A simple and straightforward method is applied to experimentally obtain the wavelength dependence of the intercore beat length for two different types of twin-core microstructured polymer optical fiber. The results are compared with numerical calculations using a full-vectorial plane-wave expansion method, which shows good agreement.
Photonic crystal fibers technology provides us with new way to obtain fibers with much higher non-linearity than
conventional techniques. Upper limits of non-linear coefficients obtainable in silica-based photonic crystal fibers have
been already investigated. Unique dispersion characteristic and enhanced non-linearity make this kind of fibers an ideal
candidate for non-linear optical devices in telecommunication applications, for measurement and sensing and for
supercontinuum generation. However, there are limitations given by material properties, which obstruct us from
achieving theoretical limits of these fibers. Extremely small core and high air-filling fraction are here needed for reach
higher non-linearity, so when material properties of conventional silica restrict us, there is a requirement on a novel
matter. This could be poly-methyl metacrylate (PMMA), a common material for plastic optical fibers manufacturing.
These microstructured polymer optical fibers are a recent technology, which gives us with new possibilities in core size,
fiber geometry and related air-filling fraction. By this kind of fiber, we could be closer to ideal non-linear fiber, which is
core strain surrounded by air, than even before. But new kind of fiber brings new issues, like which effect in fiber will be
dominant or how will be coupled light affected by outer influences - and what difference will be between predicted and
real values in general. This is a large task and hopefully, there will be answer at least for a small part in this paper.
Theoretical and experimental results are reported for a twin-core microstructured polymer fiber. A full-vectorial numerical method based supermode theory is applied in the symmetrical structure to obtain the interference between the even and odd modes. The wavelength dependence of the coupling length is measured, and compared to calculations using a full-vectorial numerical method. Both results show good agreement.
A key step towards the commercialization of microstructured polymer optical fibers is the ability to cleave and splice
them. The cleaving of polymer optical fiber (whether by cutting or fracture) depends upon the mechanical properties of
the material. These in turn depend on the conditions under which the fiber is drawn from the preform. The relationship
between fiber draw conditions, mechanical properties of the drawn fiber and the ability to cut the heated fiber with a hot
razor blade has been investigated for PMMA fibers of varying hole structure. Differential scanning calorimetry measurements
indicate that the type of PMMA used exhibits two 'relaxations' with inflexion points at 115±3<sup>o</sup>C and 80±2<sup>o</sup>C
respectively, independent of draw conditions. The first of these is in the range expected for the α-relaxation. The origin
of the second is unknown. Dynamic mechanical analysis of fiber samples indicates that the temperature dependence of
the elastic and loss moduli of the fiber vary significantly with draw conditions. The end-face produced by cutting with a
razor blade also varies with draw conditions. Fiber drawn under high tension splinters during cutting and fiber drawn
under low tension undergoes ductile deformation and fracture. However for intermediate draw conditions the fiber can
be cleanly cut with a razor blade at a temperature of 80±10<sup>o</sup>C.
In this paper we report on investigations of some of the factors that have a bearing on the reliability and repeatability of polymer fibre Bragg gratings. The main issues discussed are the fibre preform composition, the fibre drawing conditions and the thermal history of the fibre grating.
We describe recent research into devices based on fibre Bragg gratings in polymer optical fibre. Firstly, we report on the inscription of gratings in a variety of microstructured polymer optical fibre: single mode, few moded and multimoded, as well as fibre doped with trans-4-stilbenmethanol. Secondly, we describe research into an electrically tuneable filter using a metallic coating on a polymer fibre Bragg grating. Finally we present initial results from attempts to produce more complex grating structures in polymer fibre: a Fabry-Perot cavity and a phase-shifted grating.
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.