What is FBG sensor?
FBG sensors are the most popular architecture for single- and multiple-point temperature and/or strain sensing in an optical fiber [19]. An FBG is a periodic modulation, with period Λ, of the effective refractive index neff localized within the core of an optical fiber [20], as shown in Fig. 11.6.
What is fiber Bragg grating give its application?
The primary application of fiber Bragg gratings is in optical communications systems. They are specifically used as notch filters. They are also used in optical multiplexers and demultiplexers with an optical circulator, or optical add-drop multiplexer (OADM).
What is volume Bragg grating?
Volume Bragg gratings (also called volume holographic gratings) are Bragg gratings which are written inside some transparent material, e.g. in the form of a cube or a parallelepiped – in contrast to diffraction gratings made on the surface of an optical element or fiber Bragg gratings, where the grating is written into …
What is fiber Bragg grating ques10?
One embodiment is to create a fib-siner Bragg grating (FBG) in an optical fiber. This can be done by using two ultraviolet light beams to set up a periodic interference pattern in a section of the core of a germania-doped silica fiber.
What is a Bragg filter?
An optical Bragg grating is a transparent device with a periodic variation of the refractive index, so that a large reflectance (reflectivity) may be reached in some wavelength range (bandwidth) around a certain wavelength which fulfills the Bragg condition.
What is volume phase holographic grating?
Unlike traditional gratings, volume phase holographic (VPH) gratings do not have surface grooves. Instead, VPH gratings consist of a dichromated gelatin (DCG) film between two glass substrates. These VPH gratings are designed to reduce the periodic errors that can occur in blazed gratings.
How is diffraction efficiency measured?
A novel spectral test station can assess diffraction grating efficiency at specific wavelengths by simultaneously indexing incident wavelength and the unit being tested. Diffraction gratings are in most optical spectrometers covering visible, IR and UV spectra.
What is grating period?
A grating is called an SPG when the period of the grating is less than the optical wavelength, which is on the order of 1.3–1.6 μm. For typical SPG, the period of the grating is Λ = 0.5 μm. In this grating structure, the interaction of light takes place with a periodic structure, as shown in Fig.
What is thick hologram?
A thick or volume hologram is one where the thickness of the recording medium is greater than the spacing of the interference pattern. The recorded hologram is now a three dimensional structure, and it can be shown that incident light is diffracted by the grating only at a particular angle, known as the Bragg angle.
What is diffraction efficiency of grating?
Diffraction efficiency is the performance of diffractive optical elements – especially diffraction gratings – in terms of power throughput. It’s a measure of how much optical power is diffracted into a designated direction compared to the power incident onto the diffractive element of grating.
What is the pitch of a grating?
A diffraction grating consists of a large number of regularly spaced grooves on a substrate. The distance between adjacent grooves is called the pitch.
What is resolving power of grating?
Resolving Power: The resolving power of a grating is a measure of its ability to spatially separate two wavelengths. It is determined by applying the Rayleigh criteria to the diffraction maxima; two wavelengths are resolvable when the maxima of one wavelength coincides with the minima of the second wavelength.
What is the best diffraction grating?
Ruled, Blazed Diffraction Gratings Ruled blazed gratings are very efficient, and are generally the best choice for applications requiring high signal strength.
What is minimum deviation in diffraction grating?
Minimum Deviation Method Theory: Let a beam of light of wavelength ‘λ’ which is incident making an angle ‘i’ with the normal to the plane of the diffraction grating be diffracted through an angle ′ ′ (Figure 2).
What is the value of n in diffraction grating?
Obviously, d = \frac {1} { N }, where N is the grating constant, and it is the number of lines per unit length. Also, n is the order of grating, which is a positive integer, representing the repetition of the spectrum.
What is grating spacing?
For a diffraction grating, the relationship between the grating spacing (i.e., the distance between adjacent grating grooves or slits), the angle of the wave (light) incidence to the grating, and the diffracted wave from the grating, is known as the grating equation.
What is the accuracy of FBG strain sensor?
The initial accuracy of FBG strain sensor reaches 0.02 mm, is second only to an inclinometer and is much higher than other methods. The maximum sliding distance and dynamic range are also very large than those of other methods. It can collect data as long as the inclinometer is not damaged.
What are the advantages of FBG gratings?
Fiber Bragg Gratings are known to have a stable and reliable wavelength response as function of the applied strain. FBGs are therefore gaining increasing attention in the field of strain measurements. Ormocer ® coated DTG ® s can be fixed directly or integrated in a patch on the surface of the test object like normal strain gauges.
Why use FBG sensors for off-line monitoring?
Strain measurements using FBGs is an absolute measurement what makes this type of sensors ideal for off-line monitoring whereby the measurement device is not all the time connected to the sensors. FBGs are intrinsically passive (no electrical power required) and therefore can be positioned in high voltage and potentially explosive atmosphere areas.
How many FBG sensors can be installed on a single optical fiber?
Multiple FBGs (>20) can be monitored in series on one single optical fiber, no return fiber is needed. Special interrogator techniques even allow to have more than 1000 FBG sensors on a single fiber. Due to the nature of the glass, FBGs show a good corrosion resistance.