Professor Benjamin J. EggletonDirector, CUDOS ARC Centre of Excellence Director, Institute of Photonics and Optical Science (IPOS)ARC Federation FellowSchool of Physics, University of Sydneyegg@physics.usyd.edu.au

Outline

• Optical communications 101• Controlling light on the micron scale• Towards the photonic chip• Photonic crystals (semiconductors for light)• Slow light – The key to faster internet

The Semaphore:An Example from History

Electromagnetic spectrum

Light travels well through fibre

• High-refractive index core with low-index background

• Light stays in core by total internal reflection

(b)n n21

θ

θ

θ

θ1

1

1

2

θ1

(a)

8.3 m

125 mμ

μ

cladding

core

was being

All traffic carried on optical fibres worldwide …

Light propagation throughatmosphere

• Light scatters when it travels through the atmosphere

• Range limited to a few kilometers

From: http://www.cablefree.co.uk/

Across a range of communications technologies, 10 Mb/s × km has been the cross-over point to optical technology.

Information capacity within computers

Optical interconnects

Photonic chip – Photonic integrated circuit

Natural

2D Photonic CrystalMicrostructured

Optical Fibre

3DPhotonicCrystal

2D Photonic CrystalPlanar Waveguids

1D Photonic Crystal (Bragg grating and thin film stack)

Photonic crystals

Introduction: Basic parameters

Bragg condition

Ln

Position

Δn

Λ= nB 2λ

At λB and close to it: Bragg reflection due to PBGFurther from λB: dispersion

Bragg reflection occurs for range of wavelengths:

10 cm long grating

Evan

esce

nt

nn // Δ≈Δ λλ

Fiber Bragg gratings are key!

FEATURE TYPICAL MAXIMUMlength Few cm >1 meterperiods 10,000 >1000,000Δn 10-4-10-3 ~0.05

Fringe Pattern from Mask

Diffracted +1 order(~ 40%)

Diffracted +1 order(~ 40%)

UV Laser Source

Single modefiberPhase Mask (SiO2)

• Wide bandwidth and tuning range• All-fiber device• No moving parts• Continuous tuning• Compact size• Low PMD

My product (patented, developed, published, deployed $$$$$$$$$$$$$$$$$$$$$$$$)

Thermally tunable dispersion compensator for 40Gb/soptical transmission systems

1. Breakthrough technology

Ultra-tight confinement

Ultra-dispersion

Δλ = 1% ~ 50°

10μm

Photonic Crystal: Ultra-compact & ultra-control

Ultra-small

2D slab SOI structure fabricated at IBM on a 8-inch CMOS line - "S. McNab and Y.Vlasov, IBM Watson".

Hard to couple light into a PCWG

• Mode shape/size mismatch

• vg / neff mismatch

Coupling light into PCWGand how to probe these structures?

Optical fiber

Photonic crystal microcavityPhotonic crystal waveguide

2D PC slab

Silica optical nanowires

• Spliced Optical fibre tapered using standard flame brushing method (Birks & Lee, Vol. 10 JLT 1992)

• Fibre dimensions reduced by up to 500 timesFibre

Butane flame

Optical fiber nanowires

• Results by L. Tong et al, Nature 426 (12), 816–819 (2003).

• Photonics circuitry• Photonic sensing• Evanescent coupling

Evanescent coupling

Evanescent coupling between tapered fiber and a PCWG or passive resonator

Evanescent coupling to chalcogenide PC waveguides using silica nanowires

a)

b)

c)110 μm

300 μm

90 μm

Silica nanowires

Underwater Optical Fibre Network

Underwater Optical Fibre Network

Merging traffic

What & Why?

• Slow light is …– pulse propagation at velocity << c, or– optical delay comparable to pulse duration

• Fundamental interest– phase velocity (c/n): little control– group velocity (c/ng): enormous control

[e.g. L. V. Hau, Nature (1999): vg = 17 m/s]

• Device applications: – enhance nonlinear effects– optical delay lines / optical buffers

TIME

Slow light:Atomic vs Photonic

• Atomic resonance– “Cycling at the speed of light” in cold atoms– 17 m/s (Hau et al., Nature 1999)

– Narrowband (<MHz)

Slow light in photonic resonance

• Photonic resonance– Bragg grating, photonic crystal– Broadband (>GHz)– Compatible with telecom!

Problem

• Problem:– dispersive broadening– length-limited ⇒ delay-limited

(fractional delay ~ 0.1 to 3)

• Our solution:Balance dispersion with nonlinearity

⇒ Soliton!– here a gap soliton [Winful, Chen and Mills (1980’s)]

– eliminate dispersion to all orders⇒ no length/delay limitation

Fibre Bragg grating (FBG)

• Features of interest are:

1. Transmission bandgapº Bragg wavelength

2. Group velocityº

3. Dispersionº Undesirable

ndB 2=λ

ncvg /0 <<Tr

ansm

issi

ongroup

velocity

2ndλ

Laser wavelength

FBGd

Slow light in linear regime

λ

Tran

smis

sio

n

group

velocity

Launch here

Note: The average refractive index is the same for all z.

How to cancel broadening?

• Gap soliton– launched inside bandgap ⇒ strong reflection– at high intensity I

• Kerr effect

• Near bandedge⇒ Low group velocity

• Dispersion + nonlinearity = soliton⇒ No broadening

Tran

smis

sion

group

velocity

2ndλ

n = n0 + n2I

increase with intensity

Gap soliton (below threshold)

λ

Tran

smis

sio

n

Launch here

Note: The average refractive index is the same for all z.

Gap soliton (above threshold)

λ

Tran

smis

sio

n

Launch here

Note: The average refractive index is the same for all z.

eHealth

eTeaching

Defence applications

Astrophotonics

What have we achieved?

• Funding: 2003-2008, renewed 2008-2010• 12 Chief Investigators, 50 researchers, 50 students, >20 international partners• Fundamental science, Strong collaboration, Major international programs, Strong

IP, End-user engagement and commercialization path, Outreach, E&T etc

NSW, February 2008

World leading research!