230 research outputs found
Polarisation effects in optical microcoil resonators
Optical microcoil resonators (OMRs) fabricated by wrapping a microfibre around a rod to allow evanescent coupling between adjacent turns as in Fig 1. (a) have recently attracted much interest due to their high Q-factor and large extinction ratios resonances, low input and output coupling losses, large evanescent field and compactness [1,2], with applications such as sensing [3] and signal processing [4]. However, theoretical models published so far have neglected polarisation effects, and hence in order to develop a more detailed understanding we have modelled the OMR with polarisation-dependent coupled mode equations in the linear [5] and nonlinear regimes
Observation of soliton explosions in a passively mode-locked fiber laser
Soliton explosions are among the most exotic dissipative phenomena studied in
mode-locked lasers. In this regime, a dissipative soliton circulating in the
laser cavity experiences an abrupt structural collapse, but within a few
roundtrips returns to its original quasi-stable state. In this work we report
on the first observation of such events in a fiber laser. Specifically, we
identify clear explosion signatures in measurements of shot-to-shot spectra of
an Yb-doped mode-locked fiber laser that is operating in a transition regime
between stable and noise-like emission. The comparatively long,
all-normal-dispersion cavity used in our experiments also permits direct
time-domain measurements, and we show that the explosions manifest themselves
as abrupt temporal shifts in the output pulse train. Our experimental results
are in good agreement with realistic numerical simulations based on an
iterative cavity map.Comment: 5 pages, 5 figures, submitte
Improved design of a DFB Raman fibre laser
A Raman fibre laser based on phase shifted DFB structures is modelled for the first time. Using parameters of realistic devices, the model predicts low-threshold and highly-efficient laser output. The change of position and width of the phase shift were found to have a substantial impact on laser performanc
Theoretical study of noise reduction of NRZ signals using nonlinear broken micro-coil resonators
Nonlinear microcoil resonators are extremely attractive devices for nonlinear optics; however, due to their high-Q values, their use at high speeds is limited. In this letter, we analyze a simple way of increasing their bandwidth, namely breaking the fiber in several places, and show that the resulting device is suitable for noise reduction in realistic systems. Simulations show that an in-line broken resonator can significantly reduce the impact of amplitude noise on the bit-error rate of nonreturn-to-zero signals
Modelling applications of photonic bandgap fibres
Photonic crystal fibres (PCFs)[1] are one of the most exciting developments in the field of photonics that has emerged in recent years. Not only have they already led to cheap all-fibre high brightness white light sources and have sparked a renaissance in the field of nonlinear optics but they also have the potential to dramatically change the next generation of telecommunication systems. PCFs can be split into two categories, the first have a solid core and guide light by modified total internal reflection, while the second photonic bandgap fibres (PBF) guide light by photonic bandgap effects and typically have a low index core compared to the cladding. Also of interest are "arrow" fibres which have a solid core and guide light due to the arrangement of high index defects in the cladding. In this paper we will be concentrating on designing and manipulating the properties of PBFs. etc..
Nonlinear optics of fibre event horizons
The nonlinear interaction of light in an optical fibre can mimic the physics
at an event horizon. This analogue arises when a weak probe wave is unable to
pass through an intense soliton, despite propagating at a different velocity.
To date, these dynamics have been described in the time domain in terms of a
soliton-induced refractive index barrier that modifies the velocity of the
probe. Here, we complete the physical description of fibre-optic event horizons
by presenting a full frequency-domain description in terms of cascaded
four-wave mixing between discrete single-frequency fields, and experimentally
demonstrate signature frequency shifts using continuous wave lasers. Our
description is confirmed by the remarkable agreement with experiments performed
in the continuum limit, reached using ultrafast lasers. We anticipate that
clarifying the description of fibre event horizons will significantly impact on
the description of horizon dynamics and soliton interactions in photonics and
other systems.Comment: 7 pages, 5 figure
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