ARC Special Research Centre for Ultra-Broadband Information Networks

Control of Optical Fibre Communications Networks

Peter Farrell

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

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

HOW BIG?

Worldwide?

Continental

Hobart

Melbourne

Canberra

Sydney

Newcastle

Brisbane

Bundaberg

Rockhampton

Mackay

Townsville

Cairns

Hay

Parkes

Toowoomba

Charters Towers

Hughenden

CloncurryMt. Isa

Clare

Adelaide

CedunaPt. Augusta

Esperance

Perth

Geraldton

Mullewa

Kalgoorlie

Meekatharra

Mt. Newman

Sth. Hedland

Derby

Alice Springs

Tennant Creek

Katherine

Darwin

Glendambo

Established by 1997

Established by 1993

Metro

Campus

Size matters because …

• Different transmission issues for

– 100 m building / campus

– 1 km campus

– 10 km metro

– 100 km metro/continental

– 1000 kmcontinental

– 10000 km world

• All optical network requires (?) 10000 km infrastructure for a 100 m connection

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

Point to Point Link Impairments

• 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

Tx

Tx

Rx

Rx

DisCo

Point to Point Link Adjustments

• 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

Tx

Tx

Rx

Rx

DisCo

C Blue

C Red

Tx

Tx

Tx

Tx

Tx

Tx

Rx

Rx

Rx

Rx

Rx

Rx

L Blue

L Red

L Blue

L Red

Rx

Rx

Rx

Rx

Rx

Rx

Tx Terminal

Amp nAmp1

Rx Terminal

Tx

Tx

Tx

Tx

Tx

Tx

1

40

41

80

81

120

121

160

…

Transmission Fibre

Transmission Fibre

Transmission Fibre

DCF

DCF

C Blue

C Red

CCC

LM

DCF

DCF

R

LF

LF

CCC

LM

DCF

DCF

R

LF

LF

LM

DCF

DCF

LF

LF

DCF

DCF

DCF

DCF

R

LF

LF

CCC

CCC

Long Haul Link Configuration10 Gbit/s over >1000 km

Point to Point Link with OADM

Tx

Tx

Rx

Rx

DisCo

Tx

Tx

Rx

Rx

DisCo

OADM

OADM

X

OADM

All Optical Network

TxRx

RxTx

Lots of Feedback Loops …Amplifier

• Issues

– Measurement accuracy

– Signal reduction

– Transient response

Feedback & Control

Lots of Feedback Loops … Dispersion Compensator

• Issues

– Location

– Accuracy

– Signal reduction

Dispersion Compensator

Dispersion Measurement

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

j j

ji

i

TOTinew

OSNRP

OSNRP

PP

-50

-45

-40

-35

-30

-25

-20

1525 1530 1535 1540 1545 1550 1555 1560 1565 1570

Wavelength (nm)

Re

lativ

e P

ow

er

(dB

)

-50-45-40-35-30-25-201525153015351540154515501555156015651570Wavelength (nm)Relative Power (dB)

-50

-45

-40

-35

-30

-25

-20

1525 1530 1535 1540 1545 1550 1555 1560 1565 1570

Wavelength (nm)

Re

lativ

e P

ow

er

(dB

)

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

Control..

• THE WHOLE NETWORK – WORLD DOMINATION

• Link by Link

• Device by Device

All Optical Network

TxRx

RxTx

Point to Point Link Impairments

• 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

Tx

Tx

Rx

Rx

DisCo

Point to Point Link Adjustments

• 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

Tx

Tx

Rx

Rx

DisCo

Conclusion

• Model network

• Use standard control theory to construct a controller