Simulation Study of Pulse Broadening due to Material Dispersion and Bending Losses of a Single Mode Step Index Optical Fiber

Abstract

Optical fiber plays an important role in modern civilization. It is flexible and transparent which is made by silica or plastic to a diameter slightly thicker than that of a human hair. Optical fibers typically include a transparent core surrounded by a transparent cladding material with lower refractive index. It is used mostly as a means to transmit light between the two ends of the fiber and wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (i.e. data rates) than copper cable. Fibers are used instead of metal wire because signals travel along them with lesser amounts of loss. In addition, optical fibers are also immune to electromagnetic interference, a problem from which metal wires suffer excessively.  However the fiber itself has many chances to attenuate the transmitting signal. Two important sources of signal loss are the pulse broadening (which is due to the material dispersion) and bending of the fiber. Therefore it is essential and important to optimize these losses of the incoming signal.

In this thesis the result of a simulation study on pulse broadening due to material dispersion and on the losses due to bending of a single mode step index fiber (SMSIF) has been reported. SMSIF is commonly used in communication system than multi mode fiber (MMF) because of its low attenuation and dispersion loss. The study has been performed using the software “Understanding Fiber Optics on a PC”. From this study it has been found that the minimum pulse broadening due to material dispersion up to a fiber length of 90 km is obtained at an operating wavelength (λ) of 1274 nm and spectral width (Δλ) of 2 nm for 130 ps input pulse. On the other hand at 1274 nm of the operating wavelength, 4.0 µm of the core radius (a), and 0.34% of the relative refractive index  a minimum bending losses of 0.0 dB is obtained for which the normalized frequency (V) is 2.380. Using these parameters a fiber is capable to a curve of 6.75 cm bend radius without any signal loss. These results may be considered as an important milestone during the fabrication process of an optical fiber.       

• Supervision