More sensitive toxic gas sensors can provide earlier warning by detecting lower concentrations at greater distances from the source than conventional technologies. Recently, microtoroid whispering gallery mode optical resonators with selective polymer coatings have demonstrated part-per-trillion sensitivity to several gases, making them one of the most sensitive gas detection technologies. However, these sensors are currently coupled to laser sources via fragile and vibration-sensitive tapered optical fibers, hindering their translation from the laboratory into the field. Here we design and assemble periodic nanostructures onto the rim of microtoroids to improve free-space coupling efficiency, obviating the need for the tapered optical fiber.
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