A Simple Control Algorithm for Rearrangeable Switching Networks with Time Division Multiplexed Links

A simple control algorithm is proposed for a three-stage rearrangeable switching network with time division multiplexed links. The nonblocking condition is shown for the rearrangeable network controlled by the proposed algorithm. The rearrangeable nonblocking network controlled by the proposed method is more cost effective in hardware than a strictly nonblocking network for a large number of channels multiplexed on links. The computing complexity of the algorithms is not more than that for controlling the strictly nonblocking network. In the proposed algorithm, only one path must be moved in the rearrangement, thus reducing the difficulty in implementing the rearrangeable network. This algorithm is efficient for broadband switching systems or cross-connect devices where nonblocking switches are needed.     

Expanding the switching capabilities of optical crossconnects

Optical-switching technologies exhibit many characteristics that the electronic-switching technologies do not have. One such characteristic lies in switching states. An electronic crosspoint, having open and close as its two switching states, only allows one traversing signal. But an optical-switching crosspoint, such as a directional coupler or a microelectromechanical systems mirror, usually allows two traversing signals. This paper studies how to exploit the characteristic to expand the switching capabilities of an optical switch, and shows new ways of building more crosspoint-efficient rearrangeable nonblocking switches. We show that an optical 2n/spl times/2n rearrangeable nonblocking switch can be created by cascading only two n/spl times/n optical crossbars.     

One-Sided Switching Networks Composed of Digital Switching Matrices

One-sided switching networks composed of uniform digital switching matrices are considered. Such matrices mix in the same integrated circuit or in the same printed circuit board time and space switching. The conditions under which one-sided networks are nonblocking and rearrangeable are discussed.     

Rearrangeable Nonblocking 8 × 8 Matrix Optical Switch Based on Silica Waveguide and Extended Banyan Network

Based on the crossbar network and the Banyan network (BN), a new rearrangeable nonblocking structure of extended Banyan network (EBN) was proposed for implementing an 8 times 8 optical matrix switch. The interconnection characteristics of the rearrangeable nonblocking EBN were studied, and the diagram of the logic program for driving the operation of switching units was provided. A silica waveguide 8 times 8 matrix optical switch was designed and fabricated according to the calculated results. The silica waveguide propagation loss of 0.1 dB/cm and waveguide-fiber coupling loss of 0.5 dB/facet were measured. With the fabricated 8 times 8 matrix optical switch, the insertion loss of 4.6 dB, the crosstalk of -38 dB, the polarization-dependent loss of 0.4 dB, the averaged switching power of 1.6 W, and the switching time of 1 ms were achieved. A basic agreement between experimental results and theoretical calculated values was achieved     

Performance of rearrangeable nonblocking 4×4 switch matriceson LiNbO3

The design, fabrication, and characterization of rearrangeable nonblocking 4×4 switch matrices and the development of a novel ITO (indium-tin-oxide)/Au multilayer electrode that leads to low switching voltages and low DC drift is reported. Results on electrode systems, insertion loss, crosstalk, tolerances in the coupling length, and stability obtained for eight fabricated matrices are given. In comparison to the SiO₂ buffer layers, a reduction in the switching voltage of a factor of 0.66 has been achieved. Insertion losses of fiber pigtailed modules are in the range between 4 and 7 dB. The crosstalk has still to be improved. The stability of the operating points of the switches has been analyzed, showing that the devices must be operated in closed dark housings with a passivation layer in order to avoid optical damage effects from ambient light and to protect them against physical and chemical influences     

Design of Optical Rearrangeable Nonblocking MINs Under Various Crosstalk Constraints

Optical interconnection networks suffer from the intrinsic crosstalk problem that should be overcome to make them work properly. Vertical stacking of optical banyan networks is a novel scheme for constructing nonblocking optical multistage interconnection networks (MINs). Rearrangeable nonblocking optical MINs are feasible since they have lower complexity than their strictly nonblocking counterparts. In this paper, we determine the sufficient condition for these MINs to be rearrangeable nonblocking under various crosstalk constraints. We show how the crosstalk constraint affects the design of rearrangeable nonblocking MINs and demonstrate that these networks can tolerate a stricter crosstalk constraint without increasing their hardware complexity significantly. The results in the paper will be useful in designing optical MINs with reasonable hardware cost and crosstalk level.     

Nonblocking WDM switching networks with full and limited wavelength conversion

In previous years, with the rapid exhaustion of the capacity in wide area networks led by Internet and multimedia applications, demand for high bandwidth has been growing at a very fast pace. Wavelength-division multiplexing (WDM) is a promising technique for utilizing the huge available bandwidth in optical fibers. We consider efficient designs of nonblocking WDM permutation switching networks. Such designs require nontrivial extensions from the existing designs of electronic switching networks. We first propose several permutation models in WDM switching networks ranging from no wavelength conversion, to limited wavelength conversion, to full wavelength conversion, and analyze the network performance in terms of the permutation capacity and network cost, such as the number of optical cross-connect elements and the number of wavelength converters required for each model. We then give two methods for constructing nonblocking multistage WDM switching networks to reduce the network cost.     

On the CNET: a rearrangeable nonblocking optical interconnection network

A planar, circular, rearrangeable nonblocking optical switching architecture using N(N-1) Ti:LiNbO/sub 3/ directional coupler switches is suggested. Various figures of merit such as the signal-to-crosstalk ratio (SXR), insertion loss and fault tolerance are presented. The outline for a distributed routing algorithm in O(N) time is given.<>     

An Architecture for TSI-Free Nonblocking Optical TDM Switches

One of the key elements in building a time-division- multiplexed (TDM) switch is the time slot interchange (TSI). Given the current optical switching and buffer technologies, TSI-based TDM architectures have many implementation drawbacks, including severe signal attenuation. Some studies showed that some space-time equivalence diagrams can be converted into a delay-unit-based (TSI-free) TDM. This type of architecture is attractive for optical TDM switches, but the techniques discussed in those studies are for rearrangeable switches. Many applications require nonblocking switches where adding a new connection (or a flow) will not cause rearrangement of existing connections. In this paper, we present the design principle for building strictly nonblocking delay-unit-based (TSI-free) optical TDM switches.     

On Noninterruptive Rearrangeable Networks

In this paper, we study a new class of nonblocking networks called noninterruptive rearrangeable (NIR) networks, which are rearrangeable under the additional condition that existing connections are not interrupted while their paths being possibly rerouted to accommodate a new request. We give a complete characterization of NIR Clos networks built of switching elements of various nonblocking properties. In particular, we propose a novel class of NIR Clos networks that leads to recursive constructions of various cost-efficient multistage NIR networks. Finally, we present examples of such constructions and compare them with the best previously known results.     

Tradeoff of horizontal decomposition versus vertical stacking inrearrangeable nonblocking networks

A class of rearrangeable nonblocking networks is presented. The proposed networks are fault-tolerant, self-routing, and intended for a very-high-speed environment. Self-routing networks have one major problem when applied to switching: they are blocking networks. To solve this problem, two methods have been used to create self-routing rearrangeable nonblocking networks: horizontal cascading (HC) and vertical stacking (VS). The authors unify the two approaches and propose a novel class of switching networks. The proposed design principle allows the best tradeoffs among design parameters such as fault tolerance, hardware cost, and the frequency of rearrangement activities. A study of the frequency of rearrangement activities is also presented     

A New Architecture for Nonblocking Optical Switching Networks

With the current technology, all-optical networks require nonblocking switch architectures for building optical cross-connects. The crossbar switch has been widely used for building an optical cross-connect due to its simple routing algorithm and short path setup time. It is known that the crossbar suffers from huge signal loss and crosstalk. The Clos network uses a crossbar as building block and reduces switch complexity, but it does not significantly reduce signal loss and crosstalk. Although the Spanke's network eliminates the crosstalk problem, it increases the number of switching elements required considerably (to 2N ² - 2N). In this paper, we propose a new architecture for building nonblocking optical switching networks that has much lower signal loss and crosstalk than the crossbar without increasing switch complexity. Using this architecture we can build non-squared nonblocking networks that can be used as building block for the Clos network. The resulting Clos network will then have not only lower signal loss and crosstalk but also a lower switch complexity.     

Integrated folding 4/spl times/4 optical matrix switch with total internal reflection mirrors on SOI by anisotropic chemical etching

A folding rearrangeable nonblocking 4/spl times/4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20/spl times/1.6 mm/sup 2/ and a fast response of 7.5 /spl mu/s. The power consumption of each 2/spl times/2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of /spl plusmn/0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.     

Large-capacity strictly nonblocking optical cross-connects based onmicroelectrooptomechanical systems (MEOMS) switch matrices: reliabilityperformance analysis

The reliability performance of 128× 128 optical cross-connects (OXCs) based on microelectrooptomechanical systems (MEOMS) switch matrices is considered. First, we compare a strictly nonblocking wavelength selective switch with a strictly nonblocking three-stage Clos architecture. The probability of maintenance of free operation has been investigated for both OXC structures. We present our calculation results for such commonly used reliability measures as mean time between failures (MTBF), mean downtime (MDT) per gear, and steady-state unavailability. It is shown that the reliability performances of the considered OXCs are far from that requested. In this paper, we also investigate possibilities of improving the reliability performance of the considered OXCs by introducing shared redundancy of the MEOMS matrices. We propose two different protection schemes: one for the wavelength selective switch and another for the three-stage Clos architecture. It is shown that the proposed protection schemes significantly improve the reliability performance for both cases. Finally, we compare the performance of the all-optical version of the OXC based on MEOMS matrices with the optoelectronic version of the OXC based on electronic cross-point switch matrices. It is shown that from a reliability viewpoint, the optical cross-connect based on MEOMS matrices is better than that with electrical cross-point switches. The influence of capacity expansion on the system reliability is discussed     

Large modular expandable optical switching matrices

Large optical switching matrices can be assembled incrementally from identical modules by means of a rearrangement of the Clos architecture that we have labeled SKOL. The design retains the strict-sense nonblocking properties of the Clos design, identical units provide economies of manufacture, and there are also cost advantages associated with the incremental expandability. SKOL modules can be constructed in ways that do not map back to the Clos original. In this form, SKOL is a new multistage switching architecture that is well adapted for construction with integrated optical technologies. We anticipate that the SKOL design can provide the very large, expandable optical switching matrices now demanded for optical networks     

Optical Switching Networks With Minimum Number of Limited-Range Wavelength Converters

We study the problem of determining the minimum number of limited-range wavelength converters needed to construct strictly, wide-sense, and rearrangeably nonblocking optical cross-connects for both unicast and multicast traffic patterns. We give the exact formula to compute this number for rearrangeably and wide-sense nonblocking cross-connects under both the unicast and multicast cases. We also give optimal cross-connect constructions with respect to the number of limited-range wavelength converters.     

4*4 directional coupler switch matrix with an InGaAlAs/InAlAs multiquantum well structure

A 4*4 directional coupler switch matrix is developed which uses, for the first time, the quantum confined Stark effect of InGaAlAs/InAlAs multiquantum well structures. The rearrangeable nonblocking 4*4 network with six 2*2 switches is shown to be perfectly functional with switching voltages between 5 and 6 V and crosstalk below -17 dB in all the operation states.<>     

SOI热光4×4光开关阵列的研制

设计和制作了由5个2×2多模干涉马赫-曾德开关元组成的重排无阻塞型SOI 4×4热光开关阵列.阵列的最小和最大附加损耗分别为6.6和10.4dB,阵列的串扰为-12 ～-19.8dB,光开关阵列的开关速度小于30μs,单个开关元的功耗大约为330mW.     

A Two-Stage Rearrangeable Broadcast Switching Network

A new rearrangeable broadcast switching network has been invented. In its simplest form, the network has two stages. For larger networks, the switches in each stage can be replaced with two-stage networks to reduce crosspoint cost. The invention is based on an innovative approach of connecting each inlet channel to a multiplicity of first-stage switches according to a predetermined connection pattern. The network grows easily and has simple path hunt and rearrangement algorithms. It provides a general solution for any nonblocking broadcast switching application. Fewer crosspoints are required than in any other known two- or three-stage rearrangeable broadcast network. The connection arrangement exemplifies a topic heretofore unaddressed in combinatorial theory.     

Nonblocking, repackable, and rearrangeable Clos networks: fifty years of the theory evolution

The article gives an overview of major theoretical issues associated with a switching network structure proposed by C. Clos (1953). The concepts of strict-sense and wide-sense nonblocking as well as repackable and rearrangeable networks are described, showing the development of major research areas. A taxonomy of Clos switching networks and some important results for the basic network structure are given and discussed. Other research issues are enumerated.