When an optical pulse with super-Gaussian shape is transmitted in fiber, it will gradually evolve to Gaussian function
shape under suffered all kinds of effects, such as group velocity dispersion (GVD), third order dispersion (TOD), forth
order dispersion (FOD), and nonlinear effects. An interesting phenomenon is observed, that is, TOD will transfer energy
of super-Gaussian pulse from one half to another within total flat top, but TOD will split Gaussian optical pulse and bring
strong oscillation structure in the edge of pulse. Corresponding to frequency domain, super-Gaussian pulse has two
evident slide slobs arranged in both sides of main peak, but TOD can make slobs fade away and transform frequency
spectral to Gaussian function shape. In a densely dispersion managed (DDM) fiber system, the propagation performance
of super Gaussian pulse with sub-picosecond pulse width is investigated. From clear eye-diagram of propagating over
1000 km, we can conclude that the DDM fiber system is very suitable for super Gaussian optical pulse transmission
under low system power condition.
A model of photonic crystal fiber (PCF) with tapered high-index core by GeO2 doped in silica glasses is supposed. Based on finite different approximation of the semi-vector helm-holtz equation, the character of dispersion and modal field areas about this kind of PCF are investigated. Results demonstrate that dispersion parameter can change gradually in positive dispersion region or negative dispersion region, even can change from positive to negative dispersion region when the air hole and pitch are fixed, only the core radius of the PCF is tapered. The kind of PCF is designed for special dispersion-related applications. Especially, it can offer dispersion self-compensation in some optical devices.
A novel design method about photonic crystal fiber (PCF) with large area model field (LAMF) is demonstrated. Different from ordinarily design that the core of PCF formed by missing one air holes in the center of section, many air holes distributed in heartland all together come into being the core region. Air holes are arranged regularly in core region and outer cladding regions according to different periodical character, respectively. The effective refractive index (n eff ) of core region should be higher than cladding region because of total internal reflection (TIR) requirement. In this paper, two kinds of typical scheme are offered to realize LAMF-PCF. First, Λ, the spacing of neighboring air holes in whole section is fixed, once the radius of air holes in the core region rc is smaller than the cladding air holes rcla, LAMF-PCF will be formed. The modal area only lessens a little as rc is reduced. Especially, optimal size of rc can nearly make MFA insensitive to wavelength. On the contrary, dispersion parameter of PCF will take place visible change along with rc reduced, and ultra-flattened dispersion character can be realized when rc is optimized. Another method of designing LAMF-PCF is keeping all air holes uniform in the whole section of PCF, but the space of neighboring air holes in the core region Λc is longer than the cladding region Λcla, so neff of core region is higher than the cladding region and TIR can take place.