optoelectronic packaging optical backplane buschen-server.mer.utexas.edu › 2008 ›...

OptoelectronicOptoelectronicOptoelectronic

Optoelectronic

PackagingPackagingPackaging

Packaging

forforfor

for

16-Channel16-Channel16-Channel

16-Channel

OpticalOpticalOptical

Optical

BackplaneBackplaneBackplane

Backplane

BusBusBus

Bus

usingusingusing

using

VolumeVolumeVolume

Volume

HologramHologramHologram

Hologram


Optical

ElementsElementsElements

Elements

forforfor

for

HighHighHigh

High

PerformancePerformancePerformance

Performance

ComputingComputingComputing

Computing

Hai Bi, Jinho Choi, J. Ellis and R. T. Chen*

University of Texas at AustinMicroelectronic Research Center

10100 Burnet Road, Austin, Texas 78758Email: [email protected]

AbstractAbstractAbstract

Abstract

Optical backplane bus not only can fulfill the ever increasing bandwidth demands in high performance computingbut also allows the sharing of transmission medium to reduce wiring congestions. A 3-slot optical backplane busdemonstrator using photopolymer volume gratings array (PVGA) on top surface of glass substrate to fan-out lightbeam is designed to allow 16 channels of data to be exchanged between daughter slots and central slot. Alignmenttolerance of the optical interconnect system is investigated theoretically and experimentally. By analyzing thediffractive characteristics, the 3dB bandwidth limit of the optical layer is determined to be more than 36nm. Bycarefully aligning the fabrication system, the incident angle deviation from Bragg condition is reduced to below 0.1,much less than the 0.7 angular tolerance. The variation of the hologram efficiency is below 3dB by optimizing therecording beams.

In the optical sub-system, VCSELs and photodetectors packaged in the form of TO-46 can are assembled on top ofeach PVG and interleaved to reduce the crosstalk to below noise level. Three computer mother boards using FPGAare made to verify the data transmission among the slots. Interface boards between the FPGA boards and opticaltransceivers are designed and fabricated to separate the implementation of digital layer and optical layer. Above4.8Gbps aggregated data transmission is successfully demonstrated using the multi-channel system. Single channeltransmissions at 10Gbps data rate is also tested with above 100uW input power, showing the potential to improvethe total two-way bandwidth to above 102.4Gbps

Keywords: optical bus, optical interconnect, alignment tolerance, multi-channel, volume grating array

I.I.I.

I.

III

I

NTRODUCTIONNTRODUCTIONNTRODUCTION

NTRODUCTION

With the advent and popularity of multi-coreand 64bit processors in High Performance Computing(HPC) systems, the demand on transferring data

mailto:[email protected]

among multiple processing units inside a box isincreasing rapidly [1]. The electrical backplaneinterconnects in the HPCs have abandoned busarchitecture to overcome bandwidth limit of electricalbus and adopted point-to-point architecture which inturn causes wiring congestion crises and thedifficulties to seat daughter boards onto backplane [2].It was pointed out that optical interconnects possesspotential advantage to avoid wiring congestion byusing high speed bus to allow multiple boards to sharetransmission channels [3].

Based on the centralized architecture usingvolume polymer gratings with equalized fan-outpower among boards, single channel memory to CPUinterconnect [4] and interleaved optical interconnectwith 15Gbps data rate [3] were demonstrated.Because of the 2D nature of the hologram film, theoptical interconnect is anticipated to achieve Terahertzbandwidth inside an enclosure if multi-channel systemcan be built. Analysis of alignment tolerance is criticalfor optical system packaging and needs investigation.

In our work, the fully packaged optical sub-system was equipped with 48 Photopolymer VolumeGratings Array (PVGA) for each board, allowing us toinvestigate critical packaging issues such as angularmisalignment tolerance and uniformity of gratingsdiffraction among channels. In the system diagramshown in Figure 1, the optical domain includes a glasssubstrate with volume hologram grating arrays on thesurface and optoelectronics components. In thecentralized architecture, the receivers on the centraldistributor board collect the signal from any daughterslot, and then deliver the information to the upperlayer FPGA board for rebroadcast to daughter boards[4].

Layered design technology was used toseparate the electronic domain with optical domain toreduce design difficulty. However, in the future, itwill be preferred that lasers or modulators and driverscan be integrated into CMOS circuit orCMOS/BiCMOS circuits to improve the packingdensity. At current stage, individual O/E componentsare used to demonstrate the feasibility of the opticalbus interconnect.

The demonstrated computer server systemhas three optoelectronically interconnected boards,each incorporated a FPGA with PowerPC core forsupporting 32 channels of bit oriented data streams,16 inbound and 16 outbound.

Converter

FPGABoards

x

y

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agram

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In Section II, the alignment tolerance will beanalyzed for packaging purpose, and in Section III,the fabrication process will be illustrated. Section IVconcludes the paper with performance data.

II.II.II.

II.

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OLERANCE

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NALYSISNALYSISNALYSIS

NALYSIS

A.A.A.

A.


Optical

LayerLayerLayer

Layer

ConfigurationConfigurationConfiguration

Configuration

Figure 1 illustrates that hologram film at thetop surface of glass substrate works as the optical fan-in/fan-out devices so that the light signal from oneboard could be delivered to other boards. When thediffractive angle of the light is greater than 42, whichis the critical angle of the glass-air interface for TotalInternal Reflection (TIR).

For an optical backplane bus system, themost important factors that ensure the high speed datadelivery are the received optical power and noise.Therefore, the fundamental theory of the diffractiveoptics needs to be investigated first to ensure uniformand sufficient power delivery and low crosstalk. TheKogelnik’s theory [5], is widely used because itallows analytical form of solution to be obtained.

For each of the 3 boards in the opticalbackplane bus shown in Fig. 1, there is a 20m thickDuPont photopolymer (HRF-600X100-20) hologramfilm covering an area of 3cm5cm between theelectro-optical (EO) converter modules and thewaveguiding glass substrate. Because of thecentralized architecture, the central board requires adoubly multiplexed hologram [4].

The 48 individually packaged transceiverswith 4.7mm diameter were packaged in a holdingplate with 5.5mm channel pitch allocated for eachcomputer board, to facilitate the analysis of the fan-out power uniformity among multiple channels. Thethickness of the waveguiding glass substrate d is1.5cm, which gives a reasonable slot separation of 2dwhen the diffraction angle within the substrate isexactly 45.

There are 4 pairs of transceivers on each ofthe EO converter modules and all driver ICs useCurrent Mode Logic (CML) for interfacing withupper layer controller board through an electricalsignal connector (Molex 75586-0009) with 8 pairs ofdifferential I/O signal pins. The purpose of usingelectrical cable at current stage is to simplify thedesign of optical and electrical domain. The threeupper layer controller boards provided by AdvancedCommunication Concepts, Inc., use Xilinx FPGAchips to verify the integrity of data transmissionthrough PVGA.

B.B.B.

B.

AngularAngularAngular

Angular

BandwidthBandwidthBandwidth

Bandwidth

AnalysisAnalysisAnalysis

Analysis

usingusingusing

using

KogelnikKogelnikKogelnik

Kogelnik

’’’

’

sss

s

TheoryTheoryTheory

Theory

According to Kogilnik’s theory [5], thediffraction efficiency and diffractive angle can becalculated using formula (1) and the diffractionefficiency gets maximum value according to formula(2) at condition (3).

(1)

2

2

222

1

sin

(2)

SRccdn

122 sin)(sin

KKK

K

=2

cos(-) (3)

Approximately, the 3dB angular bandwidthis proportional to the design wavelength but inverseproportional to the thickness of hologram as shown in(4).

(4) ss

dB cKd

cd

2sin

23

However, the desired diffractive efficiencywill be always 100% to ensure good signal to noiseratio, so that the thickness of grating for longer

wavelength may be reduced instead of indexmodulation depth. This results in a wider acceptanceangle for longer operation wavelength. A 1550nmgrating with n1=0.017 and d=20m gives an angularbandwidth of 2.7 instead of 1.4 for 850nm. Asshown in Figure 2, if the thickness for 1550nmoperation is increased proportionally to thewavelength, the curve of the 3dB versus maximumefficiency overlaps with that for 850nm. Thisanalysis shows that: only if thickness of grating canbe reduced using higher index modulation depth, willthe tolerance be greatly improved.

C.C.C.

C.

WavelengthWavelengthWavelength

Wavelength


Bandwidth


Analysis

usingusingusing

using

KogelnikKogelnikKogelnik

Kogelnik

’’’

’

sss

s

TheoryTheoryTheory

Theory

Operating wavelength varies for individuallasers and a screening is necessary. For 0=850nm,=0 and =67.5, the product of n1 and d equal to0.3574m will ensure 100% maximum efficiency tobe obtained. Analysis shows that for wavelengthgreater than 850nm, the diffractive efficiency dropsbut the wavelength bandwidth increases, as shown inFigure 5.

0 0.2 0.4 0.6 0.8 12

2.5

3

3.5

4

4.5

max

3dB

1 = 850nm d=20.0m2 =1550nm d=20.0m3 =1550nm d=36.5m

-3dB versus max

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3dB

angularangularangular

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bandwidthbandwidthbandwidth

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versus

desireddesireddesired

desired

maximummaximummaximum

maximum

diffractivediffractivediffractive

diffractive

efficiencyefficiencyefficiency

efficiency

0 200 400 600 800 1000 12000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

wavelength deviation (nm)

Diffraction Efficiency

Designed for =850nmDesigned for =980nm

Designed for =1550nmDesigned for =1850nm

Formula (5) shows that the 3dB wavelengthbandwidth is also inverse proportional to thethickness of the grating, but proportional to thesquare of wavelength through variable K. The opticalbandwidths of the holograms are drawn in Figure 4showing different bandwidth and maximumdiffractive efficiency at different operationwavelengths.

(5)ss

dB ncdK

cd

82

2

2/3

0 0.2 0.4 0.6 0.8 120

40

60

80

100

120

140

maximum efficiency

3dB

Variation of -3dB for different maximum diffraction efficiency

1 = 850nm d=20.0m

2 =1550nm d=20.0m3 =1550nm d=36.5m

D.D.D.

D.

SystemSystemSystem

System

AlignmentAlignmentAlignment

Alignment

ToleranceToleranceTolerance

Tolerance

Figure 5 shows the transmission through a pairof 20m thick hologram gratings for 850nmwavelength vicinity. One step of the calculation is topre-calculate the incident angle for the fan-outcoupling because the wavelength deviation causesdiffractive angle to change according to formula (6).

(6) sin'sin''sin 13 nn

-40 -20 0 20 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

(nm)(nm)(nm)

(nm)


45 SIM 0 SIMPair SIM

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ure

555

5

DiffractionDiffractionDiffraction

Diffraction


efficiency

versusversusversus

versus

wavelengthwavelengthwavelength

wavelength

forforfor

for

TETETE

TE

mode:mode:mode:

mode:

dotteddotteddotted

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and

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for

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beambeambeam

beam

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go

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through

aaa

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pairpairpair

pair

ofofof

of

hologramhologramhologram

hologram

gratinggratinggrating

grating

The wavelength bandwidth is calculated tobe 36nm for TE mode coupling through a pair ofhologram film with mirrored fringe patters illustratedin Figure 2 for 850nm operation. The 3-dB fan-inbandwidth for 0 incident angle is around 45nm, andthe bandwidth for 45 fan-out process is around62nm.

Figure 6 shows that for an input beam with0 incident angle but a wavelength other than the850nm design wavelength, the diffractive angle willbe different with 45.

FigureFigureFigure

Figure

333

3

WavelengthWavelengthWavelength

Wavelength


Bandwidth

increasesincreasesincreases

increases

withwithwith

with

operatingoperatingoperating

operating


wavelength

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for

hologramhologramhologram

hologram


grating

withwithwith

with

202020

20

mmm

m

thicknessthicknessthickness

thickness

FigureFigureFigure

Figure

444

4

RelationRelationRelation

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ofofof

of

maxmaxmax

max

andandand

and

3dB3dB3dB

3dB

(nm)(nm)(nm)

(nm)

withwithwith

with

firstfirstfirst

first

orderorderorder

order

approximationapproximationapproximation

approximation

:::

:

onlyonlyonly

only

dependsdependsdepends

depends

ononon

on

thethethe

the

ratioratioratio

ratio

ofofof

of


wavelength

squaredsquaredsquared

squared

tototo

to


grating

thicknessthicknessthickness

thickness

Wavelength deviation (nm)

-40 -30 -20 -10 0 10 20 30 40-50

-40

-30

-20

-10

0

10diffr active angle

nm

FigureFigureFigure

Figure

666

6

DDD

D

iffractiveiffractiveiffractive

iffractive

angleangleangle

angle

versusversusversus

versus


wavelength

deviationdeviationdeviation

deviation

forforfor

for

TETETE

TE

mode:mode:mode:

mode:

dotteddotteddotted

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linelineline

line

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aaa

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scenarioscenarioscenario

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incident

angleangleangle

angle

andandand

and

dasheddasheddashed

dashed

linelineline

line

forforfor

for

454545

45


incident

angle.angle.angle.

angle.

Semiconductor laser for communicationpurpose usually has an output window size of 10mto 20m, which gives a divergence angle of around17. This is well beyond the angular tolerance rangeof the hologram film. Therefore, a collimation systemhas to be utilized to reduce the divergence angle. Fordemonstration purposes, commercially availablecollimators with fiber connectors to interface withconnectorized transceivers and transceivers packagedwith dome lenses were used in the system. The firstapproach is more expensive, but gives freedom to thechoice of transceivers; the second approach ischeaper, but not all kind of transceivers are availablewith dome lens. The divergence angle for collimatoroutput beam is about 0.5 for multimode fiber, and0.2 for single mode fiber, while the divergence anglefor dome lens is about 2. Larger divergence anglewill cause extra lost because the hologram gratinggives less efficiency for large incident angle, butmakes the alignment easier also because of the largerdivergence. In general, it is desirable to have athinner hologram film because angular bandwidth isinverse proportional to the grating thickness.

Experimental result shows that the detectororientation determines the detected power becausethe high speed detector area is very small. It can beshown from Figure 7 that if the incident angle isgreater than 1.4 so that the tangent of the incidentangle is greater than 100m divided by focal length,4mm, the focused light spot will be outside thedetector active region with 100m diameter.

100m

Focalplane

f

Incidentangle

FigureFigureFigure

Figure

777

7

IllustrationIllustrationIllustration

Illustration

ofofof

of

detectordetectordetector

detector

misalignmentmisalignmentmisalignment

misalignment

E.E.E.

E.

PolarizationPolarizationPolarization

Polarization

andandand

and

angularangularangular

angular

bandwidthbandwidthbandwidth

bandwidth

The fan-in diffraction efficiency versusincident angle is plot in Figure 8 to show the angulardependency of TE and TM mode. From thecalculation, the maximum efficiency of TM mode isonly 82% while it is 100% for TE mode with sameindex modulation depth. However, it can be seenfrom the normalized TM efficiency curve that theTM mode diffractive efficiency is almostproportional to that of TE mode for different incidentangle. According to this result, instead of using bothTE and TM formulas, we use TE mode only in allcalculations and it is accurate enough for angularbandwidth. However, the fan-in and fan-outefficiency will not reach 100% if the laser light hasboth TE and TM mode. In the worst case, the laseroutput consists equal amount of TE and TM power,the final throughput efficiency will be (100% 100%+ 82% 82%) / (100%+100%) = 83%. Figure 9 alsoshows that the fan-in angular bandwidth of 0incident angle is around 2 and it’s 2.8 for fan-out,both in the film. The throughput angular bandwidth is1.4 in the hologram and glass medium and it isequivalent to 2 in the air.

F.F.F.

F.

DispersionDispersionDispersion

Dispersion


Analysis

The calculated 36nm bandwidth of thehologram grating is equivalent to around 15THzwhen using WDM according to df=fd/. However,if a single laser is modulated, the bandwidth will eexpanded and therefore the light will encounterdiffractive efficiency loss and also the diffractionangle change. It can be calculated that the bandwidthdispersion for single channel laser pulse is about2.5THz, same as that experimentally verified in [6].

(nm)Diffractive angle ()

-4 -2 0 2 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

(((

(

)))

)


45 SIM TE 0 SIM TE 0 SIM TMPair SIM TE

FigFigFig

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ure

888

8

DiffractionDiffractionDiffraction

Diffraction


efficiency

versusversusversus

versus

inputinputinput

input

angleangleangle

angle

forforfor

for

TETETE

TE

andandand

and

TMTMTM

TM

mode:mode:mode:

mode:

thethethe

the

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solid

linelineline

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showsshowsshows

shows

TMTMTM

TM

modemodemode

mode

whichwhichwhich

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almostalmostalmost

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proportional

tototo

to

TETETE

TE

modemodemode

mode

ininin

in

dotteddotteddotted

dotted

line.line.line.

line.

TTT

T

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dasheddasheddashed

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the

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versusversusversus

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angleangleangle

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BRICATIONBRICATIONBRICATION

BRICATION

It is necessary to test the uniformity of thelarge area film for multi-channel alignment. The filmdivergence angle of recording beam is measured tobe less than 0.05 and power density profile has a2.5cm 3dB radius. A glass substrate with aparallelism of less than 0.1 shown in Figure 9 wasselected to minimize accumulated incident angleerrors for the daughter boards.

FigureFigureFigure

Figure

999

9

HologramHologramHologram

Hologram

filmsfilmsfilms

films

ononon

on

thethethe

the

substratesubstratesubstrate

substrate

After exposure under the 532nm laser beams forabout 1 minute, the index modulation reached to the

desired value. A comparison of the normalizeddiffraction efficiency of the hologram fromtheoretical calculation and from experimentalmeasurement is shown in Figure 10. The 4 angularrange between the first two minimums in oursimulation for a 20m thick hologram agreesreasonably well with the experimental measurement.

-4 -2 0 2 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

(

)


45 SIM 45 EXP 0 SIM 0 EXPPair SIMPair EXP

FigureFigureFigure

Figure

101010

10

CalculatedCalculatedCalculated

Calculated

andandand

and

measuredmeasuredmeasured

measured

diffractiondiffractiondiffraction

diffraction


efficiency

[7][7][7]

[7]

For an optical beam to be fanned in orfanned out by a PVG with maximum efficiency, theincident angle has to satisfy the Bragg condition, andwe call it Bragg incident angle. The fan-out hologramshould have a mirrored fringe pattern in reference tothe fan-in hologram. It is a must due to the need tobroadcast data to two opposite directions.

The fabrication system was aligned so thatthe Bragg incident angle was maintained below 0.1.The deviation of the Bragg condition of the incidentangle along the x direction in a range of 2.5cm wasalso measured, as shown in Figure 11. By moving therecording stage, the probing beam can incident fromdifferent spot on the film and therefore, thediffraction efficiency on different spots can bemonitored by detecting the power of diffracted light.The fact that measured -0 curves almost overlapimplies that the recording beams were wellcollimated and the exposure was reasonably uniformall over the 3cm5cm area.

Daughter slots

Distributor slot

3cm

5cm


0

0.2

0.4

0.6

0.8

1

-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Incident Angle (degree)Incident Angle (degree)Incident Angle (degree)

Incident Angle (degree)

30mm 35mm40mm 25mm20mm 15mm

FigureFigureFigure

Figure

111

1

111

1

MeasurementMeasurementMeasurement

Measurement

ofofof

of


incident

angleangleangle

angle


deviation

alongalongalong

along

horizontalhorizontalhorizontal

horizontal

directiondirectiondirection

direction

IV.IV.IV.

IV.

SystemSystemSystem

System


Packaging

A.A.A.

A.

MechanicalMechanicalMechanical

Mechanical


Packaging

FigureFigureFigure

Figure

111

1

222

2

PhotographsPhotographsPhotographs

Photographs

ofofof

of

thethethe

the

fabricatedfabricatedfabricated

fabricated

metalmetalmetal

metal

casecasecase

case

forforfor

for

thethethe

the

opticalopticaloptical

optical

backplanbackplanbackplan

backplan

A metal holding case shown in Figure 12 isfabricated for housing the glass substrate. The glasssubstrate and the metal plates are fixed related to theholding case. All together, there are 48 VCSELsselected with wavelength within 838 to 842nm rangeto be packaged into the system, because the grating isrecorded using 840nm probing beam. The photo ofthe system with only the central slot packaged isshown in Figure 13 to show the 16-channe fan-outspots. Four circuit boards are controlling the VCSELswith equalized DC current emit equalized power, andthen the power delivered to each channel is recorded.The measured result shows that there is around 3dBvariation. The variation can be caused by variationsof: hologram efficiency, VCSEL power-currentcharacteristics, VCSEL wavelength, and VCSEL anddetector orientation. However, 3dB is a very good

result according to future analysis of the bandwidthperformance of a real system.

FigureFigureFigure

Figure

111

1

333

3

PhotoPhotoPhoto

Photo

ofofof

of

thethethe

the

fan-outfan-outfan-out

fan-out

beambeambeam

beam

spotspotspot

spot

ofofof

of

thethethe

the

16-channel16-channel16-channel

16-channel

systemsystemsystem

system

FigureFigureFigure

Figure

111

1

444

4

PackagedPackagedPackaged

Packaged


Optical

Sub-SystemSub-SystemSub-System

Sub-System

B.B.B.

B.

SystemSystemSystem

System

PerformancePerformancePerformance

Performance

The fan-out power variance was measuredto be less than 3dB. The variance was due to factorsincluding VCSEL power, driver output current, andhologram efficiency distribution. The sub-system wasthen fully packaged as shown in Figure 14 and Figure15.

The system was tested using FPGA chipsworking at 150MHz with all 32 channels sendingpackets. There is no error observed but some lost ofpackets. However, this could be due to the 8B10Bencoding because even using electrical cable, samephenomena was observed.

Using a single 10Gbps VCSEL from AOCwith collimators, about -10dBm optical power wasdelivered to both daughter boards and 10-12 bit errorrate was estimated for 10Gbps transmission.Therefore the limit of the optical backplane bussystem is also caused by the packing density ofelectronic and optoelectronic devices, not only thealignment.

FigureFigureFigure

Figure

111

1

555

5

PackagedPackagedPackaged

Packaged

ComputerComputerComputer

Computer

SystemSystemSystem

System

usingusingusing

using

16-16-16-

16-

ChannelChannelChannel

Channel


Optical

BackplaneBackplaneBackplane

Backplane

BusBusBus

Bus

AcknowledgmentAcknowledgmentAcknowledgment

Acknowledgment

This work was sponsored by AdvancedCommunications Concepts and National SecurityAgency.

ReferencesReferencesReferences

References

[1] Ray T. Chen, L.L., Chulchae Choi, Yujie J. Liu, BipinBihari,L. Wu, Suning Tang, R. Wickman, B. Picor, M. K.Hibbs-Brenner, J. Bristow, And Y. S. Liu, Fully embeddedboard level guided-wave optoelctronic interconnects. InvitedPaper, Proceedings Of IEEE. vol.88: p. pp.780-793.

[2] Dawei Huang, T.S., Anders Landin, Rick Lytel, and HowardL. Davidson, Optical interconnects: out of the box forever?IEEE Journal of Selected Topics in Quantum Electronics. vol.9( No. 2): p. pp.614.

[3] Hai Bi, X.H., Xiaonan Chen, Jinho Choi, Wei Jiang and RayT. Chen, "15Gbps Bit-Interleaved Optical Backplane Bususing Volume Photo-polymer Holograms". IEEE PhotonicsTechnology Letters, Oct 2006. vol. 18(no. 21).

[4] Xuliang Han, G.K., G. Jack Lipovski, and Ray T. Chen, AnOptical Centralized Shared-Bus Architecture Demonstratorfor Microprocessor-to-Memory Interconnects. IEEEJOURNAL OF SELECTED TOPICS IN QUANTUMELECTRONICS, March/April 2003. 9(2).

[5] Kogelnik, H., "Coupled wave theory for thick hologramgratings,". The Bell System Technical Journal, November1969. vol. 48( no. 9): p. pp. 2909-2947.

[6] Gicherl Kim, R.T.C., "Three-dimensionally interconnectedbidirectional optical backplane," IEEE Photonics TechnologyLetters, July 1999. vol. 11(no. 7): p. pp. 880-882.

[7] Hai Bi, J.C., Wei Jiang, Xuliang Han, Jonathan Ellis and RayT. Chen, 3.2Gbps multi-channel optical backplane busdemonstrator using photopolymer volume gratings. Proc.SPIE 6478-11, Jan 2007.

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