|
Photonic crystal fibers (PCFs) have attracted much interests recently mainly because of their unique properties. Based on
the light confinement mechanisms, the photonic crystal fibers can be divided into tow classes: the index-guiding PCFs
and the photonic bandgap (PBG) PCFs. The former, with multiple air holes periodically arranged around the core,
possess numerous unusual properties, such as structure controllable chromatic dispersion, large mode areas,
birefringence and stronger optical nonlinenarity.Based on the full vector, semi vector or even the approximate-scalar
model, Lots of methods have been used to design the PCFs, such as the effective index approach, the localized function
expansion method, the plane wave expansion method, the multipole method, the beam propagation method, the finite
difference method, the finite difference time domain method, and the finite element method. Each of theses method
mentioned above are accurate and efficient for ideal PCF, however, for the real fabricated PCFs, the geometry structure
may not perfect, induced the base mode degeneracy may be destructive, and posses birefringence properties. Sometime
the birefringence properties is necessary for special usefulness, such as polarization mode dispersion (PMD)
compensation, and PCFs based polarized optical devices. In this paper, a full vector finite element is applied to
investigate the mode birefringence, mainly focus on the rectangle lattice PCFs with elliptical or circular holes. It has
been demonstrated from the calculated results that high birefringence to the order of 0.01 can be achieved by decreasing
both the pitch and the x and y ratio of the elliptical hole. To increase the birefringence of the circular holes rectangle
lattice, reduction of the width and height ratio of the lattice is necessary. Based on the simulation results, we conclude
that both single polarization transmission and high birefringence polarization maintaining can be achieved by using the
proposed structure with suitable parameters respectively. The available high birefringence at relative high frequency
regime in the fibers and also the sufficiently broad single mode region would make the fabrication of highly birefringent
photonic crystal fibers with novel properties possible.
|
