Slow light in photonic crystal waveguides
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Transcript of Slow light in photonic crystal waveguides
Slow light in photonic crystal waveguides
Nikolay Primerov
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
• Why do we need slow light?• What is slow light?• Possibilities to make a slow light• Slow light in photonic crystals waveguides• Conclusions
Outline
Nikolay Primerov
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
1. Nonlinearities2. Optical switching 3. Optical storage4. Delay lines5. Quantum optics
T.F. Krauss, J. Phys. D: Appl. Phys. 40 (2007) 2666-2670Z. Zhu et al., Science, 318 (2007) 748-750F. Morichetti et al., Opt. Express, 16 (2008) 8395-8405
Nikolay Primerov
Why do we need slow light?
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
What is a slow light?
Nikolay Primerov
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
=++++
( , ) ej k z tS z t A
Pulse signal
Nikolay Primerov
What is a slow light?
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
d d n z td d c
The peak of the pulse propagates at the Group Velocity.
1 0dnn z tc d
or 0 g
z tV
( , ) ej k z tS z t A
Pulse signal
Nikolay Primerov
What is a slow light?
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
gdnn nd
1
gg
dk cVdw n
Thus, in a material and/or structure with large first order dispersion coefficient, Vg can be drastically increased
Nikolay Primerov
Group index
Group velocityWhat is a slow light?
Doctoral program in photonics “Photonic crystals” by Romuald Houdré
Possibilities to make a slow light
Stimulated Brillouin Scattering (SBS)Stimulated Raman Scattering (SRS)Electromagneticaly induced transparency (EIT)Coherent population oscillation (CPO)Coupled ring resonatorsPhotonic crystals and others
Nikolay Primerov
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Periodically structured medium
Free space
Medium with constant n
k
ω
c= ω/k
c/n= ω/k
wVk
gdwVdk
k
ω
π/a
0gdwVdk
Band edge
Band gap
Slow light: Science and application / editors, J.B. Khurgin and R. Tucker, 388 p.
Slow light in photonic crystal waveguides
g
VS
V
2g
g g
d c cVdk n n a
Slow down factor Maximum bandwidth
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Slow light in photonic crystal waveguides
1)BackscatteringStanding wave Slow mode optical mode is close to a resonance with the structure
2) Omnidirectional reflectionNo cut-off angle, mode at k≈0 slow modes of for k=0 standing wave
T. F. Krauss, J. Phys. D: Appl. Phys. 40 (2007) 2666-2670
The band edge is the most obvious place for the slow light
Slow light in photonic crystal waveguides
But there are some problems:
1) Dispersion curve near the gand edge is typically parabolic strong group velocity dispersion (GVD)
2) Band edge presents a cut off point propagation mode turns to evanescence mode
3) Fabrication tolerance
It’s not the best region for the slow light to operate
Dispersion engineering
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
J.Li, T.P. White, et al. Opt. Express, 16(9) (2008), 6227-6232
Slow light in photonic crystal waveguides
Section of constant group velocity over approximately 20% of Brillouin zone low GVD
Ng= 30, 50, 80
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
GVD handling
Slow light in photonic crystal waveguides
Enhancement of the linear interaction
Δφ=ΔkL=π
Optical switching devices (for example, Mach-Zehnder configuration)
Δk= Δnk0
We have to distinguish between nmat and neff
Slow light regime Δk1 > fast light regime Δk2
T. F. Krauss, J. Phys. D: Appl. Phys. 40 (2007), 2666-2670D. M Beggs, et al., Opt. Lett., 33 (2008), 147-149
0 matg
VkL k n L
V
Slow light regime yields a large Δk for a given Δnmat
Slow light coupler 5 um length with Δnmat = 4×10^-3. Conventinal coupler 200 um long
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Problems to overcome1) Signal distortion by GVD2) Reflection losses due to modal mismatch between incident wave and guided wave3) Losses due to disordering in the structure4) Other loss sources5) Tunability
Solutions:
1. Chirping the waveguide properties, changing the waveguide width, changing the hole size and position of the photonic lattice close to the waveguide.
2-4. Many different effects involved. Need of transition region to build up to reduce the mode-matching problem Slow light operation away from the band-edge
5. ??
Conclusions
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Conclusions
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Main Advantages:- Relatively large bandwidth from GHz up to few THz- Room temperature operation- Availability to tune the wavelength, slowdown factor and bandwidth with the structural design
Main Disadvantages:- Tunability of the slowdown factor in given structure- Reflection and injection losses
Doctoral program in photonics “Photonic crystals” by Romuald Houdré Nikolay Primerov
Thank you for attention!