CHAVEADORES ÓPTICOS

1. ENG735 – COMUNICAÇÕES ÓPTICAS CHAVEADORES ÓPTICOS http://soe.northumbria.ac.uk/ocr/teaching/fibre/pp/Components-L2.ppt http://soe.northumbria.ac.uk/ocr/teaching/fibre/pp/opticalsw.ppt Prof. Dr. Vitaly F. Rodríguez-Esquerre

2. Types of Optical Switching Wavelength Division Switching Hybrid of Space, Wavelength and Time Space Division Switching Time Division Switching Switching is the process by which the destination of a individual optical information signal is controlled • Switch control may be: • Purely electronic (present situation) • Hybrid of optical and electronic (in development) • Purely optical (awaits development of optical logic, memory etc.)

3. Gel/oil based High Loss 3 Liquid LiNbO Crystal Indium Phosphide Mechanical Optical Switching Element Technologies / SiO Si 2 Thermo- optic Fibre ( acousto -optic) Optical Switching Element Technologies Not Scalable Polarization Dependent Poor Reliability SOA Micro-Optic (MEMS) Bubble Can be configured in two or three dimensional architectures Waveguide Free Space

4. Electro-optic Switch • Use a directional coupler • Its coupling ratio is changed by varying the refractive index • Thermo-optic Switch • Liquid-Crystal Switch • Bubble Switch • Acousto-optic Switch

6. Two axis motion Micro mirror

7. 2D MEMS based Optical Switch Matrix Output fibre Input fibre • Mirrors have only two possible positions • Light is routed in a 2D plane • For N inputs and N outputs we need N2 mirrors • Loss increases rapidly with N SEM photo of 2D MEMS mirrors

8. 3D MEMS based Optical Switch Matrix • Mirrors require complex closed-loop analog control • But loss increases only as a function of N1/2 • Higher port counts possible SEM photo of 3D MEMS mirrors

9. Total Internal Reflection LC Switch

10. Liquid crystal (Total internal Reflection) The glass and nematic liquid crystal refractive indices are chosen to be equal in the transmittive state and to satisfy the total reflection condition in the reflective state Schematic diagram of the total reflection switch: 1- glass prisms; 2- liquid crystal layer; 3-spacers

12. Optical • Electrical Limits • High power consumption: e.g. 1024x1024: 4 kW • Jitter: very large • Large switches • Need OE/EO conversion • Bipolar or GaAs 1024 512 256 128 Number of ports 64 32 16 Electrical 8 10 MHz 100 MHz 1 GHz 10 GHz 100 GHz Data rate DS3 OC3 OC12 OC48 OC192 • Provide fast switching speed • No bottleneck due to electronics speed • I/O interface and switching fabric in optics • Switching control and switching fabric in optics • Uses a simple 2x2 switch as a building block

13. Input interface Output interface Switching fabric Switching control Electrical control Electrical control Optical input Optical output Optical input Optical output

14. Optical Switches: - A comparison

15. Control Signal Optical Switch I1 Output ports Input port Ii I2 Optical Switches - Tow-Position Switch The input signal can be switched to either of the output ports without having any access to the information carried by the input optical signal • In the ideal case, the switching must be fast and low-loss. • 100% of the light should be passed to one port and 0% to • the other port.

16. Lens B B Prism A A C C Fibre Two Position Switch - contd. • The two-position switch requires three fibres with collimating lenses and a prism. Light arriving at port A needs to be switched to port C.

17. Optical Switches - Applications • Provisioning: Used inside optical cross connects to reconfigure them and set-up new path. [1 - 10 msecs] • Protection Switching: To switch traffic from a primary fibre onto another fibre in the case of a failure. [1 to 10 usecs] • Packet Switching: 53 byte packet @ 10 Gb/s. [1 nsecs] • External Modulation: To switch on-off a laser source at a very high speed. [10 psecs << bit duration] • Network performance monitoring • Reconfiguration and restoration:Fibre networks

18. Optical Switching - Technologies • Slow Switches (msecs) • Free space • Mechanical • Solid state • Fast Switches (nsecs) • LiNbO • Non-linear • InP

19. Optical Switches - Criteria • Maximum Throughput: • Total number of bits/sec switched through. • To increase throughput: • Increase the number of I/O ports • Bit rate of each line • Maximum Switching Speed • Important: • Packet switched • Time division multiplexed • Minimum Number of Crosspoints • As the size of the switch increases, so does the number of crosspoints, thus high cost • Multistage switching architecture are used to reduce the number of crosspoints.

20. Criteria - contd. • Minimum Blocking Probability: Important in circuit switching • External blocking:when the incoming call request an output port that is blocked. • Subject to external traffic conditions • Internal blocking:when no input port is available. • Subject to the switch design • Minimum Delay and Loss Probability • Important in packet switching, where buffering is used, which will introduce additional delay. • Scalability • Replacing an old switch with a new larger switch is costly. • Incrementally increasing the size of the existing switching as traffice grows is desirable • Broadcasting and Multicasting • To provide conferencing and multimedia applications

21. - Fast - Complex - Maturing - Lossy - Slow - Maturity - Reliable - Slow - Low loss & crosstalk - Inherently scalable Optical Switches - Types • Waveguide • Electro-optic effect • Semiconductor optical amplifier • LiNbO • - InP • Thermo-optic effect - SiO2 / Si - Polymer • Free Space - Liquid crystal - Mechanical / fibre - Micro-optics (MEM’s)

22. + v Electrodes Optical Switches - Thermo-Optic Effect • Some materials have strong thermo-optics effect that could be used to guide light in a waveguide. • The thermo-optic coefficient is: • Silica glass dn/dt = 1 x 10-5 K-1 • Polymer dn/dt = -1 x 10-5 K-1 • Difference thermo-optic effect results in different switch design.

23. Outputs Input Ii I1 I2 Directional coupler Thermo-Optic Switch - Silica Mach – Zehnder Configuration Analogue Heater

24. Y – Junction Configuration Digital I1 PH1 Ii PH2 I2 Thermo-Optic Switch - Polymer • If PH1 = PH2 = 0, then I1 = I2 = Ii /2 • If PH1 = Pon & PH2 = 0, then I1 = 0, and I2 = Ii • If PH1 = 0 & PH2 = Pon, then I1 = Ii, and I2 = 0

25. Parameters Switch Size 2 x 2 Si Poly. 8 x 8 Si Poly. 16 x 16 Si No. of S/W 1 1 64 112 256 Insertion Loss (dB) 2 0.6 4 10 18 Crosstalk 22 39 18 17 13 S/W time (ms) 2 1 ~3 1.5 ~4 S/W power (W) 0.6 0.005 5 4.5 15 Thermo-Optic Switch - Characteristics

26. Mechanical Switches 1st Generation – Mid. 1980’s • Loss Low (0.2 – 0.3 dB) • Speed slow (msecs) • Size Large • Reliability Has moving part • Applications: - Instrumentation - Telecom (a few) Size: 8 X 8 Loss: 3 dB Crosstalk: 55 dB Switching time: 10 msecs

27. Input fibres Output fibres Lens Flat mirror Raised mirror Micro Electro Mechanical Switches • Made using micro-machining • Free-space: polarisation independent • Independent of: • Bit-rate • Wavelength • Protocol • Speed: 1 10 ms 4 x 4 Cross point switch

28. Micro Electro Mechanical Switches This tiny electronically tiltable mirror is a building block in devices such as all-optical cross-connects and new types of computer data projectors. Lightwave

29. ... ... 1.3 mm intra-office Transponders ... ... Optical Crossconnect (OXC) ... ... Optical transport system (1.55 mm WDM) Terminating equipment | SONET, ATM, IP... Switching Fabric – contd.

30. Space Division Switching • Crossbar • Clos • Benes • Spank - Benes • Spanke

31. 1 2 Input ports 3 4 1 2 3 4 Output ports Crossbar Architectures • Each sample takes a different path through the switch, depending on its destination • Crossbar: • Simplest possible space-division switch • Wide- sense blocking: When a connection is made it can exclude the possibility of certain other connections being made Crosspoints • can be turned on or off Sessions: (1,4) (2,2) (3,1) (4,3)

32. Input channels 1 2 Input channels N X N matrix S/W Output channels - Bars 3 4 1 2 3 4 Optical switching element Output channels - Cross Crossbar Architectures - Blocking • M inputs x N outputs • Switch configuration: “set of input-output pairs simultaneously connected” that define the state of the switch • For X crosspoints, each point is either ON or Off, so at most 2X different configurations are supported by the switch. • Case 1: • - (3,2) ok • - (4,3) blocked

33. Input channels 1 2 Input channels 3 4 1 2 3 4 Output channels Crossbar Architecture - Wide-Sense Non-blocking Rule: To connect ith input to the jth output, the algorithm sets the switch in the ith row and jth column at the “BAR” state and sets all other switches on its left and below at the “CROSS” state. • Case 2: • - (2,4) ok • (3,2) ok • (4,3) ok

34. 1 1 2 4 4 Inputs 3x3 Outputs 5 N N Crossbar Architectures – 2 Layer • Only uses 6 x 9 = 54 cross points rather than 9 x 9 = 81 • Penalty is loss of connectivity

35. Crossbar Architectures - 3 Layer 1 1 2 2 3 3 4 4 Output ports 5 Input port 5 6 6 7 7 8 8 9 9 Blocking still possible http://www.aston.ac.uk/~blowkj/index.htm

36. Crossbar Architectures - 3 Layer Blocking 1 1 • The first four connections have made it impossible for 3rd input to be connected to 7th output 2 2 3 3 * 4 4 5 5 6 6 7 * 7 8 8 9 9 The 3rd input can only reach the bottom middle switch The 7th output line can only be reached from the top output switch.

37. Crossbar Architecture - Features Architecture: Wide Sense Non-blocking Switch element:N2 (based on 2 x 2) Switch drive: N2 Switch loss:(2N-1).Lse +2Lfs SNR: XT – 10log10(N-1) Where XT: Crosstalk (dB), Lse: Loss/switch element Lfs: Fibre-switch loss

38. Crossbar Architecture - Properties • Advantages: • simple to implement • simple control • strict sense non-blocking • Low crosstalk: Waveguides do not cross each other • Disadvantages • number of crosspoints = N2 • large VLSI space • vulnerable to single faults • the overall insertion loss is different for each input-output pair: Each path goes through a different number of switches

39. time 1 1 MUX time 1 2 1 2 1 2 TSI TSI 3 MUX 4 3 3 4 4 3 1 2 4 Time-Space Switching Arch. • Each input trunk in a crossbar is preceded with a TSI • Delay samples so that they arrive at the right time for the space division switch’s schedule Note: No. of Crosspoints: 4 (not 16)

40. TSI TSI TSI TSI TSI TSI TSI TSI Time-Space Switching Arch. • Can flip samples both on input and output trunk • Gives more flexibility => lowers call blocking probability • Complex in terms of: - Number of cross points - Size of buffers -Speed of the switch bus (internal speed)

41. nxp kxk pxn 1 1 1 1 n n 32 33 2 2 2 64 32 32 64 993 k p k N= 1024 Stage1 Stage 2 Stage 3 Clos Architecture • It is a 3-stage network • - 1st & 2nd stages are fully • connected • - 2nd & 3rd stages are fully • connected • - 1st & 3rd stages are not • directly connected • Defined by: (n, k, p, k, n) • e.g. (32, 3, 3, 3, 32) • (3, 3, 5, 2, 2,) • Widely used • Stage 1 (nxp) • Stage 2(kxk) • Stage 3 (pxn)

42. Clos Architecture In this 3-stage configuration N x N switch has: • 2pN + pk2 crosspoints (note N = nk) (compared to N2 for a 1-stage crossbar) • If n = k, then the total number of crosspoints = 3pN, which is < N2 if 3p < N. Problems: • Internal blocking • Larger number of crossovers when p is large.

43. Clos Architecture – Blocking • If p < 2n-1, blocking can occur as follows: • Suppose input 1 want to connect to output 1 (these could be any fixed input and outputs. • There are n-1 other inputs at k-switch (stage 1). Suppose they each go to a different switch at stage 2. • Similarly, suppose the n-1 outputs in the first switch other than output 1 at the third stage are all busy again using n-1 different switches at stage 2. • If p <  n-1 + n-1 +1 = 2n-1 then there will be no line that input 1 can use to connect to output 1.

44. Clos Architecture – Blocking • If p = 2n -1, then • Total Switch Element: 2kn(2n-1) + (2n -1)k2 • Since k = N/n, therefore • the number of switch elements is minimised when n ~(N/2) 0.5. Thus the number switch elements = 4 (2)0.5N3/2 – 4N, which is less than N2 for the crossbar switch

45. Clos Architecture – Non-blocking • If p 2n -1, • the Clos network is strict sense non-blocking (i.e. there will free line that can be used to connect input 1 to output 1) • If pn, • thenthe Clos network is re-arrangeably non-blocking (RNB) (i.e. reducing the number of middle stage switches)

46. Clos Architecture – Example • If N and n are equal to 100 and 10, respectively, then • the number of switches at the 1st & 3rd stages are N/n = 1000/10 = 100. • at the 1st stage, they are 10 x p switches • at the 3rd stage they are p x 10 switches. • the 2nd stage will have p switches of size 100 x 100. • If p = 2n-1=19, then the resulting switch will be non-blocking. • If p < 19, then blocking occurs. • For p =19, the number of crosspoints are given as follow:-

47. Clos Architecture – Example contd. • In the case of a full 1000 x 1000 crossbar switch, no blocking occurs, requiring 106 crosspoints. • For n = 10 and p = 19, • each switch at stage 1 is a 10 x 19 crossbar requiring 190 crosspoints and there are 100 such switches. Same for the third stage. So the 1st & 3rd stages use 2x190x100 = 38,000 crosspoints altogether. • The 2nd stage consists of p = 19 crossbars each of size 100 x 100, because N/n = 100. So stage 2 uses 190,000 crosspoints. • Altogether, the Clos construction uses 228,000 crosspoints Vs. the 106 points used by the complete crossbar.

48. Clos Architecture – Example contd. Since k = N/n, therefore the number of switch elements is minimised when = n ~(N/2)0.5 = (500) 0.5 =~ 32 We would then use 44 switches in the 1st & 3rd stages and p = 2n-1= 2x23 – 1 = 45. Since n = 23 does not divide 1000 evenly, thus we actually have 12 extra inputs and outputs that we could switch with this configuration ( 23x44=1012 and 1012 - 1000 = 12). So we use 2x23x44x45=91,080 crosspoints in the 1st & 3rd stages and an additional 44x44x45=87,120 crosspoints in the 2nd stage. Thus the total number of crosspoints in the best Clos construction involves fewer than 180,000 crosspoints for a non-blocking switch as compared with the 1,000,000 for the complete crossbar and about 190,000 for n = 10. This is a factor of over 11 less equipment needed to switch 1000 customers!

49. 2 2 2 2 N/2 N/2 Benes N/2 N/2 Benes N N Benes Architecture • NxN switch (N is power of 2) RNB built recursively from Clos network: • 1st step Clos(2, N/2, 2, N/2, 2) • Rearrangably non-blocking (RNB)

50. Benes Architecture - contd. • Number of stages = 2.log2N - 1 • Number of 2x2 switches /each stage = N/2 • Total number of crosspoints ~N.(log2N -1)/2 • For large N, total number of crosspoint = N.log2N • Benes network is RNB (not SNB) and so may need re-routing: • Modular switch design • Multicast switches can be built in a modular fashion by including a copy module in front of the point-to-point switch