20 and 26 Gbps uncooled 1310nm EMLs for 100 GbE applications Milind Gokhale
IEEE High Speed Study Group
January 2007, Monterey CA
2IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Overview• For 100 Gbps links up to 10km, two configurations using 1310nm
uncooled EMLs have previously been proposed:
– 5 x 20 Gb/s 1310nm, CWDM EML
– 4 x 25 Gb/s 1310nm, CWDM EML
• We report for the first time uncooled 1310nm EMLs operating at both 20 and 26 Gbps
• 20+ Gb/s uncooled EMLs are extensions to existing 10 Gbps design currently used in 10G-SONET (SR-1) and 10 GbE links
• Data indicates bandwidth > 20GHz, independent of temperature. Large signal uncooled operation up to 30Gb/s and transmission through 10km of fiber is also demonstrated.
• Merits for selecting 4 X 25 Gbps 1310nm based Tx are discussed
3IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Uncooled EML Design
Detuning (∆λ) between laser and modulator is a function of temperature
– change in detuning changes extinction ratio (ER) of the modulator
– smaller ER at low temp & lower power at high temperature
0 1 2 3 4 5 6 7 8
0.0
0.2
0.4
0.6
0.8
1.0 10oC 25oC 50oC 75oC 85oC
Nor
mal
ized
tran
smis
sion
, a.u
.
Voltage across modulator, V
Typical extinction curves vs. temperature– constant modulator drive (VP-P) used
– modulator DC bias is a linear function of temperature
Wav
elen
gth,
nm
Temperature, OC
Laser g
ain peak
Mod. absorptio
n peakLaser l (grating)
∆λ0.5
nm/O C
0.1nm/OC
Wav
elen
gth,
nm
Temperature, OC
Laser g
ain peak
Mod. absorptio
n peakLaser l (grating)
∆λ0.5
nm/O C
0.1nm/OC
Wav
elen
gth,
nm
Temperature, OC
Laser g
ain peak
Mod. absorptio
n peakLaser l (grating)
∆λ0.5
nm/O C
0.1nm/OC
4IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
LASER
MODULATOR
LASER
MODULATOR
20+G EML builds on existing 10G technology• 10G 1310nm uncooled EML based TOSAs have been available for 10GbE (LR)
and SONET(SR-1) links
• Predominant design is based on asymmetric twinguide (ATG) technology
• 10G uncooled EMLs at 1310nm and 1550nm have been demonstrated using alternate EML technologies
90oC, -1.8 dBm 8 dB ER, 21% MM
-20oC, -1.4 dBm7dB ER, 20% MM
Eyes for 10G EML in TO-can TOSA
Reference: paper PD-42, OFC March 2003
ATG based EML chip schematic
5IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Uncooled EML: Small-signal bandwidth
• 3dB bandwidth is ~22GHz, independent of temperature• Measurement for chip on submount from 5C to 85C
0 5 10 15 20 25-12
-9
-6
-3
0
3
6
Temperature 5C 25C 50C 70C 85C
S21
opt
ical
ban
dwid
th, d
B
Frequency, GHz
6IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Setup for 20+ Gbps testing
• Packaged 20+ Gbps EML chip used for demonstrating uncooledoperation
– Standard 7-pin, 10G package with GPO connector rated to ~26GHz
– Temperature (0 to 85 OC) refers to thermistor on EML submount
– 40G EA driver with ~ 3 Vpp electrical drive
• 10 Gbps, 231-1 PRBS streams electrically multiplexed to generate 20 to 30 Gbps PRBS data
• Optical eyes measured using Agilent 86109A plug-in with 30GHz optical module
7IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Electrical eyes with 40G driver
• 20G and 25 Gbps electrical eyes shown on same time scale
• Data measured with driver after mux with long cable to DCA
• DCA does not have precision time base module
20 Gbps 25 Gbps
~ 3Vpp
8IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
20 Gbps optical eyes (0 km) vs. temperature
0 oC 10 oC 30 oC
50 oC 75 oC 85 oC
• Eyes measured with 30GHz 86109A Agilent plugin
9IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
26 Gbps optical eyes (0 km) vs. temperature
0 oC 10 oC 30 oC
50 oC 75 oC 85 oC
• Eyes measured with 30GHz 86109A Agilent plugin
10IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
30 Gbps optical eyes (0 km) vs. temperature
0 oC 10 oC 30 oC
50 oC 75 oC 85 oC
• Eyes measured with 30GHz 86109A Agilent plugin
11IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Extinction ratio versus bit-rate
Unfiltered ER measured with 30GHz Agilent 86109A plug-in
ER increases with temperature at ~0.45 dB/oC from 0 to 85oC
– Constant drive voltage ~3Vpp
– Lower drive voltage at higher temperature eases requirements for driver IC
– ER for 20G and 26G almost identical
– ER drops significantly for 40G; ER > 7dB demonstrated over temperature
-10 0 10 20 30 40 50 60 70 80 90 10056789
101112131415
Extin
ctio
n ra
tio, d
B
Temperature, OC
20 Gbps 26 Gbps 30 Gbps 40 Gbps
12IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
20Gbps transmission through 10km fiberOptical eye: 10 kmOptical eye: 0 km
1310nm wavelength and EML Tx yields negligible dispersion penalty over 10km
ER = 9.8 dB ; Pave = -1dBm
ER = 11.9 dB; Pave = 0.3dBm
ER = 12.9 dB; Pave = -1.3dBm
ER = 9.1 dB
0 OC
50 OC
85 OC
ER = 11.5 dB
ER = 12.2 dB
ER = 9.8 dB ; Pave = -1dBmER = 9.8 dB ; Pave = -1dBm
ER = 11.9 dB; Pave = 0.3dBmER = 11.9 dB; Pave = 0.3dBm
ER = 12.9 dB; Pave = -1.3dBm
ER = 9.1 dB
0 OC
50 OC
85 OC
ER = 11.5 dB
ER = 12.2 dB
13IEEE HSSG : 20-26 Gbps uncooled 1310nm EML for 100GbE applicationsJan. 2007, Monterey CA
Conclusion and recommendations• Technical feasibility demonstrated for higher speed, single channel,
uncooled 1310nm EMLs operating up to 30 Gbps
– CWDM versions on 20 or 25nm spacing feasible
• Uncooled 4 x 25 Gbps CDWM configuration recommended– 1310 EML performance suggests no clear preference for 20G over 25G
– For discrete transmitters, “4 X” will be cheaper than “5 X”
– Uncooled TO-can style TOSA package is feasible
– “4 X” (LX4 type) optical mux widely available
– Assumes that “gear-box” IC is largely agnostic of channel count
– 25 Gbps driver ICs with < 3 Vpp possible using SiGe/GaAs/InP
• Next steps– Link budget and receiver configuration will set transmitter power
requirement