1

Recent Advances in Polymer and Silicon Nanophotonics

Presented at

OFC 2008

Presented by

Nanophotonics

Ray ChenNanophotonics and Optical Interconnect Research LabDepartment of Electrical and Computer Engineering

The University of Texas at Austin

Outlines

1.Introduction2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid ApproachesApproaches5.Further Applications6.Conclusion

OMJ4.pdf   

OFC/NFOEC 2008

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Competing Materials for Integrated Photonics

Feature\Material Polymer III-V Compound LiNbO3 Si/SOILoss at 1.55 μm 0.1dB/cm ~0.5dB/cm 0.1dB/cm 0.1-1dB/cm

EO Effect Better medium Good Almost NoneVolume Hologram

& Moldability Yes No No NoInterconnect Size unlimited ~6 inches ~6 inches 12 inches

Substrate Any III-V Compound LiNbO3Silicon

Δn/ΔT Large Small Small SmallAmplifier Yes Yes Yes Yes

Tg for Si CMOS ? good good goodReliability ? Highest High Medium

Cost Lowest Highest High Medium

Pros and Cons of Silicon Material

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Outlines

1.Introduction2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid ApproachesApproaches5.Further Applications6.Conclusion

Progress of Silicon Nanophotonics

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Gigahertz p-i-n Diode Embedded Silicon Photonic Crystal Mach Zehnder Interferometer (MZI) Modulator

electrodes

PCWModulationDepth 92%

Optical PerformanceKey features• Slow light in Photonic Crystal Waveguide (PCW) to enhance modulation by up to 40X•Unique electrode routing for on-

PCW line defect

Simulation

slow vg

I-V curve of photonic crystal p-i-n diode

Electrical Characterization

Unique electrode routing for onchip integration with driver•Faster speed due to the enhancement of injection current density by downscaling the device size

PCW

* Dark region: electrode/pad

80 μmNP

Electrodes

Modulation trace(1GHz, square wave)

Current injection

Electrode

P+

Anode+ -

Cathode

N+Intrinsic region

--Lanlan Gu, W. Jiang, X. Chen, L. Wang, and R. T. Chen “High speed silicon photonic crystal waveguide modulator for low voltage application,” Applied Physics Letters, 90, 071105 (2007).

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Ultra-compact , Fast Thermo-optic Silicon Photonic Crystal Mach Zehnder Interferometer (MZI) Modulator

Micro-heater

Oxide buffer layer

PCWSi core

Micro-heater

Si core layer

PCW

Conventional Structure Our Structure

Buried oxide

Si substrate

layer Buried oxide

Si substrate

Switching response time: ~100 μs Switching response time: < 20 μs

PCW80 μm

Micro-heater

Optical Performance

Key features•10~100X smaller due to slow light• novel thermal design for faster TO switching speed (<20 μm)

Micro-heater

Rise time (10% - 90%):~19μs Fall time (90%-10%): ~11μs

λ = 1548 nm, Pπ = 78 mW, Modulation depth = 84%Lanlan Gu, W. Jiang, X. Chen, R. T. Chen, “Photonic Crystal Waveguide Based Silicon-on-Insulator Thermo-optic Mach Zehnder Interferometers”, IEEE Photonics Technology Letters, 19, 342-344 (2007).

Horizontal-capacitor-based SiliconPhotonic Crystal MZI Modulator

Electrical structure

Frequency bandwidth RC constant Vπ Length Group

index Coupling loss

F dPIN1 1 5GH 600 2V 80 100 <1dB

Comparisons of existing EO structures:

ForwardPIN1 1.5GHz 600ps 2V 80μm 100 <1dB

Reverse PN 50GHz 14.7ps 10V 300μm 100 <1dB

MOS CAP2 50GHz 12.2ps 2.5V 300μm 100 1dB

Device configuration:

Horizontal capacitor

Mode profile mismatch

)

Slot PCWMode profile mismatch

)

Slot PCWMajor Challenge:

Coupling issueHorizontal capacitor

oxide

(c)substrate

n-Si thin oxide (spin-on-glass)

oxide

(c)substrate

n-Si thin oxide (spin-on-glass)

?

Slot PCW

Strip waveguide

X (µm)

Y(µ

m)

X (µm)

Y(µ

m)

Strip waveguide

x

z

y

?

Slot PCW

Strip waveguide

X (µm)

Y(µ

m)

X (µm)

Y(µ

m)

Strip waveguide

x

z

y

Advantages:

• Lower loss

• Less fabrication complexity

•Easier electrode design

OMJ4.pdf   

OFC/NFOEC 2008

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SEM pictures

Si-based Slot Photonic Crystal Waveguide

5µm

Filled Filled slot

Filled

1µm 1µm

Trenchfilling

hole hole

Multimode interference (MMI) coupler

Optical simulation of slot PCW

al η

WMLMInteference length (μm)

over

lap

inte

gr

Slot PCW

x

z

yML⋅−=Δ )( 20 ββσ

Multimode section:

mode phase difference

26

Strip waveguide

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Optical Simulation of Slot PCW

issi

on (d

B)

Slot PCW

norm

aliz

ed |E

x|

Z (µm)trans

mi

MMI

x

z

y

2

Experimental Demonstration of Slot PCW

ecto

r

si

on (d

B)

a=383nm

wav

eve

guided mode

35nm ~20dB

trans

mis

s

wavelength λ (nm)

35nm 20dB

X. Chen, W. Jiang, J. Chen, L. Gu, and R. T. Chen, Applied Physics Letters (To appear in 2007)

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Outlines

1.Introduction2 Sili b d Mi d N h t i2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid ApproachesApproaches5.Further Applications6.Conclusion

Electro-optic polymer modulator based on directional coupler

|R|2~V

Input=1

Domain inverted sections

|S|2

+Δβ, L1 -Δβ, L2

put

Domain-inverted Y-fed directional coupler ( denoted IYCM)

DR1/PMMA or CLD1/APCDR1/PMMA or CLD1/APCDR1/PMMA or CLD1/APCDR1/PMMA or CLD1/APC

electrode

UV11-3

DR1/PMMA or CLD1/APC/ /DR1/PMMA or CLD1/APCDR1/PMMA or CLD1/APC

electrode

Si

UV15

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Electro-optic polymer modulator based on directional coupler

2-section domain-inverted modulator, the IMD were suppressed 47.29 dB

Fabrication Processing of the Polymer PCW Modulator on Silicon Pillars

Thermal oxideE-beam lithographyRIE-siliconRIE-oxideFill bottom claddingFill EO polymer

Spin coat top claddingForm top electrode

Highly doped silicon substrate

SiO2

Si crystal

Thermal oxideE beam lithographyRIE siliconRIE oxideFill bottom claddingFill EO polymer

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Design of Electro-Optic Polymer Photonic Crystal Modulator

Comparison of the state-of-the-art modulators

LiNbO3 SOI Conventional EO Polymer

DARPA /MORPH and Silicon Pillar Photonic

Crystal ModulatorEO coefficients* (pm/V) 30.8 N/A 10~300 200

Electrode length (mm) ~20 5~30 ~20 0.2

Total device length(mm) 40 >25 >30 2

Driving Voltage (v) 4 5 1~3 0.2~0.5

Optical Propagation loss (dB/cm) at 1.55micron

0.2 0.5 1 20

Total insertion loss (dB) 5 ~10 ~10 ~15

Modulation bandwidth (GHz)

40 40 100 100(with specially designed electrodes)

Integration on diff. substrates

Difficult Difficult

Easy Easy

Operation Power Medium High Low Very low

Process Temperature (oC) 1000 400 150~200 150~200

Schematics of the PCW with Reduced Diameter Silicon Pillars

•

(a) (b)

(a) Defect region of silicon pillars

(c)

with reduced diameter(b) (b) band diagram showing the

defect mode with slow photon effect

(c) top view of the magnetic field intensity

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Silicon nano-pillar array withinput waveguide

Angular Sensitivity in 3D Polymer Photonic Crystals

θiθp

x

zy

x

z

XM

KU

LΓ

Propagation direction -80

-60

-40

-20

0

20

40

60

Pro

paga

tion

angl

e (d

egre

e)d

c

w

hy

z

Optical Interconnect Research Lab

Wavelength sensitivity @ ω=0.4-0.45

Propagation angle as a function of wavelength

Propagation vector

8 10 12 14 16 18 20-100

Incident angle (degree)

Dispersion surface of 3rd band

Δn=0.17

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2D Polymer Photonic Crystals Superprism Fabricated by Soft Molding

• Low cost• High throughput

(a)

(b)

(d)

(e)

Optical Interconnect Research Lab

(c) (f)

substrateZEP-520A (master) UV curable polymer

PDMS (template)

Highly Smooth surface (<2nm rms roughness)

3D Woodpile Photonic Crystals Fabricated using Layer-by-Layer Stacking Method

R =300nm(1) First layer pattern

Planarization Process SEM Pictures of 3D woodpile photonic crystals

1st

layer

3rd

layer

2nd

layer

4th

layer

x

y

z

(2) Spin-coatingRmax=7nm

Rmax=300nm

(3) Etch-backRmax=12nm

OMJ4.pdf   

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Superprism Phenomena in 3D Polymer Photonic Crystals

Tunable

IR CameraMonitor

CCD image of light incident normally on the sample

CCD

Tunable Laser Lens

Lensed Fiber

Sample

CCD image of Negative refraction in the photonic crystals

Optical Interconnect Research Lab

PhC on Si Substrate

λ=1430-1620nmLensed fiber

Ø=3 μm

Lens

Tunable Laser

CCD Camera

Superprism Phenomena in 2D Polymer Photonic Crystals

Incident angle=15°Incident angle=15

Propagation angle>0

Incident angle=12°

Propagation angle=0

Optical Interconnect Research Lab

Incident angle=11°

Propagation angle<0

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4 beam holographic fabrication of 3D photonic crystals

Ref: M. Campbell et.al Nature 404,53 (2000)

,

The polygon prism to create 4 beams and recombine them to form the interference. L1=1cm, L2=4cm and H=1.5cm in the design.

The general interference pattern

∑ ∑∑−

=

−

=>

−

=

+•×•××++•×•××+=1

1

1

100

1

0

2 )cos(2)cos(2)(N

i

N

jiijijjijiiiii

N

ii rKeeEErKeeEEErI θθ rrrrrrrrr

sθ4,,0 =−=−= NKKKGGK jiijii

iii etrGiE rrv*)exp(* ω−•The individual beam

where

(1)

and are the relative phase lags to the center beam

Simulation of The Final Structure

)1,0,0(20 −=

λπG )239.1914,-0.9-0.3314,-0(2

1 λπ

=G )391914,-0.920.3314,-0.(22 λ

π=G )0.92390,0.3827,-(2

3 λπ

=GThe individual beam

iii etrGiE rrv*)exp(* ω−• )0 , ,0 1(0 =e )7055,-0.3380.9409,0.0(1 =e )70055,0.3380.9409,-0.(2 =e )0,0,1(3 =e

Simulation of the final structure withoutconsidering the absorption during the holography process.

Simulation of the final structure considering the absorption during the holography process. The lower portion receives less dosage

(111) in-plane and perpendicular lattice spacing for the FCC-type photonic crystalare 0.63 and 2.10μm for SU8

OMJ4.pdf   

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Fabricated Devices

(a) The cleaved 3D photonic crystal on SU8. The upper-left corner inset shows thecm2 size photonic crystal. The lower-right corner inset shows the FCC-type (111) diffraction pattern. (b) SEM image of the pc structure of AZ 4620.

Bandgap Measurement for SU8 based structure Using FTIR

Bandgap in [111] direction for C-band and S-band.

Match of the simulated gap and the measured gap.

OMJ4.pdf   

OFC/NFOEC 2008

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In-plane superprism effects

55

60angular sensitive superprism effect @ 1.55um

50

55wavelength sensitive superprism effect @ -7.3 deg incident

-8.5 -8 -7.5 -7 -6.5 -615

20

25

30

35

40

45

50

grou

p ve

loci

ty a

ngle

1545 1550 1555 1560 1565 157010

15

20

25

30

35

40

45

grou

p ve

loci

ty a

ngle

input angle(degree) input wavlength(nm)

Angular sensitive superprism effect @ 1550nm

Wavelength sensitive superprism effect around 1550nm

The angle is defined as )/(tan 1yx KK−−

Outlines

1.Introduction2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid ApproachesApproaches5.Further Applications6.Conclusion

OMJ4.pdf   

OFC/NFOEC 2008

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Electrically Pumped Device Structure

• Current path in the III-V region:III-V mesa formed on the silicon waveguideP and n contacts on the top and bottom of the mesa respectivelyProton implanted mesa for lateral current confinement

38

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Hybrid Silicon Evanescent Laser

• Lasing at 1575 nm up to 40 oC

39*A.Fang,et.al., Opt Express, 10-2-2006

Hybrid Silicon Evanescent Amplifier

• Amplifier Length 1.36 mm

• 13 dB chip gain• 3 dB output

saturation power at 11 dBm

• 5 - 8 dB chip noise figure

40*H.Park,et.al., IEEE PTL, 1-2007

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Hybrid Silicon Evanescent Detector

• Responsivity Total (with coupling losses) ~.31 A/WA/WDevice responsivity ~ 1.13

• Quantum efficiency ~ 90%• Chip saturation power well

above 10 mW

41

*H.Park,et.al., Submitted for publication 1 2007

Integrated Silicon Evanescent Laser and Photodetector

• Laser

29mW max output power60 C max temp

42*A.Fang,et.al., Submitted for publication 1 2007

OMJ4.pdf   

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Fully Embedded Board Level Fully Embedded Board Level Optical InterconnectionOptical Interconnection

Unique Architecture for Optical PWB (Printed Writing Board); All the optical components are interposed inside the PCB

Solve the package problem / Reduce Cost Effects

45° micro-mirror

Cu TraceMicro-via

1x12 PINPhotodiode

1x12 VCSEL

VCSEL array

Optical PCB

12-channel PolymerWaveguide [109 cm ]

•R. T. Chen, et al, “Fully Embedded Board level Guided-wave Optoelectronic •Interconnects,” Invited paper, Proceedings of IEEE, Vol.88, pp.780-793 (2000).

Polyimide Based 1-to-48 Fanout H-tree Optical Waveguide on Si-Substrate

(c)

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Outlines

1.Introduction2 Silicon based Micro- and Nano-photonic2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid Approachespp5.Further Applications6.Conclusion

Schematic of Fully Embedded External ModulatorUsing Nano-photonic Devices

Photonic Crystal WG ModulatorVias

Photonic Crystal Laser Beam Router

CW Laser DiodeDriving Electrode Conventional

M h Z h dProposed Si PCW

M d lImprovement

FMach-Zehnder Modulator

Modulator Factor

Size ~ 4mm ~ 40 um 100 X reduction

Power consumption ~ 0.3 W ~ 0.01 W 10X to100X

reduction

Integration No integration potential

Potential for high density integration N/A

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Polymer optical circuit devices for the next generation FTTH systems

①Detached House ②Apartment House

Future Network Configuration of the FTTH System

Distribution System

WDM and Splitter modules are the key component for the FTTH system.Japan NEDO/METI Project

OMJ4.pdf   

OFC/NFOEC 2008

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Outlines

1.Introduction2 Silicon based Micro- and Nano-photonic2.Silicon based Micro- and Nano-photonic Devices3.Polymer-based Micro- and Nano-photonic Devices4.Integration: Monolithic and Hybrid Approachespp5.Further Applications6.Conclusion

Conclusion1. Compatibility with Silicon CMOS fabrication process is crucial to

both hybrid and monolithic integration.2. Monolithic integration on silicon platform is not realistic in the2. Monolithic integration on silicon platform is not realistic in the

foreseeable future due to the fact that electrically pumped silicon laser has a quantum efficiency well below 1%.

3. Electrically pumped silicon laser with quantum efficiency above 5% is the threshold to make monolithic integration meaningful

4. Insertion of functional materials such as EO polymer, liquid, etc, into silicon nanostructures has potential to produce low-power, highly efficient active deviceshighly efficient active devices.

5. Telecommunications is a very crowded space. Biomedical, instrumentation, energy conversion shall be areas of interest for high-value commercial applications.

6. Silicon nano-photonics may play a significant role for on-chip interconnect where power consumption can be drastically reduced.

OMJ4.pdf   

OFC/NFOEC 2008