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Presented at 2011 Layer 123 Terabit Optical Networking, Cannes, France, Apr. 12, 2011
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Advanced Modulation For High Data Rate Optical Transmission: 100G and Beyond
Leigh Wade, Infinera
The State of the Market Today
800G •10Gb/s •NRZ •C-band
80 ch. @ 10G = 800G
More channels
Higher Data Rates
More Spectrum
I will propose that photonic integration is an excellent solution to all three
capacity challenges
Why do we need more than 800G?
Lower Cost per Bit
More Capacity
Higher Speed Services
Fiber Exhaust & Network Economics C
ost
per
Usa
ble
Bit
Time
10G λ
40G λ
100G λ
You want to move to 40G here…
…but what if you hit fiber exhaust here?
Excess cost
Fiber exhaust can force uneconomic network decisions
Double Density Optics Mean Investment Protection and “Option Value”
Conventional 80-96 λ WDM
1 λ per 50 GHz
At 40% bandwidth growth, double-density optics mean two more years to select the lowest cost transmission.
Infinera “Double Density” WDM
1 λ per 25 GHz
800G in the C-band 1.6T in the C-band
Why doesn’t everybody offer Double Density?
Two basic reasons:
WSS ROADMs designed
around 50GHz spacing
Operational challenge of 160 discrete transponders on a single fiber!!
What are you going to see?
Adding a single PIC-based line card, with 10x10Gb/s waves
100Gb/s of capacity for the same effort as one 10Gb/s transponder
Optical Spectrum Analyzer
Stopwatch
Existing 10G waves on the fiber
“Gaps” for additional waves
PICs reduce operational burden by 10x
But the rest of the optical industry does not have access to PICs so…
They are under pressure to move to 40G and 100G as soon as possible
Not necessarily when it’s economical!
Fiber Capacity
Advanced Modulation
Coherent Detection
High Gain FEC
Table Stakes
Core Switching & Grooming 3
Large Scale PICs 2
Photonic Integration 1
Differentiators
100G Technology Features
Complex modulation requires complex optical circuits
Why do I need Complex Modulation?
Optical transmission is about: • Sending high data rates • Over very long distances • For very little money
Our biggest problem is optical fiber: • Loss • Dispersion
• Modal dispersion • Chromatic dispersion • Polarization mode dispersion
• Non-linear effects • Self phase modulation • Cross phase modulation • Four wave mixing
If you stress any one of these variables, the others will respond
For a given modulation type, the gross magnitude of these impairments scales roughly with the square of the symbol rate
Think of a light wave...
Oscillating wave
Wavelength • 1550nm
Frequency • 193.1 THz
“State of the shelf” electronics can process at ~10GHz
Electronics is about 20,000 times “too slow” for direct detection of
“wave properties”
So how do we encode and detect signals on an optical carrier?
Historically, used amplitude modulation
Measures the strength of a large number of waves
On/Off Keying (OOK) may interpret the presence of a signal as a “1”, and the absence of a symbol as a “0”
1 bit per symbol: NRZ Modulation
Laser Modulator
Detector
Tx
Rx
NRZ
Simple modulation technique Easy to implement Low power use But very sensitive to fiber impairments
as bitrate increases • This is what we’re talking about with the “square”
relationship
Increasing power will trigger non-linear effects
Phase Shift Keying
Phase is fundamental property of waves • Two waves in-phase when the peaks & troughs line up
• We say that such waves are coherent
• If non-coherent waves combine we see:
• Reinforcement, cancellation, interference
Interference can be used to extract a lower frequency modulation from a high frequency carrier
In-phase Out of phase Interference patterns
Using Phase to Apply a Signal
LD
Laser generates a constant carrier
The carrier is split into 2
The carriers travel over different paths
S
Can apply a data signal, S, to vary the delay on
one of the arms
When the carriers recombine they will “contain” the data signal encoded as a series of phase changes Tx
Rx Q: How do we recover the data signal at the receiver? Hold that thought!
MZI
Component Complexity
Tx Rx
Part 1 The Transmitter
ODB Modulation (Optical Duo-Binary)
Laser MZ Modulator
Detector
Tx
Rx
ODB
First generation 40G modulation scheme
Phase & Amplitude based modulation • Requires MZ modulator
• Can use simple, direct detection
Much more tolerant of dispersion
Limited reach
Widely used by 1st Gen 40G • Stratalight, Mintera
1 bit per symbol: DPSK
Most basic phase modulation technique
Differential technique allows phase slips to be ignored
Used by OpNext & Mintera, and their OEMs
AKA: BPSK, where local oscillator coherent detection is used
Re{Ex} 1 0
2 bits per symbol: Quadrature PSK
Advanced modulation, 4 phase states = 2 bits
More bits per symbol
2 bits per symbol: Quadrature PSK
Advanced modulation, 4 phase states = 2 bits
More bits per symbol
0,0
0,1
1,1
1,0
3 bits per symbol: 8-PSK ...And higher orders of modulation
8 phase states = 3 bits
Twice as complex, but only 50% more bits
1,0,0
0,0,1
1,1,0
1,0,1 0,0,0
0,1,1
1,1,1
0,1,0
For discrete implementations, 8-PSK seems to be too complex
The Law of Diminishing Returns Phase States vs Component Complexity
Let’s set a circuit complexity factor of 1, to be the equivalent of a simple DPSK transponder
DPSK (D)QPSK 8-PSK 16-QAM 32-QAM 64-QAM
16x
Bit/Hz
9
8
7
6
5
4
3
2
1
9
8
7
6
5
4
3
2
1
Co
mp
lexi
ty F
acto
r
Is there a better way to get to more bit/Hz?
32x
PM-QPSK, 4 bits per “symbol”
Im{Ex}
Re{Ex}
Im{Ex}
Re{Ex}
Im{Ey}
Re{Ey}
Two Polarizations
X-Polarization
Y-Polarization
Implementing Phase Modulation Using Discrete Optical Components...
S
S
Implementing Phase Modulation Using Discrete Optical Components...
This is QPSK...
S1
S2
Im{Ex}
Re{Ex}
This structure called a “Super Mach Zehnder”
This is a PM-QPSK Transmitter
PBS LD
X Polarizations
Y Polarizations
Component Complexity
Tx Rx
Part 2 The Detector
Let’s cut to the chase…
The only practical, long haul 100G implementations will be required to use Coherent Detection
What is it, and why is it useful?
What is “coherent detection”?
Physics definition • A detection technique that is based on the phase properties
of the carrier
• If you are using a phase-based detector, you could claim to be implementing coherent detection
…however…
Practical definition • The market has now come to expect a “coherent detector” to
make use of sophisticated, digital signal processing (DSP) algorithms
Conventional WDM Detection
PD
Mixture of waves on fiber… …wideband detector
How do we select the channel we want to detect?
Conventional WDM Detection
Wavelength demux
PD
Mixture of waves on fiber… …wideband detector
Direct conversion of photons into electrons that “look like” bits
…11010110…
Conventional WDM Detection
Wavelength demux
PD
Summary of “Conventional WDM Detection”
Wideband Photodetector (PD) is used
To prevent inter-channel interference, a wavelength demux is used to spatially separate channels
Modulation technique allows minimal Rx circuit complexity – essentially “direct detection”
No additional signal processing normally required
ADC DSP
Coherent WDM Detection
PD LO
We could take a mixed signal that uses a phase-based modulation technique
Use a local oscillator to choose the “color” we want to “detect”
ADC DSP
Coherent WDM Detection
PD LO …11010110…
Convert the photons to electrons
Convert the “analog electrons”
into “digital electrons”
Clean it all up!
If you need to detect 5 from 1…n, then choose a local oscillator tuned to 5
Local oscillator does not carry a signal – simply a continuous beam of light
But it is non-coherent with the received signal (ie. it is out of phase)
Use an array of interferometers to “measure” the interference patterns
Convert the interference patterns into an electronic signal, and “process it”
Why phase-based modulation?
The Detector Requires a Complex Optical Circuit Example: For PM-QPSK Modulation…
PBS
LO PBS
PD
PD
PD
PD
The signals that come out of the PD array are “analog and dirty”
PM-QPSK Signal
Two very different functions in the detector
Phase state extraction
Signal processing
• Separate the polarization components
• Create interference against a reference laser (local oscillator)
• Separate the phase components
• PD & A/D conversion
• Compensate for local oscillator instability
• Compensate for static CD
• Compensate for dynamic PMD
How do we implement these functions?
• Separate the polarization components
• Create interference against a reference laser (local oscillator)
• Separate the phase components
• PD & A/D conversion
• Compensate for local oscillator instability
• Compensate for static CD
• Compensate for dynamic PMD
Sophisticated optical circuit
(PIC)
Sophisticated digital signal processing
(DSP)
A Coherent Detector Schematic (For one wavelength only)
Incoming carrier (2 polarizations, each with 4 phase states)
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
Incoming carrier (2 polarizations, each with 4 phase states)
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
1
Step 1: Take the two optical sources – signal and local oscillator
A Coherent Detector Schematic (For one wavelength only)
Incoming carrier (2 polarizations, each with 4 phase states)
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
2
Step 2: Separate the X and Y polarizations
A Coherent Detector Schematic (For one wavelength only)
Incoming carrier (2 polarizations, each with 4 phase states)
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
3
Step 3: Generate a set of interference patterns in the SMZ array
A Coherent Detector Schematic (For one wavelength only)
Incoming carrier (2 polarizations, each with 4 phase states)
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
4
Step 4: Convert optical signals to analog electronic signals
A Coherent Detector Schematic (For one wavelength only)
Incoming carrier (2 polarizations, each with 4 phase states)
LO
PD
PD
PD
PD
ADC
ADC
ADC
ADC
DSP
AMZ
AMZ
AMZ
AMZ
Optical Circuit Electronic Circuit
PBS
PBS
ADC A/D Converter AMZ Adjustable Mach Zehnder DSP Digital Signal Processor LO Local Oscillator PD Photo Detector PS Polarization Splitter
5
Step 5: Convert analog to digital and process
A Coherent Detector Schematic (For one wavelength only)
Coherent Detection – Pros and Cons
Pros: • Operates over the existing fiber plant and amp chains
• Outstanding reach performance
• Closest thing to achieving 40G and 100G with same reach as 10G NRZ
• Significant pilot test results indicate it really does work!
Cons: • Potential non-linear interaction with 10G NRZ in same fiber
• The “cure” is managing launch power
• Probably represents the practical complexity limit for discretes
• State of the shelf DSP technology draws too much power to allow for large scale implementations (ie. multiple waves in one modules)
• Solution is to use emerging 40µm DSP technology
• DSP operation probably eliminates the chance of future line side interop
Complex modulation requires complex optical circuits
So remember…
Where have we seen this problem before?
In the 1950s computers were made from individual transistors, resistors and capacitors...
…today?
The electronics industry controlled component complexity with large scale integration
We know the same thing works for optical components – we did it 5 years ago!
Small Scale vs Large Scale Photonic Integration
Small Scale… • Operates on a single wavelength
• Primarily used to address manufacturing cost
If it works for one wave, why not…
CPUs with 2-8 cores GPUs with 200-800 cores!!
Infinera 100G Transmission Differentiators 500G, Large Scale, Monolithic PIC Implementation
500G Tx PIC
500G Rx PIC
Number of channels 5 x 100G
Monolithic InP Chips 2
Optical elements > 600
“Gold Box” Replacements > 100
Fiber Replacements > 400
COST
SIZE
POWER CAPACITY
RELIABILITY
54 © 2011 Infinera Corporation Confidential & Proprietary
How much capacity can actually be used?
Fat Pipes Are Not Enough
100 Gb/s Transmit
100 Gb/s Receive
PICs enable cost-effective OEO
100Gb/s to 1Tb/s “WDM system on a chip”
Affordable access to digital domain
Photonic Integration
56 © 2011 Infinera Corporation Confidential & Proprietary
Infinera 100G Transmission Differentiators PICs Enable Pervasive Digital Switching
1001
0101
0101
1010
1101
0101 0101 1010 1101 0101
Enables “digital” functionality
Integrated switching at every node
High functionality Digital ROADM
Dramatic network simplification
100101011101010000101011 100101010101101011010101
110101000010101110010101 001010111011010110010101
Inte
grat
ed P
ho
ton
ics
Inte
grat
ed P
ho
ton
ics
Optical (O) Electrical (E) Optical (O)
Trib
Integrated Switching + WDM
Photonic Integration
57 © 2011 Infinera Corporation Confidential & Proprietary
Infinera 100G Transmission Differentiators PICs Enable Pervasive Digital Switching
1001
0101
0101
1010
1101
0101 0101 1010 1101 0101
100101011101010000101011 100101010101101011010101
110101000010101110010101 001010111011010110010101
Inte
grat
ed P
ho
ton
ics
Inte
grat
ed P
ho
ton
ics
Pervasive Digital Switching
Integrated Switching + WDM
Photonic Integration
10010101110101010000 10010101010110101011
10010101110101010000 10010101010110101011 end-end service
Software-based “Ease-of-Use”
Digital OTN switching at every node
Unconstrained bandwidth everywhere
Lowest cost per switched Gb/s
58 © 2011 Infinera Corporation Confidential & Proprietary
Infinera 100G Transmission Differentiators PICs Enable Pervasive Digital Switching
Solving The 100G Muxponder Tax
The Problem: • Backbone waves move to 100G, but service demands still 10G or lower
• All-optical ROADMs have no inter-wavelength, or sub-wavelength grooming capability → 100G muxponders!
How big is the “Muxponder Tax”
in a real 100G network?
A B All services must go A ↔B
10GbE
10GbE
10GbE
Mu
xpo
nd
er
10GbE
Mu
xpo
nd
er
ROADM Network
A C ↔
A D ↔
B C ↔
B D ↔
Require Extra, Partially Filled
Muxponder Pairs
Service Demands:
© 2011 Infinera Corporation Confidential & Proprietary 59
100
90
80
70
60
50
40
30
20
10 Dep
loye
d C
apac
ity
(%)
Rev
enu
e G
ener
atin
g (%
) 100
90
80
70
60
50
40
30
20
10
100G Muxponder
50%
40G Muxponder
66%
Infinera Digital ROADM
92%
Infinera National Network Model Summary
• Large N. Am. Network Model: 33,084 route km, 47 core WDM links • About 10 Tb/s of customer service demands (network traffic volume)
© 2011 Infinera Corporation Confidential & Proprietary 60
Summary of Network Efficiency
A “Perfect Storm” is emerging in terms of network bandwidth efficiency: • Wavelength speeds moving to 100Gbit/s
• Majority of services demands remaining at 10Gbit/s or less for near-term
• All-optical ROADMs have no effective way to offer contentionless wavelength conversion and sub-wavelength grooming in the core
• Muxponders are simply point-point aggregators and do not do grooming
The result is that a Service Provider may need to purchase 2X Network Capacity for 1X Service Revenue
The solution is an Integrated Digital OTN Network with: • End to End, Any to Any service capability
• Integrated OTN switching and grooming in the core
• End to End intelligent optical control plane
Bandwidth Virtualization
8Tb/s
More channels
Higher Data Rates
More Spectrum
Beyond 8Tb/s?
Gridless Super-Channels
Even more complex modulation!
L-Band S-Band E-Band O-Band
Outside the scope of this discussion
What’s changed so far
Since the advent of DWDM…
now
Phase Modulation
Coherent Detection
ITU Frequency Grid
Intensity Modulation
Direct Detection
ITU Frequency Grid
63 © 2011 Infinera Corporation Confidential & Proprietary
What Comes Next For Terabit Transport?
Since the advent of DWDM…
…so what has to change
Phase Modulation
Coherent Detection
ITU Frequency Grid
Intensity Modulation
Direct Detection
ITU Frequency Grid
Quadrature Amplitude Modulation (QAM)
Coherent Wave Combining and Separation
Grid-less FlexChannels
64 © 2011 Infinera Corporation Confidential & Proprietary
Advanced Modulation Formats
Pol-Mux QPSK Pol-Mux
8-QAM
Pol-Mux 16-QAM
IM-DD
PM- BPSK
1.6 8 12 16 24
C-Band Capacity (Tb/s)
0
0.2
0.4
0.6
0.8
1
1.2
Cap
acit
y *
Re
ach
Pro
du
ct
65 © 2011 Infinera Corporation Confidential & Proprietary
Since the advent of DWDM…
…so what has to change
Quadrature Amplitude Modulation
Coherent Wave Separation
Grid-less FlexChannels
On-Off Keyed Modulation
Direct Detection
ITU Frequency Grid
What Comes Next For Terabit Transport?
66 © 2011 Infinera Corporation Confidential & Proprietary
© 2011 Infinera Corporation Confidential & Proprietary 67
Single Carrier vs Multi-Carrier
Goal: Create a 1Tb/s unit of transmission capacity
How?
Option 1: Build a single-carrier 1Tb/s
channel
Option 2: Build a multi-carrier 1Tb/s
“super-channel”
© 2011 Infinera Corporation Confidential & Proprietary 68
1Tb/s Single Carrier: The A/D Converter Problem
1 2 4 6 8 10 12
1
2
3
4
5
6
7
8
9
10
OSN
R P
enal
ty (
dB
)
Number of bits per symbol
PM-BPSK 640GBaud
PM-QPSK 320GBaud
PM-8QAM 210GBaud
PM-16QAM 160GBaud
PM-32QAM 128GBaud
PM-64QAM 105GBaud
By 2014 commercial ADCs are expected to operate at ~64GBaud
wavelength demux
DWDM Direct Detection
PD
Spacing on the fiber needed between waves: “Guard Bands”
Spatially separate the
channels using a
wavelength demux
69 © 2011 Infinera Corporation Confidential & Proprietary
wavelength demux
Spatially separate the
channels using a
wavelength demux
DWDM Coherent Detection
Spacing on the fiber needed between waves:
“Guard Bands”
ADC DSP PD LO
Use a local oscillator to choose the “color” we want
to “detect” to match the demux port color
70 © 2011 Infinera Corporation Confidential & Proprietary
How 1Tb/s Might Look… Conventional WDM vs FlexChannels
Guard bands to allow for individual wavelength demux
Fewer guard-bands
25% increase in useable amplifier spectrum
Conventional Per-Channel WDM Filtering
1Tb/s
Multi-Carrier FlexChannel
1Tb/s
71 © 2011 Infinera Corporation Confidential & Proprietary
What Comes Next For Terabit Transport?
Since the advent of DWDM…
…so what has to change
Quadrature Amplitude Modulation
Coherent Wave Separation
Grid-less FlexChannels
On-Off Keyed Modulation
Direct Detection
ITU Frequency Grid
72 © 2011 Infinera Corporation Confidential & Proprietary
FlexChannels Increase Total Fiber Capacity More complex modulation → more capacity per fiber
PM-QPSK
8-QAM
16-QAM
1Tb/s
12 Tb/s
18 Tb/s
25 Tb/s
73 © 2011 Infinera Corporation Confidential & Proprietary
Reach, Spectral Efficiency, and Co-Existence
1Tb/s PM-8QAM FlexChannel
1Tb/s PM-16QAM FlexChannel
10x100G PM-QPSK 1Tb/s PM-QPSK
FlexChannel
or
A E
B C
D
74 © 2011 Infinera Corporation Confidential & Proprietary
Summary: The Key Technologies For 1Tb/s Are Well Understood
But the implementation of those technologies will be critical to allowing service providers to differentiate their products and services
Advanced Modulation
Coherent Processing
Advanced FEC
Foundation Features
Large Scale PICs 1
FlexCoherent™ Modulation 2
Pervasive, Switched DWDM 3
Differentiators
75 © 2011 Infinera Corporation Confidential & Proprietary
Thank You! lwade@infinera.com
© 2011 Infinera Corporation Confidential & Proprietary 76
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