Some Recent Topics in Physical-Layer System Standards Felix Kapron Standards Engineering Felix Kapron Standards Engineering.

Some Recent Topics inPhysical-Layer System Standards

Some Recent Topics inPhysical-Layer System Standards

Felix KapronStandards Engineering

Felix KapronStandards Engineering

Standards Engineering3

OutlineOutline

• Spectral Bands

• CWDM and DWDM

• New Broadband Fibre

• Chromatic Dispersion Limitations

• Issues with NRZ and RZ

• Transverse and Longitudinal Compatibility

• Conclusions

• Spectral Bands

• CWDM and DWDM

• New Broadband Fibre

• Chromatic Dispersion Limitations

• Issues with NRZ and RZ

• Transverse and Longitudinal Compatibility

• Conclusions

Standards Engineering4

Allocation of Spectral Bands - Sup.dsnAllocation of Spectral Bands - Sup.dsn

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

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 Engineering5

Spectral Band ConditionsSpectral 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

• 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

Standards Engineering6

Course Wavelength Division MultiplexingCourse 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.

• 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.

Standards Engineering7

CWDM Wavelength Grid - G.694.2CWDM Wavelength Grid - G.694.2

Nominal Central wavelengths (nm)This covers all spectral bands for signals, but endpoints are illustrative only.

1270 1390 1510

1290 1410 1530

1310 1430 1550

1330 1450 1570

1350 1470 1590

1370 1490 1610

Nominal Central wavelengths (nm)This covers all spectral bands for signals, but endpoints are illustrative only.

1270 1390 1510

1290 1410 1530

1310 1430 1550

1330 1450 1570

1350 1470 1590

1370 1490 1610

Standards Engineering8

DWDM Frequency Grid - G.694.1DWDM 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 0.05where n is a positive or negative integer including zero

• 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 0.05where n is a positive or negative integer including zero

Standards Engineering9

Advanced Fibres - G.scuAdvanced Fibres - G.scu

• For broadband optical transport over theS + 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.

• For broadband optical transport over theS + 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.

Standards Engineering10

Broadband Fibre G.scu DispersionBroadband Fibre G.scu Dispersion

Wavelength (nm)1465 1625

Chromatic Dispersion Coefficient (ps/nm-km)

positive dispersion

negative dispersion

Standards Engineering11

Chromatic Dispersion Limitations - old approachChromatic 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

• 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

Standards Engineering12

CD Limitations - problemsCD 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.

• 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.

Standards Engineering13

CD Limitations - new approach (Sup.dsn)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’.

• (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’.

Standards Engineering14

Minimum CD Required for Several NRZ and RZBit-Rates and Power PenaltiesMinimum CD Required for Several NRZ and RZBit-Rates and Power Penalties

101 100

10,000

1,000

100

10

Source 20-dB Width (GHz)

Chromatic Dispersion

(ps/nm)

2

4

3

1

1: 10G NRZ, 1dB penalty

2: 40G NRZ, 1dB penalty

3: 40G NRZ, 2dB penalty

4: 40G RZ (f=1/3), 2dB penalty

Standards Engineering15

Issues with NRZ and RZIssues 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

• 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

Standards Engineering16

RZ Issues for Different ApplicationsRZ 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

• 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

Standards Engineering17

MultiSpan Longitudinal CompatibilityMultiSpan Longitudinal Compatibility

• All network elements come from one vendor.• Only the cable characteristics are specified

– attenuation, CD, PMD, reflections, ...

• All network elements come from one vendor.• Only the cable characteristics are specified

– attenuation, CD, PMD, reflections, ...

Tx Rx

Vendor A Vendor AVendor A Vendor A

Tx Rx

Vendor A Vendor AVendor A Vendor A

Standards Engineering18

Multi-Span Full Transverse CompatibilityMulti-Span Full Transverse Compatibility

Tx Rx

Vendor A Vendor CVendor B Vendor B

MPI-RMPI-S

Tx Rx

Vendor A Vendor CVendor B Vendor B

MPI-RMPI-S

Standards Engineering19

Multi-Span Single-InterfaceTransverse CompatibilityMulti-Span Single-InterfaceTransverse Compatibility

Tx Rx

Vendor A Vendor BVendor A Vendor A

MPI-R

Tx Rx

Vendor A Vendor BVendor B Vendor B

MPI-S

Tx Rx

Vendor A Vendor BVendor A Vendor A

MPI-R

Tx Rx

Vendor A Vendor BVendor B Vendor B

MPI-S

Standards Engineering20

ConclusionsConclusions

• 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).

• 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).

Standards Engineering21

Multi-Span Limited Transverse CompatibilityMulti-Span Limited Transverse Compatibility

Tx Rx

Vendor A Vendor AVendor B Vendor B

Tx Rx

Vendor A Vendor AVendor B Vendor B