Novel glasses are important optoelectronic materials, offering the possibilities of a wide transmission window, high optical non-linearity, a broad range of compositions and the ability to incorporate high concentrations of active dopants. Photonic integrated circuits based on Heavy Metal Fluoride and Fluorotellurite glasses are particularly attractive, offering geometrical flexibility in design and efficient optical amplification. In this project we are investigating a new class of planar integrated optical circuits formed by thermally bonding optical fibres onto glass substrates. We refer to the technology as ‘FOG’, Fibre-on-Glass. Initial design, simulation and fabrication results show this simple idea promises many advantages over conventional techniques.

The basic fibre-on–glass principle and its flexibility are shown in the schematic illustrations of Figure 1. One attraction of the novel glasses considered is that a broad and continuous range of compositions, and hence refractive index, can be accessed, without the lattice matching constraints of say the III-V semiconductors.  The  drawing  or   extrusion   process

Figure1 Schematic Fibre on Glass (FOG) configurations

used to fabricate the fibre need not be restricted to simple circular fibres; the use of rectangular, multilayer, multicore and photonic bandgap fibres can all be envisaged within the fibre on glass concept, substantially extending the range of practically useful circuit functions. Embedding into a pre-defined groove may help alignment and linearity. Furthermore the glasses might be suitably doped locally to provide optical amplification.

FOG samples have been prepared using the following fluorotellurite glass compositions: Fibre: 70TeO2-10Na2O-20ZnF2 (mol. %); Substrate: 65TeO2-10Na2O-25ZnF2 (mol. %). They were prepared using a Perkin Elmer TGA, and pressed using a stainless steel foot and base. For these pressing experiments the fibre diameter was 150 mm, an atmosphere of helium was used for all runs (30 ml.min.-1) and the ramp rates were 100°C.min.-1 for all stages. Figure 2 shows electron micrographs of a sample prepared with a force of 25mN, a temperature of 270°C, a pressing time of 5 minutes with a pre-anneal stage at 220°C for 5 min. The fibre-substrate interface is void free. Figure 3(a) shows a schematic of a FOG sample with the fibre overlapping the substrate and Figure 3(b) the experimental demonstration of optical waveguiding at a wavelength of 633nm in such a sample having a fibre diameter of 66mm. The substrate length is 7mm and the fibre length 13mm. The fibre loss before pressing was 0.01dB/cm

Figure 2: Electron micrograph of FOG sample (F = fibre, S = substrate and E = epoxy).

a

b