Modeling Long-Pass Filters Based on Fundamental-Mode Cutoff in Photonic Crystal Fibers

Index-guiding fibers presenting a Ge-doped photonic-crystal cladding and a pure-silica core are numerically studied for the development of efficient optical long-pass filters. They present a fundamental-mode cutoff (FMC) toward short wavelengths that leads to a high extinction ratio, sharp band edge, and bend-tunable transmission profile. The simple design poses no experimental challenge for fabrication and the relatively large obtained modal area makes these waveguides fully compatible with standard telecommunication fibers. The proposed long-pass filter compares favorably with standard, bulk, technology, and with a previously demonstrated photonic crystal fiber presenting a FMC.