April 14 2015 Putting the D back into DWDM Full-band Multi-wavelength Systems Mani Ramachandran CEO / CTO InnoTrans Communications
Perception vs. Reality of full-band multiwavelength systems 40 wavelength Broadcast / Narrowcast topology Typical full-band multi-wavelength limitations An innovative hybrid transmitter solution Migrating from BC / NC to full-band 40 wavelengths Network design examples Conclusions 2
Only 16 wavelengths are possible due to Four Wave Mixing (FWM) A custom wavelength plan is required so optical beats due to FWM fall on un-used channels Full-band QAM DWDM systems will not support the BER / MER requirements for DOCSIS 3.1 and should be replaced digital optics such as remote PHY By controlling optical power, increasing OMI & eliminating CHIRP 40 wavelengths, 40 km & >40 MER are possible with fullspectrum all QAM systems
FWM Myth vs. FMW Reality FWM is the Biggest Problem for Fullband DWDM Crosstalk is the Biggest Problem for DWDM systems FWM Happens at All Optical Powers FWM can Come and Go and is Unpredictable Once FWM is Solved, other Nonlinearities can be Ignored and Will Not Impact System FWM Simulations Predict the Actual System Performance FWM has to be Solved with Unequal WL Spacing FWM ONLY happens with Very High Launch Powers FWM is Very Predictable and Stable over Long Periods with quality lasers Even without FWM High Launch Powers Cause Numerous Problems Dispersion and Modulation must be Considered for FWM FWM is Solved with Low Powers and Frequency Offsets if needed 4
Uneven Channel Spacing FWM Work-arounds Minimizes FWM but never 100% Still Requires Offsets Requires Non-Standard Passives Not an Efficient use of the Optical Spectrum Requires Forward and Return Interleaving The Reality is: Alternative WL Plans Focus only on FWM No 16 Ch. WL Plan Totally Avoids FWM & Still Requires Offsets (Unspecified ) along with Custom Passives and Ignores other Major Limitations 5
Common topology deployed since late 90s Supports up to 40 WLs of 200 MHz QAM Current NC bandwidth requirements are exceeding 200 MHz Hub BC 1550nm EM Tx NC QAM s Headend EDFA NC QAM s NC Tx - λ1 NC Tx - λ40 M U X +3 dbm / λ 30 km -3 to -5 dbm / λ EDFA EDFA Splitter / Combiner D M U X P Typical Forward RX Level 10 km BC:~0 dbm NC: -3 to -6 dbm Narrowcast optical levels relatively low as compared to broadcast Low optical level and limited RF BW results in low FWM & Xtalk 6
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Externally modulated lasers utilized for the BC channels would provide best performance.. but at a significant cost penalty Expanding the bandwidth from 200 MHz to fullband with a Direct Modulated Laser (DML) or an Electro-absorption Modulated Laser (EML) lower cost but with a performance penalty DML lowest cost, highest CHIRP EML medium cost, lower CHIRP, poor linearity 8
RF pre-distortion is utilized to compensate for the non-linearities Laser CHIRP is compensated for a given length of fiber... but does not help for CSO/CIN degradation from filter ripple DML need to compensate for poor CSO EML need to compensate for poor CTB The technique & amount of improvement is a cost vs benefit trade-off Once the $$$ / benefit return is diminished a next step is to reduce OMI! 9
As channel count has increased, the OMI per channel is reduced plus an additional reduction due to CHIRP worsens with higher channel loading (Direct Mod Laser) Clipping, higher Peak to Average Power Ratio (PAPR) Poor linearity of electro-absorption modulated lasers (EML) To overcome low OMI. Requires higher optical input levels to EDFAs & receivers In turn Increases FWM & Xtalk Every 1 db = 2 db worse Lower OMI Low CNR High Optical Power Decrease BER Increase FWM & XTalk 10
Higher optical power leads to FWM & Xtalk issues To compensate develop elaborate WL plan where large FWM beats fall on unused channels in addition to the in-band ones & xtalk that degrade MER 11
3x fiber utilization to match 40 wavelength NC system 16 select wavelengths doesn t match the installed base of filters and need to be replaced Higher optical power levels to achieve MER / BER performance for 16 WL prohibiting 40 WLs All QAM s All QAM s Headend NC Tx λ1 NC Tx λ16 M U X +6 to 10 dbm / λ 3 to 6 db increase = 6 to 12 db FWM & XTALK EDFA D M U X Hub 30 km 10 km 0 to +3 dbm / λ Typical Forward RX Level 0 to +2 dbm 12
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External Modulated performance with lower cost! Cancels laser CHIRP at source as an alternative to predistortion compensation of fiber dispersion Eliminates fiber dispersion & filter ripple induced CIN / CSO No need to compromise OMI to improve CHIRP Distance Independent Performance (no tuning) Supports redundant fiber paths with differential primary and secondary distance Immune to Filter Ripple Custom filters not required 14
Momentary rise in the composite power of QAM signals (Peak to Average Power Ratio or PAPR) results in periodic laser clipping. PAPR of QAM signals may vary 6 to 13 db or more depending on modulation rate & number of streams. (DOCSIS 3.1 with multisubcarrier OFDM & higher QAM rate will increase PAPR) Periodic clipping can limit a transmitter s pre-fec BER link performance to 1e-5 to 1e-7. or trade off MER for >BER spec! Clipping Mitigation technology eliminates the clipping errors extending the dynamic range which allows a much higher OMI operating point & < 1e-9 pre-fec performance along with >40 db MER (With up to 40 wavelengths!!) 15
Ability to operate 3 to 4 db lower optical levels improves Xtalk / FWM by 6 to 8 db 16
High OMI maintains RF levels @ lower optical input 17
Most solutions limit the number of wavelengths due to lower OMI & high launch power 18
Clipping Mitigation allows a much higher OMI making lower launch power possible, reducing FWM & Xtalk 19
CHIRP cancelation provides additional reduction in FWM & Xtalk 20
Together the Hybrid transmitter technology allows 40 consecutive wavelengths on the ITU DWDM plan 21
CHIRP cancellation supports use of standard ITU plan filters Lower optical levels matches existing NC overlay 40 to 42 db MER optical link performance is achievable Headend Hub Typical Forward RX Level All QAM s All QAM s NC Tx λ1 NC Tx λ16 M U X +3 dbm / λ 30 km 10 km -3 to -5 dbm / λ EDFA D M U X -3 to -6 dbm 22
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40 Wavelength / 30 km / 42 MER CF-CH CF-CH CF-CH CF-CCT4-2320-M ITU 20 ITU 21 ITU 22 ITU 23 CF-CCT4-2724-M ITU 24 ITU 25 ITU 26 ITU 27 CF-CCT4-3128-M ITU 28 ITU 29 ITU 30 ITU 31 CF-CCT4-3532-M ITU 32 ITU 33 ITU 34 ITU 35 CF-CCT4-3936-M ITU 36 ITU 37 ITU 38 ITU 39 CF-CCT4-4340-M ITU 40 ITU 41 ITU 42 ITU 43 CF-CCT4-4744-M ITU 44 ITU 45 ITU 46 ITU 47 CF-CCT4-5148-M ITU 48 ITU 49 ITU 50 ITU 51 CF-CCT4-5552-M ITU 52 ITU 53 ITU 54 ITU 55 CF-CCT4-5956-M ITU 56 ITU 57 ITU 58 ITU 59-3 db 10 Band Combine 10 x 4λ transmitter (integrated mux) +3 dbm 10 band mux / dmux 23.8 km -6.0 db -3 / +3.5 dbm GCA-0620 Constant gain EDFA Add WLs without changing node levels -2 db 4 Ch Dmux -2 db 10 blocks of 4 wavelengths -3 db 10 Band Combine 4 Ch Dmux 7 km -1.8 db 2 km -0.5 db -3.5 dbm Node 1 Add 4 λ transmitter and 4 way demux as needed Node 40-2.2 dbm 24
CF-CCT4-2320-M ITU 23 CF-CH CF-CH ITU 22 ITU 21 ITU 20 CF-CCT4-2825-M ITU 28 ITU 27 ITU 26 ITU 25 CF-CCT4-3330-M ITU 33 ITU 32 ITU 31 ITU 30 CF-CCT4-3835-M ITU 38 ITU 37 ITU 36 ITU 35 CF-CCT4-4340-M ITU 43 ITU 42 ITU 41 ITU 40 CF-CCT4-4845-M ITU 48 ITU 47 ITU 46 ITU 45 CF-CCT4-5350-M ITU 53 ITU 52 ITU 51 Out Out Out Out Out Out Out +6 dbm -1.5 db Band Combine -1.5 db Band Combine -1 db Band Split -1 db C 8 WL O Stacker RTN 2 4 27 km -6.8 db Forward Path 70km total distance 39 MER 2 9-1 db C -5.3 / +4.7 dbm DSA3-1020 DSA DSA3-1218 DSA 3 4-1 db C 37.5 km -9.4 db 3 9-1 db C 8 WL O Stacker RTN -6.6 / +3.4 dbm 4 4 DSA3-1020 DSA -1 db Band Split 4 9-1.5 db Band Separater -1.5 db Band Separater -2 db 4 Ch Dmux -2 db 4 Ch Dmux 5 4 4 km -1 db -2 dbm Node 1 7 km -1.8 db Node 32-3 dbm 5 9 8 return λ ITU 50 CF-CCT4-5855-M ITU 58 ITU 57 ITU 56 Out 20-23 25-28 30-33 35-38 40-43 45-48 50-53 55-58 32 FWD λ ITU 55 25
Return Path 8 Wavelengths 32-85 MHz RF return segments 2 4 2 9 3 4 3 9 4 4 4 9 5 4 5 9 8 return λ 20-23 25-28 30-33 35-38 40-43 45-48 50-53 55-58 32 FWD λ 26
RFoG / PON High OMI & CHIRP Cancellation 1.7 in. Headend to 512 HP Remote Cabinet or IHUB ITU 37 ITU 35 ITU 33 Out EP DS: 37 to 31 US: 45 to 39 DS: 37 to 31 US: 45 to 39 ITU 31 2x10Gig XFP 4-4x32HP 4x128HP 2x10Gig XFP CF-REM-RX4M- L CF-REM-RX4M- L Upstream GPON 10 Gig Transport ITU 51 & 49 Upstream RFoG O Stacker ITU 45 to 39 Downstream RFoG ITU 37 to 31 Downstream GPON 10 Gig Transport ITU 27 & 25 CF-REM-RX4M- L -1.5 db 4 Ch Dmux 4 x 128 HP / λ Downstream 16 x 32 HP Upstream with Stacker CF-REM-RX4M- L CISCO 7604 US: XX DS: XX CHIRP cancelled supports diverse routes 10GigE Aggregation DS: XX US: XX 27
RFoG High OMI & CHIRP Cancellation 512 HP Remote Cabinet feeding PONs DS: 37 to 31 US: 45 to 39 DS: 37 to 31 US: 45 to 39 TSD O/S Cabinet 37 to 31 Demux EDFA EDFA 1610 Reduce EDFA power by >3 db 1260 to 1280 1290 to 1330 1 x 3 2 1480 to 1500 Micro Node GPON 1310/1490 ONU 1575 to 1580 1600 to 1620 TSD Stacker TSD RRS-HS XPON Up GPON Up GPON Dwn Downstream RFoG ITU 37 to 31 XPON Dwn RFoG Up 45 to 39 Mux TSD Stacker TSD RRX-HS 128 HP / λ Downstream 32 HP Upstream with Stacker US: XX DS: XX DS: XX US: XX Remote OLT GPON 1310/1490 10 GigE λs serve OLT & OLT PON λs combine with RFoG High OMI reduces EDFA power requirements at PON & >MER RFoG upstream feed O Stacker 28
40 wavelength full-spectrum systems are possible with the right technology and optical power levels to avoid FWM issues Migrating from existing BC / NC to a full-spectrum solution can be a drop in replacement The hybrid transmitter technology high density DWDM solution simplifies network planning and deployment Optical link performance of >40 db MER and pre- FEC BER of 1e-9 with 40 wavelengths and 40 km are very achievable 29
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