Photonic Crystal Resonators
and Light Emitters
Yong H. Lee
Department of Physics, KAIST
http://pbg.kaist.ac.kr
Contents
1. Wavelength-size Laser
2. Electrical Single-cell Photonic
Crystal Laser
3. µ-fiber Coupled Photonic
Crystal Laser
4. Summary
Wavelength-size Laser
Strong Photon Confinement in Very Small Volume
Æ 2-D Slab Photonic Crystal
The Smallest Laser ?
λ/2
VCSEL
2D PBG Laser
Ultimate Laser
- V ~ (λ/2n)3
(λ/2n)3
- High Speed
- High Efficiency
Monopole Mode
H. G. Park, et al., Appl. Phys.
Lett. 79, 3032 (2001).
1. λ-scale
2. Low-loss
E-4
E-3 0.01
0.1
1.0
3. Nondegenerate
4. Central-zero
Introduction of Central Post
central node
Q = ωτp
2rp
A post does not affect Q factor significantly !!!
Single-cell Resonator with Post
r =0.35a, r’ = 0.25a, a = 540nm
t =0.37a, rp= 0.5a, 1.0a
dp
Experiments:
Single-cell Cavity with Central Post
•
Optical pumping
@ ~1% duty cycle
•
Quadrupole mode
Electrically-driven
Photonic Crystal Laser
Dr. Hong-Gyu Park (Harvard)
Current Injection Scheme
tip
(current injection)
n
i InGaAsP slab
p
dielectric material
p-InP post
p-InP substrate
•
Highly-doped n-i-p structure:
mobility of electron > mobility of hole
Fabricated e-PBG Resonator
Top view
Cross-sectional view
H. G. Park et al., Science, vol. 305, 1444 (2004)
Design of Single-Cell Resonator
Chirped air-holes
- Control of position and size of
the post in wet etching processes
(locating the post at the center)
- Increase of Q factor
r = 0.28a, 0.35a, 0.385a, 0.40a, 0.41a
a = 500 nm
Characteristics of Lasing Mode
Ith ~ 260 µA
Pulse pumping : 6ns / 2.5µs
Confirmation: The Monopole Mode
<CCD near-field image> <Calculated Poynting vector>
<Calculated E-intensity>
Experimental measurements agree well with 3D FDTD computations based
on structural data taken directly from the SEM picture.
H. G. Park et al., Science, vol. 305, 1444 (2004)
Spontaneous Emission Factor β
• Record-high β value
β ~0.25
•
•
•
Effective carrier localization
by electrical pumping
Nondegenerate monopole
mode
Small modal volume
µ-fiber Coupled
Photonic Crystal Laser
Prof. In-Gak Hwang (Chun Nam University)
Curved µ-fiber Coupling
Optical I/O
µ-fiber
- D ~1.3 µm
- Curvature ~ 1/50 µm-1
250 µm
Modified PC cavity
Æ designed for efficient fiber coupling
1 µm
Modified Linear PhC Cavity
(a = 430 nm, r=0.35)
original
cavity
+ better phase matching (along x)
-modified linear cavity
+ larger mode overlap (along y)
−µ-fiber
Micro
fiber
λ /neff
Qint ~ Qair = 26000.
modified
cavity
y
y
x
(a = 500 nm, r=0.35:0.30:0.25)
z
−
0
Ey
+
PC Laser with Fiber I/O
WDM
coupler
980 nm
pump
Pfiber1
Pfiber2
single-mode
fiber
PC laser
Pfiber1 (nW)
15
All-fiber PC laser
- Low threshold of 35 µW
- High output power of >10 nW
10
30 dB
5
1450
1500
1550
1600
Wavelength (nm)
0
0
50
100
150
200
Peak pump power (µW)
250
300
- Extremely local pumping
- Highly efficient out-coupling
Computation, as fabricated
100,000
real cavity
ideal cavity
0.8
10,000
0.6
Qtotal
Coupling efficiency, η
1.0
0.4
1,000
0.2
0.0
1 µm
SEM image of real structure
0.0
0.1
0.2
0.3
0.4
air gap(µm)
Max. η estimated to be ~70%
Æ imperfectly-fabricated cavity structure
9
10
11
To Close
Toward the Ultimate Photon Source
– (λ/n)3, High-Q Resonator (Q/V)
– QD Active Material
– Photon Out-coupling
– Reliable Current Injection Scheme
– Strong Coupling Regime / Cavity QED
– On-demand Single Photon Gun ?
For more information, visit, http://pbg.kaist.ac.kr
The Team
KAIST
http://pbg.kaist.ac.kr
–
–
–
–
–
–
–
–
–
–
I. K. Hwang
H. G. Park (Harvard)
S. H. Kwon
K. H. Kim
S. H. Kim
S. K. Kim
J. K. Yang
H. J. Chang
M. K. Seo
F. Huyssen
ETRI
- J. S. Kim
- S. B. Kim
NTT Lab
- M. Notomi
Samsung
- I. Kim
CEA
- J-M Gerard
Financial Supporters:
1.
National Research Laboratory Project, Korea
2.
National R&D Project for Nano Science and Technology, Korea
3.
AOARD-05-4-69, USA