Dispersion compensation fiber using square hole PCF

In recent years photonic crystal fibers (PCFs) made of silica and air hole has provided a new approach for dispersion compensation. For dispersion compensating fibers, large negative dispersion D (ps/km-nm) is required. The refractive index profile of conventional, step-index, dispersion compensation fiber can be changed in order to obtain high waveguide dispersion, however, this needs high doping, giving rise to higher losses. PCFs are now being increasingly used as an alternative approach to dispersion compensation. This paper proposes a new geometry of PCFs, which uses `square' holes instead of circular holes, which gives large negative dispersion without high doping. Dispersion compensating photonic crystal fiber is designed with square holes with equivalent width w given as d=1.128w where w=width of square holes in PCF and d is diameter of circular holes in more conventional PCF. This relation is newly introduced between circular diameter and square width of air holes.