光互连技术在信号处理中的某些应用

叙述了近年来在天津大学研究及开发光互连网络的情况。这些研究围绕着解决信号传输中的延迟和通信带宽,开展的研究工作有：完成包括64个处理器的光电混合处理器阵列系统;giga—bit／s机群系统光互连链路;在链路中采用时分复用技术(TDM),实现了“虚拟并行传输”;在链路中设计了硬件路由功能,并组成光环网;在网络系统中实现波长路由,并建立了波长路由双环网,采用该技术可以避免路由延迟;在光互连网络中应用了MEMS光开关,实现了星型一环形二级结构;用同步光传输技术实现了多通道数据传输卡。     

4×4自由空间光开关结构及其矩阵分析

光开关是全光通信网络中的一种重要的光无源器件。提出了一种4×4自由空间光开关的结构设计方法,并进行了矩阵理论分析。该4×4光开关具有新颖的光模块化结构,该光开关结构仅由偏振分束组合棱镜,λ／4波片,λ／2波片,直角棱镜,全反镜和偏振光调制器组成,对光开关的控制与输入光束的偏振态无关。所有的输出端口可以和输入端口无阻塞地互连交换。这种新型的光开关结构具有光学元件少,结构紧凑,模块化,与偏振无关的特点。基于4×4光开关的矩阵分析得到了路由控制表,为4×4光开关从任意输人端口到任意输出端口的路由控制状态提供了理论分析手段,从而可以方便地实现无阻塞地光交换开关矩阵的路由控制功能。     

与偏振无关的双向3×3光开关结构设计

利用传统成熟的偏振控制技术,设计了一种由偏振光分束器、相位型空间光调制器、反射镜和四分之一波片构成的3×3光开关。该光开关具有结构紧凑规整、功能的实现与信号光的偏振态无关以及可以完成双向交换等特点。根据其路由控制表对该3×3光开关交换模块功能的实现进行了分析,结果表明,通过对各相位型空间光调制器状态的调整,控制通过其信号光的偏振态,完成信号光的路由,该交换模块可以完成输入信号光的全排列无阻塞输出与交换。同时,该交换模块具有一定的扩容和重构能力,对于构建大规模的交换矩阵具有一定的作用。     

Optical time division multiplexing at 160 Gbps using MZI switching

Many lower-speed data streams can be multiplexed into one high-speed stream by means of optical time division multiplexing (OTDM), such that each input channel transmits its data in an assigned time slot. The simulation is performed by a fast multiplexer switch (mux). The routing of different data streams at the end of the TDM link is performed by a demultiplexer switch (demux) and this demultiplexer is employed using MZI switch as it consists a semiconductor optical amplifier (SOA) and an optical coupler. In this paper four channel OTDM is simulated at 40 Gbit/s and further the impact of the signal power, pulse width and control signal power on BER is investigated.     

Polarization-independent bidirectional 4×4 optical switch in free space

Optical switches play an important role in all optical communication networks and multiprocessor computer systems. The 2×2 and 4×4 optical switches are the basic units of large-scale switch matrices. Using a conventional polarization control method, the optical switch system and structure is optimized, and a novel optical switch is proposed, which has the advantages of relatively low crosstalk and insertion loss, compact and simple construction, higher performance and cost effectiveness. First, a novel 2×2 optical switch is proposed using phase spatial light modulator (PSLM), polarizing beam splitter (PBS) and mirror. This configuration uses fewer optical components, is compact in structure, efficient in performance, and insensitive to polarization of the signal beam. Second, a new optical experimental module of 4×4 optical switch is presented by cascading a 2×2 optical switch. The routing method of polarization-independent bidirectional 4×4 optical switch is investigated. Finally, the operational characteristics of the polarization-independent bidirectional 2×2 and 4×2 optical switches are discussed in detail.     

与偏振无关双向2×2和4×4自由空间光开关

利用成熟的偏振控制技术，设计了一种由偏振光分束器、相位型空间光调制器和反射镜构成的2×2光开关，该光开关所用器件少，具有结构简单紧凑、控制灵活方便、功能实现与信号光的偏振态无关以及可以双向交换等特点；在此基础上通过2×2光开关的串连，设计了一种与偏振无关的双向4×4光开关的实验模块，根据其路由选择与控制方法，得到了4×4光开关实现信号光全排列无阻塞输出与交换对应的路由状态表，并对该实验模块的功能实现进行了详细的分析与讨论。     

全混洗交换Omega互连网络的光学实现

本文提出了一种由左、右全混洗和空间光开关列阵组成的等效Omega网络;成功地设计了一种实现全混洗互连的低损耗,等程的光学组合棱镜.由两块光学组合棱镜和空间光开关列阵组合成的光学系统实现了全混洗交换光学互连网络,该光学互连网络已在实验中得到了证实.     

Optical implementation of (3, 3, 2) regular rectangular CC-Banyan optical network

CC-Banyan network plays an important role in the optical interconnection network. Based on previous reports of (2, 2, 3) the CC-Banyan network, another rectangular-Banyan network, i.e. (3, 3, 2) rectangular CC-Banyan network, has been discussed. First, according to its construction principle, the topological graph and the routing rule of (3, 3, 2) rectangular CC-Banyan network have been proposed. Then, the optically experimental setup of (3, 3, 2) rectangular CC-Banyan network has been designed and achieved. Each stage of node switch consists of phase spatial light modulator (PSLM) and polarizing beam-splitter (PBS), and fiber has been used to perform connection between adjacent stages. PBS features that s-component (perpendicular to the incident plane) of the incident light beam is reflected, and p-component (parallel to the incident plane) passes through it. According to switching logic, under the control of external electrical signals, PSLM functions to control routing paths of the signal beams, i.e. the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. Finally, the discussion and analysis show that the experimental setup designed here can realize many functions such as optical signal switch and permutation. It has advantages of large number of input/output-ports, compact in structure, and low energy loss. Hence, the experimental setup can be used in optical communication and optical information processing.     

光突发交换的交换控制策略和光缓存配置

光突发交换是面向下一代互联网的光交换模式.讨论了异步光突发交换系统的交换控制策略以及相应光缓存的优化配置策略.除了传统预约模式的交换策略,还研究了非预约和改进型预约模式,它们的性能评估由计算机仿真给出.结果表明:在条件相当情况下,改进型预约模式具有最低的丢包率.同时光缓存的配置对上述几类交换控制策略的性能都有很大影响,仿真结果指出:光缓存的粒度对系统性能具有重要影响,所讨论的几类交换模式都存在最佳时延粒度,研究结果对光交换矩阵的设计有指导意义.     

Design and Performance Evaluation of Optical Ethernet Switching Architecture with Liquid Crystal on Silicon-Based Beam-Steering Technology

A non-blocking optical Ethernet switching architecture with liquid crystal on a silicon-based beam-steering switch and optical output buffer strategies are proposed. For preserving service packet sequencing and fairness of routing sequence, priority and round-robin algorithms are adopted at the optical output buffer in this research. Four methods were used to implement tunable fiber delay modules for the optical output buffers to handle Ethernet packets with variable bit-rates. The results reported are based on the simulations performed to evaluate the proposed switching architecture with traffic analysis under a traffic model captured from a real-core network.     

Wavelength division multiplexed loop buffer memory based optical packet switch

Photonic all-optical switching is widely considered as one of the technique to utilize the enormous optical bandwidth. Optical packet switching provides high speed, data rate transparency, data format transparency, efficient use of bandwidth and flexibility. To resolve the conflict during contention, packets are needed to be buffered. Due to the lack of optical RAM, fiber delay lines (FDLs) are the most suited option to buffer the packets. This paper proposes new optical packet switch architecture alongwith feedback shared buffer utilizing the advantage of WDM loop buffer memory. The loop buffer module used in this switch architecture is a new approach towards WDM buffering of packets. The mathematical modeling is done to validate the results obtained from simulation.     

AWG and EDFA based optical packet switch using feedback shared loop buffer memory

Optical packet switching provides high speed, data rate/format transparency, efficient use of bandwidth and flexibility. The major problem in the implementation of “all-optical” switching is contention which occurs when two or more packets arrive at the same time for the same destination. To resolve the contention, we have proposed an optical packet switch architecture based on WDM loop buffer memory in the feedback configuration. In that architecture, the contending packets are stored in a loop buffer module, and routed in the free time slots. The buffering duration in the recirculating loop is limited by a circulation limit. The analysis was been done to obtain the maximum number of allowed circulations. This paper proposes improved version of that optical packet switch architecture, to increase the number of maximum allowed circulations. The modification is done either by adding an extra erbium doped fiber amplifier (EDFA) in the original switch or by replacing the core space switch with arrayed waveguide grating (AWG). The performance analysis has been done by the simulations.     

Ultrafast All-Optical Serial-to-Parallel Conversion and Its Application to Optical Label Processing

A novel scheme for all-optical serial-to-parallel conversion (SPC) is proposed for label recognition of ultrafast asynchronous burst optical packets. Compact SP converter modules were developed using a fiber array or a surfaceemitting planar lightwave circuit, and 1-Tbit/s and 40-Gbit/s SPC for 16-bit optical packets is demonstrated using the modules. The key device in the converter is a spin-polarized surface-reflection all-optical switch (LOTOS) with an ultrafast switching time (250 fs) and an extremely high on/off ratio (>30 dB). Label recognition of 40-Gbit/s 16-bit burst-mode optical packets is experimentally confirmed using an optical clock-pulse generator and a complementary metal-oxide-semiconductor (CMOS) electronics circuit as well as the all-optical SP converter. 1 x 4 self-routing is also demonstrated using 2-channel control signals generated from the CMOS circuit according to a routing table.     

On the optically transparent WDM ATM multicast (3M) switches

We describe an architecture design and implementation of the optically transparent wavelength-division-multiplexed (WDM) asynchronous-transfer-mode (ATM) multicast (3M) switch for all optical high-speed networks. By using the WDM techniques, the wire complexity in both the switch fabric and the concentrator can be reduced from O(N²) to O(N). By using integrated photonic devices and highly parallel processing and pipeline control electronic circuits the switch is handling signals at the cell level (53 bytes) instead of at the bit level and can achieve very high speed and high throughput operation. Several key components, including a cell synchronizer, a photonic VCI over-writting unit, a wavelength converter, an optical concentrator, and a WDM memory, have also been proposed to realize this 3M switch. All of the photonic devices are highly integratable and are very suitable for building future large-scale, low-cost photonic ATM switches. A combination of both the ATM and WDM techniques will provide an ultimate version for optical networking with almost unlimited capacity.     

Cutting-Edge Technologies on Broadband and Scalable Photonic-Network—Packet switched networks based on all-optical label processing—

Ultra-high speed all-optical label processing methods are proposed and experimentally demonstrated. These methods dramatically increase the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are expressed as an application of optical processing technologies. First, the 40 Gbit/s/port OPS prototype with all-optical label processor, optical switch, optical buffer, and electronic scheduler is described. The feasibility of OPS networks is verified by experimental demonstrations.     

Optically controlled loop buffer using a SOA loop mirror and a circulator based reflector

In this paper, an optically controlled loop buffer is proposed and experimentally demonstrated. It utilizes a semiconductor optical amplifier (SOA) based loop mirror as a fast switch to realize the writing and reading of packets within this buffer and a circulator based optical reflector to achieve internal re-circulations. By adding fibers with different lengths between the loop mirror and the circulator, variable delay time per circulations can be obtained. We also demonstrate the performance of the 2.5 and 10 Gb/s data packets in this buffer structure, as well as the influence of the two different control signal formats on the packet signal degradation during buffering. This loop buffer has the merits of low cost and improved performance compared to other similar loop buffer structures. According to the obtained results, the achieved number of circulations is greatly increased.     

Large capacity optical router based on arrayed waveguide gratings and optical loop buffer

This paper presents optical packet switch architecture with large buffering capacity for the contention resolution of the packets. The main feature of the architecture is no requirement of Demux/Mux and splitter/combiner which are used in most of the other loop buffer based switch architectures. Therefore physical loss of the architecture is very less, and switch performance is not limited by the physical degradation of the signal. In the buffer, TWCs/SOAs are replaced by Tunable Fiber Bragg Gratings (TFBGs). The use of TFBGs inside the buffer is a novel approach towards buffering structure. The architecture presented here can be modeled as output queue buffer scheme. This paper investigates the advantages of the proposed architecture over the earlier architecture. The performance of the architecture in terms of physical layer parameters (loss analysis, power analysis and noise analysis), packaging volume and optical cost is done.     

具有旋转连接功能的双层光互连网络设计

在设计的双层光互连网络中,上层网络是星型连接,依靠数字路由结点进行通信.单通道最大传输速率为1.4 Gbps,数字路由结点吞吐率大于10 Gbps,底层为网络接口卡和结点机连成的环形网,峰值传输速率为1.056 Gbps.在底层网络中个别结点机与传感器之间配置有光纤旋转连接器,可传输动态数据.经计算,环网内最大通信延迟时间小于5.292 μs,互连网络的平均通信延迟时间为11.03 μs,环形网络的最大数据传输带宽为50 Mbit/s.     

光互连网络中四功能交换开关研究

由节点开关单元按照一定的连接规则所构成的光互连网络,在全光通信和光信息处理中具有重要的应用。基于节点开关一般实现光信号的直通和交换功能的特点,利用成熟的偏振光控制技术,通过位相型空间光调制器对信号光偏振态的控制,完成信号的路由和开关动作,从而设计出具有直通、交换、上播和下播功能的节点交换开关。与传统设计思想相比,该方法不仅能够充分利用信号光的能量,有效的减少光能量的损耗,而且还具有与偏振无关等特点。该四功能交换开关,对于优化和拓展光互连网络的结构和功能具有一定的意义。     

Design of Two-Dimensional Optimized Banyan Networks

A smart two-dimensional optical Banyan network is proposed. Polarization switching logic of light is applied for the design of this network. The main element for the connections of the network is an optical crossbar switch that is composed of a half-wave plate, a programmable polarization switch, and a couple of birefringent plates. By the proposed optical crossbar switches, all permutations of the link patterns required in the network are generated due to the optimized design of the switching logic. As a result, complicated routing control of ordinary Banyan networks is much reduced and a simple two-dimensional optical Banyan network with straight interconnections between successive stages of the networks can be realized.