Post on 03-Sep-2020
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!