Transcript No Slide Title

Some Recent Topics in
Physical-Layer System Standards
Felix Kapron
Standards Engineering
Outline
• Spectral Bands
• CWDM and DWDM
• New Broadband Fibre
• Chromatic Dispersion Limitations
• Issues with NRZ and RZ
• Transverse and Longitudinal Compatibility
• Conclusions
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Standards Engineering
Allocation of Spectral Bands - Sup.dsn
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Band
Descriptor
Range (nm)
O-band
Original
1260 to 1360
E-band
Extended
1360 to 1460
S-band
Short wavelength
1460 to 1530
C-band
Conventional
1530 to 1565
L-band
Long wavelength
1565 to 1625
U-band
Ultralong wavelength
1625 to 1675
Standards Engineering
Spectral Band Conditions
• The definition of bands is not for specification; that is left to
systems Recommendations.
• Not all fibres will use all bands for system operation or
maintenance.
• The U-band
– for possible maintenance purposes only
– fibre operation is not ensured there
– must cause negligible interference to signals in other bands
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Standards Engineering
Course Wavelength Division Multiplexing
• To allow simultaneous transmission of several wavelengths
with sufficient separation to permit the cost-effective use of
– uncooled sources, allowing some wavelength drift with
temperature
– relaxed laser wavelength selection tolerances for higher yield
– wide pass-band filters
• Wavelength spacing no less than 20 nm is optimal.
• Applications are to broadband access and metro.
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Standards Engineering
CWDM Wavelength Grid - G.694.2
Nominal Central wavelengths (nm)
This covers all spectral bands for signals, but endpoints are illustrative only.
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1270
1390
1510
1290
1410
1530
1310
1430
1550
1330
1450
1570
1350
1470
1590
1370
1490
1610
Standards Engineering
DWDM Frequency Grid - G.694.1
• Moved out of obscure Annex A of G.692.
• Channel spacings (in GHz) of 12.5, 25, 50, 100 and above.
• Example: nominal central frequencies for 50 GHz spacing.
Allowed channel frequencies (in THz):
193.1 + n  0.05
where n is a positive or negative integer including zero
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Standards Engineering
Advanced Fibres - G.scu
• For broadband optical transport over the
S + C + U bands, 1460 - 1625 nm
• With chromatic dispersion coefficient (under study)
– positive or negative
– above zero in magnitude
• to suppress four-wave mixing etc. in DWDM
– not too large in magnitude
• to avoid excessive dispersion compensation
• With specified attributes for the fibre, cable, and link.
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Standards Engineering
Broadband Fibre G.scu Dispersion
Chromatic
Dispersion
Coefficient
(ps/nm-km)
positive dispersion
1465
1625
negative dispersion
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Standards Engineering
Wavelength (nm)
Chromatic Dispersion Limitations - old approach
• Began with G.957 on SDH up to 2.5 Gbit/s
• Continues through G.693 on intra-office systems
up to 40 Gbit/s
– chromatic dispersion (ps/nm) =
worst-case fibre chromatic dispersion coefficient (ps/nm-km) 
optical path length (km)
– bit-rate  CD  source linewidth =
number depending on desired power penalty
– Allowed CD() determines the Tx wavelength window
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Standards Engineering
CD Limitations - problems
• Tied to fibre, not signal.
– Sets an artificial fibre CD limit often far below what the signal
will actually tolerate.
• Can unnecessarily limit
– transmitter wavelength window and spectral width
– the added CDs of in-line components
• Fails when the high bit-rate modulation spectrum is wider
than the narrow-line source spectrum.
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Standards Engineering
CD Limitations - new approach (Sup.dsn)
• (bit-rate  wavelength)2  CD = duty cycle 
number depending on desired power penalty
– duty cycle: 1 for NRZ, 1 for RZ
• leads to compensation requirements for longer 40G links
(G.959.1) with tuning of ‘residual dispersion’.
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Standards Engineering
Minimum CD Required for Several NRZ and RZ
Bit-Rates and Power Penalties
10,000
1: 10G NRZ, 1dB penalty
Chromatic
Dispersion
(ps/nm)
1,000
2: 40G NRZ, 1dB penalty
3: 40G NRZ, 2dB penalty
4: 40G RZ (f=1/3), 2dB penalty
1
100
3
2
4
10
1
10
100
Source 20-dB Width (GHz)
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Standards Engineering
Issues with NRZ and RZ
• RZ advantages
– Lower energy per pulse reduces nonlinear effects.
– May reduce requirements for 1st-order PMD.
• RZ disadvantages
– Increases signal bandwidth
• lower tolerable chromatic dispersion of link
• higher bandwidth at the receiver
• more sensitive to 2nd-order PMD
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Standards Engineering
RZ Issues for Different Applications
• Optimal values of duty cycle
• Other formats, e.g., CRZ
• Maximum source linewidth
• Maximum spectral density
• Minimum contrast ratio
• Maximum CD deviation
• Maximum PMD
• Partitioning and measurement of path penalties
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Standards Engineering
MultiSpan Longitudinal Compatibility
Vendor A
Vendor A
Vendor A
Tx
Rx
• All network elements come from one vendor.
• Only the cable characteristics are specified
– attenuation, CD, PMD, reflections, ...
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Vendor A
Standards Engineering
Multi-Span Full Transverse Compatibility
Vendor B
Vendor A
Vendor B
MPI-S
MPI-R
Tx
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Vendor C
Rx
Standards Engineering
Multi-Span Single-Interface
Transverse Compatibility
Vendor A
Vendor A
Vendor A
Vendor B
MPI-R
Tx
Rx
Vendor B
Vendor A
Vendor B
Vendor B
MPI-S
Tx
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Rx
Standards Engineering
Conclusions
• Spectral bands and grids in wavelength & frequency have been
well defined.
• Work on a Recommendation on a new broadband fibre is
beginning.
• 40G applications require a different method of specifying
chromatic dispersion; other applications may need corrections.
• New RZ and NRZ applications are being developed.
• Longitudinal and transverse compatibility is being actively
discussed (with implications for a new IaDI Recommendation).
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Standards Engineering
Multi-Span Limited Transverse Compatibility
Vendor A
Vendor B
Vendor B
Tx
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Vendor A
Rx
Standards Engineering