Slides for Lec. 10.

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Lecture: 10 New Trends in Optical Networks
Ajmal Muhammad, Robert Forchheimer
Information Coding Group
ISY Department
Outline



Challenges
Multiplexing Techniques
Routes to Longer Reach
Distributed amplification
Hollow core fibers

Routes to Higher Transmission Capacity
Space division multiplexing (SDM)
The Challenge



Traffic grows exponentially at approximately 40% per year
Optical system capacity growth has been approximately 20%
per year
In less than 10 years, current approaches to keep up will not
be sufficient
Main physical barriers:
Channel capacity (Shannon) + available optical bandwidth
Transmission fiber nonlinearities (Kerr)
Capacity Limits
Fiber nonlinearity
Noise
Ref:
IEEE, vol.100, No.5
May 2012
Signal launch power [dBm] 
… Moore’s Law for Ever… ?
Courtesy of
Per O. Andersson
Multiplexing Techniques
100G Fiber Optic Transmission :: DP-QPSK

DP-QPSK: Dual Polarization Quadrature Phase Shift Keying

DP-QPSK is a digital modulation technique which uses two
orthogonal polarization of a laser beam, with QPSK digital
modulation on each polarization

QPSK can transmit 2 bits of data per symbol rate, DP-QPSK
doubles that capacity

For 100Gbps, DP-QPSK needs 25G to 28G symbols per
second. Electronics have to work at 25 to 28 GHz
BPSK- Binary Phase Shift Keying
BPSK transmits 1 bit of data per symbol rate, either 1 or 0
QPSK- Quadrature Phase Shift Keying
Use quadrature concept, i.e., both sine and cosine waves to represent digital data
Two BPSK used
in parallel
Cosine wave
DP-QPSK in Fiber Optic Transmission
DP-QPSK transmits 4-bits of data per symbol rate
Sine wave
Data stream
Cosine wave
Vertical polarized
Laser source is linearly polarized
Assume horizontal
polarized laser source
Horizontal polarized
Outline



Challenges
Multiplexing Techniques
Routes to Longer Reach
Distributed Amplification
Hollow Core Fibers

Routes to Higher Transmission Capacity
Space Division Multiplexing (SDM)
Routes to Longer Reach
Deal with low SNR
Advance FEC
More power efficient modulations format
Maintain a high SNR
Ultralow noise amplifiers
Distributed amplification
Deal with more nonlinearities
Digital back-propagation
Reduce the nonlinearity
Install new large-area or hollow-core
fibers
Distributed Amplification
High SNR but will excite nonlinearities
SNR degrades due to shot noise
no issues of nonlinearity
Raman pump power= 700 mW
EDFA gain=20 dB, NF=3 dB
Ideal distributed amplification
(constant average signal power in the entire span)
Courtesy:
Peter Andrekson, Chalmers Uni.
PSA: Phase sensitive amplifier
with noise free gain medium
New Telecom Window at 2000 nm
Hollow-Core Fibers
Guiding by Photonic Bandgap Effect
Key potential attributes:
 Ultra-low loss predicted near 2000nm (not single mode operation)
(~ 0.05 dB/km predicted opt. Express, Vol.13, page 236, 2005)
 Very wide operating wavelength range (700 nm)
 Very small non-linearity: 0.001 x standard SMF
 Lowest possible latency
 Distributed Raman amplification may be challenging, however.
Hollow-Core Fiber :: SNR
Comparison of ultralow loss (0.05 dB/km) hollow-core fiber and EDFA
In conventional fiber (0.2 dB/km)
Courtesy:
Peter Andrekson, Chalmers Uni.
Hollow-Core Fiber :: SNR
Comparison of ultralow loss (0.05 dB/km) hollow-core fiber, EDFA and
distributed Raman amplification in conventional fiber (0.2 dB/km)
Span loss: 20 dB
Backward Raman (100 km)
Bidirectional Raman (100 km) (10 + 10 dB)
Courtesy:
Peter Andrekson, Chalmers Uni.
A low-loss hollow core fiber with EDFA spacing of 400 km performs similar to
backward pumped Raman system with 100 km pump spacing
Spectral Efficiency Impact of Nonlinear
Coefficient
+ 2.2 b/s/HZ for each X 10
Gamma reduction
Ref: R-J. Essiambre proc. IEEE
vol. 100, p. 1035, 2012
Thulium-Doped Silica Fiber Amplifiers (TDFA)
at 1800-2050 nm
ECOC 2013
Paper Tu.1.A.2
•
•
•
•
•
Suitable with low-loss hollow core transmission fiber
Very wide operation range (> 200nm)
Noise figure ~ 5 dB
Laser diode pumping at 1550 nm
100 mW saturated output signal power
Outline



Challenges
Multiplexing Techniques
Routes to Longer Reach
Distributed Amplification
Hollow Core Fibers

Routes to Higher Transmission Capacity
Space Division Multiplexing (SDM)
Routes to Higher Transmission Capacity
CLB= N * B * log2(1+SNR)
Overall transmission capacity:
Available optical bandwidth (B)
New amplifiers
Extend low-loss window
X
Spectral efficiency (bit/sec/Hertz)
Electronics signal processing
Low nonlinearity
X
Number of channels (N)
Install new multi-core/multimode fibers
Typical Attenuation Spectrum for Silica Fiber
Only 8-10 % is utilized in C band
With SE of 10 per polarization a fiber can support well over a Pb/s
Space Division Multiplexing (SDM)
Inter-Core Crosstalk (XT)
Inter-Core Crosstalk (XT)
From WDM Systems to SDM & WDM Systems
Flexible upgrade:
Add transponder in lambda and M
State of the Art Systems
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