Application of diamond-like carbon films in optical fibre sensors based on long-period gratings

Abstract

The paper presents diamond-like carbon (DLC) film as a coating for optical fibres with long-period gratings (LPG). The coatings were successfully obtained using the Radio Frequency Plasma Chemical Vapour Deposition (RF PCVD) method. Thin DLC coatings significantly change the properties of the LPG-based sensing elements. The sensing systems built using those elements can be very sensitive to concentration changes of various chemical solutions due to changes in their refractive index. DLC-coated LPGs can be as much as 15 times more sensitive than uncoated LPGs to variations within a specified range of the refractive index of the surrounding medium. The influence of RF PCVD process parameters on sensitivity is discussed.