Author: Dr. After the fiber, the corresponding contributions appear at different times due to different group velocities of the modes. The fundamental mode comes first, as it is the fastest. The numerical simulation has been done with the RP Fiber Power software.
|Published (Last):||25 March 2009|
|PDF File Size:||17.51 Mb|
|ePub File Size:||15.44 Mb|
|Price:||Free* [*Free Regsitration Required]|
As pulse travels down the fiber, dispersion causes pulse spreading. This limits the distance travelled by the pulse and the bit rate of data on optical fiber.
In a fiber three distinct types of distortion are observed: 1. Intramodal dispersion: Pulse broadening within a single mode is called as intramodal dispersion or chromatic dispersion.
Since this phenomenon is wavelength dependent and group velocity is a function of wavelength, it is also called as group velocity dispersion GVD. The two main causes of intramodal dispersion are as follows: a.
Material dispersion: It is the pulse spreading due to the dispersive properties of material. It arises from variation of refractive index of the core material as a function of wavelength.
Material dispersion is a property of glass as a material and will always exist irrespective of the structure of the fiber. The amount of waveguide dispersion depends on the structure of the fiber and can be varied by altering the parameters such as NA, core radius etc. Intermodal dispersion: Dispersion caused by multipath propagation of light energy is referred to as intermodal dispersion.
Signal degradation occurs due to different values of group delay for each individual mode at a single frequency. In digital transmission, we use light pulse to transmit bit 1 and no pulse for bit 0. When the light pulse enters fiber it is breakdown into small pulses carried by individual modes.
At the output individual pulses are recombined and since they are overlapped receiver sees a long pulse causing pulse broadening.
This broadening of light pulses is known as dispersion. This Increase in width of the pulses makes it very difficult to distinguish them at the receiving end. Now observe the same diagram carefully. Due to this dispersion effect broadening of light pulses the digital bit pattern at the input side is not indistinguishable at the output side as the same bit pattern. As we know that optical sources emit a band of frequencies so do not emit just a single frequency. Therefore different spectral components present in the optical source take different propagation delay while travelling through the optical fiber.