Optical waveguide monitoring

The invention features methods for detecting defects in and monitoring the transmission loss of an optical waveguide, during, for example, drawing or cabling of an optical waveguide. For example, the invention relates to monitoring the quality (e.g., monitoring transmission loss and detecting structural and compositional defects) of optical waveguides that utilize photonic bandgap confinement mechanisms for guiding light (referred to here as photonic crystal fibers), including hollow fibers. In general, defects refer to any structural, compositional or other perturbation of the fiber from its ideal design, which can affect the optical and / or mechanical performance and reliability of the fiber. Examples of defects include perturbations to core radius, perturbations to the layer thickness, delamination between layers, bubbles, particle inclusions in the core or layers, and compositional variations in the layers affecting the refractive index of the layers.

Fiber monitoring is performed