Hollow square core fibre sensor: simultaneous measurement of pressure, temperature, and curvature

A multiparameter fibre sensor for pressure, temperature, and curvature detection is proposed. The sensor is constituted by a single section of a hollow square core fibre (HSCF) spliced between a single mode fibre (SMF) and a long section of a silica capillary tube (SCT). The splicing of different fibres creates parallel interfaces that can give rise to interferometers that propagate in the fibre sections. In a reflection scheme, several Fabry-Perot (FP) cavities are enhanced in different areas of the HSCF. In a single 439 µm long sensing head, three FP cavities are excited. Using the Fourier band-pass filter method, each cavity is individually monitored towards the measurand variation. The sensor revealed a maximum pressure sensitivity of (3.23 ± 0.04) nm/MPa for FP1 within a pressure variation of 0.4 MPa. As for the temperature response, FP3 attained the highest sensitivity of (9.6 ± 0.3) pm/°C up to 110°C. On the other hand, the sensor revealed a maximum curvature sensitivity of (22 ± 1) pm/m-1 for FP3, in a range of 9 m-1. The distinct responses of the FP cavities allow for a hybrid application for simultaneous measurement of pressure, temperature, and curvature. Additionally, a sinusoidal behaviour is found in the curvature response when bending is applied for different relative positions of the fibre. The proposed sensor is robust with simple fabrication and small dimensions, demonstrating promising potential for applications where the simultaneous measurement of several physical parameters is required.