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

3 Outline 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 Engineering 4 Allocation of Spectral Bands - Sup.dsn

Standards Engineering 5 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 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 Engineering 6 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. 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 Engineering 7 CWDM Wavelength Grid - G.694.2

Standards Engineering 8 DWDM Frequency Grid - G 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): n 0.05 where 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): n 0.05 where n is a positive or negative integer including zero

Standards Engineering 9 Advanced Fibres - G.scu For broadband optical transport over the S + C + U bands, 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 the S + C + U bands, 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 Engineering 10 Broadband Fibre G.scu Dispersion Wavelength (nm) Chromatic Dispersion Coefficient (ps/nm-km) positive dispersion negative dispersion

Standards Engineering 11 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 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 Engineering 12 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. 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 Engineering 13 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 Engineering 14 Minimum CD Required for Several NRZ and RZ Bit-Rates and Power Penalties ,000 1, Source 20-dB Width (GHz) Chromatic Dispersion (ps/nm) : 10G NRZ, 1dB penalty 2: 40G NRZ, 1dB penalty 3: 40G NRZ, 2dB penalty 4: 40G RZ (f=1/3), 2dB penalty

Standards Engineering 15 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 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 Engineering 16 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 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 Engineering 17 MultiSpan Longitudinal Compatibility All network elements come from one vendor. Only the cable characteristics are specified –attenuation, CD, PMD, reflections,...

Standards Engineering 18 Multi-Span Full Transverse Compatibility

Standards Engineering 19 Multi-Span Single-Interface Transverse Compatibility

Standards Engineering 20 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). 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 Engineering 21 Multi-Span Limited Transverse Compatibility