Network Challenges for Coherent Systems. Mike Harrop Technical Sales Engineering, EXFO

Network Challenges for Coherent Systems Mike Harrop Technical Sales Engineering, EXFO

Agenda 1. 100G Transmission Technology 2. Non Linear effects 3. RAMAN Amplification 1. Optimsing gain 2. Keeping It Clean 4. Conclusion

100G Transmission Technology

A Brief History Of Line Modulation 1 0 0 1 1

A Brief History Of Line Modulation Amplitude 1 0 0 1 1 On/off keying(ook) Amplitude modulation Non-return to zero (NRZ) One bit encoding t

A Brief History Of Line Modulation Amplitude 1 0 0 1 1 On/off keying(ook) Amplitude modulation Non-return to zero (NRZ) One bit encoding t Binary phase-shift keying (BPSK) Phase modulation One bit encoding 2 states 0 & 180 t

A Brief History Of Line Modulation Quadrature phase shift keying (QPSK) Phase modulation Uses 45 o, 135 o, 225 o, 315 o phase states - 4 states 1 1 1 0 1 1 Typically used for 100G transmission Two bit encoding One time interval t Each phase state represents two bits Data rate can be transmitted with only half the baud (signaling) rate.

Polarisation Multiplexing Polarisation multiplexing (PM), also called Dual Polarization (DP) Doubles the capacity of a span by encoding the information on two different polarizations Vertical polarisation Dual polarisation Horizontal polarisation

Coherent v/s Noncoherent detection. Direct detection (noncoherent): contains a photodiode for on-off keying signals

Coherent v/s Noncoherent detection. Direct detection (noncoherent): contains a photodiode for on-off keying signals Coherent detection

Phase modulation with Coherent detection Advantages More bits/s Can undo all CD impairments More robust against PMD Dis-advantages Starting with lower powers Phase modulation more easily affected by fibre non linearities 2017 EXFO Inc. All rights reserved. 11

Non linear introduction

Non-linear effects

Scattering Stimulated Raman Scattering (SRS) High optical power causes molecular vibrations in the glass. Molecules absorb the light and re-emit at higher wavelength. Typically ~100nm shift.

Self Phase Modulation Intensity of amplitude modulated (AM) pulse changes Refractive Index of fibre Different portions of the pulse see different Refractive indices D Intensity D Refractive Index D Refractive Index D Phase (Chirp) l l 2017 EXFO Inc. All rights reserved. 16

Self Phase Modulation Intensity of amplitude modulated (AM) pulse changes Refractive Index of fibre Different portions of the pulse see different Refractive indices Causes phase modulation & pulse dispersion in AM signals D Intensity D Refractive Index D Refractive Index D Phase (Chirp) D Phase (Chirp) + Dispersion PULSE SPREADING l l t 2017 EXFO Inc. All rights reserved. 16

Cross Phase Modulation (XPM) XPM extension of SPM multiple channels interact For Phase modulated signals, Amplitude modulated signals with cause phase noise Solution - Channel grooming l 2017 EXFO Inc. All rights reserved. 17

Conflicting requirements Issue - With Dual polarization signals launch power is now 3dB lower (shared between 2 signals) Solution? Turn up launch power. Issue - 10G & 100G interaction with XPM. Solution? Solution? Channel grooming Lower launch power to reduce NLE 2017 EXFO Inc. All rights reserved. 18

RAMAN Amplification

EDFA (Basics) EDFA EDFA dbm 0-30 EDFA only

Distributed Raman Amplification Typically used as pre-amp to an inline or pre-amp EDFA EDFA EDFA dbm 0 Raman Pump -15-30 35 db EDFA With only Raman G R on/off

Distributed Raman Amplification Typically used as pre-amp to an inline or pre-amp EDFA EDFA EDFA dbm 0 Raman Pump -15 G R on/off -30 35 db EDFA With only Raman Longer fiber spans Increases power at the input to EDFA -> increases OSNR Higher capacity Increased link distance Enhanced operating margins

RAMAN Amplification Optimsing the gain

Impact of fibre attenuation on Raman Gain 1430 nm attenuation? Higher attenuation at Pump wavelength reduces Raman performance

Raman Gain Reduction (db) Impact on System Reach Assume older fiber with average loss in 1430 nm range of 0.33 db/km and 1dB connector loss 6 0.24dB/km 0.09 db higher loss at pump wavelengths 5 0.28dB/km 4 0.33dB/km 3 4 db less Raman gain 2 1 0 0 0,5 1 1,5 2 2,5 3 Connection Loss (db) 28% shorter link distance

How can we measure the Attenuation? Direction of signal Direction of Raman pump Use OTDR @ 1430nm Important to measure attenuation over region of Raman amplification

RAMAN Amplification Keeping it clean

Raman Gain Reduction (db) Impact of Connection Loss on Raman Gain Loss between Raman pump and transmission fiber is caused by Multiple connectors and patch panels Contaminated connectors Old connectors 10 Fiber bends Connector Loss 9 8 7 Signal 6 5 4 Pump 3 2 0.20dB/km 1 Raman pump 0 0 0,5 1 1,5 2 2,5 3 Connection Loss (db)

Raman Gain Reduction (db) Location of Loss Element Connector loss in proximity of Raman pump has maximum impact on Raman gain Same loss located beyond the effective length of the fiber has minimal contribution to gain reduction 10 Signal Loss Distance to loss element 9 8 7 6 5 4 0km 5km 10km 20km 3 Pump 2 1 Raman pump 0 0 0,5 1 1,5 2 2,5 3 Connection Loss (db)

Equipment Damage Permanent damage to connectors on DWDM equipment and on patch panels

How Can We Find Bad Connectors? Use an OTDR to locate (existing link) Use inspection probe to check cleanliness of connectors Remove all connectors

Conclusion Coherent technology has helped achieve higher capacity To combine with longer reach demands require additional Raman Amplifiers Some additional basic fibre characterisation required for optimal performance; Minimizing attenuation in 1430-1460nm range Keeping losses/reflectance's in the Raman window to a minimum 2017 EXFO Inc. All rights reserved. 32

Thank you