Assembly of Mechanically Compliant Interfaces between Optical Fibers and Nanophotonic Chips T. Barwicz, Y. Taira, H. Numata, N. Boyer, S. Harel, S. Kamlapurkar, S. Takenobu, S. Laflamme, S. Engelmann, Y. Vlasov, and P. Fortier Add Company Logo Here IEEE 64 th ECTC Orlando, FL, USA May 27 30, 2014
Background Silicon nanophotonics High bandwidth High density Volume manufacturing = low cost Challenge - external fiber interface Mode conversion Tight alignment (< 2 um) High cost Optical fibers Silicon photonic chip Typical approach: vertical grating coupler Active alignment = high cost Diffractive optics = low bandwidth High rigidity = chip-package interaction concerns 2
Compliant interface: concept Mechanically compliant extension with integrated polymer waveguides Standard fiber interface Adiabatic optical coupling Nanophotonic die Standard self-aligned fiber interface Integrated, flexible polymer waveguides High-speed, self-aligned assembly to chip 3
Compliant interface: section of chip interface Polymer ribbon Si chip Polymer waveguides Si waveguides Cross-sectional schematic of ribbon to chip interface Alignment ridge Alignment groove 4
Compliant interface: implementation here Lithographically defined polymer waveguides assembled to a molded ferrule Ferrule lid Mechanically compliant extension Polymer ribbon with waveguides Standard fiber interface Ferrule for interfacing to fibers Nanophotonic die Coupling region Die with nanophotonic circuits 5
Compliant interface: flex to ferrule assembly Polymer ribbon MT pin hole Ferrule Polymer ribbon Ferrule lid - Dispense adhesive - Place ribbon in ferrule - Apply pressure - UV cure adhesive MT based parallel fiber interface Self-alignment structures for high-speed machine assembly - Place lid - Cure lid adhesive - Angle polish fiber interface 6
Compliant interface: flex to ferrule accuracy Accurate fabrication + self-aligned assembly = 1-2 um placement accuracy 200.8 µm (200 µm) 199.5 µm (200 µm) Ferrule lid Polymer ribbon backing 20.5 µm (20 +1/-3 µm) 101.1 µm (100 +/-2 µm) 250.0 µm (250 µm) Polymer waveguides Ferrule 250.0 µm (250 µm) Selfalignment structure 101.1 µm (100+/-2 µm) 7
Compliant interface: flex to chip assembly Pick and place self alignment at compression UV cure adhesive Top view of flex to chip assembly Nanophotonic die Mechanical self-alignment guides Twelve-waveguide interface Polymer ribbon with waveguides 8
Compliant interface: flex to chip assembly Self-alignment structure Polymer ribbon backing Polymer ribbon Adiabatic coupling structure Lamination glue Polymer waveguide core Optical epoxy Polymer alignment ridge UV epoxy Si wafer Si alignment groove 20 um Burried oxide Si wafer Si nanophotonic waveguide Si CMP fill 5 um 9
Compliant interface: alignment accuracy readout Measure polymer waveguide to nanophotonic waveguide alignment: cross-sections and alignment accuracy readout structures Edges of polymer waveguide Alignment readout marks 4 um Si nanophotonic waveguide Si CMP fill 10
Compliant interface: self-alignment performance Starting misalignment: -10 to +10 um Resulting misalignment: ~1 um (typical), < 2 um (always) Brut data Measurement positions circled Resulting misalignment (um) 8 6 4 2 0-2 -4-6 top left top right bottom left bottom right All assemblies in allowed range -8-10 -5 0 5 10 Purposefully induced misalignment (um) 11
Compliant interface: self-alignment angle Decomposing residual misalignment into angular and lateral components see correlation between initial and final lateral misalignment Structure inaccuracy Angle (degree) 0.02 0.01 0-0.01-0.02-0.03-0.04-0.05 Angle of rotation -10-5 0 5 10 Purposefully induced misalignment (um) Resulting misalignment (um) 1.5 1 0.5 0-0.5-1 -1.5 Misalignment after subtraction of rotation 2-2 top left top right bottom left bottom right -10-5 0 5 10 Purposefully induced misalignment (um) Correlation via deformation of polymer alignment ridge 12
Conclusion What has been achieved: Self-aligned assembly of ribbon to ferrule Self-aligned assembly to silicon photonic chip Demonstrated feasibility of single-mode optics assembly in high speed microelectronics tools Single-mode optics requires < 2 um alignment Demonstrated self-alignment to 1-2 um from +/- 10 um purposeful misalignment Limit of re-alignment set by structure accuracy +/- 0.5 um for ribbon to Si alignment +/- 1.5 um for ribbon to ferrule alignment 13
Team and acknowledgments IBM Watson, NY USA Interface design, Si fabrication IBM Research - Tokyo Ribbon to ferrule assembly IBM Bromont C2MI Ribbon to Si assembly Outside partners Shotaro Takenobu Polymer waveguide fabrication Masato Shiino Ferrule fabrication Supported by 14