The broad aim of NODES is to develop a silica-on-silicon integrated optic technology which allows integration of a wide range of functionality within low-cost components. This technology will be based on spin-on sol-gel glass, which has great potential for variation of structure and composition. The research focuses on three major areas: the development of sol-gel techniques for fabrication of doped and passive waveguide materials, the fabrication and use of semiconductor-doped silica for Kerr-effect switching devices, and the fabrication and use of rare-earth doped silica for optical amplifying devices. Work will include materials development, device demonstrators, and consideration of integration issues.
The basis of a new material and fabrication technology for optoelectronics is being established based on spin on glass on silicon. Materials are being developed using sol get silica as a host material, and semiconductor and rare earth dopants for nonlinear and optical gain functions respectively, for demonstrator switching and amplifying devices.
A new pore size characterization technique for micropores in films has been developed, and initial studies of the effect of process parameters have been carried out. New results have been obtained for laser densified waveguides, and for film structure characterization by infrared spectroscopy. A real time optical monitoring technique for spin coating has also been developed and demonstrated.
Cadmium sulphur doped films have been successfully fabricated by 2 different processes: by precipitation in the sol, and by reaction of porous cadmium doped films with hydrogen sulphide gas. Both show band-gap shifts consistent with quantum confinement, and in the former type, a 3rd order nonlinearity of sufficient magnitude for device application has been measured, although photodarkening still needs to be eliminated.
Erbium doped sol gel films have also been successfully fabricated by 2 different processes. Absorption spectra have been measured which correspond will to those of equivalent bulk glasses, and fluorescence measurements are now in progress.
APPROACH AND METHODS
Sol-gel technology offers a cheap and rapid way of producing glass films, but is generally not suitable for films thicker than 1-2 micrometers. A technique recently developed by one of the partners (Imperial College) has overcome this restriction, and will be exploited by the NODES project. The consortium has three in-house techniques for waveguide definition: reactive ion etching, laser irradiation and electron irradiation. An intermediate goal will be the selection of the most suitable technique for the materials and devices under investigation. We are also investigating the use of porous layers for dopant insertion, and therefore are developing techniques for pore size measurement and control.
A variety of studies have been made on semiconductor-doped-glasses for guided-wave nonlinear optical applications. However, materials have not been specially developed for these applications, and systematic studies have not been carried out. Both of these tasks will be fundamental parts of NODES. In addition, rare-earth doping for optically pumped gain will also be developed. Although this is well established in fibre devices, important problems due to the material differences, shorter path lengths and lower waveguides performance in planar materials have yet to be overcome. The NODES programme will use several approaches in tackling these difficulties.
Silica-based glass on silicon is the most promising candidate technology for mass production of low-cost optoelectronic components. With fibre-to-the-home a virtual certainty in the next decade, the market for such products will be enormous. Europe is in a strong position with respect to relevant technologies and could become a major supplier of these devices. The NODES consortium includes a technology transfer company (GeeO), and plans to strengthen links, as the work proceeds, with industrial groups interested in exploitation.
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