Rearrangeably nonblocking 8×8 guided wave optical switch

The design and construction of a lithium niobate 8×8 optical switch with a rearrangeably nonblocking architecture is described. The design is compared with the more familiar strictly nonblocking architecture. The switch has 28 elements, a switching voltage of 26 V and a loss of 5.5 dB at 1.3 μm wavelength     

A new design for wide-sense nonblocking multicast switching networks

In this paper, we propose a new design for a wide-sense nonblocking multicast switching network, which has many comparable properties to a strictly nonblocking Clos permutation network. For a newly designed four-stage N/spl times/N multicast network, its hardware cost, in terms of the number of crosspoints, is about 2(3+2/spl radic/2)N/sup 3/2/=11.66N/sup 3/2/, which is only a small constant factor higher than that of a three-stage nonblocking permutation network, and is lower than the O(N/sup 3/2/(logN/loglogN)) hardware cost of the well-known three-stage wide-sense nonblocking multicast network. In addition, the proposed four-stage nonblocking multicast network has a very simple routing algorithm with sublinear time complexity, and does not require multicast capability for the switch modules in the input stage.     

Design of wide-sense nonblocking multicast ATM switches

Nonblocking multicast asynchronous transfer mode (ATM) switches can simplify the call admission control process and increase the external links' utilization. We derive the wide-sense nonblocking condition for multicast ATM switches based on a general Clos network. We also propose a routing algorithm to achieve wide-sense nonblocking. It is illustrated by an example that the number of required middle stages in our switch is significantly less than that of strictly nonblocking multicast switches     

Wavelength rearrangeable and strictly nonblocking networks

The concept of rearrangeably and strictly nonblocking space division networks is extended to the wavelength dimension, resulting in a new family of interconnection network called wavelength-space division switches (WSDS). The complexity and wavelength assignment in these networks are discussed with some examples.<>     

Architectures for large nonblocking optical space switches

This paper introduces three architectures for optical space switches that are based on a multiplicity of fiber interconnected optical components. The architectures eliminate the need for optical waveguide Crossovers and reduce the complexity required in the individual elements. The architectures are strictly nonblocking and allow for easy control and routing. Architecture type 1 exhibits a low system attenuation and a high system signal-to-noise ratio for very large switch dimensions. Architectures 2 and 3 are alternatives for realizing broadcast and point-to-point architectures.     

An 8 mm length nonblocking 4×4 optical switch array

A novel single-mode-single-slip-structure S³ optical switch using carrier-induced refractive index change is proposed as a unit cell for a small polarization-independent nonblocking N×N optical switch array. Sixteen S³ optical switches have been integrated into a nonblocking 4×4 optical switch array on an InP substrate. The 8-mm-length InGaAsP/InP 4×4 optical array has shown satisfactory switching characteristics and is suitable for larger scale integration of optical switch arrays and also for integration with other active optical devices such as laser diodes     

Constructions and analyses of nonblocking WDM switches based on arrayed waveguide grating and limited wavelength conversion

Constructing fast wavelength division multiplexing switches with cheap, integratable components, less power consumption and noise accumulation, and low complexity is an important problem in optical networking. Typically, there are two request models widely considered. In one model, a connection request asks to go from a wavelength on an input fiber of the WDM switch to a particular wavelength on an output fiber. In the other, a connection only needs to get to a particular output fiber, irrespective of what wavelength it will be on. In this paper, we give novel constructions of strictly nonblocking and rearrangeably nonblocking WDM switches for both request models using limited range wavelength converters and arrayed waveguide grating routers. We fully analyze their blocking characteristics. Our designs are all relatively simple and easy to be laid out, consume little power, do not accumulate much noise, and are useful for both optical circuit-switching and optical packet/burst switching. As far as we know, these are the first of such constructions.     

16×16 strictly nonblocking guided-wave optical switchingsystem

We report the first demonstration of a complete 16×16 strictly nonblocking guided-wave optical switching system. The system, based on a three-stage extended generalized shuffle network, includes 448 directional coupler switch elements in 23 packaged modules. The modules are mounted in a single equipment cabinet and are controlled with a PC-based switching algorithm. We report results of extensive measurements on device and system performance. The devices and system exhibited low uniform voltages. Low loss, low crosstalk, and broad bandwidth. This lithium niobate based system operated continuously and without maintenance for a period of 20 months     

Extended baseline architecture for nonblocking photonic switching

A new switch architecture called extended baseline networks (EBN) is proposed for nonblocking photonic switching. This switch is a space-division multistage network using 2×2 optical switch elements which may be directional couplers fabricated on titanium diffused lithium niobate (Ti:LiNbO₃) substrates. A recursive definition for the proposed architecture is presented. Some properties including the number of switch elements required, blocking characteristics, number of crossovers, system attenuation, and signal-to-noise ratio (SNR) are derived and analyzed. Most of the characteristics are shown to be better than those of other well-known networks fabricated on single Ti:LiNbO₃ substrates     

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.     

'Staggering switch': an 'almost-all' optical packet switch

An 'almost-all' optical packet switch architecture is presented, based on two rearrangeably nonblocking stages interconnected by optical delay lines with different amounts of delay. Probability of loss as a function of link use and the size of the switch is investigated. In general, with proper setting of the number of delay lines, the switch can achieve arbitrarily low probability of loss.<>     

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.<>     

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     

Optical crossconnects of reduced complexity for WDM networks withbidirectional symmetry

One promising approach to provisioning and restoration in long-haul wavelength-division-multiplexing (WDM) networks is to deploy a mesh of optical crossconnects that operate on individual wavelengths. As wavelength-count and traffic demand rapidly increase, however, this approach will likely require high-port-count optical crossconnects that severely strain the capabilities of known device technologies. Thus, it is critical to devise ways to build large crossconnects from a small number of constituent switches, each with reduced port count. We present a general means of accomplishing this for networks, such as current long-haul networks, that demonstrate bidirectional symmetry. We describe a broad class of symmetry-exploiting architectures that yield N×N crossconnects, both rearrangeably nonblocking and strictly nonblocking, using constituent switch fabrics no larger than N/2×N/2. By exploiting connection-symmetry, these architectures reduce the number of such N/2×N/2 fabrics by 30%-50% compared with corresponding fully connected three-stage Benes and Clos switch structures     

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     

Novel MEMS L-switching matrix optical cross-connect architecture: design and analysis-optimal and staircase-switching algorithms

Free-space optical cross connect (OXC) for optical switching has shown promise in replacing traditional electronic switching fabrics. Micromachined optical switches offer superior performance in terms of bit rate and protocol transparency, which make them futureproof; however, they suffer from nonuniformity in port-to-port optical losses, which limit their use in large-scale optical connects. Recent reports on a novel two-dimensional (2-D) OXC architecture, L-switching matrix, presented that it can significantly improve nonuniformity in optical losses among all output ports. The drawback of L-switching matrix is that it is rearrangeably nonblocking (RNB) and not strictly nonblocking. This paper presents solutions to optimize its switching algorithms. A staircase-switching algorithm is proposed to minimize the occurrence of internal blocking conditions.     

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.     

Blocking and nonblocking multirate Clos switching networks

This paper investigates in detail the blocking and nonblocking behavior of multirate Clos switching networks at the connection/virtual connection level. The results are applicable to multirate circuit and fast-packet switching systems. Necessary and sufficient nonblocking conditions are derived analytically. Based on the results, an optimal bandwidth partitioning scheme is proposed to reduce switch complexity while maintaining the nonblocking property. The blocking behavior of blocking switches supporting multicast connections is investigated by means of simulation. We propose a novel simulation model that filters out external blocking events without distorting the bandwidth and fanout (for multicasting) distributions of connection requests. In this way, the internal blocking statistics that truly reflect the switch performance can be gathered and studied. Among many simulation results, we have shown that for point-to-multipoint connections, a heuristic routing policy that attempts to build a narrow multicast tree can have relatively low blocking probabilities compared with other routing policies. In addition, when small blocking probability can be tolerated, our results indicate that situations with many large-fanout connection requests do not necessarily require a switch architecture of higher complexity compared to that with only point-to-point requests     

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     

Optical nonblocking multicast and broadcast interconnects usingmultidimensional multiplexing concepts

It is well known that using space-switching, an N node multistage network can be constructed with its minimum switching complexity in the order of Nlog₂N but only for the point-to-point switching applications. To allow multicast and broadcast applications, a space-switching network has to use a minimum N² switching states, i.e., a cross-bar type switch. Recently, we have shown that a multidimensional multiplexing concept can be used to reduce the switching complexity while maintaining nonblocking multicast and broadcast switching. In this paper, based on acousto-optic and other photonic switching devices, a free-space optical architecture to support the multidimensional nonblocking multicast switching applications is detailed. System parameters and performance limitations are calculated. Based on a pair of eight-channel acousto-optic Bragg deflector arrays, a proof-of-principle bench-top system was designed and experimentally built. Some performance issues of the proposed the system are studied. Various fundamental and technological limits are evaluated