Method and apparatus for absolute measurement of force by use of polarized, non-coherent light and compensation of strain-induced birefringence effects in a single mode-fiber optic waveguide

A method for the fiber-optic measurement of force, which is based on a strain-induced change in birefringence of a single-mode light waveguide, which is embedded at least along a part of its length in a plane situated vertically relative to a pretensioning force between disks which distribute said pretensioning force along the surfaces thereof, which comprises the steps of:

• beaming polarized, non-coherent light into one end of said light waveguide wherein a phase difference, of two linear modes of said light waves, which exit at an opposite end of said light waveguide, is caused by said force which acts on said light waveguide;
• and
• determining a consequent change in birefringence in order to achieve definite measurements,
• wherein fronts of said two light waves, which exit with linear modes, are directed transversely relative to a propagation direction by means of an optical component with a linearly space-dependent birefringence,
• and further wherein an autocorrelation function, which is imaged on a surface of said optical component from which said light exits, is determined by a line detector, and further wherein a selection signal sequence is evaluated in a computing process for determining a maximum of said autocorrelation function.

An apparatus for the fiber-optic measurement of force, based on a strain-induced birefringence of a single light waveguide, which comprises:

• a single-mode light waveguide;
• a plurality of disks;
• and
• a liquid crystal cell;
• wherein said single-mode light waveguide is embedded, at least along a part of its length in a plane situated vertically relative to a pretensioning force between said plurality of disks which distribute said pretensioning force along the surfaces thereof, and further wherein polarized, non-coherent light is beamed into one end of said light waveguide and a phase difference, of two linear modes of light waves, which exit at an opposite end of said light waveguide, is caused by said force which acts on said light waveguide, and further wherein at least one of a consequent change in said birefringence is compensated for in order to achieve definite measurements and a control signal, required for compensation is evaluated as a measurement for said force;
• and further wherein said liquid crystal cell, the birefringence of which is constantly changed by said control signal, is used as a compensator element, and wherein changes in intensity, which are shown on said liquid crystal cell as an image of said autocorrelation function, as a function of said control signal, are photoelectrically detected, and further wherein a selection signal is automatically checked at a maximum of said autocorrelation function.

An apparatus for the fiber optic measurement of force, based on a strain-induced change in birefringence of a single-mode light waveguide, which comprises:

• a single-mode light waveguide;
• a plurality of disks;
• an optical component with a linearly space-dependent birefringence;
• and
• a line detector;
• wherein said single-mode light waveguide is embedded, at least along a part of its length, in a plane situated vertically relative to a pretensioning force between said disks which distribute said pretensioning force along the surfaces thereof, and further wherein polarized, non-coherent light is beamed into one end of said light waveguide and a phase difference, of two linear modes of light waves which exit at an opposite end of said light waveguide, is caused by said force, which acts on said light waveguide, and further wherein a consequent change in said birefringence, is determined in order to achieve definite measurements,
• and further wherein fronts of said light waves, which exit with said linear modes, are directed transversely relative to a propagation direction by means of said optical component, and further wherein an autocorrelation function, which is imaged on a surface of said optical component from which said light waves exit, is determined by said line detector and wherein a selection signal sequence is evaluated in a computing process for determining a maximum of said autocorrelation function.