A Fibre Bragg Grating (FBG) is a novel optical sensor recorded within the core of a standard optical fibre. It reflects a narrow bandwidth of light, which responds faithfully to changes in temperature and strain. Many FBG sensors can be recorded onto a single optical fibre and interrogated simultaneously with a single instrument - the effect is a very low cost mechanism for distributed monitoring of strain and/or temperature within large structures, particularly suited to design validation and structural health monitoring.

  • Optical strain and/or temperature sensor
  • Zero power, EMI immune
  • Intrinsically safe
  • Highly stable
  • Multiple km signal integrity
  • Available singly or in multiple FBG arrays
  • Suitable for composite embedment
  • Can be used to manufacture smart sensors and transducers
  • Suitable for long-term SHM

Related FAQs

FAQ. What is the warranty period for Smart Fibres' interrogators?

All of our fibre optic interrogators come with a standard one year warranty. This warranty can be increased on a year by year basis. Extended warranty is available at the time of initial purchase on request.

FAQ. How do I compensate for the thermal effect on the strain measuring FBG?

We recommend that a second FBG, which is completely isolated from strain, is fitted close to the strain measuring FBG. Temperature compensation can be achieved in 2 methods, loose FBG or a strain isolated coupon with a known CTE. Our SmartSoft software includes a utility to automate this temperature compensation process.

FAQ. Can FBGs be supplied with a protective sleeve and connector?

Yes, Smart Fibres can supply protective sleeves to suit the requirement of your application and terminate with an FC/APC connector.

FAQ. How reliable are FBG sensors?

Optical fibre fatigue reliability is very high and FBG sensors benefit from this fact. For instance, client tests found that Smart Fibres’ SmartPatch sensors were still 100 % functional after 6 x107 cycles of tensile and compressive fatigue loading.

FAQ. How do I calculate which wavelength to use for my FBGs to maximise the number of sensors on a particular channel?

Smart Fibres has created a wavelength budget calculation tool for FBG wavelength selection.

Please Email Us or call +44 1344 484111 with details of your application and we can help you create a wavelength budget.

FAQ. How do I choose the correct fibre coating and FBG recoating?

Please refer to the table below as a guide.

For strain measurement we recommend to use a Polyimide recoat over the FBG due to its superior strain transfer properties.

Measurement and environment conditionRecommended fiber coating and re-coat material
Strain measurement > 85 °CPolyimide coated fiber with Polyimide recoat (P/P)
Strain measurement < 85 °CAcrylate coated fiber with Polyimide recoat (A/P)
Temperature measurement > 85 °CPolyimide coated fiber with Polyimide recoat (P/P)
Temperature measurement < 85 °CAcrylate coated fibre with Acrylate recoat (A/A)

Please Email Technical Support or call +44 1344 484111 if you need more help on this point.

FAQ. Under which conditions are FBG wavelengths normalised? i.e., if I order a FBG with 1550 nm reflective wavelength, at what conditions will it reflect the 1550 nm wavelength?

Nominal wavelengths are at room temperature, unloaded. The exact value depends on manufacturing tolerances –typically +/- 0.3 or 0.5 nm.

FAQ. What fibre type is used in your systems?

Single mode fibre with a 9 µm core, 125 µm cladding, and a 155 µm Polyimide or 245 µm Acrylate coating. Optical Fibers with pure silica core, bend tolerant and small core e.g. 6/125 or 4/125, can also be used but with some optical power losses. Multi mode fibre cannot be used.

FAQ. Which length of FBG should I select for my application?

Longer FBGs have a higher reflectivity, but are narrower in wavelength. Our SmartScan instrument range is optimised for best accuracy and resolution with 2 mm or 5 mm FBGs. SmartScope instruments can accommodate narrower FBGs and fiber optic sensors with different spectral features.

You may need to choose the length of the FBG based on the size and strain distribution of the substrate you are planning to measure. E.g., choose a FBG smaller than the substrate length. Also, if there is a strong strain gradient where you want to measure, a shorter FBG is better because the reflection peak of a longer FBG is more likely to become distorted and hard to measure.

Please Email Technical Support or call +44 1344 484111 if you need more help on this point.

FAQ. How do I find the FBG on the fibre?

The typical marking scheme is two black marks per FBG, which are about 10 to 15 mm apart. The FBG is within these marks.

FAQ. What is the minimum and maximum distance between FBGs on an FBG array?

FBGs can be spaced anywhere on the fibre greater than 1.5 mm apart.

FAQ. Can we put different sensor types on the same fibre?

Yes, Smart Fibres’ WDM products allow the user to combine different sensors types, e.g. temperature, strain and vibration all on a single fibre.

FAQ. Do you have a procedure for mounting FBG sensors onto a substrate?

Yes, please send your request to [email protected].