The infrared (IR) spectrum is of significant importance in many defence applications including free-space communication, thermal imaging and chemical sensing. The materials used in these applications must exhibit a number of suitable properties including mid-IR transparency, rare-earth solubility and low optical loss. When moving towards miniaturised optical devices one tends to adopt the concepts introduced by integrated optics; multiple devices operating harmoniously on a single photonic chip. Our work focuses on the use of a laser to directly write into a novel chalcogenide glass to engineer optical waveguide devices. Our material of choice is gallium lanthanum sulphide (Ga:La:S) glass, an exceptional vitreous chalcogenide material possessing these aforementioned properties as well as a broad range of other properties. These Ga:La:S glasses have a wide transmission window between 0.5 to 10 μm. Furthermore, these low-phonon energy glasses have a high transition temperature (Tg = 560°C), high refractive index, the highest reported non-linearity in a glass, excellent rare-earth solubility with well documented near-mid IR spectroscopic properties. We report on low loss single-mode active channel waveguides in Ga:La:S glass engineered through direct laser writing (λ= 244 nm). We discuss laser operation at 1.075 µm (neodymium) and IR emission at 1.55, 2.02 and 2.74 µm (erbium) from these waveguides.
The advantages of gallium lanthanum sulphide (GLS) based glass over other competing glasses for active and infrared applications are evident through its low-phonon energy, high rare-earth solubility, high transition temperature and non-toxicity. However this glass often devitrifies during fibre drawing due to a small separation between the crystallisation and fibre thawing temperatures. Improving GLS fabrication technology may hold the key to achieving practical optical waveguide devices. In this paper, we describe the cunent GLS research status, methods ofimproving glass purity and our directions toward alternatives to traditional fibre technology, in particular planar channel waveguides and holey or microstructured fibres.