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Ph.D. Presentation

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Colm Browning

on 25 February 2014

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Transcript of Ph.D. Presentation

OFDM for Next Generation Optical Networks
Dr. Colm Browning

Network Architectures
OFDM in Optical Networks
Experimental Work
OFDM is an excellent candidate for NG PONs (Access)
Optical injection helps to overcome nonlinear limitations
Direct modulation of a tuneable laser with OFDM has been demonstrated
Suitable for WDM-PON applications (>10Gb/s per user)

OFDM is also a suitable candidate for Burst Mode networks (Metro)
OFDM in a switching environment has been demonstrated
Allows for increased network capacity (smaller grid sizes)
Network Architectures
OFDM for Optical Networks
Main Contributions
Performance improvement of OFDM-PON by optical injection.

Direct Modulation of a tuneable DM laser with AM-OFDM.

Demonstration of optical Burst Mode OFDM.
OFDM with Optical Injection
OFDM with Tuneable Lasers
Burst Mode OFDM
Direct Modulation is desirable.
Polarisation Independence
Introduction of nonlinearities.
OFDM performs poorly in a nonlinear channel.
Employ optical injection to shift region of nonlinearity.
Colourless Operation
Design all ONU's to be identical
Capable of operating on any wavelength
Reduce cost
Increase reconfigurability

Require low cost tuneable laser
Direct modulation preferable
OFDM-PON (tuneable laser)
Direct Modulation of DM laser
Various wavelengths across C-band
Ensure single mode lasing
Seven channels chosen for transmission
Vary in modulation bandwidth
Vary in output power
>10Gb/s on most channels over 50km
Upgrade device for ITU grid compatibility
Tuneable Laser
Slotted FP laser: 'Discrete Mode Laser'
Low cost
Two sections
Independent bias
Tune using bias currents
Tune using temperature control
Burst Mode SSB-OFDM
Implement switching environment
Clock back section of SG-DBR laser
Vary burst time
Vary WDM grid: 50, 25, 12.5GHz
Raw Data Rate: 18.7 Gb/s
Spectral efficiency of 1.2b/s/Hz
Direct detection
Burst Mode SSB-OFDM
Grid size and burst time impact performance
Investigate on subcarrier basis
16-QAM on each OFDM subcarrier
12.5GHz WDM grid spacing:
Aggregate BER < FEC limit after 8ns
NG Metro networks: Burst Mode operation
Greater spectral efficiency required
Greater number of optical carriers
Smaller WDM grid
Need to overcome dispersion.

Use SSB-OFDM with external modulator
Implement PON scenario.
Monolithically integrated lasers for optical injection.
Direct Modulation:
10Gb/s OFDM (16-QAM)
Adaptively Modulated OFDM.
10Gb/s OFDM
Channel estimated with pilots.
Improvement quantified in terms of throughput.
Injection allows higher order QAM on each OFDM subcarrier.
New applications driving bandwidth demand
On demand HD video (soon 4K UHD)
Video conferencing

Require higher speed, more flexible networks

Orthogonal Frequency Division Multiplexing
Multi-Carrier Modulation scheme
Highly spectrally efficient
Tolerant to CD
Access Networks
Passive Optical Networks (PON)
Time Division Multiple Access (TDMA)
EPON (IEEE 802.3ah)
GPON (ITU-T G.984)
Difficult to scale
Complex control algorithm
Burst Mode receiver required
Metro Networks
Metro networks: Burst Mode
Large grid spacing
Greater data rates required at smaller grid spacing... Spectral efficiency
OFDM Passive Optical Network
ONUs designated portions of OFDM spectrum
Allows for simple reconfigurability

ONU designated specific wavelength
Each carries OFDM signal
(De)Mux with AWG at RN
Burst Mode OFDM
OFDM suitable for Metro:

High spectral efficiency
Allow smaller WDM grid sizes
=> greater number of optical carriers

Tolerance to CD
Avoid complex time domain EQ
Bit/Power loading for non-injected (a) and injected (b) cases.
Limitation due to nonlinearity in non-injected case.
Injection overcomes limitation and improves error floor.
Rx. sensitivities differ due to dispersive fading.
Urata et. al, OFC 2012, NTh3E.4 (Google)
Kanonakis et. al, IEEE Commun. Mag., Aug. 2012
Yuang et. al, J. Lightwave Technol., Aug. 2013
Marie Curie International Research Staff Exchange Scheme Fellowship within the FP7
Optical Communications lab, IITM
Prof. Deepa Venkitesh
Aravind Anthur
Saikrishna Reddy
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