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Emittance of the ion beam extracted from an ion source is dependent on the initial focusing action at the plasma sheath. The properties of the plasma sheath is further dependent on the local electric fields and charge densities around the sheath. Experiments are conducted for creating different sets of conditions around the plasma sheath in an H- multicusp filament ion source and the resulting emittance of the extracted H- ion beam is measured. Variation of beam emittance under different plasma densities, electrode voltages and gas flows are analysed. peerReviewed

International audience

We report on the direct UV-writing of channel waveguides in annealed proton-exchanged (APE) and reverse proton-exchanged (WE) layers in LiNbO3 and demonstrate efficient guiding within single mode channels at telecom wavelengths.

1. Background: A new class of optical fiber has recently emerged which shows considerable promise; holey fibers have highly tailorable optical properties arising from their design flexibility [1, 2]. Typically holey fibers (HFs) are made from undoped silica, and have a cladding region formed by air holes running along the fiber length. The holes are often arranged in a periodic lattice [as in Fig. 1(a)], and the core is formed by an absent air hole. However the holes do not need to be periodically arranged or even be of constant size for the HF to guide light [3] [see Fig. 1(b)]. Either type of HF can guide because the cladding has a lower effective refractive index than the core. Although this guidance mechanism is conceptually simple, the optical properties of HFs vary dramatically depending on the hole arrangement. This is because the holes are on the same scale as the wavelength, and so the effective cladding index is strongly dependent on both the wavelength and the hole arrangement. A small subset of HFs of the type shown in Fig. 1(a) (i.e. with periodically arranged holes) can guide light via band gap effects [4], but we do not consider this more exacting mechanism here.

Recent advances in the development of holey optical fibres are described. We review the basic physical properties of the various fibre types, the status of current fibre fabrication efforts and discuss numerous end applications.

The area of fiber lasers has undergone rapid developments in recent years. Gone are the days when fiber lasers were seen as something of an irrelevant curiosity, offering interesting performance features, but always with power levels or other performance limitations, that made them unsuitable for all but a few applications. Improvements in the area of high-power, high-brightness semiconductor pump lasers, and the development of techniques, such as cladding-pumping, have changed this viewpoint markedly. Most significantly, fiber lasers have shed the "low power" label and it is now widely appreciated that the heat-dissipation characteristics of the fiber environment, coupled with the high efficiencies demonstrated (in excess of 80%), actually make fiber lasers a preferred candidate for many high-power applications. Moreover, major advances in fiber Bragg grating fabrication and more sophisticated fiber designs and pump coupling techniques, have at the same time improved device performance and increased the versatility, functionality and practicality of the technology; allowing the development of a broad range of robust, practical optical sources.

We discuss recent experimental results concerning the use of microstructured optical fibres as novel nonlinear media. Continuum generation, short wavelength soliton propagation and optical frequency comb generation have been obtained thanks to a combination of unusual dispersive properties and the small mode area available in holey fibres.

Fibre Bragg gratings (FBGs) consist of a periodic modulation of the refractive index along the core of the fibre. This periodicity creates a photonic bandgap and results in strong reflectivity near the Bragg wavelength. The narrow bandwidth and large dispersion of FBGs makes them ideal for linear dispersion compensator and for add/drop filters in WDM systems. In the nonlinear regime Bragg gratings are bistable devices and thus could potentially form the basis of all-optical switches. Recently we have demonstrated three types of nonlinear switching in Bragg gratings: a simple self-induced nonlinear switch, an all-optical AND gate, and a pump induced switch (the optical pushbroom). To understand these switches it is necessary to recall the basic nonlinear properties of Bragg gratings.