Technical Basics
The use of Optical Fibres has drastically increased the last 2 decades, especially in the fields of data transmission, optical sensors, analog and digital data connections, laser power guiding and special effects lighting applications.
Most important reasons for using fibre optics are
- small size and weight
- enormous potential in terms of bandwidth
- immunity of electromagnetic interference (EMI) and crosstalk
- no danger of explosion
- high signal integrity
- low transmission loss
- ruggedness and flexibility
- low cost
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There are several types of fibres we use
- Polymer Cladded Fibre (PCF, POF, Quartzfibres)
- Step Index multimode Fibre
- Gradient Index Multimode Fibre
- Single Mode / Monomode Fibre
Typical coating materials are acrylate (one or two layers) and polyimide .
As optical connectors mostly FC/APC connectorization is used in our systems.
The Fibre Bragg Grating (FBG) reflects light with a certain frequency (Color) which is determined by by the physical structure of the grating. This frequency shifts by strain or heat which is locally induced in the active sensor region.
FBG - Sensors for Material Strain Monitoring show following advantages:
- Long term stability, due to "inscribed" physical structure
- Low attenuation of the sensor's signal over long distances
- Immunity against electromagnetic interference
- Multiple sensors in one fibre (cascading)
Most important technical features of the FBG for strain sensors are:
- Maximum strain for the FBG: 1 % = 10,000 µstrain
- Strain resolution : 1 strain
- Accuracy : 5 µstarin
- FBGs can be cascaded (aligned along one fibre)
- Distribution and number of gratings in one string depends on the maximum of expected strain for each measurement point
Most important technical features for FBG temperature sensors are
- Max. temperature: + 120 °C without coating, up to 600 °C with special metal coatings
- Temperature resolution : 0,08 °C
- Temperature accuracy : 0,4 °C
- Can be produced as a string
- Local distribution and number of gratings depend on the maximum expected temperature difference for each measurement point