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http://photonics.intec.UGent.bePhotonics Research Group

Silicon Photonics

Roel BaetsGhent University – IMEC

[email protected]

ESA February 9 2006

Photonics Research Group© intec 2005

AcknowledgementsThe Photonic Research Group at Ghent University – IMECThe European Union

IST-PICCO IST-PICMOSIST-ePIXnet

The European Space AgencyThe Belgian IAP-PHOTON networkThe Flemish Institute for the industrial advancement of Scientific and Technological Research (IWT)The Flemish Fund for Scientific Research (FWO-Vlaanderen)The Silicon Process division at IMECThe P-line at IMEC


Outline

Silicon Photonics: why and how?

Passive wavelength routers in Silicon

Active photonic functions in Silicon

Silicon photonics: what for?


Silicon Photonics: why and how?Why?• Functionality + performance• Technology• CostHow?• Wafer-level fabrication• Packaging


Silicon photonicsFunctionality and performance: spectacular breakthroughs in last 2 years• low loss waveguides (IMEC, NTT, IBM…)• compact wavelength routers (IMEC…)• ultra-compact microcavities (U. Kyoto…)• >>10 Gb/s receivers (LETI…)• 10 Gb/s modulators (INTEL, LUxtera…)• Raman Silicon laser (INTEL…)• (velocity tunable) slow light (IBM…)• all-optical switching + λ-conversion (NICT+IMEC…)• integration with CMOS (Luxtera…)


DARPA: EPICObjectives

Si nanophotonics with CMOS processesApplication-specific EPICNew photonic devices in Si (lasers, wavelength converters, amplifiers, ...)

PartnersMITLuxteraSunFreescale

Budget: 12M$ www.darpa.mil/mto/epic


Nanophotonic waveguidesSilicon on Insulator

Transparent at telecom wavelengths (1.55µm and 1.3µm)

High refractive index contrastin-plane: 3.45(Si) to 1.0 (air)out-of-plane: 3.45 (Si) to 1.45 (SiO2)

Typical dimensions:Thickness: 200 nm Width: 500 nmRequired accuracy: 1-10 nm

Compatible with CMOS processes

Si substrate

silica


SOI-nanophotonic wires

EBeamyes1110.0 600260Oct. 03ColumbiaEBeamyes119.0300300Oct. ‘04NEC

5.0 500200DUVyes115.0 300300Apr. '05LETI / LPMG-lineyes132.0 500200Dec. '01MITEBeamno1105.0 400320Dec. '02Yokohama

EBeamyes37.82.8

300400

300200

Feb. '05NTTEBeamno35.0 470270Aug. '03CornellEBeamno23.6 445220Apr. '04IBMDUVno12.4 500220Apr. '04IMECFab.

top clad

BOX [um]

loss [dB/cm]

w [nm]

h [nm]DateGroup


Waveguide bendsSpirals

Long waveguides (up to 50mm)

Many bends (up to 560)

(b)

Transmission [dB]600

500

400

300

200

100

00 20 40 60

Total length [mm]

# 90

°be

nds

-2

-4

-6

-8

-12

-10

-14

R = 5µm

Exc

ess

bend

loss

[dB

/90°

]

0.08

0.06

0.04

0.02

01 2 3 4 5

0.004dB/900.01dB/90°

0.027dB/90°

0.09dB/90°


Bends

4040

0.150.05

2.05.0

500220LETI/LPM

2 bends1.3resonant 400340Columbia

poly-Si0.3resonant 12 bends0.51.0 500200MIT

31.0 400320Yokohama0.173.0

24 bends0.462.0 300300NTT0.0045.0 0.0272.0

> 500 bends0.091.0 500220IMEC05.0

0.0132.0 20 bends0.0861.0 445220IBMNote

Loss [dB/90]

Radius [um]

w [nm]

h [nm]Group

(Table partly from Vlasov, McNab, Opt. Expr. ’04, pp1630)


Nano ?Feature size: a few 100nmRequired accuracy of features: < 10nmFor wavelength-dependent structures:

Fabrication ?Classical optical lithography too low resolutionE-beam lithography, focused ion beam too slowDeep UV lithography (used for CMOS)

248nm, 193nmFabrication in IMEC CMOS-pilot line 200mm wafers

nm-scale wavelength accuracy : O(1nm) dimensional accuracy !

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅

δλδλ

cladcorennf

dd~


Fabricated Structures


Low cost• Wafer-scale fabrication on large wafers with high yield• Wafer-scale testing• Low cost packaging


Coupling into SOI nanophotonics

Single-mode fiber

1µm

SOI wire

Important:Low loss

Large bandwidth

Coupling tolerance

FabricationLimited extra processingTolerant to fabrication

Polarization


Coupling to fiber – Inverse taper

0.4µm

80nm

0.2µm

200 µm

polished facet

< 2dB3x1.3Polymer175.0175.0 500200IMEC(DUV)3x3

?x?2x2

Cladding Size

0.8Polymer/Si3N460.0200.0 300300NTT (ebeam)

< 4dBSiO2100.040.0 470270Cornell (e-b)< 1dBPolymer75.0150.0 445220IBM (e-beam)

LossCladding Material

tip width [nm]

L [um]w [nm]

h [nm]

Group


Coupling to fiber – Grating couplerAlternative: Grating couplers

Waferscale testing

Waferscale low cost packaging

High alignment tolerance

deep trench

shallow fibre coupler

Towards optical circuit

Single modefiber core

From Fibre

-40

-35

-30

-25

-20

-15

-10

-51500 1520 1540 1560 1580 1600

Tran

smis

sion

[dB

]

Wavelength [nm]

∆λ1dB = 35nm

33% efficiencymeasured


Alignment tolerancesgood alignment tolerances

measurement of P/Pmax versus fiber position

Z

X

Taillaert et al, JQE 38(7), p. 949 (2002)


Coupling to fiber – Grating couplerImproved design

Apodise grating efficiency 63%

Add bottom reflector efficiency over 90%


Theoretical coupling efficiency 78%

Bonded SOI-coupler with gold bottom mirror

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

1500 1520 1540 1560 1580 1600

wavelength

coup

ling

effic

ienc

y

s1_golds2_no_golds1_gold_fits2_no_gold_fit

Si

Au

Measured coupling efficiency:69% (1.5 dB loss)

air

BCB-buffer

SiO2 box layer

Pyrex-substrate

BCB

Grating coupler

waveguide


Polarisation problemProblem: nanophotonic circuits are highly polarisation dependentOur solution:

2D grating

Couples each fiber polarisationin its own waveguide

In the waveguides the polarisation is the same (TE)

Allows for polarisationdiversity approach

Single modefiber core

Taillaert et al. PTL 15(9) p. 1249 (2003)


Polarisation Diversity Circuit

2-D grating

y-polarization

split polarisations

light in

identicalcircuits

x-polarization

x

yz

xy

light out

single-modefiber

2-D grating

combine polarisations


Polarisation Diversity Circuit

2-D grating

y-polarization

split polarisations

light in

identicalcircuits

x-polarization

x

yz

xy

light out

single-modefiber

2-D grating

combine polarisations

Results 2D-coupler:• 20 % efficiency • 1dB bandwidth ~ 35 nm• Extinction ratio > 18dB


Outline






WDM switched optical backplanerouting functionality (w/o switches): passive λ-based routing using tunable lasers

Switching speed determined by tuning speed and by burst-mode receivers

passive

WDM-router

2 single fibers or MT fiber ribbon

Tx/Rx..

.

...

.

.Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx

Tx/Rx


connectorchip

SOI wavelength router4 x 4 wavelength router

Commercial connector with8 fibers

Vertical fiber couplers

4 x 4 AWG

200 GHz channel spacing


SOI wavelength router

in

reference waveguides

4 x 4 wavelength routerFour input and four output fibers

250 GHz channel spacing

shallow star couplers, 3µm radius bends

3.5dB device insertion loss (waveguides and star coupler), -12 to -14 dB sidelobes

connectorchip


AWG16-channel AWG, 200GHz 200µm x 500µm area

-3dB insertion loss

-15dB to -20dB crosstalk

-40

-35

-30

-25

-20

-15

-10

-5

0

1520 1525 1530 1535 1540 1545 1550 1555 1560 1565 1570

wavelength [nm]

Tran

smis

sion

[dB

]

12345678910111213141516

100µm


Outline






Active photonic functionsThe options for modulation, switching, tuning at high speed:• all Silicon approach

carrier density based optical effects + electric field induced carrier sweep away

All-optical approach using two-photon absorption

• Silicon + III-V-membrane integrationUsing ultra-fast carrier lifetime in III-V

Also allowing light emission, gain, detection


Heterogeneous integrationSilicon waveguide structure

Passive only

Heterogeneous circuit

Active + passive

Silicon substrate

InP thin film

Polymer bonding layer (BCB)

2um

SiliconSilicon

InP

InP

InP

InP


Die-to-wafer bondingMolecular bonding

InP on SOI-waveguides on CMOS demonstrated (LETI, TRACIT)

Polymer bondingPlanarization and bonding in single step (IMEC)

Ultra-thin bonding layers (sub 200nm demonstrated)

InP-layer

Si-wire


Die to wafer bonding technology

Processed SOI substrate

InP/InGaAsPthin film

Good chemical resistance


InGaAs Detectors on SOI

Measured response of 4 detectors

To detectors


InP tunable ring resonators

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1530 1535 1540 1545 1550 1555 1560

Golflengte (nm)

Tra

nsm

issie

(a.u

.)


InP Fabry-Perot lasersGood functionality

Damp-heat testing as proof of reliability of the BCB bonding process

Component 11

0

0.02

0.04

0.06

0.08

0.1

0.12

0 100 200 300 400 500I [mA]

P [m

W]

ref48u100u250u500u

damp heat testing (85°C, 85% RH) for 48, 100, 250 and 500 hours


Electrically pumped InP microdisk laser


InP DFB laser diode coupled to SOI

Low k

BCB

SOI/CMOS wafergrat

ing

coup

ler


Outline







• WDM components • switches for high speed backplanes• single chip high speed low power transceivers• on-chip optical interconnect• sensors• labs on a chip

Siliconphotonics

With CMOS

With InP


Conclusion

Silicon photonics is a generic technologywith a wide range of

high volume applicationsfor which the

industrial technology baselargely exists

today.

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