Lateral force sensing system based on different photonic crystal fibres

Four types of photonic crystal fibres (PCFs) with different structures and values of birefringence have been evaluated and cross-compared in terms of their corresponding characteristics and sensitivities to lateral force (or pressure), considering this as a function of fibre orientation and the magnitude of the applied external force, as the basis of an all-fibre sensor system. In addition, the force/pressure sensitivities of different pairs of these PCFs when they were fusion-spliced together were evaluated and cross-compared. To obtain an optimum output from these systems, a polarization controller is used in a fibre loop mirror configuration to ensure that a fusion-spliced pair of PCFs is created having the same birefringence angle. The results obtained show that PCFs of low birefringence (Low-Bi) are more sensitive than those of high birefringence (Hi-Bi), although the former require a greater length to achieve a similar effect due to the birefringence. Compared to conventional, non-PCF Hi-Bi fibres (e.g. Panda and Bow-Tie fibres), PCFs demonstrate a much lower temperature sensitivity, allowing them to be well suited to measuring force, pressure and mass in real time (when the temperature is varying) by using a fibre loop mirror (FLM)configuration. In addition, the results obtained show that the sensitivity of the fusion-spliced fibre pairs is lower than that of a single PCF with low and medium birefringence, but more sensitive than that of a single PCF with high birefringence.