Fiber optic sensors with POF

Fiber optic sensors are used in many technical areas as an alternative to electrical sensor systems. Typical areas of application are

  • Construction industry (strain measurement, vibration measurement),
  • Mechanical engineering (vibration measurement),
  • Chemical industry (temperature measurement), and also
  • Medical and biotechnology (minimally invasive measurement inside living organisms).

Fiber optic sensors that are mainly used today are based primarily on glass fibers. However, the costs for such sensor systems are so high that a decision can only be made to purchase them after a comprehensive economic analysis and, in many cases, the purchase is not made.

POF sensor systems have many advantages over fiber optic systems:

  • POF is not brittle like glass fiber and can be stressed much more in strain sensors.
  • The transceiver technology required for a POF fiber optic sensor is much easier to manufacture, more robust and easier to install on site thanks to the large core diameter of the POF.
  • A technical team of specialists with expensive measurement technology is normally not required to assemble a POF sensor system. The wavelengths used in a POF sensor are visible to the human eye and can be checked with comparatively simple measuring technology.
  • Compared to fiber optic sensors, POF sensors can be offered at significantly lower costs.

The advantages mentioned outweigh the disadvantage of the POF-based sensor system compared to the glass fiber-based sensor system with regard to higher attenuation and thus shorter range in many cases.

For these reasons, DieMount has been working on POF sensor systems for a number of years, initially focusing on the required components and the physical measuring principles. Since the beginning of 2017 we can offer complete sensor systems, especially the POF installation tester. The following publications show important development steps in the course of our sensor development.

Measuring principle duplex E2

Measuring principle duplex E2

Measuring principle for fiber optic color measurement with POF cable

The measuring principle of fiber optic sensors is described in the publication ( “Sensors for color measurement via optical polymer fibers” ) from 2010. It shows how POF-coupled LED modules of different wavelengths and passive optical components (splitters) enable the construction of color-sensitive sensors for transmission and reflection.

3 fiber-coupled LED modules of different wavelengths couple their light via a 1 × 3 splitter to a mixed fiber, which guides the light to the test object via a wire of a duplex cable. There it is reflected, returned via the second wire of the duplex cable and detected. The electronics ensure that the 3 wavelengths are differentiated via time or frequency multiplex. In this way, the measuring system receives information about the reflection behavior of the measuring object for each of the 3 wavelengths.

By carefully selecting the LED wavelengths, it is possible to obtain spectral information that is adapted to the test object.

Sensor signal for vibration measurement

Sensor signal for vibration measurement

POF reflection sensor for vibration measurement

The development of a POF vibration sensor published in 2015, which can measure the mechanical vibrations of a beam or a machine part with a single POF wire, is available for download under the link  “Polymer optical fiber (POF) based sensors for the measurement of elongation via a single fiber ¨ . The sensor electronics contain a POF splitter with extremely high crosstalk attenuation so that the sensor signal reflected by the sensor head is not disturbed too much by the transmitted signal.