an optical fiber exhibits varying transmission characteristics in different strain states and can have an s - shaped microbend . for producing such a fiber it is heated locally in a small region , as viewed in the longitudinal direction of the fiber , and then the portions of the fiber located at the two sides of the heated region are displaced in relation to each other in a transverse direction in relation to the longitudinal direction of the fiber . it can be performed in a conventional fusion - splicing apparatus for optical fibers . alternatively , a laser can be used as a heating source , what is particularly suitable for processing optical fibers having longitudinal cavities in order to infer to it similar transmission characteristics . the optical fibers produced by this method are suited for use as sensors , e . g . strain gauges .