Distributed fiber optic chemical and physical sensors provide a relatively highly uniform response over the length of the fiber by, for example, varying such properties as the core/cladding index of refraction ratio to compensate for the non-linearity in sensitivity due to the loss of higher order modes in multi-mode fibers. The variation of the ratio changes the absorption coefficient of the fiber and can be used to compensate for any non-linearity in response. Other techniques for compensation also are disclosed.
Hydrogen sensor apparatus and method of fabrication 6,535,658
A porous glass rod is treated to include tungsten oxide and palladium in an arrangement that is sensitive to hydrogen to produce a color change that is a function of the hydrogen concentration. The rod is attached to the tip of a double fiber into one of which light is launched by a light source. A detector at the end of the second fiber is responsive to light reflected by the rod. The process for forming the rod includes the steps of doping the glass with a tungsten compound and a palladium compound with intervening and subsequent heating steps to bond the tungsten oxide and palladium to available oxygen atoms of the porous glass.