Measurements of mode field diameter and effective area for photonic crystal fibers by far field scanning technique

We have demonstrated that the correction factor k_n = A_eff/(πw²), is above 1.20 for photonic crystal fibers (PCFs) with structural parameters in the range of d/Λ ≅ 0.40-0.90. By using the far field scanning (FFS) technique and the finite difference method (FDM), the results of experimental measurements and numerical simulations differed by only 0.8% to 3.0% for two types of PCFs. The finding that k_n≠1.0 for PCFs indicates that their electrical field distribution is non-Gaussian and cannot be determined by assuming a conventional step-index structure distribution for PCFs.