Péter Barta Alcatel-Lucent 10. October 2012

WDM in backbone

2

1. ROADM solutions

2. 40G, 100G, 400G

AGENDA

3

1.

ROADM solutions

4

ROADM solutions What to achieve?

Typical 1st gen (fix multiplexer architecture) WDM network:

HUB

Ch 1-8

Ch 25-32

Ch 17-24

Ch 9-16

Ch

1-8

Ch

25-3

2

Ch

17-2

4

Ch

9-1

6

OADM

OADM

OADM

OADM

Physical WDM Ring

5

ROADM solutions What to achieve?

The targeted ROADM DWDM node provides:

1. Optical pass-trough and add/drop switching possibility for any single channel

2. Multidegree configuration in order to interconnect multiply rings and to offer the possibility to deploy meshed optical networks

3. Directionless arichitecture to allow to connect any client to any direction

4. Tunable multiplexer architecture to make short service provisioning times possible and to ensure restoration mechanisms to find spare routes if capcities are just available

Just as in any state of the art network technology in the electrical domain: any port to any direction

…

Clients

Line

… … …

Line

Line

OT

6

Key element: WSS

• WSS does

­ Mux/demuxing

­ switching (between directions)

­ spectrum alignment

WSS offers (why WSS):

­ mutidegree

­ colorless

­ all these in the optical domain (bit rate, protocol independent)

7

RX vs. TX WSS

RX WSS

Colorless ports by default

Less optimal for long reach

Efficient for Metro

TX WSS

Colorless ports not provided by default

Optimized for long reach

Efficient for Long Haul

8

RX WSS architectures 4-degree T/ROADM

CWR8

Filter (East) THRU

WDM IN

AMP IN

AMP OUT

WDM IN

AMP OUT

AMP IN

Filter (West)

CWR8

Xp

dr

CWR8

Filter (North) THRU

WDM IN

AMP IN

AMP OUT

WDM IN

AMP OUT

AMP IN

Filter (South)

CWR8

Xp

dr

Xp

dr

Xp

dr

Xp

dr

Xp

dr

Xp

dr

Xp

dr

FMUX

FMUX FMUX

FMUX

6 colorless ports BB

port

BB

port

BB

port

BB

port

6 colorless ports

6 colorless ports 6 colorless ports

9

RX WSS architectures Directionless/Colored R-OADM archistructure

Local side Line Side

WR

8

WR

8

WR

8

WR

8

Direction 1

Interconnectons

Direction 2

Direction 3

Direction 4

WR

8

OM

DX

6

5

4

3

2

1

X TRBD

TRBD

Ad

d/D

rop

ch

an

nels

TX WSS based architectures Directionless/Colorless (limited) TOADM

Multiple A/D block

istances scaling up

AnyDir A/D

Block

Mesh/Thru Connections

TX WSS

MESH4

TX WSS

MESH4

TX WSS MESH4 TX WSS

MESH4

TX WSS

RX WSS

8 O

Ts

……..

TX WSS

RX WSS

8 O

Ts

Local

A/D Block

FMUX

11

ROADM solutions What to achieve?

1. Optical pass-trough and add/drop switching possibility for any single

channel

2. Multidegree configuration in order to interconnect multiply rings and to offer the possibility to deploy meshed optical networks

3. Directionless arichitecture to allow to connect any client to any direction

4. Tunable multiplexer architecture to make short service provisioning times possible and to ensure restoration mechanisms to find spare routes if capcities are just available

5. Changing the WDM channel („recoloring”) in optical domain -> not achieved X

Just as in any state of the art network technology in the electrical domain: any port to any direction

…

Clients

Lin

e

… … …

Lin

e

Lin

e

OT

12

Functionality benchmark

1st gen WDM New gen WDM Technologies of the electrical domain (SDH, Ethernet, IP)

Meshed topology (multidirectional nodes)

No Yes Yes

End to end mangement

Partially Yes Yes

Free channel selection (colorless)

No Yes * Yes

Free direction selection (directionless)

No Yes * Yes

* depending on the node construction

FLEXIBLE GRID

Flexible Grid

Flexible Bandwidth

Fix Grid

the bandwidth of the WDM channel may vary (rate, modulation format, etc.)

Optical switch fabric (e.g. WSS) with fine granularity (e.g. 3 or 6 or 12 GHz) without filtering between the adjacent grid elements -> channel bandwidth according to the actual need

14

1/b

Meshed operation

Wavelength tracker

Wavelength Tracker™ Operation

Each channel is encoded with a unique WaveKey pair

that allows the channel to be identified and its power

monitored

The assignment of WaveKeys is managed by the NEs,

which maintain a database of the WaveKeys used in

the network.

At each detection point, the WaveKeys are detected

and their power measured.

Integrated per-channel eVOAs

serve multiple functions

­ Automatic optical power

adjustment and unique

wavelength coding

Encode once, decode many times

for fault location capability

­ Provides a transponderless

demarcation point

­ Provides intra-node optical

performance monitoring

(OPM) at all line cards

Decode based on DSP, correlation

and orthogonal coding

Low Freq signal

time

frequency

Payload (noise)

Integrated

eVOA’s for

source power

management

Internal

or

Alien

Sub-carrier

modulation

DSP

DSP WT

Decode WT

Encode

Uniquely identifies each service/wavelength in the network

MU

X AMP

16

Wavelength Tracker™ Encode/Decode Points

= Wavelength Tracker Detection Point

Tra

nsp

on

de

r

= Wavelength Tracker Insertion Point

Filter (East)

A

THRU WDM IN

AMP IN

AMP OUT

Filter (West)

A

WDM IN

Tra

ns

po

nd

er

AMP OUT

AMP IN

ADD/DROP

Each channel is encoded with a unique WaveKey pair that allows the channel to be identified and

its power monitored.

WaveKeys are encoded onto the channel at each Transponder and act as “Optical J0” Trace

Identifiers.

The assignment of WaveKeys is managed by the NEs, which maintain a database of the WaveKeys

used in the network.

Wavelength Tracker WaveKeys are detected on the following cards:

Amplifiers

Wavelength Routers

At each detection point, the WaveKeys are detected and their power measured.

Alcatel-Lucent solution: Wavelength Tracker™

Service-aware management of the optical layer

Features:

Wavelength path trace

Fault sectionalization & isolation

Remote optical power control

Threshold alarming

Automated fault correlation

Optical Fiber View Management of all wavelength on a

selected fiber

Optical Path View Management of all points along one

wavelength

18

2.

40G, 100G, 400G

Moving foreward in system capacity

19

Increasing the system capacity

• Ways of increasing the total capacity of a WDM system:

­ increasing the number of channels

­ denser grid

­ broader used band

­ increasing the data rate per channel

­ using other physical properties like polarisation

20

Increasing the number of the channels

• Current status

­ most commonly used band: C (~1530-~1565nm) -> effectively amplified by EDFA

­ todays number of channels in C band:

­ 40 (100GHz/0,8nm)

­ 80 (50GHz/0,4nm)

­ 10G/channel

• Increasing the number of channels

­ use of broader band (e.g. introducing of band L) -> rather complex (and more expensive) amplifiers, concerns in case of a migration, residual CD issues

­ denser grid in band C: less than 50GHz grid (e.g. 25GHz in case of 160 channels -> doubles only ones but blocks the way to higher bitrates (channel bandwidth)

21

Increasing the data rate per channel

• Needs rather complex modulation formats those of used up to 10G

­ Steps until now:

­ 2,5G: simplest NRZ/RZ OOK colored signals w/o any enchancements

­ 10G: still OOK but use of FEC to ensure similar performances (reach) as that of 2,5G

• Interoperability issues

­ between different modulation formats and bit rates

­ channel type dependent reach: rather complex system designs

By the time this way appears the most benefiting for system capacity upgrade.

• E.g. system capacities:

­ with 10G channels: 80x 10G: 800Gb/s

­ with 100G channels: 80x 100G: 8Tb/s

22

Transmission challenges beyond 10G

• Transmission beyond 10G is in general much more sensitive than 10G to the optical transmission impairments, e.g. 40G:

­ 4 times more sensitive to optical noise (OSNR)

­ 4 times more sensitive to fiber polarization-mode dispersion (PMD)

­ 16 times more sensitive to fiber chromatic dispersion (CD)

­ more sensitive to single-channel (“intra-channel”) nonlinear effects

• So, while at 10G the plain NRZ modulation format is sufficient to cover most LH/ULH applications, at 40G alternative modulation formats are needed to overcome these limitations

Increasing transmission challenges requiring a new modulation format

23

• new modulation format is need to overcome the impairments

• phase modulation instead of OOK

• less complex implementation: differencial PSK

• sufficient for 40G however can’t catch 10G performance

­ ~3dB improvment in OSNR tolerance but extended CD and PMD sensitivity remains

DPSK at 40G

direct detection with delay demodulation

Adjacent bit is phase reference information in phase difference

direct detection with delay demodulation

Adjacent bit is phase reference information in phase difference

24

• Local oscillator is mixed with the incoming signal

• architecture to detect any level of phase modulations

Coherent detction for better tolerance

25

Dig

ital C

lock R

ecovery

Fre

quency

and C

arr

ier

Phase

recovery

Sym

bol

identi

ficati

onPola

rizati

on

Dem

ult

iple

xin

g a

nd

Equalizati

on

Fre

quency

and C

arr

ier

Phase

recovery

Re-s

am

pling

CD

com

p.

CD

com

p.

BER

& Q

²

Sym

bol

identi

ficati

on

BER

& Q

²

j

j

Dig

ital C

lock R

ecovery

Fre

quency

and C

arr

ier

Phase

recovery

Sym

bol

identi

ficati

onPola

rizati

on

Dem

ult

iple

xin

g a

nd

Equalizati

on

Fre

quency

and C

arr

ier

Phase

recovery

Re-s

am

pling

CD

com

p.

CD

com

p.

BER

& Q

²

Sym

bol

identi

ficati

on

BER

& Q

²

j

j

ADC

ADCDSP

ADC

ADCDSP

PD2

PD3

PD3

Sam

pling S

cope

PD1

Digital signal processing

26

• Coherent detection features:

­ ability to detect absolute phase value

­ separation of polarisations (basis for polarisation multiplexing)

­ better sensitivity (detectors operate beside more optimal optical levels)

• DSP features:

­ removing (compensating) linear impairments (CD, PMD)

­ catching with the polarisation unstability -> enabling the polarisation multiplexing

­ measure of the CD and PMD: supporting operation

­ eliminating DCUs: in coherent only networks, less latency

­ w/o DCUs the high CD value along the fiber mitigates non-linear effects -> extends the reach

Rules of coherent receiver and DSP

27

• 40G: used to catch up with 10G reach

• 100G: the only way of implementing it

• 400G: also based on coherent detection wit further extensions

Modulation formats:

• 40G: PDM-BPSK, 20 GBaud symbol rate

• 100G: PDM-QPSK, 25 GBaud

• 400G: PDM-16QAM dual carrier, 25 GBaud per carrier

Symbol rate

• keep it low to fit in 50GHz spacing (80ch in C band)

• be clearly above 10G to minimize the impairments casued by 10G channels

Coherent detection in practice

PDM

28

• Issues to solve:

­ 100G can’t catch up in reach with pure coherent detection & DSP

­ 400G is even more difficult

• Alcatel-Lucent’s answer: Photonic Service Engine chip

Further improvements in coherent transmission

29

400G PHOTONIC SERVICE ENGINE Working elements

Coherent Rx Enhanced algorithms Advanced frequency & phase recovery

New modulations Dynamic demodulation HD SD

Ultra-fast ADC/DAC Higher bit converter Faster sampling

Tx DSP Wave shaping

30

• Not only a firm decesion is made if the bit is „1” or „0” as in case of classical HD-FEC but a probability is also provided

• needs more overhead

SD-FEC

31

• universal tool for different cases

• can be used for 40/100/400G transmission

• in case of 40/100G it extends the reach

­ in case of 100G the multiplier is >1,5x, needed to reach 10G / 40G coherent performance

• in case of 400G the enabler of implementation

PSE applications

PSE Year 2010 2012

Speed 100 Gb/s 400 Gb/s

Line rates 40G, 100G 40G, 100G, 400G

Capacity 8.8T >23T

Reach 2,000 Km > 3,000 Km

Power/Gb* 6500 mW 4250 mW

32

2/b

Nonlinearities

33

-20

-15

-10

-5

0

5

10

15

20

1 3 5 7 9 11 13 15 17 19 21 23 25

Effect of nonlinearity

• Resilience to OSNR and fiber nonlinearity are key factors limiting the attainable transmission reach

• 1 dB less resilience in nonlinearity is as limiting as 1 dB less resilience to OSNR

Maximum power per channel to

limit the nonlinear effects

Minimum power per channel to

guarantee the required OSNR

Number of spans

Po

wer

pe

r c

ha

nn

el [a

.u.]

Attainable reach

34

XPM

35

Penalty by XPM