengths is shown to be effective and can be economical when a path restoration technique is used. It is also particularly suitable for high-bandwidth optical crossconnect nodes where the number of input and output ports are generally small. Based on the simulation results, the amount of redundancy required for fill protection is dependent on the protection approach employed. Two algorithms for finding and allocating spare wavelengths are introduced. The algorithms are based on the genetic and heuristic algorithms.     

Performance analysis of dedicated protection and shared protection for waveband switching based on multi-granularity optical cross-connect

In order to save the switching ports and the cost of Multi-Granularity Optical Cross-Connect (MG-OXC), the waveband switching technique was proposed to groom multiple wavelength-level traffic to a few waveband tunnels to be switched by a few switching ports in MG-OXC. At the same time, protection for fibers is very important to ensure the service continuity since each wavelength carries a lot of traffic. Although existing works have addressed the waveband switching protection, most of them separately considered only the dedicated protection or shared protection in static demand scenario and did not deeply analyze and compare the dedicated protection and shared protection in dynamic demand scenario. Therefore, in this paper, we deeply study the consumptions of wavelengths in fibers and ports in MG-OXCs for Waveband Shared Protection (WSP) and Waveband Dedicated Protection (WDP) in dynamic demand scenario, and propose the port-cost calculation and update methods based on a new waveband layered auxiliary graph that is developed based on MG-OXC structure. In simulations, we compare WSP, WDP, traditional end-to-end waveband shared protection and traditional end-to-end waveband dedicated protection. Simulation results show that the shared protection has smaller port-cost, better wavelength utilization efficiency and lower blocking probability than the dedicated protection with the same waveband switching policy, and the sub-path waveband switching has bigger port-cost, better wavelength utilization efficiency and lower blocking probability than the end-to-end waveband switching with the same backup wavelength assignment policy.     

Protection and restoration of ring in packet switched wavelength division multiplexed transport networks

In this paper, the dedicated protection of six node ring network has been demonstrated by taking normal fiber link and the protection fiber link. The restoration has been shown by switching of the traffic from the normal link to the protection link when an outage is occurred in the normal link. The normal link is again repaired and the traffic is switched back to the normal link. The network restoration time is measured as well as the signal transmission through nodes and the links is observed.     

波长重用-扩大基于单纤连接节点的WDM星形单跳网容量

针对可利用的有限信道波长数对基于单纤连接节点的WDM星形单跳网容量限制问题,本文提出了一种有效的解决方案-波长重用.根据该方案,在信道波长数一定的条件下,至少可使网络所支持的节点数-网络容量扩大一倍;在网络节点数不变时,则可大大减少网络节点的排队时延,缓和网络中各通信节点对数据信道波长使用权的竞争矛盾,使网络吞吐量增加1～3倍,有效地改善网络性能.本文首先论述了该基于单纤连接节点的波长重用WDM星形单跳网结构,接着分析了网络的波长重用特性,进而对所要求的光放大器增益和输出功率进行了计算;最后计算了网络的最大节点数和最大信道波长数.     

A Simple Configuration for Discontinuous Wavelength-tuning Optical Pulse Source

A simple configuration is proposed to perform wavelength switching in actively mode-locked fiber ring lasers, in which a sampled fiber Bragg grating and a tunable optical filter are cascaded in the ring cavity to exactly select the operating wavelength. The switching of four wavelengths with a spacing of 1.6 nm is obtained. The experimental results demonstrate that this technique is reliable and convenient.     

A Simple Configuration for Discontinuous Wavelength-tuning Optical Pulse Source

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Electrical Wavelength Switching of Ultrashort Pulses in a Mode-Locked Er-Doped Fiber Ring Laser with Fiber Gratings

Electrical wavelength switching of picosecond pulses was demonstrated in an actively mode-locked Er-doped fiber ring laser with fiber gratings by changing the electrical driving frequency of the modulator. Laser pulses switchable between two wavelengths spaced from 0.5 to 18 nm apart were achieved. The switching speed between the two wavelengths was of the order of several hundred kilohertz.     

Wavelength assignment for all-to-all broadcast in bidirectional WDM optical ring with limited drops

All-to-all broadcast is to disseminate a unique message from each node to every other node in a network. This problem is significant in the context of control plane design as it relates to status information dissemination. In this paper, a wavelength assignment method to reduce the number of wavelengths is proposed to establish all-to-all broadcast in a bidirectional WDM ring network. The network model is an all-optical network, in which a message from source node can be dropped (or split) only at a limited number of destination nodes along a light path due to power loss of dropping optical signals. An expression for the upper bound on the number of wavelengths required to support all-to-all broadcast is derived for certain cases of WDM ring while for other cases, an attractive algorithm is given to identify the lengths of connection sets that can be grouped together with suitable wavelength assignment strategies. Numerical results are computed to show that the results obtained are close to the lower bound.     

Wavelength assignment for all-to-all broadcast in WRMD WDM linear array and ring

This paper proposes a wavelength assignment method for all-to-all broadcast in wavelength reusable multi-carrier distributed (WRMD) wavelength division multiplexing (WDM) linear array and ring networks with wavelength reuse. An expression on the minimum number of wavelengths required to establish all-to-all broadcast is also derived for the networks. It is observed that one carrier regeneration per wavelength significantly reduces the number of wavelengths compared to that without carrier regeneration. The results also show that regenerating carriers more than once has little effect on the required number of wavelengths.     

Injection-switchable erbium-doped fiber laser with two output ports

An injection-switchable erbium-doped fiber laser (EDFL) with two output ports based on a ring structure is proposed. Wavelength switching together with the switching of the dominating output port of the fiber laser is achieved by controlling the power of a tunable injection laser. The characteristics of the wavelength switching for different levels of the pump laser power and different wavelengths of the injection laser are studied experimentally.     

Enhancement of ring network in presence of optimized semiconductor optical amplifiers

By utilization of optimized semiconductor optical amplifiers, the design of ring network is achieved for a large number of nodes with reasonable quality and zero power penalty. The gain fluctuation occurs due to variation in parameters of the semiconductor optical amplifier for ring network. It is evaluated that nodes go on decreasing with increase in gain saturation of the semiconductor optical amplifier.     

Dynamics of twist effect in a dual-frequency nematic liquid crystal

The dynamics of the electrooptical 90° twist effect in a dual-frequency nematic liquid crystal is investigated for wavelengths of 0.65 and 1.55μ m. It is shown that the boundary conditions of the interaction between the phases affect the optical threshold of the twist effect, the contrast, and the working voltage range. The switching time of the twist effect from the off to the on state upon a variation of the amplitude of a rectangular dc voltage pulse from 15 to 50 V changes from 1.5 to 0.3 ms for a thickness of the nematic crystal layer of about 7 μ m. The minimal time of switching from the “on” to the “off” state was 3 ms in the case when relaxation of molecules in a cell with asymmetric boundary conditions was controlled electrically. The dynamic range of transmittance variation at a wavelength of 1.55 μm extended to 30 dB.     

一种通用的时隙环网时隙调度机制

提出一种新颖的时隙环网公平机制——环分布式时隙调度(DTSR), 该机制是分布式的, 适合所有目的节点剥离业务的时隙环网。DTSR通过在单向信道上循环传输的时隙控制头(TCH)内增加一个简单的域, 实现对环上“饿死”节点信息的动态收集, 协调各个节点占用资源的时间, 确保各节点之间的公平性; 在发现环上有“饿死”节点后, DTSR利用时隙环网空间重用的特性, 调度相关节点向不经过“饿死”节点的其他节点发送数据, 充分利用了环网资源; 此外DTSR机制具有良好的算法收敛性, 且接入时延较传统算法更小。最后,对DTSR的性能进行仿真, 并和几个典型的时隙环网的公平机制进行了比较。     

Switchable dual-wavelength Erbium-doped fiber ring laser with cascaded fiber Bragg gratings

We have experimentally shown wavelength mode switching in a dual-wavelength Erbium-doped single cavity fiber laser where the initial two wavelengths of 1 nm spacing are determined by the cascaded reflection type short-period fiber Bragg gratings having two different centre wavelengths of 1550.5 and 1551.5 nm. The lasing mode depends on the polarization in the ring cavity to migrate from one wavelength to another or operates in both modes in a polarization beam splitter output. To effectively control the polarization in the ring cavity, the polarization controllers were positioned before and after the polarization beam splitter. This method of wavelength switching provides a simple way of mode tuning in dual-wavelength fiber lasers.     

外加电场法制备LiNbO3周期畴的反转电流特性研究

采用外加电场法制备了LiNbO₃单晶周期畴结构. 在对不同尺寸周期畴的反转电流进行比较研究的基础上,提出了一种确定反转畴成核时间和纵向贯穿速率的方法. 根据这一方法,得到在电场强度为25.1kV/mm,脉冲宽度为50 ms的脉冲方波作用下,LiNbO₃单晶反转畴的成核时间约为80ns,纵向贯穿速率约为0.1667m/s. 关键词： 3单晶周期极化')" href="#">LiNbO₃单晶周期极化 反转电流 反转畴成核时间 反转畴纵向贯穿速率     

Broadcasting, Scalability, and Reconfigurability Aspects in an All-Optical Network Architecture

All-optical networks are a sound answer to the huge data traffic demand expected for the forthcoming information society. Interesting networking aspects are the broadcasting, scalability, and reconfiguration in an all-optical environment. These issues are addressed in the present article for an all-optical network called MATRIX, which is time slotted and uses packet switching. The architecture enables the all-optical interconnection of a large number of nodes with both a small number of wavelengths and wavelength continuity based on a consequent exploitation of wavelength-division multiplexing and space-division multiplexing (i.e., multiple fibers per cable are used). For an efficient use of the resources, each node is equipped with multiple transmitters and receivers, respectively. Two different broadcasting schemes are investigated. An analytical model is developed, and the corresponding simulation results are in good agreement. It is further shown how different networks of arbitrary size can be interconnected to larger all-optical network clusters, thereby providing scalability not only with respect to the number of nodes but also to the geographical extension. Finally, wavelength reassignments allow change of optical paths through the network in case of changing traffic patterns or network failures in order to best exploit the available network resources. The total number of possible configurations is determined by the theory of Latin Squares.     

Protection switching schemes of multi-granularity p-cycles in survivable WDM networks

In this paper,a novel concept of multi-granularity p-cycle is proposed.In conventional p-cycle concept,all on-cycle spans have the same capacity.However,in multi-granularity p-cycle,each on-cycle span could have different capacity.Results show that multi-granularity p-cycles are much more capacity-efficient and cost-effective than conventional p-cycles.We also propose two protection switching schemes for all types of p-cycle networks. One is wrapping protection, in which only two end nodes do real-time switching when a span failure happens.The other is steering protection,in which at most four nodes do real-time switching when a span fails.In steering protection switching scheme,the restoration path for the failure traffic demand has the least hops.     

飞控系统的光传网络的可靠性及实时性

调研了传统光传(FBL)网络的几种拓扑结构, 就可靠性和实时性两方面对它们进行了分析和比较。选择采用一个包含256个节点的mesh光交换网络, 它具有冗余拓扑结构能承受3处链路故障, 保证了网络的可靠性。以网络中发生链路故障的数目, 及多个故障同时发生时故障的邻近程度来衡量网络故障的严重性。对所有链路故障情形进行仿真, 测试端到端的通信延迟。仿真结果表明, 采用这种网络拓扑结构的光传网络, 即使在发生较为严重的故障的情况下, 端到端通信路由的跳数增加不大, 仍能满足实时通信的要求。     

Eleven-wavelength switchable fiber ring laser with a dispersion compensation fiber and a delayed interferometer

We demonstrate a fiber ring laser with a dispersion compensation fiber (DCF) and a delayed interferometer (DI) with temperature control, which is able to switch eleven wavelengths one by one. In ring cavity, DCF supplies different effective cavity lengths for different wavelengths, DI generates a wavelength comb corresponding to the ITU grid, a flat-gain erbium-doped fiber amplifier (EDFA) provides uniform gain for each lasting wavelength, and a semiconductor optical amplifier (SOA) not only acts as active modulator, but also alleviates homogeneous broadening effect of EDFA. Stable pulse trains with a pulsewidth about 40 ps at 10 GHz have been obtained by injecting external optical control signals into the laser. Wavelength switching process among eleven wavelengths is achieved by merely tuning an intracavity optical delay line.