How does a fiber Bragg grating work?

How does a fiber Bragg grating work?

Fiber Bragg Gratings are made by laterally exposing the core of a single-mode fiber to a periodic pattern of intense laser light. All the reflected light signals combine coherently to one large reflection at a particular wavelength when the grating period is approximately half the input light’s wavelength.

What is fiber Bragg grating and its application?

Fiber Bragg Gratings (FBGs) are considered excellent sensor elements, suitable for measuring various engineering parameters such as temperature, strain, pressure, tilt, displacement, acceleration, load, as well as the presence of various industrial, biomedical and chemical substances in both static and dynamic modes of …

What is a fiber Bragg grating sensor?

A fiber Bragg grating (FBG) is a microstructure typically a few millimeters in length that can be photo inscribed in the core of a single mode fiber. This is done by transversely illuminating the fiber with a UV laser beam and using a phase mask to generate an interference pattern in its core.

What is a 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 period of grating?

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 grating strength?

The grating strength can be estimated from the following parameters: the grating period (Λ), refractive index difference (Δn) and the averaged refractive index (〈n〉) between the etched and unetched regions, the grating order (m), and the duty cycle (D) of the grating: κ = 1 Λ Δ n 〈 n 〉 sin ( m π D ) .

Which element of a passive optical network uses a Bragg grating filter?

Which element of a passive optical network (PON) uses a Bragg grating filter? Optical line terminal (OLT).

Where is a Bragg grating filter used?

Fiber Bragg gratings are used e.g. for fixing the wavelengths of fiber lasers, for filtering out certain wavelength components, for gain flattening of fiber amplifiers, and in fiber-optic sensors.

How does DFB laser work?

In a DFB laser, the grating and the reflection is generally continuous along the cavity, instead of just being at the two ends. As the temperature and current changes, the grating and the cavity shift together at the lower rate of the refractive index change, and there are no mode-hops.

What is grating element?

A grating is an arrangement consisting of a large number of parallel slits of same width and separated by equal opaque spaces. (a+b) is called grating element or grating constant. It can be seen that distance between two consecutive slits is grating element.

How many types of grating are there?

In general, there are four types of diffraction gratings: ruled gratings, holographic gratings, transmission gratings, and reflection gratings.

What happens the wavelength of light reflected by a Bragg fiber when the temperature of the fiber is increased?

2.14 shows the reflectivity of the upper sideband as a function of the Bragg wavelength in a thermal cycle ranging from 45°C to 85°C. At temperatures higher than 45°C, the reflectivity reduces monotonically from 20% to 3% as temperature rises.

What are the advantages of fiber Bragg gratings?

One of the main advantages of this technology is its intrinsic multiplexing capability. In fact, hundreds of fiber Bragg gratings can be written on a single optical fiber, which can be as close as a few millimeters or separated by a few kilometers (fig. 5).

What is a Bragg reflectance grating?

This means that if light from a broadband source is injected in the optical fiber, only light within a very narrow spectral width centered at the Bragg wavelength will be back-reflected by the grating.

What is the Bragg wavelength (λ B)?

The Bragg wavelength (λ B) is essentially defined by the period of the microstructure (Λ) and the index of refraction of the core (n ef ). A fiber Bragg grating has unique characteristics to perform as a sensor. For example, when the fiber is stretched or compressed, the FBG will measure strain.

How does FBG measure strain in optical fiber?

For example, when the fiber is stretched or compressed, the FBG will measure strain. This happens essentially because the deformation of the optical fiber leads to a change in the period of the microstructure and, consequently, of the Bragg wavelength.