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.     

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.     

Modeling and design of WDM optical buffers in asynchronous and variable-length optical packet switches

This paper aims to analyze the influence of wavelength conversion on the design of optical fiber delay line (FDL) buffers in a wavelength-division multiplexing (WDM) packet switch. We focus on the network scenario that variable-length packets arrive at the optical switch asynchronously. Through a detailed analysis of the behaviors of packets in the WDM FDL buffer, an approximate analytical traffic model is established. And the theoretical model is proved to be reasonable by simulations. Based on the model, it is clear that, under the same traffic load per wavelength channel, the utilization of tunable wavelength converters (TWCs) to resolve the output contention significantly reduces the number of fiber delay lines (FDLs) in optical buffers, and to achieve a given packet loss probability under a certain number of FDLs, the required number of tunable wavelengths can be predicted. The model can also estimate the optimal value of the basic time unit of the FDLs, and examine the influence of WDM on the optimal value. Finally, the impact of wavelength conversion on the optical switch size is analyzed. To the best of our knowledge, it is the first time that modeling on this problem is presented.     

An optical multicast packet switching architecture shared with limited-range multi-wavelength converter and full-range wavelength converters

Optical packet switch with multicast capability can inspire a broad range of multipoint to multipoint applications in future optical networks. An optical multicast packet switching architecture, equipped with feedback shared small number of limited-range multi-wavelength converters (LMWCs) and output shared some full-range wavelength converters (FRWCs), is proposed for a wavelength-division multiplexed optical multicast network to improve multicast performance in the paper. The FRWCs are used to overcome the performance degradation in terms of packet loss probability due to only use LMWCs. In the architecture, the two converters are shared by all the multicast packets importing to the optical multicast switch node. A maximum bipartite matching with minimum edges weights strategy was designed to employ fewer wavelength converters and avoid useless degradation of optical signal quality for the architecture to improve the node performance. The simulation results show that the proposed architecture and its wavelength converter scheduling algorithm can reduce the multicast packet loss probability with relatively lesser wavelength conversion cost.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Wideband optical comb generation using an injection-locked feedback loop

This paper presents a novel circuit for wideband optical comb generation which will be useful in DWDM applications. The injection-locked feedback loop broadens the bandwidth of the optical comb. The injection-locked laser diodes perform amplification, bandpass filtering as well as laser RIN suppression. Several hundred GHz bandwidth optical comb can be generated by this circuit within a reasonable power envelope.     

Experimental demonstration and cascadability analysis of a tunable optical buffer based on a re-circulating loop consisting of optical SSB modulator and FBG filter

We demonstrate a tunable optical buffer with variable time delays for label switching applications using an optical single sideband modulator in a fiber Bragg grating-filter loop. This optical buffer realizes payload storage with optional wavelength conversion function, providing flexibility in packet router design. Small sensitivity penalty is observed in our experiment after the payload circulating in the buffer loop three times. The cascadability of the tunable optical buffer is investigated. We provide analysis of the optical signal to noise ratio degradation due to accumulated amplified spontaneous emission noise, and the penalty caused by loss ripple and group delay ripple of the fiber Bragg grating.     

A novel all-optical label processing based on multiple optical orthogonal codes sequences for optical packet switching networks

This paper proposes an all-optical label processing scheme that uses the multiple optical orthogonal codes sequences (MOOCS)-based optical label for optical packet switching (OPS) (MOOCS-OPS) networks. In this scheme, each MOOCS is a permutation or combination of the multiple optical orthogonal codes (MOOC) selected from the multiple-groups optical orthogonal codes (MGOOC). Following a comparison of different optical label processing (OLP) schemes, the principles of MOOCS-OPS network are given and analyzed. Firstly, theoretical analyses are used to prove that MOOCS is able to greatly enlarge the number of available optical labels when compared to the previous single optical orthogonal code (SOOC) for OPS (SOOC-OPS) network. Then, the key units of the MOOCS-based optical label packets, including optical packet generation, optical label erasing, optical label extraction and optical label rewriting etc., are given and studied. These results are used to verify that the proposed MOOCS-OPS scheme is feasible.     

基于Norland紫外固化胶的热光开关器件

采用新型聚合物材料Norland紫外固化胶（NOA）制备了聚合物M-Z型热光开关器件。对NOA薄膜材料的光学性质进行了表征,采用感应耦合等离子体（ICP）方法制备出形貌良好的波导器件。测得在1 550 nm波长下,长2.2 cm的直波导插入损耗为8.3 dB。在电极上施加直流信号,测得热光开关的消光比为11 dB,驱动功率为85 mW。引入直流偏置网络,获得了器件的开关特性曲线,测得开关器件的上升时间为1.085 ms,下降时间为489.5μs。实验结果表明：NOA材料在热光开关及其它聚合物光波导集成器件的制备中具有很大的应用潜力。     

Design of ternary Multiplexer and De-multiplexer circuit with optical nonlinear material (OPNLM) based switch

Multiplexer and De-multiplexer operation play a very important role in all-optical computation, communication and control. Considerable number of multiplexing – de-multiplexing scheme in digital optical processing have already been reported. A design of all-optical ternary Multiplexer De-multiplexer circuit with optical nonlinear material (OPNLM) based switch is proposed and described in this paper. Different logic states have been represented by different polarization states of light. Logical simulation is also included here. This circuit will be useful in future all-optical multi-valued logic based computing and information processing system.     

Proposal for loadable and erasable optical memory unit based on dual active microring optical integrators

A novel approach for loadable and erasable optical memory unit based on dual microring optical integrators is proposed and studied. The optical integrator, which can generate an optical step function for data storing, is synthesized using active media for loss compensation and a tunable phase shifter for data reading at any time. The input data into the memory is return-to-zero (RZ) signal, and the output data read from the memory is also RZ format with a narrower pulse width. An optical digital register based on the proposed optical memory unit is also investigated and simulated, which shows the potential for large scale data storage and serial-to-parallel data conversion. A great number of such memory units can be densely integrated on a photonic circuit for future large scale data storage and buffer.     

Improvement of switching properties and cascadability of an ultra-fast reconfigurable optical crosspoint switch matrix using DPSK payloads

In this paper, we demonstrate mitigation of pattern-induced degradation in an optical crosspoint switch (OXS) matrix by utilizing differential phase shift keying (DPSK) modulation format. We experimentally demonstrate 4 × 4 unicast optical packet switching and dynamic reconfiguration for 4-channel, 200 GHz spacing of RZ-DPSK payloads. Reconfigurable time as fast as 2 ns is achieved owing to the optimized control circuit and device fabrication. The power and wavelength dependence are obtained for the RZ-DPSK payload. We also investigate the cascadability of the OXS based on re-circulating loops. Due to the great suppression of the pattern effect in OXS, DPSK has shown dramatical improvement of switching properties compared to conventional ON-OFF keying (OOK) signal. The DPSK payload can outperform OOK for 3.2 dB after 9 hops optical switching.     

Optical computation based on nonlinear total reflectional optical switch at the interface

A new scheme of binary half adder and full adder is proposed. It realizes a kind of all-optical computation which is based on the polarization coding technique and the nonlinear total reflectional optical switches.      

Electro-optic polymer assisted optical switch based on silicon slot structure

One kind of electro-optic polymer assisted Mach-Zehnder optical switch based on silicon slot structure is presented in this paper. The interference arms of the switch are slot structures instead of regular single-mode waveguides. By filling electro-optic material in the void slot of the arms, direct electro-optic modulation can be introduced. Theoretical model and detailed analysis are given in this paper. The length-independent product V_πL is about 74 mV cm when slot width is 100 nm, and 37 mV cm when slot width is 50 nm, when the polymer with a electro-optical coefficient of γ₃₃ = 130 pm/V is assisted. An ultralow energy consumption of only 37 fJ/bit is achievable, and the turn-on time of the switch is less than 1.5 ps.     

Performance comparison of wavelet packet transform based and conventional coherent optical OFDM transmission system

In this work, the performance of WPT-COOFDM system is investigated and compared to that of FFT-COOFDM system over a fiber link. Simulation results show that the longer length of wavelet filters achieve a better performance, whereas the complexity is higher. For different wavelet mother functions employed in WPT-COOFDM systems, the chromatic dispersion robust of John64E wavelet outperforms that of other wavelets, and which could be a viable alternative for coherent optical OFDM to be considered in short distance transmissions. The simulation results also show that most of the developed wavelet mother functions mainly for image processing are not suitable for COOFDM transmission for its sensitivity to chromatic dispersion.     

Flexible integration of optical switch with optical power splitting and attenuating functions for optical fiber-based networking applications

A flexible integration of optical switch with optical power splitting and attenuating functions has been proposed to optimally serve optical fiber-based networking applications. In this switch, an etched binary-slope sidewall reflector is electrostatically actuated in and out of the plane to manipulate optical signals between input and output optical fibers. The fabrication process is a simple combination of a bulk-silicon micromachining process and silicon-to-glass anodic bonding where fiber alignment grooves, reflectors and actuators are fabricated on the same silicon substrate. Ball-lensed fibers are assembled with the device to achieve high coupling efficiency. Performances of the fabricated devices are measured and discussed. The switching time is less than 9 ms at 31 V. The excess loss of the device is less than 3 dB and the controllable attenuation range is up to 38 dB at 139 V, respectively. Moreover, polarization-dependent loss is less than 0.7 dB in the whole attenuation and splitting range.     

Feed-Forward- and Shared-Buffer-Based Optical Packet Switch Architecture

Abstract

This architecture incorporates wavelength-routed loop-buffer modules in the feed-forward configuration, and the buffering in these modules is recirculating in nature, using shared memory. The signal quality will deteriorate during each revolution, due to the insertion loss of the various optical components; therefore, it will impose a limit on the number of circulations that a packet can take in the buffer before its correct reception. Generally, this limit has not been considered in the past, but one should have to take care of it in the current scenario for the actual switching systems.     

基于半导体光放大器中非线性偏振旋转效应单一光缓存环全光时隙交换处理能力研究

对基于半导体光放大器(SOA)中非线性偏振旋转效应(NPR)效应的单一光缓存环多数据包的全光时隙交换(TSI)处理能力进行了理论和实验研究,在使用归纳法导出单一缓存环实现多数据包全光时隙(TSI)必要条件的基础上,针对各种全光TSI操作要求得出了相应光数据包的调度方案,在实验上,以基于SOA中NPR效应的单一光缓存环实验系统,开展了多数据包全光TSI操作的实验研究,根据上述光数据包理论调度方案进行相应系统参数设定,进行了速率为10 Gb/s的3个和4个数据包的全光TSI实验,实验结果与理论预期相符合,研究成果为减少昂贵SOA元件的用量、简化基于光缓存环全光TSI系统的结构提供了可靠依据,对推进全光TSI技术的发展具有重要意义。     

Dynamical switching and memory via incoherent pump assisted optical bistability

We analyze the dynamical behavior of all-optical switching and memory based on tunable optical bistability in a three-level Λ-type atomic system driven by a probe field circulating in an optical ring cavity, a coherent coupling field and an incoherent pump field outside cavity. Owing to the incoherent pump process, the absorption and Kerr nonlinearity near the atomic resonance change dramatically as a result of varied population distribution and atomic coherence, and then the switch-up and switch-down thresholds, as well as the width (or area) of bistable curve, can be manipulated effectively. By tuning the intensity of either coherent coupling field or incoherent pump field, we can make the system output flip between the lower and upper branches of different bistable hysteresis loops while the cavity input keeps to a constant value. Accordingly, all-optical switching and memory can be implemented via dynamical control of the bistable behavior under the assistance of incoherent pump. The proposed scheme can find potential applications in all-optical communication and computation.     

Investigation on performance of all optical buffer with large dynamical delay time based on cascaded double loop optical buffers

Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dynamical delay time is carried out based on cascaded double loop optical buffers (DLOBs). It is found that pulse distortion can be restrained by a negative optical control mode when the optical packet is in the loop. Noise analysis indicates that it is feasible to realise a large variable delay range by cascaded DLOBs. These conclusions are validated by the experiment system with 4-stage cascaded DLOBs. Both the theoretical simulations and the experimental results indicate that a large delay range of 1-9999 times the basic delay unit and a fine granularity of 25 ns can be achieved by the cascaded DLOBs. The performance of the cascaded DLOBs is suitable for the all optical networks.