1. WP 3: Applications of Cavity Soliton Lasers
WP managers: T. Ackemann1, R. Jäger2
1Department of Physics, University of Strathclyde, Glasgow, Scotland, UK
2ULM Photonics, Lise-Meitner-Str. 13, Ulm, Germany
Industrial Advisers Annual Meeting

2. Motivation Task 2: High frequency carrier pulses trains on demand
Task 1: All-optical delay line
Task 2: High frequency carrier pulses trains on demand
What is the best „bang“ you get from a cavity soliton ?
Enabling conceptional new approaches
Impact !

3. Cavity solitons versus „pixels“
broad-area laser with CS
array of micro-fabricated bistable elements
bistable
memory
switch
 translational degree of freedom easily excited
discrete
continuous
self-luminous
2D displays; memory or pattern recognition systems; massively parallel and reconfigurable all-optical packet
switching and routing schemes; optical delay lines; shift registers and beam fanning. To all these schemes
one can add the possibility of high-frequency self-pulsing in the case of a pulsed CSL.
control position and motion by small external perturbations
reconfigurable  „plasticity“
in particular: gradients  drift

4. All-optical delay line
parameter gradient
read out at other side
inject train of solitons here
time delayed version of input train
all-optical delay line
buffer register
completely different approach to
slow light
for free: serial to parallel conversion and beam fanning
note: won‘t work for non-solitons / diffractive beams
G. Harkness 1998 (USTRAT)

5. Experimental realization
sodium vapor driven in vicinity of D1-line with single feedback mirror B Na
adressing beam
holding beam
AOM
tilt of mirror
 soliton drifts
t = 0 ms
t = 80 ms
t = 64 ms
t = 48 ms
t = 32 ms
t = 16 ms
ignition of soliton by addressing beam
proof of principle, quite slow, but in a semiconductor microresonator this is different !
Schäpers et. al., PRL 85, 748 (2000), Proc. SPIE 4271, 130 (2001); AG Lange, WWU Münster

6. Status in semiconductor microresonators
driven VCSEL
(vertical-cavity regenerative amplifier)
add additional broad-area holding beam at an angle  fringes 
change angle  fringes move and change periodicity
demonstrates clearly that CS react on external perturbations
dragged along if period  soliton width
strong influence of small-scale inhomogeneities
X. Hachair, S. Barland, M. Giudici, J. Tredicce, INLN, unpublished

7. Drifting !? good news: it drifts !
small-scale irregularities  CS do not exist at all positions
ignite CS at unfavorable position  it moves away
CS can be dragged back to initial by addressing beam  steering
good news: it drifts !
however uncontrolled and not very far
steering of CS  soliton force microscope technique
18 µm in 38 ns  470 m/s = 1700 km/h
map relative – possibly absolute – gradients in transverse plane by measuring the displacement between CS and a (small-amplitude) steering beam
X. Hachair et al., PRA 69 (2004) (INLN, INFM)

8. probably related to speed of medium response
Drift velocity
but: plenty of room at the top
limits ?
probably related to speed of medium response
unit velocity 5103 µm/ns
(k=300109/s, l=1 µm, n=3.5)
velocity of CS: 5 µm/ns = 5000 m/s
assume diameter of CS of 10 µm
transit time 2 ns
some 100 Mbit/s
strength of gradient
Maggipinto et al., Phys. Rev. E 62, 8726, 2000 (USTRAT and INFM Bari)

9. „Slow media“: Non-instantaneous Kerr cavity
g  0.01  semiconductor
velocity determined by response time of medium
saturation for instantaneous medium 
faster medium will speed up response !
limits for increasing gradients need to be accessed by numerical simulation
log (velocity / gradiant)
slope 1
log (g)
A. Scroggie, USTRAT, unpublished
(1D, perturbation analysis)

10. Pinning of drift motion
motion of CS might be affected
– in extreme case pinned –
by modulations or localized inhomogenities
study motion of CS on
noisy backgrounds
position along device 
dashed line: perturbation
solid line: speed of CS
soliton averages over scales < CS width
A. Scroggie, unpublished (USTRAT)

11. Work plan
Year 1:
experiment: driven VCSELs below threshold new devices with increased homogeneity of cavity resonance soliton force microscopy techniques  map inhomogeneities by dragging soliton around
theory: investigate principal limits in model systems analyze concrete experimental situation inverse problem for soliton force microscopy
Year 2:
optimization of device and delay line homogeneity, determination of characteristics, investigation of capacity and speed limits
theoretical analysis of delay line based on CSL emerging from WP1, especially on the possibility of using spontaneously drifting laser CS
Year 3:
experimental study of characteristics of laser CS based delay line supported by theoretical analysis and device improvements by material groups

12. Task 2:High-frequency carrier pulses trains on demand
pulse trains with a high repetition rate are needed in optical communications
time-division multiplexing (TDM)
demultiplexing
regeneration
routing
self-pulsing CSL, ideally a mode-locked CSL
array of self-pulsing laser sources  carrier pulse trains with high repetition rate in a large number of output channels
all-optical control  „high-frequency carrier pulse train on demand“
e.g. Stubkjaer, IEEE Sel. Top. QE 6, 1428 (2000)

13. Anticipated scheme control beams de-multiplexing optical regeneration
routing
time scales  packet manipulation
advanced schemes might use plasticity of CLB  processing, direct routing
self-pulsing
CSL

14. Work plan Year 2 (starting around month 18):
theoretical analysis of switching procedures for self-pulsing CSL in simple models how to control: coherent or incoherent switching, amplitude, duration, timing
adaptation and improvement of high-frequency detection schemes and of short pulse lasers for addressing beams
decision which pulsed CSL from WP2 is pursued
Year 3:
study of switching characteristics of self-pulsing CS in close collaboration and iteration between theory, experiment and fabrication
aim: at least two channels

15. Summary Task 1: All-optical delay line
immediate start (actually ongoing)
depends heavily on device quality
side benefit: lots of information on device homogeneity (soliton force microscope)
conceptionally very different approach to slow light
Task 2: High-frequency carrier pulses trains on demand
relies on success of WP2
achievable degree of control unclear
potentially very rewarding

16. 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
EIT in cold vapor1 6
17 m/s
230 µm
~ 10 µs
300 kHz
2.1
EIT in SC QD1 4 (calc)
m/s
1 cm
8 ns
10 GHz 81
SC QW (PO) 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
> 1
Raman in fiber2
2 km
0.16 ns
> tens of GHz
> 8
CS (calc,
more ambitious)
10000 m/s
250 µm
25 ns
5 GHz
125
CS (calc, conservative)
5000 m/s
100 µm
20 ns
0.25 GHz 5
1Tucker et al., Electron. Lett. 41, 208 (2005); 2Dahan, OptExp 13, 6234(2005); 3GonsalezHerraez, APL (2005); 4ChangHasnain Proc IEE
(2003); 5Ku et al., Opt Lett 29, 2291(2004); 5Hau et al., Nature 397, 594 (1999)

17. Transition between locking and drift
example:
single-mirror feedback system with Na as nonlinear medium
locking of hexagonal patterns
(not solitons !)
at large-scale envelope
produced by pump profile
transition discontinous
possibly we are close in semiconductors !?
Seipenbusch et. al., PRA 56, R4401 (1997); AG Lange, WWU Münster

18. Relevance of modulated backgrounds
a) advantageous
improve accuracy and robustness of optical memories
in general modulations of the pump or the refractive index can be used
It is generally believed that cavity solitons get stuck at the maxima of the background modulation.
b) limiting
provides pinning mechanism for drifting CS

19. CS in reverse gear
We have predicted and measured the CS-velocity v(K) induced by the phase modulation when changing its wave-vector K for fixed m
v(K)
REVERSED MOTION K
Reversed motion
In these points CS are stationary EVERYWHERE in spite of background modulations K E
A. Scroggie et al., Phys. Rev. E 71, (2005)

20. Application: pixel array
solution: pinning of spatial solitons due to intentionally introduced inhomogeneities,
e.g. periodic phase (and amplitude) modulations
(Firth + Scroggie, PRL 76 (1996) 1623; Spinelli et al., PRA 58 (1998) 2542)
‘optical’ pinning reconfigurable  advantage compared to micromachined pixels
introduce square aperture in input beam  diffractive ripples 
input beam
pinning of positions of LS by amplitude modulations
 defined positions, diffusive movement due to noise suppressed
 pixel array,
however not all cells are bistable at the same time (residual inhomogeneities)
Schäpers et. al., PRL 85, 748 (2000), Proc. SPIE 4271, 130 (2001); AG Lange, WWU Münster