Photonic Integrated Circuits Made in Berlin

Fraunhofer Heinrich Hertz Institute Photonic Integrated Circuits Made in Berlin Photonic integration Workshop, Columbia University, NYC October 2015 Moritz Baier, Francisco M. Soares, Norbert Grote Fraunhofer Heinrich Hertz Institute, Einsteinufer 37, 10587 Berlin www.hhi.fraunhofer.de

Outline What does InP offer as a material system? Challenges for photonic integration in InP Overview over our process flow Overview over our building blocks 22.10.2015 2

Our Material System of Choice Glass Fiber Window 22.10.2015 3

Advantages of InP/InGaAsP Bandgap can reach from 1 µm to 1.6 µm Ideal for telecom applications due to the transmission windows in glass-fiber! Direct bandgap Epitaxial growth technology is well established for this material 22.10.2015 4

One Bandgap for Each Application Let s assume we use photons of energy E ph Let a device s bandgap be E g Functionality Low-loss waveguide Gain Detector Bandgap Condition E g >>E ph E g =E ph E g <E ph 22.10.2015 5

One Bandgap for Each Application We want a solution for the C-band E ph = [1530,1570] nm Functionality Bandgap Low-loss waveguide Gain Detector ~1100 nm ~1550 nm 1650 nm 22.10.2015 6

Challenges for Integration How to implement all of them? We chose a combination of: Vertical evanescent coupling Selective regrowth Functionality Bandgap Low-loss waveguide Gain Detector ~1100 nm ~1550 nm 1650 nm 22.10.2015 7

Evanescent Coupling A PIN diode is deposited on top of the waveguide (Q1.06) The Absorber is InGaAs Higher refractive index than in waveguide The guided mode naturally couples strongly to the absorber 22.10.2015 8

Evanescent Coupling A PIN diode is deposited on top of the waveguide (Q1.06) The Absorber is InGaAs Higher refractive index than in waveguide The guided mode naturally couples strongly to the absorber Functionality Bandgap Low-loss waveguide Gain Detector ~1100 nm ~1550 nm 1650 nm 22.10.2015 9

Layer Stack for Gain A wafer only for gain-based devices could look like this: Quantum Wells (QW) for gain A Q1.3 waveguide Doped regions to form a PIN diode Using this waveguide, we also implement Bragg mirrors (using direct ebeam writing): 22.10.2015 10

Butt-Joint Growth 1) Start with complete gain structure QWs p-inp active core n-inp Fe-InP substrate 2) etch doped layers outside of active regions QWs p-inp active core n-inp Fe-InP substrate 3) selective-area growth of passive core & PD layers 22.10.2015 11

Butt-Joint Growth Functionality Bandgap Low-loss waveguide Gain Detector ~1100 nm ~1550 nm 1650 nm 22.10.2015 12

Selective Area Regrowth 400 nm < λ/n Q(1.3) Q(1.06) 22.10.2015 13

Butt-Joint Growth Strong index contrast between both waveguides Taper necessary for optimal coupling < 1 db coupling loss experimentally achieved 22.10.2015 14

Challenges for Integration We established integration using two basic principles: Vertical evanescent coupling Selective regrowth Functionality Bandgap Low-loss waveguide Gain Detector ~1100 nm ~1550 nm 1650 nm 22.10.2015 15

Putting It All Together 1) epi-growth n-inp & QW layer QWs active core n-inp Fe-InP substrate 2) define QW regions & gratings QWs active core n - InP Fe - InP substrate 3) epi-growth p-inp QWs p-inp active core n-inp Fe-InP substrate 4) Define active mesas outside of active regions QWs p-inp active core n-inp Fe-InP substrate 5) selective-area growth of passive core & PD layers QWs p - InP active core n - InP Fe - InP substrate 6) pattern devices laser /SOA/ Eamod. phase shifter QWs p - InP active core n - InP Fe - InP substrate PD InGaAs passive core passive waveguide PD passive core 22.10.2015 16

Putting It All Together To access everything electrically, we metallize all p- and n-contacts and then electro-plate them We also passivate the wafer so we can put metal tracks on it: 22.10.2015 17

Overall Process Flow 27 lithographic masks 1 direct ebeam lithography step 3 epitaxial growth steps Wafer thinning Cleaving Anti-reflection coating Currently 4-5 months overall 22.10.2015 18

Overview Building Blocks Low-loss WG Gain Detectors Shallow Medium Deep 22.10.2015 19

Passive Waveguides < 1 db/cm 150 µm bend radius Can be used for couplers, AWGs, etc. 22.10.2015 20

Polarisation Splitter ER above 25 db for both polarizations 150mW power consumption 2.5 db insertion loss Baier et al., Tu-D3-4, IPRM 2014 22.10.2015 21

SOA Includes Butt-joint loss 500µm long SOA Angled SSC PD Q1.06 WG 22.10.2015 22

Current Injection Phase Sections 250µm 500µm II ππ LL 00. 77 mmmm mmmm 22.10.2015 23

Tunable Grating 22.10.2015 24

Compound BB: 4-Section DBR Grating SOA φ Grating 22.10.2015 25

Conclusions One process to rule them all An ideal starting point to climb mount improbable, i.e. mimic CMOS success Laser / SOA phase shifter passive waveguide PD Functionality Bandgap QWs p - InP active n - InP core passive core Low-loss waveguide Gain ~1100 nm ~1550 nm Fe - InP substrate Detector 1650 nm 22.10.2015 26