Fabrication of heavy metal fluoride glass, optical planar waveguides by hot-spin casting

Abstract

Hot-spin casting is further investigated using a customised rig for making optical planar waveguides from inorganic-compound-glasses. The rig enables a controlled mass of core-glass, held above its liquidus, to be gravity-cast onto the top surface of a spinning cladding-glass substrate that has been pre-heated to around its glass transformation temperature. Spinning encourages the cast liquid to spread as a film over the top surface of the glass substrate. The mass of liquid cast is controlled by the timed opening of an orifice in the base of the core-glass melt-crucible. The resulting step index, slab optical waveguides are annealed, then cooled to room temperature; they comprise a higher refractive index, glass film core, on top of a lower refractive index glass substrate cladding. The glass film core is air-clad. at its upper surface. The process is applied to two heavy metal fluoride core/clad. glass pairs, namely ZBLANPb/ZBLAN and ZBLALiYPb/HBLANY (where ZBLANLiYPb is ZrF 4–BaF 2–LaF 3–AlF 3–LiF–YF 3–PbF 2 and H is HfF 4) to give waveguides of small and large numerical aperture (NA) (e.g. at 643.8 nm wavelength, NA is 0.18 and 0.33, respectively). The Hot-Spin-Cast waveguides exhibit a guiding region whose top surface tends to be parallel to the upper surface of the underlying substrate. However, flatness of the top surface of the guiding region is limited by the flatness of the top surface of the underlying substrate. Multimode slab waveguiding is demonstrated for both NA waveguide types for glass film cores of depths ⩾10 μm.