Optical Input / Output Considerations for Photonic Integrated Circuit Coupling & Packaging

Transcription

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

2 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 2 September 2016

3 Bias Disclosure: Surface Coupling Surface Coupling Edge Coupling 3 September 2016 Vertical Grating Couplers Waveguide Facet

4 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 4 September 2016

5 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, (2017/02/20)

6 6 September 2016 Electrical, Layout and Fixturing Considerations Electrical design Single-end vs differential RF Minimize RF line lengths Test fixturing that considers test needs, e.g. compatible connectors 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

7 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 temperaturesensitive 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. 7 September 2016

8 8 September 2016 Optical Considerations Spectral range / fiber needs Number of channels Polarization sensitivity: PM channels Edge vs. surface coupling Optical performance expectations (transmission losses, polarization and temperature sensitivity) 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

9 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) Bandwidth Insertion Loss Fiber-to-die Mode Field Diameter [Alignment Tolerances] 1 Wade, 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, April 2015: 78nm 1-dB bandwidth fabricated in a 45nm commercially available microelectronics SOI CMOS process. Other considerations include: IP, Overall package design, thermal management.. 9 September s of nm 2 db typ. Deceptive 1-2 µm typ. [ µm] (Inverted taper) 30 nm (1 db) typ. Improving: 75 (1 db) 130 nm (3 db) db typ. Improving: < 1.5 db 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)

10 Optical Coupling Technologies Free Space Optics Lensed Fiber Lens National Chung Hsing U., Taiwan Fiber and Fiber Arrays V-Groove Arrays High NA fiber Multicore Fiber Pitch Reducing Optical Fiber Array (PROFA) Micro-Optic for Arrayed Lenses Interposers Planar Fiber Coupling (TIR) Tyndall National Institute Planar Fiber Coupling (TIR) Tyndall National Institute Interposer Chip PLC Connections Passive Alignment Adiabatic Coupling IBM Silicon Nanophotonic Packaging Wafer-level PhotonicBump 10 September 2016 Photonic Wire Bonds Karlsruhe Institute of Technology EU FP7 Initiative PHASTFlex Teramount Ltd.

11 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) 11 September 2016 LETI s silicon photonics chip with PhotonicBumps PhotonicPlug on LETI s silicon photonics wafer

12 Vanishing Core Fiber Concept Vanishing Core n 3 Secondary Core Standard NA (MFD 10 µm) n 2 n 1 Tailored NA Waveguide Fiber Cladding (Ø 125 µm) Dual, concentric core design and choice of glass refractive indices (n 1, n 2 ) enable device to be compatible with standard fibers (on left). Light is confined within secondary core, tailored (n 2, n 3 ) to be compatible with reduced mode field diameter (MFD) of coupled to waveguide The central core (n 1 ) effectively vanishes relative to light traveling through tapered region. 12 September 2016

13 Vanishing Core Fiber Concept Vanishing Core n 3 Secondary Core Standard NA (MFD 10 µm) n 2 n 1 Tailored NA Waveguide Fiber Cladding (Ø 125 µm) n 1 - n 2 < n 2 - n 3 - reduced MFD n 1 - n 2 > n 2 - n 3 - expanded MFD n 1 - n 2 = n 2 - n 3 - preserved MFD V.I. Kopp and A.Z. Genack, Nature Photonics 5, 470 (2011) Endface for PM coupling Configurable output geometry for polarization control and mode shape adaptation 13 September 2016

14 Pitch Reducing Optical Fiber Array (PROFA) Common cladding (n 3 ) Vanishing inner cores (n 1 ) Channel 2 MFD 1 Low NA, SM or MM p 1 Configurable NA, SM or MM p (MFD ~ 10 µm) 2 MFD 2 MFD 2 Channel 2 MFD 1 Outer (new) cores (n 2 ) Conventional single-lens focusing: if p 1 > p 2 then MFD 1 > MFD 2 PROFA: if p 1 > p 2 then MFD 1 > MFD 2 OR MFD 1 < MFD 2 OR MFD 1 = MFD 2 14 September 2016

15 PROFA Products PROFA1D 1-6 Channel Optical Couplers (linear) MFD ~ 2 mm (1/e 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 15 September 2016

16 PROFA Products PROFA2D 1-61 Channel Optical Couplers (2D) MFD ~ 4-10 mm (1/e nm Channel spacing ~ µm optimal: 37 µm mm position tolerance Insertion Loss (IL) < 1 db No air gap within optical path Crosstalk < -35 db 16 September 2016

17 17 September 2016 PROFA1D vs. PROFA2D PROFA1D PROFA2D Typical for coupling to Edge Surface Mode field size (µm) ~ 2 ~ 4-10 Array Lattice Linear Hexagonal Channel spacing (µm) (37 optimal) Channels currently available Singlemode (SM) / Polarization Maintaining (PM) availability Typical coupling loss (fiber-tochip, db) Alignment accuracy required (µm) SM / PM SM Price per channel (Qty:1)* ~ USD 400 ~ USD 30 * Pricing can be reduced significantly in quantity and depending on configuration PROFA 2D 61-Channel Array PROFA 1D 6-Channel Array PROFA 1D Single Channel

18 Face Coupling: 37 Channels, 1 Port Pitch Reducing Optical Fiber Array µm PROFA channel pattern superimposed on 1x32 splitter tree Coupling loss 3 db (1 db on top of VGC coupling loss) 0.7 db standard deviation across all 37 channels 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 September 2016

19 PROFA-Based Fiber Fanout for Multicore Fiber Currently Available Configurations: Channel pitch: µm MFD: 6 10 µm NA: Insertion Loss < 0.9 db Crosstalk < - 48 db 19 September 2016

20 20 September 2016 The World s First Open Access Photonic Packaging Pilot Line

21 PIXAPP (Advanced Training Programme) First Course January 2017 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) 21 September 2016

22 PIXAPP (The Packaging Technologies) Photonic Integrated Circuit (PIC) Mechanical Package Fibre Optics Micro Optics Thermal Management Source Integration Electrical Packaging Electronic Integration 22 September 2016

23 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 23 September 2016

24 Freedom Photonics Overview and Products Developer and manufacturer of photonic integrated circuit based products (InP, GaAs, Sidielectric, Si Photonics) - Fast turn-around small lot wafer fabrication at Nanotech cleanroom facility Products and product development: , 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 24

25 PROFA2D-Flex: Enabling Robust Low Profile Packaging 12 mm channel spacing in coated flexible portion Multichannel transceiver 125 mm channel spacing prototype (16 Tx/16 Rx) with expected 1,600 Gb/s aggregate bandwidth (50 Gb/s/channel) PROFA holder or MCF connector 37 mm channel spacing at the PIC coupling plane 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 42 nd European Conference and Exhibition on Optical Communications, p.755, September 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 September 2016

26 Tailorable Mode Field Size and Density: 1.5 µm x 2 Channels 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) 26 September 2016

27 Tailorable Mode Field Size and Density: 2 µm x 10 Channels Doany et al., IEEE J. of Lightwave Technology 29, 475 (2011) 27 September 2016

28 PIC Development Package - Edge Removable cover Two single-channel PROFA1Ds Two I/O ports Open package design for electrical probing Cryogenically stable package Work done with OpSIS 28 September 2016

29 PIC-PROFA1D Interface PIC Development Package Close-up 1550 nm PANDA fiber coupled to 220 x 200 nm Si waveguide < 2 db coupling loss < -20 db polarization crosstalk Work done with OpSIS 29 September 2016

30 FTNIR Spectrometer Oil & Gas Industry Hermetic Butterfly Package PROFA1D Single-channel PROFA1D 1550 nm PANDA fiber coupled to Si waveguide Work done with Luxmux Technology Corporation 30 September 2016

31 Conclusion Plan for coupling and packaging at the earliest design stage Internally review coupling/packaging needs Form an informed optical I/O opinion Engage with packaging house(s) early 31 September 2016