一种改进的空分交换型OPS节点结构及其性能分析

提出了一种改进的空分交换型光分组交换(OPS)节点结构--共享反馈和输出缓存(SFOB)结构.该结构不但结合了基本的OPS节点结构的优势(将反馈缓存与共享缓存组合配置),而且在缓存使用方面改进了每根光纤延迟线(FDL)独立使用的做法,增加了将反馈缓存和共享缓存中两根FDL串联使用的机制,并据此设计了相应的缓存调度算法.最后使用计算机仿真的方法对该结构在随机网络负载下的丢包率性能进行了研究.仿真结果表明在相同缓存容量条件下该结构比传统的共享存储光分组(SMOP)交换结构具有更好的交换性能.     

Packet communications via satellite with buffer and multiple downlinks

Abstract

Previous results on packet communications via a processing satellite with n slotted ALOHA uplinks and m TDM downlinks are extended to include a buffer in the switching node. Throughput and delay at equilibrium are obtained, and an alternative derivation for the expected number of retrials for any packet is also given. It is demonstrated through examples that on‐board storage provides results equivalent to multiple uplinks in obtaining gains in throughput, efficiency, and margin against instability. The analysis of system performance with respect to the number of uplinks, the number of downlinks, and the size of the on‐board storage is now complete.     

Optical signal processing using integrated multi-element SOA-MZI switch arrays for packet switching

The use of discrete but interconnected SOA-MZI switches for performing logical and highly functional processing tasks, demonstrating the multi-functional potential of the photonic switching elements is discussed. An all-optical 3R burst-mode receiver consisting of four SOA-MZI switches and operating error-free with 40-Gb/s optical bursts, proving that interconnection of multiple switching units can lead to the realisation of key network node functionalities offering increased intelligence at the physical layer is presented. In order to allow for easier interconnectivity between the SOA-MZI switches and to provide compactness and cost effectiveness to the developed subsystems, the integration of multiple switches into the same platform is proposed. To this end, the implementation of the first integrated quadruple SOA-MZI switch array is reported, increasing the integration density level and reducing packaging and pigtailing costs. Finally, possible applications of integrated multiple switch arrays are discussed, indicating their suitability for producing compact circuits performing common processing tasks in a multi-wavelength environment, as well as their potential to lead to the development of an all-optical high-speed packet switched node by implementing critical packet switching functionalities in a compact and efficient way.     

Polarization-controlled multistage switch based on polarization-selective computer-generated holograms

We describe a polarization-controlled free-space optical multistage interconnection network based on polarization-selective computer-generated holograms: optical elements that are capable of imposing arbitrary, independent phase functions on horizontally and vertically polarized monochromatic light. We investigate the design of a novel nonblocking space-division photonic switch architecture. The multistage-switch architecture uses a fan-out stage, a single stage of 2 x 2 switching elements, and a fan-in stage. The architecture is compatible with several control strategies that use 1 x 2 and 2 x 2 polarization-controlled switches to route the input light beams. One application of the switch is in a passive optical network in which data is optically transmitted through the switch with a time-of-flight delay but without optical-to-electrical conversions at each stage. We have built and characterized a proof-of-principle 4 x 4 free-space switching network using three cascaded stages of arrayed birefringent computer-generated holographic elements. Data modulated at 20 MHz/channel were transmitted through the network to demonstrate transparent operation.     

Design and analysis of hybrid optical and electronic buffer based optical packet switch

Optical packet switching has the potential to be used as next generation data transfer technology. This paper, introduces an Arrayed Waveguide Gratings (AWG) switch where hybrid buffer (electronic + optical) is used for the buffering of contending packets. Power budget analysis has been carried out under various switch designs. Comparison of optical and electronic buffering is done in terms of power required for the correct operation of the switch. Energy consumption per bit is also evaluated for both optical and electronic buffers for various buffering time ranges from nano-seconds to milli-seconds. In the switch analysis it has been found that, amplified switch requires five times less power, in comparison to un-amplified switch for correct operation. Energy consumption analysis reveals that for shorter duration storage, optical buffer would be a better choice.     

256 × 256 Turnover-type free-space multichannel optical switch based on polarization control using liquid-crystal spatial light modulators

Free-space multichannel optical switches using polarization control are attracting interest for future telecommunication networks and interconnection networks in computers. We describe a switching architecture, the turnover type, for such free-space multichannel optical switches. The architecture makes it possible to realize a large-scale and transparent optical switch that is also compact. A 256 × 256 multichannel optical switch based on the architecture is designed and fabricated. To the authors' knowledge, the channel number of the fabricated switch is the largest yet reported among rearrangeable optical switches. Switching operation and signal transmission at 400 Mbits/s are performed successfully with a prototype switch.     

Wavelength-division-multiplexing optical packet switch with heterogeneous wavelength conversion capabilities

Among the wavelength-division-multiplexing (WDM) optical packet switches (OPSs) using wavelength converters (WCs), a shared-per-node switch architecture has been considered as a way to utilize WCs efficiently. We propose a new switch control algorithm for the architecture. The proposed algorithm, different from previous algorithms, focuses on using the heterogeneous WC blocks (HeWCBs), where a HeWCB consists of WCs with different wavelength conversion degrees (WCDs). The results show that the WDM OPS architecture using HeWCBs reduces the number of WCs with a higher WCD, while minimizing the packet loss from wavelength contention at outbound links.     

Near‐Infrared Annihilation of Conductive Filaments in Quasiplane MoSe2/Bi2Se3 Nanosheets for Mimicking Heterosynaptic Plasticity

It is desirable to imitate synaptic functionality to break through the memory wall in traditional von Neumann architecture. Modulating heterosynaptic plasticity between pre‐ and postneurons by another modulatory interneuron ensures the computing system to display more complicated functions. Optoelectronic devices facilitate the inspiration for high‐performance artificial heterosynaptic systems. Nevertheless, the utilization of near‐infrared (NIR) irradiation to act as a modulatory terminal for heterosynaptic plasticity emulation has not yet been realized. Here, an NIR resistive random access memory (RRAM) is reported, based on quasiplane MoSe₂/Bi₂Se₃ heterostructure in which the anomalous NIR threshold switching and NIR reset operation are realized. Furthermore, it is shown that such an NIR irradiation can be employed as a modulatory terminal to emulate heterosynaptic plasticity. The reconfigurable 2D image recognition is also demonstrated by an RRAM crossbar array. NIR annihilation effect in quasiplane MoSe₂/Bi₂Se₃ nanosheets may open a path toward optical‐modulated in‐memory computing and artificial retinal prostheses.     

First principle study of the self‐switching characteristics of the guanine based single optical molecular switch using carbon nanotube electrodes

The switching property of an optical single molecular switch based on a single DNA molecule guanine with a single walled carbon nanotube electrode has been investigated using density functional theory along with non‐equilibrium Green''s function based first principle approach. The semi‐empirical model of this single bio‐molecular switch has been operated at an ultra‐high 25 THz frequency in mid‐UV range. This single bio‐molecule comprises switching activity upon UV photo‐excitation. The influence of the highest occupied molecular orbital and lowest unoccupied molecular orbital gap and the quantum ballistic transmission into the switching activity are discussed in detail in this study. It has been observed that the maximum ON–OFF ratio, i.e. 327 is obtained at +0.8 V bias voltage. Theoretical results show that current through the twisted form is sufficiently larger than the straightened form, which recommends that this structure has smart prospective application in the future generation switching nanotechnology.Inspec keywords: molecular electronic states, density functional theory, ab initio calculations, DNA, organic compounds, molecular electronics, Green''s function methods, molecular biophysics, single‐wall carbon nanotubes, optical switches, orbital calculationsOther keywords: nonequilibrium Green''s function, semiempirical model, single bio‐molecular switch, UV photo‐excitation, lowest unoccupied molecular orbital gap, first principle study, single optical molecular switch, switching property, optical single molecular switch, single DNA molecule guanine, single walled carbon nanotube electrode, density functional theory, highest occupied molecular orbital gap, switching nanotechnology     

Fast response and low power consumption 1×2 thermo-optic switch based on dielectric-loaded surface plasmon polariton waveguides

Abstract

In this paper, we present a 1 × 2 thermo-optic (TO) switch based on the integration of the dielectric-loaded surface plasmon polariton (SPP) waveguides with the silicon nanowires. Liquid-curable fluorinated resin (LFR) made of perfluorinated polymer was adopted as the ridge, which has a TO coefficient twice more than that of polymethyl methacrylate, leading to a significant decrease in the power consumption. It was shown that the response time of the dielectric-loaded SPP waveguide could be improved through optimizing the dimensions of the LFR polymer ridge without loss of relative high figure of merit and large confinement factor. Performance characteristics of such a 1 × 2 TO switch operating at a telecom wavelength of 1550 nm was investigated theoretically from the analysis of both heat and optical fields. The results reveal that a switching power as low as 7 mW and an extremely short switching time (with rise time of 3 μs and fall time of 6.7 μs) could be achieved with the proposed dielectric-loaded SPP-based 1 × 2 TO switch. In addition, the crosstalk could be enhanced to at least 40 dB with the applied power of 7 mW at the wavelength of 1550 nm, and it could be retained to be above 20 dB in the wavelength spectrum of 1500–1600 nm during the on/off state.     

Hybrid Flexible Resistive Random Access Memory‐Gated Transistor for Novel Nonvolatile Data Storage

Here, a single‐device demonstration of novel hybrid architecture is reported to achieve programmable transistor nodes which have analogies to flash memory by incorporating a resistive switching random access memory (RRAM) device as a resistive switch gate for field effect transistor (FET) on a flexible substrate. A high performance flexible RRAM with a three‐layered structure is fabricated by utilizing solution‐processed MoS₂ nanosheets sandwiched between poly(methyl methacrylate) polymer layers. Gate coupling with the pentacene‐based transistor can be controlled by the RRAM memory state to produce a nonprogrammed state (inactive) and a programmed state (active) with a well‐defined memory window. Compared to the reference flash memory device based on the MoS₂ floating gate, the hybrid device presents robust access speed and retention ability. Furthermore, the hybrid RRAM‐gated FET is used to build an integrated logic circuit and a wide logic window in inverter logic is achieved. The controllable, well‐defined memory window, long retention time, and fast access speed of this novel hybrid device may open up new possibilities of realizing fully functional nonvolatile memory for high‐performance flexible electronics.     

All-optical 100-Gbit/s word packet time-division-multiplexed access node in a looped-back configuration: enabling technologies for sequential add-drop functionality

We experimentally demonstrate the adding, dropping, and passing through of 100-Gbit/s word packets in a looped-back all-optical time-division-multiplexed (TDM) access node. Packets are routed with a 17-dB contrast ratio and demultiplexed with a 20-dB contrast ratio. This node uses short 100-Gbit/s words to demonstrate its potential to process data packets from multiple sources and to perform packet switching in a multinode ring network configuration. The ability to tolerate timing jitter as well as varying input signal characteristics is essential to an all-optical access node in a multinode network. For 2-ps input pulses, the header processor has a timing window of ~5 ps, and the demultiplexer has a timing window of ~5.5 ps. This allows for tolerance to bit-to-bit timing jitters or to an increase in the pulse width of as much as 3 ps. Packet-to-packet timing jitter is detected and compensated by the technique used to synchronize the local source to each packet. The key enabling technologies of an all-optical TDM packet add-drop multiplexer are discussed, including an erbium-doped fiber laser, a nonlinear optical loop mirror logic gate, self-synchronization to incoming packets with a fast-saturation/slow-recovery gain element followed by an intensity discriminator, a two-wavelength nonlinear optical loop mirror demultiplexer, and synchronization of new packets to the network packet rate with a phase-locked loop. The local source is automatically synchronized to the incoming packet, because it uses an extracted pulse from the packet, which has a contrast ratio of >20 dB to the rest of the packet. Finally, new packets are added by use of a local laser and a synchronization method, which gives a timing jitter of ~1 ps. Using a statistical method of measuring Q value with picosecond resolution, we show that a header processor with two cascaded logic gates has a Q value of 7.1 with a 95% confidence level.     

An Ultrabroadband Mid‐Infrared Pulsed Optical Switch Employing Solution‐Processed Bismuth Oxyselenide

Pulsed lasers operating in the mid‐infrared (3–25 µm) are increasingly becoming the light source of choice for a wide range of industrial and scientific applications such as spectroscopy, biomedical research, sensing, imaging, and communication. Up to now, one of the factors limiting the mid‐infrared pulsed lasers is the lack of optical switch with a capability of pulse generation, especially for those with wideband response. Here, a semiconductor material of bismuth oxyselenide (Bi₂O₂Se) with a facile processibility, constituting an ultrabroadband saturable absorber for the mid‐infrared (actually from the near‐infrared to mid‐infrared: 0.8–5.0 µm) is exhibited. Significantly, it is found that the optical response is associated with a strong nonlinear character, showing picosecond response time and response amplitude up to ≈330.1% at 5.0 µm. Combined with facile processibility and low cost, these solution‐processed Bi₂O₂Se materials may offer a scalable and printable mid‐infrared optical switch to open up the long‐sought parameter space which is crucial for the exploitation of compact and high‐performance mid‐infrared pulsed laser sources.     

Switching near a network of rotating nodes

We study the dynamics of a Z ₂ ⊕ Z ₂-equivariant vector field in the neighbourhood of a heteroclinic network with a periodic trajectory and symmetric equilibria. We assume that around each equilibrium the linearization of the vector field has non-real eigenvalues. Trajectories starting near each node of the network turn around in space either following the periodic trajectory or due to the complex eigenvalues near the equilibria. Thus, in a network with rotating nodes, the rotations combine with transverse intersections of two-dimensional invariant manifolds to create switching near the network; close to the network, there are trajectories that visit neighbourhoods of the saddles following all the heteroclinic connections of the network in any given order. Our results are motivated by an example where switching was observed numerically by forced symmetry breaking of an asymptotically stable network with O(2) symmetry.     

Guided-wave Electro-optic X-type Switches: Symmetry,Switching Characteristics and Cross-talk

Abstract

The influence of branching asymmetry and electrode offset on the switching characteristics and cross-talk of X-type switches is analysed theoretically. The relationship between the switch symmetry (i.e. the existence of a plane or centre of inversion) and the switching characteristics is found. Cross-talk levels of slightly asymmetric Ti:LiNbO₃ switches are calculated.     

Serialised batch scheduling algorithm for optical burst switching networks

A new scheduling algorithm called serialised batch scheduling (SBS) for optical burst switching (OBS) networks is proposed. SBS aggregates and serialises bursts along a shared path into one composite burst, which is switched as one unit. There are two major processes in SBS, namely, batching and serialising. While the batching process chooses a set of bursts to form the composite burst, the serialising process determines how to organise the OBS bursts within the composite burst and generates a corresponding control packet for this burst. Several SBS batching and serialising schemes are introduced and analysed here. The study by the authors shows that the guard band and burst overlap can be reduced in the SBS and, thus, the packet loss rate and the number of switch reconfigurations can be significantly reduced. In addition, it is indicated that the proposed SBS algorithm can be coupled with other OBS scheduling algorithms and reduce the requirements for a high-speed optical switch in OBS networks.     

弧型波导全光开关的优化设计

应用光束传输法对基于三阶非线性材料的弧型波导全光开关的开关特性进行了模拟,对两波导中心距、宽度及其不对称性等几何参数对开关特性的影响进行了分析,并对其进行了优化设计。结果表明,优化设计后的弧型波导全光开关具有较低的平均开关功率、数值化多次开关特性,有着弱光非线性全光开关的应用前景。     

Oxygen pressure dependent VO2 crystal film preparation and the interfacial epitaxial growth study

High quality VO₂ crystal films have been prepared on sapphire substrates by pulsed laser deposition method and the effects of oxygen pressure on the crystal phase structure are investigated. Results indicate that the phases and microstructures of VO₂ films are strongly sensitive to oxygen pressure. High oxygen pressure tends to form coarse B-VO₂ nanocrystals while low pressure favors a flat M1-VO₂ film epitaxial growth. X-ray diffraction φ-scan patterns confirm the [020] epitaxial growth orientation of the M1-VO₂ film and the in-plane lattice epitaxial relationship at the interface is also examined. Raman spectra indicate that M1-VO₂ phase has much stronger Raman scattering modes than B-VO₂, and the clear phonon modes further confirm the idea stoichiometry of VO₂ crystal film. Infrared transmittance spectra as the function of temperature are recorded and the results show that M1-VO₂ crystal films undergo a distinct infrared transmittance variation across metal insulator transition boundary, while B-VO₂ exhibits negligible thermochromic switching properties in the temperature range concerned. The pronounced phase transition behavior of the M1-VO₂ crystal film makes it a promising candidate for optical filter/switch and smart window applications in the future.     

Alternative Polarisation Geometries in Tests of Bell Inequalities

Abstract

The unitary transformation induced by an optical element on polarisation vectors corresponds to a rotation of the associated vectors in polarisation space on the Poincaré sphere. The degree of violation of a Bell inequality, which is of central interest in discriminating between hidden variable and quantum theories, involves only scalar products in polarisation space, and so is invariant under joint transformation of the relevant polarisation vectors. Conventionally, the plane of polarisation of any analyser is switched by an angle ψ of, say, π/8. The same violation is predicted if, instead, the analyser switching is performed by adding a relative phase of 2ψ through field-dependent birefringence. As with recent optical demonstrations of the Berry phase, the doubling of the angle indicates the simplicity of a unified analysis of both types of switching in polarisation space.     

Optical Pulse Shaping with an Electro-optic Modulator and Quadratic Electronic Feedback

Abstract

A digital optical repeater employing an electro-optic modulator and nonlinear electronic feedback provides optical bistability at a smaller value of the received optical power. The switching time is improved by increasing the local oscillator power and the overall gain of the feedback loop. The spread of the received optical pulses may be effectively reduced, leading to a considerable reduction in the intersymbol-interference power penalty. An optical amplification results in an improved system gain that exceeds the degradation due to a slight extinction penalty.