A new asymptotic analysis of the equations for a mode-locked laser exhibiting a Q-switching instability is proposed. We determine the Hopf bifurcation point responsible for this instability and discuss its behavior in terms of the laser parameters. Our analysis is valid for all class B lasers exhibiting slowly damped relaxation oscillations which include solid state and semiconductor lasers. In the limit of weak nonlinearities, we recover Haus stability conditions. In the case of strongly nonlinear losses, as for the usual picosecond and femtosecond laser devices, we determine the stability conditions.
Polarization modulation instability in photonic crystal fibers
R. J. Kruhlak,
G. K. Wong,
J. S. Chen,
S. G. Murdoch,
R. Leonhardt,
J. D. Harvey,
N. Y. Joly,
J. C. Knight
Polarization modulation instability (PMI) in birefringent photonic crystal fibers has been observed in the normal dispersion regime with a frequency shift of 64 THz between the generated frequencies and the pump frequency. The generated sidebands are orthogonally polarized to the pump. From the observed PMI frequency shift and the measured dispersion, we determined the phase birefringence to be 5.3×10−5 at a pump wavelength of 647.1 nm. This birefringence was used to estimate the PMI gain as a function of pump wavelength. Four-wave mixing experiments in both the normal and the anomalous dispersion regimes generated PMI frequency shifts that show good agreement with the predicted values over a 70 THz range. These results could lead to amplifiers and oscillators based on PMI.
Cross-phase modulation instability in photonic crystal fibers
J. S. Chen,
G. K. Wong,
S. G. Murdoch,
R. J. Kruhlak,
R. Leonhardt,
J. D. Harvey,
N. Y. Joly,
J. C. Knight
We report on the observation of cross-phase modulation instability in a highly nonlinear photonic crystal fiber. In such fibers the presence of higher orders of dispersion results in a complex phase-matching curve. We are able to observe this behavior experimentally and obtain excellent agreement between the measured and predicted shifts.
Raman-like light scattering from acoustic phonons in photonic crystal
fiber
P Dainese,
PSJ Russell,
GS Wiederhecker,
N Joly,
HL Fragnito,
V Laude,
A Khelif
Raman and Brillouin scattering are normally quite distinct processes that take place when light is resonantly scattered by, respectively, optical and acoustic phonons. We show how few-GHz acoustic phonons acquire many of the same characteristics as optical phonons when they are tightly trapped, transversely and close to modal cut-off, inside the wavelength-scale core of an air-glass photonic crystal fiber (PCF). The result is an optical scattering effect that closely resembles Raman scattering, though at much lower frequencies. We use photoacoustic techniques to probe the effect experimentally and finite element modelling to explain the results. We also show by numerical modelling that the cladding structure supports two phononic band gaps that contribute to the confinement of sound in the core. (c) 2006 Optical Society of America
Spectrally smooth supercontinuum from 350 nm to 3 mu m in sub-centimeter
lengths of soft-glass photonic crystal fibers.
FG Omenetto,
NA Wolchover,
MR Wehner,
M Ross,
A Efimov,
AJ Taylor,
VVRK Kumar,
AK George,
JC Knight, et al.
The conversion of light fields in photonic crystal fibers ( PCFs) capitalizes on the dramatic enhancement of several optical nonlinearities. We present here spectrally smooth, highly broadband supercontinuum radiation in a short piece of high-nonlinearity soft-glass PCF. This supercontinuum spans several optical octaves, with a spectral range extending from 350 nm to beyond 3000 nm. The selection of an appropriate propagation-length determines the spectral quality of the supercontinuum generated. Experimentally, we clearly identify two regimes of nonlinear pulse transformation: when the fiber length is much shorter than the dispersion length, soliton propagation is not important and a symmetric supercontinuum spectrum arises from almost pure self-phase modulation. For longer fiber lengths the supercontinuum is formed by the breakup of multiple Raman-shifting solitons. In both regions very broad supercontinuum radiation is produced. (c) 2006 Optical Society of America.
Stimulated Brillouin scattering from multi-GHz-guided acoustic phonons
in nanostructured photonic crystal fibres
P. Dainese,
P. St. J. Russell,
N. Joly,
J. C. Knight,
G. S. Wiederhecker,
H. L. Fragnito,
V. Laude,
A. Khelif
Wavelength-scale periodic microstructuring dramatically alters the optical properties of materials. An example is glass photonic crystal fibre(1) ( PCF), which guides light by means of a lattice of hollow micro/nanochannels running axially along its length. In this letter, we explore stimulated Brillouin scattering in PCFs with subwavelength-scale solid silica glass cores. The large refractive-index difference between air and glass allows much tighter confinement of light than is possible in all-solid single-mode glass optical fibres made using conventional techniques. When the silica-air PCF has a core diameter of around 70% of the vacuum wavelength of the launched laser light, we find that the spontaneous Brillouin signal develops a highly unusual multi-peaked spectrum with Stokes frequency shifts in the 10-GHz range. We attribute these peaks to several families of guided acoustic modes each with different proportions of longitudinal and shear strain, strongly localized to the core(2,3). At the same time, the threshold power for stimulated Brillouin scattering(4) increases fivefold. The results show that Brillouin scattering is strongly affected by nanoscale microstructuring, opening new opportunities for controlling light-sound interactions in optical fibres.
Kontakt
Forschungsgruppe Nicolas Joly
Professur für Photonik Friedrich-Alexander-Universität Erlangen-Nürnberg
und
Max-Planck-Institut für die Physik des Lichts Staudtstr. 2 91058 Erlangen, Germany
