Work Area: Multilayered Materials for Silicon-Compatible Opto-Electronics
Keywords sol-gel films, optical non-linearity, optically pumped gain, waveguides
Start Date: 1 September 92 / Duration: 36 months / Status: running
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Abstract NODES aims to establish the basis of a new material and fabrication technology for optoelectronics based on spin-on glass on silicon. We are developing materials using sol-gel silica as a host material, and semiconductor and rare-earth dopants for nonlinear and optical gain functions respectively, for demonstrator switching and amplifying devices. The long-term goal is to develop a complete technology for low-cost mass production of multi-functional optoelectronic products.
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.
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.
A new pore size characterisation 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 characterisation by infra-red spectroscopy. A real-time optical monitoring technique for spin-coating has also been developed and demonstrated.
CdS-doped films have been successfully fabricated by two different methods - by precipitation in the sol, and by reaction of porous cadmium-doped films with H2S 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 two different processes. Absorption spectra have been measured which correspond well to those of equivalent bulk glasses, and fluorescence measurements are now in progress.
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.
The main routes for dissemination will be through publications in refereed journals, conference presentations, and interaction between NODES and other projects in which the partners are involved. As part of the Eighth Cimtec Forum on New Materials, to be held in Florence July 1-4 1994, we are organising a session on Sol-Gel Integrated Optics, which will be combined with NODES workshop 2 (contact coordinator).
Imperial College of Science, Technology and Medicine - UK
Department of Electrical and Electronic Engineering
UK - LONDON SW7 2BT
Groupement d'Electromagnetisme Experimental et d'Optoelectonique (GeeO) - F
INPG - TIRF - F
Centro di Eccelenza Optronica - I
INESC - P
Dr. E.M. Yeatman
NODES - 6993, August 1994
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html version of synopsis by Nick Cook