Slow light using cavity solitons in semiconductor resonators

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Slow light using cavity solitons in
semiconductor resonators
T. Ackemann, W J Firth, G L Oppo, A J Scroggie
and A M Yao
SUPA and Department of Physics, University of
Strathclyde, UK
willie_at_phys.strath.ac.uk
INLN (Nice) FIRST EXPERIMENT!
acknowledgements FunFACS partners
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All-optical buffers and delay lines

• buffers can enhance performance of networks
• future high-performance photonic networks
  should be all-optical
• need for all-optical buffers with
  controllable delay

Boyd et al., OPN 17(4) 18 (2006)
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"Slow light"
OR Use small transverse component of light
velocity - this talk
Hau et al., Nature 397, 594 (1999)
Boyd et al., OPN 17(4) 18 (2006)
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Writing solitons in a vertical cavity

• writing cavity solitons (CS) stores pulses
  indefinitely ? "stopped light"
• an ideal homogeneous system has
• translational symmetry
• ? ability to choose position in plane at will

• in systems with translational symmetry
  translation is a neutral mode
• no energy is needed for translation
• any odd perturbation (gradient) couples easily
  to neutral mode and causes lateral drift ?
  "slow light"

Saturable absorber model Harkness et al.,
Strathclyde (1998)
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All-optical CS delay line
parameter gradient
inject train of solitons here

• for free serial to parallel conversion and beam
  fanning

• note wont work for non-solitons/diffractive
  beams

Saturable absorber model Harkness et al.,
Strathclyde (1998)
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First experiments in semiconductors
spatio-temporal detection system 6 local
detectors synchronized digital
oscilloscopes Bandwidth about 300 MHz

• 920 µm VCSEL (Ulm Photonics) 200 µm diam pumped
  above transparency but below threshold?
  amplifier
• pump "stripes" for quasi-1D
• gradient along the stripes
• Spontaneous patterns and solitons mostly aligned
  to stripes.
• Home in on "soliton" in red ring.

F. Pedaci, S. Barland, M. Giudici, J. Tredicce,
INLN, Nice, 2006 (unpublished)
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Optical addressing
gate addressing beam with an electro-optical
modulator rise/fall times lt 1 ns
100 ns
F. Pedaci, S. Barland, M. Giudici, J. Tredicce,
INLN, Nice, unpublished
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Velocity in experiment (and theory)

• experiment suggests speed of about 2 µm/ns 2
  km/s (slow-ish!)

• in line with theoretical expectations for VCSEL
  amplifier model

speed

• E field, N carriers. J current, P input.
• ?? response ratio, small, 0.01
• P constant amplitude, but constant phase
  gradient K.

phase gradient K
see also Kheramand et al., Opt. Exp. 11,
3612(2003)
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Comparison to other systems

• slow light in the vicinity of resonances
  electro-magnetically induced transparency, linear
  cavities, photonic crystals interplay of
  useful bandwidth and achievable delay

system speed length delay bandwidth bandwidth times delay
EIT in cold vapor1 6 17 m/s 230 µm 10 µs 300 kHz 2.1
EIT in SC QD1 4 (calc) 1250000 m/s 1 cm 8 ns 10 GHz 81
SC QW (PO, calc) 5 9600 m/s 0.2 µm 0.02 ns 2 GHz 0.04
SBS in fiber3 70500 km/s 2 m 18.6 ns 30-50 MHz gt 1
Raman in fiber2 2 km 0.16 ns 10 GHzgt THz 2 (demonstr.) gt 160 (pot.)
CS (demonstrated) 2000 m/s 25 µm 12 ns 300 MHz 3.6
CS (optimise delay) 2000 m/s 200 µm 100 ns 300 MHz 30
CS (optimise BW) 40000 m/s 200 µm 5 ns 6 GHz 30
1Tucker et al., Electron. Lett. 41, 208 (2005)
2Dahan, OptExp 13, 6234(2005) 3GonsalezHerraez,
APL 87 081113 (2005) 4ChangHasnain Proc IEE
91 1884 (2003) 5Ku et al., Opt Lett 29,
2291(2004) 5Hau et al., Nature 397, 594 (1999)
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Bandwidth and bit rate

• observed velocity 2 µm / ns CS diameter
  typically 10 µm ?
• a local detector would see a signal of length
  10 µm/(2 µm/ns) 5 ns ? bit rate 100 Mbit/s

• limit time constant of medium (carriers) 1 ns ?
  10 µm/ 3 ns 3.3 µm /ns

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How close can cavity solitons be packed?
Space-time plots of E for response ratio
g0.01, phase gradient K0.471with different
time delays between address pulses
time ?
space ?
Simulation of VCSEL cavity soliton buffer with
independent soliton "bits"
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Solitons are pretty robust against gradient
Soliton for K0.471, g0.01 large gradient,
modest distortion and some asymmetry
Soliton for K0.0196, g0.01 small gradient,
little distortion
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Résumé CS-based delay line

• drifting CS are a novel approach to slow light
  with promising features
• potentially very large delays with good figure
  of merit
• lots of things to do
• theory saturation behaviour Auger
  etc. patterning effects
• fabrication homogeneity, built-in gradients
• experiment control gradients, improve
  ignition, larger distances ...
• in a cavity soliton laser1 there are additional
  possibilities

• relaxation oscillations are faster than carrier
  decay time and modulation frequency of modern
  SC lasers is certainly faster (at least 10 Gbit/s)

• possibility of fast spontaneous motion (Rosanov,
  2002)

1 FunFACS project objective