Research on the characteristics of hole-assisted lightguide fiber

Hole-assisted lightguide fiber (HALF) is a microstructured fiber composed of a high index core, a low index cladding and a small number of air holes surrounding the core. The characteristics of HALF are studied by using the full-vector finite element method. The contour lines of power flow intensity and transverse electric distributions are plotted for the fundamental mode and the first four higher order modes. The effect of the structural parameters, such as hole-to-core spacing and relative size of air holes to the cutoff wavelengths of fundamental mode and higher order mode, core power confinement factor, and mode field diameter is analyzed. Due to these holes, there are variations between HALF and conventional step-index fiber. It's found that when the distance between the air holes and core is shorter or the relative size of air holes becomes larger, the effect of air hole on the HALF turns greater: core power confinement factor becomes larger; mode diameter becomes smaller; the cutoff wavelengths of fundamental mode and higher order mode move to shorter wavelength. In terms of waveguide design, the structural parameters of erbium-doped HALF are optimized to obtain high-efficiency operation of a fiber laser or amplifier.