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WDM PON:Systems and Technologies

Ning Cheng and Frank EffenbergerAdvanced Technology DepartmentUS R&D Center, Huawei Technologies

ECOC workshopTurino, Italy, 2010

HUAWEI TECHNOLOGIES CO., LTD.

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WDM PON Overview

WDM PON Technologies

System Performance Limitations

Summary and Discussions


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WDM PON Systems

Dedicated bandwidth, guaranteed QoS Physical P2MP, logical P2P Protocol and data-rate transparency Simple fault localization Low ODN Loss Better security

OLT ONUsWDM TRx array Colorless ONUs

16~32 wavelengths


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WDM PON Applications

Broadband service: Residential: Fiber to the home/curb Enterprise: Fiber to the business

Backhaul Applications: Mobile backhaul: 2G/3G/4G GPON/EPON backhaul

2G

4G4G3G

3G

Enterprise

ResidenceCentralOffice

GPON


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WDM PON Deployment

KDDI (2008~2009) WDM-PON field trial

Small field trials are in Korea, Europe and others No large scale commercial deployment yet.

Agder (Norway, 2009) FTTH, field trial with 100 lines

100M/

UNET (Netherland, 2009) Business, field trial with 100 lines

100M/

KT (2005~2009) FTTC&FTTH,

150k lines field trial;

100M/

1.25G/

(TL and wavelength reuse WDM-PON)

Hancock (USA, 2009) FTTB

field trial

100M/

Source: FSAN workshop


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TunableLaser

IL FP Laser RSOA

Cost &Performance

Technology Challenges

Colorless ONU is mandatory OAM and inventory issue with colored ONUs Possible colorless ONU solutions:

Tunable laser Injection locked FP lasers Reflective semiconductor optical amplifiers

Key determining factors Economics: compared to 10G PONs? Performance: >1Gb/s per lambda and >20km reach


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WDM PON Overview





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Colorless Light Sources Spectrum Sliced Broadband Lightsource

LED/SLED/SOA as colorless lightsource Spectrum sliced by AWG for appropriate channels

Injection locked FP laser Specially designed FP laser as colorless lightsource FP laser operates on the wavelength of external injected lightwave

Reflective Semiconductor Optical Amplifier Semincoductor optical amplifier as lightsource External injected lightwave is amplified, modulated and reflected to CO Using the saturation property of SOA, the downstream wavelength can be used

as an injection to SOA and hence reused for upstream transmission Tunable Laser

Widely tunable semiconductor laser as colorless lightsource Need protocol to set the operating wavelength


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Spectrum Slicing

Because of the low bit rate, spectrum slicing is not a good option for WDM PON

AdvantagesLow cost; no seed light is needed.

DisadvantagesLow bit rate (


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Tunable Lasers

AdvantagesNo Seed light is neededHigh bit rate(>2.5Gb/s), long transmission distance (~80km)

DisadvantagesVery expensive; dynamic wavelength assignment algorithm is needed

Tx/Rx

Tx/Rx

Rx

CO

WDM

TL

ONU

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

AWG

1 2 n-1 n

RxWDM

TL

ONU


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Injection Locked FP Laser

AdvantagesLow cost

DisadvantagesSeed light is neededLimited bit rate and transmission distance

AWG

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Rx

ONU

WDM

IL F-P Laser

Upstream data

BroadbandLightsource

Free running spectrum

Coupler

1530nm 1565nm

1 2 n-1 n downstream

1

2

n-1

nFiltered ASE spectrum

Injection Locked

ASE seed

upstream

Downstreamdata

CO


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Reflective Semiconductor Optical Amplifiers

Advantages Relatively higher bit rate

DisadvantagesSeed light is neededLimited transmission distance

Tx/Rx

Tx/Rx

Tx/Rx

Rx

ONU

WDM

RSOA

m

i

r

r

o

r

Amplified & reflected output from RSOA

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

BroadbandLightsource

Coupler

1530nm 1565nm

ASE seed

1 2 n-1 n downstream

Filtered ASE spectrum

RSOA

AWG

Upstream data

Downstreamdata

CO


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Coherent Injection

Advantages Better performance: higher rate and longer reach

DisadvantagesDFB array is more expensive than broadband lightsource

Tx/Rx

Tx/Rx

Rx

WDM

RSOA

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Coupler

AWG

Upstream data

Downstreamdata

DFB

DFB

DFB

DFB

Seed source: DFB array

AWG

CORx

WDM

IL F-P Laser

Upstream data

Downstreamdata


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Self Seeding

Advantages lower cost: without seed

DisadvantagesPoorer performance

Tx/Rx

Tx/Rx

Tx/Rx

Rx

ONU

WDM

RSOA

m

i

r

r

o

r

Amplified & reflected output from RSOA

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Filtered ASE spectrum

RSOA

AWG

Upstream data

Downstreamdata

CO

Partial reflection

mirror


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Wavelength Reuse

Advantages lower cost: without seed

DisadvantagesErase of downstream pattern is a challenge if downstream uses intensity modulation

Tx/Rx

Tx/Rx

Tx/Rx

Rx

ONU

Couple

r

RSOA

AWG

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

AWG

Upstream data

Downstreamdata

CO

Residuedownstream

pattern

UpstreamEyediagram

Alternative modulation formats (DPSK, SCM & IRZ) used to facilitate the erasure of D/S pattern


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Comparison of Colorless LightsourcesScheme Bit rate/channel No.

channels Pros Cons

Spectrum slicing: LED Low, 1.25Gb/s Medium, ~32

InexpensiveNo seed needed

Non-standard FP needed (wide gain spectrum)Polarization dependent upon injection

RSOA: with ASE injection Medium, 10 Gbit/s Low, long reachNo seed neededWavelength flexible

ExpensiveExternal modulator neededWavelength assignment algorithm needed


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WDM PON Overview





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System Impairments Fiber Loss Fiber dispersion Intensity noise from BLS Rayleigh backscattering

Backscattering of BLS seed Backscattering of upstream and downstream signals

Noise from colorless ONUs ASE noise from RSOAs Intensity noise and mode partition noise from IL FP lasers

Reflection in the fiber link Not an intrinsic issue; can be minimized with proper installation of ODN


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RSOAs with BLS Seeding System Impairments

Fiber dispersion Rayleigh backscattering and ASE noise

Transmission Limits Dispersion limit

OSNR limit

km 30 spacing, channel 100GHzFor 25.0|| LTLD

2/12/

21

41

21

21

20

22

22

min__

_

SGSG

eGPSPeGBFhGerP

ePG

OSNRPPPP

POSNR

AWGL

seedseedAWGL

nAWGL

seed

AWGL

seed

scatteringsigscatteringseedASERIN

sigRx

+++

=

+++

=

2)1( 2 SLeCS =Rayleigh scattering coefficient


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RSOAs with BLS Seeding

0 5 10 15 20 25 30-4

-2

0

2

4

6

8

10

12

14

16

RSOA Gain (dB)O

S

N

R

(

d

B

)

20 km30 km40 km

Fiber Length

0 10 20 30 40 50 600

2

4

6

8

10

12

14

16

18

20

Fiber Length (km)

O

S

N

R

(

d

B

)

G = 15 dBG = 20 dBG = 25 dBOptimized Gain

RSOA gain

Dispersion limit for100 GHz channel spacing

OSNR vs. Fiber Length OSNR vs. RSOA Gain

System design implication: RSOA gain needs to be optimized for different fiber length


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IL FP Lasers with BLS Seeding System Impairments

Fiber dispersion: not a big issue at 1.25Gb/sThe linewidth of well-locked FP laser is less than 0.1nm

Rayleigh scattering and ASE noise

Transmission Limits OSNR Limit

min22

2

2/12/)(

41 OSNR

SGSG

ePSPePNGerP

ePOSNR

m

mLsigseedAWG

LseedFPAWG

Lseed

AWGL

sig

+++

=

2)1( 2 SLeCS =Rayleigh scattering coefficient

+= pi

dHPNkS seedphcFP ])[()(2)( 224RIN from FP laser

= dSPN FPseedFP )()(


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IL FP Lasers with ASE Seeding

0 10 20 30 40 50 600

5

10

15

20

25

30

35

40

Fiber Length (km)

O

S

N

R

(

d

B

)

0 dBm3 dBm6 dBm

Seed Power

0 10 20 30 40 50 600

5

10

15

20

25

30

35

40

Fiber Length (km)

O

S

N

R

(

d

B

)

0 dBm3 dBm6 dBm

IL FP Power

System design implications Once IL FP laser is in well-locked condition, higher seed power results in worse performance

due to ASE noise and backscattering. Higher output power from IL FP laser leads to better performance need higher bias current.

When FP laser operates with higher bias current, more optical injection power is needed.


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IL FP Lasers with ASE Seeding

System Design Implications Higher front facet reflectivity leads to better performance

Higher front facet reflectivity stronger filtering of intensity noise from seed lightHigher front facet reflectivity Lower gain lower Rayleigh scattering for upstream

However, front facet reflectivity has to be kept small FP laser gain spectrum broadening wider operating wavelength range more channels

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.414

15

16

17

18

19

20

21

22

23

24

Front Facet Reflectivity

O

S

N

R

(

d

B

)

Fiber Length 20 km

Fiber Length 30 km

Fiber Length 40 km

0 10 20 30 40 50 600

5

10

15

20

25

30

35

40

Fiber Length (km)

O

S

N

R

(

d

B

)

R1 = 0.01R1 = 0.03R1 = 0.1

Front Facet Reflectivity


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Tunable Lasers System Impairments

Fiber dispersion is not an issue at 1.25Gb/s Fiber loss is the limiting factor

Transmission Limits Loss budget

Transmission distance is limited by Tx power and Rx sensitivityTx power: 0 dBm, Rx sensitivity: -30 dBm, Fiber Loss: 0.3 dB/kmTransmission distance: 100 km

recAWGL

sig PeP 2 i.e. ( )recAWGsig PPL 2ln1


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WDM PON Overview





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Conclusions WDM PONs are attractive due to

Logical P2P connection, guaranteed bandwdith Protocol and data rate transparency, better security

However, significant cost reduction of WDM PONs is needed!

Key challenges for WDM PONs: Colorless ONUs RSOAs and IL FP lasers is less expensive, but performance need improvement Tunable laser has better performance but cost is a big issue

System Impairments in WDM PONs are reviewed Fiber loss and dispersion ASE noise and Rayleigh backscattering

Design trade-off for seeded WDM PONs RSOA with BLS seed

RSOA gain needs to be optimized for different fiber length IL FP laser with BLS seed

BLS power need to be optimized to achieve the best OSNRFront facet needs to be optimized for OSNR and operating wavelength range

Thank you

HUAWEI TECHNOLOGIES CO., LTD. Page 27

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