Hybrid Integration of Laser Diodes with Alignment Tolerant ... · PDF fileHybrid Integration of Laser Diodes with Alignment Tolerant Couplers ... Baseline%Single%Mode%gra1ng%design%for

Lehr- und Forschungsgebiet Integrierte Photonik Prof. Jeremy Witzens, Ph. D.

RWTH Aachen University

Hybrid Integration of Laser Diodes with Alignment Tolerant Couplers

J. Witzens, S. Romero-García, F. Merget, B. Marzban

ECOC 2014

2 Alignment Tolerant Couplers ECOC, 2014

Hybrid Integration of III-V Lasers on SOI

Typical Laser Profile FWHM ≈ 1 µm – 1.5 µm

Sub-micrometric SOI Interconnection Waveguide

Si

SiO2

Size 250 µm x 350 µm

III-V Laser Diodes

Height = 0.22 µm Width = 0.4 µm

λ = 1520 nm – 1570 nm

2 µm

1.25 µm

Si

Challenges

!  Mode Size Conversion !  Alignment and Attachment !  Optical Isolation !  Heat-Sinking

Coupling efficiency and wall-plug efficiency translate directly into how many channels can be implemented in parallel (€/Gbps).

!  Known Good Die !  Burn-In !  State-of-the-art wall-plug efficiency !  State-of-the-art RIN

Process &

Devices

3

Hybrid Integration of III-V Lasers on SOI

!  High%Complexity%with%mul1ple%op1cal%elements%

!  Good%Alignment%Tolerances%:%±%2%µm,%1%dB%Loss%penalty%%

!  Inser1on%Losses%%3.36%dB*%+%Gra1ng%Inser1on%Loss%%%%%%

*Snyder B. et al, “Hybrid Integration of Wavelength-Tunable Laser with Silicon Photonic Integrated Circuit”, JLT Vol. 3 (2013)

!  Simple%Integra1on%Concept%!  Low%Losses%%(%%̴1%dB%best%case%simulated%tapered%down%to%180%nm%1p)%%

!  Stringent%Alignment%Tolerances%(±%0.5%µm,%1%dB%Loss%penalty)%%%

*M. Kapulainen et al., IEEE Conf. Group IV Photonics 2008.

Alignment Tolerant Couplers ECOC, 2014

Edge-Coupling with Spot Size Converters (Inverse Tapers)

Out-of-Plane Coupling with Ball Lens, Prism and Grating Couplers (Luxtera, Tyndall)


Single Mode Coupling Structures

±0.5 σ0"

±1.2 σ0"

- 2.3 dB"

Single(mode(coupling(structure:(Ground%mode%lateral(1/e(half!width(σ((

PIC%Laser%

x((Lateral)%z

Input%Laser%Beam%modeled(as(a(Gaussian:(lateral(1/e(half!width(σ0%%

COUPLING%EFFICIENCY:((•  Simple(field(overlap(•  Scales(directly(with(σ(

%%%%%%%%TRADEOFF%Inser1on%Efficiency%%%%%%%%%%%%%%%%%vs%%Misalignment%Tolerance((((

y((Ver1cal)%


Combined Splitter / Edge Coupler

3 dB splitter with built-in inverse tapers

Power at output waveguide equally split independently of power splitting at the input, assuming a and b to be in phase (lateral displacement).

" Consequence of the quadrature condition.

PIC%

Laser%

x-displacement (lateral) The image cannot be displayed. Your computer

may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

P = a2 + b2( ) 2

P = a2 + b2( ) 2

ab

ΔβL = π2+mπ


Multimode Coupling Structures

- 0.3 dB"

±1.2 σ0"

±1.2 σ0"

Coupling Versus Misalignment

Relaxing alignment tolerance by coupling into a multimode structure:

!  Using light coupled into the first two modes.

!  Separating the modes into two isolated waveguides where they are in quadrature.

Modal Decomposition

ΔβL = π2+mπ

x axis (µm)

y ax

is (µ

m)

-4 -3 -2 -1 0 1 2 3 4-3

-2

-1

0

1

2

3

x axis (µm)

y axis

(µm

)

-4 -3 -2 -1 0 1 2 3 4-3

-2

-1

0

1

2

3

Supermodes of the structure


0 1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

9

Input Beam Width (µm)

1 dB

Misa

lignm

ent T

oler

ance

(µm

)

Multimode σ = 2 σ0 : 1 dB Centered Ins. EfficiencyMultimode σ =1.5 σ0: 0.3 dB Centered Ins. EfficiencySingle-mode, optimal width

Typical Laser diodes Beam sizes"

Standard Monomode Fiber SMF-28"1550 nm"Lensed Fiber"

Monomode Fiber VIS"500 nm"

Typical%Laser%diodes:%Beam%size%σ0%~1.2%μm%(Lateral%1%dB%Misalignment%tolerance:%•  Single(mode(coupler:(~±0.6(μm(•  MulDmode(coupler:(~±1.8(μm(with(<(1(dB(total(loss( x 3

Lateral%Misalignment%tolerance%enhancement%%

Single Mode vs. Multimode Coupling Structures


Edge Coupler I: Optical Characterization

-2 -1 0 1 2-10

-8

-6

-4

-2

0

Lateral Misalignment (µm)

Coup

ling

Effic

iency

(dB)

Output 1Output 2Output 1 + Output 2

0 1 2 3 4-7

-6

-5

-4

-3

-2

-1

0

Laser to Chip Distance (µm)Co

uplin

g Ef

ficien

cy (d

B)

Output 1Output 2Total

-1.5 -1 -0.5 0 0.5 1 1.5-10

-8

-6

-4

-2

0

Vertical Misalignment (µm)

Coup

ling

Effic

iency

(dB)

Output 1Output 2Total

±1.4 µm ±0.35 µm

3 µm

Measured%with%FP%Laser%mounted%on%a%XYZ%nanoposi1oner%stage.

2 dB Insertion Loss (center)

Measured%with%lensed%fiber%%and%tunable%laser%

Reduced bandwidth due to imprecise cleaving


Edge Coupler II: Optical Characterization

3.1 dB Insertion Loss (center) (vs. 2.2 dB in simulations)

Measured%with%lensed%fiber%%and%tunable%laser%

±1.9 µm ±0.5µm

Reduced bandwidth due to imprecise cleaving

Measured%with%FP%Laser%mounted%on%a%XYZ%nanoposi1oner%stage.

10

Multimode Focusing Grating Coupler

Top%view%

Baseline%Single%Mode%gra1ng%design%for(fiber((MFD(=(10.4(μm)(coupling:(!  Uniform(pitch((630nm)(and(fill(factor((duty(cycle:(50%)(!  (DiffracDon(angle:(11(degrees(at(1550(nm(!  (BOX(layer(thickess(=(2(μm(!  Input(Waveguide(width(=(12.5(μm((

Max.%Effiency%=%f2.6%dB%%%

1%dB%Misalignament%%tolerance%=%±%2.1%μm%%

!  Mul1mode%focusing%gra1ng%design%for(fiber(coupling:(

±7.5 μm"

3D%FDTD%Simula1ons%

!(Total%Centered%Inser1on%Efficieny%=%f%3.8%dB%%%(1.2%dB%excess%loss%at%nominal%alignment)%f%1%dB%Misalignment%Tolerance%=%±7.5%μm%!(Total(length(=(120(μm((

x%3.5%%

Lateral%Misalignment%tolerance%

enhancement%%

Ground and 1st Order Waveguide Modes

Corresponding beams coupled to from the fiber


Summary

Multimode Edge-Coupler I

Multimode Edge-Coupler II

Multimode Focusing Grating

Coupler

Insertion Loss 2 dB (measured with FP laser)

3.1 dB (measured with FP laser)

GC + 1.2 dB (simulated coupling to a

single mode Fiber)

x & z axis 1 dB Misalign. Tol.

± 1.4 µm ± 1.9 µm ± 7.5 µm (x axis) ± 2.1 µm (z axis)

y (vertical) axis 1 dB Misalign. Tol.

± 0.35 µm ± 0.5 µm > 5 µm

Bandwidth 60 nm (measured) 90 nm (design)

28 nm (measured) 50 nm (improved design)

40 nm (simulation)

Back-Reflection < -20 dB < -20 dB


References

•  S. Romero-García, B. Marzban, F. Merget, B. Shen, J. Witzens, “Edge Couplers with relaxed Alignment Tolerance for Pick-and-Place Hybrid Integration of III-V Lasers with SOI Waveguides,” J. Sel. Top. Quant. Elec. 20(4), special issue on Silicon Photonics, Art. 8200611 (2014).

•  S. Romero-García, B. Marzban, S. Sharif Azadeh, F. Merget, B. Shen, J. Witzens, “Misalignment tolerant couplers for hybrid integration of semiconductor lasers with silicon photonics parallel transmitters,” Proc. SPIE 9133, Article 91331A (2014).

Acknowledgements

13

Frontier of Integrated Silicon Nanophotonics in Telecommunications

Safe and Secure European Router

Broadband Integrated and Green Photonic Interconnects for high-Performance computing and Enterprise Systems

Dr. Florian Merget

Alignment Tolerant Couplers ECOC, 2014

Mr. Sebastian Romero García

Mrs. Bahareh Marzban

Thank you for your attention!


Hybrid Integration of Laser Diodes with Alignment Tolerant ... · PDF fileHybrid Integration of Laser Diodes with Alignment Tolerant Couplers ... Baseline%Single%Mode%gra1ng%design%for

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