A photonic wavelength-division switching system using tunable laserdiode filters

A photonic wavelength-division switching system using semiconductor tunable wavelength filters is proposed. A switching system using wavelength switches and multistage switching networks is discussed. A crucial point in developing this switching system is to achieve a large number of wavelength-division channels. The potential of 100 wavelength-division channels in such switching systems is estimated, based on InP optical integrated circuits. A wavelength network synchronization which permits the network to utilize such a large number of wavelength-division channels without wavelength misalignment and drift is proposed. An eight-channel wavelength-division switching experiment, using phase-shift-controlled distributed feedback laser diodes as tunable wavelength filters, is reported     

Tree-type photonic switching networks

The enormous bandwidth offered by optical systems makes photonic switching a very attractive solution for broadband communications. Tree-type architectures play an important role in the design of photonic switching networks. The authors present and discuss all known tree-type space-division photonic switching networks architectures in a unified framework, and propose a number of new solutions. The discussed networks can be implemented with guided-wave-based switching elements, or laser diodes and passive splitters and combiners. The following network types are considered: conventional, simplified, and two-active stage networks. Techniques for improving SNR as well as waveguide crossover minimization are presented and discussed     

A class of directional-coupler-based photonic switching networks

A class of photonic switching networks composed of directional couplers is proposed. These networks require only two switching stages containing active elements. Both point-to-point and multicast architectures are presented. Various characteristics of the networks are compared to those of networks previously known with respect to insertion loss, SNR, number of crossovers, and number of active elements     

Architectural considerations for photonic switching networks

Photonic technologies are reviewed that could become important components of future telecommunication systems. Photonic devices and systems are divided into two classes according to the function they perform. The first class, relational, refers to devices, that map the input channels to the output channels under external control. The second class, logic, perform some type or combination of Boolean logic functions. Some of the strengths and weaknesses of operating in the photonic domain are presented. Relational devices and their applications are discussed. Optical logic devices and their potential applications are reviewed     

An efficient media access protocol for packet-switched wavelength-division multiplexed photonic networks

A reservation-based protocol based on a Pipelining Cyclic Scheduling Algorithm (PCSA) is proposed for packet-switched single-hop photonic networks. This protocol contains a mechanism to avoid contention at the receivers. Packets arrive in order and the transmission delay and its variations are optimized. The effects of propagation delay and processing time are almost compensated for by a pipelining technique. Analytical models and analysis are developed. The transmission delay is calculated as a function of the offered load, the number of nodes, propagation delay and processing time. Finally, the results of the analysis and simulations are compared.     

Wavelength switching components for future photonic networks

This article provides a review of integrated laser and semiconductor optical amplifier components that have been configured to provide a variety of all-optical functions such as wavelength conversion, routing, signal regeneration, and add-drop multiplexing. The components have been devised so that they can be reliably and simply used within a multiwavelength network. The article introduces the components by outlining the current leading techniques for wavelength conversion using SOAs, namely by way of cross-gain modulation, cross-phase modulation, and four-wave mixing. The integrated SOA distributed feedback laser is then shown to provide excellent regeneration properties, not only overcoming fiber dispersion limitations but also polarization mode dispersion. Finally, the devices are shown to make possible a regenerative wavelength switching node where routing is achieved using a tunable laser to provide regenerative wavelength conversion followed by an arrayed waveguide router. This switch shows promise for use in future photonic packet switching architectures     

Modified dilated Benes networks for photonic switching

A modified dilated Benes (1965) network composed of directional couplers is proposed. This structure is introduced to improve the signal-to-noise ratio (SNR) characteristics of dilated Benes networks. A new estimation of the SNR for dilated Benes networks is derived, and it is shown that this SNR is much worse than that previously known. The SNR for modified dilated Benes networks is estimated and compared to dilated Benes and other network architectures. Some other properties including the number of switching elements required, number of crossovers, and system attenuation are also derived and analyzed. Most of the characteristics are shown to be similar to dilated Benes networks and better than those of other well-known networks fabricated in Ti:LiNbO ₃     

A coherent OFDM switching system for flexible optical networkconfiguration

A coherent optical switching node based on the combination of a frequency conversion stage with a space switching matrix is proposed for flexible interconnection of future integrated broadband communication networks. The basic system concept is presented together with the architecture of a demonstrator, which allows one to study the functionality available in future networks. The major subsystems and components of the demonstrator are described, and experimental results concerning frequency stabilization, frequency switching, and space switching are presented     

基于液体选择填充光子晶体光纤的波分解复用器研究

设计了一种基于液体选择填充三芯光子晶体光纤的1.31/1.55um波分解复用器。中间为缺失一个空气孔的普通二氧化硅纤芯,左右两纤芯填充了不同折射率的液体材料。根据光纤的消逝场耦合的模式理论,不对称相邻波导存在波长相关耦合。不同填充折射率的两纤芯与中间纤芯分别耦合,构成两个不同响应波长的光滤波器。通过选择合适光纤长度,可实现不同波长光的分离。采用全矢量有限元法分析了光纤的传输特性,讨论了填充不同折射率液体时波导间的模式耦合,得到了其匹配波长与耦合长度。基于光束传播法仿真发现,长度为4.88 mm的光纤能实现1.31/1.55 um波长光的解复用。     

Investigation on 2D photonic crystal-based eight-channel wavelength-division demultiplexer

In this paper, eight-channel wavelength-division demultiplexer (WDDM) is proposed and designed using two-dimensional photonic crystal (2DPC) ring resonator whose corresponding functional parameters such as transmission efficiency, resonant wavelength, Q factor are investigated. The proposed structure consists of bus waveguide, dropping waveguide and square ring resonators. Eight different channels are dropped by altering the cavity size and radius of the defect rods. The plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods are employed to analyse the photonic band gap (PBG) of periodic and non-periodic structure and to arrive normalized transmission spectra, respectively. The resonant wavelengths of eight-channel demultiplexers are 1496.9, 1502.3, 1506.9, 1512.3, 1515.0, 1520.4, 1525.3 and 1530.6 nm. The average transmission efficiency, Q factor and spectral width of proposed demultiplexer are 81%, 825 and 1.8 nm, respectively. The mean channel spacing is about 4.2 nm. The size of the demultiplexer is small; hence, it can be utilized for photonic integrated circuits (PIC).     

A 32-channel tunable receiver module for wavelength-division multiple-access networks

We report the realization of a 32-channel tunable optical receiver module for packet-switched multiwavelength computer networks. The tunable receiver consists of a planar array waveguide grating demultiplexer, photodetector array and followed by selectable receivers. The channel selection is based on sequential switching of the received optical signals in stages at the analogue level. Typical receiver sensitivity is -24 dBm at 10/sup -9/, using a 700-Mb/s nonreturn-to-zero (NRZ) pseudorandom binary sequence (PRBS). The channel switching time is /spl sim/40 ns.     

Dense wavelength-division multiplexing millimeter-wave-band radio-on-fiber signal transmission with photonic downconversion

Photonic downconversion (PDC) technique for dense wavelength division multiplexing (DWDM) millimeter-wave-band radio-on-fiber (ROF) uplink systems is investigated. The PDC technique is carried out for a lump of all uplink wavelength division multiplexing (WDM) ROF signals at a central station. Each channel is optically separated, photodetected, and demodulated individually without serious signal degradation due to the fiber dispersion effect. Error-free 25-GHz-spaced DWDM transmission and demultiplexing of two 60-GHz-band, 155-Mb/s differential phase-shift keying (DPSK) ROF signals over 25-km-long standard single-mode fiber (SMF) are experimentally demonstrated.     

A perspective on photonic multiprotocol label switching

Various MPLS-based IP over WDM integration techniques are considered in this article. In particular, this includes the circuit-switching MPλS framework for providing logical IP-layer topologies over optical lightpath routing networks. Additionally, an optical code label switching technique for photonic packet switching and its application to MPLS is also introduced, termed OC-MPLS. The related advantages and challenges of both of these approaches are discussed, and various future research issues are addressed     

A wavelength-buffering scheme for dynamic traffic in optical wavelength-division multiplexing networks

In optical wavelength-division multiplexing (WDM) networks, traffic can be very “bursty” at a fine time scale, even though it may seem to be smooth at coarser scales (e.g., Poisson or Poisson-related traffic). This paper analyzes the instantaneous characterization of Poisson traffic at a fine time scale. The analysis shows that the irregular oscillation of the instantaneous traffic load and the occurrence of blockings in a light-loaded network are highly correlated. Specifically, most blockings occur concentratively at the peaks of the instantaneous load. In some other time, network resources may not be sufficiently utilized. To make better utilization of network resources, a novel wavelength-buffering (WB) scheme is proposed for the first time in this paper. By reserving a portion of resources in a “wavelength buffer” under light loading and releasing them when the load goes up, a number of blockings brought by the oscillation of the traffic load can be avoided. Simulation results show that compared with other schemes such as adaptive routing, wavelength conversion (WC), and rerouting, the novel wavelength-buffering scheme achieves significantly better performance with respect to the network utilization and overall blocking probability.

Collision avoidance in all-optical wavelength-division multiplexed packet networks

In future all-optical wavelength-division multiplexed (WDM) packet networks, the ability to detect the presence or absence of optical packets without regard to the transmission bit rate may be essential in achieving collision-free transmission. Using this feature, we present the use of baseband carrier sensing-the direct detection of baseband optical signals-to facilitate optical carrier-sense multiple access with collision avoidance (CSMA/CA) networks. Central to the technique is the use of baseband carrier-sense circuits (BCSCs) to perform carrier sensing. We investigate the physical limits of baseband carrier sensing, governed by the characteristics of the BCSC. Our investigations reveal that there exists a reliable operating range of received optical power at the circuit, bounded at the lower end by the sensitivity of the circuit and at the higher end by considerations of transmission efficiency. We further investigate the dependence of the reliable operating range on the bandwidth of the BCSC, demonstrating that there exists an optimum bandwidth that maximizes the operating range. Investigations performed over an order of magnitude change in bandwidth show that the BCSC has a sensitivity of higher than -50 dBm and operates reliably over a 25-dB range. There is enormous potential in employing our simple, nonintrusive, yet efficient baseband carrier-sensing technique to realize collision-free transmission in future optical CSMA/CA packet networks.     

Traffic scheduling in a photonic packet switching system with QoSguarantee

The main challenge in the design of future broadband networks is to efficiently support high-bandwidth multimedia services. Recent advances in the optical networking reveal that all optical networks offering multigigabit rate per wavelength may soon become economical as the underlying backbone in wide area networks, in which photonic switch plays a central role. Two issues are the essential in the design of photonic packet switching, the support of end-to-end virtual connections and the support of diverse quality-of-service (QoS) services. Existing work in wide-area optical networks has largely focused on the former, relatively less attention has been given to support heterogeneous traffic types and to satisfy the potentially different QoS requirements of different types of traffic. In this paper, we introduce a novel hierarchical scheduling framework to use in a class of photonic packet switching systems based on WDM, in which we separate the flow scheduling from the transmission scheduling. We show such separation is essential for achieving scalability such that large input-output ports can be accommodated, and also for offering flexibility in that optimal scheduling algorithms can be derived in different level that can be best tuned to the specific system requirements. The salient feature of the proposed scheduling mechanism is that it takes into account potentially different QoS requirements from different traffic flows. A number of interesting findings are observed from the results obtained by both analysis and simulation: (1) QoS requirements can be satisfied for both real-time and nonreal-time flows; (2) the impact Of the real-time traffic head-of-line (HoL) blocking on the system throughput can be effectively alleviated with the prevailing number of traffic flows. In addition, we investigate a variety of performance measures under different system configurations     

Measurement of crossphase modulation in coherent wavelength-division multiplexing using injection lasers

Light from two InGaAsP injection lasers of different wavelengths was multiplexed into a 15 km-long single-mode fibre. Owing to the nonlinear refractive index, the phase of light in one channel was changed by power changes in the other channel. A 1 mW power charge in one channel produced a 1.4° phase shift in the other channel.     

Signal self-thresholding using wavelength-division multiplexed differential transmission for photonic ATM switches

A single self-thresholding method is proposed that eliminates rapid signal level fluctuations in photonic ATM switches. A 3 Gbit/s data stream with nanosecond-order level fluctuations can be discriminated. A bit error rate of 10/sup -10/ is obtained for switching cells of power -8.0 and -16.0 dBm.<>     

Semiconductor devices in photonic switching

Three types of photonic switching networks have been proposed, namely, optical space-division switching, optical wavelength-division switching. Optional function devices required for each switching network are as follows: optical switch matrix for space-division switching; optical memory and optical write/read gate for time-division switching; and tunable wavelength filter and wavelength converter for wavelength-division switching. Recent progress in semiconductor functional devices such as modulators, switching devices, bistable devices, and wavelength control devices, which would be key devices to build switching networks, is reviewed