Waveguide-Integrated Optical Antenna nanoleds for On-Chip Communication Michael Eggleston, Kevin Messer, Seth Fortuna, Eli Yablonovitch, Ming C. Wu Department of Electrical Engineering and Computer Sciences University of California Berkeley Eggleston 1
Power Consumption in Modern CPUs 50% - 80% of CPU power dissipation is in wire interconnects Energy Required to charge a wire ~CV 2 Minimum energy to send one bit across a chip: Intel s 45nm Process Interconnect Layers (Source: Intel) CV 2 2 pf cm 1cm 1V 2 = 2pJ Concept Drawing of 3D Integrated Processor with Optical Interconnects (Source: IBM) 17 photons @ 0.8eV/photon = 2aJ Eggleston 2
Optical Source for Energy-Efficiency Interconnect Semiconductor Laser: Ecessive energy consumption due to bias current e.g., for lasers with 1µA threshold, and bias at 5 threshold, E ~ 400 aj/bit at 10Gbps Optical antenna-enhanced nanoled: No bias current Optical antenna enhance bandwidth by up to 1000 (10 to 100 Gbps possible) Energy consumption ~2 photon energy Semiconductor Emitter Semiconductor Emitter Eggleston 3
Arch-Dipole Antenna Based nanoled Optical Antenna LC matching circuit Gold Epected Enhancement: Gap Spacing (d) = 35nm Length (L) = 400nm τ o τ = 1 4 L d 2 33 Antenna Arms Free-Standing Structure TiO 2 Eggleston, et. al, IEEE 23 rd ISLC (2012). Optical Emission Spectra 2000 1500 Antenna Bare Ridge Counts 1000 35 Antenna Coupled Eggleston 4 500 0 1200 Bare 1300 1400 1500 Wavelength (nm) 1600 150nm
Energy Density (db) InP Waveguide Design Arch-Dipole on InP Substrate Arch-Antenna n = 1 Arch Antenna 0-3.5% InP y n = 3.1-20- Radiated Power 96.5% Arch-Dipole on InP Waveguide n = 1.56 y n = 1 InP Waveguide 14% 57% Radiated Power 14% 15% Eggleston 5
InP Waveguide Design Thicker InP Substrate y n = 1.56 n = 1 InP Waveguide 24.5% 38% Radiated Power 24.5% 13% Yagi-Uda Structure y n = 1.56 n = 1 InP Waveguide 15% 22% Radiated Power 50% 13% Eggleston 6
Waveguide Fabrication Ridge Arch-Antenna n = 1.56 InP InGaAs Etch Stop InP Substrate Wet-etch InP Waveguide InP InGaAs Etch Stop InP Substrate Etch ridge and deposit antenna n = 1 InP InP Bond to carrier wafer and remove substrate Hardmask Arch-Antenna Ridge 200nm InP Waveguide 150nm Eggleston 7 InP Waveguide
Optical Emission Measurements Optical emission is collected with a front-side 0.8NA objective and imaged on a LN-cooled CCD. 100 NA 0.8 Linear InGaAs CCD Waveguide- Coupled Antennas Sample probed with a 720nm Ti:Sapphire fspulsed laser from the back-side. 100 NA 0.8 250nm fs-laser Probe InP Waveguide Eggleston 8
Eggleston 9 Total Light Emitted From Waveguide Coupled nanoled Bare Ridge Antenna Coupled 100nm Yagi-Uda Coupled Counts 7000 6000 5000 4000 3000 2000 1000 Bare 12 Antenna Yagi-Uda 1100 0 1200 1300 1400 1500 Wavelength (nm) Epected Enhancement: Gap (d) = 40nm, Length (L) = 300nm τ o τ = 1 2 L 14 4 d
Counts 30000 Optical Emission Spatial Map Bare Ridge 15000 0 10sec Integration η coupling 50% Antenna Coupled 30000 15000 η coupling 50% 100nm 0 Yagi-Uda Coupled 30000 η coupling 70% 15000 Front Back = 1.6 1 Eggleston 10 Backward-coupled Light 0-30 -20-10 0 10 20 30 Distance Along Waveguide(um) Uncoupled Light 50um *3:1 with narrower waveguides Forward-coupled Light
Integration with Silicon Photonics Epitaial Lift-off is used to transfer III-V chips to Silicon substrates III/V Epi Layer Carrier III/V Epi Layer Carrier III/V Epi Layer InP Substrate Grow an epitaial film on InP InP Substrate Bond chip to temporary carrier Remove InP Substrate InP/ Epitaial Layer 100nm III/V Epi Layer Silicon Eggleston 11 Al 2 O 3 Silicon Cross-sectional SEM Transfer Epi to Silicon and remove Carrier
Silicon Photonics with Active III/V Material Silicon wafers and Silicon processing technology can be used to make large-area photonics chips with active III/V Matieral Al 2 O 3 InP Silicon 1mm Top View SEM of Fabricated III/V on Silicon Waveguides 500nm Perspecive SEM of III/V on a Silicon Waveguide Eggleston 12
Summary Demonstrated a nanoled with enhanced spontaneous emission coupled to a multi-mode InP Waveguide 70% Coupling Efficiency 50% Forward coupling Directional emission of 3:1 Future Work Integrate nanoled with single mode waveguide on Silicon Photonics platform Eggleston 13
Acknowledgements Financial support from: NSF Science and Technology Center for Energy Efficient Electronics Science (E 3 S) AFOSR Support from BSAC and the Berkeley Marvell Nanolab Eggleston 14