A force sensor and a force sensing method use crystal rods as both force responsive elements and light transmission media in combination with light input circuitry and processing circuitry to sense an applied force, such as oil or gas well pressure or fluid flow friction.

Force sensor and sensing method using crystal rods and light signals

We describe an original technique that permits a specially accurate measurement of the variations of the transmittance of optical fibers vs the incidence of launched light. For large-diameter large-aperture fibers, which prefer light power transmission, the transmittance may be modeled using geometric optics. Taking into account the reflection losses at both ends, the core attenuation and a very weak lack of reflectivity at the core–cladding interface, good agreement is obtained between calculated variations and experimental results for the three kinds of fiber tested. The remaining difference has to be attributed to the mode coupling process which may be thus evaluated. The too high attenuation coefficient, which is attributed to the cladding to account for the losses at the core–cladding interface, characterizes in fact a thin perturbed layer where the materials contact. Thus, this method is a good means to evaluate separately the various processes contributing to the attenuation of open beams along the fibers and to determine which process should be worked on to improve the transmittance.

Accurate characterization of the transmittivity of large-diameter multimode optical fibers

A novel multimode fibre-optic differential pressure sensor based on fibre macrobending is described. Pressure changes are measured through the intensity variation of light in a fibre fixed to a hollow flattened deformable cylinder. Results of sensor performance are given and compared with a theoretical model which relates the sensitivity of the sensor to the experimental bending loss and the mechanical parameters of the cylinder.

http://iopscience.iop.org/article/10.1088/0022-3735/20/1/008/pdf

Fibre-optic differential pressure sensor

A sensor and method are disclosed for determining if a region, defined by two end points, in a structure has exceeded a predetermined amount of strain The sensor has an optical waveguide which has two ends for receiving and emitting light and which is fixable at two locations thereon to respective ones of the end points to define a sensing region therebetween The sensing region has a first portion with a first length and a first cross-sectional area, and a second portion with a second length and a second cross-sectional area which is smaller than the first cross-sectional area The lengths and cross-sectional areas are sized so that the optical waveguide has a strain failure point equal to the predetermined amount of strain The lengths and cross-sectional areas are approximately sized according to the formula R=α+1/ (α/β+1), wherein R=the ratio of the amount of strain in the second portion which will cause the optical waveguide to fail to the predetermined amount of strain in the structure, α=the ratio of the length of the first portion to the length of the second portion, and β=the ratio of the cross-sectional area of the first portion to the cross-sectional area of the second portion

Optical fiber strain-to-failure sensor

Optical fibers, which can be sharply bent without high transmission losses, are called bend insensitive fibers. These fibers were developed to meet the increased demand of Fiber-To-The-Home (FTTH) applications, to allow for miniaturization of fiber optic sensors and telecom photonic components, etc. Ordinarily the structure and design of these fibers is described and its advantages specified without an explanation of how it functions. In this paper, a model of bent fiber function is proposed. With an improved capability for analysis, accurate calculations and a simplified understanding of bend insensitive fiber function should permit the expansion of fiber applications. The model presented here is based on mode-ray equivalence and applied to multimode bend insensitive fiber with low refractive index trench. A study is made of the influence of directional properties of a light source exciting a waveguide and of the parameters of the fiber on the sensitivity to bending. The dependences of light transmission on the bending radius are derived for various optical fibers and compared with experimental results.

Light transmission of bend insensitive optical fiber

An analysis is made of the dependence of the transmission of light on the bending radius of a waveguide from the point of view of mode–ray equivalence. A study is made of the influence of directional properties of a radiation source exciting a waveguide and of the parameters of the waveguide itself on the sensitivity to bending. The dependences of light transmission on the bending radius are derived for various waveguides and angular distributions of the radiation emitted by a source.

Light transmission of bent multimode optical fibers

Device for measuring the angle of inclination

Optical-fibre level indicator

Fiber-optical strain gauge

The temperature dependences of the transmission of light by bent multimode fiber waveguides were determined experimentally and analyzed. A study was made of the influence of the directionality of the radiation from a source exciting a waveguide, of the bending of a waveguide, and of the parameters of quartz-polymer and quartz-quartz fibers on the sensitivity of waveguides to temperature. The information on the sensitivity should be useful in the design of displacement and temperature sensors constructed from bent multimode waveguides.

http://iopscience.iop.org/article/10.1070/QE1984v014n11ABEH006473/pdf

Patlakh Anatolij L

Papers

Light transmission of bent multimode optical fibers

Device for measuring the angle of inclination

Optical-fibre level indicator

Fiber-optical strain gauge

Influence of temperature on the transmission of light by bent multimode fiber waveguides