Hollow-core fiber made of ultralow expansion glass: Toward the ultimate stability for room-temperature fiber optics.

Optical fibers have revolutionized many fields including communications, sensing, and manufacturing. Better performance and further applications are expected from emerging hollow-core fibers (HCFs) in which light propagates through a central void. Such propagation eliminates most of the light-glass interaction responsible for most of the transmission impairments in current optical fibers. However, impairments resulting from glass elongation that make the phase and the propagation time of guided light change with external temperature remain even in HCFs. Here, we demonstrate an HCF made from an ultralow expansion glass that exhibits a three orders of magnitude lower coefficient of thermal delay than traditional fibers. This performance, added to the other unique properties of HCFs, opens the door to ultrastable fiber-based applications.