Photonic Crystal Resonatorsand Light Emitters

Yong H. Lee

Department of Physics, KAIST

http://pbg.kaist.ac.kr

Contents

1. Wavelength-size Laser2. Electrical Single-cell Photonic

Crystal Laser3. µ-fiber Coupled Photonic

Crystal Laser4. Summary

Wavelength-size Laser

Strong Photon Confinement in Very Small Volume

2-D Slab Photonic Crystal

The Smallest Laser ?

λ/2

VCSEL 2D PBG Laser

(λ/2n)3

Ultimate Laser- V ~ (λ/2n)3

- High Speed

- High Efficiency

1.00.10.01E-3E-4

Monopole Mode

1. λ-scale

2. Low-loss

3. Nondegenerate

4. Central-zero

H. G. Park, et al., Appl. Phys. Lett. 79, 3032 (2001).

Introduction of Central Post

2rp

central node

A post does not affect Q factor significantly !!!

Q = ωτp

r =0.35a, r’ = 0.25a, a = 540nmt =0.37a, rp= 0.5a, 1.0a

dp

Single-cell Resonator with Post

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

• Highly-doped n-i-p structure: mobility of electron > mobility of hole

dielectric material

p-InP substrate

p-InP post

nip

InGaAsP slab

tip (current injection)

Fabricated e-PBG Resonator

Top view Cross-sectional view

H. G. Park et al., Science, vol. 305, 1444 (2004)

Design of Single-Cell Resonator

- 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

Chirped air-holes

Characteristics of Lasing Mode

Pulse pumping : 6ns / 2.5µsIth ~ 260 µA

Confirmation: The Monopole Mode

Experimental measurements agree well with 3D FDTD computations based on structural data taken directly from the SEM picture.

<CCD near-field image> <Calculated Poynting vector> <Calculated E-intensity>

H. G. Park et al., Science, vol. 305, 1444 (2004)

Spontaneous Emission Factor β

• Record-high β value

• Effective carrier localization by electrical pumping

• Nondegenerate monopole mode

• Small modal volume

β ~0.25

µ-fiber CoupledPhotonic Crystal Laser

Prof. In-Gak Hwang (Chun Nam University)

Curved µ-fiber Coupling

250 µm

1 µmModified PC cavitydesigned for efficient fiber coupling

µ-fiber- D ~1.3 µm - Curvature ~ 1/50 µm-1

Optical I/O

+ better phase matching (along x)-modified linear cavity

+ larger mode overlap (along y)−µ-fiber

original cavity

Ey− 0 +

modifiedcavity

Microfiber

(a = 430 nm, r=0.35)

(a = 500 nm, r=0.35:0.30:0.25)x

y

z

y

Qint ~ Qair = 26000.

λ /neff

Modified Linear PhC Cavity

0 50 100 150 200 250 300

0

5

10

15

Pfib

er1 (

nW)

Peak pump power (µW)

1450 1500 1550 1600

30 dB

Wavelength (nm)

PC Laser with Fiber I/O

Pfiber1

WDMcoupler

Pfiber2

single-mode fiber

980 nmpump

PC laser

All-fiber PC laser- Low threshold of 35 µW- High output power of >10 nW

- Extremely local pumping- Highly efficient out-coupling

Max. Max. ηη estimated to be ~70% estimated to be ~70%

imperfectlyimperfectly--fabricated cavity structurefabricated cavity structure

1 µm

SEM image of real structure

0.0 0.1 0.2 0.3 0.4 9 10 110.0

0.2

0.4

0.6

0.8

1.0 real cavity ideal cavity

Qtotal

air gap(µm)

Cou

plin

g ef

ficie

ncy,

η

1,000

10,000

100,000

Computation, Computation, as fabricatedas fabricated

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 TeamKAIST

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

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

NTT Lab- M. Notomi

Samsung- I. Kim

CEA- J-M Gerard