Lecture: 10 New Trends in Optical Networks

1
Lecture 10 New Trends in Optical Networks
Ajmal Muhammad, Robert Forchheimer Information
Coding Group ISY Department
2
Outline

• Challenges
• Multiplexing Techniques
• Routes to Longer Reach
• Distributed amplification
• Hollow core fibers
• Routes to Higher Transmission Capacity
• Space division multiplexing (SDM)

3
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 Transmissi
on fiber nonlinearities (Kerr)
4
Capacity Limits
Fiber nonlinearity
Noise
Ref IEEE, vol.100, No.5 May 2012
Signal launch power dBm ?
5
Moores Law for Ever ?
Courtesy of Per O. Andersson
6
Multiplexing Techniques

7
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

8
BPSK- Binary Phase Shift Keying

BPSK transmits 1 bit of data per symbol rate,
either 1 or 0
9
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
10
DP-QPSK in Fiber Optic Transmission

DP-QPSK transmits 4-bits of data per symbol rate
Sine wave
Data stream
Vertical polarized
Cosine wave
Laser source is linearly polarized
Assume horizontal polarized laser source
Horizontal polarized
11
Outline

• Challenges
• Multiplexing Techniques
• Routes to Longer Reach
• Distributed Amplification
• Hollow Core Fibers
• Routes to Higher Transmission Capacity
• Space Division Multiplexing (SDM)

12
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 Redu
ce the nonlinearity Install new
large-area or hollow-core fibers
13
Distributed Amplification

High SNR but will excite nonlinearities
SNR degrades due to shot noise no issues of
nonlinearity
Raman pump power 700 mW EDFA gain20 dB, NF3 dB
Courtesy Peter Andrekson, Chalmers Uni.
Ideal distributed amplification (constant
average signal power in the entire span)
PSA Phase sensitive amplifier with noise free
gain medium
14
New Telecom Window at 2000 nmHollow-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.

15
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.
16
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
17
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
18
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 (gt 200nm)
• Noise figure 5 dB
• Laser diode pumping at 1550 nm
• 100 mW saturated output signal power

19
Outline

• Challenges
• Multiplexing Techniques
• Routes to Longer Reach
• Distributed Amplification
• Hollow Core Fibers
• Routes to Higher Transmission Capacity
• Space Division Multiplexing (SDM)

20
Routes to Higher Transmission Capacity

• CLB N B log2(1SNR)

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/multi-
mode fibers
21
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
22
Space Division Multiplexing (SDM)

23
Inter-Core Crosstalk (XT)

24
Inter-Core Crosstalk (XT)

25
From WDM Systems to SDM WDM Systems

Flexible upgrade Add transponder in lambda and M
26
State of the Art Systems

27
(No Transcript)