Dr. Michael Ritter September 26th, 2014

WDM Networking Fundamentals

Dr. Michael Ritter September 26th, 2014

What the heck is DP-QPSK?

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Optical Spectrum

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DWDM Functional Schematic

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Attenuation

Rayleigh Scattering

Absorption

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Dispersion

Total Chromatic Dispersion

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Other Nonlinear Effects

Four-Wave Mixing Stimulated Brillouin scattering

Stimulated Raman scattering

Self-phase modulation

Four-wave mixing

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Attenuation Curve

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Modulation Format

PM-RZ-DQPSK Phase-Shift Keying (phase modulation)

Quaternary (4-state modulation) Differential (pre-coding)

Return-to-Zero (pulse shaping) Polarization-Multiplexed (a.k.a. Dual-Polarization, DP)

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Why complex modulated optical signals?

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Spectral Efficiency Needs to Increase

On/off-keying faces limitations when data rates reach 100 Gbps

OOK (10Gbps)

OOK (100Gbps)

50GHz 50GHz

DP-QPSK (100Gbps)

Channel Interference

Simple hardware

Wide spectrum

High dispersion impairment

Complex hardware

Narrow spectrum

Low dispersion impairment

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Leveraging Radio Transmission Technology

Utilizing frequency, amplitude and phase

Using all parameters of a light wave for encoding information

Polarization division multiplexing

Pulse-shaping filters

Y-Polarization

X-Polarization

Frequency

()

0 -100 100

Pulse Shaped

Unshaped

Transversal Electromagnetic Wave

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Combining Modulation Techniques

Complex modulation reduces the required optical spectrum

0 100 100 200 200

OOK

QPSK

DP-QPSK

Pulse-shaped DP-QPSK

Factor of 2

Factor of 2

Spectral narrowing

Offset [GHz]

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Shannon Limit Non-Linear Effects

No More Limits to Spectral Efficiency?

Both Shannon Limit and non-linear effects are limiting factors

C Channel Capacity

B Bandwidth Spectrum

S Signal Power

N Noise Power

= log(1 +

)

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Advanced coding concepts

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Coding Two Bits to a Symbol

Much larger number of bits can be defined by a single symbol

0 0 1 0 1 1 1 0 0 1 0 1 0 0 1 0 0 0 1 1 0 0 1 0

B D A D C C B D B A B D

Original binary data stream

Symbol stream for coding 2 bits per symbol

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Mathematical Description of a Wave

Making use of all degrees of freedom to encode information

=

=

() =

+ +

()

Light is a transversal electromagnetic wave

Frequency Division Multiplexing

Phase Modulation

Amplitude Modulation

Polarization Division Multiplexing

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Constellation Diagrams

A symbol corresponds to a point in the constellation diagram

E Amplitude

Phase

Polar Coordinates

A

I In-phase or real part

Q Quadrature or imaginary part

Complex Plane E

(I, Q)

Q

I

()

+ +

()

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Quadrature Phase Shift Keying (QPSK)

The four symbols differ in phase, not in amplitude

Q

I

A D

B C

11

01 00

10

A B C D

I

Q

Signal

Bit Sequence

Symbol

Time Domain Waveforms

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DP-QPSK Now We Understand

Transmitting a 100 Gbps signal utilizing 50 GHz of spectrum

100 Gbaud 50 Gbaud 25 Gbaud

Y-Polarization

X-Polarization

Frequency

DP - QPSK

Q

I

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Example Constellation Diagrams

OOK QPSK 8QAM 16QAM BPSK

10 Gbps

0.2 bits/s/Hz

40 Gbps

0.8 bits/s/Hz

100 Gbps

2 bits/s/Hz

200 Gbps

3 bits/s/Hz

400 Gbps

4 bits/s/Hz

Q

I

Q

I

Q

I

Q

I

Q

I

Larger distance between points results in increased OSNR performance

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Reach vs. Efficiency Tradeoff

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Which scheme fits my application?

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Factors Influencing the Optimum Choice

Highest coding efficiency is not always the right choice

Occupied Spectrum

Reach

Dispersion Tolerance

Technical Feasibility

Cost

Existing Infrastructure

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Coherent Detection Differential Phase-Shift Keying

Detecting Phase Changes

Coherent detection significantly increases dispersion tolerance

Time Domain Waveform

Data Stream

Delayed

Result for Direct Detection

By One Period

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What about security?

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Tapping Fiber Optic Networks

Y-Bridge for Service Activities

Fiber Coupling Device

Street Cabinet Splice Boxes / Cassettes

(Outdoor / Inhouse)

There are multiple ways to gain access to fiber

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Secure Optical Transport

APPS APPS

Securing the connection in addition to HW, SW and physical access

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Strong AES 256 Cipher

Secure Diffie-Hellman Key Exchange

Authentication and Restricted Access

Optical Layer Encryption

Highest data security at lowest latency and minimum cost

mritter@advaoptical.com

Thank You

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WDM Networking FundamentalsWhat the heck is DP-QPSK?Optical SpectrumDWDM Functional SchematicAttenuationDispersionOther Nonlinear EffectsAttenuation CurveModulation FormatWhy complex modulated optical signals?Spectral Efficiency Needs to IncreaseLeveraging Radio Transmission TechnologyCombining Modulation TechniquesNo More Limits to Spectral Efficiency?Advanced coding conceptsCoding Two Bits to a SymbolMathematical Description of a WaveConstellation DiagramsQuadrature Phase Shift Keying (QPSK)DP-QPSK Now We UnderstandExample Constellation DiagramsReach vs. Efficiency TradeoffWhich scheme fits my application?Factors Influencing the Optimum ChoiceDetecting Phase ChangesWhat about security?Tapping Fiber Optic NetworksSecure Optical TransportOptical Layer EncryptionThank You