Abstract
A novel optical fiber sensor has been developed using a femtosecond laser which emits single pulses of
210 fs, 3.6 μJ irradiation at a wavelength of 800 nm. Femtosecond laser machining has successfully
been applied to create a bending direction sensing function in an optical fiber sensor, which has previously
been impossible for conventional fiber sensors. The sensing portion of the fiber has an internal array
micro-voids aligned along the optical fiber axis. The non-axisymmetric disposition of the micro-void
array allows bending direction to be detected by observing increases and decreases in the light intensity
propagated in the core. In this paper, the performances of fiber bending sensors are shown in terms of
directional bending detection capability, sensitivity, reproducibility and laser machining conditions for
sensor fabrication. A 2 mm-long sensor element gives average sensitivities of －0.08 and +0.06 dB/mm
over a 5 mm displacement range for bending in opposite directions.
