Microstructured or 'air-clad' fibers, with air holes surrounding a large core, have demonstrated much wider light acceptance angles than conventional fibers. Recently, a new method employing leaky modes has been used to determine the numerical aperture in highly multimode air-clad microstructured fibers. It shows that an exceptionally high NA can only be achieved when bridge thickness is much smaller than the wavelength. The physical basis of these
key results is understood in terms of the conditions for efficient excitation of bridge local modes, which radially propagate power into the outer jacket. A number of microstructured polymer optical fibers (mPOF) have been fabricated with a large core suspended by thin supporting bridges. Such mPOFs provide freedom in microstructure geometry, combined with greater mechanical flexibility. This makes them particularly suited to applications demanding high light capture efficiency from broad-beam sources with irregular shapes and in situations involving tight bends. A demonstration of the technology is presented and the measured numerical apertures of these fibres show robust agreement with theoretical calculations over a broad wavelength range.
Microstructured Polymer Optical Fibers (MPOF) were first made in 2001, and subsequent development has aimed at exploiting the material and design opportunities they present. Most effort has been focused on developing approaches for high bandwidth MPOF, and investigating the properties of multimode microstructured fibers. We also consider new applications in endoscopy and photonic interconnects, as well as the use of organic dopants in MPOF.
Microstructured optical fibres (MOFs) have aroused great interest in recent years because of their unusual optical properties. These include their ability to be effectively single moded over a very large range of wavelengths, tailorisable dispersion, high or low non-linearity(depending on the hole design) and large core single mode fibres. We have recently fabricated the first Microstructured Polymer Optical Fibres (MPOFs), which further extend the range of possibilities in MOFs. The properties of polymers can be tailored to specific applications (eg:made highly non-linear or having gain) in a way that is not possible in glass. Further, the large range of fabrication methods available in polymers, including casting and extrusion, mean that the structures that can be obtained are very difficult to make by capillary stacking- the method used in glass MOFs. Here we present the latest results from our group using MPOFs, including single mode fibre and Bragg fibres.