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Transmission Technology: what’s the big deal?

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Fiber Optronics In-Line Amplification (ILA) Erbium-Doped Fiber Amplifiers (EDFA) Dispersion Compensation Gain Equalization Optical Add/Drop Multiplexing ... – PowerPoint PPT presentation

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Title: Transmission Technology: what’s the big deal?


1
Transmission Technology whats the big deal?
  • Hint We are not talking about manual or
    automatic transmissions for cars!

2
Transmission Technology
  • The simplest transmission system is a fiber
    jumper from one piece of client equipment to
    another
  • Data goes in, data comes out
  • No complex operations, no settings
  • Just a piece of glass

Cisco Catalyst 6509
Cisco Catalyst 6509
Systems
Systems
10GE Transmission System
Fiber pair lt80km (Transmit and Receive)
3
Essentially a Semaphore
  • The transmitter turns a laser on and off 10
    billion times per second. The receiver converts
    the light back to an electrical signal.
  • For non-WDM systems, the source laser is a
    non-temperature controlled source that consumes a
    broad spectral bandwidth.
  • Nominal frequencies are typically 1310 or 1550.

11111010101
Power
Time
1550nm
Power
20nm
Wavelength
4
Optical Limitations
  • Attenuation in fiber (dB loss)
  • Chromatic Dispersion (CD)
  • Polarization Mode Dispersion (PMD)
  • Non-linear Optical Fiber effects
  • Due to non-linear index of refraction
  • Four Wave Mixing (FWM)
  • Self Phase Modulation (SPM)
  • Cross Phase Modulation (XPM)
  • Due to stimulated scattering
  • Raman
  • Brillouin
  • Ultimately Optical Signal to Noise Ratio (OSNR)

5
Fiber Loss
80 km ? 100x loss
6
Optical Amplifiers Compensate Loss
Amplifier
80-100km
Input
After Loss
After Amplifier
Added Noise
Power
Wavelength
7
Chromatic Dispersion
Frequency components of modulated signal travel
at different velocities in fiber
8
Data distortion from dispersion
0110
10101
010
160 km
80 km
Propagation Distance
1s
0 km
0s
Time
NRZ distortion very pattern dependent!
9
Dispersion Compensation
  • For longer reaches, dispersion compensation
    devices provide dispersion of opposite sign and
    slope to the transmission fiber
  • The precision required in these devices scales as
    the square of the bit rate
  • Compensation is incorporated in systems and is
    available for common fiber types

10
DWDM
  • To get more information on a single fiber, use
    more wavelengths!
  • DWDM systems use temperature controlled lasers to
    lock laser wavelength to a very specific
    frequency.

0.6nm
11
Example Fiber Nonlinearity (FWM)
Output
Input
Number of Mixing Terms M ½(N3 N2)
31,200 terms for 40ch.
  • 25 km Dispersion-Shifted Fiber
  • 3 mW/Channel

12
Optical System Limitations
  • Optical amplifiers generate noise
  • Total noise is proportional to number of
    amplifiers x gain of each amplifier
  • Various effects limit the amount of optical power
    that can be launched
  • At the receiver, the signal power must be some
    fixed ratio larger than the noise (OSNR)

Combined, these effects constrain the length and
capacity of a given system.
13
Transmission System Building Blocks
  • Fiber
  • Optronics
  • In-Line Amplification (ILA)
  • Erbium-Doped Fiber Amplifiers (EDFA)
  • Dispersion Compensation
  • Gain Equalization
  • Optical Add/Drop Multiplexing (OADM)
  • Terminal
  • Optical Muxing/DeMuxing
  • Transceivers
  • Tributaries

14
Transmission Technology and Fiber Choice
  • Fiber Choice
  • 100s of thousands of fiber miles and multiple
    national networks were installed over the last
    several years
  • New fiber types, large count cables
  • Factors affecting performance
  • Chromatic Dispersion (CD)
  • Polarization-Mode Dispersion (PMD)
  • Fiber Non-linearity (FWM, SPM, XPM, Raman, etc)

15
Commonly Available Fiber Types
Fibers before 1993 may have significant PMD!
16
1550nm Low-Loss Wavelength Band
At 1550nm, wide region of low-loss wavelengths is
irresistible for WDM systems even with high
dispersion.
17
Conventional Single-Mode Fiber (SMF)
  • First single-channel systems operated at 1310nm
    (good laser materials)
  • Zero dispersion point at 1310nm.
  • WDM systems moved to 1550nm wide low-loss
    window, but higher dispersion
  • Disp.-Limit 1000 km at 2.5Gb/s in SMF, so not
    really a problem for OC-48.

D(1530-1565nm) 16 - 19 ps/nmkm DD 0.065
ps/nm2km Aeff 85 um2
18
Dispersion-Shifted Fiber (DSF) Oops!
  • Move the zero dispersion point to 1550nm, so no
    dispersion compensation required for 1550nm
    signals, even at 10G.
  • However, lack of dispersion at 1550 aggravates
    FWM and severely limits optical power levels for
    C-band DWDM systems. Thus, DSF was a bad idea
    for DWDM.
  • Substantial amounts of DSF in some U.S. networks.
  • Small effective core area, so very nonlinear.

19
Dispersion-Shifted Fiber
L-band systems attractive for DSF because of
reasonable dispersion values
20
Lucent TrueWave Classic
  • Some dispersion is good for DWDM systems because
    the optical power is reduced, thus reducing FWM.

SMF-28 DSF TWC
D(1550nm) 2 ps/nmkm
21
Lucent TrueWave - RS
  • If some dispersion is good for DWDM, then more
    must be even better!
  • Increase dispersion from 2ps to 4ps/nmkm _at_ 1550
  • Significantly reduced dispersion slope
  • But small effective area

D(1530-1565nm) 2.6 6.0 ps/nmkm D(1565
1600nm) 4.0 - 8.6 ps/nmkm DD 0.045
ps/nm2km Aeff 55 um2
SMF-28 DSF TWC TWRS
22
Corning E-Leaf
  • 4 ps/nmkm average dispersion
  • Larger dispersion slope, but
  • Increased effective core area to equal SMF

D(1530-1565nm) 2.5 - 6 ps/nmkm DD 0.083
ps/nm2km Aeff 75 um2
SMF-28 DSF TWC TWRS E-LEAF
23
Transmission System Building Blocks
  • Fiber
  • Optronics
  • In-Line Amplification (ILA)
  • Erbium-Doped Fiber Amplifiers (EDFA)
  • Dispersion Compensation
  • Gain Equalization
  • Optical Add/Drop Multiplexing (OADM)
  • Terminal
  • Optical Muxing/DeMuxing
  • Transceivers
  • Tributaries

24
  • Most sites in inter-city deployments are
  • In-Line Amplifiers (ILAs)
  • ILAs include
  • Optical Amplification
  • Dispersion Compensation
  • Gain Equalization
  • Management

Boston
108
ILA
104
72
ILA
81
ILA
85
Ann Arbor
ILA
New York
30
Detroit
85
71
95
59
ILA
Cleveland
109
111
ILA
Chicago
Princeton
86
96
ILA
103
102
ILA
73
81
Philadelphia
56
ILA
Pittsburgh
98
ILA
ILA
ILA
54
ILA
99
ILA
ILA
72
100
80
Baltimore
110
71
78
ILA
ILA
78
ILA
ILA
ILA
65
Washington DC
107
ILA
97
Richmond
90
ILA
104
ILA
ILA
ILA
95
83
91
91
Raleigh
ILA
Nashville
89
75
Memphis
Charlotte
105
96
No OSA
Little Rock
101
OSA
ILA
ILA
101
ILA
80
90
102
108
91
81
ILA
ILA
Huntsville
ILA
108
ILA
89
ILAGE
ILA
ILA
ILA
ILA
109
101
ILA
95
Terminal
95
ILA
Atlanta
90
Birmingham
ILA
89
OADM
105
ILA
Dallas
Splice
103
104
90
100
ILA
ILA
ILA
25
Erbium-Doped Fiber Amplifier (EDFA)
Spools of Erbium-doped fiber are gain medium.
G F F
Stage 1
Stage 2
EDF
EDF
VOA
Pump
Pump
Pump
Pump
Two-stage EDFA
Laser pumps provide power.
Dispersion Compensator
DCM
Compensates for accumulated chromatic
dispersion.
26
Distributed Raman Amplifier
Plant fiber is gain medium!
Couples pump power (800mW to 1W) in
counter-propagating direction.
Coupler
Pump
Pump
Compensates for accumulated chromatic
dispersion.
Pump
Pump
Dispersion Compensator
DCM
Laser pumps provide power. Pump frequencies 100nm
lt ls
27
Gain Equalization
  • Gain equalization is required due to
  • Amplifier gain is frequency (channel) dependent
  • Fiber attenuation is frequency (channel)
    dependent
  • Channels interact with each other in fiber (FWM,
    Raman, etc.)
  • Channels accumulate power variations resulting in
    reduced OSNR!
  • Gain equalization restores optimal channel power
    across the spectrum.
  • Various mechanisms are available
  • Demux-VOA-Mux
  • Grating-LCD

28
DGE Architecture
Ingress composite signal
Egress composite signal
Collimating Lens
Collimating Lens
Imaging Lens
Imaging Lens
Grating
Grating
LCD Array
LCD array selectively attenuates individual
wavelengths under software control.
First grating disperses wavelengths.
Second grating converges wavelengths.
29
Boston
  • Sites can also be Terminals or OADM.
  • Terminals and OADMs include
  • Optical Muxing and De-muxing
  • Amplification and Dispersion Compensation
  • Channel termination on client equipment
  • Regeneration
  • Management

108
ILA
104
72
ILA
81
ILA
85
Ann Arbor
ILA
New York
30
Detroit
85
71
95
59
ILA
Cleveland
109
111
ILA
Chicago
Princeton
86
96
ILA
103
102
ILA
73
81
Philadelphia
56
ILA
Pittsburgh
98
ILA
ILA
ILA
54
ILA
99
ILA
ILA
72
100
80
Baltimore
110
71
78
ILA
ILA
78
ILA
ILA
ILA
65
Washington DC
107
ILA
97
Richmond
90
ILA
104
ILA
ILA
ILA
95
83
91
91
Raleigh
ILA
Nashville
89
75
Memphis
Charlotte
105
96
No OSA
Little Rock
101
OSA
ILA
ILA
101
ILA
80
90
102
108
91
81
ILA
ILA
Huntsville
ILA
108
ILA
89
ILAGE
ILA
ILA
ILA
ILA
109
101
ILA
95
Terminal
95
ILA
Atlanta
90
Birmingham
ILA
89
OADM
105
ILA
Dallas
Splice
103
104
90
100
ILA
ILA
ILA
30
Terminals
  • Terminals provide for
  • Optical amplification and dispersion compensation
  • Optical muxing, de-muxing, and gain equalization
  • OE/EO termination/generation of line-side optical
    wavelengths
  • FEC generation/recovery and performance
    monitoring
  • Electrical muxing/de-muxing of tributary signals
  • OE/EO termination/generation of client
    connections (tributaries)
  • OEO Regeneration
  • Management
  • Terminals exist at
  • Locations at the end of a route
  • Locations where regeneration is required
  • Locations at intermediate sites on a route via
    OADM or GOADMTM
  • Locations in a metro area via Distributed
    TerminalsTM

31
Basic Terminal Architecture
Client Equipment
Tributaries
Transceivers
ITU l
Optical Muxing
Optical Amplification
Dispersion Compensation
DCM
Router
Transceiver
10GE
Post Amp
MUX
Transceiver
TDM
OC-192
Mgmt
Transceiver
ATM
4xOC48
Ethernet
Transceiver
4x1GE
Pre- Amp
De-MUX
DCM
Trib-side
Line-side
32
Regeneration
  • Regeneration is required in traditional long-haul
    (LH) systems to extend reach beyond a single
    systems capabilities.
  • On LH systems, regeneration is generally required
    every 500-600km.
  • Required due to OSNR limitations in LH systems
    optical design
  • No or limited FEC
  • Simple NRZ modulation
  • Simplistic dispersion compensation
  • No gain equalization
  • Operation in C-band or multiple bands
  • Ultra-Long-Haul (ULH) systems achieve reaches of
    2000 to 6000km, thus eliminating the need for
    most regeneration.

33
Regeneration
  • Regeneration takes two basic forms
  • Back-to-Back terminals with patches between
    tributaries.

DCM
DCM
Transceiver
Transceiver
Post Amp
Post Amp
Transceiver
Transceiver
MUX
De-MUX
Transceiver
Transceiver
Transceiver
Transceiver
DCM
DCM
Transceiver
Transceiver
Pre- Amp
Post- Amp
Transceiver
Transceiver
De-MUX
MUX
Transceiver
Transceiver
Transceiver
Transceiver
Terminal
Terminal
34
Regeneration
  • Regeneration takes two basic forms
  • Back-to-Back terminals with patches between
    tributaries.
  • Special regeneration modules.

DCM
DCM
Regenerator Module
Post Amp
Post Amp
Regenerator Module
MUX
De-MUX
Regenerator Module
Regenerator Module
DCM
DCM
Regenerator Module
Pre- Amp
Post- Amp
Regenerator Module
De-MUX
MUX
Regenerator Module
Regenerator Module
Regenerator
35
  • Regeneration adds cost and complexity to
    networks!
  • Example of LH system with 5-span reach
  • 12 regeneration sites have been added
  • Some systems are short due to city placement
  • Some regens are in locations that are difficult
    to service (MoNLA)
  • Provisioning express wavelengths becomes very
    difficult
  • Incremental wavelengths become very expensive

Boston
108
ILA
104
72
ILA
81
ILA
85
Ann Arbor
ILA
New York
30
Detroit
85
71
95
59
ILA
Cleveland
109
111
ILA
Chicago
Princeton
86
96
ILA
103
102
ILA
73
81
Philadelphia
56
ILA
Pittsburgh
98
ILA
ILA
ILA
54
ILA
99
ILA
ILA
72
100
80
Baltimore
110
71
78
ILA
ILA
78
ILA
ILA
ILA
65
Washington DC
107
ILA
97
Richmond
90
ILA
104
ILA
ILA
ILA
95
83
91
91
Raleigh
ILA
Nashville
89
75
Memphis
Charlotte
105
96
No OSA
Little Rock
101
OSA
ILA
ILA
101
ILA
80
90
102
108
91
81
ILA
ILA
Huntsville
ILA
108
ILA
89
ILAGE
ILA
ILA
ILA
ILA
109
101
ILA
95
Terminal
95
ILA
Atlanta
90
Birmingham
ILA
89
OADM
105
MoNLA
Dallas
GOADMTM
103
104
90
100
Splice
ILA
ILA
ILA
36
Optical Add/Drop Multiplexers (OADM)
On LH or ULH systems, OADMs are utilized to add
and/or drop wavelengths at intermediate sites
(non-terminals) while allowing express
wavelengths to continue in the optical domain.
Terminal
Terminal
OADM
TXR
TXR
OADM
ILAs
TXR
TXR
TXR
TXR
TXR
TXR
Site A
Site B
Site C
Site D
  • There are two basic types of OADM architectures
  • Static (a.k.a. Fixed or Banded)
  • Dynamic

37
Static OADM
  • Fixed or banded OADM designs pre-determined
    which wavelengths are added/dropped based on
    static filters placed during the initial
    installation
  • Advantages Cheap capital costs.
  • Disadvantages
  • Requires precise fore-knowledge of add/drop
    configuration
  • Non-flexible static configuration that is
    difficult to change
  • Express wavelengths in add/drop band are
    regend at OADM sites

OADM
TXR
TXR
OADM
ILAs
TXR
TXR
TXR
TXR
TXR
TXR
Channels are statically dropped via filters
during the initial installation.
38
Static OADM
Static Thin-Film Filter (TFF) selects specific
wavelengths to be dropped.
Non-dropped wavelengths are optically passed
through.
G F F
TFF
TFF
DCM
EDF
EDF
VOA
Pump
Pump
Pump
Pump
OADM
Typically, 4 to 8 specific channels are dropped.
Terminal
Dmx
Mux
Wavelengths are optically de-muxed.
Express wavelengths that are dropped must be
regend (OEO).
R x
R x
R x
T x
T x
T x
Receivers perform OEO conversion to client signal.
R
39
Dynamic OADM
  • Dynamic OADMs allow wavelengths to be
    added/dropped on an individual wavelength basis
    via dynamically re-configurable devices
  • Advantages
  • Wavelength topology can be dynamically changed to
    match needs.
  • Minimization of unnecessary OEO of express
    wavelengths
  • Minimized operational costs (no visits to
    intermediate sites)
  • Disadvantages More expensive capital costs.

OADM
TXR
TXR
OADM
ILAs
TXR
TXR
TXR
TXR
TXR
TXR
Individual channels are dynamically dropped via
software control of switching devices.
40
Dynamic OADM
3dB coupler splits optical power and broadcasts
all wavelengths to drop port.
Software controlled DGE blocks dropped channels
and gain equalizes through channels
DGE
DCM
Coupler
Coupler
EDF
EDF
EDF
Pump
Pump
Pump
Pump
Pump
Pump
OADM
All wavelengths appear on drop port!
Terminal
Only added wavelengths are coupled back into
route.
Dmx
Mux
Wavelengths are optically de-muxed.
R x
R x
R x
T x
T x
T x
Receivers perform OEO conversion to client signal
only for dropped wavelengths.
Transmitters perform OEO conversion from client
signal only for added wavelengths.
R
41
Generalized OADM (GOADMTM)
  • Generalized OADMs allow individual wavelengths
    to be cross-connected between different routes
    without leaving the optical domain.
  • Useful at fiber junctions.
  • Cost effective at high express channel counts

TXR
Channels are dynamically cross-connected via
software control of switching device.
TXR
GOADMTM
OADM
TXR
TXR
ILAs
TXR
TXR
TXR
TXR
TXR
TXR
42
Boston
  • Washington DC becomes a GOADMTM
  • Wavelengths can be provisioned, completely
    optically, between any two points without
    regeneration up to the maximum system reach.

108
ILA
104
72
ILA
81
ILA
85
Ann Arbor
ILA
New York
30
Detroit
85
71
95
59
ILA
Cleveland
109
111
ILA
Chicago
Princeton
86
96
ILA
103
102
ILA
73
81
Philadelphia
56
ILA
Pittsburgh
98
ILA
ILA
ILA
54
ILA
99
ILA
ILA
72
100
80
Baltimore
110
71
78
ILA
ILA
78
ILA
ILA
ILA
65
Washington DC
107
ILA
97
Richmond
90
ILA
104
ILA
ILA
ILA
95
83
91
91
Raleigh
ILA
Nashville
89
75
Memphis
Charlotte
105
96
No OSA
Little Rock
101
OSA
ILA
ILA
101
ILA
80
90
102
108
91
81
ILA
ILA
Huntsville
ILA
108
ILA
89
ILAGE
ILA
ILA
ILA
ILA
109
101
ILA
95
Terminal
95
ILA
Atlanta
90
Birmingham
ILA
89
OADM
105
ILA
Dallas
GOADMTM
103
104
90
100
Splice
ILA
ILA
ILA
43
Metro Solutions - Distributed TerminalTM
DCM
Post Amp
50km
MUX
Transceiver
DCM
DCM
Transceiver
Transceiver
Post Amp
Pre- Amp
Transceiver
MUX
De-MUX
Transceiver
Terminal
DCM
Transceiver
Transceiver
Pre- Amp
DCM
Transceiver
De-MUX
Post Amp
MUX
Terminal
Transceiver
DCM
Transceiver
Transceiver
Distributed Terminals allow sets of wavelengths
to be extended into a metropolitan area up to
50km.
Pre- Amp
Transceiver
De-MUX
Terminal
44
Metro Solutions - Tributary Extension
  • Tributary interfaces may be optically extended to
    remote locations via
  • Extended reach tributary optics for single
    channel over dark fiber
  • IR-1 (20km_at_1310), IR-2 (40km_at_1550)
  • LR-1 (40km_at_1310), LR-2 (80km_at_1550)
  • 10GE LR (40km) and ER (80km)
  • GigE 1000Base-ZX (100km)
  • CWDM
  • 8 wavelengths of GigE/OC-48 up to 80km
  • Passive external muxing
  • GBICs and SFFPs available
  • ITU DWDM
  • Up to 32 channels of 10GE/OC192 up to 80km
  • Passive external muxing
  • ITU Grid DWDM MSAs available
  • Eliminates separate metro systems for
    distribution in metro area.

Transceiver
10GE
Transceiver
OC-192
Transceiver
4xOC48
Transceiver
8x1GE
45
Metro Solutions - GOADMTM (Metro Switching
Application)
  • Metro connectivity can be achieved with GOADMTM
  • Supports Metro connectivity and ULH connectivity
    completely optically.
  • More cost-effective Metro-reach transceivers
    can be utilized within a city for
    terminal-to-terminal connectivity.
  • ULH/XLH-reach transceivers can be utilized for
    inter-city wavelengths.
  • Both card variations can exist in same system
    simultaneously.
  • Diverse Metro routes can be supported for
    protection applications.

To ATL
To DEN
DALLAS
Gateway
ULH Path
Metro Locations
ULH Xcvr
Terminal Regen GOADM Router/BXC Metro Xcvr ULH
Xcvr
46
Its a Complex Problem
  • Long haul systems are impacted by a variety of
    effects
  • The design of these systems requires a mix of
    experts
  • Optical effects
  • Electronics
  • Software
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