Method of putting a bend into a fiber to make a strain sensor

A method of manufacturing an optical fiber having transmission characteristics responsive to different strain states of the optical fiber for a fiber optical strain sensor, the method comprising the sequential steps of:

• providing an optical fiber having a substantially straight shape;
• retaining the optical fiber at two retained regions with a free region between the two retained regions and with the optical fiber extending rectilinearly throughout the retained regions and the free region;
• heating the optical fiber locally over only a first portion of the free region to make the first portion soft, non-heated second portions of the free region extending from the retained regions and connected to or surrounding the first region and all non-heated regions of the optical fiber having a rigidity or elasticity:
• while locally heating the optical fiber, displacing the retained regions laterally relative to one another to make the non-heated second portions of the free region connected to or surrounding the soft first portion also be displaced laterally in a parallel way by the rigidity or elasticity of the non-heated regions to produce a bend of the optical fiber in the first portion;
• and
• allowing the optical fiber to cool.