The role of Nanostructures in Integrated Photonics James S. Harris Department of Electrical Engineering Stanford University 3rd U.S.-Korea Forum on Nanotechnology Seoul, Korea April 3 & 4, 2006 U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 1 1993 Photonic Integrated Circuit Soref, Proc. IEEE, 1687 (1993) z Waveguide architecture with butt coupled fibers and edge emitting lasers z Hybrid bonding (non-monolithic) of different structures z Mostly III-V devices, very little electronics U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 2 First Photonic Crystal Device DBR (Distributed Bragg Reflector z Single longitudinal mode emission, z 20-40 quarter wavelength independent of temperature and current injection different index layers (~70 nm) z Circular beam pattern z One-dimensional photonic crystal z Vertical emission--2-D array U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 3 Dimensional Mismatch Between Optics and Electronics U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 4 Unique Photonic Crystal Functionality Electric Field Strength U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 5 Nanoscale Plasmonic Waveguides z 90° bends and splitters can be designed with 100% transmission from microwave to optical frequencies z Provides bridge between dimensions of electronics and photonics z Provides design flexibility for optoelectronic ICs U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 6 A New Si-Based Optical Modulator Quantum-confined Stark effect (QCSE) z Strongest high-speed optical modulation mechanism z Used today for high-speed, low power telecommunications optical modulators but in III-V semiconductors z QCSE in germanium quantum wells on silicon substrates z Fully compatible with CMOS fabrication z Surprises z works in “indirect gap” semiconductor actually better than in III-V z higher speed (100 GHz) possible Y. H. Kuo, Y. Lee, Y. Ge, S. Ren, J. E. Roth, T. I. Kamins, D. A. B. Miller & J. S. Harris, Nature 437, 1334 (2005) U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 7 Integrated Optoelectronics on Si Platform Looks Feasible z Silicon waveguides and integration with CMOS process now demonstrated z Germanium-based detectors viable and integrable with CMOS z Working modulators in silicon z carrier density index change modulators z Quantum-confined Stark effect in Ge quantum wells on silicon demonstrated z much stronger absorption mechanism smaller devices, higher speed and lower power z Many opportunities in nanophotonics for enhanced and new devices U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 8 Integrated Optoelectronics z Mostly Electronics, many “optical” functions done electronically--transistors are FREE (< 1µ¢ ea) z Multi-layered nanometer deposition of compatible compatible high index of refraction materials z Si on Oxide (SOI) CMOS Electronics z GaAs/AlAs(AlOx) z Dielectric, semiconductor, and metal lithographic fabrication at deeply sub- wavelength scales z Silicon CMOS compatible processes z Excellent quantum optoelectronic phenomena demonstrated in Si based devices z Ge quantum wells on silicon z A platform, based on CMOS technology z Electronics z Optoelectronics Photonic Crystal Passive elements z Optics z waveguides z resonators U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 9 Quantum Dot Microdisk Laser A ZERO threshold laser possible? U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 10 Nonlinear Optical Processes How to increase the conversion efficiency? 2 Pout(2ω ) L 2 Tightly confining waveguide ∝ Pin(ω ) F Pin(ω ) A High-Finesse (F) cavity, resonant at the fundamental frequency, increases L λ the circulating power F = Q A L High-F cavity can be realized in tightly confining waveguides using photonic bandgap crystal (PBG) structures Cavity design Length ~ 200 µm Finesse ~ 60 Waveguide PBG mirror Î enhancement of a factor ~400 Achievable internal conversion efficiency~ 4000 % / W (comparable to current 5-cm-long state-of-the-art PPLN waveguides) U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 11 Second Harmonic Generation 2 Pout (2ω) / Pout (ω) Internal Conversion efficiency [1/W] AlOx AlAs converted layer GaAs Substrate Sample length AlOx AlAs conversion critical = 550 µm processing technology and unique to GaAs based systems Æefficiency limited by SH loss Å U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 12 Stopping Light All-Optically Resonator Light pulses can be stopped and stored coherently using a system of coupled waveguide and high-Q cavities. Waveguide Suspended Si waveguide on SOI Resonator U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 13 Photonic Crystal Add/Drop Filter Two resonant modes with even and odd symmetry. • Modes must be degenerate. • Must have the same decay rate. U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 14 Nanometallic Enhancement of Photodiodes and Lasers In a conventional aperture C-aperture z Sub-wavelength (0.01 λ2) C- shaped gold apertures z Reduced device area z lower capacitance z higher speed 4 w z lower power w <<λ ⇒ PT ∝ λ Laser Detector U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 15 Integrated Photonic Crystal Resonant Filter Sensor Water out Water solution Water in above sensor SiNx layer with PC Thin bio-sensor layer SiO2 Light from VCSEL reflected intensity 1.0 Integrated VCSEL/Detector 0.8 0.6 0.4 Reflection 0.2 Peak width [FWHM] 0.0 at 850 nm = 2.7 nm Q= 314 820 830 840 850 860 870 880 at 841.3 nm = 0.8 nm Q= 1078 Wavelength (nm) U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 16 New Wave of Chip Scale Technologies Sub λ Diffraction Limit Plasmonics THz Photonics Photonic Crystals RC Delay Limit GHz Operating Speed MHz Electronics The Past kHz 1 nm 10 nm100 nm1 µm 10 µm 100 µm 1 mm Critical Device Dimension U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 17 Opportunities for Nanophotonics z Compact, highly functional components z Control and separate optical modes z Wavelength and space z Deep sub-wavelength field concentration z very small photodetectors with high efficiency z match optical wave and electronic device sizes z Very high Q/V cavities z enhance emission, optical nonlinear response z Slow light z Negative refractive index z metal-dielectric-metal structures z Integrated quantum information processing? U.S.-Korea Forum on Nanotechnology-Korea-4/3/06 JSH 18.