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Nonlinear interaction of ultrashort laser pulses in photonic crystal fibers

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Title: Nonlinear interaction of ultrashort laser pulses in photonic crystal fibers


1
Nonlinear interaction of ultrashort laser pulses
in photonic crystal fibers
  • Alexander Podlipensky

Max-Planck Research Group (IOIP), University of
Erlangen-Nuremberg Guenther-Scharowsky Str.
1/Bau 24, 91058 Erlangen, Germany www.pcfiber.com
apodlipensky_at_optik.uni-erlangen.de
Symposium Mikro- und Nanomaterialbearbeitung mit
Kurzpulslasern (SYLM)
2
Ultrashort pulse propagation in a fiber can
involve numerous processes (dispersion,
attenuation, SPM, solitons, stimulated Raman
scattering, FWM,)
Nonlinear interaction
Group velocity dispersion (GVD) D (or ?2)
for silica n22.6x10-20 m2/W
3
Conventional fiber
SEM image of a NL PCF
PCF
n1
nc
nsilica
The calculated GVD of circular strands of silica
glass compared with the dispersion of bulk glass
(Ref. P.Russell, JLT 24, pp. 4729-4749 (2006) ).
nsilica-neff gt 0.1
n1-nc 0.003
  • The core diameter in PCF can be ltlt 1 µm
  • g can be higher than 100 W-1km-1
  • GVD in PCF can be tailored in very broad spectral
    range

4
Supercontinuum generation in fs regime
Soliton Self Frequency Shift (SSFS)
Break up of higher order solitons
TFWHM gt 75 fs
- peak power of j-th soliton
TFWHM lt 75 fs
- pulse width of j-th soliton
J. P. Gordon, Opt. Lett. 11, 662-664 (1986). J.
Herrmann, A. Nazarkin, Opt. Lett. 19, 2065-2067
(1994).
Y. Kodama, A. Hasegawa, IEEE J.QE-23
p.510-524(1987)
P1gtP2gt.gtPN
T1ltT2lt.ltTN
w1ltw2lt....ltwN
Problems
an assumption that the energy of the high-order
soliton is equal to the sum of the energies of
its components The formulas can not be valid
for the ultrashort laser pulses (T056fs) and
Ngt10 (formation of subcycle solitons)
5
Nonlinear Schrödinger equation (NLSE)
GVD
attenuation
self-steepening
SPM, FWM, Raman
- the slowly varying envelope of the pulse
g - the nonlinear parameter of the fiber
- the coefficients in the Taylor expansion of the
propagation constant
a - power attenuation
- the Raman response function
Q. Lin and G. P. Agrawal, Raman response
function for silica fibers, Opt. Lett. 31,
3086-3088 (2006).
NLSE has been solved using the symmetrized split
step Fourier method
6
Modeling
GVD of a HN PCF
Power dependence of the spectra in HNL PCF (18.5
cm long)
pump wavelength 800 nm
  • ZDW _at_707 nm
  • ?2-21.8 ps2/km _at_800 nm
  • Core diameter 1.5 µm
  • pitch 2.75 µm
  • diameter of holes 2.7 µm
  • _at_ 800 nm 98 W-1km-1
  • Excitation _at_800nm, TFWHM110 fs

7
Modeling
P2.78 kW, N7
Spectral pulse evolution
Power dependence of the spectra
Temporal pulse evolution
There is quite good agreement with the fission
theory for Nlt8
8
Modeling
P4.69 kW, N9
Spectral pulse evolution
Power dependence of the spectra
Temporal pulse evolution
ejection of a pair of quasi stable bound solitons
9
Modeling
P5.9 kW, N10
Spectral pulse evolution
Power dependence of the spectra
Temporal pulse evolution
Ejection of a pair of solitons. The solitons
approach each other and collide. Energy transfer
between solitons is caused by intrapulse Raman
scattering.
10
Experiment
max7 nJ, 56 kW Coupling efficiency 45
LD_at_800nm 17.9 cm min LNL 0.4 mm
ZDW 707 nm D_at_800nm 64 ps/km/nm (?2-21.8
ps2/km) Core diameter 1.5 µm pitch 2.75
µm diameter of holes 2.7 µm g at 800 nm 98
W-1km-1
11
Evolution of the spectra with increasing input
power
experimental data
L 2.1 cm
L 4.2 cm
L 18.5 cm
modeling
12
Evolution of the spectra with the length
A.Podlipensky et al, Optics Express 15, pp.
1653-1662 (2007)
Cut-back measurement
Input power corresponds to the case of minimum
inter-solition spacing (180 mW)
The pair of adjacent solitons appears after a few
cm in the fiber and propagates with minimum
spectral spacing
Do the solitons co-propagate in time?
13
Study of temporal soliton evolution by Frequency
Resolved Optical Gaiting (FROG)
R. Trebino, Frequency-Resolved Optical Gaiting
the measurement of ultrashort laser pulses,
(Kluwer Academic Publishers, 2000).
Input power corresponds to the minimum
inter-solition spacing (180 mW)
fiber length 70 cm
Input power lt 180 mW
A delay between SF and SH peaks Is caused by the
delay between the pulses
SF
SF
SH
With increasing power - the frequencies of the
solitons approach each other - delay between the
solitons decreasing
Minimum delay corresponds to the minimum spectral
spacing (400 fs)!
14
Study of temporal soliton evolution by Frequency
Resolved Optical Gaiting (FROG)
fiber length 150 cm
With increasing power - the frequencies of the
solitons approach each other - delay between the
solitons decreasing
Minimum delay corresponds to the minimum spectral
spacing (400 fs)!
15
Summary
The fission process (break up of higher order
solitons) in highly nonlinear fibers strongly
depends on the input peak power
  • low power (Nlt8) - solitons are ejected one by
    one and separated in spectra and time
  • high power (Ngt9) ejected solitons collide
    demonstrating energy transfer caused by
    intrapulse Raman scattering
  • bound solitons have been observed for the peak
    power corresponding to the N9

16
Microprocessing in PCF with fs laser pulses
17
Selective hole blocking in the PCF
A mode converter in PCF
K.Lai et al., OL 32, 328 (2007)
Schematic longitudinal cross section of the
inflation
The output mode from the converter
Optical micrographs
Collapse of the blocked holes
A reliable and precise technique is required for
the blocking of holes
18
Selective hole blocking in the PCF
Photonic crystal woodpile structures fabricated
by 2PP
A. Ovsianikov, A. Ostendorf, B.N. Chichkov
Three-dimensional photofabrication with
femtosecond lasers for applications in photonics
and biomedicine, Applied Surface Science 253,
6599 (2007)
Size of the modified area and peak pulse intensity
Decrease of the peak pulse intensity down to the
modification threshold
Size of structure ltlt ?
19
Selective hole blocking in the PCF
Polymer Ormocore b59Ormothin (12)
Optical micrograph
1.
Filling with polymer
Holes are filed by capillary forces
2. Irradiation with the laser
800 nm, 1 µJ, 130 fs, 250 kHz
Objective 20x
3. Cleaning of the non-irradiated holes
Acetone gas (N2)
20
Laser drilling of side-channels in HC PCF
Optical micrographs of the fiber
21
Acknowledgment
Professor Dr. Philip Russell Dr. Nicolas Joly Dr.
Tijmen Euser PhD students Przemislaw
Szarniak Johannes Nold Jocelin Chen Hemant Tyagi
Thank you for your attention!
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