Transcript Tunable Lasers

Update on WDM-PON
TNC15, Porto, June 2015
Dr. Klaus Grobe, ADVA Optical Networking SE, Advanced Technology
Content
2
•
Introduction
•
NG-PON2 Status and Variants
•
Tunable Lasers
•
AMCC and Tuning
•
WR-ODN vs. WS-ODN
•
Conclusion
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Introduction
3
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Why and where WDM-PON?
• Requirement for broadband access (between PoPs and clients) technology
• Fixed-Mobile Convergence including mobile fronthaul (Digital RoF), Big Data, Cloud, …
• Increased access reach, 20…80 km
• Scalability to very high access bit rates (beyond 10 Gb/s)
• Low latency and jitter, possibly high sync requirements
• Leads to WDM-PON
• “Pure” WDM-PON, e.g., ITU-T G.metro
• NG-PON2 variants, ITU-T G.989 Series
Based on tunable lasers
• Relevant question: WS-ODN vs. WR-ODN?
WDM-PON: Wavelength-Domain Multiplex Passive Optical Network, WS: Wavelength-Selected, WR: Wavelength-Routed, ODN: Optical Distribution Network
4
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WDM-PON Application in NRENs
DWDM Backbone
Core
Core
• Connections between
backbone PoPs and end
users over up to 80 km,
PoP
OLT
mostly passive
PoP
OLT
• Transparent, low-latency
Long-Reach
WDM-PON
PN
PN
Campus
FTTB / FTTH
MSAN FTTCab MSAN
FTTdp
PN
5
Passive Node (WDM Filter)
PN
PN
Wireless Backhaul and
Fronthaul
PN
RE
channels up to 10 Gb/s now,
and N×28G / 40G, 100G in
the near future
• Automated self-tuning
PN FTTH
Campus
RE Reach Extender (Amplifier, optional)
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FTTH:
FTTB:
FTTCab:
FTTdp:
PoP:
Fiber
Fiber
Fiber
Fiber
Point
to
to
to
to
of
the Home
the Building
the Cabinet
the Distribution Point
Presence
NG-PON2 Status and Variants
6
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NG-PON2 Requirements and Variants
• Initial (operators’) requirements in ITU-T SG15-Q.2
• 40 Gb/s accumulated capacity (downstream, with symmetry option)
• 20…40 km passive reach (60 km with reach extension)
• Legacy ODN support and possible coexistence in particular w/ G-PON
• Colorless ONUs (with tunable lasers)
• Optional additional PtP WDM overlay
• Main Variants
• TWDM vs. PtP WDM PON
• TWDM 2G5 vs. 10G (in upstream and/or downstream), PtP WDM w/ 1G, 2G5, 3G, 5G, 10G, …
• Shared vs. Expanded Spectrum
Loss
N1
N2
E1
W1
W2
• Power-split (WS-) vs. filtered (WR-) ODN
Min. 14 dB 16 dB 18 dB 20 dB 7 dB 15 dB
• Reach options (N1, N2, E1, E2, W1, W2)
Max. 29 dB 31 dB 33 dB 35 dB 16 dB 24 dB
TWDM: Time- and Wavelength-Domain Multiplex, PtP: Point-to-Point, WS: Wavelength-Selected, WR: Wavelength-Routed
7
E2
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Basic NG-PON2 and ODN Configurations
SNI
S/R-CG
R/S
UNI
• Power-Split (PS) ODN for Shared-Spectrum NG-PON2
WS-ODN
OLT
ONU
PS
WM2
WM1
OLT
• Up to 8 wavelength pairs for TWDM (8  32…64 users)
PS
WR-ODN
• Co-existence of NG-PON2 and G-PON possible
ONU
• Up to 16 PtP WDM wavelength pairs possible
ONU
• Expanded-Spectrum PtP WDM PON on WR-ODN (greenfield)
• Overlap with ITU-T SG15-Q.6 G.metro WDM-PON
ONU
• Can have 32…48 WDM channel pairs (at ~100 GHz)
• Full-band tunables lasers required
OLT
WMx
Hybrid ODN
PS
ONU
• Hybrid of WR-ODN and WS-ODN
ONU
• Eliminates need for tunable RX filters
ONU
• Many other hybrid ODNs possible
ONU
OLT: Optical Line Terminal (head end), ONU: Optical Network Unit (tail end), WM: Wavelength Multiplexer, SNI: Service-Network Interface
8
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Tunable Lasers
9
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Why tunable Lasers in Access?
• Requirement for high
(bit-rate  passive-reach) product, see Introduction
• This is simpler to achieve with tunable laser diodes, rather than seeded/reflective approaches
[G. Berrettini et al., Int. J. Comm. Networks and Distributed Syst., Vol. 5, Nos. 1/2, 2010 pp. 193]
• For high performance, the simple RSOA cannot be used anymore (would require REAM-SOA)
• Doubtful that >10 Gb/s can be achieved
• Remaining problem (still): cost
RSOA: Reflective Semiconductor Amplifier, REAM-SOA: Reflective Electro-Absorption Modulator (with) Semiconductor Amplifier
10
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Full-Band Tunable Laser Diodes
SOA
DS-DBR LD
Gain Phase Rear
HR
Metal
Gain Region
Micro-ElectroMechanical Vertical
Cavity SurfaceEmitting Laser
SG Y-Branch LD
Sampled-Grating Y-Branch LD
Reflector 2
Silicon / SOI
• Thermally tuned Bragg reflector gratings (Vernier effect)
• Gratings, Multi-mode interferometer (MMI), modulators,
and electronics integrated in silicon or SOI substrate
• Gain chip bonded onto silicon
MEM-VCSEL
Tuning
p
n
Reflector 1
MMI
AR
Electronic tuning
Bragg gratings generate and select super modes
SOA as shutter, AMCC modulator, booster
Can be hybrid integrated with modulator
Curved Top
Mirror
Gain Phase
Digital Supermode
Distributed Bragg
Reflector Laser Diode
Substrate
AR
•
•
•
•
Front
Polymer-Chip
Bragg Grating
Gain
PD
MD Diplexer
PolymerIntegrated
Transceiver
Bottom Mirror
• Simple Mechanical tuning by MEM-DBR mirror
• Thermally tuned Bragg grating
• Monolithic integration possible
• Relatively low output power
• Direct modulation
• Polymer-integrated grating, receiver, monitoring
• Gain chip bonded onto polymer
• Direct modulation
AR: Anti Reflection, HR: High Reflection, MD: Monitoring Diode, PD: Photo Diode, SOI: Silicon on Insulator
11
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Making tunable Lasers Low-Cost
• Get rid of any sub-component which is not absolutely needed
• Possibly also the TEC (cooler)
Remove Wavelocker
• Reduce specs where possible
• Packaging
• Optical
• Reduce calibration effort
Remove TEC
• High production volumes
Reduced Package Specs
TEC: Thermo-Electric (Peltier) Cooler
12
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Monolithic
Integration of LD
and Modulator
[Source: Oclaro Inc.]
• Integrated wavelength locker
The Problems of the Low-Cost Tunable
•
Threat of cannibalization of T-SFP+ market
•
Hence, need to reduce some specs
•
•
CD tolerance
•
OSNR
•
Line width
•
Launch power?
•
Sensitivity?
Can make it useless for amplified long-haul
Can make it useless for coherent RX
No useful option for PON
Technically, it is also difficult to combine full-band tunability and high power budget
(N1 Class or even higher) in SFP+ format with ≤1.5 W power consumption
T-SFP+: Tunable Small-Formfactor Pluggable (+)
13
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AMCC and Tuning
14
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Why an AMCC?
• Without being told, an ONU cannot know where to tune
• This must be done via an Auxiliary Management and Control Channel, AMCC
• AMCC must be transparent to payload data signals
• It is modulated via baseband on-off keying which is added with small extinction ratio to the payload
• I2C and baseband overmodulation allow ~150 kb/s AMCC bit rate
Data In
PWR
LDD
SOA
AMCC out
DC/DC
I 2C
µC
AMCC in
Data Out
15
T-TOSA
CTRL ASIC
LPF
TIA
APD ROSA
PWR: Power
LDD: Laser-Diode Driver
LPF: Low-Pass Filter
TIA: Trans-Impedance Amplifier
APD: Avalanche Photo Diode
T-TOSA: Tunable Transmit Optical Sub-Assembly
ROSA: Receive Optical Sub-Assembly
CTRL ASIC: Control Application-Specific IC
µC: Micro Controller
DC/DC: Direct-Current-Direct-Current Converter
I2C: Inter-Integrated Circuit (bus)
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ONU Activation Procedure WR-ODN
• This is the simplest activation procedure, valid only for
Start
• WR-ODN (in WS-ODN, there‘d be heavy crosstalk)
Activate respective DS with AMCC
• Calibrated lasers (uncalibrated lasers require some additions)
+
Activate & tune ONU RX / AMCC
DS AMCC locked?
DS signal US wavelength
Set said US wavelength
Establish US / DS, incl. AMCC
• Lower part is optional for AMCC-assisted fine tuning
N
• For CBR (non-burst-mode) channels, the combination of WS-ODN
and uncalibrated lasers leads to much more complicated ONU
activation
+
N
AMCC Fine Tuning?
Perform fine tuning
End
16
DS: Downstream, US: Upstream, CBR: Constant Bit Rate
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WR-ODN vs. WS-ODN
17
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WR-ODN vs. WS-ODN – Potential Differences
• Operations-related aspects
• Support of legacy ODN
• Energy consumption – slightly higher in WS due to Tunable Filters (TF) and Reach Extenders (RE)
• Operations and maintenance cost – slightly higher in WS due to TF and RE
• Performance-related aspects
• Reach (which can translate to the OpEx aspects of running active RE in the ODN)
• Required transceiver complexity and resulting CapEx – added TF, RE in WS
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WR-WDM-PON vs. WS-WDM-PON
...
L
C
AMCC US
1:N WM
CT N
Central
Tuning
Control
PN
1:N WM
...
L
C
APD
TIA
SoC
µC
T-LD
LDD
SFP+
SoC
CAWG: Cyclic Arrayed Waveguide Grating
OLT
CT 1
ONU
AMCC DS
1:N CAWG
CT 1
1:N WM
OLT
L
C
ONU
L
AMCC DS
C
TF1
APD
PS
1:M
TF2
TIA
PN
T-LD
µC
SoC
AMCC US
Central
Tuning
Control
1:N WM
CT N
LDD
SFP+
T-LD: Tunable Laser Diode, TF: Tunable Filter, CT: Channel Termination, SoC: System on Chip, PN: Passive Node, C/L: C/L-Band filter
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SoC
Reach
Component
IL [dB]
1:40 AWG PoP / ODN
5.0 / 6.0
1:80 AWG PoP / ODN
6.0 / 7.0
1:8 AWG CO
2.5
C/L Bandfilter ONU
1.0
C/L Bandfilter OLT
0.5
Tunable Filter
1.0
PS 1:8 / 1:32 / 1:64
9.9 / 16.5 / 19.8
RXmin, 10G APD [dBm]
-26.0
TXmin [dBm]
+1.0
Fiber Loss C/L [dB/km]
0.35
R [km] = (TXmin [dBm] - RXmin [dBm] - IL [dB] - Penalties [dB]) / αF [dB/km]
Limits and Penalties
[dB]
OPP EML 10G 40 km [dB]
1.0
For RE, these limitations are considered
EOL Penalty [dB]
2.0
Crosstalk Penalty [dB]
1.0
SBS Ch. Max. [dBm]
8.0
• Max. per-channel launch 8 dBm to avoid (anti) SBS (means)
Laser Safety Class 1M
21.3
• Max. gain of 21 dB of suitably low-cost amplifiers
Max. Cost-eff. Gain [dB]
21.0
• Max. total launch 21.3 dBm for Laser Safety Class 1M (C plus L band)
SBS: Stimulated Brillouin Scattering, OPP EML: Optical Path Penalty (of) Externally-Modulated Laser, EOL: End of Life
20
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SMSR
Amplitude
Coherent Interferometric Crosstalk
Co. XT
Incoh. XT
Co. XT
Incoh. XT
f
From ITU-T Rec. G.Sup39
Penalty [dB]
3
Single Interferer
6 dB ER
Ideal Signal
2
1
0
-40
-35
-30
-25
-20
• The upstream in WS-ODN is subject to
strong Coherent Interferometric Crosstalk
• Caused by interferer side modes which cannot
be rejected in OLT demultiplexer
-15
Interferometric Crosstalk [dB]
SMSR: Side-Mode Suppression Ratio, ER: Extinction Ratio
21
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Crosstalk and Laser-Diode Side Modes
• Crosstalk caused by
Relative Power at 0.1 nm RBW [dB]
10
• ODN differential path loss
0
(with poor filter isolation)
-10
• Unsuppressed side modes
-20
-30
• Can lead to heavy penalties which
-40
require very high SMSR or additional
-50
tunable filters in the ONUs
-60
PSM = PTXmin - ε - POP - LDODN - 10 log (N)
Differential
Path Loss
-70
-80
1465
Path Penalty
1475
1485
1495
Wavelength [nm]
Measurement Curtesy of British Telecom
22
(WS-ODN: no multiplex filter)
46 dB
1505
1515
Crosstalk Allowance
Weakest Victim Launch Power
Allowed Side-Mode Power
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Number of
Aggressors
Conclusions
23
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Conclusion
• WDM-PON based on low-cost tunable lasers is becoming available
• It can support 10-Gb/s services today, and 28…100 Gb/s per channel in the future
• For long-reach (>20 km) access, WR-ODN has several advantages
• CapEx (no tunable filters, fewer RE)
• Reach (lower insertion loss of filters)
• Slightly better energy consumption (for the above reasons)
• Far better crosstalk immunity
(and therefore much less susceptible to broadband crosstalk attacks)
24
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Thank You
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