Harsh environment sensor applications are becoming more accessible due to the implementation of single-crystal optical materials and devices. In particular, fossil energy applications like gas turbines or coal gassifiers require new, more robust sensing technologies compatible with modern control schemes. Fabricating common devices in sapphire or YAG fibers rather than standard fused silica can extend the operating temperature range significantly beyond the current state of the art. Here, we discuss configuration of our Laser Heated Pedestal growth (LHPG) system with a novel control algorithm that permits the growth of fibers with non-uniform diameters along the fiber’s length. This algorithm controls the molten zone height, laser power, and drawing rates simultaneously to reduce the mismatch between instantaneous diameter changes and current diameter. We detail the range of structural possibilities achievable using this control technique, and subsequently evaluate the spectral properties of as-grown devices like sapphire long-period gratings. Finally, we make recommendations regarding new single-crystal sensor devices which will be shown to maintain operational stability over a wide range of operating temperatures.
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