Advanced Modulation For High Data Rate Optical ... - Infinera

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

Lower Cost per Bit 

Why do we need 

more than 800G? 

Higher Speed Services 

More Capacity

Cost per Usable Bit 

Fiber Exhaust & Network Economics 

10G λ 

40G λ 

You want to move 

to 40G here… 

Excess 

cost 

100G λ 

…but what if you hit 

fiber exhaust here? 

Time 

Fiber exhaust can force uneconomic network decisions

Double Density Optics Mean Investment Protection 

and “Option Value” 

Conventional 80-96 λ WDM 

Infinera “Double Density” WDM 

1 λ per 50 GHz 

800G in the C-band 

1 λ per 25 GHz 

1.6T in the C-band 

At 40% bandwidth growth, double-density optics mean 

two more years to select the lowest cost transmission.

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 PICbased 

line card, with 

10x10Gb/s waves 

100Gb/s of capacity for 

the same effort as one 

10Gb/s transponder 

“Gaps” for 

additional waves 

Optical 

Spectrum 

Analyzer 

Existing 10G waves 

on the fiber 

Stopwatch

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!

100G Technology Features 

Differentiators 

3 

2 

1 

Core Switching & Grooming 

Large Scale PICs 

Photonic Integration 

Table 

Stakes 

Advanced 

Modulation 

Fiber Capacity 

Coherent 

Detection 

High Gain FEC

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 

Electronics is about 20,000 times 

“too slow” for direct detection of 

“wave properties” 

“State of the shelf” 

electronics can process at 

~10GHz

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 

Rx 

Laser 

Modulator 

Detector 

NRZ 

Tx 

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 

In-phase Out of phase Interference 

patterns 

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

Using Phase to Apply a Signal 

Tx 

Laser generates a 

constant carrier 

LD 

MZI 

The carriers travel 

over different paths 

When the carriers 

recombine they will 

“contain” the data signal 

encoded as a series of 

phase changes 

The carrier is 

split into 2 

S 

Can apply a data signal, 

S, to vary the delay on 

one of the arms 

Rx Q: 

How do we recover the data signal at the receiver? 

Hold that thought!

Component Complexity 

Tx 

Rx 

Part 1 

The Transmitter

ODB Modulation (Optical Duo-Binary) 

Rx 

Laser MZ Modulator 

Detector 

ODB 

Tx 

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 

1 0 

Re{Ex} 

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

2 bits per symbol: Quadrature PSK 

Advanced modulation, 4 phase states = 2 bits 

More bits per symbol

2 bits per symbol: Quadrature PSK 

1,1 

0,1 

1,0 

0,0 

Advanced modulation, 4 phase states = 2 bits 

More bits per symbol

3 bits per symbol: 8-PSK 

...And higher orders of modulation 

0,1,1 

0,1,0 

1,1,0 

0,0,1 

1,1,1 

0,0,0 

1,0,0 

1,0,1 

8 phase states = 3 bits 

Twice as complex, but only 50% more bits 

For discrete implementations, 8-PSK seems to be too complex

The Law of Diminishing Returns 

Phase States vs Component Complexity 

Complexity Factor 

Let’s set a circuit complexity factor of 1, to be the 

equivalent of a simple DPSK transponder 

9 

8 

7 

Is there a better way to 

get to more bit/Hz? 

16x 

32x 9 

8 

7 

6 

6 

Bit/Hz 

5 

4 

5 

4 

3 

3 

2 

2 

1 

1 

DPSK (D)QPSK 8-PSK 16-QAM 32-QAM 64-QAM

PM-QPSK, 4 bits per “symbol” 

Two Polarizations 

Im{E x } 

Im{E x } 

Re{E x } 

X-Polarization 

Re{E x } 

Im{E y } 

Re{E y } 

Y-Polarization

Implementing Phase Modulation Using Discrete 

Optical Components... 

S

Implementing Phase Modulation Using Discrete 

Optical Components... 

S

This is QPSK... 

Im{E x } 

S1 

Re{E x } 

This structure called a “Super Mach Zehnder” 

S2

This is a PM-QPSK Transmitter 

X Polarizations 

LD 

PBS 

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 

How do we select the 

channel we want to detect? 

PD 

Mixture of waves on fiber… 

…wideband detector


Wavelength demux 

PD 

Mixture of waves on fiber… 

…wideband detector


Wavelength demux 

Direct conversion 

of photons into 

electrons that 

“look like” bits 

PD 

…11010110…

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

Coherent WDM Detection 

We could take a mixed signal that uses a 

phase-based modulation technique 

LO 

PD 

ADC 

DSP 

Use a local oscillator to choose the 

“color” we want to “detect”

Coherent WDM Detection 

Convert the 

photons to 

electrons 

Clean it all up! 

LO 

PD 

ADC 

DSP 

…11010110… 

Convert the 

“analog electrons” 

into “digital 

electrons”

Why phase-based modulation? 

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”

The Detector Requires a Complex Optical Circuit 

Example: For PM-QPSK Modulation… 

PD 

PM-QPSK Signal 

PBS 

PD 

PD 

The signals that come 

out of the PD array are 

“analog and dirty” 

PD 

LO 

PBS

Two very different functions in the detector 

Phase state 

extraction 

• Separate the polarization components 

• Create interference against a 

reference laser (local oscillator) 

• Separate the phase components 

• PD & A/D conversion 

Signal processing 

• Compensate for local oscillator 

instability 

• Compensate for static CD 

• Compensate for dynamic PMD

How do we implement these functions? 

Sophisticated 

optical circuit 

(PIC) 

• Separate the polarization components 

• Create interference against a 

reference laser (local oscillator) 

• Separate the phase components 

• PD & A/D conversion 

Sophisticated digital 

signal processing 

(DSP) 

• Compensate for local oscillator 

instability 

• Compensate for static CD 

• Compensate for dynamic PMD

DSP 

A Coherent Detector Schematic 

(For one wavelength only) 

Optical Circuit 

Electronic Circuit 

Incoming carrier 

(2 polarizations, each 

with 4 phase states) 

AMZ 

PD 

ADC 

PBS 

AMZ 

PD 

ADC 

LO 

PBS 

AMZ 

PD 

ADC 

ADC A/D Converter 

AMZ Adjustable Mach Zehnder 

DSP Digital Signal Processor 

LO Local Oscillator 

PD Photo Detector 

PS Polarization Splitter 

AMZ 

PD 

ADC



DSP 






AMZ 

PD 

ADC 

1 

LO 

PBS 

PBS 

AMZ 

AMZ 

PD 

PD 

ADC 

ADC 







AMZ PD ADC 

Step 1: Take the two optical sources – signal and local oscillator



DSP 






AMZ 

PD 

ADC 

LO 

PBS 

2 

PBS 

AMZ 

AMZ 

PD 

PD 

ADC 

ADC 







AMZ PD 

Step 2: Separate the X and Y polarizations 

ADC



DSP 






AMZ 

PD 

ADC 

LO 

PBS 

PBS 

AMZ 

3 

AMZ 

PD 

PD 

ADC 

ADC 







AMZ PD ADC 

Step 3: Generate a set of interference patterns in the SMZ array



DSP 






AMZ 

PD 

ADC 

LO 

PBS 

PBS 

AMZ 

AMZ 

PD 

4 

PD 

ADC 

ADC 







AMZ PD ADC 

Step 4: Convert optical signals to analog electronic signals



DSP 






AMZ 

PD 

ADC 

LO 

PBS 

PBS 

AMZ 

AMZ 

PD 

PD 

ADC 

ADC 

5 







AMZ PD ADC 

Step 5: Convert analog to digital and process

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

So remember… 

Complex modulation requires 

complex optical circuits

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 

COST 

CAPACITY 

RELIABILITY 

500G 

Tx PIC 

500G 

Rx PIC 

SIZE 

POWER 

Number of channels 

5 x 100G 

Monolithic InP Chips 2 

Optical elements > 600 

“Gold Box” Replacements > 100 

Fiber Replacements > 400 

54 © 2011 Infinera Corporation Confidential & Proprietary

Fat Pipes Are Not Enough 

How much capacity can 

actually be used?


PICs Enable Pervasive Digital Switching 

Photonic 

Integration 

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 




Integrated Photonics 


Optical (O) Electrical (E) Optical (O) 

Photonic 

Integration 

Integrated 

Switching + WDM 

100101011101010000101011 

100101010101101011010101 

110101000010101110010101 

001010111011010110010101 

1001 

0101 

Trib 

0101 

1010 

1101 

0101 

0101 

1010 

Enables “digital” functionality 

1101 

0101 

Integrated switching at every node 

High functionality Digital ROADM 

Dramatic network simplification 






10010101110101010000 

10010101010110101011 

end-end service 

Photonic 

Integration 

Integrated 

Switching + WDM 

Pervasive Digital 

Switching 

10010101110101010000 

10010101010110101011 

100101011101010000101011 

100101010101101011010101 

110101000010101110010101 

001010111011010110010101 

1001 

0101 

0101 

1010 

1101 

0101 

0101 

1010 

1101 

Software-based “Ease-of-Use” 

0101 

Digital OTN switching at every node 

Unconstrained bandwidth everywhere 

Lowest cost per switched Gb/s 


Muxponder 

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! 

Service Demands: 

A ↔ C 

Require Extra, 

Partially Filled 

A ↔ D Muxponder Pairs 

10GbE 

10GbE 

Muxponder 

ROADM Network 

B 

B 

↔ 

↔ 

C 

D 

10GbE 

10GbE 

How big is the 

“Muxponder Tax” 

in a real 100G 

network? 

A 

All services must go A ↔B 

B 

59 

© 2011 Infinera Corporation Confidential & Proprietary

Deployed Capacity (%) 

Revenue Generating (%) 

Infinera National Network Model Summary 

50% 

66% 

92% 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

100 

90 

80 

70 

60 

50 

40 

30 

20 

10 

100G 

Muxponder 

40G 

Muxponder 

Infinera Digital 

ROADM 

• Large N. Am. Network Model: 33,084 route km, 47 core WDM links 

• About 10 Tb/s of customer service demands (network traffic volume) 

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: 

Bandwidth 

Virtualization 

• End to End, Any to Any service capability 

• Integrated OTN switching and grooming in the core 

• End to End intelligent optical control plane

Beyond 8Tb/s? 

8Tb/s 

More 

channels 

Higher 

Data Rates 

More 

Spectrum 

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… 

Intensity Modulation 

Direct Detection 

ITU Frequency Grid 

Phase Modulation 

Coherent Detection 


now 


What Comes Next For Terabit Transport? 


Intensity Modulation 



Quadrature Amplitude 

Phase 



(QAM) 

Coherent Wave Combining 

and Separation 

Detection 

ITU Grid-less Frequency FlexChannels Grid 

…so what has to change 


Capacity * Reach Product 

Advanced Modulation Formats 

Pol-Mux 

QPSK 

Pol-Mux 

8-QAM 

1.2 

1 

PM- 

BPSK 

Pol-Mux 

16-QAM 

0.8 

0.6 

0.4 

0.2 

0 

IM-DD 

1.6 8 12 16 24 

65 © 2011 Infinera Corporation Confidential & Proprietary 

C-Band Capacity (Tb/s)



On-Off Keyed Modulation 





Coherent Wave Separation 

Grid-less FlexChannels 



Single Carrier vs Multi-Carrier 

Goal: Create a 1Tb/s unit of transmission capacity 

How? 

Option 1: 

Build a singlecarrier 

1Tb/s 

channel 

Option 2: 

Build a multicarrier 

1Tb/s 

“super-channel” 

67 


OSNR Penalty (dB) 

1Tb/s Single Carrier: The A/D Converter Problem 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

By 2014 commercial ADCs are 

expected to operate at ~64GBaud 

PM-BPSK 

640GBaud 

PM-8QAM 

210GBaud 

PM-QPSK 

320GBaud 

PM-16QAM 

160GBaud 

PM-64QAM 

105GBaud 

PM-32QAM 

128GBaud 

1 2 4 6 8 10 12 

Number of bits per symbol 

68 


DWDM Direct Detection 

Spatially separate the 

channels using a 

wavelength demux 

Spacing on the fiber 

needed between waves: 

“Guard Bands” 

PD 

wavelength 

demux 


DWDM Coherent Detection 

Spatially separate the 

channels using a 

wavelength demux 

Spacing on the fiber 

needed between waves: 

“Guard Bands” 

LO 

PD 

ADC 

DSP 

wavelength 

demux 

Use a local oscillator to 

choose the “color” we want 

to “detect” to match the 

demux port color 


How 1Tb/s Might Look… 

Conventional WDM vs FlexChannels 

Conventional Per-Channel 

WDM Filtering 

1Tb/s 

Guard bands to allow for 

individual wavelength demux 

Multi-Carrier FlexChannel 

1Tb/s 

Fewer guard-bands 

25% increase in useable 

amplifier spectrum 




On-Off Keyed Modulation 





Coherent Wave Separation 

Grid-less FlexChannels 



FlexChannels Increase Total Fiber Capacity 

More complex modulation → more capacity per fiber 

PM-QPSK 

12 Tb/s 

8-QAM 

18 Tb/s 

1Tb/s 

16-QAM 

25 Tb/s 


Reach, Spectral Efficiency, and Co-Existence 

A 

B 

C 

D 

E 

10x100G PM-QPSK 

1Tb/s PM-QPSK 

FlexChannel 

1Tb/s PM-8QAM 

FlexChannel 

1Tb/s PM-16QAM 

FlexChannel 

or 


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 

Differentiators 

3 

2 

1 

Pervasive, Switched DWDM 

FlexCoherent Modulation 

Large Scale PICs 

Foundation 

Features 



Coherent 

Processing 


FEC 


Thank You! 

lwade@infinera.com 

© 762011 

Infinera Corporation Confidential & Proprietary

Advanced Modulation For High Data Rate Optical ... - Infinera

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