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Lecture: 10 New Trends in Optical Networks

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 f ibers Routes to Higher Transmission Capacity

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Lecture: 10 New Trends in Optical Networks

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  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 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 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 (> 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 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

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