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
Transmission fiber nonlinearities (Kerr)

4. Capacity Limits Signal launch power [dBm]  Fiber nonlinearity Noise
Ref:
IEEE, vol.100, No.5
May 2012
Signal launch power [dBm] 

5. … Moore’s 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
Reduce 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 gain=20 dB, NF=3 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 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: 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) ( 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 (> 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(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
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