Large area mode field photonic crystal fiber design

Abstract

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 <i>_eff</i> ) 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, &#923;, the spacing of neighboring air holes in whole section is fixed, once the radius of air holes in the core region r_<i>c</i> is smaller than the cladding air holes r<i>_cla</i>, LAMF-PCF will be formed. The modal area only lessens a little as r_<i>c</i> is reduced. Especially, optimal size of r_<i>c</i> can nearly make MFA insensitive to wavelength. On the contrary, dispersion parameter of PCF will take place visible change along with r_<i>c</i> reduced, and ultra-flattened dispersion character can be realized when r_<i>c</i> 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 &#923;_<i>c</i> is longer than the cladding region &#923;_<i>cla</i>, so n_<i>eff</i> of core region is higher than the cladding region and TIR can take place.