Fiber Bragg Gratings

FBG (fiber Bragg grating) is a periodic circuit created in a fiber core. It has a capability to reflect certain emission wavelengths and transmit the others. The refraction index periodic variation in the fiber core causes the reflection generating a wavelength-specific dielectric mirror. Hence, fibre Bragg grating performs as an inline fiber optic filter blocking or reflecting specific wavelengths.

Fiber Bragg gratings may serve as:

  • Sensing elements in FBG sensors
  • High Reflector (HR) and Outpur Coupler (OC) mirrors in laser cavities
  • Spectral filters (optical fiber filters)
  • Dispersion compensators in telecommunications.

FBG spectral specifications are based on the periodic change of fiber core refractive index at different lengths and depend on the optical heterogeneity diffraction.

A fiber Bragg grating can be of different lengths from 0.3 to 50 mm.

The length of periodic fiber optic grating changes when mechanical compression and tension are applied; hence, the reflected wavelengths are adjusted as well.

FBG key advantages:

  • Narrowband optic emission reflection
  • Made of optical fiber
  • Low optical loss
  • Small size
  • Relatively simple and low-cost production

Fiber Bragg grating spectra specifications of reflected signals can be checked through comparing the grating length and strain gradients of FBG sensors.

Specifications

Central Wavelength, nm 430 - 2200
Wavelength Tolerance, nm < 0.1
Reflectivity, % 3 – 99.9
Bandwidth (FWHM), nm 0.015 - 3
Sidelobe Suppression Ratio (SLSR), dB > 20
FBG Length, mm 0.3 - 50
Tensile strength, N 10
Coating Acrylate; Polyimide; No coating
Temperature range (acrylate), °C -20 … +85
Temperature range (polyimide), °C -200 … +350
Connector FC/PC; FC/APC; any other

Optromix manufactures various optical fiber Bragg grating products. We can accommodate your special requirements and design a fiber product catered specifically for your needs.

Our capacities:

  • apodized fiber Bragg gratings;
  • FBGs inscription into non-photosensitive fiber (with a pure silica core) or writing through the coating. It is quite efficient to use them for the monitoring of facilities with harsh environment (for example, in oil & gas industry);
  • π-phase-shifted fiber Bragg gratings. Typically we write pi phase shifted FBGs into passive fibers only;
  • long-period fiber gratings (LPFG). Incription of long-period fiber gratings is carried out by the method of femtosecond modification of the fiber core refractive index. LPFGs can be efficiently used as spectral filters of high power fiber lasers as well as high temperature sensors;
  • tilted fiber Bragg gratings;
  • chirped FBGs;
  • customized fiber Bragg gratings;
  • FBGs writing into special optical fibers (Panda, active, PCF, etc.).

FBG fabrication is a complex process. Bragg grating is usually written into a single mode fiber with an acrylate or polyimide coating. Unlike a multimode fiber, a single mode fiber has a much smaller core diameter.

Acrylate fiber is inexpensive, easy to clean up (with a mechanical or thermal stripper), but it is suitable only for regular operating conditions (it can withstand constant exposure to -20 … +85°C temperature range, and for a short period of time up to + 100°C).

Polyimide fiber is significantly more expensive, it is more difficult to clean up (with an electric arc or concentrated sulfuric acid), it is suitable for more aggressive environments with operating temperature -200 ... +350°C. Some polyimide high temperature optical fibers can withstand temperatures up to 800°C.

Currently, there are three known methods of FBGs inscription:

  1. interferometric method, when fiber core is illuminated with a fringe pattern created by a phase mask (in this case FBG period is defined by a phase mask period);
  2. direct point-by-point method, when each FBG “pitch” is formed as a result of the nonlinear fs laser pulse absorption (in this case FBG period is defined by laser pulse repetition rate and by velocity of a fiber translation along its axis);
  3. continuous core-scanning method, when fiber position is modulated in transverse plane (in this case FBG period is defined by modulation frequency and by velocity of a fiber translation along its axis).

Optromix is able to write fiber Bragg gratings by all 3 techniques, using 4 available laser stands.

Optromix will write a tailored fiber Bragg grating based on your specific requirements, which can be used with any type of optical fiber sensor technology. We will make sure to analyze your fiber optic applications and deliver the most suitable solution.

If you would like to purchase FBGs (Fiber Bragg Gratings), please contact us: or +1 617 558 98 58