Robert Evert

Polymer optical fibers doped with organic materials as luminescent solar concentrators

This paper provides an analysis of the emission properties of different polymer optical fibers doped with organic materials with the aim of investigate their performance as luminescent solar concentrators. We present a study of the light propagation along the fibers, together with the experimental measurements of two different efficiencies: side illumination coupling efficiency and fluorescent fiber solar concentrator efficiency. The results obtained for all the fibers are compared and discussed.

Eu-doped polymer fibers

Polymer optical fibers are a very good choice for flexible and robust short range optical data links. We have developed PMMA with Eu3+-doped polymer chains. From this optically active material we draw fibers. These fibers can be used for UV pumped polymer fiber amplifiers in cases where larger distances have to be bridged. This paper presents the fabrication of these fibers, their optical characteristics and results of first gain measurements.

Methacrylate-Based Copolymers for Polymer Optical Fibers

Waveguides made of poly-methyl-methacrylate (PMMA) play a major role in the homogeneous distribution of display backlights as a matrix for solid-state dye lasers and polymer optical fibers (POFs). PMMA is favored because of its transparency in the visible spectrum, low price, and well-controlled processability. Nevertheless, technical drawbacks, such as its limited temperature stability, call for new materials. In this work, the copolymerization technique is used to modify the properties of the corresponding homopolymers. The analytical investigation of fourteen copolymers made of methyl-methacrylate (MMA) or ethyl-methacrylate (EMA) as the basis monomer is summarized. Their polymerization behaviors are examined by NMR spectroscopy with subsequent copolymerization parameter evaluation according to Fineman-Ross and Kelen-Tüdös. Therefore, some r-parameter sets are shown to be capable of copolymerizations with very high conversions. The first applications as high-temperature resistant (HT) materials for HT-POFs are presented. Copolymers containing isobornyl-methacrylate (IBMA) as the comonomer are well-suited for this demanding application.

Universal fibre laser model used for the simulation of 2 µm Thulium fibre lasers

A universal simulation model for rare earth doped cw fibre lasers is presented. The model is based on generic rate and gain equations and therefore is very compact. It can be used for any fibre doped with one or several rare earth ions. The model allows for spectral simulations as well as radial discretization of the fibre. An algorithm was developed which optimizes the longitudinal fibre segmentation of the model. Spectroscopic parameters for Thulium doped fibre lasers are taken from the literature or derived from calculations. Calculated multiphonon up-conversion rates take the thermalisation of closely spaced states into account. The simulation is compared with measurement results of a coupled wavelength shift observed in a tunable fibre ring laser. The simulation allows to investigate possible explanations and it indicates that the phenomenon is a measurement artefact.

Numerical simulation of optical amplifiers based on Eu-doped polymer optical fibers

We model the light amplification in Eu-doped PMMA polymer optical fibers by solving our own rate equations that describe the physical system. These equations are firstly solved in stationary state, for a constant pump power. In this case, we determine the optimum fiber length for maximum output power. We also solve the time-dependent equations to be able to launch a pulse of signal power at the input end, together with pulsed or constant pump power. The results are useful to determine the influence of some important design parameters, such as the temporal pump width or the fiber concentration.

Single-mode polymer optical fibers

The mechanical properties of polymer optical fibers (POF) make them very interesting candidates for fiber optical sensors. Today POFs are mainly used for short range data communication. These fibers have a very large core of 980 μm. This large core is beneficial for handling and maintenance in fiber networks. Fiber sensors however, often need high optical intensity or optical coherence (e.g. in fiber Bragg gratings). For such applications there is a need for single mode polymer optical fibers (SMPOF). It turns out that the fabrication process of SMPOFs is not just a matter of scaling, but requires new approaches to obtain high quality fibers.