wdm networking fundamentals
TRANSCRIPT
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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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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
𝐸𝑥𝑒𝑖𝜑𝑥
𝐸𝑦𝑒𝑖𝜑𝑦 𝑒𝑖(𝜔∙𝑡−𝑘∙𝑧)
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
𝐶 = 𝐵 log(1 +𝑆𝑁
)
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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
𝐸 = 𝐸𝑥𝐸𝑦
= 𝐸𝑥𝑒𝑖𝜑𝑥
𝐸𝑦𝑒𝑖𝜑𝑦 𝑒𝑖(𝜔∙𝑡−𝑘∙𝑧) =
𝐼𝑥 + 𝑖𝑄𝑥𝐼𝑦 + 𝑖𝑄𝑦
𝑒𝑖(𝜔∙𝑡−𝑘∙𝑧)
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
ϕ Phase
Polar Coordinates
• A
I In-phase or real part
Q Quadrature or imaginary part
Complex Plane E
(I, Q)
φ
Q
I
𝐸𝑥𝑒𝑖𝜑𝑥
𝐸𝑦𝑒𝑖𝜑𝑦 𝑒𝑖(𝜔∙𝑡−𝑘∙𝑧)
𝐼𝑥 + 𝑖𝑄𝑥𝐼𝑦 + 𝑖𝑄𝑦
𝑒𝑖(𝜔∙𝑡−𝑘∙𝑧)
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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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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
Thank You
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