Characterization of Semiconductor Lasers for

Radiation Hard High Speed Transceivers

Sérgio Silva, Luís Amaral, Stephane Detraz, Paulo Moreira, Spyridon Papadopolos, Ioannis Papakonstantinou, Henrique Salgado, Christophe Sigaud, Csaba Soos, Pavel Stejskal, Jan

Troska, François VaseyTWEPP, 21-25 of September, 2009Abstract: In the context of the versatile link project, a set of semiconductor lasers were studied and modelled

aiming at the optimization of the laser driver circuit. High frequency measurements of the laser diode devices in terms of reflected and transmission characteristics were made and used to support the development of a model that can be applied to study their input impedance characteristics and light modulation properties. Furthermore the interaction between the laser driver, interconnect network and the laser device itself can be studied using this model. Simulation results and measured data show good agreement, therefore validating the laser model and methodology used. Radiation-hard optical link for the experiments system outline:

–Fast read-out capabilities.–Transmission of command instructions and synchronization signals. –Based essentially on COTS: qualify for rad-hard.

Interaction between LASER and driver should be characterized:–Electrical impedance mismatch should be kept < 10%–Design a matching network–Study peaking circuit / Pre-Emphasis–DC electrical interface (Bias-T): magnetic field insensible.

Bias T LD PD

+ -

VI

VR VR

VI P

LDD

Requirements of the LASER model:–Should give an accurate representation of the static behavior–Should represent the real device input impedance (within the bandwidth of interest)–Should mimic the dynamic performance of the real laserMeasurements lead to simplified laser model:–Chip & Package model–Intrinsic Laser Diode (ILD) model

IS(t)+IBias O(t)

Parameters

Laser Model

Current Optical Power

Extract Laser model from measurements:–L-I-V Curve extraction–S-Parameters measurements–Relative Intrinsic Noise measurements–Qualitative analysis with TDR

Bias-T

LD

E/O VNA

Current Source

OSA

E/E VNASpectrum Analyzer

Laser Model Parameter Extraction

Intrinsic Laser Diode Parameters

Extraction

Test Fixture De-embedding

Parasitic Circuit Parameters Extraction

Global Response Parameters Adjustment

S-Parameters

ILD Parameters

PC Parameters

Complete Model Parameters

S21(f, IBias)

S11(f, IBias)

S(f, IBias)

Open, Short & Load Test Fixture S-Parameters

RIN(f, IBias)

Source Chip & Package Intrinsic LaserTest Fixture

ILD

LP2 RP2 RS

Z0

L

CP2

CSUB

RSUB

Z0IS

LP1 RP1

CP1

Source Test Fixture Laser lead Wire bond Package and substrate

Intrinsic Laser Diode

ZIn

Parasitic Circuit Model Ideal Laser Model

ILD modelled using:– Differential equations

explicitly– Linear approximation

at bias point

Design of the SFP (transceiver) prototype:

Predict the performance of the system by using the laser driver, electric network simulation and laser

model

100 200 3000 400

-0.2

0.0

0.2

-0.4

0.4

Time (pS)

Optic

al Po

wer (

mW

)

Measured data vs. Model fit

0 1 2 3 4 5 6 7 8 9 10-45

-40

-35

-30

-25

-20

-15

-10

-5

0

5Measurement data & Complete Laser Model

Am

plitu

de (dB

)

Frequency (GHz)

Data I1Data I2Data I3Data I4Model I1Model I2Model I3Model I4

Good model fit:– Modelled transfer function follows closely the measurements– Clear dependence on bias– Bandwidth increases as bias increases

ILD Parameters

1 2 3 4 5 60

2

4

6

8x 10

-18

m3

1 2 3 4 5 61

2

3

4

5x 10

-12

m3 s-1

1 2 3 4 5 60

2

4

6

8x 10

-23

m3

1 2 3 4 5 60

1

2

3

4x 10

24

m-3

1 2 3 4 5 60

0.5

1

1.5

2x 10

-3

-

1 2 3 4 5 60

0.02

0.04

0.06

0.08

-

1 2 3 4 5 60.5

1

1.5

2

ps

1 2 3 4 5 60

2

4

6

ns

V g0

N0m

p

n

Good ILD model fit:– The FP laser (1) has the highest active

volume value – The VCSEL LW laser (2) has an active

volume that is larger than the SW lasers– The high BW (1, 2, 5 and 6) show

simultaneously low photon and carrier lifetimes.

Parameters obtained for a set of FP, SW VCSELs and LW VCSELs Lasers

LW F

P

LW V

E

SW

VE

SW V

E

SW V

E

SW V

E

LW F

P

LW V

E

SW

VE

SW V

E

SW V

E

SW V

E

Parasitic Circuit Parameters

1 2 3 4 5 60

50

100

Rs

1 2 3 4 5 60

0.2

0.4

0.6

0.8

pF

Cs

1 2 3 4 5 60

2

4

6

8

pF

Cp1

1 2 3 4 5 60

2

4

6

8

nH

Lp1

1 2 3 4 5 60

0.5

1

Rp1

1 2 3 4 5 60

1

2

3

pF

Cp2

1 2 3 4 5 61

2

3

4

5

Device

nH

Lp2

1 2 3 4 5 60

2

4

6

Device

Rp2

Good parasitic model fit:– Active area resistance higher for the

VCSELs – Active area resistance even higher for

the SW-VCSELs– Remaining parameters similar:

identical packages

Parameters obtained for a set of FP, SW VCSELs and LW VCSELs Lasers

LW F

P

LW V

E

SW

VE

SW V

E

SW V

E

SW V

E

LW F

P

LW V

E

SW

VE

SW V

E

SW V

E

SW V

E

IBias

Large Hadron Collider at CERN:– Largest particle accelerator for high-energy physics research.

– An upgrade of the current LHC (Super LHC), planned for 2013-18.

– A tracking detector operating at the Super LHC will require ten times more readout data bandwidth and radiation tolerance than at the current LHC detectors.

– Necessary to design a digital transceiver capable of operating at high speed (multiple GBits/s) in harsh environment:

–High radiation levels–High magnetic fields–Low temperatures

Conclusion: Using simple assumptions, a broadly applicable model was developed that can be used with many different types of semiconductor lasers. This model is modular in order to separate the analysis made for package parasitic from the laser parameters. Very good agreement between the model and the measurements was obtained, which is fundamental for a correct study of the design of a robust transceiver with demanding requirements.