LightPath Networking

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LightPath Networking
2
Light Propagation

• Light propagates due to total internal reflection
• Light gt critical angle will be confined to the
  core
• Light lt critical angle will be lost in the
  cladding

3
Fiber Types

• Multi-Mode supports hundreds paths for light.
• Single-Mode supports a single path for light

4
Fiber Types

• Multi-Mode
• 50/62.5um core, 125um clad
• Atten-MHz/km 200 MHz/km
• Atten-dB/km 3dB _at_ 850nm
• MMF has an orange jacket

• Single-Mode
• 9um core, 125um cladding
• Atten-dB/km 0.4/0.3dB 1310nm/1550nm
• SMF has a yellow jacket

5
Attenuation Vs. Wavelength
6
Degradation In Fiber Optic Cable

• Attenuation
• Loss of light power as the signal travels through
  optical cable
• Dispersion
• Spreading of signal pulses as they travel through
  optical cable

7
Technologies Available

• Transmitters (Light Sources)
• LEDs - 850/1310nm
• Used with MMF up to 250Mb/s
• Short distances lt1 Km
• Semiconductor Lasers 850/1310/1550nm
• VCSELs, Fabry Perot and DFB
• 1310/1550 can be used with MMF or SMF
• Short to long distances
• Low to High data rates (Mb/s to Gb/s)

8
FP and DFB Laser Spectrum

• FP laser
• Emits multiple evenly spaced wavelengths
• Spectral width 4nm
• DFB laser
• Tuned cavity to limit output to single
  oscillation / wavelength
• Spectral width 0.1nm

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Which Laser Type is Better?

• Distributed Feed Back
• Used in wavelength division multiplexing systems
• Less susceptible to dispersion than FP laser
• Used for medium and long haul applications

• Fabry Perot
• Ideal for low cost pt-pt
• MMF or SMF
• Not suitable for WDM due to /- 30nm ? variation
• Dispersion is a serious issue at Gb/s rates

10
Technologies Available

• Receivers (Detectors)
• PIN Photodiodes
• Silicon for shorter ?s (eg 850nm)
• InGaAs for longer ?s (eg 1310/1550nm)
• Good optical sensitivity
• Avalanche Photodiodes (APDs)
• Up to 50 more sensitivity than PIN diodes
• Primarily for extended distances in Gb/s rates
• Much higher cost than PIN diodes

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Dispersion - Single-Mode

• FP and DFB lasers have finite spectral widths and
  transmit multiple wavelengths
• Different wavelengths travel at different speeds
  over fiber
• A pulse of light spreads as it travels through an
  optical fiber eventually overlapping the
  neighboring pulse
• Narrower sources (e.g DFB vs. FP) yield less
  dispersion
• Issue at high rates (gt1Ghz) for longer distances
  (gt50Km)

12
Dispersion - Multi-Mode Fiber

• Modal Dispersion
• The larger the core of the fiber, the more rays
  can propagate making the dispersion more
  noticeable
• Dispersion determines the distance a signal can
  travel on a multi mode fiber

13
Attenuation

• It is the reduction of light power over the
  length of the fiber.
• Its mainly caused by scattering.
• It depends on the transmission frequency.
• Its measured in dB/km (
  )

14
Chromatic Dispersion (CD)

• Light from lasers consists of a range of
  wavelengths, each of which travels at a slightly
  different speed. This results to light pulse
  spreading over time.
• Its measured in psec/nm/km.
• The chromatic dispersion effects increase for
  high rates.

Source www.teraxion.com
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Transmission Bands

• Optical transmission is conducted in wavelength
  regions, called bands.
• Commercial DWDM systems typically transmit at the
  C-band
• Mainly because of the Erbium-Doped Fiber
  Amplifiers (EDFA).
• Commercial CWDM systems typically transmit at
  the S, C and L bands.
• ITU-T has defined the wavelength grid for xWDM
  transmission
• G.694.1 recommendation for DWDM transmission,
  covering S, C and L bands.
• G.694.2 recommendation for CWDM transmission,
  covering O, E, S, C and L bands.

Band Wavelength (nm)
O 1260 1360
E 1360 1460
S 1460 1530
C 1530 1565
L 1565 1625
U 1625 1675
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Single Mode Fiber Standards I

• ITU-T G.652 standard Single Mode Fiber (SMF) or
  Non Dispersion Shifted Fiber (NDSF).
• The most commonly deployed fiber (95 of
  worldwide deployments).
• Water Peak Region it is the wavelength region
  of approximately 80 nanometers (nm) centered on
  1383 nm with high attenuation.

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Single Mode Fiber Standards II

• ITU-T G.652c - Low Water Peak Non Dispersion
  Shifted Fiber.

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Single Mode Fiber Standards III

• ITU-T G.653 Dispersion Shifted Fiber (DSF)
• It shifts the zero dispersion value within the
  C-band.
• Channels allocated at the C-band are seriously
  affected by noise due to nonlinear effects (Four
  Wave Mixing).

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Single Mode Fiber Standards IV

• ITU-T G.655 Non Zero Dispersion Shifted Fiber
  (NZDSF)
• Small amount of chromatic dispersion at C-band
  minimization of nonlinear effects
• Optimized for DWDM transmission (C and L bands)

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Single Mode Fiber Standards
ITU-T Standard Name Typical Attenuation value (C-band) Typical CD value (C-band) Applicability
G.652 standard Single Mode Fiber 0.25dB/km 17 ps/nm-km OK for xWDM
G.652c Low Water Peak SMF 0.25dB/km 17 ps/nm-km Good for CWDM
G.653 Dispersion-Shifted Fiber (DSF) 0.25dB/km 0 ps/nm-km Bad for xWDM
G.655 Non-Zero Dispersion-Shifted Fiber (NZDSF) 0.25dB/km 4.5 ps/nm-km Good for DWDM
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Multiplexing - WDM
WDM Multiplexed signal
Signal 1
Signal 1
Signal 2
Signal 2
MUX
DEMUX
Signal 3
Signal 3
Single-mode Fiber
Signal 4
Signal 4

• Wavelengths travel independently
• Data rate and signal format on each wavelength is
  completely independent
• Designed for SMF fiber

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Multiplexing - WDM

• WDM Wave Division Multiplexing
• Earliest technology
• Mux/Demux of two optical wavelengths
  (1310nm/1550nm)
• Wide wavelength spacing means
• Low cost, uncooled lasers can be used
• Low cost, filters can be used
• Limited usefulness due to low mux count

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Multiplexing - DWDM

• DWDM Dense Wave Division Multiplexing
• Mux/Demux of narrowly spaced wavelengths
• 400 / 200 / 100 / 50 GHz Channel spacing
• 3.2 / 1.6 / 0.8 / 0.4 nm wavelength spacing
• Up to 160 wavelengths per fiber
• Narrow spacing higher cost implementation
• More expensive lasers and filters to separate ?s
  
• Primarily for Telco backbone Distance
• Means to add uncompressed Video signals to
  existing fiber

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Multiplexing - CWDM

• CWDM Coarse Wave Division Multiplexing
• Newest technology (ITU Std G.694.2)
• Based on DWDM but simpler and more robust
• Wider wavelength spacing (20 nm)
• Up to 18 wavelengths per fiber
• Uses un-cooled lasers and simpler filters
• Significant system cost savings over DWDM
• DWDM can be used with CWDM to increase channel
  count or link budget

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CWDM Optical Spectrum

• 20nm spaced wavelengths

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DWDM vs. CWDM Spectrum
1.6nm Spacing
dB
1470 1490 1510 1530 1550
1570 1590 1610
Wavelength
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xWDM Technology
Dense WDM

• Fine channel spacing, 0.8 nm typical
• High precision stabilization of Lasers
• High component cost

0,8 nm
l/nm
1550
Coarse WDM

• Wide channel spacing, 20 nm typical
• Lower precision of Lasers
• Significantly lower component cost

20 nm
1550
1570
1590
1610
1470
1490
1510
1530
l/nm
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DWDM Migration
Capacity Expansion
l/nm
1550
1470
1490
1510
1530
1570
1590
1610

• Each CWDM channel can be utilized with 8 DWDM
  channels
• Resulting maximum system capacity
• 8 x 8 64 DWDM channels
• CWDM and DWDM channels can be mixed
• Soft migration path

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DWDM Migration
CWDM to DWDM Channel utilization
2,5 Gbps
ch1
8ch DWDM

DWDM
ch2
CWDM DWDM
CWDM

ch8
ch8

• 8 channel DWDM system per CWDM channel
• Soft migration path
• Mixing of CWDM and DWDM channels
• No interruption of CWDM channels

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Amplification CWDM vs. DWDM
80 km
80 km
Requires 1 amplifier per wavelength
CWDM wavelengths

1 EDFA amplifies all wavelengths in the C-band
EDFA
C-band
(DWDM wavelengths)

Requires 1 amplifier per wavelength
L-band

• EDFA Erbium-doped Fibre Amplifier
• DWDM is typically used for longer distance
  transport, because EDFA amplifiers enable very
  long spans more cost-effectively than CWDM.
• Amplifiers typically cost approximately US 20k
  or more

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How Much Capacity ?
100Gbps Duo-binary Wave-locker 1b/s/Hz 16 symbol levels 4 bits per symbol required. 256 symbol levels 8 bits per symbol required.
40Gbps NRZ/CS-RZ/ Wave-locker 10G overlay ? 0.4b/s/Hz Duobinary Wave-locker 0.8b/s/Hz 16 symbol levels 4 bits per symbol
10Gbps No issue NRZ 0.1b/s/Hz Reduced reach Wave-locker NRZ 0.2b/s/Hz Reduced reach No ROADMs Wave-locker 0.4b/s/Hz
100GHz 50GHz 25GHz
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Optical Routing - Definitions

• Optical Routers Optical IN , Optical OUT
• Photonic Routers Optical IN OUT but 100
  photonic path
• OOO- Optical to Optical to Optical switching
• Optical switch fabric
• OEO- Optical to Electrical to Optical conversion
• Electrical switch fabric
• Regenerative input and outputs

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Photonic Technologies

• MEMS (Micro Electro-Mechanical System)
• Liquid Crystal
• MASS (Micro-Actuation and Sensing System )

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MEMS Technology

• Steer the Mirror
• Tilted mirrors shunt light in various directions
• 2D MEMS
• Mirrors arrayed on a single level, or plane
• Off or On state Either deployed (on), not
  deployed (off)
• 3D MEMS
• Mirrors arrayed on two or more planes, allowing
  light to be shaped in a broader range of ways
• Fast switching speed (ns)
• Photonic switch is 11 IN to OUT (i.e. no
  broadcast mode)

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Liquid Crystal Technology

• Gate the light
• No Moving Parts
• Slow switch speed
• Small sizes (32x32)
• Operation based on polarization
• One polarization component reflects off surfaces
• Second polarization component transmits through
  surface

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MASS Technology

• Steer the fiber
• Opto-mechanics uses piezoelectric actuators
• Same technology as Hard Disk Readers and Ink Jet
  Printer Heads
• Small-scale opt mechanics no sliding parts
• Longer switch time (lt10msec)

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OEO Technology
Fiber
Inputs
High BW Electrical XPNT
Fiber
Outputs
Electrical
Inputs
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
EQ
Electrical
Outputs
Local
Monitoring
CPU
Indication
Interface
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OEO Routing

• Optical ltgt Electrical conversion at
  inputs/outputs
• Provides optical gain (e.g. 23 dB)
• High BW, rate agnostic electrical switching at
  core
• SD, HD, Analog Video (digitized), RGBHV, DVI
• Fast switching (lt10us)
• Full broadcast mode
• One IN to ANY/Many outputs
• Build-in EO / OE to interface with coax plant
• Save converter costs

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Regeneration - Optical vs Photonic

• Photonic is a lossy device that provide no
  re-amplification or regeneration
• Signal coming in at 23dBm leaves at 25dBm
• OEO router provides 2R or 3R (re-amplify,
  reclock, regenerate)
• Signals come in at any level to 25dBm
• Leave at 7dBm (1310nm) or 0dBm (CWDM)

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Applications - Design Considerations

• Types of signals
• Signal associations
• Fiber infrastructure
• Distance/Loss
• Redundancy
• Remote Monitoring

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Types of Signals
FacilityLINK - Fiber Optics Platform
MULTI WAVELENGTH
MULTI FIBER
SDI HDSDI ANALOG DVB-ASI RGB
OR
VIDEO
AES ANALOG DOLBY E INTERCOM
AUDIO
OPTICAL ROUTING
WDM CWDM DWDM
SPLITTERS PROTECTION SWITCHING
RS232/422/485 GPI/GPO
CONTROL
10/100 ETHERNET GBE FIBER CHANNEL
DATACOM
70/140 MHz I/F L-BAND CATV
RF
SONET OC3/12 T1/E1 DS3/E3
TELECOM
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Design Considerations

• Fault Protection
• Protection against fiber breaks
• Important in CWDM and DWDM systems
• Need 21 Auto-changeover function with switching
  intelligence
• Measurement of optical power levels on fiber
• Ability to set optical thresholds
• Revert functions to control restoration

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Design Considerations

• Remote monitoring is key due to distance issues
• Monitor
• Input signal presence and validity
• Laser functionality and bias
• Optical Link status and link errors
• Pre-emptive Monitoring
• Input cable equalization level
• CRC errors on coax or fiber interface
• Optical power monitoring
• Data logging of all errord events
• Error tracking and acknowledgment

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Design Examples Single Link
-7dBm _at_ 1310nm
-32dBm
SDI _at_ 270Mb/s
SDI _at_ 270Mb/s
SD OE
SD EO
40 Kms
-23dBm
-7dBm _at_ 1310nm
HDSDI _at_ 1.485Gb/s
HDSDI _at_ 1.485Gb/s
HD OE
HD EO
40 Kms
Loss Budget
Dispersion
SD HD HD
FP DFB
TX Power (dBm) -7 -7 0
RX Sens (dBm) -32 -23 -23
Available Budget 25 16 23
Distance (Km) 40 40 40
Fiber Loss (0.35dB/km_at_1310) 14 14 14
Connectors 4 4 4
Connector Loss 1 1 1
Total Loss 15 15 15
Headroom 10 1 8
SD HD HD
FP DFP
FP Line width (nm) 4 4 0.2
Dispersion (ps/nm.km) 2 2 2
Distance (km) 40 40 40
Dispersion (ps) 320 320 16
RX Jitter Tolerance (UI) 0.4 0.4 0.4
RX Jitter Tolerance (ps) 1480 270 270
Headroom (ps) 1160 -50 254
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Post House Facility Link New
Location 2
Location 1
E to O O to E
SDI _at_ 270Mb/s
O to E E to O
SDI _at_ 270Mb/s
1310
E to O O to E
O to E E to O
HDSDI _at_ 1.485Gb/s
HDSDI _at_ 1.485Gb/s
Analog Video Analog Audio
Mux EO OEDemux
DemuxOE EO Mux
Analog Video Analog Audio
Mux EO OEDemux
DemuxOE EO Mux
Analog Video Analog Audio
Analog Video Analog Audio
CWDM D16
CWDM M16
2 Kms
Gbe
Gbe
GBE
GBE
10/100 Mb/s Ethernet
10/100 Mb/s Ethernet
10/100
10/100
RS422
RS422
RS422
RS422
Mux EO Demux OE
Demux OE Mux EO
AES
AES
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RF Over fiber optics -Applications
Satellite Receiver
Typical Satellite Application With SNMP Monitoring
Satellite Receiver
L-Band Downlink (950Mhz 2250Mhz)
Satellite Receiver
Vertical
Satellite Receiver
BPX-RF
DA8-RF
LB EO
LB OE
Router
Horizontal
Satellite Receiver
BPX-RF
LB OE
LB EO
LNB Power
Satellite Receiver
Remote SNMP Monitoring Control
Satellite Receiver
Ethernet / SNMP
Ethernet / SNMP
Ethernet / SNMP
HPA
DA-RF
Video Mod
C or Ku Up Conv
BPX-RF
IF OE
IF EO
DA-RF
Video Mod
IF Uplink (70/140Mhz)
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Large Video MAN Fully protected
KABC
Circle seven
LA Zoo
5.75
TV
Gaming
7.25
Dodger
Stadium
2.5
7.5
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Single Fiber Technology
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4Gbps CWDM Link

• SANET, AMREJ cheapest solution
• Gigabit Ethernet,
• Low cost switches as repeaters (Cisco 3550)
• CWDM

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Modular xWDM System
Passive Optical Modules

• Options
• 8 channels Mux/Demux
• 2 channels Add/Drop
• 4 channels Add/Drop

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Modular xWDM System
Line Interface Modules
Standard Duplex
Internal Line
Power2
Power1
Passive Optical
Standard Simplex
Internal Line
Active Optical
Line Interf.
Protected West
Protected East

• Options
• Standard Line Interface (duplex)
• Standard Line Interface (simplex)
• Protected Line Interface
• Add/Drop Line Interface

Internal West
External West
Internal East
External East
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Modular xWDM System
Configurable Channels (CWDM Lambdas)

• Wavelength color code
• 1470 nm
• 1490 nm
• 1510 nm
• 1530 nm
• 1550 nm
• 1570 nm
• 1590 nm
• 1610 nm

gray
violet
blue
green
yellow
orange
red
brown
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Modular xWDM System
Configurable Channels (Local Interface)
Fiber Wavel. Speed MM 850 nm 1.25
Gbps SM 1300 nm 1.25 Gbps SM 1300 nm 2,48
Gbps
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Optical drop/insert mux
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Multicast

• Drop and continue optical splitter pipes
• IPTV multicast
• Broadband Video put them all on the one
  wave-length

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GMPLS Technologies for Dynamic Optical Networks

• GMPLS standards are still evolving for optical
  networks
• Growing interest for dynamic lightpath
  configurations
• Meritons path management includes a number of
  GMPLS concepts
• OSPF routing on NEs (used for management network
  today)
• GMPLS LMP for auto network discovery, lightpath
  testing, and cable mis-wiring
• Meriton will implement GMPLS in step with
  customers key requirements for mesh networking
• Pre-provisioned shared protection (enabled by
  GMPLS signaling)
• Dynamic (best-effort) signaled protection
• Operator signaled lightpaths (S-LPs)
• Client on-demand wavelengths (O-UNI signaling)
• Participation in initiatives such as Internet2
  HOPI, CANARIE UCLP, etc., is critical