Fiber optic sensor

A fiber optic sensor (FOS ) is a special sensor (sensor ) for optical measurement method based on fiber-optic cables (FOC). In fiber optic sensors, the measured variable is not represented or transferred by an electrical quantity, but by an optical.

Optical waveguides are in the news and communication technology for data transmission, or also in automation technology, and excel in addition to high bandwidth especially by the fact that they permit a transfer that is not susceptible to external influences, for example, to electromagnetic fields. Despite this the general good and uninterrupted transmission properties, the optical signals in optical fibers can be attenuated or altered by internal and external influences, see Article optical waveguides. They react strongly among other geometric changes of the waveguide by bending, train, pressure or torsion, and more generally, to change the light guiding properties, such as damage of the cladding material. At this point, put on fiber optic sensors. For them, the influence of the light signals through external parameters is explicitly desired.

Evaluates the change various parameters of the light used, these include above all the intensity, wavelength (color) and polarization and the duration of the signals. The easiest way to change the intensity and thus the transmission characteristics of a damping measurement record. The other parameters will typically require a somewhat more complex measurement set-up, as a spectrometer, and for detecting the polarization of the polarizers and corresponding modulators are required for the detection of the wavelength change.

There are two classes of fiber optic sensors:

• Fiber optic pressure sensors, in which, through pressure -induced bending losses to changes in transmission in the fiber.
• Fiber optic temperature measurement for spatially resolved temperature measurement by temperature-dependent Raman scattering in the fiber.
• A gyroscope for measuring the angular velocity of two by means of interference in a coiled optical fiber in opposite circumferential beams (based on the Sagnac interferometer ).
• The fiber optic hydrophone for measuring pressure fluctuations in the water ( underwater microphone ) can be built on the principle of Mach-Zehnder interferometer. One of two fiber coil is protected against environmental influences, the other is in the water. Pressure fluctuations in the water altering the optical length of the fiber coil. The sensitivity increases with the number of the windings. Alternative shapes of the fiber optic hydrophone is coated end faces of the fiber, which also allows a change in length with change in pressure or an interferometric measurement using the piezo- optical effect ( the refractive index is the water pressure dependent).
• In fiber-optic dosimeters, the effect is exploited that by ionizing radiation defects in the glass occur which lead to reduced transmission. Since the effect is cumulative and virtually irreversible, these dosimeters have a greater range of linearity, and the display is long -term stable than other types of construction.

• Fiber in which the pyrometer used for measuring the temperature of infrared radiation can be transported to difficult accessible places measurement ( blast furnace, etc.).
• Fiber optic temperature probe in which the temperature-dependent kinetics of the phosphorescence is used by mounted on the tip of the glass fiber magnesium Fluorgermanats for temperature measurement.
• Optical microphones ( fiber transducer ) in which the sound pressure is converted to changes in optical intensity of the membrane changes. by reflection of laser light on the moving membrane
• Fiber optic photoelectric sensors, are used for object detection in automation technology. Optics and electronics are disposed separately in this case, in favor of the application.