Optical sensors with fiber optic components
The Polymer Optical Fiber (POF) offers new opportunities for the fiber optic measuement in sensors technology. Generally it is necessary to place the light emitter, e.g. a LED or a laser diode, close to the object to be measured. By the use of a POF coupled light emitting module the module can be mounted distant from the device under test and the light is transmitted via POF to the object. All electronic equipment including the thermal control units for the optical module is at a remote place.
Using POF splitters measurements with different wavelengths are feasible. The figure below shows a typical POF based setup for the fiber optic colour measurement:
3 fiber coupled LED-modules with different wavelengths couple light over a 1×3 splitter to a mixing fiber that guides the light via one waveguide core of a duplex POF cable to the device under test. The reflected light is guided back via the second duplex cable core and detected. By time or frequency multiplex the electronics is able to determine a reflection factor for each wavelength.
Appropriate selection of LED wavelengths allows to determine the relevant spectral information of the decice under test.
Further technical improvements allow to take into account aging and temperature variations of the LED module optical power. If there is very little space for the POF cable, the duplex cable can be substituted by a simplex cable.
Further details of the measurement principle are enclosed in the presentation “Sensoren für die Farbmessung über die Optische Polymerfaser” (Download, in German language). Further questions to the system are welcome.
We developed POF vibration sensor which measures the mechanical vibration of a bar or a machine part with one POF core. Download: “Polymer optical fiber (POF) based sensors for the measurement of elongation via a single fiber“. The sensor electronics continues a POF-Splitter with extremly high crosstalk loss, so the sensor signal reflected from the sensor head is not disturbed too much by the transmitting signal.
POF Reflection Meter