OPTICAL-BOWERS by xiangpeng

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									       Optical Switching Challenges
3-D MEMS-based Dynamically Reconfigurable
      Optical Packet Switch (DROPS)


   John E. Bowers, Hsu-Feng Chou, and Chi-Heng Huang
       Department of Electrical and Computer Engineering
           University of California, Santa Barbara, CA

                      Roger Helkey
                      Calient Networks

 Acknowledgement: Farzam Toudeh-Fallah, and Russ Gyurek
             Cisco Systems, Inc., San Jose, CA
                                                           1
             Transparent Networks: Wave of the Future?

λ Is there a need?
   λ Low cost switches and networks
   λ Reconfigurable networks
λ Is there a solution?
   λ Optical switching




                                  B. Bosch (Verizon) NFOEC 2002.
                                                                   2
           How Many Ports Can a
          Nonblocking Switch Have?
• 320x320 is commercially available.
• 1100x1100 demonstrated
• What is possible?




                                       3
             2D: Crossbar Switches
                               λ N ports
                               λ N2 2x2 switches
                               4
                        1 10



                                                       2D
                        8000




                        6000




                        4000



                                                                 3D
                        2000




                           0
                                   0   20   40    60        80   100   120

      8x8 Switch                            Number of Ports
Large switches only possible with 3D architectures
                                                                       4
                      MEMS Integration




λ Current MEMS dominated by electrical IO




  75% of the area consumed by pads (4 per mirror)   5
                  382 mirror integration
    8 die/wafer                24 die/wafer




                                Denser bump bonds (200 micron pitch)




λ 1000 mirror integration with pad size reduction
  (limited by ceramic stability) or using via
  technology
λ 10,000 mirror integration requires integrated
  drivers (IO due to address/data lines)
                                                                6
                      Scaling to 10,000 ports…
          parameter           symbol   scaling
    Beam radius at waist        w0     N.5
    Beam radius at MEMS        wm      N.5
N   mirror                                       If scaling is followed:
                                                 320 port switch: 1.5 dB median loss
    Mirror diameter                    N.5
                                                 1000 port switch: 1.5 dB median loss
                                D
                                                 5000 port switch: 1.5 dB median loss
    Mirror array area
                                A       N2           Volume becomes large!!
    Optical path length
                                L       N
     Active switching
    volume                      V       N3


    Diffraction dominates!!



                                                                              7
       Bigger Switches Using Clos Architectures
      input                                output
      port 1                               port 1
               p x 2p             2p x p
                        kxk

               p x 2p             2p x p
                        kxk




                        kxk

               p x 2p             2p x p
      port N                               port N



λ 256 port switches can be used in a 3 stage
  Clos architecture to make a 32,000 port
  nonblocking switch


                                                    8
            How Many Ports Can a
           Nonblocking Switch Have?
• 320x320 is commercially available.
• 1100x1100 demonstrated
• Low loss 5000x5000 possible—beyond
  this point, diffraction loss becomes
  significant.
• Challenges:
  – Single die: denser electrical drive—CMOS
    integration


                                               9
          Switching Speed
λ Can MEMS switch faster than 50 ms?




                                       10
                                                                Switching Speed

                             λ Can MEMS switch faster than 50 ms?

                             0.5ms MEMS Switching
                                    λ    Simulations indicate limited by 8 kHz D-A sampling rate
                                    λ    Should be able to substantially reduce ringing with higher sampling
                                         rate

                                    λ    Mirror redesign will allow faster switching

                                                                                                     0
                       0
                                                                 connection                                                0.5 ms
                                               4.5 ms                         Relative Power (dB)
                                                                  port 0-2
Relative Power (dB)




                                                                                                     -5
                       -5
                                                                                                              connection             connection
                                 connection                                                                                           port 0-2
                                                                                                               port 0-1
                                  port 0-1                                                          -10
                      -10


                      -15                                                                           -15


                      -20                                                                           -20
                            -2           0      2           4    6        8                               0           0.5              1          1.5        2
                                                    Time (ms)                                                                       Time (ms)           11
       How much power is needed to
       optically switch?
λ 50 W typical now




                                     12
             MEMS: Small and low power

λ Electrostatic drive: 10 nA at 100 V (1 mW/mirror)
  λ (Research to achieve 1 nA at 20 V: 20 nW ?)
λ Present Switching module: 50 W. System: 500 W
  λ (Research to achieve 1 mW switch. 100 mW system?
    This is over 100 Tbit/s per W. 100,000 lower than
    present OEO electrical switching systems).
λ Present Size: 1 rack per 256 ports (10 Tbit/s)
  λ (Research to achieve credit card size 10 Tbit/s switch.
    This is 1000x more dense than present electrical
    switches. Research to integrate DWDM with switch).




                                                       13
            Size

λ Present networking equipment is large.
λ Switching cards possible.


                                     Small: .001 m3
                                     Sealed
                                     Self contained




                                                14
          Metrics: Motivation for Photonic Switching
λ Photonic switching has the highest throughput: 100
  Tbit/s (32 10 Gbit/s wavelengths per fiber on 320 fibers)
λ Photonic switching has the lowest power consumption:
  1 W I.e. just 10 mW/port! (vs. 10W/port for 10 Gbit/s
  electronic switching)
λ Photonic switching has the highest density: 1 shelf for
  320 40 Gbit/s ports (vs. 2 racks for 256 10 Gbit/s
  electronic switch ports)
λ Photonic switching has the lowest cost: $100/port in
  volume i.e. $10/Gbit/s for switching one 10 Gbit/s line.
  (Electrical switch costs are dominated by transponder
  costs)
λ Photonic switching allows fiber, waveband and
  wavelength switching, and is bit rate independent.
                                                       15
            Dynamically Reconfigurable Optical
                Packet Switch (DROPS)




• Combining a spectral switch and a spatial switch to
increase flexibility of a routing node
• MEMS-based spatial switch is a preferred choice for its
large port count and capacity
•Recent Cisco funded project at UCSB                        16
             Advantages of DROPS (1)

Advantage 1: Reconfigurability
• An AWGR based packet switch has a fixed mapping from
ingress to egress ports in which specific wavelengths in
each ingress port would exit from specific egress ports
based on a permutation mechanism
• In contrast, a DROPS-based switch has the potential of
routing any wavelength from any ingress port to any egress
port




                                                           17
                      Advantages of DROPS over AWGR (1)

                           Mapping of a 8x8 AWGR Router
                                  (Permutation)
                                      AWGR output port
                      l1   l2    l3     l4        l5     l6   l7   l8

                  1   1    8     7      6         5      4    3    2

                  2   2    1     8      7         6      5    4    3

                  3   3    2     1      8         7      6    5    4
AWGR input port




                  4   4    3     2      1         8      7    6    5

                  5   5    4     3      2         1      8    7    6

                  6   6    5     4      3         2      1    8    7

                  7   7    6     5      4         3      2    1    8

                  8   8    7     6      5         4      3    2    1


                                                                        18
                         Advantages of DROPS over AWGR (1)

                                          Mapping of a 8x8 DROPS
                                             (Reconfigurable)
                                                        DROPS output port
                          l1         l2         l3         l4         l5         l6         l7         l8

                   1   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   2   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   3   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8
DROPS input port




                   4   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   5   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   6   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   7   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8

                   8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8   1,2,3,…8


                                                                                                               19
         Advantages of DROPS over AWGR (2)

Advantage 2: Extra Degree of Freedom
• The combination of spectral and spatial degrees of
freedom in the DROPS mechanism provides far more
flexibility in controlling the routing of the packet in a switch
fabric as compared to only one degree of freedom
(wavelength control) in an AWGR mechanism




                                                               20
         Advantages of DROPS over AWGR (3)

Advantage 3: Scalability
• The DROPS mechanism provides scalability for a packet
switching application due to the potential scalability of the
number of ingress/egress ports in MEMS to 5000 ports.
• State of the art MEMS switch: 1100 x 1100 ports




                                                                21
        Advantages of DROPS over AWGR (4)

Advantage 4: Fast Recovery without l change
• The dynamical reconfigurability of the DROPS mechanism
would allow fast recovery from a line card or path failure
without any need for modifying the packet wavelength,
which is not the option in AWGR-based approach. This
provides more flexibility in fast recovery scenarios.




                                                         22
               Example of DROPS Application




• Example of a non-blocking DROPS node using NxN AWGRs and MEMS switch
• Several AWGRs can be connected by a large scale MEMS switch to extend the
total capacity of the switching node

                                                                          23
                Example of Integrated DROPS




• Free space grating can be integrated with a 3-D MEMS switch for compactness


                                                                           24
        Experimental Demonstration of DROPS




• Demonstrate DROPS with 10-Gb/s optical packets
• Using O-E-O style wavelength converter and 1x40 AWG (100GHz spacing)
• Calient DiamondWave® PX 256x256 port 3-D spatial switch
                                                                         25
3-D MEMS Spatial Switch (2)




                              26
               O-E-O Packet Wavelength Converter

       -0.7 dBm
       1550 nm                              Vpp=5.5 V                                                            Electrical Signal
                              PD
                                                                                                         ~0 dBm
                                                                                                      Any l in C-band
                        V-I          SGDBR                             LiNbO3
     Packets         Converter        Laser                             MOD                                            ~ 3 dB penalty


                                     Tuning signal

                  DC Probes
                                   l Switching time ~ 1 ns                                                   l Converted Packets

                                                                                                               Spectrum

                                                                                         -10




                                                     Intensity (dBm)
                                                                                         -20




                                                                       Intensity (dBm)
Photo of
                                                                                         -30
Fast-Tunable
SGDBR Laser                                                                              -40


                                                                                         -50


                                                                                               1540   1545      1550    1555    1560   1565
                                                                                                             Wavelength (nm)

                  RF Probes                                                                            Wavelength (nm)                 27
                     Eye Diagrams of Routed Packets
10-Gb/s NRZ signal, λ=1550 nm



 Continuous Signal




     Input Packets      Wavelength Converted
                                                            Output port 1      Output port 1
Long packet: 160 ns     Long packet  1546.8 nm
Short Packet: 120 ns    Short packet  1552.2 nm
Guard time: 140 ns
(Guard time chosen
                                                            Output port 2       Output port 2
for 50% gating cycle)

                                          Ch23: 1546.8 nm    State 1           State 2
                                                                            (Reconfigured)

                                          Ch30: 1552.2 nm
                                                                                                28
                             BER Results

        Short Packets (120 ns)                  Long Packets (160 ns)




• Received power of each curve adjusted to match the continuous case
• Power penalties are less than 3 dB, dominated by the wavelength converter
• Switching of routing status does not impose extra power penalty

                                                                          29
                           Summary


» A Dynamically Reconfigurable Optical Packet Switch (DROPS)
  is proposed and demonstrated for increased flexibility in a
  packet switching node
» 3-D MEMS spatial switch is preferred for its large port count
» The combination of both spectral and spatial switching in
  DROPS has advantages in:
       1. Reconfigurability
       2. Extra Degree of Freedom
       3. Scalability
       4. Fast Recovery with Wavelegnth Change
» Experimental results show that no power penalty is imposed
  by adding the spatial switch


                                                                  30

								
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