Novel materials, micro-, nano-scale photonic devices, and 'photonic systems on a chip' have become important focuses for global photonics research and development. This interest is driven by the rapidly growing demand for broader bandwidth in optical communication networks, and higher connection density in the interconnection area, as well as a wider range of application areas in, for example, health care, environment monitoring and security. Taken together, chalcogenide, heavy metal fluoride and fluorotellurite glasses offer transmission from ultraviolet to mid-infrared, high optical non-linearity and the ability to include active dopants, offering the potential for developing optical components with a wide range of functionality. Moreover, using single-mode large cross-section glass-based waveguides as an optical integration platform is an elegant solution for the monolithic integration of optical components, in which the glass-based structures act both as waveguides and as an optical bench for integration. We have previously developed a array of techniques for making photonic integrated circuits and devices based on novel glasses. One is fibre-on-glass (FOG), in which the fibres can be doped with different active dopants and pressed onto a glass substrate with a different composition using low-temperature thermal bonding under mechanical compression. Another is hot-embossing, in which a silicon mould is placed on top of a glass sample, and hot-embossing is carried out by applying heat and pressure. In this paper the development of a fabrication technique that combines the FOG and hot-embossing procedures to good advantage is described. Simulation and experimental results are presented.
We previously demonstrated light guiding in fiber-on-glass (FOG) dielectric waveguides using fluoro-tellurite glasses.
These waveguides were fabricated by mechanically pressing a fiber onto a polished planar glass substrate of lower
refractive index above the glass transition temperatures. However, two handling constraints have been discovered in this
approach. In practice, for novel inorganic compound glasses, the minimum dimension of fiber that can be handled is
preferably around 30μm. The minimum refractive index difference between the fiber and the substrate that can be
reliably achieved at present with these glasses is 0.01. Our simulation results showed that, taken together, these
restrictions provide a practical barrier to achieving single-mode FOG operation at telecommunications wavelengths.
Here we present simulation and experimental results for a new inorganic glass FOG waveguide that simultaneously
meets these handling constraints and achieves mono-mode operation around 1.55 μm. In this new design, a
homogeneous glass fiber is partially embedded lengthwise in a substrate of higher refractive index glass; the nonembedded
part of the fiber is air clad. Simulation results presented for fluoro-tellurite FOG waveguides confirm the
success of the new design in realizing single-mode propagation at 1.55 μm for a fiber diameter of 30 μm and a fibersubstrate
refractive index difference of 0.01. The design is robust, with good dimensional fabrication tolerance, but
predicted losses are over 6 dBcm-1. A proof-of-principle demonstrator is fabricated using two commercially available
multi-component silicate glasses (Schott F2 and F4). This shows multimode waveguiding at 0.633 μm, guidance around
a curve, and appears mono-mode at 1.575 μm.