فهرست مطالب مهناز عصاری

In this paper the dependence of single mode region of air-silica microstructures on the structural parameters، the period and diameter of air hole array have been studied theoretically. The calculations have been done for three kinds of microstructures with one، two or three holes missing in the center of fiber by using scalar effective index method. The structures which we call them MOF1، MOF3 and MOF7 respectively have different single mode region. It is shown that MOF1 microstructure has larger single mode region. Optical confinement factor of the MOF1، MOF3 and MOF7 structures have been calculated versus different values of hole diameter، d، and period ، and two values of wavelength =0. 98 & 1. 55 m. Numerical calculations show that MOF7 microstructure has larger confinement factor so this structure is more suitable for optical power transmission. Confinement factor increases with increasing the ratio of d/.

In this paper the threshold characteristics of an Er-doped λ/4 phase-shifted DFB fiber laser have been studied theoretically. The main purpose of this analysis is to investigate the dependence of threshold pump power and threshold gain on the coupling coefficient. The numerical results show that threshold pump power and threshold gain of Er-doped DFB fiber laser decreas with increasing the normalized coupling coefficient، κL. In this paper the gain margin of laser، the threshold gain difference between the main and side modes، has been evaluated. The obtained results show that the gain margin decreases with increasing of κL. The gain margin is a single mode operation norm of laser. As a result، grating and coupling coefficient have important role in designing the DFB fiber lasers. Numerical ca-lculations have been done by solving the rate equation and coupled wave equations simultaneously using tra-nsfer matrix method