i. One embodiment is to create a fiber 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.
ii. Since this material is sensitive to ultraviolet light, the interference pattern induces a permanent periodic variation in the core refractive index along the direction of light propagation. This index variation is illustrated in Fig. 4.8, where $n_1$ is the refractive index of the core of the fiber, $n_2$ is the index of the cladding, and Λ is the period of the grating.
iii. If an incident optical wave at $λ_0$ encounters a periodic variation in refractive index along the direction of propagation, $λ_0$ will be reflected if the following condition is met: $λ_0=2n_{eff} Λ, $ where n effective $(n_{eff} )$ is the average weighting of the two indices of refraction $n_1$ and $n_2$.
iv. When a specific wavelength $λ_0$ meets this condition, that wavelength will get reflected and all others will pass through.
v. In the FBG illustrated in Fig. 4.8, the grating spacing is uniform along its length. It is also possible to have the spacing vary along the length of the fiber which means that a range of different wavelengths will be reflected by the FBG. This is the basis of what is known as a chirped grating.
Application of Fibre Gratings:
• Dispersion compensation,
• Stabilizing laser diodes,
• Add/drop multiplexing
• WDM Systems
and 5 others joined a min ago.
teamques10
★ 68k