1 September 2016 Photonics Summit and Workshop 2017 ♦ 06 Sep 2017 ♦ San Jose, CA, USA

Optical Input / Output

Considerations for

Photonic Integrated

Circuit Coupling &

Packaging

Dan Neugroschl

Chiral Photonics, Inc.

Pine Brook, New Jersey USA

T. J. Seok, et. al., "High Density Optical Packaging of High Radix Silicon

Photonic Switches," in Optical Fiber Communication Conference

Postdeadline Papers, OSA Technical Digest (online) (Optical Society of

America, 2017), paper Th5D.7.

2 September 2016

Agenda

1. Why Should I Care about Probing & Packaging?

➢ When should I care about probing & packaging?

2. What are my Probing/Package Requirements?

➢ Self assessment for out- or in-sourcing

3. Optical I/O Considerations & Options

4. Packaging Service Providers and Exemplary

Services

3 September 2016

Bias Disclosure: Surface Coupling

Surface Coupling Edge Coupling

Vertical Grating Couplers Waveguide Facet

4 September 2016

Why Should I Care about Probing & Packaging?

1. Proper testing of your PIC demands it

2. May want to get off lab bench/probe station and test in real world

➢ Even if not your initial goal

3. 80:20 electronic vs. 20:80 photonic chip:package costs (?)

4. Achilles’ Heel: [Definition: Weakness in spite of overall strength, leading to downfall]

➢ “Can you package my 2 μm MFD channels on 127 μm pitch?”

➢ Packaging can be a strong asset and need not be painful

➢ Start discussing it when you purchase your design software

• Perhaps as a prerequisite – can software model optical coupling?

• Certainly at earliest stage of design

5 September 2016

Basic Probing / Packaging Requirements

Map out your testing:

1. How will I systematically and granularly verify my design?

• Electrical

• Optical

➢ Independently verify electrical and optical, e.g. pure optical

alignment / measurements uncomplicated by detector or

modulator verification

2. Do you want to do wafer-level probing?

➢ Consider addition of taps and vertical grating couplers (VGCs)

➢ Erasable VGCs: M. Milosevic, "Towards autonomous testing of photonic

integrated circuits," Proc. SPIE 10108, Silicon Photonics XII, 1010817

(2017/02/20)

6 September 2016

Electrical, Layout and Fixturing Considerations• Electrical design

• Single-end vs differential RF

• Minimize RF line lengths

• Electrical I/O design: Wire bonds vs. Flip-chip (solder bump, Cu pillar)

• Copper pillar offers: Higher I/O density, improved electromigration resistance,

improved thermal conductivity, simplified underbump metallization and

underfill

• Often a progression of designs

• Die bonding electrical needs, e.g. grounding

• Layout considerations

• Die Size: L x W x H

• Minimize conflicts between electrical and optical I/O

• Keep die edges unmixed: electrical OR optical

• Use opposite edges for optical when 2 edges are needed

• Clearance between optical and electrical probe “pads” for simultaneous

probing

• Test fixturing that considers test

needs, e.g. compatible connectors

7 September 2016

Thermal Management & Application-Specific Considerations

• Thermal Design

• Especially relevant when PIC contains: laser, resonators, AWGs, WDM

components, amplifiers or components that generate heat or are temperature-

sensitive

• Thermal modeling

• Thermoelectic cooler (TEC) and feedback/control

• On-chip temperature measurement

• Thermistors with feedback to TEC

• Die bonding requirements

• Application-specific packaging needs

• Package design and environmental needs: form factor / testing:

• Testing requirements: Telcordia to biocompatible (e.g. sterilizable) to

hermiticity to vacuum-compatible to cryogenic, etc.

8 September 2016

Optical Considerations• Spectral range / fiber needs

• Number of channels

• Polarization sensitivity: PM channels

• Edge vs. surface coupling

• Surface coupling may be desirable for wafer level testing even when edge

coupling packaged device

• Mode Field Diameter (Spot Size) at die interface: waveguide facet or VGC

• VGC diffraction angle

• Experimentally verified mode field dimensions preferred

• Pigtailed vs. pluggable

• Active alignment design / equipment needs

• Alignment channels / taps / fiducials

• On-chip detector / source

• Package materials needs – stability

• Hermiticity needs

• Package process sequence

• Optical performance expectations

(transmission losses, polarization and

temperature sensitivity)

9 September 2016

PIC Optical Coupling: Edge vs. Surface

➢ Die to fiber: Submicron to ~ 10 μm spot size (1550 nm) conversion needed

Edge

Coupler

Vertical Grating

Coupler (VGC)

Other considerations include: IP, Overall package design, thermal management…..

1Wade, M.T. et.al. "75% efficient wide bandwidth grating couplers in a 45 nm microelectronics CMOS process," in Optical Interconnects Conference (OI), 2015 IEEE , pp.46-47, 20-22 April 2015: 78nm 1-dB bandwidth fabricated in a 45nm commercially available microelectronics SOI CMOS process.

Bandwidth 100s of nm30 nm (1 dB) typ.

Improving: 75 (1 dB) – 130 nm (3 dB)1

Insertion LossFiber-to-die

2 dB typ.3-4 dB typ.

Improving: < 1.5 dB1

Mode Field Diameter [Alignment Tolerances]1-2 µm typ. [0.1-0.2 µm]

(Inverted taper)6-10 µm typ. [0.6 - 1 µm]

Arrays / # of Channels 1-dimensional / 10s 2-dimensional / 100s

Edge preparation Yes: etch (ledge), polish No (also enhanced stability)

Wafer-level Probing (KGD, Foundry vs. BE) No Yes

Polarization Maintaining Yes No 2D PM fiber couplers yet

Polarization Handling On-chip PM splitters Polarization diversity VGCs (IL penalty)

Deceptive

10 September 2016

www.plcconnections.com

Interposer Chip

PLC Connections

Interposers

Fiber and Fiber Arrays

V-Groove Arrays

High NA fiber

Planar Fiber Coupling (TIR)

Tyndall National Institute

Multicore Fiber

Optical Coupling TechnologiesFree Space Optics

LensLensed Fiber

Micro-Optic for

Arrayed Lenses

National Chung Hsing U., Taiwan

Planar Fiber Coupling (TIR)

Tyndall National Institute

Pitch Reducing Optical Fiber Array (PROFA)

Adiabatic Coupling

EU FP7 Initiative PHASTFlex

IBM Silicon Nanophotonic Packaging

Passive Alignment

Teramount Ltd.

Wafer-level

“PhotonicBump”

Photonic Wire Bonds Karlsruhe Institute of Technology

11 September 2016

LETI’s silicon photonics chip with PhotonicBumps

PhotonicPlug• Provide passively aligned optical I/O via standard pick & place

equipment: +/- 6 µm placement accuracy• PhotonicBump via wafer-level process

• PhotonicPlug via standard pick & place equipment

• Fiber array: SM, 250 µm spacing

• Performance (standard flip chip equipment, 1500 UPM): < 0.5 dB coupling loss

• Introduction: 2H 2018 (working with customers now)

PhotonicPlug on LETI’s silicon photonics wafer

12 September 2016

Vanishing Core

Cladding (Ø ≈ 125 µm)

Secondary Core

Tailored NA

n1

n2

n3

Standard NA

(MFD ≈ 10 µm)

Fiber

Waveguide

• Dual, concentric core design and choice of glass refractive indices (n1, n2) enable device to be

compatible with standard fibers (on left).

• Light is confined within secondary core, tailored (n2, n3) to be compatible with reduced mode field

diameter (MFD) of coupled to waveguide

• The central core (n1) effectively “vanishes” relative to light traveling through tapered region.

“Vanishing Core” Fiber Concept

13 September 2016

Vanishing Core

Cladding (Ø ≈ 125 µm)

Secondary Core

Tailored NA

n1

n2

n3

Standard NA

(MFD ≈ 10 µm)

Fiber

Waveguide

“Vanishing Core” Fiber Concept

n1 - n2 < n2 - n3 - reduced MFD

n1 - n2 > n2 - n3 - expanded MFD

n1 - n2 = n2 - n3 - preserved MFD

Endface for

PM coupling

V.I. Kopp and A.Z. Genack, Nature Photonics 5, 470 (2011)

Configurable output geometry for polarization

control and mode shape adaptation

14 September 2016

Conventional single-lens focusing:

if p1 > p2 then MFD1 > MFD2

Common cladding (n3)“Vanishing” inner cores (n1)

Outer (new) cores (n2)

Low NA, SM or MM

(MFD ~ 10 µm)Configurable NA, SM or MMp1

p2

Channel 2 MFD1

MFD2

MFD2

Channel 2 MFD1

Pitch Reducing Optical Fiber Array (PROFA)

PROFA:

if p1 > p2 then MFD1 > MFD2 OR

MFD1 < MFD2 OR

MFD1 = MFD2

15 September 2016

PROFA Products – PROFA1D

• 1-6 Channel Optical Couplers (linear)

• MFD ~ 2 mm (1/e2 intensity) @ 1550 nm

• 12 um channel pitch, ≤ 0.2 mm position

tolerance

• Insertion loss (IL) < 1 dB

• Crosstalk < -40 dB

• No air gap within optical path

• PM aligned and coupled: typical PER ≥

20 dB

• Slow axis ↔ TE

• Fast axis ↔ TM

16 September 2016

PROFA Products – PROFA2D

• 1-61 Channel Optical Couplers (2D)

• MFD ~ 4-10 mm (1/e2 intensity) @ 1550 nm

• Channel spacing ~ 35-50 µm – optimal: 37 µm

• ≤ 0.4-1 mm position tolerance

• Insertion Loss (IL) < 1 dB

• No air gap within optical path

• Crosstalk < -35 dB

17 September 2016

PROFA1D PROFA2D

Typical for coupling to Edge Surface

Mode field size (µm) ~ 2 ~ 4-10

Array Lattice Linear Hexagonal

Channel spacing (µm) 1235-50

(37 optimal)

Channels currently available 1-6 1-61

Singlemode (SM) /

Polarization Maintaining (PM)

availability

SM / PM SM

Typical coupling loss (fiber-to-

chip, dB)2 3-4

Alignment accuracy required

(µm)≤ 0.2 ≤ 1

Price per channel (Qty:1)* ~ USD 400 ~ USD 30

* Pricing can be reduced significantly in quantity and depending on configuration

PROFA 1D – 6-Channel Array

PROFA 1D – Single Channel

PROFA 2D –

61-Channel Array

PROFA1D vs. PROFA2D

18 September 2016

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423324169

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34251710

600 µm5548403122147

49413223158

544739302113

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423324169

52453728

34251710

600 µm600 µm

V. I. Kopp, et. al., "Two-dimensional, 37-channel, High-bandwidth Ultra-dense Silicon Photonics Optical Interface," in

Optical Fiber Communication Conference: Postdeadline Papers, (Optical Society of America, 2014), paper Th5C.4.

• Coupling loss 3 dB (1 dB on top of VGC coupling loss)

• 0.7 dB standard deviation across all 37 channels

PROFA channel pattern

superimposed on 1x32

splitter tree

Pitch Reducing Optical Fiber Array

Face Coupling: 37 Channels, 1 Port

19 September 2016

Currently Available Configurations:

• Channel pitch: 35 – 45 µm

• MFD: 6 – 10 µm

• NA: 0.1 – 0.21

PROFA-Based Fiber Fanout for Multicore Fiber

Insertion Loss < 0.9 dB

Crosstalk < - 48 dB

20 September 2016

The World’s First Open Access Photonic Packaging Pilot Line

21 September 2016

PIXAPP (Advanced Training Programme)

• PIC Design for Packaging

• Package Design (optical, electrical, thermal, mechanical)

• PIC Fabrication Fundamentals (lab based training)

• PIC Packaging Processes (lab based training)

• Application Examples (telecom, medical, sensors)

First Course

January 2017

22 September 2016

Micro Optics

Electronic Integration

Source Integration

Electrical Packaging

Fibre Optics

Thermal Management

Mechanical Package

Photonic Integrated Circuit

(PIC)

PIXAPP (The Packaging Technologies)

23 September 2016

PIXAPP Optical I/O Offerings

• Fibers: UV cure and laser weld attachment for both edge and

grating coupled PICs

• Micro optics: Wafer scale integration of micro optics on Si-PIC

grating couplers for fiber-free coupling

• Photonic Wirebonds: KIT (Germany) is partner

Freedom Photonics Overview and Products

24

▪Developer and manufacturer of photonic integrated circuit based products (InP, GaAs, Si-dielectric, Si Photonics) - Fast turn-around small lot wafer fabrication at

Nanotech cleanroom facility

▪Products and product development: - 1310, 1550 and 1650nm Monolithic tunable lasers

- Monolithic tunable transmitters

- High power, high speed photodetectors

▪Optical I/O Offerings: Collimating micro-optics

to couple into fiber- Flexibility in shaping the beam for the fiber

Freedom Photonics LLC Proprietary

25 September 2016

37 mm channel spacing at the PIC coupling plane

PROFA holder or MCF connector

12 mm channel spacing in coated flexible portion

125 mm channel spacing •Multichannel transceiver

prototype (16 Tx/16 Rx) with

expected 1,600 Gb/s aggregate

bandwidth (50 Gb/s/channel)

•Coupling loss < 3.5 dB per VGC

•Crosstalk < -30 dB

• V. I. Kopp, et. al., “Flexible, Multi-channel, Ultra-dense

Optical Interface for Silicon Photonics," in 42nd European

Conference and Exhibition on Optical Communications,

p.755, September 2016.

PROFA2D-Flex: Enabling Robust Low Profile Packaging

• P. De Heyn, et. al. "Ultra-Dense 16x56Gb/s NRZ GeSi

EAM-PD Arrays Coupled to Multicore Fiber for Short-

Reach 896Gb/s Optical Links," in Optical Fiber

Communication Conference, OSA Technical Digest

(online) (Optical Society of America, 2017), paper Th1B.7.

26 September 2016

19 mm spacing, dual

channel array coupled to

an InP Multi-Wavelength

Coherent Receiver

(Alcatel-Lucent)

C. R. Doerr, L. Zhang, and P. J. Winzer, OFC paper PDPB1, San Diego, CA, USA (2010)

Tailorable Mode Field Size and Density: 1.5 µm x 2 Channels

27 September 2016

Doany et al., IEEE J. of Lightwave Technology 29, 475 (2011)

Tailorable Mode Field Size and Density: 2 µm x 10 Channels

28 September 2016

Work done with OpSIS

http://opsisfoundry.org/

Removable cover

• Two single-channel PROFA1Ds

• Two I/O ports

• Open package design for electrical probing

• Cryogenically stable package

PIC Development Package - Edge

29 September 2016

Work done with OpSIS

http://opsisfoundry.org/

1550 nm PANDA fiber coupled to 220 x 200 nm Si waveguide

< 2 dB coupling loss

< -20 dB polarization crosstalk

PIC-PROFA1D InterfacePIC Development Package Close-up

30 September 2016

Work done with Luxmux Technology Corporation

http://www.luxmux.com//

• Single-channel PROFA1D

• 1550 nm PANDA fiber coupled to Si waveguide

FTNIR Spectrometer – Oil & Gas IndustryHermetic Butterfly Package – PROFA1D

31 September 2016

Conclusion

• Plan for coupling and packaging at the earliest

design stage

• Internally review coupling/packaging needs

➢Designguide@chiralphotonics.com

➢Form an informed optical I/O opinion

• Engage with packaging house(s) early