Interplay of form and material birefringence in photonic crystal fibers: application for sensing

We discuss how material anisotropy influences the modal birefringence of photonic crystal fibers. We introduce an efficient numerical method for the calculation of the modal structure which accounts for material anisotropy. The approach relies on solving the fully vectorial wave equation for the transverse magnetic field and the respective propagation constants within the general framework of plane-wave methods. This analysis is relevant to certain application areas, and, in particular, to fiber sensing, where material birefringence arises due to pressure or mechanical strain. We compare the sensitivity calculations with experimental data and discuss novel potentialities of photonic crystal fibers for sensing; the discussion includes the possibility of temperature insensitivity, a wide range of sensitivity tailoring options, and novel sensing mechanisms with the use of the photonic bandgap.