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
ω How to increase the conversion efficiency? 2 Pout(2ω ) L 2 Tightly confining waveguide ∝ Pin(ω ) F Pin( ) 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 λ z higher speed 4 w z lower power w << ⇒ 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