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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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49413223158
544739302113
5346382920
423324169
52453728
34251710
600 µm5548403122147
49413223158
544739302113
5346382920
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
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