introduction to optical networking
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Introduction to Optical Networking:From Wavelength Division Multiplexing
to Passive Optical Networking
Dr. Manyalibo J. Matthews
Optical Data Networking Research
Bell Laboratories, Lucent Technologies
Murray Hill, NJ 07974 USA
University of Tokyo Visit March 22, 2004
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T.Harris A.Harris M.Matthews1997 2000
AT&T Lucent Uber Alles Lucent A la Carte
1996 2001
spectroscopy,NSOM,Confocaldevice physics network subsystems!
Evolution of Lucent and Matthews/Harris Lab:
Akiyama MatthewsTunableLasers
TelecomLasersSemiconductor Laser
Device Physics
QuantumWire Lasers
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Outline
Introduction Overview of Optical Networking
Types of Networks Fiber, Lasers, Receivers
Coarse Wavelength Division
Multiplexing Ethernet Passive Optical Networks Conclusions & Future
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Emergence of Optical Networks
Optical
L
ineSystem
OLS 40/80GOLS 400G800G/1.6T
Mesh
BackboneNetwork Regional
Pointof
Presence
CO-1
CO-n
Core/Backbone/LongHaul
Regional/Metro
Access/Enterprise
EPON
node
Metro
DMX
LocalServiceNodeMetro
Edge
Switch
Metro
Edge
Switch
OpticalCross
Connect
Metro
DMX
Access
Node
PassiveW
DM
PassiveWDM
C/DWDM
C/DWDM
C/DWDM
MetroEdge
Switch
DSL,FTTH
PON
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Wavelength Division Multiplexed (WDM)
Long-Haul Optical Fiber Transmission System
Transmitter
Transmitter
Transmitter
Receiver
Receiver
Receiver
M
UX
D
E
M
U
XOptical Amplifier
1
2
3
WDM Routers Erbium/Raman Optical Amplifier
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Categorizing Optical Networks
Who Uses
it?
Span
(km)
Bit Rate
(bps)
Multi-
plexing
Fiber Laser Receiver
Core/
LongHaul
Phone
Company,
Govt(s)
~103 ~1011
(100s of
Gbps)
DWDM/
TDM
SMF/
DCF
EML/
DFB
APD
Metro/
Regional
Phone
Company,
Big Business
~102 ~1010
(10s of
Gbps)
DWDM/
CWDM/
TDM
SMF/
LWPF
DFB APD/ PIN
Access/
LocalLoop
Small
Business,
Consumer
~10 ~109
(56kbps
- 1Gbps)
TDM/
SCM/
SMF/
MMF
DFB/ FP PIN
DWDM: Dense Wavelength Division Multiplexing (
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Optical Fiber Attributes
Attenuation: Due to Rayleigh scattering and chemical absorptions,the light intensity along a fiber decreases withdistance. This optical loss is a function of wavelength(see plot).
Dispersion: Different colors travel at different speeds down the
optical fiber. This causes the light pulses to spreadin time and limits data rates.
Types of Dispersion
Chromatic Dispersionis caused mainly by thewavelength dependence of the index ofrefraction (dominant in SM fibers)
Modal Dispersionarises from the differences ingroup velocity between the modes travelling
down the fiber (dominant in MM fibers)
t
t t
t
launch receive
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Non-Linear Effects in Fibers
Self-Phase Modulation: When the optical power of a pulse isvery high, non-linear polarization termscontribute and change the refractiveindex, causing pulse spreading and delay.
Four-wave Mixing: Non-linearity of fiber can cause mixingof nearby wavelengths causinginterference in WDM systems.
Stimulated BrillouinScattering: Acoustic Phonons create sidebands that
can cause interference.
Cross-Phase Modulation: Same as SPM, except involving more than
one WDM channel, causing cross-talkbetween channels as well.
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800 900 1000 1100 1200 1300 1400 1500 1600 1700
0.5
1.0
1.5
2.0
2.5
3.0
FirstWindow Second
Window
ThirdWindow
ATTENUATION
(dB/km
)
WAVELENGTH (nm)
1310nm 1550nm
Attenuation/Loss in Optical Fiber
First Window @ 850nm
High loss; First-gen. semiconductor diodes (GaAs)
Second Window @ 1310nm
Lower Loss; good dispersion; second gen. InGaAsP
Third Window @ 1550nm
Lowest Loss; Erbium Amplification possible
850nm
First window, second window,third window correspond(roughly) to first, second andthird generation opticnetwork technology
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Dispersion Characteristics*
1310nm 1550nm850nm
800 900 1000 1100 1200 1300 1400 1500 1600 1700
-120
-90
-60
-30
0
3.0
FirstWindow
SecondWindow
ThirdWindow
DISPERSIO
NC
OEFF
,D
(ps
/km-n
m)
WAVELENGTH (nm)
Standard SMF has zero dispersion at 1310nm
Low Dispersion => Pulses dont spread in time
Dispersion compensation needed at 1550nm
Limits data transmission rate due to ISI (inter-symbolinterference)
Dispersion not so important at 850nm
Loss usually dominates
* Modal dispersion notincluded
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Characterization of System Quality
Bit Error Rate: input known pattern of 1s and 0s and see how many
are correctly recongnized at output.Eye Diagram: Measure openness of transmitted 1/0 pattern using
scope triggered on each bit.
Eye opening
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Effect of Dispersion and Attenuation on Bit Rate
30
10
1
Bit rate (Mb/s)
Distance
(km
)
0.1 10 100 1000 10,0001
1550nm
1310nm850nm
Dispersion limitedAttenuation limited
sing
le-m
odefib
er
multi-m
odefiber
Coaxialcable
For short reaches (1-2 km), all optics are Gigabit capable
For longer reaches (~10 km), only 1310/1550 nm optics are Gigabit capable
20
x x
Cat 3limit
Cat 7limit
Cat 5limit
x
Twisted Pair
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Technology Trends
850nm & 1310nm Preferred by high-volume,
moderate performancedata comm manufacturers
1310nm & 1550nm Preferred by high performancebut lower volume (today)
telecomm manufacturers
Reason? You need lots of them, they dont need to go far,and youre not using enough fiber ($) to justify wavelength
division multiplexing (WDM), I.e. low-quality lasers are OK.
Reason? You dont need lots, but they have to be goodenough to transmit over long distances cost of fiber (andTDM) justifies WDM 1550nm is better for WDM
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DFB vs. FP laser
Simple FP
mirror
gain
cleave
+
-mirror
gain
AR coating
+
-Etchedgrating
DFB
FP: Multi-longitudinal Mode
operation Large spectral width
high output power
Cheap
DFB: Single-longitudinal Mode
operation Narrow spectral width
lower output power
expensive
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Fiber Bragg Grating External CavityLaser for Access/Metro Networks
SHOW PLOTS OF FBG-ECL DATA
SHOW PICTURE OF XPONENTS EXTENDED REACH FP
Typical FBG-ECL:
Bell Labs FBG-ECL:
HR AR
gainFBGLensed
tip
T=25C
T=85C
HR AR
gainFBG
XB regionT=25,85C
1-2nm grating
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Fiber Bragg Grating External Cavity Laser
FBG-ECLoutput
TypicalFP output
1305 1310 1315 1320 1325-70
-60
-50
-40
-30
-20
Power(dB)
wavelength (nm)
Narrow FBG bandwith limitsoutput ~1nm for extended
reach or WDM applications.
Simple design (AR-coated FP,XBR, butt-coupled FBG)
Mode-hop free operation
over 0-70C
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20 30 40 50 60 70 80
1310.3
1310.4
1310.5
1310.6
1310.7
1310.8
1310.9
1311.0
ave
dependence 0.008nm/C
Wavelength(nm)
Temperature (oC)
Wavelength Stability of FBG-ECL
CW, ~40mA bias
DFB drift ~ 0.1nm/oC
FP drift ~ 0.3nm/oC
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Filter bandwidths ofWDM Mux/Demux
0.8nm (100GHz)
>100 channels (C+L+S)
20nm
18 channels (O,E,S,C,L)
3.2nm (400GHz)
32-64 channels (C+L+S)
DWDM: High channel count, narrow channel spacing Temp-stablized DFBs required Temp-stablized AWGs required (typically)
CWDM: Low channel count, large channel spacing Uncooled DFBs can be used Filters can be made athermal
xWDM?: Moderate channel count, moderate channel spacing FBG-ECL or Temp-stablized DFBs required Filters can be made athermal suitable for athermal WDM PON!
1260nm 1610nm
1480nm 1610nm
1480nm 1610nm
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Example 1: 10Gbps Coarse WDM
-Used currently in Metro systems (rings, linear, mesh)-Spacing of CWDM grid determined by DFB wavelength drift-Current systems limited to 2.5Gbps due to cheaper optics-Possible upgrade to 10Gbps?
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CWDM Lasers
16 uncooled, directly modulated CWDM lasers (DMLs)
rated for2.5 Gb/s direct modulation (cheap! - $350 a piece)
NRZ-modulation at 10 Gb/s (careful laser mounting; no device selection)
2.5-Gb/s DML 50 line
47 chip resistor
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CWDM System Improvement usingElectronic Dispersion Compensation
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Example 2: Ethernet Passive OpticalNetworks
NO Active Elements in Outside Plant
Enable triple-play services
Simple & cheap
IP Video
Services
PSTN
Internet PON
Headend/COHomes/Businesses
Outside Plant
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Choices of PONs
Architecture/Layout Upstream Multiplexing
OLT
ONU
ONU
OLT
WDM:simple, expensive
TDM: simple, cheap
SCM: complex, expensive
Linear Bus: lossy, fiber lean
Ring: lossy, protected
OLT
ONU
Simple or Cascaded Star: low loss
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
ONU
OLT=Optical Line Termination (head-end)ONU=Optical Network Unit (user-end)
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EPON Access Platform
Video/IPTelevisionVoice/IP POTS serviceHigh-speed data
Residence
MetroEdge
Voice/IP
Services
Business
Broadcast Video
VOD
Management
MetroNetwork
Data
10G Ethernet
Or up to 61GbE
EPON
opticalsplitter
opticalsplitter
32 subscribers
Per EPON
Panther EPON OLT Chassis
1232384 subscribersDynamic bandwidthGuaranteed QOS
premium access
.
..
12 EPONS
Lucent
EPON ONU
+ Gateway
Note on Lasers:-Use DFB at headend (shared)
-Use FP at Homes (not shared)
DFB
FP
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ONU Design
ReportGenerator
PacketMemory
TX
RX
ControlParser
Demux
watchdog0
watchdog1
discoveryPeriodicReport
generatorEPON driver
EPON core
RX
TX
EPON MAC
Mux
TimestampCRCLLIDMemory
managerQueue
manager
GMII
SERDES&
Optics
CPUFPGA
SerialPort
GigE uplink
Packetmemory
1.25G BMBiDi Xcvr
Flash (CPU)memory
10/100bTdiagnosticport
SERDES(w/CDR)
PON
FPGA w/EmbeddedProcessor
CHILD
BOARD
PARENT
BOARD
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ONU
GrantList
GateGenerator
Packet
Memory
RTT table
TX
RX
ControlParser
Demux
watchdog0
watchdog1
discovery Keepalive scheduler
EPON driver MPCP driver
EPON core MPCP core
RX
TX
EPON MAC
Mux
TimestampCRCLLIDMemory
managerQueue
manager
RTT Processor
Report processor
GMII
SERDES&
Optics
Reporttable CPUFPGA
OLT Design
SerialPort
GigE uplink
Packetmemory
1.25G BMBiDi Xcvr
Flash (CPU)memory
10/100bTdiagnosticport
SERDES(w/CDR)
PON
FPGA w/EmbeddedProcessor
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Downstream: continuous, MAC addressed Uses Ethernet Framing and Line Coding Packets selected by MAC address QOS / Multicast support provided by Edge Router
Upstream: Some form of TDMA ONU sends Ethernet Frames in timeslots Must avoid timeslot collisions Must operate in burst-mode BW allocation easily mapped to timeslots
EPON downstream/upstreamtraffic
1 2 3 2
1
2 2
3
1 2 3 21
2 2
3
1
23
2
12
32
1
2
3
2
1
2
2
OLT
OLT
3
3
33
O
NU
O
N
UO
N
U
O
N
UO
NUO
N
U
EdgeRouter
ONU: Optical Network Unit
OLT: Optical Line Termination
EdgeRouter
Control Gates
Control Reports
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PON TDMA BURSTMODE OPTICS
Because upstream transmissions must avoid collisions, each ONU musttransmit only during allowed timeslot
Transmitting 0s during quiet time is not allowed!
Average 0 power ~ -10 to 5 dBm
Summing over 16 ONUs would result in a ~1dBm noise floor
Distinct from Bursty nature of Ethernet TRAFFIC Ethernet transmitters never stop transmitting (Idle characters)
CDR circuit at receiver stays locked even when no data is transmitted
Besides PONs, other systems use burstmode
Wireless Shared buses/backplanes
Optical burst switched (OBS) systems
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BURSTMODE TRANSMITTERS
Tx FIFO Encoder Serializer TransmitterData
Clock
Prebias
PhysicalMedia
currentIth
Opticaloutput
0
1
Modulationcurrent
off
Driving LD belowThreshold causes
Jitter Off-state ~ -40dBm
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BURST-MODE RECEIVERS
PROBLEM OF FAST CDR LOCKING
GAIN LEVELING & DYNAMIC
RANGE OF OPTICAL RECEIVER
Rx FIFO CDRLimiting
AmpReceiverData
Clock
DeserializerDecoder
Reset
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IMPACT ON EFFICIENCY
~1460 Bytes64 Bytes
CRC
DMAC
SMAC
VL
AN
HLEN
TOS
LEN
ID
OFF
ST
TTL
PROT
CHK
SM
SIP
DIP
ACK
HLEN
FL
AGS
WSZE
CHK
SM
URG
SPT
DPT
SEQ Data
1:4OLT
ONU 1
1:8ONU 2
...
Upstream BurstsCascaded PON
guardband
ONU 1ONU 2
Ethernet IP TCP
Laseron
AGCsettle
CDRlock
Bytesync
ONU1 payload(Ethernet Frames)
Laseroff
Throughput Efficiency
0.7
0.75
0.8
0.850.9
0.95
1
1.05
0 1000 2000 3000
AGC+CDR+LASER ON/OFF (ns)
Utilisation Our current situation
Standar
d GE
transcei
vers
Burst-mode transceivers
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Conclusions
Optical Networking getting closer andcloser to end user For Metro, CWDM is lowest cost solution,
but must be improved to handle 10Gbps
PON systems could deploy in mass overnext 1-2 years, with EPON one of theleading standards
Lasers dominate cost, therefore useful tostudy physics of low-cost laser structures!
THANK YOU VERY MUCH!(Domo Arigato Gozaimashita!)
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Spare Slides
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SYSTEM PENALITIES in PONs
Attenuation in PONs dominated by power splitters:
Dispersion penalty for MLMs (Agrawal 1988)
Typical p-i-n receivers w/ ~150nA current noise, 1.25Gbps, R~1
-27dBm (about1W) Typical 1310nm FP lasers 0dBm output power (about1mW)
dBBDLISI 8.2)(142++=
(For N=32, L=20km; typically ~ 24-26dB w/ connectors, splices, etc.)
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MODE PARTITION NOISE EFFECT
Mode Partition Noise is due to fluctuations
in individual Fabry Perot modes coupled
with optical fiber dispersion.
Due to uncontrolled temperature and
wavelength drift in FP diodes, d/dT ~0.3nm/oC, and D()~S
0, the magnitude of
this penalty will change with time.
Due to lack of screening of FP mode
partition coefficient, k, the magnitude of
this penalty will also depend on particularFP!
D(ps
/nm.km)
(nm)0
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Bit Rate and Reach Limits due to MPN
Reach dependent on quality of laser (k factor)
(another) Reason why asymmetry in PONs (e.g., 155/622Mbps) are favored GigE?
Worst-case isnt quite fair statistical model shows most fiber-laser combinations, D
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REDUCING MPN
Dispersion Compensation at OLT Additional Loss, some cost
One-size wont fit all, SMF 0~ 1300-1325nm
High-pass filtering using SOA
Low frequency MPN components are partially removed
Very low noise FP LD driver
Replace FP w/ narrow-line source DFB is current solution
1310nm VCSEL (high-power) Fiber Bragg Grating ECL also a possibility if cost/integration
improves
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Structure of WDM MUX/DEMUX(Arrayed Waveguide Grating)
(100) Si
B,P-doped v-SiO2
Thermal v-SiO2
P-doped v-SiO2 core
} core layer
TM, y
TE, x
Input
waveguides
Output
waveguides
Arrayed
waveguides Star coupler
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Types of Lasers & Receivers used for
Telecommunications
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