130 research outputs found
Suppression and splitting of modulational instability sidebands in periodically tapered optical fibers due to fourth-order dispersion
We study the modulational instability induced by periodic variations of
group-velocity dispersion in the proximity of the zero dispersion point.
Multiple instability peaks originating from parametric resonance coexist with
the conventional modulation instability due to fourth order dispersion, which
in turn is suppressed by the oscillations of dispersion. Moreover isolated
unstable regions appear in the space of parameters due to imperfect phase
matching. This confirms the dramatic effect of periodic tapering in the control
and shaping of MI sidebands in optical fibers
Stable integrated hyper-parametric oscillator based on coupled optical microcavities
We propose a flexible scheme based on three coupled optical microcavities
which permits to achieve stable oscillations in the microwave range, the
frequency of which depends only on the cavity coupling rates. We find the
different dynamical regimes (soft and hard excitation) to affect the
oscillation intensity but not their period. This configuration may permit to
implement compact hyper-parametric sources on an integrated optical circuit,
with interesting applications in communications, sensing and metrology.Comment: 4 pages, 5 figure
Recurrence in the high-order nonlinear Schr\"odinger equation: a low dimensional analysis
We study a three-wave truncation of the high-order nonlinear Schr\"odinger
equation for deepwater waves (HONLS, also named Dysthe equation). We validate
our approach by comparing it to numerical simulation, distinguish the impact of
the different fourth-order terms and classify the solutions according to their
topology. This allows us to properly define the temporary spectral upshift
occurring in the nonlinear stage of Benjamin-Feir instability and provides a
tool for studying further generalizations of this model
Strong Raman-induced non-instantaneous soliton interactions in gas-filled photonic crystal fibers
We have developed an analytical model based on the perturbation theory in
order to study the optical propagation of two successive intense solitons in
hollow-core photonic crystal fibers filled with Raman-active gases. Based on
the time delay between the two solitons, we have found that the trailing
soliton dynamics can experience unusual nonlinear phenomena such as spectral
and temporal soliton oscillations and transport towards the leading soliton.
The overall dynamics can lead to a spatiotemporal modulation of the refractive
index with a uniform temporal period and a uniform or chirped spatial period
Modelling and Characterization of Guiding Micro-structured Devices for Integrated Optics
In this thesis we show several modelling tools which are used to study nonlinear photonic
band-gap structures and microcavities. First of all a nonlinear CMT and BPM were implemented
to test the propagation of spatial solitons in a periodic device, composed by an array
of parallel straight waveguides. In addition to noteworthy theoretical considerations, active
functionalities are possible by exploiting these nonlinear regimes. Another algorithm was developed
for the three-dimensional modelling of photonic cavities with cylindrical symmetry,
such as microdisks. This method is validated by comparison with FDTD. We also show the
opportunity to confine a field in a region of low refractive index lying in the centre of a silicon
microdisk. High Q-factor and small mode volumes are achieved. Finally the characterization
of microdisks in SOI with Q-factor larger than 50000 is presente
Nonlinear stage of Benjamin-Feir instability in forced/damped deep water waves
We study a three-wave truncation of a recently proposed damped/forced
high-order nonlinear Schr\"odinger equation for deep-water gravity waves under
the effect of wind and viscosity. The evolution of the norm (wave-action) and
spectral mean of the full model are well captured by the reduced dynamics.
Three regimes are found for the wind-viscosity balance: we classify them
according to the attractor in the phase-plane of the truncated system and to
the shift of the spectral mean. A downshift can coexist with both net forcing
and damping, i.e., attraction to period-1 or period-2 solutions. Upshift is
associated with stronger winds, i.e., to a net forcing where the attractor is
always a period-1 solution. The applicability of our classification to
experiments in long wave-tanks is verified.Comment: 8 pages, 4 figure
Vector modulational instability induced by parametric resonance in periodically tapered highly-birefringent optical fibers
We study the modulational instability induced by periodic variations of
group-velocity dispersion and nonlinear coefficients in a highly birefringent
fiber. We observe, for each resonance order, the presence of two pairs of
genuine vector type sidebands, which are spectrally unbalanced between the
polarization components for nonzero group-index mismatch, and one pair of
balanced sidebands emerging and dominating at increasing group-index mismatch.
As the conventional modulational instability manifests itself, it is partially
suppressed by the proximity of these new unstable regions.Comment: 8 pages, 8 figures, generalizes the methods of arXiv:1208.348
Random telegraph dispersion-management: modulational instability
We study modulational instability in a fiber system resembling a
dispersion-managed link where the sign of the group-velocity dispersion varies
randomly according to a telegraph process. We find that the instability gain of
stochastic origin converges, for long fiber segment mean length (the inverse of
the transition rate between the two values), to the conventional values found
in a homogeneous anomalous dispersion fiber. For short fiber segments, the gain
bands are broadened and the maximum gain decreases. By employing correlation
splitting formulas, we obtain closed form equations that allow us to estimate
the instability gain from the linearized nonlinear Schr\"odinger equation. We
compare the analytical to the numerical results obtained in a Monte Carlo
spirit. The analysis is proven to be correct not only for a fluctuating
group-velocity dispersion, but also including fourth-order dispersion (both
constant or varying according to a synchronous or independent telegraph
process). These results may allow researchers to tailor and control
modulational instability sidebands, with applications in telecommunications and
parametric photon sources.Comment: 12 pages, 6 figure
Oscillatory dynamics in nanocavities with noninstantaneous Kerr response
We investigate the impact of a finite response time of Kerr nonlinearities
over the onset of spontaneous oscillations (self-pulsing) occurring in a
nanocavity. The complete characterization of the underlying Hopf bifurcation in
the full parameter space allows us to show the existence of a critical value of
the response time and to envisage different regimes of competition with
bistability. The transition from a stable oscillatory state to chaos is found
to occur only in cavities which are detuned far off-resonance, which turns out
to be mutually exclusive with the region where the cavity can operate as a
bistable switch
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