Fibre-optical strain-gauge

The present invention relates to a fibre optic strain-gauge of the kind using a mechanical construction providing a linear, strain-dependent relative movement of oppositely positioned spaced-apart first and second optical fibre-holding elements in a direction substantially perpendicular to the axial direction of the optical fibres, in which the varying transmission of light between the two fibres is used as an indication of the strain. In a fiber-optical strain-gauge of the kind comprising a mechanical construction providing a linear, strain-dependent relative movement of oppositely positioned spaced-apart first and second optical fiber-holding elements in a direction substantially perpendicular to the axial direction of the optical fibers, and in which the varying transmission of light between the two fibers is used as an indication of the strain, the main new feature is that the strain-gauge is manufactured using the following steps: a) prestressing an optical fibre by applying a pulling force, or prestressing the mechanical construction by applying a compressing force; b) fixing said optical fiber to the fiber-holding elements in the mechanical construction; and c) cleaving the optical fiber at the interspace between the fiber-holding elements. With this arrangement the optical fiber ends are aligned in an exact position in a simple manner without using any expensive micro-manipulation tools, and a high precision of the gap between the two fiber ends can be provided in a simple manner by controlling the prestressing of the optical fiber, or the mechanical construction.