1,721,028 research outputs found
Modelling confinement loss in practical small-core holey optical fibres
No full textMicrostructured optical fibres (MOFs) are all-silica fibres that guide light by means of an arrangement of air-holes that run down the entire fibre length. In the kind of MOFs here considered, also named holey fibres (HFs), guidance arises from average-index effects: the holes form the cladding region around the solid core. The modes of such fibres are leaky because the core refractive index is the same as the index beyond the (finite) cladding region. HFs with a core diameter of the scale of an optical wavelength and large holes have been fabricated, resulting in the smallest effective area ever measured in a fibre at 1550 nm [1]. Such small effective areas make these fibres attractive for nonlinear applications. The cladding of a HF is usually comprised of hexagonally-packed rings of holes, and when the hole-to-hole spacing (Lambda) is of the order of the wavelength, several rings of holes are required to reduce the confinement loss to a practical value. Fibre fabrication feasibility on the other hand constrains the number of rings that can be used. Therefore in order to optimise the design of this class of fibres, it is necessary to study the loss characteristics for small-core HFs
Effect of periodic background loss on grating spectra
No full textThe effect of periodic loss on the performance of refractive-index gratings has been studied in detail. It is shown that the loss periodicity and relative phase strongly affects the symmetry of the reflection, transmission, and loss spectra. This asymmetry is explained successfully through consideration of the overlap between the standing-wave intensity distribution and the periodic loss pattern
A theoretical study into the fundamental design limits of devices based on one-and two-dimensional structured fibres
No full textThe sub-wavelength perturbation of an originally uniform material in order to manipulate light is the basis of two of the latest key technologies used to produce optical fibre devices for telecommunication system applications. The first technology (fibre Bragg gratings) concerns the 1-dimensional perturbation of the refractive index of an optical fibre (i.e. along the propagation axis of the fibre), whereas the second technology (microstructured optical fibres) concerns a 2-dimensional perturbation of the refractive index (i.e. in the transverse plane of the fibre).Regarding the fibre Bragg gratings, the effect of background losses on uniform gratings and of cladding mode losses on linearly chirped gratings have been studied by means of two extended versions of coupled-mode theory. The possibility of compensating the cladding mode losses acting on the chirped grating profile is also analysed. Considering the microstructured optical fibres, an extensive study of highly nonlinear, small-core, silica holey fibres has been performed with the implementation of the multipole method, which was chosen after a careful consideration of other available modelling techniques. Guidelines were produced for optimising the design of holey fibres for particular device applications especially when trade-offs between small effective mode area and low confinement loss are important. The work on modelling highly nonlinear holey fibres was extended to include a preliminary study of the use of higher refractive index glasses and their future device applications
Confinement loss in highly nonlinear holey optical fibres
No full textIn conclusion, we have applied the multipole approach to holey optical fibres with cladding features of the order of the wavelength of light guided in the structure. By applying this method to real structures, we find that it is a useful tool for predicting the magnitude of the confinement loss in single-material fibres, a loss mechanism that has been found to be particularly significant for small-core fibres
Fundamental properties of small core holey fibres
No full textWe explore some of the fundamental limits in small core silica holey fibres that have a direct bearing on nonlinear device applications. In particular, we examine issues related to coupling and polarization in these fibres
Cladding mode losses in chirped fibre Bragg gratings
No full textAn extended model for the interaction between core and cladding modes in chirped grating is developed and used to study mode dynamics and spectral equalisation
The role of confinement loss in highly nonlinear silica holey fibers
Full text linkSmall-core holey fibers (HFs) can offer tight mode confinement, and are, therefore, attractive for highly nonlinear fiber applications. However, we show here that confinement loss can significantly degrade the performance of devices based on such small core fibers. We also identify a range of fiber designs that result in high fiber nonlinearity and low confinement loss. In particular, we show that pure silica HFs can exhibit effective nonlinearities more than 50 times higher than conventional fibers, and that the confinement loss can be lowered below the loss of standard fiber types
Time-resolved quantification of plasma accumulation induced by multi-pulse laser ablation using self-mixing interferometry
Full text linkIn this work a method based on self-mixing interferometry (SMI) is presented for probing the concentration of plasma plumes induced by multi-pulse laser ablation. An analytical model is developed to interpret the single-arm interferometric signal in terms of plasma electron number density. Its time dependence follows a power-law scaling which is determined by concurrent effects of plume accumulation and propagation. The model has been applied for the experimental study of plume formation at variable laser pulse frequencies on different materials. The plume expansion dynamics has been observed with high-speed imaging, and the SMI measurements allowed for a time-resolved estimation of the electron number density. The intrinsic advantages of the SMI technique in terms of robustness and low intrusiveness would allow for its usage as a fast diagnostic tool for the dynamical scaling of laser-induced plumes. Moreover it can be easily applied in laser-based manufacturing technologies where plasma concentration monitoring and control is important
Long-wavelength supercontinuum generation in bismuth-silicate fibres
No full textA broad smooth supercontinuum has been generated at long wavelengths in a highly-nonlinear bismuth silicate fibre pumping near the zero-dispersion wavelength of the cladding glass
High sensitivity refractometric sensor based on embedded optical microfiber loop resonator
No full textA novel refractometric sensor based on an embedded optical microfiber loop resonator is presented. The device sensitivity has been studied in two typical configurations and its dependence on the nanowire diameter and coating thickness determined
- …
