Next Generation Requirements for DWDM network

NG Requirements for DWDM network: Outline Optical Transport Network Metro vs. Long-Haul Requirements Next Generation DWDM requirements Fiber plant, Amplification, ROADM, and Transceivers Current ROADM Node Architecture Next Generation ROADM Architectures Colorless Colorless and Directionless Colorless, Directionless, and Contentionless (CDC) Scaling to beyond 100G Flexible Channel Bandwidth Conclusions Verizon copyright 2011 2

Optical Transport Network: DWDM: Metro vs. LH Requirements Metro DWDM network: Optimized towards 1000km of un-regenerated optical reach 15-20 ROADM pass-throughs for optical path 880Gbs transmission capacity per fiber (88 wavelengths @ 10Gbps) up to 8 fiber directions Today: optimized for 10Gbs per channel transmission (intensity modulation) Higher bit rates: 40Gpbs and 100Gbps (phase modulation) can be deployed but fiber capacity is de-rated especially when 100Gbps channels are transmitted (no flexible grid required) Optical amplifiers optimized to support rates of 10G (Raman amplification is not required) ROADM architecture is colored, directional, and has wavelength contention 3

Optical Transport Network: DWDM: Metro vs. LH Requirements Long-Haul DWDM network: Optimized towards 2500km un-regenerated optical reach 4 8 ROADM pass-throughs for optical path 10 Tbs transmission capacity per fiber (100wavelngths @ 100Gbps) up to 8 fiber directions Optimized for 100Gbps per channel transmission Higher bit rates: 400Gbps and 1Tbps can be deployed without de-rating fiber capacity (flexible grid required) Optical amplifiers optimized towards supporting data rates of 100G and beyond (Raman amplification is required) ROADM architecture is colorless, directionless, and contentionless (CDC) 4

Optical Transport Network: DWDM Transport Node Evolution DWDM introduction to SONET/SDH networks: Needed for Capacity Enhancement Support point-to-point topology Multiplexing/Demultiplexing at each node Next step for DWDM Support multi-node linear and ring configurations Need to support add/drop and passthrough OADM Channel Add/Drop function is static Reconfigurability + OADM = ROADM Wavelength switching Channel Add/Drop is dynamic and under software control Additional flexibility DWDM Multiplexing/Demultiplexing DWDM Add/Drop 5

Current ROADM node architectures Current Optical Networks Move towards meshed topologies Basic building blocks Optical Splitter/Coupler Wavelength Mux/Demux Wavelength Selective Switch (WSS) Transmitters w/tunable lasers Receivers w/broadband photo-detectors Current ROADM architecture: Limitations: colored architecture Due to Add/Drop structure design and not because of transponder or receiver 6

NG ROADM node architectures: Colorless In colorless design any wavelength can be assigned to any port on mux/demux structure WSS replaces fixed port mux/demux structure Colorless combining requires control of laser side mode suppression ratio or filter the signal Limitations: each Add/Drop structure is unique to each degree 7

NG ROADM node architectures: Colorless and Directionless Directionless Add/Drop structure allows to direct a channel to any degree of the ROADM Add 1xM coupler to Add structure Add 1xM WSS to Drop structure No Add/Drop structure is associated w/particular degree Limitations: not contention-free 8

NG ROADM node architectures: Colorless, Directionless, Contentionless Contentionless ROADM design removes wavelength restrictions from Add/Drop structure Transmitter can be assigned to any wavelength and any degree as long as long as the number of channels w/the same wavelength is not more than the number degrees in the node Add/Drop port can be any color and connect to any degree Only one Add/Drop structure is needed in the node 9

NG ROADM node architectures: CDC Example CDC design example This design does not use MxN WSS for add/drop structure MxN WSS switch is not commercially available today Add/Drop structure may be based on using photonic (fiber) switches (with small port counts), optical couplers, and tunable filters This design is scalable in the number of add/drop ports Maintains full flexibility of contentionless design 10

ROADM CDC design with coherent detection: Banded access 1xN WSS divides incoming channel into smaller groups All access Photonic switch with large port count Design challenge is to discriminate one channel out of band of channels NG ROADM node Architectures: CDC with Coherent Detection 11

NG ROADM Node Architectures: Summary of Evolution ROADM evolution Colored, fixed add/drop Colorless Colorless and Directionless Colorless, Directionless, and Contentionless (CDC) 12

NG ROADM Node Architectures: CDC Architecture West North East Architecture: 4-Degree ROADM with unrestricted add/drop Wavelength switching to route wavelengths between fiber directions Add/drop wavelength routing Tunable wavelength selection in add/drop structure South Transponder Transponder Transponder Transponder Add/drop Transponder Transponder Transponder Benefits Any add/drop port can go any direction with any wavelength Each add/drop port can be assigned any color Add/drop wavelength can be routed to any direction No restrictions on color re-use in add/drop structure 13

Scaling beyond 100G: Flexible Channel Bandwidth As bit rates have increased to 100Gb/s (even with more spectrally efficient modulation techniques such as PM-QPSK) most of the available channel bandwidth is being utilized Problem is manageable at 100 Gb/s, but supporting 400 Gb/s or even 1Tb/s with 50 GHz channel spacing will require very high SNR and will limit optical reach Network can be future proofed by supporting flexibility in the channel spacing that allows channel bandwidth to be increased with bit rate 10 Gb/s λ 40 Gb/s λ 10 Gb/s λ 40 Gb/s λ 40 Gb/s λ 1569.59 1569.18 1568.77 1568.36 1567.95 1531.12 1530.72 1530.33 C band, fixed 50 GHz grid 100 Gb/s λ 40 Gb/s λ 40 Gb/s λ 50GHz 50GHz 75GHz 75GHz 150GHz 100 Gb/s λ 100 Gb/s λ 400 Gb/s λ 400 Gb/s λ 1 Tb/s λ 1569.59 1569.18 1568.77 1568.36 1567.95 1531.12 1530.72 1530.33 C band, 50 200 GHz Flexible Grid (in 25 GHz increments) λ, nm λ, nm 14

Scaling Beyond 100G: Options for implementation Single carrier approach: Increase constellation size (symbol rate stays the same, bitrate increases) Coded modulation will probably be required (since separating coding and modulation is not optimal for multi-level signaling) TCM as an example is bandwidth efficient modulation Coding gain must outweigh power disadvantage of going to the higher constellation Reach is not comparable to 100G Component bandwidth scaling maybe a problem Multiple carrier approach (Super channel): Apply OFDM concepts for closer spacing between the carriers Technologies are more mature at lower date rates per channel Not as efficient spectrum utilization as in single carrier approach Requires flexible grid support in WSS 15