Photonics in Switching: Architectures, Technologies and Systems

1. Photonics in Switching: Architectures, Technologies and Systems A tutorial from Network of Excellence Research results from Virtual Department on Optical Switching Systems (VD-S)

2. e-Photon/ONe+ Optical Networks: Towards Bandwidth Manageability and Cost Efficiency The Network of Excellence (NoE) e-Photon/ONe+, funded by the European Commission, focuses on the 'Broadband for All' strategic objective of the IST 4th call of FP6, targeting network-oriented and system-oriented aspects of the optically enabled broadband. The project has been built upon the experience gained within the previous NoE e-Photon/ONe, funded within the IST 1st call of FP6. The NoE consortium is composed by 40 partners coming from Turkey to Portugal, and integrates academic and industrial partners, including major system companies, important device manufacturers and European telecommunication operators. The project co-ordinator is Politecnico di Torino. The project manager is Prof. Fabio Neri of the Electronics Department. He leads a research group on optical networks inside the Telecommunications Networks Group . The overall management of the project, regarding administrative, financial and legal issues, is carried out by the EU Affairs Office.

3. Contributors Carla Raffaelli, Michele Savi DEIS – University of Bologna, I-40136 Bologna, Italy e-mail: carla.raffaelli@unibo.it Kyriakos Vlachos, Manos Varvarigos Computer Engineering and Informatics Dept. & Research Academic Computer Technology Institute, University of Patras , GR26500, Rio, Greece Email: kvlachos@ceid.upatras.gr Pablo Pavón-Marino, Joan García-Haro, Juan Veiga-Gontán Department of Information Technologies and Communications PolytechnicUniversity of Cartagena , 30202, Cartagena, Spain Email: {pablo.pavon, joang.haro}@upct.es, javg@alu.upct.es Jakob Buron, Sarah Ruepp Department of Communications, Optics & Materials Technical University of Denmark, Kgs. Lyngby, Denmark Email: {jbu, sr}@com.dtu.dk Nicola Andriolli, Mirco Scaffardi Scuola Superiore Sant’Anna, Pisa, Italy Email: {nick, scaffardi}@sssup.it

4. Contributors Slavisa Aleksic Vienna University of Technology Institute of Broadband Communications Favoritenstrasse 9/388 A-1040 Vienna  e-mail: slavisa.aleksic@tuwien.ac.at Olga Zouraraki, Dimitris Apostolopoulos School of Electrical and Computer Engineering National Technical University of Athens 15773 Zographou, Athens, Greece Email: ozour@mail.ntua.gr Karsten Schulze Valencia Nanophotonics Technology Center, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia (Spain), Email: karsc@ntc.upv.es

5. Content Part I: System Perspective Part II: Technology perspective

6. Part I: System Perspective of Photonic in Switching • Key techniques for optical switching and networking • Photonic Switching fabrics • Contention resolution • GMPLS Optical Switching and experiments • Hybrid Switching: the WONDER/OSATE projects Packet • Reliable switching

7. Photonics in switching • Optical circuit switching (OCS) • Relatively mature technology today • Providing lightpaths • WDM network elements • OLT, OADM, OXC • Optical packet switching (OPS) • Not available today due to some technological problems • Controllable optical memory for optical buffering • Control functions in the optical domain • Synchronization, etc • Optical burst switching (OBS) • Hybrid packet switching: a feasible solution?

8. Photonic switching fabric • Basic Architectures • Optical switching, called also photonic switching, enables optical signals to be switched directly from inputs to outputs without conversion to electronic form. Used in: • optical cross-connect systems installed in emerging automated switched optical transport networks (AOTN), • switching nodes using packet, burstand ATM switching. • Multi-stage architectures • Photonic Switching Fabric’s Control

9. Photonic Switching Fabric Architectures • OADM of small capacity • uses 2 × 2 switching elements, • depending on the state of 2 × 2 element the wavelength is either switched through or dropped, • when the wavelength is dropped, the same wavelength is also added through the switch. • The same function can be realized using the switching fabric of greater capacity.

10. OADMs Architectures with switching elements with the switching fabric

11. OXC with Separate Switching Fabrics for Each Wavelength (1) • Wavelengths from each input fiber are demultiplexed. • Each wavelength is switched by the different switching fabric. • Each switching fabric switches only the same wavelength. • After switching, wavelengths are back multiplexed to optical fiber.

12. OXC with Separate Switching Fabrics for Each Wavelength (2)

13. Switch Technologies and Switching Types • To construct optical switching elements two different technologiesare being used: • guided lightwave based switches – they use fibers or waveguides for transmitting and switching lightwaves, • free-space switches – lightwaves • Each category can be further divided into different classes, depending on the physical phenomena used to switch lightwaves between inputs and outputs. • electro-optic switches – they use an electro-optic effect of a material, i.e. changes of the refractive index due to the application of an electric filed, • acousto-optic switches – they use an acousto-optic effect of a material, i.e. changes of the refractive index due to the application of acoustic waves,

14. Switch Technologies and Switching Types • thermo-optic switches – they use an thermo-optic effect of a material, i.e. changes of the refractive index due to changes of temperature, • MEMS switches – they use micro-electro-mechanical systems to move fibers, micro-mirrors or prisms, • liquid-crystal switches – they use properties of liquid-crystal materials, where the refractive index is determined by molecular alignment controlled by electric fields, • switches based on optical semiconductor amplifiers.

15. Popular electro-optic 2 × 2 switch • The titanium diffused lithium-niobate (Ti:LiNbO3) directional coupler. • Capacity of 2 × 2. • Can be in one of two states: • cross or • bar. Two states of the directional coupler:

16. Different implementations and capacities of MEMS switches (1) on-off switch 2 × 2 switch

17. Different implementations and capacities of MEMS switches (2) 1 × N switches with moving fibers, lenses, and mirrors

18. Different implementations and capacities of MEMS switches (3) N × N switch

19. Switch Architectures and Experiments • Information from different users transferred through a switch can be multiplexed in different ways: • space-division multiplexing (SDM) – signals from different users are sent using separate fibers, • time-division multiplexing systems (TDM) – links are shared in time, where data from different users are sent in different time intervals called time slots, • wavelength-division multiplexing (WDM) – when data are sent through the same fiber using different wavelengths(or frequency).

20. Space-division switching fabrics Whole data are transfered from an input fiber to an output fiber. SDM TDM WDM

21. Time-space-division switching In time-division switchingfabrics any time slot of any input TDM link can be connectedto any time slot of any outputTDM link. Also calledtime-division switching fabrics.

22. Wavelength-division switching fabrics • Any wavelength from any input fiber can be switched on any wavelength on any output fiber. • A wavelength conversion may be necessary to ensure full connectivity between wavelengths in input and output terminals • when two wavelengths of the same length in two input terminals are to be connected to the same output terminal, • one of these wavelengths is to be switched to another wavelength. • Waveband switching: • a set of wavelengths (called a waveband) on an incoming fiber is switched to an outgoing fiber.

23. Wavelength-division switching fabrics

24. Switching Fabrics • A capacity of an optical switch is limited by technology constrains. • To construct switches of greater capacity, many switches are connected between themselves and form a switching fabric. • Many parameters has to be taken into account when designing a switching fabric. Important characteristics used in evaluating optical switching fabrics are: • attenuation and • signal-to-noise ratio (SNR). • The number of switching elements is a measure of the networks’ cost. • Number of drivers – in some architectures one driver may control more than one switching element.

25. Combinatorial properties of switching fabrics (1) • The strict-sense nonblocking • There is a possibility to connect any free input with any free output regardless the switching fabric’s state and the way of choosing resources. • The wide-sense nonblocking • There is a possibility to connect any free input with any free output regardless the switching fabric’s state, but we have to use the special control algorithm to choose resources.

26. Combinatorial properties of switching fabrics (2) • The rearrangeable nonblocking • There is possible to connect any free input and any free output but special control algorithm has to be used and one or more of existing connections may have to be rerouted. • The repackable nonblocking • Similarly like in rearrangeable switching fabrics but rerouting is done after disconnection of one ofexisting connection. • Blocking • Sometimes it is impossible to connect free input with free output because of the current state of the switching fabric.

27. Hardware complexity vs. control complexity • Strict-sense nonbloncking (SSNB) • Wide-sense nonblocking (WSNB) • Rearrangeable (RRNB) • Repackable (RPNB) • Blocking

28. The crossbar switching fabric (1)

29. The crossbar switching fabric (2) Correct! Incorrect! Blocks for example 2-0

30. The tree-type switching fabric and 1 × 8 splitter construction

31. The N × N simplified tree architecture

32. The 4 × 4 simplified tree switching network

33. Recursive rule of building the Beneš switching fabric

34. The 16 × 16 Beneš switching fabric

35. The general structure of the Clos switching fabric

36. The planar switching fabric

37. The log2(8,0,p) switching fabric

38. The log2(8,1,p) switching fabric

39. Attenuation for various switching fabrics Loss in every switch = 0.2 dB n=log2N

40. The worst case SNR for various switching fabrics |X| = 20 dB, k = 0.01 n=log2N

41. Number of waveguide crossover for various switching fabrics n=log2N

42. Number of switching elements for various switching fabrics n=log2N

43. Photonic Switching Fabric’s Control • The connecting path has to be set up (or disconnected) in the switch fabric between input module (IM) and required output module (OM). • The control device sends an order to the switch fabric controller to set up (disconnect) the connecting path between the input and the output terminals requested. • This path consists of the input terminal, the output terminal, switches, and links between these switches. • When a new call is to be set up, the controller has to: • find a connecting path in the switch fabric, • check whether it is available (i.e. some elements are not occupied by other calls), • issue respective control signals to change states of switches, • update the current state of the switch fabric.

44. Photonic Switching Fabric’s Control General idea of switching node control Example

45. Connection types • Point-to-point connection • Exactly between one input and one output of the switching fabric. • Broadcast connection • Exactly between one input and all outputs of the switching fabric. • Multicast connection • Between one input and some outputs of the switching fabric. It holds point-to-point and broadcast connections as the special cases

46. Classification of control algorithms (1) • Control algorithms in multi-path switching fabrics can be divided into three major groups: • Path searching algorithms – are used for finding a connecting path through a switching fabric for one call at a time. • Rearrangement algorithms – can be used when a path searching algorithm fails. Their task is to find connecting paths which can be re-routed to unblock a new call. • Repacking algorithms – some connecting paths are also re-routed in a switching fabric but in contrast to rearrangements, they are executed after one of existing calls is terminated.

47. Classification of control algorithms (2)

48. Types of connecting paths • Single path switching fabrics – there is only one connecting path between any pair of input-output terminals. • Standard connecting path switching fabrics – there is more than one connecting path between any pair of input-output terminals but only one is used every time (crossbar switching fabric). • Multi-path switching fabrics – there are several connecting paths to connect any input terminal with any output terminal.

49. Path setup in the tree architecture (single path switch fabric)

50. Path searching algorithms for Clos switching fabrics (1) • To set up the new connection in the three stage Clos switching fabric the center stage switch with free links to input and output switches is to be found. • This center stage switch is called free or available for the new connection. • Random (RAN) • Check center stage switches randomly and set up the connection through the first available switch. • Sequential (SEQ) • Check center stage switches sequentially starting form the center stage switch Mk, 1 ≤ k ≤ m, and choose the first available switch. • Minimum index (MINIX) • This algorithm is the same as sequential, but k = 1.