20 and 26 Gbps uncooled 1310nm EMLs for 100GbE...

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


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


∆λ0.5

nm/O C

0.1nm/OC

Wav

elen

gth,

nm

Temperature, OC

Laser g

ain peak

Mod. absorptio


∆λ0.5

nm/O C

0.1nm/OC


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


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


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


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


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



0 oC 10 oC 30 oC

50 oC 75 oC 85 oC



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


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


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

20 and 26 Gbps uncooled 1310nm EMLs for 100GbE...

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