An optical fiber is provided with a Bragg grating formed along a portion of its core and a mechanical structure arranged adjacent to the Bragg grating for amplifying longitudinal strain on the fiber in the vicinity of the grating. The mechanical structure is designed to convert ambient pressure into longitudinal strain on the fiber in the vicinity of the grating and to allow the fiber to pass through the structure so that several pressure measuring apparatus may be arranged along a single optical fiber. An intermediate structure is provided between the fiber and the mechanical structure for minimizing buckling of the fiber. The methods of the invention include converting pressure into longitudinal strain on an optical fiber, amplifying the effect of pressure on the longitudinal strain, measuring pressure by determining the spectral location related to peaks (or minimums) of light reflected from an optical grating subjected to longitudinal strain.