Write a short note dispersion shifted dispersion flat fiber, Electrical Engineering

Write a short note on dispersion shifted and dispersion flatted fibers?

The dispersion features of a fiber is display below:

1090_flatted fibers.png

The overall dispersion is the sum of material dispersion and waveguide dispersion.
At wavelength larger than the zero material dispersion (ZMD) point within most general fibre designs, the material and waveguide elements are of opposite sign and can thus be made to cancel at a few longer wavelengths. Therefore the wavelength of first order chromatic dispersion can be shifted to the lowest loss wavelength for silicate glass fiber at 1.55 µm to gives both low dispersion and low loss fiber. This may be achieved through such mechanisms as a reduction in the fiber core diameter along with an accompanying raise in the relative or fractional index difference to create so known as dispersion shifted (DS) fiber.

An alternative modification of the dispersion characteristics of single mode fibers includes the achievement of a low dispersion window over the low loss wavelength region among 1.3 µm and 1.6 µm. like fibers, which relax the spectral requirements for optical sources and permit flexible wavelength division multiplexing are called as dispersion flatted (DF) fibers.

A huge variety of single mode fibers refractive index profiles are capable of modifications within order to tune the zero dispersion wavelength point λ0 to a exact wavelength inside a region adjacent to the zero material dispersion (ZMD) point. The simplest profile is in which of a step index fiber, as shown below:

1021_matched cladding.png

λ0 could be shifted to longer wavelength through altering the material composition of the fiber, which is through increasing the level of germanium doping in the fiber core. We use various profiles for DS as display below:

1084_Triangular profile.png

Fig: Triangular profile

1545_Depressed cladding triangular profile.png

Fig: Depressed cladding triangular profile

842_Gaussian profile.png

Fig: Gaussian profile

For better results we use advanced refractive index profiles like as

380_Triangular profile multiple index.png
Fig: Triangular profile multiple index

2477_segmented-core triangular profile design.png

Fig: segmented-core triangular profile design

1159_Dual shaped core design.png

Fig: Dual shaped core design

In dispersion flatted fibers there are two wavelengths of zero dispersion. For getting this window of low dispersion we use various profiles as display below:

1299_Double clad.png

Fig: Double clad

112_Triple clad.png

Fig: Triple clad

740_quadruple clad.png

Fig: quadruple clad

The graphical representation of the DS and DF fibres is given below:

1109_DS and DF fibres.png

Posted Date: 5/14/2013 5:28:50 AM | Location : United States

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