Analytical model for chromatic dispersion and dispersion slope compensation using linearly chirped apodized fiber bragg grating

Abstract

Chromatic dispersion (CD) is a phenomenon caused by wavelength dependent group velocity of an optical signal which travels at slightly different speeds in an optical fiber and leads to inter-symbol interference that eventually results in data loss and traffic interruption. As bit rates of optical fiber communication are increased, CD and dispersion slope also increase and hence it creates a big problem to transmit the data. The traditional means of decreasing the CD and dispersion slope by the deployment of dispersion compensating fiber (DCF) bundles throughout the optical network. Insertion loss and nonlinearity are the main drawbacks of using DCF for CD and dispersion slope compensation. CD and dispersion slope compensation using reflective Fiber Bragg Grating (FBG) is technically sound and cost effective. FBGs are also compact and provide no nonlinearity. In this thesis, an attempt is made to develop analytical models for CD and dispersion slope compensator using linearly chirped FBG by suppressing the reflected side lobes. Side lobes of the FBGs limit the CD compensation performance and introduce noise in the transmission system. Apodization is usually used to suppress the side lobes. Different apodization functions are compared to find out the best fit for CD compensation. It is found that the sinc apodization function is the most appropriate function to achieve significant negative dispersion in terms of strength factor and FBG length. Results show that a 10 cm FBG provides maximum negative dispersion (-70 ps/nm) and dispersion slope (-9 ps/nm2) at 1558 nm wavelength. Using the developed models MATLAB simulation is carried out to compensate CD for an optical transmission of various link length, input power and bit rate. The analysis and findings of this thesis will be helpful in designing appropriate dispersion compensation mechanism in modern high bit rate optical transmission system.