Abstract: A device for converting transverse spatial profile of intensity of a light beam, using a microstructured optical fiber. Transverse dimensions of the fiber vary longitudinally and both its ends have opto-geometrical parameters such that at the wavelength of the beam the fiber has a fundamental mode having two different profile shapes at its two ends. Thus by introducing the beam with one of the profiles through one of the two ends, the beam emerges through the other end with the other profile, whose shape is different from that of the profile of the introduced beam.

Abstract: The fibre comprises a core (2) having an index N and diameter of 10 ?m or more, surrounded by a ring (4) having an index N+?n and thickness ?R, and cladding (6) surrounding the ring and comprising for example air gaps (8). According to the invention: ?n?10?3 and ?R=?/(?n)? [1] where: 5×10?4 ?m???5×10?2 ?m and 0.5???1.5. The numbers ? and ? are dependent on the wavelength ? of the light guided by the fibre, the number of missing gaps therein, the diameter d of the gaps, the spacing ? thereof and N. To design the fibre, ?, the number of missing gaps, d/?, the core doping content, ?0 and ?n are chosen; and ?R is determined using equation [1] so as to obtain a flattened fundamental mode.

Abstract: The microstructured optical fibre comprises a core (4) surrounded by a sheath (1) comprising a base material having a refraction index (ni) and a plurality of at least two different types of inclusion: a first type of inclusion (2) having a refraction index n2 (n2>n1), and a second type of inclusion (3) having a refraction index n3 (n3<n1). The inclusions (2, 3) are arranged and dimensioned in such a way as to ensure guidance, by total internal reflection (RTI), of a fundamental mode of the light, centred on a wavelength ?RTI, and of a fundamental mode of the light in the first photonic forbidden band (BG1), centred on a wavelength ?BG1, which is different to that ?RTI of the fundamental mode guided by total internal reflection (RTI).

Abstract: The microstructured optical fibre comprises a core (4) surrounded by a sheath (1) comprising a base material having a refraction index (ni) and a plurality of at least two different types of inclusion: a first type of inclusion (2) having a refraction index n2 (n2>n1), and a second type of inclusion (3) having a refraction index n3 (n3<n1). The inclusions (2, 3) are arranged and dimensioned in such a way as to ensure guidance, by total internal reflection (RTI), of a fundamental mode of the light, centred on a wavelength ?RTI, and of a fundamental mode of the light in the first photonic forbidden band (BG1), centred on a wavelength ?BG1, which is different to that ?RTI of the fundamental mode guided by total internal reflection (RTI).