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
z
z
Waveguide architecture with butt coupled fibers and
edge emitting lasers
Hybrid bonding (non-monolithic) of different structures
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 20-40 quarter wavelength
different index layers (~70 nm)
z One-dimensional photonic crystal
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
z Single
longitudinal mode emission,
independent of temperature and
current injection
z Circular beam pattern
z Vertical emission--2-D array
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
90° bends and splitters can be designed with 100% transmission from
microwave to optical frequencies
z
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
higher speed and lower power
smaller devices,
z Many
opportunities in nanophotonics for enhanced
and new devices
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
JSH 8
Integrated Optoelectronics
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 subwavelength 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
Photonic Crystal Passive elements
z Optoelectronics
z waveguides
z Optics
z
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
z
resonators
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?
Pout ( 2ω )
Pin (ω )
F =Q
Waveguide
λ
L2
∝ Pin (ω ) F 2
A
A
Tightly confining waveguide
L
L
High-Finesse (F) cavity, resonant at
the fundamental frequency, increases
the circulating power
High-F cavity can be realized in
tightly confining waveguides using
photonic bandgap crystal (PBG)
structures
PBG mirror
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
Cavity design Length ~ 200 µm
Finesse ~ 60
Î enhancement of a factor ~400
Achievable internal conversion
efficiency~ 4000 % / W (comparable to
current 5-cm-long state-of-the-art
PPLN waveguides)
JSH 11
Second Harmonic Generation
Pout (2ω) / Pout (ω)2
Internal Conversion efficiency [1/W]
AlOx AlAs converted layer
GaAs Substrate
Sample length
= 550 µm
AlOx AlAs conversion critical
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.
Suspended Si waveguide on SOI
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
Waveguide
Resonator
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
 w
w << λ ⇒ PT ∝  
λ
C-aperture
4
Laser
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
Sub-wavelength (0.01 λ2) Cshaped gold apertures
z Reduced device area
z lower capacitance
z higher speed
z lower power
z
Detector
JSH 15
Integrated Photonic Crystal
Resonant Filter Sensor
Water out
Water solution
above sensor
SiNx layer with PC
Water in
Thin bio-sensor layer
SiO2
Light from VCSEL
1.0
Integrated VCSEL/Detector
reflected intensity
Reflection
0.8
0.6
0.4
0.2
Peak width [FWHM]
at 850 nm = 2.7 nm Q= 314
at 841.3 nm = 0.8 nm Q= 1078
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
0.0
820 830 840 850 860 870 880
Wavelength (nm)
JSH 16
New Wave of Chip
Scale Technologies
Operating Speed
Sub λ Diffraction Limit
THz
Plasmonics
Photonic Crystals
Photonics
RC Delay
Limit
GHz
MHz
Electronics
The Past
kHz
1 nm
10 nm
100 nm
1 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,
z Control
z
highly functional components
and separate optical modes
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
z Integrated
structures
quantum information processing?
U.S.-Korea Forum on Nanotechnology-Korea-4/3/06
JSH 18