Control of Optical Fibre Communications Networks

1
Control of Optical Fibre Communications Networks

• Peter Farrell

2
Utopian VisionALL OPTICAL NETWORK

• Analogy with Internet
• Transmitter sends photons through the network
  (transparently) to Receiver
• Format independent
• Bit-rate independent
• Protocol independent
• The Network is very clever (BRIGHT?) and can
  figure everything out so that your information
  goes to its destination perfectly
• A bit like
• electricity too cheap to meter from the nuclear
  industryOR
• the paper free office

3
Interesting Problems to Solve to build Utopia

• Finance
• All the routing problems in the Network
• BIG optical switches
• Control of adjustable elements in the Network

4
HOW BIG?
5
Worldwide?
6
Continental
7
Metro
8
Campus
9
Size matters because

• Different transmission issues for
• 100 m building / campus
• 1 km campus
• 10 km metro
• 100 km metro/continental
• 1000 km continental
• 10000 km world
• All optical network requires (?) 10000 km
  infrastructure for a 100 m connection

10
Optical Network Control

• Most published work is on making connections,
  fault location, contention avoidance and so on
• Very little on control of adjustable elements in
  the network to optimise or at least improve the
  performance
• Alternative is to grossly over engineer the
  hardware

11
Point to Point Link Impairments
DisCo

• Tx
• Chirp
• Noise
• Finite extinction ratio
• Mux/Demux
• Filter drift
• Crosstalk
• Transmission fibre
• Loss
• Dispersion
• Nonlinear effects

• Amplifiers
• ASE/ Noise
• Crosstalk
• Wavelength dependent gain
• Rx
• Finite sensitivity
• Noise
• Bandwidth
• Everywhere
• PMD

12
Point to Point Link Adjustments
DisCo

• Tx
• Power, wavelength, chirp, modulation format,
  extinction ratio
• MUX/DEMUX
• Temperature
• Amplifier
• Gain, gain flattening filter, tilt
• Dispersion compensation
• Rx
• Gain (APD or preamp gain)
• Decision Threshold
• Decision Point

13

Long Haul Link Configuration10 Gbit/s over gt1000
km
Tx Terminal
Rx Terminal
Rx
Tx
?1
C Blue
C Blue
Rx
Tx
Rx
Tx
?40
DCF
DCF
Amp n
Amp1
Transmission Fibre
Transmission Fibre
Transmission Fibre
Tx
Rx
?41
DCF
DCF
DCF
DCF
Tx
Rx
C Red
C Red
R
R
R
Rx
Tx
?80

Tx
Rx
?81
L Blue
L Blue
Tx
Rx
Tx
?120
DCF
Rx
DCF
DCF
DCF
DCF
DCF
CCC
CCC
Tx
?121
Rx
Tx
Rx
L Red
L Red
Tx
Rx
?160
14
Point to Point Link with OADM
DisCo
OADM
DisCo
15
OADM
X
16
OADM
17
All Optical Network
Rx
Tx
Rx
Tx
18
Lots of Feedback Loops Amplifier

• Issues
• Measurement accuracy
• Signal reduction
• Transient response

19
Lots of Feedback Loops Dispersion Compensator

• Issues
• Location
• Accuracy
• Signal reduction

20
Lots of Feedback Loops Pre-emphasis

• Shares OSNR, BER or received power equally among
  channels by adjusting transmit power with time
  varying disturbances
• Simple linear iterative algorithm (and variations
  on this theme)(Chraplyvy et al 1992)
• Non-linear channel!!!!
• Like to know
• if non-linearity is significantly affecting
  performance
• Origin of non-linearity

21
Feedback Loops

• What do we measure and where?
• BER
• Channel Powers
• OSNR
• Dispersion
• Non-linearity
• Crosstalk
• Local?
• Central?
• Tradeoffs between non linearity, dispersion and
  gain
• How many channels?
• Circuit switched or Packet switched?
• Interaction with routing algorithms

22
Control..

• THE WHOLE NETWORK WORLD DOMINATION
• Link by Link
• Device by Device

23
All Optical Network
Rx
Tx
Rx
Tx
24
Point to Point Link Impairments
DisCo

• Tx
• Chirp
• Noise
• Finite extinction ratio
• Mux/Demux
• Filter drift
• Crosstalk
• Transmission fibre
• Loss
• Dispersion
• Nonlinear effects

• Amplifiers
• ASE/ Noise
• Crosstalk
• Wavelength dependent gain
• Rx
• Finite sensitivity
• Noise
• Bandwidth
• Everywhere
• PMD

25
Point to Point Link Adjustments
DisCo

• Tx
• Power, wavelength, chirp, modulation format,
  extinction ratio
• MUX/DEMUX
• Temperature
• Amplifier
• Gain, gain flattening filter, tilt
• Dispersion compensation
• Rx
• Gain (APD or preamp gain)
• Decision Threshold
• Decision Point

26
Conclusion

• Model network
• Use standard control theory to construct a
  controller