Specialty Optical Fibers Handbook

coating removal) after the fiber is drawn. Noncontact measurements of electrical

resistance and laser scattering techniques have been used to measure resistivity

and coating thickness, respectively [28, 30].

One analysis of the applied carbon material indicated that the layer consists of

disordered graphitic platelets that are randomly oriented and bonded on the

surface of the glass fiber in a continuous structure [5]. Thus, to close down

pathways between the graphite platelets for water or hydrogen ingression, the

carbon layer needs to have a thickness more than some minimum value. One

study concluded that the carbon thickness should be more than 20 nm to prevent

fatigue and 25 nm to delay hydrogen ingression [28]. It is important to realize

that